Professional Paper 1770

U.S. Department of the Interior

U.S. Geological Survey

GROUNDWATER RESOURCES PROGRAM 

Groundwater Availability of the 

Denver Basin Aquifer System, Colorado

Domestic well

Municipal wells

Irrigation

well

South Platte River Denver
Groundwater Availability of the 

Denver Basin Aquifer System, Colorado

Edited by Suzanne S. Paschke

Chapter A

Introduction, Conceptual Model, Hydrogeologic Framework, 

and Predevelopment Groundwater Availability of the Denver Basin

Aquifer System

By Suzanne S. Paschke, Edward R. Banta, Jean A. Dupree, and Joseph P. Capesius

Chapter B

Effects of Development on Groundwater Availability in the 

Denver Basin Aquifer System

By Suzanne S. Paschke, Edward R. Banta, and David W. Litke

Chapter C

Groundwater Flow Simulations of the Denver Basin Aquifer 

System, Colorado

By Edward R. Banta, Suzanne S. Paschke, and David W. Litke

Groundwater Resources Program

Professional Paper 1770

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

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Suggested citation:

Paschke, S.S. ed., 2011, Groundwater availability of the Denver Basin aquifer system, Colorado: U.S. Geological 

Survey Professional Paper 1770, 274 p.

Library of Congress Cataloging-in-Publication Data

Groundwater availability of the Denver Basin aquifer system, Colorado / 

edited by Suzanne S. Paschke.

p. cm. -- (Professional paper ; 1770)

Includes bibliographical references.

ISBN 978-1-4113-3121-1 (pbk.)

1. Groundwater--Colorado. 2. Groundwater--Denver Basin. 3. Water table--Colorado. 

4. Water table--Denver Basin. 5. Aquifers--Colorado. 6. Aquifers--Denver Basin. I. Paschke, S. S. (Suzanne Smith) 

II. Series: U.S. Geological Survey professional paper ; 1770. 

GB1025.C6G78 2011

551.49’09788--dc23 2011021191
iii

Foreword

Although often overlooked, groundwater is increasingly important to all our lives. Groundwater 

is the Nation’s principal reserve of freshwater. It provides half our drinking water and is essential to United States food production while facilitating business and industry in promoting 

economic well-being. Groundwater is also an important source of water for sustaining the 

ecosystem health of rivers, wetlands, and estuaries throughout the country. 

Large-scale development of groundwater resources with accompanying declines in groundwater 

levels and other effects of pumping have led to concerns about the future availability of groundwater to meet all our Nation’s needs. The depletion of groundwater to satisfy the country’s thirst 

and the compounding effects of recent droughts emphasize the need for an updated status of the 

Nation’s groundwater resources. Assessments of groundwater resources provide the science and 

information needed by the public and decisionmakers to evaluate water availability and its effects 

on the water supply, as well as, to manage and use the water resources responsibly. Adding to this 

already complex task of resource assessment is the analysis of potential future effects because of 

climate variability, which can further exacerbate an already challenging situation.

The U.S. Geological Survey’s (USGS) Groundwater Resources Program is conducting large-scale 

multidisciplinary regional studies of groundwater availability, such as this study of the Denver 

Basin Aquifer System. These regional studies are intended to provide citizens, communities, and 

natural resource managers with clearer knowledge of the status of the Nation’s groundwater 

resources and how changes in land use, water use, and climate have affected those resources, 

and to develop tools to forecast how these resources may change in the future. Over time, the 

findings from these individual regionally integrated groundwater assessments of principal aquifers will be combined to provide a national assessment. Results derived from these studies will 

provide much needed answers to basic questions about the Nation’s ability to meet current and 

future demands for groundwater.

William H. Werkheiser, Associate Director for Water

U.S. Geological Survey
iv

Acknowledgments

The Denver Basin groundwater availability study was funded by the U.S. Geological Survey 

Groundwater Resources Program. The authors gratefully acknowledge the insight and support 

provided by USGS leadership to develop this and other large-scale groundwater availability 

studies. Additional support was provided by the Colorado Water Conservation Board and the 

Colorado Division of Water Resources, which enabled coordination between this study and 

the State-sponsored South Platte Decision Support System. The authors thank Kenneth Watts, 

Kevin Dennehy, Robert Davis, Betty Palcsak, Keith Lucey, and Mary Kidd of the U.S. Geological 

Survey and Brian Ahrens formerly of the Colorado Division of Water Resources for thoughtful reviews of the document. Thanks also go to Joy Monson of the U.S. Geological Survey for 

graphic design and report publication. This study would not have been possible without the 

work of many previous and contemporary scientists and policymakers from the U.S. Geological 

Survey, the Colorado Division of Water Resources, the Colorado Water Conservation Board, the 

Colorado Geological Survey, the Denver Museum of Nature and Science, the Colorado School 

of Mines, water providers, consultants, and concerned citizens who have contributed to the 

understanding of geology, water resources, and groundwater flow modeling in the Denver Basin. 

The authors acknowledge all of these previous workers and their sustained efforts to understand 

water resources in the Denver Basin.
v

Executive Summary

The Denver Basin aquifer system is a critical water resource for growing municipal, industrial, 

and domestic uses along the semiarid Front Range urban corridor of Colorado. The confined 

bedrock aquifer system is located along the eastern edge of the Rocky Mountain Front Range 

where the mountains meet the Great Plains physiographic province. Mining, transportation, agricultural, and urban activities developed along the Front Range beginning in the 1800s, and today 

urban and suburban land use extends north from Denver to Fort Collins and south to Colorado 

Springs. Population of the metropolitan areas overlying the Denver Basin aquifer system has 

approximately doubled from 1.3 million in 1970 to about 2.7 million in 2005 and is expected to 

double again in the next 50 years. On the west side of the basin between Denver and Colorado 

Springs, where development has been especially rapid and extensive, population growth is 

supported by Denver Basin groundwater resources that are used for municipal water supply. 

Domestic groundwater use is less than municipal use but is widespread across the basin, and 

many rural and incorporated areas depend on self-supplied groundwater for water supply.

Continued population growth and the resulting need for additional water supplies in the Denver 

Basin and throughout the Western United States emphasize the need to continually monitor 

and reassess the availability of groundwater resources. Denver Basin groundwater is administratively recognized as nonrenewable because the aquifers are primarily confined and receive 

little precipitation recharge. Permitted pumping rates are based on the concept of a 100-year 

aquifer life for a given parcel of land. Because Denver Basin groundwater resources are limited, 

there is an ongoing need to understand groundwater availability in support of management 

practices. Adequate monitoring and modeling of the hydrologic system are important to evaluate the effects of continued pumping on storage depletion and provide tools for future watermanagement decisions.

In 2004, the U.S. Geological Survey initiated large-scale regional studies to provide updated 

groundwater-availability assessments of important principal aquifers across the United States, 

including the Denver Basin. This study of the Denver Basin aquifer system evaluates the hydrologic effects of continued pumping and documents an updated groundwater flow model useful 

for appraisal of hydrologic conditions. To assess the effects of development on Denver Basin 

groundwater resources, transient groundwater flow in the bedrock and overlying alluvial aquifers 

was simulated for the period 1880 through 2003 by using a fully three-dimensional groundwater 

flow model. The model uses the modular finite-difference groundwater flow computer program 

MODFLOW-2000 and includes several enhancements over previous modeling efforts because of 

additional data availability, improved modeling capabilities, and improved computer technology. 

Groundwater budget and hydraulic head results from the calibrated Denver Basin groundwater 

flow model were evaluated to describe the system response to continuing development, and 

model sensitivity results were used to identify geographic areas of the system where additional 

data collection would be most beneficial. Model predictions for the period 2004 to 2053 provide 

estimates of the future hydrologic system response and allowed computation of the predictive 

sensitivity of the model results to various parameters. The Denver Basin groundwater flow model 

is a useful tool for analyzing past and present conditions, predicting future aquifer response to 

continued development, and evaluating future hydrologic monitoring and assessment.
vi

Study results are presented in the three chapters of this Professional Paper. Chapter A presents 

an introduction, previous work, methods, the hydrogeologic framework of the aquifer system, 

and a description of predevelopment (pre-1880) water budgets and groundwater flow conditions 

based on modeling results. The hydrogeologic framework includes discussion of depositional 

history, stratigraphic nomenclature, extent, depth, thickness, and hydrologic properties of the 

Denver Basin aquifer system. Chapter B describes the effects of development on the Denver 

Basin aquifers including changes to the water budgets and groundwater flow directions from 

1880 through 2003 primarily based on results from the calibrated groundwater flow model as 

compared to available data. Chapter B also includes results from predictive simulations and a 

discussion of future monitoring needed to improve model calibration and to provide the necessary data for future and recurring hydrologic analysis. Chapter C presents details of the groundwater flow model used for the groundwater-availability analysis including model setup, calibration, sensitivity, and future work. The following sections of this Executive Summary summarize 

results from each of the Professional Paper chapters.

Chapter A Summary. Introduction, Conceptual Model, Hydrogeologic 

Framework, and Predevelopment Groundwater Availability of the Denver 

Basin Aquifer System, Colorado

The Denver Basin aquifer system is composed of Late Cretaceous to Tertiary-age sandstone 

bedrock aquifers and intervening claystone confining units that occur in the uppermost layers 

of the structural Denver Basin above the Cretaceous Pierre Shale confining layer. From oldest to 

youngest, the four primary aquifers are the Laramie–Fox Hills, Arapahoe, Denver, and Dawson. 

The Arapahoe and Dawson aquifers are further differentiated into upper and lower units in parts 

of the basin. The synclinal structure of the Denver Basin causes the bedrock aquifer units to crop 

out in a ring pattern where the oldest rocks of the Laramie–Fox Hills aquifer crop out around the 

outer margins of the basin and the youngest rocks of the Dawson aquifer crop out in the center 

of the basin. Confined groundwater conditions generally are found in the bedrock aquifers where 

they are overlain by younger units, and unconfined groundwater conditions are generally found 

in outcrop areas. Alluvial sand, gravel, and clay deposits overlie the bedrock formations primarily 

along stream channels in the South Platte and Arkansas River basins, and these materials form 

an unconfined alluvial aquifer where saturated.

The Laramie–Fox Hills aquifer is the oldest, deepest, and most extensive of the bedrock aquifers 

underlying the area, and its extent defines the limit of the Denver Basin aquifer system. The 

Laramie–Fox Hills aquifer is composed of poorly to moderately consolidated sandstone units 

of the upper Cretaceous Fox Hills Sandstone and the lower Laramie Formation, and the basealtitude map of the Laramie–Fox Hills aquifer reflects the bowl shape and dipping margins of 

the Denver Basin geologic structure. The deepest part of the Laramie–Fox Hills aquifer base, 

and therefore also the deepest part of the Denver Basin aquifer system, occurs in Douglas 

County just north of Parker, Colorado, at an altitude of approximately 3,410 feet. Depth to the 

base of the Laramie–Fox Hills aquifer near the structural center of the basin is approximately 

2,200 to 2,300 feet below land surface, and the total thickness of the aquifer system reaches 

a maximum of approximately 3,200 feet beneath the topographic high of the Palmer Divide. 

The Cretaceous upper Laramie Formation, composed of gray to black shale, coal seams, and 

minor amounts of siltstone and sandstone, overlies the Laramie–Fox Hills aquifer and forms 
vii

a confining unit that separates the Laramie–Fox Hills aquifer from the overlying aquifers. The 

Laramie confining unit forms a wedge-shaped layer that thins from a mountain-front thickness 

of as much as 700 feet to less than 100 feet on the eastern margin of the basin.

The Arapahoe aquifer consists of a 400- to 600-foot-thick sequence of interbedded conglomerate, sandstone, siltstone, and shale of Cretaceous age. In the northern one-third of the basin, 

shale is more prevalent, and the Arapahoe aquifer is administratively divided into upper and 

lower aquifers with an intervening shale confining unit. In the southern two-thirds of the basin, 

extensive conglomerate and coarse-grained sandstone units were deposited as alluvial fans 

along the mountain front during the Laramide Orogeny. These coarse-grained sandstones of the 

lower Arapahoe aquifer are thickest and the most conductive in Douglas and El Paso Counties 

where they form a productive bedrock aquifer that is heavily used for municipal and domestic 

water supply. The base altitude of the lower Arapahoe aquifer ranges from 6,200 feet along 

the southwest basin margin to approximately 4,100 feet at the basin center just north of Parker, 

Colorado. Depth to the base of the lower Arapahoe aquifer near the structural center of the 

basin is approximately 1,700 feet below land surface, and the maximum depth to the base of 

the aquifer is approximately 2,600 feet below land surface at the Palmer Divide.

The Denver aquifer and confining units consists of a 600- to 1,200-foot-thick heterogeneous 

sequence of interbedded shale, claystone, siltstone, sandstone, coal, and volcanic ash deposits 

of Cretaceous to Tertiary age. The Arapahoe, Denver, and lower Dawson aquifers represent 

the synorogenic deposition of sediments in the Denver Basin during Laramide uplift of the 

Rocky Mountain Front Range. The well-formed alluvial fans mapped in the western part of the 

basin for the lower Arapahoe aquifer also are observed in the Denver sequence. However, in 

other parts of the basin, the Denver sequence is, in general, finer grained than the underlying Arapahoe aquifer sequence and is composed of isolated channel sandstones contained 

in extensive fine-grained deposits. The Cretaceous-Tertiary boundary occurs in the upper part 

of the Denver aquifer sequence and is closely established by vertebrate fossils. Despite poor 

correlations between Denver-aquifer sandstones in some parts of the basin, the base-altitude 

maps of the Denver aquifer and confining units depict the regional structure of the Denver Basin 

and provide reasonable representations of layering within the Denver sequence. Altitude of the 

Denver sequence base ranges from approximately 4,600 to 6,300 feet, and the maximum depth 

of the sequence is approximately 2,100 feet below land surface at the Palmer Divide. The greatest silt-plus-sand thickness in the Denver aquifer (400 to 600 feet) occurs along the western 

basin margin in southern Douglas County. The Denver confining units are thin (mean thicknesses 

of 50 feet) compared to the thickness of the Denver aquifer (mean thickness of 550 feet).

The Dawson aquifer sequence consists of a 100- to 1,100-foot-thick heterogeneous sequence 

of Tertiary-age, fluvial conglomerate, sandstone, siltstone, and shale. In the northern two-thirds 

of the Dawson extent, a clay and shale confining layer is present, and the Dawson aquifer is 

administratively separated into upper and lower aquifers. The lower Dawson aquifer forms the 

upper part of the Laramide synorogenic sequence, and separation of the lower Dawson aquifer 

from the underlying Denver aquifer sequence is an administrative boundary. The base altitude of 

the lower Dawson aquifer ranges from 5,400 feet at the northern edge of its extent to 6,800 feet 

on the southern edge of its extent and the base is 1,100 feet below land surface at the Palmer 

Divide. The greatest silt-plus-sand thickness (200 to 375 feet) is located in the west-central part 

of the basin along the Douglas-El Paso County line, similar to the Denver and Arapahoe aquifers. The Dawson confining unit consists of a shale-rich layer at the top of the lower Dawson 

sequence. The upper Dawson aquifer consists of arkosic, coarse-grained, poorly consolidated 
viii

sandstones with some interbedded overbank mudstone deposits in a distribution pattern quite 

different from that of the underlying sediments. Sandstones of the upper Dawson aquifer are 

more uniform in composition than those from the underlying layers and were likely derived from 

the Pikes Peak area to the south rather than from the Front Range source area to the west. 

Paleochannels at the base of the lower Dawson aquifer are evident from the base-altitude configuration map, and one such paleochannel aligns with the present-day course of Cherry Creek.

A summary of hydraulic-conductivity values from pumping tests for the bedrock aquifers indicates that the Arapahoe aquifer is the most permeable of the bedrock units (median of 1.8 feet 

per day [ft/d]; geometric mean of 1.6 ft/d) followed by the Dawson aquifer (median of 0.80 ft/d; 

geometric mean of 0.7 ft/d), the Denver (median of 0.45 ft/d; geometric mean of 0.42 ft/d), and 

the Laramie–Fox Hills aquifers (median of 0.40 ft/d; geometric mean of 0.40 ft/d). Hydraulicconductivity values for the alluvial aquifer are many orders of magnitude greater than those 

for the bedrock aquifers ranging from about 18 ft/d to about 2,560 ft/d with a median of about 

480 ft/d based on pumping-test results. The difference in hydraulic conductivity between alluvial 

and bedrock aquifers is an important part of the Denver Basin conceptual model because it 

affects the water budget and water movement in the basin. Estimates of specific-yield values 

were compiled from previous studies and varied somewhat from values used for water administration. Mean specific-yield values of 15.2 percent for the Dawson aquifers, 13.3 percent for the 

Denver aquifer, 17.8 percent for the Arapahoe aquifers, and 18.6 percent for the Laramie–Fox 

Hills aquifer are reported by the current study and are used in the groundwater flow simulations.

Predevelopment groundwater availability discussions describe conditions prior to 1880 and 

are based on previous studies as well as interpretations and results from the steady-state 

stress period of the calibrated groundwater flow model. Predevelopment sources of water to 

the Denver Basin aquifers were precipitation recharge, irrigation return flow, streams, and 

interaquifer flow between hydrogeologic units. Because agricultural irrigation, primarily by 

surface-water diversions, began in the South Platte River valley before 1880, irrigation recharge 

is included as the predevelopment recharge estimates. Predevelopment outflow components 

of the water budget were discharge to evapotranspiration, streams, springs, and interaquifer 

flow. Discharge to pumping wells was assumed negligible before 1880 and was not included in 

the predevelopment simulation or groundwater budget. Predevelopment groundwater budgets 

are presented in Chapter A for the entire system (sum of all model layers), the alluvial aquifer 

(model layer 1), and the bedrock units (model layers 2 through 12) and are discussed in terms of 

individual water-budget components.

Precipitation plus irrigation recharge was the primarily inflow component of the predevelopment groundwater budget for the entire system (630 cubic feet per second [ft3

/s], 98 percent of 

inflow), the alluvial aquifer (454 ft3/s, 90 percent of inflow), and the bedrock aquifers (176 ft3/s, 

94 percent of inflow) and is an important source of water in this semiarid region. However, 

much of the precipitation goes to surface-water runoff and evapotranspiration with only a small 

part of precipitation providing recharge to the bedrock aquifers. Simulated predevelopment net 

recharge (recharge minus evapotranspiration) to the alluvial aquifer was 147 ft3/s (84 percent 

of net inflow to the alluvial aquifer), and simulated predevelopment net recharge to the bedrock 

units was 41 ft3/s (100 percent of net inflow to the bedrock units). In areas where bedrock crops 

out with little to no overlying alluvium, deep infiltration of precipitation provides direct recharge 

to the bedrock aquifers. Inflow from streams and interaction between the alluvial aquifer and 

the bedrock units accounted for small percentages of predevelopment groundwater inflow.
ix

Evapotranspiration and streams were the primary outflow components of the predevelopment 

water budget. Simulated evapotranspiration was 442 ft3/s (68 percent of outflow) for the entire 

system, 307 ft3/s (61 percent of outflow) for the alluvial aquifer, and 135 ft3/s (72 percent of outflow) for the bedrock units. Streams accounted for 182 ft3

/s (28 percent of the outflow) from the 

entire system, 164 ft3/s (33 percent of outflow) for the alluvial aquifer, and 18 ft3/s (10 percent 

of outflow) for the bedrock units. Streams provided inflow to and outflow from the system, but 

the net flow was from aquifers to streams. Simulated net outflow to streams from the alluvial 

aquifer was 151 ft3/s (88 percent of net outflow) and 14 ft3/s (34 percent of net outflow) from 

bedrock aquifers.

In areas overlain by alluvial aquifers, groundwater moves between the alluvial aquifer and bedrock units. Simulated outflow from the bedrock units to the alluvial aquifer for predevelopment 

conditions was 34 ft3/s (7 percent of alluvial aquifer inflow), and simulated outflow from the 

alluvial aquifer to the bedrock units was 8 ft3/s (4 percent of bedrock inflow), resulting in a net 

outflow from the bedrock units to the alluvial aquifer of 26 ft3/s (64 percent of net outflow from 

the bedrock units and 16 percent of net inflow to the alluvial aquifer).

The Denver Basin aquifers are confined over much of their area where overlain by lesspermeable claystone and shale confining units. Unconfined, or water-table, conditions occur in 

the near-surface parts of the Denver Basin bedrock aquifers and in the alluvial aquifer. Potentiometric-surface maps for predevelopment conditions for the seven aquifers show areas of high 

hydraulic head near the recharge area of the Palmer Divide and areas of low hydraulic head near 

discharge areas, with groundwater flow toward downgradient streams and alluvial aquifers 

in all directions. Groundwater also moved vertically down to underlying bedrock aquifers for 

predevelopment conditions. The lower potentiometric altitude in the underlying bedrock aquifers 

promotes downward water movement, and although the low vertical hydraulic conductivities 

limit the rate of downward water movement, this vertical leakage is an important source of 

recharge to underlying bedrock aquifers.

Chapter B Summary. Effects of Development on Groundwater 

Availability in the Denver Basin Aquifer System, Colorado

Changes in land and water use have altered the Denver Basin groundwater flow system compared to predevelopment conditions. The expansion of urban/suburban land use and(or) irrigated 

agriculture since the 1950s has increased water use on the landscape, which has increased 

recharge, evapotranspiration, streamflow, and the overall quantity of water entering and leaving 

the groundwater system in this semiarid region. Groundwater pumping from the bedrock aquifers also has increased steadily since the 1950s, primarily in response to increased municipal 

water-supply needs. The combination of these changing land- and water-use distributions has 

increased groundwater availability in the alluvial aquifer and shallow parts of the hydrologic 

system while reducing bedrock discharge to the surficial system, removing water from storage, 

and decreasing groundwater availability in the bedrock aquifers.

Present-day land use in the Denver Basin is 60 percent nonirrigated grassland and rangeland, 

16 percent nonirrigated agriculture, 11 percent irrigated agriculture, 9 percent developed urban 

and suburban land use, 3 percent forested, and 1 percent open water. Nonirrigated grassland 

and rangeland cover much of the central and southern basin and irrigated and nonirrigated 
x

agricultural land is primarily located along the South Platte River valley in the northern basin. 

Developed urban and suburban land use is primarily on the western side of the basin along 

the Front Range urban corridor. Small towns, rural residences, and farms are spread across the 

less-populated parts of the basin including the forested areas at the higher elevations along the 

Palmer Divide. Population of the metropolitan areas overlying the Denver Basin aquifer system 

has approximately doubled from 1.3 million in 1970 to about 2.7 million in 2005. Development 

has been especially rapid and extensive on the west side of the basin between Denver and 

Colorado Springs. Three primary areas of development are identified that rely on groundwater 

for water supply: (1) the area north of Denver in Weld and Adams Counties; (2) the south Denver 

metropolitan area encompassing Littleton, Parker, Franktown, and Castle Rock; and (3) the 

Monument area northeast of Colorado Springs. Because groundwater in the Denver Basin 

bedrock aquifers is mostly considered nontributary to streams and is not subject to the priorappropriation doctrine, it has been a readily available source of water to support growing and 

recently established municipalities in areas with limited surface water, limited tributary alluvial 

groundwater, limited available water rights, or all of the above.

Because actual pumping in the Denver Basin is not monitored, this study estimated pumping 

from 1880 through 2003 from the Colorado Division of Water Resources well-permit database 

following methods implemented in previous studies. Analysis results compare favorably to 

previous pumping estimates and were used as input to the groundwater flow model. About 

52,000 permitted pumping wells with sufficient well location and completion data were included 

in the analysis. About 8,000 wells (15 percent) were completed in the alluvial aquifer and the 

remaining 44,000 wells (85 percent) were completed in the bedrock aquifers in 2003. Total 

pumping from the Denver Basin alluvial and bedrock wells was estimated at about 305 ft3/s 

(221,000 acre-ft/year) in 2003. About 62 percent of the pumping was from alluvial wells 

(187 ft3/s), and about 38 percent of the pumping was from bedrock wells (118 ft3/s). While most 

of the wells (85 percent) are completed in the bedrock aquifers, most of the estimated pumping 

(62 percent) is from the alluvial aquifer. These results are consistent with the conceptual understanding of the system and reflect the inherent difference in hydraulic conductivity between the 

more transmissive alluvial aquifer and the less transmissive bedrock aquifers.

Categorized by water use, total pumping from the entire system (alluvial plus bedrock aquifers) 

was about 62 percent irrigation, 20 percent municipal, 12 percent domestic, and 6 percent 

commercial/industrial in 2003. For the alluvial aquifer, most of the wells were used for domestic 

(56 percent) and irrigation (38 percent) purposes, although most of the pumping (90 percent) 

was used for irrigation purposes in 2003. For the bedrock aquifers, most of wells also were 

used for domestic purposes (94 percent), and only 2 percent of the bedrock wells were used for 

municipal purposes in 2003. However, because assumed pumping rates for municipal wells are 

greater than those for domestic wells, estimated municipal pumping accounted for 41 percent 

and domestic pumping accounted for 28 percent of the bedrock pumping in 2003. The upper and 

lower Arapahoe aquifers were the most heavily pumped of the bedrock aquifers (41 percent of 

bedrock pumping) in 2003. Bedrock domestic wells are located throughout the basin and are 

generally completed in the bedrock aquifer nearest to the surface, while bedrock municipal 

wells are associated with development on the west side of the basin.

The simulated transient water budget for the entire Denver Basin modeled area (bedrock 

and alluvial aquifers) from 1880 through 2003 indicates that recharge from precipitation and 

irrigation was the largest inflow component of the postdevelopment water budget and that 

outflow to evapotranspiration, pumping, and streams were the primary outflow components. 
xi

All components of the water budget remained relatively constant until the 1950s when urban 

development in the Denver metropolitan area, irrigated agriculture, and associated water use 

began increasing. After 1953, there was an overall increase in the entire water budget because 

of the water-use increase. Total estimated pumping increased steadily from about 44 ft3/s in 

1953 to about 280 ft3/s in 2003 and was accompanied by a net aquifer storage-depletion rate of 

about 63 ft3/s.

Separating water budgets for the alluvial and bedrock aquifers indicates that the majority 

of water moving in and out of the system is moving through the alluvial aquifer. On average 

from 1880 through 2003, 80 percent of net recharge was directly to the alluvial aquifer, while 

20 percent of net recharge was directly to the bedrock aquifers. Most net outflow to streams 

(90 percent on average) also was from the alluvial aquifer, while approximately 10 percent of 

net outflow to streams was directly from bedrock aquifers for the model-calibration period from 

1880 to 2003. Simulated pumping from the alluvial aquifer increased rapidly from 40 ft3/s in 

1953 to about 143 ft3/s in 1971 and then more gradually to about 170 ft3/s in 2003. Simulated 

pumping from the bedrock aquifers increased steadily from about 8 ft3/s in the 1950s to about 

111 ft3/s in 2003. Flow from bedrock units to the alluvial aquifer decreased from approximately 

34 ft3/s for predevelopment (pre-1880) conditions to about 27 ft3/s in 2003, and flow from the 

alluvial aquifer to the bedrock aquifer increased from about 8 ft3/s for predevelopment conditions to about 12 ft3

/s in 2003. These changes resulted in a decrease in the net flux to the 

alluvial aquifer from bedrock units from about 26 ft3/s in 1880 to about 15 ft3/s in 2003. Similar 

to other water-budget components, downward interaquifer flow from the Denver aquifer and 

lower Denver confining unit to the upper and lower Arapahoe aquifers increased substantially 

over time and was induced by the increased pumping from the Arapahoe aquifers.

Simulated alluvial and bedrock aquifer storage responded to changes in pumping and net recharge. 

Based on simulation results for the model-calibration period 1880–2003, storage changes for the 

alluvial aquifer have varied depending on recharge and pumping, with storage replenished in wet 

years and depleted in dry years. Bedrock aquifer storage-depletion rates have increased since 

predevelopment because of pumping. By 2003, dry climatic conditions, coupled with continued 

pumping, resulted in a simulated storage-depletion rate of about 7 ft3/s for the alluvial aquifer 

and a storage-depletion rate of about 57 ft3/s for the bedrock aquifers. Pumping is removing water 

from storage in all of the bedrock aquifers. The Denver aquifer experienced the greatest storagedepletion rate by 2003 (about 26 ft3

/s) because of pumping from the aquifer, downward flow to the 

underlying Arapahoe aquifers, and conversion to unconfined conditions.

The cumulative volume of water removed from alluvial-aquifer storage increased in response 

to pumping during the 1960s through 1980s and reached a maximum cumulative storage loss of 

about 326,000 acre-feet in 1986. After 1986, the simulated area of urban recharge increased in 

areas overlying the alluvial aquifer, which resulted in additional simulated recharge to the alluvial aquifer and about 200,000 acre-feet of storage recovery. There were about 25,000 acre-feet 

of cumulative storage loss from the alluvial aquifer simulated from 2000 to 2003 in response to 

drought conditions. The simulated cumulative volume of water removed from bedrock-aquifer 

storage increased from zero under predevelopment conditions to about 690,000 acre-feet 

(30 million cubic feet) in 2003. Drought conditions, simulated in the model from 2000 to 2003, 

coupled with continued pumping increases, caused an exponential increase in simulated cumulative storage depletion from the bedrock aquifers since 1999. Storage depletion is expected to 

increase substantially as the confined aquifers experience drawdown and convert to unconfined 
xii

conditions because more water is released from drainable (unconfined) storage than from 

confined storage for a unit decrease in hydraulic head. Spatially, 50 percent of the 2003 storage 

depletion from the bedrock units was from the south Denver metropolitan area where groundwater provides most of the municipal water supply to a growing population. The other 50 percent of the loss was from remaining parts of the basin.

The change in recharge patterns caused by development as well as pumping and the removal of 

groundwater from storage have lowered the potentiometric heads and altered groundwater flow 

directions in the Denver Basin aquifer system. Changes in hydraulic head in the alluvial aquifer 

are less pronounced than those in the bedrock aquifers because of connection between the 

alluvial aquifer and streams and the large hydraulic conductivity and recharge rates compared to 

the bedrock aquifers. Pumping from each of the bedrock aquifers resulted in substantial drawdown of their respective potentiometric surfaces and an increase in unconfined conditions for 

some layers. For the upper Dawson aquifer, simulated pumping south of the Denver metropolitan 

area near Castle Rock and Parker has lowered the potentiometric head up to 100 feet below 

predevelopment conditions in the Cherry Creek basin creating a regional discharge area that 

was not present under predevelopment conditions. The greatest concentration of pumping wells 

in the Arapahoe aquifer occurs in the south Denver metropolitan area where the aquifer is thickest and most conductive. Drawdown through 2003 was greatest in all bedrock aquifer model 

layers in the south Denver metropolitan and Monument areas, but the drawdown patterns were 

somewhat different between the two areas because of contrasts in hydraulic conductivity. In 

the south Denver metropolitan area, drawdown cones for individual wells in the lower Arapahoe 

aquifer coalesced into a large area of regional drawdown within an extensive lobe of transmissive sandstone. However, drawdown in the lower Arapahoe aquifer in the Monument area was 

restricted to individual cones of depression with steep hydraulic gradients surrounding pumping 

centers because the aquifer exhibits a lower hydraulic conductivity and sandstones are discontinuous. The spatial distribution of 1880 through 2003 drawdown for the Laramie–Fox Hills 

aquifer is slightly different from that of the other bedrock aquifers with the greatest drawdown 

occurring in the northern Denver suburbs in addition to the south Denver metropolitan area.

Predictive simulations were used to calculate model predictive sensitivities and to demonstrate 

use of the model to evaluate future groundwater conditions. Predictive simulations represented 

conditions 50 years into the future from the end of the model calibration period (December 31, 

2003) to 2053. Predictive simulations represent hypothetical temporal changes to pumping and 

lend insight to long-term effects of continued pumping on the groundwater system. The first 

predictive simulation to 2053 assumes dry climatic conditions and that pumping continues at 

the 2003 rate. The second predictive simulation to 2053 demonstrates the use of the model to 

evaluate future conditions and simulates reduced pumping from municipal wells completed 

in the lower Arapahoe aquifer. As expected, results from the first predictive simulation indicate continued drawdown, an increase in unconfined areas, and continued storage loss in all 

model aquifer layers. Results from the second predictive simulation indicate up to 400 feet less 

drawdown for the lower Arapahoe potentiometric surface from 2009 to 2053 if pumping from 

the lower Arapahoe aquifer was ceased in the south Denver metropolitan area. Because of the 

hydraulic connection between the Denver and Arapahoe aquifers, results from the second predictive simulation also predict about 150 feet less drawdown in the Denver aquifer potentiometric surface by 2053 if pumping was ceased in the lower Arapahoe aquifer. Results from predictive simulations indicate bedrock discharge to the alluvial aquifer will continue to decrease and 
xiii

storage loss will continue through 2053 if pumping is maintained at the 2003 rates. Simulation 

results also indicate that storage-depletion rate may be reduced and the useful aquifer life could 

be extended by reducing pumping from the bedrock aquifers.

Further studies of the Denver Basin aquifers would benefit from additional and continued data 

collection and interpretation. The Colorado Division of Water Resources maintains centralized databases of well-permit records (with drilling logs) and geophysical logs. Maintenance 

and updating of these databases in a consistent manner is essential to further the availability 

of well and geologic data in the Denver Basin. As drilling and construction of water-supply 

wells continues in the basin, continued compilation of hydrogeologic data, such as geologic 

layering information, aquifer tests, and water levels, into a centralized database would allow 

more effective sharing of data between Federal, State, and local governments and scientists. 

Currently (2010), there is no centralized database for pumping records from the Denver Basin 

aquifers. Individual water providers meter and record pumping as part of daily operations, but 

these data are not compiled on a regional basis. Implementation of a metering and reporting 

system for pumping information would provide discharge information for the basin with which 

to better evaluate aquifer drawdown and storage depletion and could be used to reduce model 

uncertainty. Future water-level monitoring efforts in the Denver Basin would benefit from an 

expanded network of dedicated monitoring wells constructed of material resistant to corrosion with screened intervals placed to monitor selected bedrock units. Based on analysis of the 

present network, water-level measurements collected in the spring represent ambient heads in 

the nonirrigation season, while fall measurements are useful to evaluate the effects of summer 

irrigation pumping. Retaining existing wells in a long-term network should be considered if there 

already is a long-term water-level record for the well and the well condition and completion 

interval are appropriate for inclusion in the network.

Bedrock groundwater storage is being depleted in the Denver Basin. While the length of time 

over which this resource may be available is uncertain, the conclusions of this and other studies 

indicate that pumping from the Denver Basin bedrock aquifers is not indefinitely sustainable and 

that renewable water supplies will be needed in the future. Conjunctive-use projects, conservation, water reuse, and importation of renewable water will enhance the prudent management 

of Denver Basin groundwater resources and can likely extend the practical usable life of the 

aquifers. Recurring monitoring and analysis of groundwater availability is especially important to 

guide groundwater management in areas such as the Denver Basin, where a growing population 

presently relies on this important and limited resource.

Chapter C Summary. Groundwater Flow Simulations of the Denver 

Basin Aquifer System, Colorado

Groundwater flow in the Denver Basin bedrock aquifers and overlying alluvial aquifer is simulated with a three-dimensional groundwater flow model to provide a framework for analysis of 

aquifer and confining bed materials, hydrologic stresses, field observations of past hydrologic 

conditions, and predictions of future hydrologic conditions. The model uses the U.S. Geological 

Survey modular finite-difference groundwater flow modeling program MODFLOW-2000 and 

includes several enhancements over previous modeling efforts because of additional data availability, improved modeling capabilities, and improved computer technology.
xiv

The Denver Basin model grid encompasses the Denver Basin bedrock aquifer system and 

immediately adjacent areas of the alluvial aquifer of the South Platte River with 84 columns 

and 124 rows of square cells; each cell measures 1 mile by 1 mile. A fully three-dimensional 

approach was used to simulate lateral and vertical flow and storage changes in all hydrogeologic units of the aquifer system. Each of the six bedrock aquifers, five bedrock confining units, 

and the alluvial aquifer are explicitly represented in the model with aquifer base altitudes 

defined from geophysical logs and geologic mapping from previous work. The alluvial aquifer 

is simulated as unconfined, the bedrock aquifers are simulated as convertible from confined to 

unconfined, and the bedrock confining units are simulated as confined. The model simulates 

steady-state conditions prior to 1880 and transient groundwater conditions from 1880 through 

2003 by using 16 stress periods of durations ranging from 2 to 27 years.

Horizontal hydraulic conductivity for the bedrock units is represented in the model by using 

several adjustable parameters whose values were calibrated through parameter estimation. 

Vertical hydraulic conductivity was assumed equal to horizontal hydraulic conductivity in the 

bedrock units, such that resistance to vertical flow among the bedrock aquifers is primarily 

controlled by the hydraulic conductivity of the confining units. For model layers representing the 

Denver, Arapahoe, and Laramie–Fox Hills aquifers, hydraulic-conductivity parameterization used 

the pilot-point approach. Pilot points are locations in the model where a parameter, hydraulic 

conductivity in this study, is calibrated by parameter estimation. The estimated parameter 

values at pilot points are then interpolated between locations within a model layer to assign 

a parameter (hydraulic conductivity) distribution to the layer. Finally, the calibrated hydraulicconductivity values for each layer were multiplied by the percentage of coarse-grained materials 

(silt-plus-sand fraction) for each model cell to obtain an equivalent hydraulic conductivity for the 

overall aquifer thickness represented by each cell. For the alluvial aquifer, horizontal hydraulic 

conductivity was assigned a value of 200 ft/d for the alluvial aquifer in the South Platte River 

Basin and a value of 5 ft/d for the alluvial aquifer in the Big Sandy and Black Squirrel Creek 

Basins. The ratio of horizontal to vertical hydraulic conductivity for the alluvial aquifer in the 

South Platte River Basin was represented by an adjustable parameter whose final value (9.9) 

was determined through model calibration. A fixed parameter value of 10 was assigned to the 

ratio of horizontal to vertical hydraulic conductivity for the alluvial aquifer in the Big Sandy and 

Black Squirrel Creek Basins.

Aquifer storage properties of specific storage for confined units and specific yield for unconfined units were represented in the model by using several estimated and assigned parameters. 

Specific storage was represented using two adjustable parameters. One specific-storage 

parameter was estimated for the model layers representing aquifers, and one specific-storage 

parameter was estimated for the model layers representing confining units. The final calibrated 

specific-storage values of 5.2 × 10-7/ft for aquifers and 1.7 × 10-6/ft for confining units are in 

the range of reasonable values for materials in the Denver Basin. Specific-yield values were 

assigned for each aquifer unit based on previous field studies in the basin and were multiplied 

by the percentage of coarse-grained materials (silt-plus-sand fraction) for each model cell to 

obtain an equivalent specific yield for the overall aquifer thickness represented by each cell.

Hydrologic stresses simulated by the model include recharge from precipitation plus irrigation 

return flows, evapotranspiration, streams, springs, reservoirs, pumping wells, interaquifer flow, 

flow across basin boundaries, and storage. The percentage of precipitation becoming recharge 

was represented in the model by using several adjustable parameters whose values were calibrated through parameter estimation. Model-calibration results indicate about 1 to 2 percent of 
xv

precipitation becomes recharge to the bedrock aquifers, and an estimated 7 percent of precipitation becomes recharge to the alluvial aquifer. Recharge rates in irrigated areas were assigned 

values of 2.5 inches per year (in/yr) for urban irrigation return flows (urban recharge) and 10 in/yr 

for agricultural irrigation return flows. Evapotranspiration was simulated using a piecewise 

linear function in which evapotranspiration decreased as depth to groundwater increased over 

the entire modeled area. Streamflow was simulated using the SFR2 Package, reservoirs were 

represented using the RIV Package, and springs were simulated with the DRN Package. Flow 

across the southern basin boundary was simulated using the GHB Package and across the 

northeast basin boundary using the FHB Package. Pumping was simulated using the WEL and 

MNW Packages and was estimated for each aquifer model layer on the basis of well locations, 

depths, and water use taken from the Colorado Division of Water Resources well-permit database as described in Chapter B. The GMG Package and an alternative adaptive damping method 

were used to solve the highly nonlinear system of finite-difference equations, which provided a 

solution in a reasonable execution time and with a relatively small number of deactivated cells.

The Denver Basin model was calibrated using nonlinear regression methods as implemented in the 

parameter estimation program PEST in combination with manual adjustments to parameters that 

proved resistant to calibration by automated methods. Seventy-seven parameters were included in 

the model, 52 of which were adjusted during parameter estimation and 23 of which had assigned 

values. Estimated parameters included hydraulic conductivity and recharge parameters. The modelcalibrated distributions of aquifer hydraulic conductivity and recharge are consistent with previous 

data, previous modeling efforts, and the hydrogeologic conceptual model. Calibrated hydraulic-conductivity values for various model layers also are in appropriate relative proportion to each other, 

which is consistent with the hydrogeologic conceptual understanding.

Model fit was evaluated by comparing model-computed heads and flow to observed values. A 

total of 4,984 transient head observations from 1883 through 2003, 147 base-flow observations 

from 1941 through 2003, and 20 flow observations from historical flowing wells were used 

to calibrate the model. The model is well calibrated to the transient heads with a mean head 

residual of –16 ft and a RMSE of 85 ft, which is approximately 3 percent of the 3,024-ft range of 

head observations in the model. The head residuals appear to be independent of measured head 

and do not appear to be spatially correlated across the study area. The weighted-flow residuals 

are biased positively, indicating simulated flows are, in general, less than the observations. Flow 

observations were assigned small weights in the nonlinear regression to minimize the effects 

of inaccurate flow observations on estimated model parameters. Composite scaled sensitivities 

indicate simulated equivalents of observations were most sensitive to estimated parameters 

that control percent precipitation recharged to the Dawson and alluvial aquifers, vertical anisotropy within the bedrock units, specific storage of the bedrock aquifers, and pumping rates for 

wells with the greatest assigned production. Additional data collection or refinement of these 

parameters would have the greatest influence on reducing overall model uncertainty. Composite 

scaled sensitivity values computed from the flow observations indicate that the simulated flows 

are most sensitive to parameters representing the percentage of precipitation recharge to the 

Dawson aquifer, hydraulic conductivity of the upper Dawson aquifer, and the hydraulic conductivity of streambed materials in tributaries. Additional data collection or refinement of these 

parameter values might improve the model fit to the observed flows.

One benefit of the automated techniques used to calibrate the Denver Basin model is that the 

results can be used in an analysis of the relations among uncertainties in parameters, observations, and predictions. For the Denver Basin model, the potentiometric surface for the lower 
xvi

Arapahoe aquifer at the end of the prediction period (2053) is of particular predictive interest 

because of the aquifer’s importance as a water supply. The Observation-Prediction (OPR) and 

Parameter-Prediction (PPR) statistics were calculated for a subset of cells in this model layer (10) 

to identify prediction uncertainty and the effects of additional observations on predictions. Maps 

of the PPR statistic values for a selected parameter were used to identify areas where prediction uncertainty would be most effectively decreased as a result of improved information about 

the parameter. Maps of the OPA statistic values for a selected parameter were used to identify 

areas where parameter uncertainty would be most effectively decreased by adding observations 

(in this case, head observation). Maps of the OPR statistic values were used to identify areas 

where additional head observations likely would be most beneficial in reducing the uncertainty 

in the model-calculated potentiometric surface and drawdown. An OPR statistic map for the 

lower Arapahoe aquifer indicates additional observations in aquifer layers in the north-central 

and south-central parts of the basin would likely reduce uncertainty in the model-calculated 

potentiometric surface of the lower Arapahoe aquifer.

The Denver Basin groundwater flow model developed by this study provides an updated representation of groundwater flow conditions from 1880 through 2003 by using reasonable aquifer 

properties and boundary conditions. The current model is considered an improvement over 

previous models because it explicitly represents the major aquifers and confining units in the 

basin. The current model also represents temporal changes in recharge, evapotranspiration, and 

pumping in a more detailed manner and includes more calibration targets than previous models. The model is well suited for evaluating changing regional groundwater flow directions and 

water budgets through time, making predictions of changing conditions into the near future, and 

guiding future detailed investigations in the study area. Simulation results indicate that development in the Denver Basin has increased water use at the land surface, while pumping from the 

confined sandstone bedrock aquifers is depleting aquifer storage and lowering hydraulic heads. 

The lowered hydraulic heads result in reduced flow from the bedrock units to the alluvial aquifer 

and streams, increased downward interaquifer flow between bedrock layers, and conversion of 

some parts of the system to unconfined conditions. This research supports a conceptual model 

of finite groundwater resources in the Denver Basin and provides a useful tool for guiding future 

groundwater management and monitoring.
xvii

Contents

Foreword ........................................................................................................................................................iii

Acknowledgments........................................................................................................................................iv

Executive Summary.......................................................................................................................................v

Chapter A Summary.............................................................................................................................vi

Chapter B Summary.............................................................................................................................ix

Chapter C Summary...........................................................................................................................xiii

Chapter A

Introduction, Conceptual Model, Hydrogeologic Framework, and Predevelopment Groundwater 

Availability of the Denver Basin Aquifer System

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................3

Previous Work .......................................................................................................................................3

Study Methods ......................................................................................................................................6

Data Compilation..........................................................................................................................6

Model Construction and Calibration.........................................................................................9

Evaluation of Modeling Results...............................................................................................10

Conceptual Model of the Denver Basin Aquifer System ......................................................................10

Overview...............................................................................................................................................11

Physiography.......................................................................................................................................11

Climate..................................................................................................................................................13

Surface-Water Hydrology .................................................................................................................13

Hydrogeologic Framework................................................................................................................17

Bedrock Aquifers and Confining Units...................................................................................18

Laramie–Fox Hills Aquifer ...............................................................................................21

Laramie Confining Unit.....................................................................................................23

Arapahoe Aquifers and Confining Unit .........................................................................23

Denver Aquifer and Confining Units ..............................................................................30

Dawson Aquifers and Confining Unit ............................................................................40

Alluvial Aquifer...........................................................................................................................40

Aquifer Hydraulic Properties ............................................................................................................49

Hydraulic Conductivity and Transmissivity............................................................................49

Storage Parameters ..................................................................................................................50

Predevelopment Groundwater Availability.....................................................................................52

Predevelopment Groundwater Budget ..................................................................................52

Groundwater Budget for the Entire Modeled Area.....................................................59

Groundwater Budget for the Alluvial Aquifer 

and Bedrock Units...............................................................................................59

Groundwater Budget Components ................................................................................59

Recharge and Evapotranspiration ........................................................................59

Groundwater/Surface-Water Interaction............................................................62

Discharge to Springs...............................................................................................63

Interaquifer Flow......................................................................................................66

Groundwater Storage .............................................................................................66

Predevelopment Hydraulic Heads and Groundwater Flow Directions.............................66

Summary........................................................................................................................................................82

References....................................................................................................................................................85
xviii

Chapter B

Effects of Development on Groundwater Availability in the Denver Basin Aquifer System

Introduction...................................................................................................................................................95

Development of the Denver Basin Aquifer System................................................................................95

Land Use...............................................................................................................................................95

Water Use and Groundwater Administration.................................................................................96

Denver Basin Pumping History.........................................................................................................99

Effects of Development on Groundwater Availability in the Denver Basin......................................109

Overview.............................................................................................................................................109

Changes to the Groundwater Budget............................................................................................112

Groundwater Budget for Entire Modeled Area ..................................................................112

Groundwater Budget for Alluvial and Bedrock Aquifers ..................................................115

Alluvial Aquifer Groundwater Budget .........................................................................115

Bedrock Groundwater Budget .....................................................................................116

Groundwater Budget Components .......................................................................................116

Recharge and Evapotranspiration ...............................................................................117

Discharge to Wells .........................................................................................................129

Groundwater/Surface-Water Interaction...................................................................129

Interaquifer Flow.............................................................................................................137

Change in Aquifer Storage............................................................................................138

Changes in Hydraulic Heads and Groundwater Flow Directions .............................................141

Alluvial Aquifer.........................................................................................................................141

Upper Dawson Aquifer ...........................................................................................................144

Lower Dawson Aquifer...........................................................................................................144

Denver Aquifer.........................................................................................................................144

Arapahoe Aquifer ....................................................................................................................151

Laramie–Fox Hills Aquifer ......................................................................................................151

Simulated Predictions of Future Conditions.................................................................................157

Predictive Simulation Results................................................................................................157

Discharge to Streams and the Alluvial Aquifer .........................................................157

Storage .............................................................................................................................161

Changes in Predicted Hydraulic Heads ...............................................................................161

Monitoring the Hydrologic System .........................................................................................................168

Geologic Framework and Aquifer Properties .....................................................................168

Recharge and Discharge .......................................................................................................173

Water-Level Data.....................................................................................................................173

Groundwater Sustainability and Management.....................................................................................175

Summary......................................................................................................................................................176

References..................................................................................................................................................179
xix

Chapter C

Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado

Introduction.................................................................................................................................................181

Model Development ..................................................................................................................................182

Model Conceptualization and Parameterization ..................................................................................182

Model Area and Spatial Discretization .........................................................................................182

Temporal Discretization...................................................................................................................184

Hydrogeologic-Unit Properties.......................................................................................................184

Hydraulic Conductivity............................................................................................................186

Specific Storage and Specific Yield .....................................................................................188

Hydrologic Stresses .........................................................................................................................190

Recharge...................................................................................................................................190

Evapotranspiration ..................................................................................................................191

Streams......................................................................................................................................192

Reservoirs .................................................................................................................................192

Springs.......................................................................................................................................194

Groundwater Flow Across Basin Boundaries ....................................................................194

Historical Flowing Wells .........................................................................................................194

Pumping.....................................................................................................................................195

Multiaquifer Wells ...................................................................................................................195

Solver ................................................................................................................................................195

Model Calibration.......................................................................................................................................195

Pilot-Point Approach to Hydraulic-Conductivity Estimation......................................................206

Calibration Targets............................................................................................................................206

Hydraulic Head.........................................................................................................................207

Stream Base Flow....................................................................................................................213

Historical Flowing Wells .........................................................................................................213

Model-Calibration Results...............................................................................................................213

Calibrated Hydraulic-Conductivity Distribution ..................................................................218

Calibrated Recharge Parameters .........................................................................................222

Comparison of Simulated and Observed Hydraulic Heads...............................................222

Comparison of Simulated and Observed Stream Base Flow............................................224

Parameter Sensitivity..............................................................................................................225

Simulated Groundwater Budgets...................................................................................................226

Simulated Hydraulic Heads.............................................................................................................227

Predictive Simulations ..............................................................................................................................228

Model-Based Statistical Evaluation of Potential Monitoring Locations ..........................................228

Comparisons Between Current and Previous Models .......................................................................262

Model Uncertainty and Limitations ........................................................................................................267

Future Model Maintenance and Applications ......................................................................................269

Summary......................................................................................................................................................270

References..................................................................................................................................................272
xx

Figures

Chapter A

A1. Location of the Denver Basin aquifer system, Colorado ................................................................. 2

A2. Conceptual block diagram of the Denver Basin aquifer system for 

predevelopment conditions .................................................................................................................. 11

A3. Land-surface alititude of the Denver Basin aquifer system, Colorado ...................................... 12

A4. Spatial distribution of mean annual precipitation in the Denver Basin aquifer 

system, 1931–2003, in inches................................................................................................................ 14

A5. Temporal distribution of mean annual precipitation in the Denver Basin aquifer 

system, 1931–2003................................................................................................................................... 15

A6. Locations of streams, stream-gaging stations, and extent of alluvial aquifer 

for the Denver Basin aquifer system.................................................................................................. 16

A7. Photograph of Cherry Creek in Castlewood Canyon State Park near Franktown................... 17

A8. Photograph looking north along Cherry Creek downstream from Castlewood 

Canyon State Park where stream and topographic gradients flatten........................................ 17

A9. Streamflow, estimated base flow, and 180-day moving average of estimated 

base flow for site Cherry Creek at Franktown.................................................................................. 18

A10. Photograph of hogbacks along the western margin of the Denver Basin................................ 18

A11. Location of springs and extent of Denver Basin aquifers and confining units......................... 20

A12. Altitude of the base and total thickness of the Laramie–Fox Hills aquifer................................ 22

A13. Silt-plus-sand thickness of the Laramie–Fox Hills aquifer............................................................ 24

A14. Simulated silt-plus-sand fraction of the Laramie–Fox Hills aquifer............................................ 25

A15. Altitude of the base and total thickness of the Laramie confining unit...................................... 26

A16. Altitude of the base of the lower Arapahoe aquifer and total thickness of the

combined Arapahoe aquifers and confining unit............................................................................ 27

A17. Altitude of the base and thickness of the Arapahoe confining unit............................................ 28

A18. Altitude of the base and thickness of the upper Arapahoe aquifer............................................ 29

A19. Silt-plus-sand thickness of the lower Arapahoe aquifer............................................................... 31

A20. Simulated silt-plus-sand fraction of the lower Arapahoe aquifer............................................... 32

A21. Silt-plus-sand thickness of the upper Arapahoe aquifer............................................................... 33

A22. Simulated silt-plus-sand fraction of the upper Arapahoe aquifer............................................... 34

A23. Altitude of the base and total thickness of the Denver lower confining unit............................ 35

A24. Altitude of the base and total thickness of the Denver aquifer.................................................... 36

A25. Altitude of the base and total thickness of the Denver upper confining unit............................ 37

A26. Silt-plus-sand thickness of the Denver aquifer................................................................................ 38

A27. Simulated silt-plus-sand fraction of the Denver aquifer................................................................ 39

A28. Altitude of the base and total thickness of the lower Dawson aquifer...................................... 41

A29. Silt-plus-sand thickness of the lower Dawson aquifer.................................................................. 42

A30. Simulated silt-plus-sand fraction of the lower Dawson aquifer.................................................. 43

A31. Altitude of the base and total thickness of the Dawson confining unit...................................... 44

A32. Altitude of the base and total thickness of the upper Dawson aquifer...................................... 45

A33. Silt-plus-sand thickness of the upper Dawson aquifer.................................................................. 46

A34. Simulated silt-plus-sand fraction of the upper Dawson aquifer.................................................. 47

A35. Altitude of the base and total thickness of alluvial sand and gravel deposits 

in the Denver Basin................................................................................................................................. 48

A36. Distribution of hydraulic-conductivity values from pumping tests for the 

Denver Basin bedrock aquifers ........................................................................................................... 50
xxi

A37. Simulated specific-yield distribution for the Laramie–Fox Hills aquifer..................................... 53

A38. Simulated specific-yield distribution for the lower Arapahoe aquifer....................................... 54

A39. Simulated specific-yield distribution for the upper Arapahoe aquifer....................................... 55

A40. Simulated specific-yield distribution for the Denver aquifer........................................................ 56

A41. Simulated specific-yield distribution for the lower Dawson aquifer .......................................... 57

A42. Simulated specific-yield distribution for the upper Dawson aquifer.......................................... 58

A43. Predevelopment (pre-1880) groundwater budget for the Denver Basin 

aquifer system.......................................................................................................................................... 61

A44. Predevelopment (pre-1880) groundwater budget inflow and outflow components 

for the entire Denver Basin aquifer system...................................................................................... 62

A45. Predevelopment (pre-1880) groundwater budget inflow and outflow components 

of the Denver Basin alluvial aquifer and bedrock units ................................................................. 63

A46. Estimated areas of predevelopment (pre-1880) agricultural irrigation as simulated 

in the Denver Basin model .................................................................................................................... 64

A47. Spatial distribution of simulated predevelopment (pre-1880) precipitation plus 

irrigation recharge for the Denver Basin modeled area................................................................ 65

A48. Monthly average measured evaporation for three NOAA weather stations near 

the Denver Basin..................................................................................................................................... 66

A49. Spatial distribution of simulated predeveopment (pre-1880) evapotranspiration 

for the Denver Basin modeled area.................................................................................................... 67

A50. Spatial distribution of simulated predevelopment (pre-1880) recharge minus 

evapotranspiration for the Denver Basin modeled area ............................................................... 68

A51. Simulated (A) predevelopment (pre-1880) recharge, evapotranspiration, and net

recharge for the Denver Basin alluvial aquifer and individual bedrock units, and 

(B) net recharge for the Denver Basin alluvial aquifer and individual bedrock units............. 70

A52. Spatial distribution of simulated predevelopment (pre-1880) groundwater flow to 

and from streams for the Denver Basin modeled area.................................................................. 71

A53. Simulated (A) predevelopment (pre-1880) groundwater flow to and from streams

for the Denver Basin alluvial aquifer and individual bedrock units, and (B) net flow 

to streams from the Denver Basin alluvial aquifer and individual bedrock units .................... 72

A54. Simulated predevelopment (pre-1880) interaquifer flow for individual Denver 

Basin bedrock units ................................................................................................................................ 73

A55. Simulated predevelopment (pre-1880) potentiometric surface and groundwater 

flow directions for the alluvial aquifer (model layer 1) ................................................................... 75

A56. Simulated predevelopment (pre-1880) potentiometric surface and groundwater 

flow directions for the upper Dawson aquifer (model layer 2)..................................................... 76

A57. Simulated predevelopment (pre-1880) potentiometric surface and groundwater 

flow directions for the lower Dawson aquifer (model layer 4)..................................................... 77

A58. Simulated predevelopment (pre-1880) potentiometric surface, groundwater 

flow directions, and calculated areas of predevelopment confined and unconfined

conditions for the Denver aquifer (model layer 6)........................................................................... 78

A59. Simulated predevelopment (pre-1880) potentiometric surface and groundwater 

flow directions for the upper Arapahoe aquifer (model layer 8).................................................. 79

A60. Simulated predevelopment (pre-1880) potentiometric surface, groundwater 

flow directions, and calculated areas of predevelopment confined and unconfined

conditions for the lower Arapahoe aquifer (model layer 10)........................................................ 80

A61. Simulated predevelopment (pre-1880) potentiometric surface, groundwater 

flow directions, and calculated areas of predevelopment confined and unconfined

conditions for the Laramie–Fox Hills aquifer (model layer 12)...................................................... 81
xxii

Chapter B

B1. An agricultural area in the South Platte River valley...................................................................... 96

B2. Urbanization along Cherry Creek in downtown Denver................................................................. 96

B3. Land use in the Denver Basin for 2001............................................................................................... 97

B4. Population for the areas overlying the Denver Basin aquifer system and for the 

fastest growing counties in the Denver Basin, 1970–2005............................................................ 98

B5. Aerial photograph of suburban area in the south Denver metropolitan area .......................... 99

B6. A Denver Basin domestic well in a rural residential setting with new subdivision 

on the horizon........................................................................................................................................... 99

B7. Locations of late 19th century artesian wells reported by Emmons and others (1896) 

in downtown Denver, Colorado.......................................................................................................... 100

B8. Total number of Denver Basin wells, 1880–2003............................................................................ 102

B9. Number of Denver Basin alluvial wells categorized by water use for (A) 1880–2003, 

and (B) 2003............................................................................................................................................. 102

B10. Locations of Denver Basin alluvial wells within limits of simulated alluvial 

aquifer, 2003 ............................................................................................................................................ 103

B11. Number of Denver Basin bedrock wells categorized by water use for (A) 1880–2003,

and (B) 2003............................................................................................................................................. 104

B12. Number of Denver Basin bedrock wells categorized by aquifer for (A) 1880–2003, 

and (B) 2003............................................................................................................................................. 104

B13. Locations of Denver Basin bedrock domestic wells categorized by aquifer, 2003 ............... 105

B14. Locations of Denver Basin bedrock municipal wells categorized by aquifer and 

areas of concentrated municipal pumping, 2003........................................................................... 106

B15. Total estimated pumping from Denver Basin alluvial and bedrock wells for 

(A) 1880–2003, and (B) 2003................................................................................................................. 107

B16. Estimated pumping from Denver Basin alluvial and bedrock wells categorized 

by water use, 2003................................................................................................................................. 108

B17. Estimated pumping from Denver Basin alluvial wells categorized by water use 

for (A) 1880–2003, and (B) 2003........................................................................................................... 108

B18. Estimated pumping from Denver Basin bedrock wells categorized by water use 

for (A) 1880–2003, and (B) 2003........................................................................................................... 109

B19. Estimated pumping from Denver Basin bedrock wells categorized by aquifer for 

(A) 1880–2003, and (B) 2003................................................................................................................. 110

B20. Estimated pumping from individual Denver Basin bedrock aquifers categorized 

by aquifer and by water use, 2003..................................................................................................... 110

B21. Conceptual block diagram of the Denver Basin aquifer system for developed 

conditions................................................................................................................................................ 111

B22. Groundwater budget for entire Denver Basin aquifer system, the alluvial aquifer, 

and bedrock units, 2003........................................................................................................................ 111

B23. Simulated transient groundwater budget for (A) the entire Denver Basin modeled 

area, (B) the alluvial aquifer, and (C) the bedrock aquifers and confining units, 

1879–2003................................................................................................................................................. 114

B24. Groundwater budget inflow and outflow components for the entire Denver Basin 

aquifer system at the end of the model calibration period, 2003 ............................................... 116

B25. Groundwater budget inflow and outflow components for the Denver Basin alluvial

aquifer and bedrock units at the end of the model calibration period, 2003........................... 120

B26. Estimated areas of agricultural and urban irrigation as simulated by the Denver 

Basin model, 1940–1953....................................................................................................................... 121

B27. Estimated areas of agricultural and urban irrigation as simulated by the Denver 

Basin model, 1954–1986....................................................................................................................... 122
xxiii

B28. Estimated areas of agricultural and urban irrigation as simulated by the Denver 

Basin model, 1987–2003....................................................................................................................... 123

B29. Simulated transient recharge, evapotranspiration, and recharge minus 

evapotranspiration for the alluvial aquifer and bedrock units in the Denver Basin,

1879–2003................................................................................................................................................. 124

B30. Spatial distribution of simulated precipitation plus irrigation recharge for the 

Denver Basin modeled area, 2003..................................................................................................... 125

B31. Simulated transient precipitation plus irrigation recharge for individual Denver 

Basin bedrock units, 1879–2003......................................................................................................... 127

B32. Spatial distribution of simulated evapotranspiration for the Denver Basin modeled

area, 2003................................................................................................................................................. 128

B33. Simulated transient evapotranspiration for individual Denver Basin bedrock units,

1879–2003................................................................................................................................................. 129

B34. Spatial distribution of simulated recharge minus evapotranspiration for the 

Denver Basin modeled area, 2003..................................................................................................... 130

B35. Simulated transient recharge minus evapotranspiration for individual Denver 

Basin bedrock units, 1879–2003......................................................................................................... 131

B36. Simulated transient pumping from Denver Basin alluvial and bedrock aquifers,

1879–2003................................................................................................................................................. 131

B37. Simulated transient pumping from individual Denver Basin bedrock aquifers, 

1879–2003................................................................................................................................................. 132

B38. Spatial distribution of simulated groundwater flow to and from streams for the 

Denver Basin modeled area, 2003..................................................................................................... 133

B39. Spatial distribution of change in sumulated groundwater flow to and from 

streams for the Denver Basin modeled area, 1880–2003............................................................. 134

B40. Simulated transient groundwater flow to and from streams from the alluvial 

aquifer and bedrock units for the Denver Basin modeled area, 1879–2003............................ 135

B41. Simulated transient net groundwater flow to streams from individual bedrock 

aquifers in the Denver Basin modeled area, 1879–2003 .............................................................. 135

B42. Simulated transient flow between the alluvial aquifer and bedrock units for 

the Denver Basin modeled area, 1879–2003................................................................................... 136

B43. Simulated transient net flow between the alluvial aquifer and individual bedrock 

aquifers for the Denver Basin modeled area, 1879–2003 ............................................................ 136

B44. Simulated transient net flow between bedrock units in the Denver Basin modeled

area, 1879–2003...................................................................................................................................... 137

B45. Change in simulated net flow between bedrock units in the Denver Basin modeled

area, 1880–2003...................................................................................................................................... 138

B46. Simulated transient net storage loss (positive) and gain (negative) rates for the 

alluvial aquifer and bedrock units in the Denver Basin modeled area, 1879–2003 ............... 139

B47. Simulated transient net storage-depletion rates for individual bedrock units in 

the Denver Basin modeled area, 1879–2003................................................................................... 140

B48. Simulated transient cumulative volume of water removed from storage for bedrock

units in the Denver Basin modeled area, 1880–2003..................................................................... 140

B49. Location of wells in the Colorado Division of Water Resources Denver Basin 

water-level monitoring network......................................................................................................... 142

B50. Simulated 2003 potentiometric surface and hydraulic-head change from 1880 

to 2003 for the alluvial aquifer (model layer 1)................................................................................ 143

B51. Simulated 2003 potentiometric surface and hydraulic-head change from 1880 

to 2003 for the upper Dawson aquifer (model layer 2).................................................................. 145
xxiv

B52. Hydrographs of measured and simulated hydraulic head for selected wells 

completed in the upper Dawson aquifer......................................................................................... 146

B53. Simulated 2003 potentiometric surface and hydraulic-head change from 1880 

to 2003 for the lower Dawson aquifer (model layer 4).................................................................. 147

B54. Hydrographs of measured and simulated hydraulic head for selected wells 

completed in the lower Dawson aquifer.......................................................................................... 148

B55. Simulated 2003 potentiometric surface and hydraulic-head change from 1880 

to 2003 for the Denver aquifer (model layer 6)................................................................................ 149

B56. Hydrographs of measured and simulated hydraulic head for selected wells 

completed in the Denver aquifer....................................................................................................... 150

B57. Calculated areas of confined and unconfined conditions for the Denver aquifer 

(model layer 6), 2003.............................................................................................................................. 152

B58. Simulated 2003 potentiometric surface and hydraulic-head change from 1880 

to 2003 for the upper Arapahoe aquifer (model layer 8)............................................................... 153

B59. Simulated 2003 potentiometric surface and hydraulic-head change from 1880 

to 2003 for the lower Arapahoe aquifer (model layer 10)............................................................. 154

B60. Hydrographs of measured and simulated hydraulic head for selected wells 

completed in the lower Arapahoe aquifer ...................................................................................... 155

B61. Calculated areas of confined and unconfined conditions for the lower Arapahoe 

aquifer (model layer 10), 2003 ............................................................................................................. 156

B62. Simulated 2003 potentiometric surface and hydraulic-head change from 1880 

to 2003 for the Laramie–Fox Hills aquifer (model layer 12).......................................................... 158

B63. Calculated areas of confined and unconfined conditions for the Laramie–Fox Hills

aquifer (model layer 12), 2003 ............................................................................................................. 159

B64. Hydrographs of measured and simulated hydraulic head for selected wells 

completed in the Laramie–Fox Hills aquifer.................................................................................... 160

B65. Simulated transient flow between the Denver Basin alluvial aquifer and bedrock 

units for model-calibration period and predictive simulations, 1879–2053.............................. 161

B66. Simulated cumulative volume of water removed from storage for Denver Basin 

bedrock units, 1880–2053..................................................................................................................... 162

B67. Simulated 2053 potentiometric surface and hydraulic-head change from 2004 

to 2053 for the upper Dawson aquifer (model layer 2) for predictive simulation 1 ................ 163

B68. Simulated 2053 potentiometric surface and hydraulic-head change from 2004 

to 2053 for the lower Dawson aquifer (model layer 4) for predictive simulation 1................. 164

B69. Simulated 2053 potentiometric surface and hydraulic-head change from 2004 

to 2053 for the Denver aquifer (model layer 6) for predictive simulation 1 .............................. 165

B70. Calculated areas of confined and unconfined conditions for the Denver aquifer 

(model layer 6) in 2053 for predictive simulation 1......................................................................... 166

B71. Simulated 2053 potentiometric surface and hydraulic-head change from 2004 

to 2053 for the lower Arapahoe aquifer (model layer 10) for predictive simulation 1 ........... 167

B72. Simulated 2053 potentiometric surface and hyraulic-head change from 2004 to 

2053 for the Laramie–Fox Hills aquifer (model layer 12) for predictive simulation 1 ............. 169

B73. Calculated areas of confined and unconfined conditions for the Laramie–Fox Hills

aquifer (model layer 12) in 2053 for predictive simulation 1 ........................................................ 170

B74. Simulated 2053 potentiometric surface for reduced pumping conditions and 

hydraulic-head difference between predictive simulations 1 and 2 for the lower

Arapahoe aquifer (model layer 10).................................................................................................... 171

B75. Simulated 2053 potentiometric surface for reduced pumping conditions and 

hydraulic-head difference between predictive simulations 1 and 2 for the Denver

aquifer (model layer 6).......................................................................................................................... 172
xxv

Chapter C

C1. Extent of Denver Basin model grid, active model cells, and uppermost model layer........... 183

C2. Temporal discretization of (A) annual precipitation from station data, and 

(B) simulated pumping.......................................................................................................................... 185

C3. Location of pilot points for estimating hydraulic-conductivity distributions for 

model layers 6 (Denver aquifer), 8 and 10 (upper and lower Arapahoe aquifers 

undifferentiated), and 12 (Laramie–Fox Hills aquifer)................................................................... 189

C4. Evapotranspiration as a function of depth to water used for the Denver 

Basin model ............................................................................................................................................ 192

C5. Locations of boundary condition cells for the Denver Basin model......................................... 193

C6. Calibrated hydraulic-conductivity distribution and hydraulic-conductivity values 

estimated from aquifer tests for the Denver aquifer..................................................................... 219

C7. Calibrated hydraulic-conductivity distribution and hydraulic-conductivity values 

estimated from aquifer tests for the lower Arapahoe aquifer.................................................... 220

C8. Calibrated hydraulic-conductivity distribution and hydraulic-conductivity values 

estimated from aquifer tests for the Laramie–Fox Hills aquifer................................................. 221

C9. Head observations in relation to simulated heads for the Denver Basin model.................... 222

C10. Distribution of head residuals for the Denver Basin model ........................................................ 223

C11. Head observations in relation to head residuals for the Denver Basin model....................... 223

C12. Weighted head observations in relation to simulated head for the Denver 

Basin model ............................................................................................................................................ 224

C13. Spatial distribution of head residuals for the Denver Basin model, 1978 ................................ 225

C14. Flow observations in relation to simulated flows for the Denver Basin model...................... 226

C15. Simulated equivalents in relation to weighted flow residuals for the Denver 

Basin model ............................................................................................................................................ 226

C16. Composite scaled sensitivities for the parameters of the final calibrated Denver 

Basin model for (A) all head and flow observations; (B) head observations only; 

and (C) flow observations only........................................................................................................... 227

C17. Simulated 1956 potentiometric surface and pumping rates for the alluvial aquifer

(model layer 1)........................................................................................................................................ 233

C18. Simulated 1978 potentiometric surface and pumping rates for the alluvial aquifer

(model layer 1)........................................................................................................................................ 234

C19. Simulated 2003 potentiometric surface and pumping rates for the alluvial aquifer

(model layer 1)........................................................................................................................................ 235

C20. Simulated 1956 potentiometric surface and pumping rates for the upper Dawson 

aquifer (model layer 2).......................................................................................................................... 236

C21. Simulated 1978 potentiometric surface and pumping rates for the upper Dawson 

aquifer (model layer 2).......................................................................................................................... 237

C22. Simulated 2003 potentiometric surface and pumping rates for the upper Dawson 

aquifer (model layer 2).......................................................................................................................... 238

C23. Simulated 1956 potentiometric surface and pumping rates for the lower Dawson 

aquifer (model layer 4).......................................................................................................................... 239

C24. Simulated 1978 potentiometric surface and pumping rates for the lower Dawson 

aquifer (model layer 4).......................................................................................................................... 240

C25. Simulated 2003 potentiometric surface and pumping rates for the lower Dawson 

aquifer (model layer 4).......................................................................................................................... 241

C26. Simulated 1956 potentiometric surface and pumping rates for the Denver aquifer

(model layer 6)........................................................................................................................................ 242

C27. Simulated 1978 potentiometric surface and pumping rates for the Denver aquifer

(model layer 6)........................................................................................................................................ 243
xxvi

C28. Simulated 2003 potentiometric surface and pumping rates for the Denver aquifer

(model layer 6)........................................................................................................................................ 244

C29. Simulated 1956 potentiometric surface and pumping rates for the upper Arapahoe

aquifer (model layer 8).......................................................................................................................... 245

C30. Simulated 1978 potentiometric surface and pumping rates for the upper Arapahoe

aquifer (model layer 8).......................................................................................................................... 246

C31. Simulated 2003 potentiometric surface and pumping rates for the upper Arapahoe

aquifer (model layer 8).......................................................................................................................... 247

C32. Simulated 1956 potentiometric surface and pumping rates for the lower Arapahoe

aquifer (model layer 10)........................................................................................................................ 248

C33. Simulated 1978 potentiometric surface and pumping rates for the lower Arapahoe

aquifer (model layer 10)........................................................................................................................ 249

C34. Simulated 2003 potentiometric surface and pumping rates for the lower Arapahoe

aquifer (model layer 10)........................................................................................................................ 250

C35. Simulated 1956 potentiometric surface and pumping rates for the Laramie–Fox Hills

aquifer (model layer 12)........................................................................................................................ 251

C36. Simulated 1978 potentiometric surface and pumping rates for the Laramie–Fox Hills

aquifer (model layer 12)........................................................................................................................ 252

C37. Simulated 2003 potentiometric surface and pumping rates for the Laramie–Fox Hills

aquifer (model layer 12)........................................................................................................................ 253

C38. Parameter-prediction statistic (PPR) distribution for parameter p12_10................................. 255

C39. Parameter-prediction statistic (PPR) distribution for parameter p12_09................................. 256

C40. Parameter-prediction statistic (PPR) distribution for parameter pKa_11................................ 257

C41. Observation-parameter (OPA) statistic distribution for parameter p12_10............................. 258

C42. Observation-parameter (OPA) statistic distribution for parameter p12_09............................. 259

C43. Observation-parameter (OPA) statistic distribution for parameter pKa_11............................ 260

C44. Observation-parameter (OPA) statistic distribution for parameter p10_03............................. 261

C45. Observation-prediction (OPR) statistic distribution for the lower Arapahoe aquifer............ 263

C46. Observation-prediction (OPR) statistic distribution for the Laramie–Fox Hills aquifer......... 264

Tables

Chapter A

A1. Geostatistical models, model-fitting parameters, and cross-validation statistics 

for Denver Basin bedrock units ............................................................................................................. 7

A2. Index of Denver Basin hydrogeologic framework spatial data...................................................... 8

A3. Geology, hydrogeology, and water-use characteristics of the Denver Basin aquifers,

Colorado (adapted from Kirkham and Ladwig [1979]; Robson [1987]; Nichols and 

Fleming [2002]; Raynolds [2002]; Lapey-Woodard and others [2002]; Thorson, [2003]) .......... 19

A4. Summary of simulated aquifer areas.................................................................................................. 21

A5. Summary of hydraulic-conductivity values calculated from pumping tests (adapted

from Colorado Division of Water Resources [2005])....................................................................... 51

A6. Summary of specific-yield values ....................................................................................................... 52

A7. Simulated predevelopment (pre-1880) groundwater budget for entire Denver Basin

aquifer system, the alluvial aquifer, and the bedrock units........................................................... 60

A8. Simulated predevelopment (pre-1880) groundwater budget for individual bedrock

aquifer and confining units in the Denver Basin.............................................................................. 69

A9. Estimated unconfined groundwater storage for individual bedrock aquifers in the 

Denver Basin............................................................................................................................................ 74
xxvii

Chapter B

B1. Estimated pumping rates assigned to wells in the Denver Basin model................................. 101

B2. Simulated transient groundwater budget for the entire Denver Basin aquifer system 

during the model-calibration period, 1879–2003............................................................................ 112

B3. Simulated transient groundwater budget for the Denver Basin alluvial aquifer during 

the model-calibration period, 1879–2003 ......................................................................................... 117

B4. Simulated transient groundwater budget for the Denver Basin bedrock aquifers and 

confining units during the model-calibration period, 1879–2003................................................ 118

B5. Simulated groundwater budget for individual bedrock aquifers and confining units in 

the Denver Basin, 2003......................................................................................................................... 126

Chapter C

C1. Vertical discretization of Denver Basin aquifers and confining units....................................... 184

C2. Temporal discretization for the Denver Basin model-calibration period................................. 186

C3. Hydraulic-conductivity conceptualization and parameterization ............................................. 187

C4. Parameters of exponential models fitted to semi-variograms of log hydraulicconductivity data from aquifer tests................................................................................................. 190

C5. Specific-yield conceptualization and parameterization .............................................................. 190

C6. Recharge conceptualization and parameterization...................................................................... 191

C7. Properties assigned to Denver Basin model features representing the South Platte 

River and streams.................................................................................................................................. 194

C8. Properties assigned to Denver Basin model features representing reservoirs .................... 194

C9. Tabulation of well locations, depths, head, discharge, and assigned model locations 

for late 19th century wells listed in Emmons and others (1896) ................................................. 196

C10. Historical head observations derived from Emmons and others (1896)................................... 208

C11. Summay of stream base-flow observations for eight surface-water gaging stations 

in the Denver Basin............................................................................................................................... 214

C12. Drain observations derived from historical data provided by Emmons and others (1896)....214

C13. Calibrated Denver Basin model parameter values ....................................................................... 215

C14. Simulated transient inflows for the Denver Basin entire modeled area, alluvial 

aquifer, and bedrock units, 1879–2003.............................................................................................. 230

C15. Simulated transient outflows for the Denver Basin entire modeled area, alluvial 

aquifer, and bedrock units, 1879–2003.............................................................................................. 231

C16. Simulated transient net water budget for the Denver Basin entire modeled area, 

alluvial aquifer, and bedrock units, 1879–2003................................................................................ 232

C17. Denver Basin model predictive simulation stress periods.......................................................... 254

C18. Parameters with the highest ranking parameter-prediction (PPR) statistic values 

from the Denver Basin model............................................................................................................. 254

C19. Comparison of vertical hydraulic-conductivity values between the current and 

previous Denver Basin models .......................................................................................................... 265

C20. Comparison of predevelopment groundwater budget for current and previous Denver 

Basin models .......................................................................................................................................... 266

C21. Comparison of outflow to the surficial system (streams, springs, and the alluvial 

aquifer) from bedrock aquifers and confining units for predevelopment conditions 

of the current and previous Denver Basin models........................................................................ 267
xxviii

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

acre 0.4047 hectare (ha)

acre 0.4047 square hectometer (hm2) 

acre 0.004047 square kilometer (km2)

square foot (ft2) 929.0 square centimeter (cm2)

square foot (ft2) 0.09290 square meter (m2)

square inch (in2) 6.452 square centimeter (cm2)

section (640 acres or 1 square mile) 259.0 square hectometer (hm2) 

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3) 

million gallons (Mgal) 3,785 cubic meter (m3)

cubic foot (ft3) 28.32 cubic decimeter (dm3) 

cubic foot (ft3) 0.02832 cubic meter (m3) 

acre-foot (acre-ft) 1,233 cubic meter (m3)

acre-foot (acre-ft) 0.001233 cubic hectometer (hm3) 

Flow rate

acre-foot per day (acre-ft/d) 0.01427 cubic meter per second (m3/s)

acre-foot per year (acre-ft/yr) 1,233 cubic meter per year (m3/yr)

acre-foot per year (acre-ft/yr) 0.001233 cubic hectometer per year (hm3/yr)

foot per second (ft/s) 0.3048 meter per second (m/s)

foot per day (ft/d) 0.3048 meter per day (m/d)

foot per year (ft/yr) 0.3048 meter per year (m/yr)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

cubic foot per day (ft3/d) 0.02832 cubic meter per day (m3/d)

gallon per minute (gal/min) 0.06309 liter per second (L/s)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

Specific capacity

gallon per minute per foot [(gal/min)/ft)] 0.2070 liter per second per meter [(L/s)/m]

Hydraulic conductivity and velocity

foot per day (ft/d) 0.3048 meter per day (m/d)

miles per hour (mi/hr) 1.61 kilometer per hour (km/hr)

Hydraulic gradient

foot per mile (ft/mi) 0.1894 meter per kilometer (m/km)

Transmissivity*

foot squared per day (ft2/d) 0.09290 meter squared per day (m2/d) 

Leakance

foot per day per foot [(ft/d)/ft] 1 meter per day per meter

inch per year per foot [(in/yr)/ft] 83.33 millimeter per year per meter [(mm/yr)/m]

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F–32)/1.8

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).
xxix

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

*Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times 

foot of aquifer thickness [(ft3/d)/ft2]ft. In this report, the mathematically reduced form, foot 

squared per day (ft2/d), is used for convenience.

NOTE TO USGS USERS: Use of hectare (ha) as an alternative name for square hectometer 

(hm2) is restricted to the measurement of small land or water areas. Use of liter (L) as a special 

name for cubic decimeter (dm3) is restricted to the measurement of liquids and gases. No prefix 

other than milli should be used with liter. Metric ton (t) as a name for megagram (Mg) should be 

restricted to commercial usage, and no prefixes should be used with it.

Abbreviations

BFI Base Flow Index

CDWR Colorado Division of Water Resources

CWCB Colorado Water Conservation Board

DRN MODFLOW Drain package

ETS MODFLOW Evapotranspiration Segment package

FHB MODFLOW Flow and Head Boundary package

GHB MODFLOW General-Head Boundary package

IDW Inverse-distance weighted contouring method

MNW MODFLOW Multi-Node Well package

NED National elevation dataset

NOAA National Oceanic and Atmospheric Administration

NWIS National Water Information System

OPR Observation-Prediction statistic

PPR Parameter-Prediction statistic

RASA Regional Aquifer System Analysis

SB85-5 Colorado Senate Bill SB 85-5

SB96-74 Colorado Senate Bill SB 96-74

SFR2 MODFLOW Streamflow-Routing package

SMWSS South Metro Water Supply Study

SPDSS South Platte Decision Support System

USGS U.S. Geological Survey

WEL MODFLOW Well package

Chapter A. Introduction, Conceptual Model, Hydrogeologic 

Framework, and Predevelopment Groundwater Availability 

of the Denver Basin Aquifer System, Colorado

By Suzanne S. Paschke, Edward R. Banta, Jean A. Dupree, and Joseph P. Capesius

Municipal and domestic water supplies use Denver 

Basin groundwater resources to support population and housing 

growth in the Front Range urban corridor (Hillier and others, 

1978; Moore and others, 2007). Municipal utilities manage public water supplies in the basin and rely on a combination of surface water from the mountains of the Front Range, groundwater 

from alluvial aquifers, and groundwater from the Denver Basin 

bedrock aquifers. Because the prior appropriation doctrine 

governs water rights in Colorado, older established municipalities such as Denver hold water rights senior to more recently 

established development. Growing and recently established 

municipalities, such as those in Douglas and El Paso Counties, 

typically rely on Denver Basin groundwater for water supply 

because they are in areas with limited surface water, or limited 

available surface-water rights, or both (Hillier and others, 1978). 

Denver Basin bedrock groundwater provides more than 70 percent of the water supply in the south Denver metropolitan area, 

and some water providers consider groundwater availability in 

this area insufficient for long-term demand (South Metro Water 

Supply Study Board, written commun., 2003; Colorado Water 

Conservation Board, 2004a). Domestic groundwater use is less 

than municipal use but is widespread across the basin, and rural 

areas on the semiarid plains depend solely on self-supplied 

groundwater for water supply.

The Denver Basin aquifer system is administratively 

recognized as nonrenewable because the aquifers are primarily confined and receive little precipitation recharge (Graham 

and VanSlyke, 2004). As population and groundwater use 

increased in the 1970s and 1980s, Colorado Senate Bill 85–5 

(SB85–5) was implemented, which required the Colorado 

State Engineer to promulgate rules and regulations governing 

the withdrawal of groundwater from the Denver Basin aquifer 

system. SB85–5 adopted a 100-year aquifer life to determine 

decreed pumping rates for a given parcel of land and accepted 

storage depletion by not protecting artesian head or aquifer 

water levels (Graham and VanSlyke, 2004). Population, housing development, and associated groundwater pumping in 

the Denver Basin have continued to increase since the 1980s, 

causing renewed concern for groundwater availability and the 

usable life of the Denver Basin aquifer system (Moore and 

others, 2007).

Introduction

The Denver Basin aquifer system is a critical water 

resource for growing municipal, industrial and domestic uses 

along the semiarid Front Range urban corridor of Colorado. 

The confined aquifer system consists of Upper Cretaceousto Tertiary-age bedrock sandstones, which underlie about 

7,000 square miles (mi2) of the Great Plains along the eastern front of the Rocky Mountain Front Range (fig. A1) 

(Fenneman, 1931; Robson, 1987, 1989). Unconsolidated 

Quaternary alluvial and eolian deposits overlie the bedrock 

sandstone aquifers and claystone confining units, and the 

Quaternary deposits form a productive unconfined alluvial 

aquifer where saturated, primarily along present-day stream 

channels (Hunt, 1954; Scott, 1960; Robson, 1989, 1996). 

Streams draining eastward into the Denver Basin are generally 

perennial and originate as snowmelt runoff from the Rocky 

Mountain Front Range. Streams that originate on the semiarid 

plains within the Denver Basin are generally ephemeral and 

intermittent because they receive water primarily from local 

precipitation runoff and groundwater discharge. Groundwater 

in alluvial and bedrock aquifer interacts with surface water as 

streams cross the basin, and there is groundwater movement 

between the alluvial and bedrock aquifers (Robson, 1996).

Mining, transportation, agricultural, and urban activities 

developed along the Front Range beginning in the 1800s, with 

Denver serving as a local and regional transportation hub for 

agricultural products from the South Platte River Valley and 

mining products from the Front Range. Today, urban and suburban land use extends north from Denver to Fort Collins and 

south to Colorado Springs in an area known as the Front Range 

urban corridor (Robson, 1989). Population of the metropolitan 

areas overlying the Denver Basin aquifers has approximately 

doubled from 1.3 million in 1970 to about 2.7 million in 2005 

(T.L. Arnold, U.S. Geological Survey, written commun., 2009). 

Development has been especially rapid and extensive on the 

west side of the basin between Denver and Colorado Springs. 

This area experienced the fastest housing growth of any county 

in the United States in 2002 (Perry and Mackun, 2002) with a 

population increase in Douglas County of approximately thirtyfold from 1970 to 2005.
2 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Groundwater availability studies provide information 

and tools for water administrators, providers, consumers, 

and interested citizens to make informed decisions with 

respect to regional water-management planning (Reilly and 

others, 2008). In the Denver Basin, there is an ongoing need 

for monitoring and modeling to improve understanding of 

groundwater availability and to assess water use, water-level 

decline, and storage depletion on a recurring basis. Adequate 

monitoring of the hydrologic system is important to evaluate 

the effects of continued pumping (Taylor and Alley, 2001), 

and monitoring data are used to build, calibrate, and refine 

groundwater flow models. In turn, groundwater flow models 

serve as tools for predicting future aquifer conditions and 

guiding water-management decisions for complex aquifer 

systems such as the Denver Basin (Taylor and Alley, 2001).

Assessing groundwater availability is an ongoing process, 

which requires continual or periodic renewed evaluation 

of monitoring and modeling as available data, technology, 

water use, and other issues of concern change over time 

(Reilly, 2005). To understand and simulate a groundwater 

system, basic data regarding the hydrogeologic framework, 

water-budget components, hydraulic-head distribution, 

and aquifer properties of hydraulic conductivity and storage are needed (Reilly, 2005). Computer simulations of 

groundwater flow use this basic information to quantify flow 

and hydraulic heads for the system of interest and provide 

useful tools for quantifying and evaluating system changes 

over time.

!

!

!

!

!

Yampa River

White Riv er

Colorado River

Rio Grande

San Juan R

Arkansas River

South Platte River

Gunnison River

Denver 

Basin

Arkansas River 

Basin

South Platte 

River Basin Great Plains

Rocky Mountain Front Range

Pueblo

Denver

Fort

Collins

Grand

Junction

Colorado

Springs

Palmer Div ide

108° 107° 106° 105° 104° 103°

40°

39°

38°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W 0 50 100 KILOMETERS

0 50 100 MILES

C O L O R A D O

Figure A1. Location of the Denver Basin aquifer system, Colorado.
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 3

Two broad themes categorize groundwater issues in the 

Denver Basin: (1) hydrologic effects of continued pumping 

on future groundwater availability and (2) political, legal, 

and social concerns related to usable aquifer life and effective management of regional water resources. In 2004, the 

U.S. Geological Survey (USGS) initiated large-scale regional 

studies to provide updated assessments of groundwater availability in important principal aquifers across the United States, 

including the Denver Basin. This study of the Denver Basin 

aquifer system evaluates the hydrologic effects of ongoing 

pumping and documents an updated groundwater flow model 

used for assessing hydrologic conditions. The calibrated 

groundwater flow model provides quantitative estimates of 

groundwater flow conditions and provides a useful tool for 

managers to analyze temporal changes to the hydrologic 

system in response to changing climatic conditions and future 

groundwater development.

Purpose and Scope

The purpose of this Professional Paper is to describe 

groundwater availability in the Denver Basin aquifer system. 

A basin-scale evaluation of groundwater resources in the 

Denver Basin aquifer system is provided that advances the 

understanding of system response to development. Specific 

objectives of this Denver Basin groundwater availability analysis were to (1) advance the understanding of the three-dimensional nature of the hydrogeologic framework including the 

extent and thickness of aquifers and confining units; (2) advance 

the understanding of regional groundwater budgets and components including recharge, discharge, and aquifer storage for 

the entire system and separately for the bedrock and alluvial 

aquifers; (3) evaluate recent and future system response to 

development at a scale relevant to basinwide water-management 

decisions; and (4) explore the use of modeling to evaluate 

hydrologic monitoring of system changes.

The document consists of three chapters describing 

groundwater availability in the Denver Basin. This chapter, 

Chapter A, presents the introduction, previous work, study 

methods, and a conceptual model of the hydrogeologic setting 

including the hydrogeologic framework and predevelopment 

groundwater availability. Chapter B describes the land and 

groundwater-use changes in response to population growth 

in the Denver Basin and the effects of that development on 

groundwater availability. The changes in land and groundwater use are used as input to the groundwater flow model as 

described in Chapter C, and the interpretations of the effects 

of development on the groundwater flow system are based 

largely on modeling results from this study. Effects included 

in the discussion are changes to recharge and discharge 

components of the groundwater budget (recharge, evapotranspiration, pumping, groundwater/surface-water interaction, interaquifer flow, and storage) and the effects of those 

changes on groundwater levels and flow directions from 1880 

through 2003. Chapter B also presents predictions of future 

hypothetical conditions and a discussion of monitoring data 

needs. Chapter C presents details of the groundwater flow 

model used for the groundwater availability analysis including model setup, calibration results, parameter sensitivity, and 

future work.

Previous Work

Artesian groundwater conditions and the underlying 

structural geology of the Denver Basin were first recognized 

and described by Cross and others (1884), Emmons and 

others (1896), Darton (1905), and Richardson (1915). Since 

this early work, numerous geologic and hydrologic publications have described the Denver Basin tectonics, structural 

geology, stratigraphy, geologic history, energy resources, hazards, and groundwater. The Rocky Mountain Association of 

Geologists published compilations of papers related to Denver 

Basin geology (Katich and Bolyard, 1963; Rocky Mountain 

Association of Geologists, 1978) and Colorado Geology (Kent 

and Porter, 1980), which contain several papers cited herein. 

Other publications consist of indexes and bibliographies of 

early reports addressing the geology and hydrology of the 

Denver Basin (Chronic and Chronic, 1974; Hampton and 

others, 1974; Hampton, 1975; Anna, 1975; Norris and others, 

1983; and Wireman and Romero, 1989). In addition, a few 

documents provide overviews of groundwater resources for 

the State of Colorado, including Pearl (1974), Aikin and others 

(2000), and Topper and others (2003). The following discussion of previous work focuses on those studies most pertinent 

to this groundwater availability report.

Available geologic maps for the eastern plains encompassing the Denver Basin include the Geologic Map of Colorado 

(Tweto, 1979), geologic maps for 1° × 2° quadrangle sheets 

(Scott and others, 1978; Sharps, 1976, 1980; Bryant and others, 

1981), and maps for individual 1:24,000-scale quadrangles 

(for example Scott, 1963a, 1963b). The Colorado Geological 

Survey (CGS) currently (2010) is updating geologic maps of 

the Front Range Urban Corridor as part of the STATEMAP 

program of the National Geologic Mapping Act of 1997 (Carroll 

and Crawford, 2000), and several quadrangle maps have been 

completed for the southwest part of the Denver Basin (Carroll 

and Crawford, 2000; Thorson and others, 2002; Madole, 2003; 

Madole and Thorson, 2003; Rowley and others, 2003; Thorson 

and Madole, 2003; Thorson, 2003, 2004a, 2004b, 2005a, 2005b, 

2006, 2008; Thorson and Himmelreich, 2004; Morgan and 

others, 2005a, 2005b).

Systematic hydrogeologic characterization of the 

Denver Basin aquifers began in the 1970s as part of developing nontributary groundwater rules established by Colorado 

Senate Bill 213 (Graham and VanSlyke, 2004). The Laramie–

Fox Hills was the first aquifer mapped in 1971 (Romero 

and Hampton, 1972), and collaborative work between the 

Colorado Division of Water Resources (CDWR) and the 

USGS continued through the 1970s and 1980s, differentiating, mapping, and characterizing the four recognized aquifer 
4 Groundwater Availability of the Denver Basin Aquifer System, Colorado

units (Romero, 1976). Results of these efforts included 

hydrologic atlases by Robson and Romero (1981a, 1981b), 

Robson, Romero, and Zawistowski (1981), and Robson, 

Wacinski, and others (1981), which presented the geologic 

structure, hydrology, and water quality of the Dawson, 

Denver, Arapahoe, and Laramie–Fox Hills aquifers. Robson 

(1983) tabulated hydraulic-conductivity, transmissivity, and 

storage-coefficient data for individual bedrock aquifers. The 

hydrologic atlases and data compiled through the 1980s later 

supported construction of a groundwater flow model of the 

Denver Basin aquifers (Robson, 1987). The CDWR updated 

hydrologic atlases of the Denver Basin in 1988 using additional available data to create maps of geologic structure, 

silt-plus-sand thickness, and areas of nontributary groundwater 

for each of the bedrock aquifers (VanSlyke and others, 1988a, 

1988b, 1988c, 1988d). The updated hydrologic atlases formed 

the basis for defining aquifer boundaries since 1988 (Graham 

and VanSlyke, 2004).

Other water-resources studies have examined specific 

parts of the Denver Basin aquifer system. For example, 

Livingston and others (1975, 1976) evaluated surface-water 

and groundwater resources in El Paso County. Hillier and 

others (1978) examined the hydrology and water quality of 

the Arapahoe aquifer in the Englewood–Castle Rock area 

south of Denver, and Schneider (1980) examined the hydrology and water quality of the Laramie–Fox Hills aquifer in 

parts of Adams, Boulder, Jefferson, and Weld Counties. The 

hydrogeology of Cretaceous and older formations below the 

Denver Basin aquifers was investigated as part of the USGS 

Central Midwest Regional Aquifer-System Analysis (RASA), 

and results were reported by Robson and Banta (1987). The 

Central Midwest RASA report (Robson and Banta, 1987) 

presented geologic structure, hydraulic characteristics, and 

water-quality data for the Paleozoic and Mesozoic rocks of 

the Denver Basin up through the Laramie Formation and Fox 

Hills Sandstone.

The Laramie and Denver Formations contain coal and 

lignite beds, which, along with associated coal-bed methane, 

are potential energy resources in the Denver Basin (Colton 

and Lowrie, 1973; Soister, 1978a; Gaggiani and others, 1987; 

Britton and Gaggiani, 1989; Wray and Koenig, 2001; Roberts, 

2005). More than 130 million tons of coal and lignite were 

mined from the Denver region from 1883 to 1979, mostly 

from the Laramie Formation in the Boulder-Weld coal field 

near Boulder, Colorado, and more than 99 percent of the 

mined coal came from underground mines (Britton and 

Gaggiani, 1989). Several previous investigations provide 

geologic and coal resource information for the Denver Basin 

including Soister (1972, 1974, 1978a), Kirkham (1978), 

Kirkham and Ladwig (1979, 1980), Brand (1980), Brand 

and Caine (1980), Murray (1980), Eakins and Ellis (1987), 

Nichols (1999), and Carroll (2004). The potential for coal 

mining to affect Denver Basin surface-water and groundwater 

resources was addressed by Kirkham and Ladwig (1977) and 

Gaggiani and others (1987). Wray and Koenig (2001) discuss 

the coal-bed methane potential of the Laramie and Denver 

Formations based on previous work and provide electronic 

images and geographic information system (GIS) data files of 

selected maps and plates from previous studies by Kirkham 

and Ladwig (1979, 1980).

Two field studies examined stratigraphy and hydrologic 

properties of the Denver Basin bedrock aquifers by coring and 

geophysical logging deep boreholes through the units. The 

Castle Pines core hole, located about 20 miles south of Denver, 

was drilled and logged in 1987 to a depth of 3,110 ft below 

land surface and fully penetrated the Arapahoe aquifer (Raforth 

and Jehn, 1990). Laboratory analyses of selected core samples 

collected during drilling yielded mineralogy, grain size, bulk 

and grain density, porosity, specific yield, and specific retention 

data for the Denver Basin bedrock aquifers (Robson and Banta, 

1993; Robson, 1995). The study also collected water-level 

data, atmospheric-pressure measurements, aquifer-compression 

measurements, and borehole geophysical logs for a 2,400-ftdeep test hole constructed adjacent to the Castle Pines core hole 

(Robson and Banta, 1990; Robson and Banta, 1993).

The Kiowa core hole was drilled in the town of Kiowa, 

Colorado, in 1999 to a depth of 2,256 ft below land surface 

(Raynolds and others, 2001). The Kiowa core hole penetrated 

the full stratigraphic section of the Denver Basin aquifers in 

the central part of the basin where fine-grained strata were 

anticipated (Raynolds and others, 2001). Core samples from 

the Kiowa core hole were analyzed to determine the porosity, 

permeability, hydraulic conductivity, palynology, paleomagnetism, mineralogy, petrography, and fission-track properties 

of the Denver Basin bedrock aquifers (Raynolds and others, 

2001). Geophysical logging of the Kiowa core hole included 

caliper, gamma ray, spontaneous potential, resistivity, compensated density, and full-waveform sonic; data for a short seismic 

line were obtained adjacent to the core hole by using Vibroseis 

techniques, and the core hole was completed as a groundwater 

monitoring well (Raynolds and others, 2001). A series of 

publications from 2001 to 2004 present results from the Kiowa 

core hole and related Denver Basin field studies (Lapey, 

2001; Carpenter and Young, 2002; Farnham and Kraus, 2002; 

Kelly, 2002; Kelly and Blackwell, 2002; Lapey-Woodard and 

others, 2002; Nichols and Fleming, 2002; Obradovich, 2002; 

Raynolds, 2002, 2004; Raynolds and Johnson, 2002, 2003; 

Wilson, 2002; Barclay and others, 2003; Eberle, 2003; Ellis and 

others, 2003; Hicks and others, 2003; Hutchinson and Holroyd, 

2003; Johnson and others, 2003; Wheeler and Michalski, 2003; 

Barkmann, 2004; Kittleson, 2004).

Historical water-level data collection for Denver Basin 

bedrock aquifers has been irregular, and water-level monitoring efforts have decreased since the 1980s (Colorado Water 

Conservation Board, 2004b, 2006a). The first effort at bedrock 

water-level monitoring in the Denver Basin was the work of 

Emmons and others (1896), which included an inventory of 

wells, available water levels (or artesian pressures), and estimated artesian flow for wells completed in downtown Denver 

in the 1880s. Model calibration by this study used these waterlevel estimates to represent hydraulic head in the late 1880s as 

discussed in the “Model Calibration” section of Chapter C. The 
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 5

USGS measured the first set of basinwide water levels from 

1956 to 1963, and McConaghy and others (1964) published the 

results. Major and others (1983) published a second comprehensive set of water-level data for the bedrock and alluvial 

aquifers through 1981. The Robson (1987) groundwater flow 

model incorporated routine water-level measurements made 

by the USGS through the 1980s, and the data are available 

through the USGS National Water Information System (NWIS) 

database (http://waterdata.usgs.gov/co/nwis/). Model calibration by this study used the USGS NWIS data as discussed in 

the “Model Calibration” section of Chapter C. The CDWR 

established a water-level monitoring network of approximately 

278 wells in the 1980s, and data from that network are published in annual data reports (for example, Colorado Division 

of Water Resources, 2003, 2004). Model calibration by this 

study did not use the CDWR water-level data primarily because 

of uncertainty related to well-completion intervals and pumping status. However, this study does compare selected data 

from the CDWR water-level network to simulation results in 

the section “Changes in Hydraulic Heads and Groundwater 

Flow Directions” in Chapter B. The South Platte Decision 

Support System (SPDSS) published a compilation and bibliography of all available water-level data for bedrock and alluvial 

aquifers through 2004 (Colorado Water Conservation Board, 

2004b, 2006a).

Numerous studies have examined the alluvial aquifers 

of the South Platte River and its tributaries. Stratigraphy 

of the alluvial deposits was originally described by Hunt 

(1954) and Scott (1960) and later by Scott (1963a). Several 

workers developed maps of the South Platte alluvial-aquifer 

extent, thickness, and depth to water beginning in the 1950s 

(Bjorklund and Brown, 1957; Smith and others, 1964; Duke 

and Longenbaugh, 1966; Nelson and others, 1967; Hurr, 

Schneider, and others, 1972a, 1972b, 1972c; Hurr and others, 1975; Konikow, 1975; Nadler and Schumm, 1981; Robson, 1996; and Robson, Arnold, and Heiny, 2000a, 2000b; 

Robson, Heiny, and Arnold, 2000a, 2000b), and the SPDSS 

compiled selected maps into GIS data sets (Colorado Water 

Conservation Board, 2006b). Other workers developed data 

and maps for the major alluvial aquifers in the southern Denver Basin draining toward the Arkansas River as follows: 

(1) Black Squirrel Creek (Jenkins, 1961; Erker and Romero, 

1967; Bingham and Klein, 1973; and Buckles and Watts, 

1988); (2) Big Sandy Creek (Coffin, 1962; Willard Owens 

Associates, 1971); and (3) the Nussbaum Alluvium (Scott, 

1963c; Soister, 1967; Paschke, 1992). Many of the alluvial 

aquifer reports cited above and Robson (1989) describe the 

interconnection between bedrock and alluvial aquifers.

The aquifer system was previously evaluated using 

groundwater flow models by the USGS (Robson, 1987) and 

the CDWR (Colorado Division of Water Resources, 1998). 

Previous Denver Basin groundwater flow models used the 

USGS computer program MODFLOW (McDonald and 

Harbaugh, 1988) and its precursor simulation codes in quasithree-dimensional configurations. A quasi-three-dimensional 

groundwater flow model explicitly represents the geologic 

layers of aquifers, but confining units between aquifers are 

represented implicitly using vertical conductance variables 

rather than being explicitly represented as model layers.

The first numerical model of the Denver Basin aquifers 

was developed as a four-layer groundwater flow model (Robson, 

1987) using the USGS groundwater simulation code developed 

and described by Trescott (1975), Trescott and Larson (1976), 

and Trescott and others (1976), which predated MODFLOW. 

The Robson (1987) four-layer Denver Basin model served as the 

basis for all subsequent groundwater resource evaluations conducted by the USGS, CDWR, and various municipal and county 

governments until 1996. The four-layer Denver Basin model was 

superseded by a model constructed by CDWR between 1996 

and 1998 in response to Colorado Senate Bill 96–74 (SB96–74; 

Colorado Division of Water Resources, 1998). The CDWR 

SB96–74 model incorporated additional hydrogeologic data 

(Robson and Banta, 1993; Robson and others, 1998; VanSlyke 

and others, 1988a, 1988b, 1988c, 1988d) in a six-layer quasithree-dimensional groundwater flow model (Colorado Division 

of Water Resources, 1998) and used MODFLOW (McDonald 

and Harbaugh, 1988). This report compares modeling results 

from the current study to results of previous models (Robson, 

1987; Colorado Division of Water Resources, 1998) in the section “Comparisons between Current and Previous Models” in 

Chapter C. The CDWR SB96–74 model was further updated in 

2002 using MODFLOW-2000 (Harbaugh and others, 2000; Hill 

and others, 2000) as part of the South Metro Water Supply Study 

(SMWSS) funded by a consortium of water suppliers in the south 

Denver metropolitan area. The SMWSS model used the CDWR 

SB96–74 model and updated Douglas County water-use estimates to the year 2000 (South Metro Water Supply Study Board, 

written commun., 2003).

Two previous USGS investigations evaluated the potential 

effects of increased groundwater pumping from the bedrock aquifers in El Paso County. Banta (1989) simulated increased pumping in the southern Denver Basin, on the basis of projected water 

needs in the Colorado Springs vicinity, using the Robson (1987) 

four-layer quasi-three-dimensional groundwater flow model with 

a refined finite-difference grid. The Banta (1989) modeling study 

indicated increased pumping would result in drawdowns of as 

much as 1,300 ft and large decreases in groundwater storage after 

100 years of pumping. Model simulations also indicated a decline 

in groundwater discharge to streams through time and, eventually, pumping-induced stream recharge to aquifers (Banta, 1989). 

Buckles and Watts (1988) simulated the effects of continued 

pumping on the Black Squirrel Creek alluvial aquifer in El Paso 

County and emphasized the importance of evapotranspiration 

as a hydrologic process in the Denver Basin. Watts (1995) later 

developed a three-dimensional model of the Black Squirrel 

Creek Basin and simulated the effects of increased Denver Basin 

pumping on water levels in the alluvial aquifer. Model results 

indicated continued pumping of the Denver Basin bedrock aquifers would lead to water-level declines and groundwater storage 

decreases in the Black Squirrel Creek alluvial aquifer and could 

reverse the flow direction between alluvial and bedrock aquifers 

(Watts, 1995).
6 Groundwater Availability of the Denver Basin Aquifer System, Colorado

The most recent Denver Basin legislation, Senate 

Bill 96–74 (SB96–74) was implemented in 1996 and provided 

funds for a study of the Denver Basin and South Platte aquifer 

systems in anticipation of developing a SPDSS (Graham and 

Van Slyke, 2004). The SPDSS development currently (2010) 

is in progress under the direction of the Colorado Water 

Conservation Board (CWCB) and the CDWR and addresses 

many areas of water management in the South Platte River 

Basin, including surface-water diversions, consumptive water 

use, irrigated lands, land use, and groundwater (Colorado 

Water Conservation Board, 2004a). The SPDSS groundwater studies focus primarily on the alluvial aquifer of the 

South Platte River and its tributaries, and this study used data 

compilations from the SPDSS as the basis for aquifer characterization (Colorado Water Conservation Board, 2004b; 2006a, 

2006b, 2006c). This groundwater availability study in the 

Denver Basin began in 2004 as part of the USGS Groundwater 

Resources Program and focused on the bedrock aquifers. The 

present study and the SPDSS support each other in furthering 

the simulation of interaction between the bedrock and alluvial 

aquifers in the South Platte River Basin.

Study Methods

Study methods included compiling existing hydrologic 

data and developing a numerical groundwater flow model of the 

Denver Basin aquifer system using the U.S. Geological Survey 

(USGS) modular finite-difference groundwater flow computer 

program MODFLOW-2000 (Harbaugh and others, 2000; Hill 

and others, 2000). Model-input and model-calibration data sets 

were derived from geologic and hydrologic data collected since 

previous modeling efforts. The calibrated model was evaluated 

for model fit, and the simulation results were used to assess 

changes in groundwater availability through time. The model 

considers future groundwater conditions by simulating two 

hypothetical predictive scenarios and evaluating the sensitivity 

of the predictions to assess data needs and hydrologic monitoring. This section presents an overview of the methods used 

by the Denver Basin groundwater availability study and refers 

the reader to the appropriate Professional Paper chapter for 

detailed explanations.

Data Compilation

The hydrogeologic framework for the bedrock and alluvial aquifers, transient model boundary conditions (recharge, 

evapotranspiration, and well pumping), and calibration 

datasets of hydraulic head and stream base flow were developed from the data compilation. Additional hydrogeologic 

data collected since the SB96–74 model publication (Colorado 

Division of Water Resources, 1998) include updated geologic 

mapping of the extent of Denver Basin bedrock and alluvial 

aquifers (Robson, 1996; Robson and others, 1998); additional 

geophysical logs in the basin with which to further define 

aquifer layering; additional streamflow, precipitation, and 

land-use data; and an updated State well-permit database, 

which was used to revise pumping estimates for the bedrock 

and alluvial aquifers.

The hydrogeologic framework for the Denver Basin 

groundwater model consists of GIS data sets, which define the 

lateral extent, base altitude, and thickness of each aquifer and 

confining unit represented in the model. This study modified maps showing the extent of aquifers and confining units 

published by the CDWR (VanSlyke and others, 1988a, 1988b, 

1988c, 1988d) along the western basin margin to include geologic contacts mapped by Robson and others (1998), and the 

results defined the extent of active cells for each model layer. 

Topographic altitude data for land surface and streamflow 

routing were derived from the 30-meter-resolution National 

Elevation Dataset (NED) (U.S. Geological Survey, 1999).

Maps of the altitude of the base of the bedrock aquifers and confining units, silt-plus-sand thickness, and percent silt-plus-sand for bedrock aquifers were generated in 

ArcGIS 9.2 (Environmental Systems Research Institute, 

Inc., 1999–2004) from the CDWR Denver Basin geophysical log database (Brian Ahrens, Colorado Division of Water 

Resources, written commun., 2003) using ordinary kriging 

and inverse-distance weighed (IDW) methods. The CDWR 

geophysical-log database contains top and bottom elevations 

for each of the six bedrock aquifers (geophysical log “picks”) 

for about 4,400 geophysical logs. The geophysical log picks 

were processed into ArcGIS point-data shapefiles representing 

the base altitude for each of the six bedrock aquifers and five 

confining units, and the altitude data points were contoured 

using an ordinary kriging method available in ArcGIS. For 

many logs in the CDWR geophysical-log database, a silt-plussand thickness value was recorded for each bedrock aquifer. 

These silt-plus-sand-thickness values also were processed 

into ArcGIS point-data shapefiles, and the data points were 

contoured using either an ordinary kriging method or an IDW 

method available in ArcGIS, depending on which method 

resulted in the least error. Percent silt-plus-sand-thickness 

values were calculated from the silt-plus-sand-thickness point 

data for each of the six bedrock aquifers as the silt-plus-sand 

thickness divided by the total layer thickness, and the percent 

silt-plus-sand-thickness values were contoured using an IDW 

method available in ArcGIS. Averaged percent silt-plus-sand 

values for each model grid cell were used as multiplier arrays 

for hydraulic-conductivity and specific-yield values in the 

model as described in the “Hydrogeologic-Unit Properties” 

section of Chapter C. Contouring methods and model-fitting 

parameters are listed in table A1, and the results are presented 

in the “Hydrogeologic Framework” section of Chapter A.

The contours shown on the maps in this report and the 

data points on which they were based are available electronically as spatial data at http://water.usgs.gov/lookup/getgislist/. 

Table A2 lists file names and an abbreviated description of the 
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 7

Table A1. Geostatistical models, model-fitting parameters, and cross-validation statistics for Denver Basin bedrock units.[na, not applicable]

Variable Number of data points Contour method Model type

Model-fitting parameters Cross-validation statistics

Lag

(feet)

Range

(feet)

Sill

(square

feet)

Nugget

(square

feet)

Mean

error

(feet)

Root-meansquared error

(feet)

Average

standardized

error

(feet)

Mean

standardized

error

(feet)

Root-mean-squared

standardized

error

(feet)

Upper Dawson aquifer, 

base altitude

275 Ordinary 

kriging

Spherical 16,534 195,982 86,597 0.0 –2.10 69.4 54.4 –0.013 1.9

Upper Dawson aquifer, 

silt-plus-sand thickness

123 Inversedistance

weighted

na na na na na –0.62 62.7 na na na

Dawson confining unit, 

base altitude

331 Ordinary 

kriging

Spherical 15,484 18,3536 88,584 0.0 –0.75 64.9 54.1 0.0017 1.7

Lower Dawson aquifer, 

base altitude

631 Ordinary 

kriging

Spherical 23,012 272,767 259,340 0.0 –0.60 57.4 71.6 –0.0047 1.1

Lower Dawson aquifer, 

silt-plus-sand thickness

402 Ordinary 

kriging

Spherical 20,721 245,612 11,852 1,008 0.05 54.2 39.1 –0.0012 1.3

Denver upper confining unit, 

base altitude 

613 Ordinary 

kriging

Spherical 23,832 282,487 266,480 0.0 –0.24 59.9 72.2 –0.006 1.29

Denver aquifer, 

base altitude

1,180 Ordinary 

kriging

Spherical 36,370 431,103 297,480 0.0 –0.82 52.3 68.1 –0.009 1.07

Denver aquifer, 

silt-plus-sand thickness

763 Ordinary

kriging

Spherical 35,107 91,565 13,993 0.0 0.12 75.0 34 –0.015 4.08

Denver lower confining unit, 

base altitude

1,589 Ordinary 

kriging

Spherical 40,153 475,944 1,321,700 0.0 –0.38 50.4 57.6 –0.007 1.17

Upper Arapahoe aquifer, 

base altitude

637 Ordinary 

kriging

Spherical 20,954 248,373 68,871 0.0 –0.12 46.9 41.4 –0.002 1.38

Upper Arapahoe aquifer , 

silt-plus-sand thickness

520 Inversedistance 

weighted

na na na na na –1.39 29.9 na na na

Arapahoe confining unit, 

base altitude

617 Ordinary 

kriging

Spherical 21,893 236,396 78,553 0.0 0.16 49.6 46.6 0.0028 1.28

Lower Arapahoe aquifer, 

base altitude

1,770 Ordinary 

kriging

Spherical 42,846 507,865 309,540 0.0 0.05 54.2 65.1 0.00083 1.05

Lower Arapahoe aquifer, 

silt-plus-sand thickness

1,488 Inversedistance 

weighted

na na na na na 0.66 46.41 na na na

Laramie confining unit, 

base altitude

2,286 Ordinary 

kriging

Spherical 50,177 594,762 403,283 0.0 0.08 39.2 67.4 0.00086 2.57

Laramie–Fox Hills aquifer, 

base altitude

2,567 Ordinary 

kriging

Spherical 53,378 632,704 41,942 0.0 0.28 44.4 67.4 0.0023 2.17

Laramie–Fox Hills aquifer, 

silt-plus-sand thickness

1,674 Ordinary 

kriging

Spherical 46,032 362,451 1,187 560 0.07 24.2 25.2 0.0029 0.95
8 Groundwater Availability of the Denver Basin Aquifer System, Colorado

spatial data prepared for this study. The file names are a combination of the Professional Paper report number (PP1770) and 

a data descriptor. For example, the name of the spatial data 

set of contours of the generalized altitude of the base of the 

Laramie–Fox Hills aquifer is PP1770_alt_base_KLF_con.

The altitude of the base of the alluvial aquifer system 

was derived from a compilation of alluvial aquifer mapping. Substantial alluvial aquifers considered by this study 

include (1) present-day and prehistoric stream channels of the 

South Platte River and its tributaries, (2) the Black Squirrel 

Creek drainage, and (3) the Big Sandy Creek drainage and 

the Nussbaum Alluvium south of Big Sandy Creek. The 

base altitude of alluvial aquifers in the South Platte River 

basin was mapped for individual basins by various previous 

efforts (Bjorklund and Brown, 1957; Smith and others, 1964; 

Duke and Longenbaugh, 1966; Nelson and others, 1967; 

Hurr, Schneider, and others, 1972a, 1972b, 1972c; Robson, 

1996; Robson, Arnold, and Heiny, 2000a, 2000b; Robson, 

Heiny, and Arnold, 2000a, 2000b), which were compiled 

as part of the SPDSS (Colorado Water Conservation Board, 

2006b). Base-altitude contours for Black Squirrel Creek 

(Erker and Romero, 1967; Buckles and Watts, 1988), Big 

Sandy (Willard Owens Associates, 1971), and the Nussbaum 

Alluvium (Paschke, 1992) were compiled for this study and 

combined with the alluvium base-altitude contours from 

the Colorado Water Conservation Board (2006b) to depict a 

Table A2. Index of Denver Basin hydrogeologic framework spatial data.

Spatial data file name Data type Data description

PP1770_seo_geologs_point Points Location and selected attributes of geophysical logs (Colorado Division 

of Water Resources, 2004)

PP1770_NED30M_raster Raster Altitude of land surface

PP1770_alt_base_UTDW_point Points Altitude of the base of the upper Dawson aquifer 

PP1770_alt_base_TDWC_point Points Altitude of the base of the Dawson confining unit 

PP1770_alt_base_LTDW_point Points Altitude of the base of the lower Dawson aquifer 

PP1770_alt_base_TKDUC_point Points Altitude of the base of the Denver upper confining unit 

PP1770_alt_base_TKD_point Points Altitude of the base of the Denver aquifer 

PP1770_alt_base_TKDLC_point Points Altitude of the base of the Denver lower confining unit 

PP1770_alt_base_UKA_point Points Altitude of the base of the upper Arapahoe aquifer 

PP1770_alt_base_KAC_point Points Altitude of the base of the Arapahoe confining unit 

PP1770_alt_base_LKA_point Points Altitude of the base of the lower Arapahoe aquifer 

PP1770_alt_base_KLC_point Points Altitude of the base of the Laramie confining unit

PP1770_alt_base_KLF_point Points Altitude of the base of the Laramie–Fox Hills aquifer

PP1770_alt_base_UTDW_con Contours Generalized altitude of the base of the upper Dawson aquifer 

PP1770_alt_base_TDWC_con Contours Generalized altitude of the base of the Dawson confining unit 

PP1770_alt_base_LTDW_con Contours Generalized altitude of the base of the lower Dawson aquifer 

PP1770_alt_base_TKDUC_con Contours Generalized altitude of the base of the Denver upper confining unit 

PP1770_alt_base_TKD_con Contours Generalized altitude of the base of the Denver aquifer 

PP1770_alt_base_TKDLC_con Contours Generalized altitude of the base of the Denver lower confining unit 

PP1770_alt_base_UKA_con Contours Generalized altitude of the base of the upper Arapahoe aquifer 

PP1770_alt_base_KAC_con Contours Generalized altitude of the base of the Arapahoe confining unit 

PP1770_alt_base_LKA_con Contours Generalized altitude of the base of the lower Arapahoe aquifer 

PP1770_alt_base_KLC_con Contours Generalized altitude of the base of the Laramie confining unit

PP1770_alt_base_KLF_con Contours Generalized altitude of the base of the Laramie–Fox Hills aquifer

PP1770_thickness_sand_UTDW_point Points Silt-plus-sand thickness of the Dawson aquifer

PP1770_thickness_sand_LTDW_point Points Silt-plus-sand thickness of the lower Dawson aquifer 

PP1770_thickness_sand_TKD_point Points Silt-plus-sand thickness of the Denver aquifer 

PP1770_thickness_sand_UKA_point Points Silt-plus-sand thickness of the upper Arapahoe aquifer 

PP1770_thickness_sand_LKA_point Points Silt-plus-sand thickness of the lower Arapahoe aquifer 

PP1770_thickness_sand_KLF_point Points Silt-plus-sand thickness of the Laramie–Fox Hills aquifer

PP1770_thickness_sand_UTDW_con Contours Generalized silt-plus-sand thickness of the Dawson aquifer

PP1770_thickness_sand_LTDW_con Contours Generalized silt-plus-sand thickness of the lower Dawson aquifer 

PP1770_thickness_sand_TKD_con Contours Generalized silt-plus-sand thickness of the Denver aquifer 

PP1770_thickness_sand_UKA_con Contours Generalized silt-plus-sand thickness of the upper Arapahoe aquifer 

PP1770_thickness_sand_LKA_con Contours Generalized silt-plus-sand thickness of the lower Arapahoe aquifer 

PP1770_thickness_sand_KLF_con Contours Generalized silt-plus-sand thickness of the Laramie–Fox Hills aquifer
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 9

base-altitude surface for the major alluvial aquifers overlying 

the Denver Basin bedrock aquifers. The base-altitude contours 

were converted to a GIS raster, and alluvium thickness was 

computed as the difference between land surface (30-meter 

digital elevation model [DEM], U.S. Geological Survey, 1999) 

and the base altitude on 1,000-ft raster grid spacing.

Estimates of hydraulic conductivity, transmissisivity, 

storage coefficient, and specific yield for the Denver Basin 

bedrock and alluvial aquifers were recently compiled from 

previous studies by the SPDSS (Colorado Water Conservation 

Board, 2006c), and the results are discussed in the “Aquifer 

Hydraulic Properties” section of Chapter A.

Recharge and discharge estimates were derived by various methods, the details of which are described in Chapter C. 

Precipitation records from 1930 to 2003 were obtained for 

National Weather Service sites in and adjacent to the Denver 

Basin, and the data were contoured into long-term mean 

precipitation maps for the period of record and for stress 

periods simulated in the groundwater flow model. The resulting precipitation-distribution maps were used as input to the 

groundwater flow model recharge estimates as described in the 

“Recharge” subsection of “Hydrologic Stresses” in Chapter C. 

Areas of urban/suburban and agricultural irrigation were 

mapped for the periods 1880–1919, 1920–1939, 1940–1953, 

1954–1986, and 1987–2003 from ditch-diversion records, historical maps, and census records. Streamflow records for eight 

sites in the Denver Basin were used to estimate base flow from 

groundwater. Base flow for the period of record at each site 

was estimated using the Base Flow Index (BFI) method (Wahl 

and Wahl, 1988).

Actual pumping rates and volumes from wells in the 

Denver Basin currently (2010) are not recorded or compiled 

into a central database in the State of Colorado. Previous 

modeling efforts estimated transient groundwater pumping 

based on the CDWR well-permit database (Colorado Division 

of Water Resources, 2005), which records the owner, location, 

depth, completion interval, permitted pumping rate, use, and 

dates of first use and abandonment for all permitted wells in 

the State of Colorado. The CDWR well-permit database is the 

only basinwide well database and was used by this study to 

estimate pumping locations, depths, and rates through time. 

Detailed methods and results of the pumping analysis are 

described in the section “Denver Basin Pumping History” 

of Chapter B.

Calibration data for the Denver Basin groundwater flow 

model included hydraulic-head and streamflow measurements through time available from the USGS NWIS database 

(http://waterdata.usgs.gov/co/nwis) and the CDWR State 

database, Hydrobase (Colorado Division of Water Resources, 

2005). Hydraulic-head estimates and estimates of discharge 

from flowing wells in the 1890s were interpreted from data 

tables presented by Emmons and others (1896). Calibration 

datasets are documented in Chapter C.

Model Construction and Calibration

A transient (time-varying), fully three-dimensional 

groundwater flow model of the Denver Basin bedrock and alluvial aquifers, representing the time period from predevelopment 

(pre-1880) through 2003, was developed using the groundwater 

flow simulation code MODFLOW-2000 (Harbaugh and others, 

2000; Hill and others, 2000). Groundwater flow modeling capabilities and computer technology have advanced considerably 

since previous models of the Denver Basin were developed, 

and the Denver Basin model reported by this study is considered 

an enhancement over previous efforts because the following 

capabilities were implemented:

• A fully three-dimensional representation of the aquifer 

system that includes explicit definition of all Denver 

Basin aquifers and confining layers. Previous models 

used a quasi-three-dimensional approach, which 

represented confining layers by using a verticalconductance term.

• Explicit representation of the alluvial aquifer system 

as the uppermost layer in the model. Previous models 

simulated the alluvial aquifer as constant-head cells 

(Robson, 1987) or as head-dependent-flow boundaries using the MODFLOW River Package (Colorado 

Division of Water Resources, 1998).

• Updated streamflow routing simulation capabilities 

(SFR2, Niswonger and Prudic, 2005), which allow 

a more-detailed representation of streams than in 

previous models. Previous models did not explicitly 

represent streams.

• Inclusion of evapotranspiration as a simulated hydrologic process (ETS, Banta, 2000). Previous models did 

not explicitly simulate evapotranspiration as a hydrologic process.

• Availability of new parameter-estimation and sensitivity 

software and transient-calibration techniques. Parameter estimation was used to estimate model hydraulic 

parameters and guide transient model calibration (PEST, 

Doherty, 2006). Model sensitivity to parameters was calculated with UCODE_2005 (Poeter and others, 2005).

• Availability of new MODFLOW numerical solvers 

and parallel-computing capabilities. New numericalsolution software (GMG Package, Wilson and Naff, 

2004; Banta, 2006) available in MODFLOW-2000 

provided improved model convergence for this highly 

nonlinear model. The software Parallel PEST (Doherty, 

2006) was used with multiple networked computers 

to simultaneously simulate various combinations of 

model parameters during model calibration.

Chapter C presents the groundwater flow model conceptualization, construction, calibration, and sensitivity analysis. 

An overview of the groundwater flow model construction and 

calibration is presented in the following paragraphs.
10 Groundwater Availability of the Denver Basin Aquifer System, Colorado

A three-dimensional grid was defined to represent the 

Denver Basin aquifer system in MODFLOW-2000. Vertically, 

the model is discretized into 12 layers explicitly representing 

the six bedrock aquifers, five aquifer confining units, and the 

alluvial aquifer. The explicit representation of all hydrogeologic units is a fully three-dimensional approach, which allows 

simulation of lateral and vertical flow and calculation of storage 

changes in all model layers. The altitude of land surface and 

the base of each model layer were assigned from the surfaces 

developed during data compilation and described in the section “Hydrogeologic Framework” of Chapter A. In map view, 

the model area is divided into one-square-mile grid cells, and 

the model grid is composed of 124 rows by 84 columns with 

a north-south/east-west orientation. Aquifer specific-storage 

and specific-yield values were assigned on the basis of available data, and aquifer hydraulic conductivity was a modelcalibration parameter.

The Denver Basin model simulates steady-state groundwater conditions prior to 1880 and transient groundwater conditions from 1880 through 2003. Predevelopment conditions 

are represented by a steady-state stress periods, and the period 

1880–2003 is discretized into 15 stress periods with lengths 

varying from 2 to 27 years, depending on climatic and pumping conditions. Sources of recharge simulated by the model 

include time-varying precipitation recharge, agricultural irrigation return flow, and urban/suburban recharge in developed 

areas. Streams are simulated using the Streamflow-Routing 

package (SFR2, Niswonger and Prudic, 2005), springs are 

simulated using the Drain package (DRN), and evapotranspiration is simulated using the Evapotranspiration Segments 

package (ETS, Banta, 2000). Pumping is simulated using the 

Well (WEL) package for wells completed in a single aquifer 

and using the Multi-Node Well package (MNW, Halford and 

Hanson, 2002) for wells completed in more than one aquifer. 

Other simulated flows in the model are drain cells to represent 

pre-1900 flowing wells; General-Head Boundary (GHB) cells 

to represent groundwater flow out of the basin in the alluvial 

aquifers of Black Squirrel Creek and the Nussbaum Alluvium; 

and Flow and Head Boundary (FHB, Leake and Lilly, 1997) 

cells to represent groundwater underflow out of the study area 

in the South Platte River alluvial aquifer.

Model calibration was achieved using nonlinearregression methods implemented in PEST (Doherty, 2006) 

in combination with manual adjustment of parameters that 

proved resistant to calibration by automated methods. Model 

fit was evaluated by comparing model-simulated values for 

hydraulic head and streamflow to values observed in the 

field or derived by analysis of field data. For each pair of 

observed values and corresponding model-simulated values, 

a residual was defined by subtracting the simulated value 

from the observed value. Each observation was assigned 

a weight based on an estimate of the standard deviation 

or coefficient of variation associated with the observation. Hydraulic-conductivity and recharge parameters were 

adjusted within a reasonable range of values during model 

calibration until a best fit was obtained between modelsimulated and observed values. The resulting hydraulicconductivity and recharge distributions provide reasonable 

representations of aquifer conditions as compared to pumping-test results for hydraulic conductivity, the conceptual 

understanding of recharge in the basin, and previous groundwater modeling studies.

Evaluation of Modeling Results

Groundwater flow models can contribute substantially 

to understanding of groundwater availability in complex aquifer systems such as the Denver Basin. Models can represent 

multiple hydrologic processes that change through time, and 

they facilitate detailed calculations of groundwater budget and 

water levels that are too voluminous to calculate manually. 

Time-varying water budgets and hydraulic-head distributions calculated by the calibrated Denver Basin model were 

evaluated in detail as measures of groundwater availability 

and are described in the section “Effects of Development on 

Groundwater Availability in the Denver Basin” of Chapter B. 

A sensitivity analysis indicated which model-calibration 

parameters were most important to achieving a successful model calibration and indicates the model is suitable for 

reasonable basin-scale predictions. Model sensitivity calculations using Observation-Prediction (OPR) and ParameterPrediction (PPR) statistics (Hill and Tiedeman, 2007) were 

used to evaluate benefits of additional data collection, and the 

calibrated model was used in a predictive mode to estimate 

the hydrologic system response to two pumping scenarios for 

the period 2004 through 2053. Chapter C describes model 

sensitivity and prediction simulations along with a comparison 

of model results to previous models. The model developed by 

this study is not an end unto itself but rather a necessary tool 

for continued evaluations of basinwide groundwater resources. 

The results provide quantitative estimates of system changes 

through time; however, continued monitoring and updates to 

the model are considered necessary for future assessments of 

groundwater availability.

Conceptual Model of the 

Denver Basin Aquifer System

Following an overview of the Denver Basin hydrogeologic conceptual model, this report section presents the 

physiographic and climatic setting, hydrogeologic framework, 

and predevelopment groundwater budget and flow conditions 

for the aquifer system. The discussion synthesizes compiled 

hydrologic and geologic data with groundwater flow model 

input parameters and results. Chapter B of this Professional 

Paper describes temporal changes to groundwater budgets 

and flow conditions.
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 11

Overview

The Denver Basin aquifer system is composed of 

Tertiary- to Cretaceous-age bedrock sandstones that overlie 

the Cretaceous Pierre Shale (fig. A2) such that the basin 

extent is equivalent to the extent of the Upper Cretaceous 

Fox Hills Sandstone (Robson, 1987). From oldest to youngest, 

the four primary units are the Laramie–Fox Hills aquifer, 

the Arapahoe aquifer, the Denver aquifer, and the Dawson 

aquifer (Romero, 1976; Robson, 1983; Robson, 1987). The 

Dawson and Arapahoe aquifers are further divided into upper 

and lower units in parts of the basin (VanSlyke and others, 

1988a, 1988c) so that six bedrock aquifers are recognized 

for administrative purposes (Colorado Division of Water 

Resources, 1998). The Denver Basin aquifers comprise 

the uppermost layers of the larger structural Denver Basin 

with high-angle dips along the western basin margin and 

low-angle dips in the central and eastern parts of the basin 

(Anderman and Ackman, 1963; Nwangwu, 1977; Robson, 

1987; Robson and others, 1998). About 5,200 ft of lowpermeability Cretaceous Pierre Shale underlie the Laramie–Fox Hills aquifer, forming the base of the Denver Basin 

aquifer system (Nwangwu, 1977; Robson, 1983). The aquifer 

materials are synorogenic sediment deposited east of the 

Rocky Mountain Front Range during the Laramide Orogeny 

and exhibit substantial horizontal and vertical heterogeneity 

in the stratigraphic section (Scott, 1963b; Weimer, 1973; 

Epis and others, 1976; Weimer and LeRoy, 1987; Robson, 

1987; Raynolds, 2002). A detailed discussion of Denver 

Basin stratigraphy is provided in the section “Hydrogeologic 

Framework” of Chapter A.

Groundwater exists primarily under confined conditions 

in the bedrock sandstones, although unconfined conditions 

exist where bedrock aquifers lie near the land surface (fig. A2). 

Quaternary alluvial, colluvial, and eolian deposits overlie the 

Denver Basin bedrock aquifers primarily along present-day 

stream channels (Hunt, 1954; Scott, 1960), and these surficial 

materials form an unconfined alluvial aquifer where saturated 

(Robson, 1989; Robson, 1996). The alluvial aquifer is in 

hydraulic connection with streams draining the area as well as 

underlying bedrock aquifers where present (Robson, 1996). In 

general, regional groundwater flow in all aquifers is away from 

the topographic high and recharge area of the Palmer Divide, 

downgradient to the north toward the discharge area of the 

South Platte River and downgradient to the south toward the 

discharge areas of Monument, Black Squirrel, and Big Sandy 

Creeks (Robson, 1987). Recharge to the bedrock and alluvial 

aquifers is from infiltration of precipitation, lawn-irrigation 

return flow in developed areas, agricultural irrigation return 

flow in agricultural areas, streams, and interaquifer flow. On the 

basis of modeling results, recharge has increased through time 

as a result of irrigation return flow in developed and agricultural 

areas. Natural discharge from bedrock aquifers is to springs, 

streams, alluvial aquifers, and evapotranspiration. Groundwater 

development of the Denver Basin aquifer system has steadily 

increased since the 1950s, resulting in water-level declines 

and storage depletion in the bedrock aquifers as described in 

Chapter B of this Professional Paper.

Physiography

The Denver Basin is located in the Colorado Piedmont of 

the Great Plains physiographic province where rolling hills and 

dissected plains characterize the topography (Trimble, 1980a). 

The topographic high, approximately 8,000 ft, is located in the 

southern one-third of the Denver Basin along the Palmer Divide 

(fig. A3; Trimble, 1980a), which is the drainage divide between 

Figure A2. Conceptual block diagram of the Denver Basin aquifer system for predevelopment conditions.

Water

level

Denver aquifer

Dawson aquifer

Laramie-Fox Hills aquifer

Arapahoe aquifer

Pierre Shale

South Platte River
12 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A3. Land-surface alititude of the Denver Basin aquifer system, Colorado.

Box Elder Creek

Adobe Creek

BadgerCreek

MiddleBijouCreek

East Bi oj uC reek Middle Rush Creek

Mustang Creek

Horse Creek

Steels Fork

Brackett Cr

Black Squirrel Creek

Fountain Creek

Big Sandy Creek

Running

Cree k

Kiowa Creek

Wolf Creek

Comanche Creek

Dr y Creek

Antelope Cr

Bijou Creek

Lost Creek

Sou th Platte R iver

Big Thompson R

Little Thompson R

Cache la PoudreR

Saint Vrain Cr

Bould er Cr

Coal Creek

Big Dr y Cr

Clear Creek

West Sand Creek

LittleDryCr

Dry Cr

First Creek

Sand Creek

Cook Cr

West Plum Cr

Bear Cr

Kettle Cr

Cherry Cr West Kiowa Cr

West Bijou Cr

P ul m Cr

MuddyCreek

Rock Creek

PALMER

DIVIDE

PALMER

DIVIDE

!

!

!

!

! ! !

!

!

!

!

!

!

!

! !

!

!

!

!

!

!

!

!

! !

!

!

! !

Boulder

Loveland

Brighton

Fort

Lupton

Lafayette

Golden

Lakewood Denver

Highlands 

Ranch

Aurora

Littleton

Parker

Longmont

Broomfield

Englewood

Kiowa

Morrison

Franktown

Elizabeth

Castle

Rock

Calhan

Monument

Colorado

Springs

Limon

Simla

Deer

Trail

Fort

Morgan

Wiggins

Greeley

Bennett

Boulder

Loveland

Brighton

Fort

Lupton

Lafayette

Golden

Lakewood Denver

Highlands 

Ranch

Aurora

Littleton

Parker

Longmont

Broomfield

Englewood

Kiowa

Morrison

Franktown

Elizabeth

Castle

Rock

Calhan

Monument

Colorado

Springs

Limon

Simla

Deer

Trail

Fort

Morgan

Wiggins

Greeley

Bennett

Barr 

Lake

Milton

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

MORGAN

ARAPAHOE

JEFFERSON

WASHINGTON

BROOMFIELD

DOUGLAS

ADAMS

BOULDER

TELLER

DENVER

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

MORGAN

ARAPAHOE

JEFFERSON

WASHINGTON

BROOMFIELD

DOUGLAS

ADAMS

BOULDER

TELLER

DENVER

§ ̈¦70

§ ̈¦25

§ ̈¦76

104°

40°

39°

105°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Land-surface altitude, Denver Basin aquifer system extent

 in feet

High: 7,992

Low: 4,318

Stream

Perennial

Ephemeral
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 13

the tributaries of the South Platte River to the north and those 

of the Arkansas River to the south. Surface drainage generally 

is north toward the South Platte River in the northern two-thirds 

of the Denver Basin. The South Platte River flows east out of 

the mountains through Waterton Canyon and into Chatfield 

Reservoir, crosses the western part of the Denver Basin flowing 

north through Denver, and then flows northeast toward Greeley. 

The topographic low of approximately 4,300 ft lies along the 

South Platte River on the northeast edge of the basin (fig. A3). 

Approximately the southern one-third of the basin drains south 

toward the Arkansas River.

Native vegetation over much of the Denver Basin 

consists of grasslands with mixed-grass prairie and low 

shrubs (Keith and Maberry, 1973). Open stands of mountain 

mahogany, Gambel shrub oak, and other rangeland shrubs 

cover areas along the foothills (Keith and Maberry, 1973). At 

the higher elevations near the Palmer Divide, where precipitation is greatest and coarse sandy soils are present, native 

vegetation consists of open stands of Ponderosa pine and 

shrubs mixed with grass meadows (Keith and Maberry, 1973; 

Driscoll, 1975). Phreatophytes such as cottonwood trees and 

willows grow in valley bottom lands and flood plains (Keith 

and Maberry, 1973; Driscoll, 1974, 1975).

Climate

Topography of the Rocky Mountain Front Range 

affects the semiarid climate and weather over the plains in 

the Denver Basin east of the Rocky Mountain front (Robson, 

1989). In general, prevailing westerly winds carry moisture 

from the Pacific Coast toward Colorado. As air rises over 

the mountains of Colorado, it cools and deposits precipitation as rain and snow on the mountains along the Continental 

Divide. This orographic effect on weather also causes a rain 

shadow on the eastern slope of the mountains and the Denver 

Basin, which has a semiarid climate (Scott, 1963a; Robson, 

1989). Warm, moist air masses from the Gulf of Mexico also 

move into Colorado from the south, causing upslope storms 

that may deposit many feet of snow on the plains of eastern 

Colorado (recent blizzards of 2003 and 2006 are examples; 

http://severewx.atmos.uiuc.edu/index.15.html, accessed 

February 17, 2009). Wide variations in weather also are 

characteristic of the Denver Basin (Scott, 1963a; Robson, 

1989). Record high summer temperatures range from 100° to 

107°F, and record low winter temperatures range from –30° to 

–45°F (National Oceanic Atmospheric Administration, 2004). 

Downslope (chinook) winds frequently exceed 50 miles per 

hour (mi/hr) during the winter and have exceeded 135 mi/hr 

along the foothills of the Front Range (Robson, 1989). During 

the summer, orographic thunderstorms develop over the higher 

elevations of the Denver Basin and the Front Range, which 

can produce, on rare occasions, as much as 24 inches of rain in 

local areas in a few hours (Robson, 1989).

Analysis of long-term mean annual precipitation data from 

129 individual weather stations in the vicinity of the Denver 

Basin indicates mean annual precipitation over the basin ranges 

from approximately 11.5 to 20 inches for the period 1931–2003 

(National Oceanic Atmospheric Administration, 2004) (fig. A4). 

About 70 percent of the precipitation falls during the 6-month 

period from April through September, and the remaining 30 percent of precipitation is winter snowfall (Hansen and others, 

1978). The Palmer Divide creates a local orographic effect on 

storms in the Denver Basin, such that precipitation rates are 

greater at higher elevations near the divide (Hansen and others, 

1978; fig. A4). The long-term mean annual precipitation at the 

highest altitudes along the western basin margin and the Palmer 

Divide is about 20 inches per year, whereas the long-term average annual precipitation at lower elevations along the South 

Platte River and in the southernmost part of the basin is about 

11 to 12 inches per year.

Basinwide mean annual precipitation (mean of annual 

precipitation for all active weather stations within a given 

year) ranges from 8.7 to 21.5 inches per year for the period 

1930–2003 with a long-term annual mean of about 15.2 inches 

(fig. A5). The 1930–2003 period of record exhibits several 

periods defined as exhibiting variable to dry conditions (shown 

in brown in fig. A5). Basinwide average precipitation was 

less than the long-term annual mean from 1931 to about 1940 

(during the 1930s drought) and from 1948 to 1956 (during the 

1950s drought; fig. A5). Variable to dry conditions also are 

noted for 1962 through 1964, 1966, 1968, 1970 through 1971, 

and 1974 through 1978 (fig. A5). The period 1979–1999 had 

variable to wet precipitation conditions, which resulted in an 

overall upward trend for basinwide mean annual precipitation 

over the period of record (fig. A5). Variable to dry conditions 

began in 2000 when effects of a recent drought (McCabe and 

others, 2004) become apparent (fig. A5).

Surface-Water Hydrology

The Denver Basin contains perennial and ephemeral 

surface drainages. Streams originating in the Front Range 

enter the west side of the Denver Basin and are generally 

perennial because they receive water primarily from snowmelt 

runoff in the mountains. Streams that originate on the semiarid plains within the Denver Basin are generally ephemeral 

and intermittent because they receive water primarily from 

local precipitation runoff and groundwater discharge from 

the Denver Basin aquifers. Drainage within the Denver Basin 

east of the mountains is radial to the north, east, and south 

away from the drainage divide between the South Platte and 

Arkansas Rivers, known as the Palmer Divide. North of the 

Palmer Divide, streams drain toward the South Platte River, 

and south of the Palmer Divide, streams drain toward the 

Arkansas River (fig. A6). Perennial streams entering the western side of the basin include the main stem of the South Platte 

River and its major tributaries of Plum, Bear, Clear, Coal, and 
14 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A4. Spatial distribution of mean annual precipitation in the Denver Basin aquifer system, 

1931–2003, in inches.

South Platte

River

Cac he la Poudre R

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

Big Thompson R

PALMERPALMER DIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

MORGAN

ARAPAHOE

JEFFERSON

WASHINGTON

BROOMFIELD

DOUGLAS

ADAMS

BOULDER

TELLER

DENVER

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

MORGAN

ARAPAHOE

JEFFERSON

WASHINGTON

BROOMFIELD

DOUGLAS

ADAMS

BOULDER

TELLER

DENVER

Boulder

Loveland

Brighton

Fort

Lupton

Lafayette

Golden

Lakewood Denver

Highlands

Ranch

Aurora

Littleton

Parker

Longmont

Broomfield

Englewood

Kiowa

Morrison

Franktown

Elizabeth Castle

Rock

Calhan

Monument

Colorado

Springs

Limon

Simla

Deer

Trail

Fort

Morgan

Wiggins

Greeley

Bennett

Boulder

Loveland

Brighton

Fort

Lupton

Lafayette

Golden

Lakewood Denver

Highlands

Ranch

Aurora

Littleton

Parker

Longmont

Broomfield

Englewood

Kiowa

Morrison

Franktown

Elizabeth Castle

Rock

Calhan

Monument

Colorado

Springs

Limon

Simla

Deer

Trail

Fort

Morgan

Wiggins

Greeley

Bennett

(

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12.4

12.6

15.9

16.1

12.2

14.1

11.4

12.9

17.3

12.2

14.4

16

13.1

14.9

16.7

14.9 12.8

14.5 13

14

16

15.1

17.1 18.6

18.8

19.6

14.7 17.1

17.4

16.1

18.1

17.5

18.8

17

16

10.5

12.1

21.4

15.1

17.1

20.7

17.6

22.9

11.5

18.4

15.9

17.3

17.9

19

24.2 13.7

12.3

18.8

17.1

14.5

15.2

13.9

14.8

13.3 18.6

13.1

16.1

16.7

14.6

15.7

15.9

16.1

13.9

14.8

12.8

11.9

14.8

24

16.1

21.4

18.8

19.3

20.2

18.6

17

17

18.4

14.3

14.7

16.4

16.3

15.4

14.7

15.4

18.3

20.8

24.2

12.4

12.6

15.9

16.1

12.2

14.1

11.4

12.9

17.3

12.2

14.4

16

13.1

14.9

16.7

14.9 12.8

14.5 13

14

16

15.1

17.1 18.6

18.8

19.6

14.7 17.1

17.4

16.1

18.1

17.5

18.8

17

16

10.5

12.1

21.4

15.1

17.1

20.7

17.6

22.9

11.5

18.4

15.9

17.3

17.9

19

24.2 13.7

12.3

18.8

17.1

14.5

15.2

13.9

14.8

13.3 18.6

13.1

16.1

16.7

14.6

15.7

15.9

16.1

13.9

14.8

12.8

11.9

14.8

24

16.1

21.4

18.8

19.3

20.2

18.6

17

17

18.4

14.3

14.7

16.4

16.3

15.4

14.7

15.4

18.3

20.8

24.2

12

12

12 12

12

12

15

14

18

18

19

17

15

14

13

12

16 16

15

13

15

15

15

16

12

12

12 12

12

12

15

14

18

18

19

17

15

14

13

12

16 16

15

13

15

15

15

16

§ ̈¦70

§ ̈¦25

§ ̈¦76

104°

40°

39°

105°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27' N and 37°45' N, central meridian 105°00'W 

Precipitation data from National Oceanic and Atmopheric Administration, 2004.

EXPLANATION

Mean annual precipitation cokriged Denver Basin aquifer system extent

 with altitude, 1931–2003, in inches

11.5 to 12

12 to 13

13 to 14

14 to 15

15 to 16

16 to 17

17 to 18

18 to 19

19 to 20

Line of equal mean annual precipitation, 

 1931–2003, in inches. Contour interval 1 inch

Stream

Perennial

Ephemeral

Precipitation station and mean annual 

 precipitation, 1931–2003, in inches

16.1

0 10 20 MILES

0 10 20 KILOMETERS
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 15

Boulder Creeks (fig. A6). Ephemeral and intermittent streams 

that originate within the Denver Basin include the South Platte 

River tributaries of Cherry, Running/Box Elder, Lost, Kiowa, 

Comanche, and Bijou Creeks (fig. A6). Ephemeral and intermittent tributaries of the Arkansas River that originate in the 

Denver Basin include Monument, Black Squirrel, Adobe, and 

Big Sandy Creeks (fig. A6).

Surface water interacts with groundwater where streams 

flow across the Denver Basin. Surface-water diversions from 

perennial streams decrease streamflow as streams enter the 

basin, but some perennial flow is generally maintained year 

round in mountain-front streams, and they interact with 

groundwater in the alluvial and bedrock aquifers as they 

cross the Denver Basin. In general, groundwater discharge 

from bedrock and alluvial aquifers maintains perennial flow 

in upstream reaches of streams originating within the Denver 

Basin (fig. A7). Topographic gradients of these streams flatten 

in a downstream direction away from the Palmer Divide, and 

the streams lose water to the extensive and permeable alluvial 

aquifers along their channels (fig. A8); little to no perennial 

surface water flows in downstream reaches of Running/Box 

Elder, Kiowa, Bijou, and Black Squirrel Creeks. In developed 

drainages such as the lower South Platte River and Plum and 

Cherry Creeks, groundwater discharge, reservoir releases, 

wastewater-treatment plant discharge, agricultural irrigationreturn flow, and lawn-irrigation return flow contribute to 

perennial flow.

Streamflow records for eight sites in the Denver Basin 

(fig. A6) were used to estimate base flow from groundwater 

for comparison to model simulations (table C11 discussed in 

the “Calibration Targets” section of Chapter C). The Cherry 

Creek site near Franktown (06712000) is located upstream 

from urban/suburban development, represents natural baseflow conditions, and has the longest period of record of any 

of the Denver Basin surface-water gaging stations. Streamflow 

data and estimated base flow from this site indicate a range 

in streamflow from 0.2 to 1,400 ft3/s and a range in estimated base flow from 0.2 to 62 ft3

/s for 1939–2004 (fig. A9). 

Streamflow and estimated base flow at this site mimic the 

mean annual precipitation values and the wet and dry periods, 

indicating that streamflow at the site responds to variable 

climatic conditions. Decreases in streamflow and base flow 

are observed during the variable to dry periods of 1948–1957, 

1962–1965, 1970–1973, 1974–1979, and 2002–2004 (fig. A9). 

Similarly, there are increases in streamflow and base flow 

during the variable to wet periods of 1958–1961, 1973, and 

1980–2001 (fig. A9).

Figure A5. Temporal distribution of mean annual precipitation in the Denver Basin aquifer system, 1931–2003.

Basinwide annual mean

Basinwide long-term mean

Five-year moving average

Linear trend of annual mean

Variable to dry conditions

Variable to wet conditions

EXPLANATION

1931193319351937193919411943194519471949195119531955195719591961196319651967

19691971197319751977197919811983198519871989199119931995199719992001

2003

Basinwide mean annual precipitation, in inches

Year

5

10

15

20

25
16 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A6. Locations of streams, stream-gaging stations, and extent of alluvial aquifer for the 

Denver Basin aquifer system.

South Platte

River

Cac he la Poudre R

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryC

P

r

lum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

Big Thompson R

PALMER DIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

#

#

#

#

#

#

#

#

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

07103990

06759000

06758200

06720460

06712000

07103990

06759000

06758200

06720460

06712000

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

104°

40°

39°

105°

Black Squirrel Creek

alluvial aquifer

Nussbaum

alluvial aquifer

Big Sandy Creek

alluvial aquifer

South Platte River

and tributaries

alluvial aquifer

0 10 20 MILES

0 10 20 KILOMETERS

Base from U.S. Geological Survey digital data, 2009, 1:100,000 

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27' N and 37°45' N, central meridian 105°00'W

EXPLANATION

Denver Basin aquifer system extent

Alluvial aquifer extent

Stream

Perennial

Ephemeral

# Stream-gaging station used for model 

 calibration and site identification number
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 17

Figure A7. Photograph of Cherry Creek in Castlewood Canyon 

State Park near Franktown.

Figure A8. Photograph looking north along Cherry Creek 

downstream from Castlewood Canyon State Park where stream 

and topographic gradients flatten.

Hydrogeologic Framework

The hydrogeologic framework of an aquifer system 

describes the extent, thickness, depth, and layering of the 

encompassed aquifers. Numerous workers have mapped and 

conceptualized the hydrogeologic framework of the Denver 

Basin aquifer system beginning with Emmons and others 

(1896) as discussed in the “Previous Work” section of this 

chapter. This “Hydrogeologic Framework” section provides 

an overview of the structural geology and geologic history 

compiled from previous studies followed by detailed descriptions of the geometry and characteristics of the Denver Basin 

aquifers as developed by this study and used as input to the 

groundwater flow model.

The structural Denver Basin is a bowl-shaped, doubleplunging syncline located at the base of the Rocky Mountain 

Front Range in eastern Colorado (Anderman and Ackman, 

1963). The basin axis is oriented approximately north-south 

and parallel to the mountain front of the Front Range (Soister, 

1978a). The basin axis is located near the western margin of 

the asymmetric basin, so that sedimentary rocks on the western basin margin dip steeply (as much as 70°) off the Front 

Range toward the basin axis (Anderman and Anderson, 1963; 

Nwangwu, 1977; Robson, 1987), and sedimentary rocks on 

the eastern margin dip gently toward the axis (Tweto, 1980). 

Away from the mountain front, the dip of sedimentary rocks 

is generally less than 5° toward the basin axis (Nwangwu, 

1977; Tweto, 1980). The eastern flank of the Front Range is an 

east-dipping monocline formed during the Laramide Orogeny 

by crustal shortening beneath the range (Nesse, 2006). South 

of Boulder and along the western edge of the Denver Basin, 

east-directed (west-dipping) thrust faults form the structural 

boundary between the mountains and the Denver Basin 

(Robson and others, 1998; Nesse, 2006). In the northwest 

part of the Denver Basin, near Boulder County, numerous 

northeast-trending faults have offset the Fox Hills Sandstone 

and Laramie Formation (Weimer, 1973; Colton and Lowrie, 

1973; Davis and Weimer, 1976; Tweto, 1979; Schneider, 

1980; Kittleson, 2004; Sterne, 2006). The faulting affects only 

a small area of the Denver Basin; this and previous studies assume that the faulting has no substantial effect on the 

Upper Cretaceous to Tertiary aquifer system at a regional scale 

(Robson, 1987; Robson and others, 1998).

Sedimentary rocks forming the structural Denver Basin 

range from Pennsylvanian to Tertiary in age (Anderman 

and Ackman, 1963; Scott, 1963b). Sandstone of the 

Pennsylvanian- to Permian-age Fountain Formation crops 

out along the western basin margin (DeVoto, 1980), forming prominent hogbacks (Scott, 1963b; Weimer and LeRoy, 

1987) at well-known locations such as the Flatirons near 

Boulder, Red Rocks Amphitheatre near Morrison (fig. A10), 

and Garden of the Gods Park near Colorado Springs. The 

Early Cretaceous Dakota Group, which represents transgression of the Cretaceous sea in eastern Colorado (Berman and 

others, 1980), contains sandstones that also form a prominent 

hogback parallel to the mountain front (the Dakota Hogback) 

along the western basin margin (Scott, 1963b, fig. A10). Overlying the Dakota Group are Late Cretaceous marine shales and 

limestones with minor amounts of sandstone, deposited by the 

Cretaceous sea (Scott, 1963b; Berman and others, 1980). The 

Late Cretaceous Pierre Shale, a marine shale about 5,200 ft 

thick, is the uppermost Cretaceous shale in the Denver Basin 

(Scott, 1963b; Weimer, 1973) and is considered the base of 

the Denver Basin aquifer system because of its low permeability and great thickness (Romero, 1976). Late Cretaceousto Tertiary-age sandstone aquifers and intervening claystone 

confining units overlying the Pierre Shale comprise the Denver 

Basin aquifer system (Scott, 1963b, Weimer, 1973; Romero, 

1976). Alluvial deposits along tributaries to the South Platte 

River north of the Palmer Divide and along tributaries to the 

Arkansas River south of the Palmer Divide form unconfined 

alluvial aquifers where saturated (Robson, 1989, 1996).
18 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Bedrock Aquifers and Confining Units

Colorado State legislation administrating the Denver 

Basin recognizes and defines four primary bedrock aquifers 

(Romero, 1976; Robson, 1987; Graham and VanSlyke, 2004). 

From oldest to youngest (bottom to top), the four primary units 

are the Laramie–Fox Hills aquifer, the Arapahoe aquifer, the 

Denver aquifer, and the Dawson aquifer. In parts of the basin, 

confining units further divide the Arapahoe and Dawson aquifers into upper and lower units (table A3). Thus, the six Denver 

Basin bedrock aquifers and five intervening confining units used 

to develop geologic layers for the groundwater flow model, 

from oldest to youngest, are the Laramie–Fox Hills aquifer, 

Laramie confining unit, lower Arapahoe aquifer, Arapahoe 

confining unit, upper Arapahoe aquifer, lower Denver confining unit, Denver aquifer, upper Denver confining unit, lower 

Dawson aquifer, Dawson confining unit, and upper Dawson 

aquifer (table A3).

Structural geology, layered stratigraphy, and topography control the areas of outcrop, and thus, areas of potential 

recharge and discharge for the Denver Basin aquifers and 

confining units. The bedrock aquifers and confining units crop 

out in a ring pattern because of the synclinal structure of the 

Denver Basin, with the oldest rocks of the Laramie–Fox Hills 

aquifer cropping out around the outer margins of the basin and 

the youngest rocks of the Dawson aquifer cropping out in the 

center of the basin (fig. A11). The alluvial aquifer is the uppermost stratigraphic layer in the basin and overlies parts of all 

bedrock units. All (100 percent) of the simulated alluvial aquifer 

is exposed at the land surface, and the alluvial aquifer comprises 

about 30 percent of the total basin area (table A4). The upper 

Dawson aquifer is the uppermost bedrock unit of the basin, and 

only a small part of the simulated unit (2 percent) is overlain by 

the alluvial aquifer, such that 98 percent of the simulated upper 

Figure A9. Streamflow, estimated base flow, and 180-day moving average of estimated base flow for site Cherry Creek at Franktown.

Figure A10. Photograph of hogbacks along the western margin 

of the Denver Basin. View looking south.

100

1,000

10,000

0

1

10

Date

Flow, in cubic feet per second 1/1/1939

1/1/19441/1/19491/1/19541/1/19591/1/19641/1/19691/1/19741/1/19791/1/19841/1/19891/1/1994

1/1/19991/1/2004

Total streamflow

Estimated base flow

180-day moving average base flow

Variable to dry conditions

Variable to wet conditions

EXPLANATION
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 19

Table A3. Geology, hydrogeology, and water-use characteristics of the Denver Basin aquifers, Colorado (adapted from Kirkham and Ladwig [1979]; Robson [1987]; Nichols and Fleming [2002]; Raynolds [2002]; Lapey-Woodard and others [2002]; Thorson, [2003]).

Age Stratigraphic unit Hydrogeologic unit Model layer

Stratigraphic

nomenclature

of Raynolds

(2002)

Stratigraphic

nomenclature

in Black Forest 

quadrangle

(Thorson, 2003)

Lithologic

description

Range of

thickness for

entire section

(feet)

Hydrogeologic

description

Quaternary Alluvial, flood plain, terrace, 

colluvial, and eolian sand, gravel, and clay deposits

Alluvial aquifer 

where saturated

1 Unconsolidated sand and 

gravel with clay lenses

0 to 175 Productive unconfined alluvial 

aquifer where saturated.

Eocene Dawson Arkose upper Dawson 

aquifer

2 D2 sequence Dawson Formation

facies unit 5

Arkosic fluvial sandstone 

and conglomerate with interbedded claystone

200 to 840 Productive unconfined to 

confined aquifer.

Paleocene Dawson Arkose Dawson

confining unit

3 Paleosol Paleosol Claystone 1 to 350 Claystone confining unit in northern 

part of Dawson extent.

Paleocene Dawson Arkose lower Dawson 

aquifer

4 D1 sequence Dawson Formation

facies unit 4

Mixed arkosic and andesitic 

fluvial sandstone with interbedded claystone, lignite, and volcanics

100 to 570

where

undifferentiated

Productive confined aquifer.

Cretaceous/Paleocene

(K/T) boundary

Denver Formation upper Denver 

confining unit

5 Dawson Formation

facies unit 3/2

Predominantly claystone with 

interbedded sandstone, lignite, and volcanics

1 to 150 Fine-grained confining unit in 

upper Denver Formation.

Late Cretaceous Denver Formation Denver aquifer 6 Dawson Formation

facies unit 1

Mixed arkosic and andesitic 

fluvial sandstone 

280 to 1,100 Confined to unconfined aquifer. 

Lower hydraulic conductivity and less production than Arapahoe aquifers.

Denver Formation lower Denver 

confining unit

7 Predominantly claystone with 

andesitic fluvial sandstone 

5 to 150 Fine-grained confining unit at base 

of Denver Formation. 

Arapahoe Formation upper

Arapahoe

aquifer

8 Lower part of 

Dawson Formation

Arkosic fluvial sandstone 

with interbedded claystone

50 to 300 Productive confined aquifer above 

Arapahoe confining unit in northern one-third of basin.

Arapahoe Formation Arapahoe

confining

unit

9 Predominantly claystone 50 to 180 Claystone confining unit in 

northern one-third of basin.

Arapahoe Formation Lower 

Arapahoe

aquifer

10 D1 sequence/ 

Wildcat

Mountain fan

Alluvial fan conglomerate and 

sandstone with interbedded claystone

200 to 600

where

undifferentiated

Productive confined aquifer. 

Greatest thickness and hydraulic conductivity in west-central part of basin.

Laramie Formation Laramie 

confining unit

11 Laramie

Formation

Laramie Formation Gray to black shale, coal, 

siltstone, and sandstone

100 to 500 Thick confining unit limits 

downward movement of water from Arapahoe to Laramie–Fox Hills aquifer.

Laramie Formation Laramie–Fox 

Hills aquifer

12 Laramie

Formation

Laramie Formation Clean, well-sorted, nearlywhite, poorly consolidated 

fluvial delta-front sandstone

100 to 500 Productive confined to unconfined 

aquifer composed of sandstones from lower Laramie Formation and Fox Hills Sandstone. Fox Hills Sandstone Fox Hills

Sandstone

Fox Hills Sandstone Yellow brown marine deltafront and beach sandstone

Pierre Shale Pierre Shale 

confining unit

Not

applicable

Pierre Shale Pierre Shale Dark to light gray marine 

shale

5,200 Low permeability base of Denver 

Basin aquifer system.
20 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A11. Location of springs and extent of Denver Basin aquifers and confining units.

South Platte

River

Cac he la Poudre R

Little ThompsonR

Boulder C r Coal Creek

Big D ry Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

Big Thompson R

PALMER

DIVIDEDIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

104°

40°

39°

105°

Base from U.S. Geological Survey digital data, 2009, 1:100,000 

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27' N and 37°45' N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Alluvial aquifer Denver Basin aquifer system extent

Upper Dawson aquifer

Lower Dawson aquifer

Denver aquifer

Upper Arapahoe aquifer

Lower Arapahoe aquifer

Laramie–Fox Hills aquifer

Confining unit

Stream

Perennial

Ephemeral

Mapped spring
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 21

Dawson aquifer crops out at the land surface (table A4). The 

Denver aquifer underlies much of the topographically flatter 

parts of the basin and thus exhibits the greatest outcrop area of 

the bedrock aquifers (about 1,310 mi2; table A4). About 40 percent of the Denver aquifer crops out at the land surface, and 

its outcrop area represents the greatest proportion of bedrock 

outcrop in the basin (about 20 percent of the total basin area, 

table A4).

The synorogenic sedimentary sequence above the Pierre 

Shale records regression of the Interior Cretaceous Seaway in 

the Late Cretaceous followed by episodic uplift of the Rocky 

Mountain Front Range during the Laramide Orogeny (Emmons 

and others, 1896; Scott, 1963b, Weimer, 1973; Tweto, 1980; 

Raynolds, 2002). As the Cretaceous Seaway gradually retreated 

from what is now central Colorado, the Fox Hills Sandstone 

marine beach sand was deposited as a series of shingles interbedded with the upper Pierre Shale (Weimer, 1973; Raynolds, 

2002). As the seaway regressed farther, the Cretaceous Laramie 

Formation was deposited in a backswamp and deltaic environment dominated by overbank claystones and coal with interbedded fluvial channel sandstones (Weimer, 1973; Raynolds, 2002). 

The Laramie–Fox Hills aquifer includes both the marine Fox 

Hills Sandstone and nonmarine sandstones of the lower Laramie 

Formation (Romero, 1976), and these sandstones are relatively 

continuous across the basin. The upper Laramie Formation forms 

an overlying confining unit (Romero, 1976).

Above the Laramie Formation confining unit are the 

Arapahoe, Denver, and Dawson aquifers. Because of depositional 

facies changes across the basin and the resulting heterogeneity, 

previous workers have variously defined stratigraphic nomenclature for these sediments (see for example, Raynolds (2002) 

or Thorson (2003) for a synopsis of stratigraphic nomenclature). 

Raynolds (2002) describes a nomenclature reflective of depositional history for the Arapahoe, Denver, and Dawson aquifers 

where two pulses of synorogenic sedimentation are recognized. 

The lower (D1) sediment sequence, composed of the Arapahoe, 

Denver, and lower Dawson aquifers, represents the first pulse of 

sedimentation (Raynolds and Johnson, 2003). The D1 sequence 

includes basal conglomerates of the Arapahoe Formation near 

the mountain front, such as the Wildcat Mountain fan, which are 

alluvial fan deposits shed off the rising Front Range (Raynolds, 

2004). Farther east, away from the mountain front, the D1 

sequence contains claystone, coal, and volcanic ash deposited 

in terrestrial backswamp environments of the Denver Formation 

(Kirkham and Ladwig, 1979). The appearance of andesitic 

volcanic clasts and volcanic rocks within the sediments traditionally defined the mapped Denver Formation, although questions 

remain regarding the lateral continuity of the volcanic input to 

the D1 sequence (Thorson, 2003). The upper (D2) sedimentary 

sequence is equivalent to the upper Dawson aquifer and represents a separate pulse of sedimentation (Raynolds and Johnson, 

2003). The Pikes Peak area southwest of the Denver Basin is considered the source area for the arkosic sand in the D2 sequence 

(Raynolds, 2002), although Thorson (2003) notes that there may 

be multiple sources for the D2 sediments. The Dawson paleosol 

(Soister and Tschudy, 1978) represents an erosional unconformity 

between the D1 and D2 sequences (Raynolds, 2002) and generally correlates to the Dawson confining unit. The most recent 

geologic mapping by the CGS (for example, Thorson, 2003) uses 

an older nomenclature (Richardson, 1915; Scott, 1963b), which 

uses the term Dawson Formation to describe the entire D1 and 

D2 interval (Arapahoe, Denver, and Dawson aquifers). Depositional facies within the upper Dawson sediments are used as the 

basis for ongoing mapping rather than differentiating between 

Arapahoe, Denver, and Dawson Formations (Thorson, 2003; 

Thorson, 2007; Peter Barkmann, Colorado Geological Survey, 

oral commun., 2009).

Laramie–Fox Hills Aquifer

The Laramie–Fox Hills aquifer is the deepest and most 

extensive of the bedrock aquifers. It underlies an area of 

approximately 6,900 mi2 and the geographic outline of its base 

defines the lateral extent of the Denver Basin aquifer system 

(fig. A12). The Laramie–Fox Hills aquifer is composed of 

poorly to moderately consolidated sandstone units of the Upper 

Cretaceous Fox Hills Sandstone and the lower Laramie Formation (Romero, 1976; Schneider, 1980; Robson, Wacinski, and 

Table A4. Summary of simulated aquifer areas.

Aquifer or confining

unit name

Aquifer or confining 

unit abbreviation

Model

layer

Simulated

outcrop area

(square miles)

Simulated

layer area

(square miles)

Percentage

of layer that

crops out

Percentage

of simulated outcrop 

area within

basin modeled area

Alluvium QAL 1 2,212 2,212 100.0 31.3

Upper Dawson aquifer UTDW 2 696 710 98.0 9.9

Dawson confining unit TDWC 3 38 749 5.1 0.5

Lower Dawson aquifer LTDW 4 558 1,350 41.3 7.9

Denver upper confining unit TKDUC 5 92 1,447 6.4 1.3

Denver aquifer TKD 6 1,310 3,246 40.4 18.6

Denver lower confining unit TKDLC 7 158 3,490 4.5 2.2

Upper Arapahoe aquifer UKA 8 86 1,136 7.6 1.2

Arapahoe confining unit KAC 9 45 1,198 3.8 0.6

Lower Arapahoe confining unit LKA 10 538 4,668 11.5 7.6

Laramie confining unit KLC 11 733 5,841 12.5 10.4

Laramie–Fox Hills aquifer KLF 12 592 6,966 8.5 8.4

Basin modeled area 7,060
22 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A12. Altitude of the base and total thickness of the Laramie–Fox Hills aquifer.

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WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

4,500

4,700

4,900

5,500

5,100

4,100

4,300

5,300

3,900

5,700

3,500

3,700

5,900

4,500

4,700

4,900

5,500

5,100

4,100

4,300

5,300

3,900

5,700

3,500

3,700

5,900

PALMER

DIVIDEDIVIDE

104°

40°

39°

105°

0 10 20 MILES

0 10 20 KILOMETERS

Base from U.S. Geological Survey digital data, 2009, 1:100,000 

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27' N and 37°45' N, central meridian 105°00'W

EXPLANATION

Total thickness of Laramie–Fox Hills 

 aquifer, in feet

100 to 200

200 to 300

300 to 400

400 to 500

Laramie–Fox Hills aquifer extent

Line of equal base altitude, in feet.

 Contour interval 100 feet

Base-altitude data point
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 23

others, 1981; Robson, 1987). The Fox Hills Sandstone is a 

marine beach and delta-front sand deposited during regression 

of the Cretaceous sea through Colorado (Scott, 1963b; Weimer, 

1973). The Fox Hills Sandstone generally is 150–200 ft thick, 

a dusky yellow-brown in color, and contains marine fossils (Scott, 1963b; Robson, 1987). Sandstones of the lower 

Laramie Formation were deposited in freshwater delta-front 

fluvial channels subsequent to the Cretaceous sea regression 

(Weimer, 1973). The Laramie Formation sandstones generally 

are composed of clean, well-sorted, very fine- to mediumgrained sandstones with minor amounts of silt and clay and are 

nearly white (Scott, 1963b). A 10- to 20-ft-thick shale bed may 

separate the Laramie sandstones into two units, and a shale bed 

5 to 20 ft thick generally separates the Laramie and Fox Hills 

sandstones (Robson, 1987). Local sandstones also are present 

in the upper 100 to 200 ft of the Pierre Shale and represent a 

transitional depositional environment between the Cretaceous 

marine shale and Fox Hills sandstones (Scott, 1963b; Kiteley, 

1977; Nwangwu, 1977). Where present, sandstones in the upper 

Pierre Shale are considered part of the Laramie–Fox Hills aquifer (Robson, 1987).

The base-altitude configuration of the Laramie–Fox 

Hills aquifer shows the bowl shape and dipping margins of the 

Denver Basin geologic structure (fig. A12). The lowest part 

of the Laramie–Fox Hills aquifer base, and therefore also the 

lowest part of the Denver Basin bedrock aquifer system, is in 

Douglas County just north of Parker, Colorado, at an altitude of 

approximately 3,410 ft. Depth to the base of the Laramie–Fox 

Hills aquifer near the structural center of the basin is approximately 2,200 to 2,300 ft below land surface, and the total thickness of the aquifer system reaches a maximum of approximately 

3,200 ft beneath the topographic high of the Palmer Divide. 

Total thickness of the Laramie–Fox Hills aquifer ranges from 

0 to about 500 ft, and two distinct northwest- to southeasttrending areas of greatest aquifer thickness (300 to 400 ft) are 

noted (fig. A12). One area having aquifer thickness greater than 

300 ft trends northwest to southeast near the center of the basin, 

and a second area having aquifer thickness greater than 400 ft 

is present in the northeast part of the basin. The silt-plus-sand 

thickness of the Laramie–Fox Hills aquifer ranges from about 

100 to 250 ft (fig. A13). Areas having the greatest silt-plus-sand 

thickness (fig. A13) and the areas simulated with the greatest 

percent silt-plus-sand (fig. A14) coincide with the northwest- to 

southeast-trending area near the center of the basin having the 

greatest total aquifer thickness (fig. A12).

Laramie Confining Unit

The Laramie confining unit overlies the Laramie–Fox 

Hills aquifer and consists of the Cretaceous-age upper Laramie 

Formation, which is composed of gray to black shale, coal 

seams, and minor amounts of siltstone and sandstone (Robson, 

1987). The lowermost coal seams of the Laramie Formation 

occur just above the Laramie sandstones of the Laramie–Fox 

Hills aquifer and form the upper boundary of the aquifer unit 

(Murray, 1980; Robson, 1987). The subbituminous to lignitic 

coal seams are as much as 10 ft in thickness and have been 

extensively mined along the northwest and southwest margins of the basin (Colton and Lowrie, 1973; Kirkham, 1978; 

Kirkham and Ladwig, 1979).

The base-altitude configuration of the Laramie confining 

unit (fig. A15) is similar to that of the underlying Laramie–Fox 

Hills aquifer (fig. A12) and reflects the bowl shape and dipping 

margins of the Denver Basin. The lowest part of the Laramie 

confining unit is in Douglas County just north of Parker at an 

altitude of approximately 3,700 ft. The Laramie confining unit 

forms a wedge-shaped layer that is thickest (as much as 700 ft) 

along the mountain front and thins southeastward to less than 

100 ft (fig. A15).

Arapahoe Aquifers and Confining Unit

The Arapahoe aquifer consists of a 400- to 600-ft-thick 

sequence of interbedded conglomerate, sandstone, siltstone, 

and shale (Romero, 1976; Robson, Romero, and Zawistowski, 

1981; Robson, 1987). In the northern one-third of the basin, 

shale is more prevalent, and the Arapahoe is divided into the 

upper Arapahoe aquifer and the lower Arapahoe aquifer with 

an intervening shale that forms the Arapahoe confining unit 

(Robson, 1987). The upper and lower Arapahoe aquifers each 

generally consist of 150 to 200 ft of sandstone and siltstone with 

interbedded shale. Conglomerate and coarse-grained sandstone 

common in the lower Arapahoe aquifer are feldspar- and quartzrich, reflecting an erosional source from nearby Front Range 

Precambrian and Paleozoic rocks and deposition at the mountain 

front during the Laramide Orogeny (Scott, 1963b; Weimer, 1973; 

Trimble, 1980a; Tweto, 1980, Raynolds, 2002).

The base-altitude configuration of the lower Arapahoe 

aquifer (fig. A16) has a bowl-shaped form similar to the bases 

of the underlying Laramie confining unit and Laramie–Fox Hills 

aquifer. The altitude of the base of the lower Arapahoe aquifer 

ranges from 6,200 ft along the southwest basin margin to about 

4,100 ft at the basin center, just north of Parker, Colorado 

(fig. A16). Depth to the base of the lower Arapahoe aquifer near 

the structural center of the basin is approximately 1,700 ft below 

land surface, and the maximum depth to the base of the aquifer 

is approximately 2,600 ft below land surface near the Palmer 

Divide. Total thickness of the Arapahoe aquifer (fig. A16) represents the entire thickness of the Arapahoe aquifers and confining 

unit and ranges from less than 100 to as much as 745 ft with a 

mean of about 475 ft based on mapping by this study.

The base altitude of the Arapahoe confining unit (fig. A17) 

ranges from 5,400 ft along the northwest edge to about 4,400 ft 

on the southern edge of the confining unit, and the contours 

indicate a structural low toward the south and the center of the 

Denver Basin. Thickness of the Arapahoe confining unit ranges 

from 0 up to about 250 ft with a mean of about 90 ft. The greatest 

thickness of the Arapahoe confining unit is near the center of the 

confining-unit extent in southwest Adams County. The base of the 

upper Arapahoe aquifer (fig. A18) is similar in shape and altitude 

to that of the Arapahoe confining unit and ranges in altitude from 

more than 5,400 ft along the northwest edge to about 4,400 ft on 

the southern edge of the aquifer. Thickness of the upper Arapahoe 

aquifer ranges from 0 to about 350 ft with a mean of about 170 ft.
24 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A13. Silt-plus-sand thickness of the Laramie–Fox Hills aquifer.

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EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

150

200

100

PALMER

DIVIDEDIVIDE

105° 104°

40°

39°

0 6 12 MILES

0 6 12 KILOMETERS

Base from U.S. Geological Survey digital data, 2009, 1:100,000 

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27' N and 37°45' N, central meridian 105°00'W

EXPLANATION

Silt-plus-sand thickness, in feet Laramie–Fox Hills aquifer extent

Line of equal silt-plus-sand thickness, 

 in feet. Contour interval 50 feet

Silt-plus-sand thickness data point

93 to 100

100 to 125 200 to 225

225 to 250

175 to 200

125 to 150

150 to 175

!
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 25

Figure A14. Simulated silt-plus-sand fraction of the Laramie–Fox Hills aquifer.

DIVIDE

PALMER

DIVIDE

PALMER

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

§ ̈¦70

§ ̈¦25

§ ̈¦76

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

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105° 104°

40°

39°

0 10 20 MILES

0 10 20 KILOMETERS

Base from U.S. Geological Survey digital data, 2009, 1:100,000 

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27' N and 37°45' N, central meridian 105°00'W

EXPLANATION

Simulated silt-plus-sand fraction of 

 total thickness

0.15 to 0.2

0.2 to 0.3

0.3 to 0.4

0.4 to 0.5

0.5 to 0.6

0.6 to 0.7

0.7 to 0.8

0.8 to 0.94

Laramie–Fox Hills aquifer 

 simulated extent (model 

 layer 12)
26 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A15. Altitude of the base and total thickness of the Laramie confining unit.

DIVIDE

PALMER

DIVIDE

PALMER

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ARAPAHOE

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WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

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ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS Limon

Simla

Kiowa

Parker

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Calhan

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Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

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Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

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Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

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§ ̈¦70

§ ̈¦25

§ ̈¦76

4,900

4,700

4,800

4,600

5,000

5,100

5,300

5,200

5,400

5,500

4,500

5,600

4,400

4,300

4,200

5,800

4,100

5,700

3,900

4,000

3,800

5,900

4,900

4,700

4,800

4,600

5,000

5,100

5,300

5,200

5,400

5,500

4,500

5,600

4,400

4,300

4,200

5,800

4,100

5,700

3,900

4,000

3,800

5,900

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000 

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27' N and 37°45' N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Total thickness of Laramie confining 

 unit beneath the lower Arapahoe 

 aquifer, in feet

0 to 100

100 to 200

200 to 300

300 to 400

400 to 500

500 to 600

600 to 700

Lower Arapahoe aquifer extent

Laramie–Fox Hills aquifer extent

Laramie confining unit extent

Line of equal base altitude, in feet.

 Contour interval 100 feet ! Base-altitude data point
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 27

Figure A16. Altitude of the base of the lower Arapahoe aquifer and total thickness of the 

combined Arapahoe aquifers and confining unit.

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WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

PALMER

DIVIDEDIVIDE

§ ̈¦70

§ ̈¦25

§ ̈¦76

4,800

5,200

5,100

5,300

5,500

5,400

5,600

5,000

5,700

4,900

5,800

4,700

5,900

4,600

4,500

4,300

4,400

4,200

6,000

6,100

4,100

4,800

5,200

5,100

5,300

5,500

5,400

5,600

5,000

5,700

4,900

5,800

4,700

5,900

4,600

4,500

4,300

4,400

4,200

6,000

6,100

4,100

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Laramie–Fox Hills aquifer extent

Lower Arapahoe aquifer extent

Denver lower confining unit extent

Line of equal base altitude, in feet.

 Contour interval 100 feet ! Base-altitude data point

Total thickness of the Arapahoe aquifers

 and confining unit beneath the Denver 

 lower confining unit, in feet

0 to 100

100 to 200

200 to 300

300 to 400

400 to 500

500 to 600

600 to 700

700 to 745
28 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A17. Altitude of the base and thickness of the Arapahoe confining unit.

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WELD

ELBERT

LARIMER

ADAMS

BOULDER

ARAPAHOE

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

WELD

ELBERT

LARIMER

ADAMS

BOULDER

ARAPAHOE

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Kiowa

Parker

Golden

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Fort

Lupton

Castle

Rock

Highlands

Ranch

Aurora

Littleton

Lafayette

Englewood

Kiowa

Parker

Golden

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Fort

Lupton

Castle

Rock

Highlands

Ranch

Aurora

Littleton

Lafayette

Englewood

§ ̈¦25

§ ̈¦76

4,800

4,900

4,700

5,000

4,600

4,500

5,100

4,400

5,400

4,800

4,900

4,700

5,000

4,600

4,500

5,100

4,400

5,400

105° 104°30'

40°

39°30'

0 5 10 MILES

0 5 10 KILOMETERS

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

EXPLANATION

Total thickness of Arapahoe confining 

 unit, in feet

0 to 50

50 to 100

100 to 150

150 to 200

200 to 250

Laramie–Fox Hills aquifer extent

Lower Arapahoe aquifer extent

Arapahoe confining unit extent

Line of equal base altitude, in feet.

 Contour interval 100 feet

Base-altitude data point
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 29

Figure A18. Altitude of the base and thickness of the upper Arapahoe aquifer.

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ELBERT

LARIMER

ADAMS

BOULDER

ARAPAHOE

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

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LARIMER

ADAMS

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ARAPAHOE

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

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Parker

Golden Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Fort

Lupton

Castle

Rock

Highlands

Ranch

Aurora

Littleton

Lafayette

Englewood

Kiowa

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Golden Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Fort

Lupton

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Rock

Highlands

Ranch

Aurora

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§ ̈¦25

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105° 104°30'

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Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Total thickness of upper 

 Arapahoe aquifer, in feet

0 to 100

100 to 200

200 to 300

Line of equal base altitude, in feet.

 Contour interval 100 feet

Laramie–Fox Hills aquifer extent

Lower Arapahoe aquifer extent

Upper Arapahoe aquifer extent

Base-altitude data point
30 Groundwater Availability of the Denver Basin Aquifer System, Colorado

The silt-plus-sand thickness of the lower Arapahoe 

aquifer ranges from about 8 to as much as 490 ft with a mean 

of about 175 ft (fig. A19). The greatest silt-plus-sand thickness for the lower Arapahoe aquifer is along the western 

basin margin in Douglas and El Paso Counties and coincides 

with simulated areas of greatest percent silt-plus-sand (up to 

about 85 percent silt-plus-sand; fig. A20). The area of greatest silt-plus-sand thickness and greatest percent silt-plussand corresponds with the location of the Wildcat Mountain 

alluvial fan reported by Raynolds (2004). The lower Arapahoe 

sandstones of the Wildcat Mountain fan were deposited at the 

mountain front as distributary alluvial fans during the Late 

Cretaceous (Raynolds, 2004). The coarse-grained sandstones 

of the lower Arapahoe aquifer form a transmissive bedrock 

aquifer in Douglas and El Paso Counties that is heavily used 

for municipal and domestic water supply. The silt-plus-sand 

thickness for the upper Arapahoe aquifer ranges from about 

5 to about 250 ft with a mean of about 90 ft (fig. A21), and 

the percent silt-plus-sand ranges from about 16 to 80 percent 

(fig. A22). There is no discernible alluvial-fan pattern in the 

upper Arapahoe aquifer.

Denver Aquifer and Confining Units

The Denver aquifer and confining units consist of 

a 600- to 1,200-ft-thick sequence of Late Cretaceous- to 

Tertiary-age interbedded shale, claystone, siltstone, sandstone, 

coal, and volcanic rocks (Romero, 1976; Robson, Wacinski, 

and others 1981; Robson, 1987). The depositional environment during Denver Formation sedimentation consisted of 

continued alluvial fan deposition near the mountain front, 

where sandstone beds are more prevalent (Crifasi, 1992; 

Kirkham and Ladwig, 1979), with overbank and swamp 

deposition of finer grained sediments and coal farther from 

the mountain front (Kirkham and Ladwig, 1979). The prominent Wildcat Mountain alluvial fan mapped in the lower 

Arapahoe aquifer (lower D1 sequence; Raynolds, 2004) also 

is present in the Denver and lower Dawson portions of the 

sequence as mapped by this study. Because volcanic activity 

increased in the Rocky Mountain Front Range during deposition of the Denver Formation, the sequence contains andesitic 

sandstones and volcanic ash layers (Epis and others, 1976; 

Kirkham and Ladwig, 1979; Tweto, 1980; Robson, Wacinski, 

and others; 1981; Thorson, 2007). The Denver Formation 

commonly is distinguished from the underlying Arapahoe 

Formation and overlying Dawson Arkose by its olive, greengray, brown, and tan sediment colors, which are caused by 

the presence of iron-rich sediment derived from erosion of 

basalts and andesitic lava (Weimer, 1973; Robson, Wacinski, 

and others, 1981; Robson, 1987). Some researchers define 

the Denver Formation by the appearance of volcanic debris 

in the stratigraphic section (Weimer, 1973). The Cretaceous/

Tertiary boundary is in the upper part of the Denver aquifer 

sequence and is closely established by vertebrate fossils 

(Tweto, 1980) and pollen (Barclay and others, 2003; Nichols 

and Fleming, 2002).

The Denver aquifer is, in general, finer grained than the 

underlying Arapahoe aquifer sequence and is composed of isolated channel sandstones contained in extensive fine-grained 

deposits (Robson, Wacinski, and others, 1981; Robson, 1987; 

Raynolds, 2004). Because of the difficulty correlating individual sandstones between wells even on a local scale, it 

also is difficult to map the Denver aquifer on a regional scale 

(Raynolds, 2002, 2004). For administrative purposes, the 

Denver stratigraphic interval is divided into a lower confining unit (Denver lower confining unit), an aquifer (Denver 

aquifer), and an upper confining unit (Denver upper confining 

unit), where the confining units contain a larger proportion of 

fine-grained sediments than the aquifer. Despite the limitations 

of sandstone correlations within the Denver interval, the basealtitude maps of the Denver aquifer and confining units depict 

the regional structure of the Denver Basin, similar to other 

aquifer base-altitude maps, and provide reasonable representations of layering within the Denver aquifer and confining units 

(figs. A23–A25). The base altitudes of the Denver aquifer and 

confining units range from about 4,600 to 6,300 ft, and the 

maximum depth of the base is about 2,100 ft below land surface near the Palmer Divide (figs. A23–A25). Total thickness 

of the Denver lower confining unit ranges from 0 to as much 

as 300 ft with a mean of about 50 ft (fig. A23), and total thickness of the Denver aquifer ranges from about 20 to 1,055 ft 

with a mean of about 550 ft (fig. A24). The Denver upper confining unit has a smaller extent than that of the Denver aquifer 

and occurs at higher altitudes. The Denver upper confining 

unit base altitude ranges from about 5,400 ft near the center of 

the basin to 6,800 ft on the southern edge of the confining unit 

(fig. A25). Total thickness of the Denver upper confining unit 

ranges from 0 to as much as 200 ft, with a mean of about 50 ft.

Silt-plus-sand thickness for the Denver aquifer ranges 

from about 5 to about 665 ft with a mean of about 190 ft 

(fig. A26). The area with the greatest silt-plus-sand thickness 

(400 to 600 ft) is along the western basin margin in southern 

Douglas County (fig. A26) and corresponds with an area where 

40 to 72 percent of the total thickness is silt-plus-sand (fig. A27) 

as well as the location of the Wildcat Mountain fan in the D1 

synorogenic deposition sequence (Raynolds, 2004). These siltplus-sand thickness results indicate that the lower Arapahoe and 

Denver aquifers, as administratively defined by the CDWR and 

mapped herein, contain the lower and upper parts, respectively, 

of the Wildcat Mountain Fan. The Denver lower confining unit 

is thin (generally less than 50 ft thick) where Denver aquifer 

silt-plus-sand thickness is greatest, indicating a potential for 

hydraulic connection between the Denver aquifer and the lower 

Arapahoe aquifer especially on the west-central margin of the 

basin. The Denver aquifer contains less than 40 percent sand 

over much of its extent (Robson, 1987; fig. A27).
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 31

Figure A19. Silt-plus-sand thickness of the lower Arapahoe aquifer.

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WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

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Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

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Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

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Fort

Lupton

Fort

Morgan

Castle

Rock

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Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦25

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0 10 20 MILES

0 10 20 KILOMETERS

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

EXPLANATION

Silt-plus-sand thickness of lower 

 Arapahoe aquifer, in feet

8 to 100

100 to 150

150 to 200

200 to 250

250 to 300

300 to 400

400 to 500

Laramie–Fox Hills aquifer extent

Lower Arapahoe aquifer extent

Arapahoe confining unit extent

Line of equal silt-plus-sand thickness, 

 in feet. Variable contour interval

Silt-plus-sand data point !
32 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A20. Simulated silt-plus-sand fraction of the lower Arapahoe aquifer.

PALMER

DIVIDEDIVIDE

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EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

§ ̈¦70

§ ̈¦25

§ ̈¦76

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

105° 104°

40°

39°

0 10 20 MILES

0 10 20 KILOMETERS

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

Hydraulic conductivity data from Colorado Water Conservation Board, 2006

EXPLANATION

Simulated silt-plus-sand fraction 

 of total thickness

0.08 to 0.2

0.2 to 0.3

0.3 to 0.4

0.4 to 0.5

0.5 to 0.6

0.6 to 0.7

0.7 to 0.85

Laramie–Fox Hills aquifer simulated extent 

 (model layer 12)

Lower Arapahoe aquifer simulated extent 

 (model layer 10)
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 33

Figure A21. Silt-plus-sand thickness of the upper Arapahoe aquifer.

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WELD

ELBERT

LARIMER

ADAMS

BOULDER

ARAPAHOE

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

WELD

ELBERT

LARIMER

ADAMS

BOULDER

ARAPAHOE

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Kiowa

Parker

Golden

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Fort

Lupton

Castle

Rock

Highlands 

Ranch

Aurora

Littleton

Lafayette

Englewood

Kiowa

Parker

Golden

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Fort

Lupton

Castle

Rock

Highlands 

Ranch

Aurora

Littleton

Lafayette

Englewood

§ ̈¦25

§ ̈¦76

105° 104°30'

40°

39°30'

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES 

0 5 10 KILOMETERS

EXPLANATION

Silt-plus-sand thickness of upper 

 Arapahoe aquifer, in feet

6 to 50

50 to 100

100 to 150

150 to 200

200 to 256

Laramie–Fox Hills aquifer extent

Lower Arapahoe aquifer extent

Upper Arapahoe aquifer extent

Line of equal silt-plus-sand thickness, 

 in feet. Contour interval 50 feet

Silt-plus-sand data point
34 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A22. Simulated silt-plus-sand fraction of the upper Arapahoe aquifer.

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WELD

ELBERT

LARIMER

ADAMS

BOULDER

ARAPAHOE

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

WELD

ELBERT

LARIMER

ADAMS

BOULDER

ARAPAHOE

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Kiowa

Parker

Golden

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Fort

Lupton

Castle

Rock

Highlands

Ranch

Aurora

Littleton

Lafayette

Englewood

Kiowa

Parker

Golden

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Fort

Lupton

Castle

Rock

Highlands

Ranch

Aurora

Littleton

Lafayette

Englewood

§ ̈¦25

§ ̈¦76

105° 104°30'

40°

39°30'

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Simulated silt-plus-sand fraction 

 of total thickness

0.16 to 0.3

0.3 to 0.4

0.4 to 0.5

0.5 to 0.6

0.6 to 0.7

0.7 to 0.8 Laramie–Fox Hills aquifer simulated extent 

 (model layer 12)

Lower Arapahoe aquifer simulated extent 

 (model layer 10)

Upper Arapahoe aquifer simulated extent 

 (model layer 8)
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 35

Figure A23. Altitude of the base and total thickness of the Denver lower confining unit.

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LINCOLN

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ADAMS

MORGAN

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TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

PALMER

DIVIDEDIVIDE

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,600

5,700

5,300

5,100

5,900

5,500

5,400

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5,200

5,800

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4,900

4,800

4,700

6,100

6,200

4,600

5,600

5,700

5,300

5,100

5,900

5,500

5,400

6,000

5,200

5,800

5,000

4,900

4,800

4,700

6,100

6,200

4,600

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Total thickness of Denver lower 

 confining unit, in feet

0 to 50

50 to 100

100 to 200

200 to 300

Laramie–Fox Hills aquifer extent

Lower Arapahoe aquifer extent

Denver lower confining unit extent

Line of equal base altitude, in feet.

 Contour interval 100 feet ! Base-altitude data point
36 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A24. Altitude of the base and total thickness of the Denver aquifer.

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PALMER

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BROOMFIELD

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Simla

Kiowa

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Golden

Calhan

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Greeley

Boulder

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Loveland

Morrison

Lakewood

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Longmont

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Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,600

5,100

5,800

5,700

5,500

5,400

5,300

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5,900

5,200

5,000

4,900

4,800

6,100

6,200

4,700

6,300

5,600

5,100

5,800

5,700

5,500

5,400

5,300

6,000

5,900

5,200

5,000

4,900

4,800

6,100

6,200

4,700

6,300

105° 104°

40°

39°

0 10 20 MILES

0 10 20 KILOMETERS

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

EXPLANATION

Total thickness of Denver aquifer, in feet

17 to 200

200 to 400

400 to 600

600 to 800

800 to 1,055 Laramie–Fox Hills aquifer extent

Lower Arapahoe aquifer extent

Denver aquifer extent

Line of equal base altitude, in feet.

 Contour interval 100 feet ! Base-altitude data point
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 37

Figure A25. Altitude of the base and total thickness of the Denver upper confining unit.

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JEFFERSON

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Golden

Calhan

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Boulder

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Loveland

Morrison

Lakewood

Monument

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Franktown

Elizabeth

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Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

6,000

6,100

6,500

6,200 6,300

5,900

5,800

6,400 5,700

6,600

5,600

6,700

5,500

6,800

5,400

6,000

6,100

6,500

6,200 6,300

5,900

5,800

6,400 5,700

6,600

5,600

6,700

5,500

6,800

5,400

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Total thickness of Denver upper 

 confining unit, in feet

0 to 50

50 to 100

100 to 150

150 to 200

Laramie–Fox Hills aquifer extent

Lower Arapahoe aquifer extent

Denver aquifer extent

Denver upper confining unit extent

Line of equal base altitude, in feet.

 Contour interval 100 feet

! Base-altitude data point
38 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A26. Silt-plus-sand thickness of the Denver aquifer.

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WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

100

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DIVIDEDIVIDE

§ ̈¦70

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105° 104°

40°

39°

0 10 20 MILES

0 10 20 KILOMETERS

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

EXPLANATION

Silt-plus-sand thickness of the Denver 

 aquifer, in feet

5 to 50

50 to 100

100 to 150

150 to 200

200 to 250

250 to 300

300 to 350

350 to 400

400 to 665

Laramie–Fox Hills aquifer extent

Lower Arapahoe aquifer extent

Denver aquifer extent

Line of equal silt-plus-sand thickness, 

 in feet. Variable contour interval ! Silt-plus-sand data point
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 39

Figure A27. Simulated silt-plus-sand fraction of the Denver aquifer.

PALMER

DIVIDEDIVIDE

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WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Simulated silt-plus-sand fraction of 

 total thickness

0.06 to 0.1

0.1 to 0.2

0.2 to 0.3

0.3 to 0.4

0.4 to 0.5

0.5 to 0.6

0.6 to 0.72 Laramie–Fox Hills aquifer simulated extent 

 (model layer 12)

Lower Arapahoe aquifer simulated extent 

 (model layer 10)

Denver aquifer simulated extent (model 

 layer 6)
40 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Dawson Aquifers and Confining Unit

The Dawson aquifer sequence consists of a 100- to 

1,100-ft-thick sequence of interbedded fluvial conglomerate, sandstone, siltstone, and shale (Romero, 1976; Robson, 

Romero, and Zawistowski, 1981; Robson, 1987). In general, the conglomerates and sandstones are coarse-grained, 

feldspathic, and poorly to moderately consolidated (Robson, 

1987). In the northern two-thirds of its extent, a clay and 

shale confining layer is present in the Dawson, and the aquifer 

is separated into an upper and lower aquifer. The confining 

layer is difficult to identify in the southern part of the Dawson extent, and the entire 600-ft-thick sequence of sediment 

in this area is assigned to the lower Dawson aquifer.

The lower Dawson aquifer forms the upper part of the 

D1 sequence described by Raynolds (2002) and represents 

continued Laramide synorogenic fluvial deposition in an 

environment similar to that which existed during deposition of 

the Denver Formation (Soister, 1978b; Raynolds, 2004). The 

base altitude of the lower Dawson aquifer ranges from about 

5,400 ft at the northern edge of its extent to about 6,800 ft on 

the southern edge of its extent, and the shape of the aquifer 

base again reflects the synclinal shape of the Denver Basin 

(fig. A28). The base of the lower Dawson aquifer is 1,100 ft 

below land surface near the Palmer Divide. Total thickness of 

the lower Dawson aquifer ranges from about 75 to about 790 ft 

with a mean of about 310 ft. Silt-plus-sand thickness ranges 

from 0 to about 375 ft with a mean of 85 ft, and the area with 

the greatest silt-plus-sand thickness (200 to 375 ft) is in the 

southwestern part of the basin along the Douglas–El Paso 

County line (fig. A29). The simulated percent silt-plus-sand is 

greatest along the northern and western aquifer margins and in 

the southern part of Douglas County (fig. A30).

The Dawson confining unit consists of a shale-rich 

layer at the top of the D1 sequence (Raynolds, 2002) and the 

Dawson paleosol series that caps the shale-rich layer (Soister, 

1978b; Soister and Tschudy, 1978; Trimble, 1980b; Bryant 

and others, 1981; Raynolds, 2002). The Dawson confining unit 

base altitude ranges from about 5,600 ft at the northern edge 

of its extent to about 6,650 ft on the southern edge of its extent 

(fig. A31). Total thickness of the Dawson confining unit ranges 

from 0 to about 300 ft with a mean of about 80 ft. The Dawson 

confining unit is thinnest in the southern part of its extent and 

thickens to the north (fig. A31).

The upper Dawson aquifer is equivalent to the D2 

sequence of Raynolds (2002). The upper Dawson aquifer 

consists of arkosic, coarse-grained, poorly consolidated sandstones with some interbedded overbank mudstone deposits in 

a distribution pattern quite different from that of the underlying D1 sequence (Raynolds, 2002). Sandstones of the upper 

Dawson aquifer are more uniform and less variable in composition than those from the underlying layers and likely were 

derived from the Pikes Peak area of the Front Range (Morse, 

1979; Crifasi, 1992; Raynolds, 2002; Thorson, 2003). The 

base altitude of the upper Dawson aquifer ranges from about 

5,650 ft at the northern edge of its extent to about 6,800 ft on 

the southern edge of its extent. Paleochannels at the base of 

the lower Dawson aquifer are evident from the base-altitude 

map, and one such paleochannel aligns with the presentday course of Cherry Creek (fig. A32), indicating that some 

present-day drainage patterns began to develop in Eocene 

time (Bader and others, 2007). The upper Dawson aquifer 

is the uppermost bedrock unit of the Denver Basin, so its 

thickness is calculated as the land-surface altitude minus the 

aquifer-base altitude where alluvium is not present (fig. A32). 

Thickness is greatest at the southern edge of the aquifer extent 

(about 840 ft) and thinnest along drainages of Plum and 

Cherry Creeks where deposits are incised by present-day erosion. Mean thickness is about 350 ft. Silt-plus-sand thickness 

for the upper Dawson aquifer ranges from 3 to about 275 ft 

with a mean of about 107 ft (fig. A33). The greatest silt-plussand thicknesses in the upper Dawson are located in an area 

that trends northeast from Douglas County (fig. A33), which 

the model represents with a northeast-trending area where 

simulated percent silt-plus-sand ranges from 30 to 60 percent 

(fig. A34).

Alluvial Aquifer

The alluvial aquifer overlies parts of the Denver Basin 

bedrock aquifers and consists of Quaternary alluvial, colluvial, and eolian deposits. These deposits form an extensive, 

transmissive, unconfined alluvial aquifer where interconnected 

and saturated, primarily along present-day stream channels 

(Robson, 1989). Substantial alluvial aquifers considered by 

this study include (1) present-day and prehistoric stream channels of the South Platte River and its tributaries (Bjorklund 

and Brown, 1957; Smith and others, 1964); (2) the Black 

Squirrel Creek drainage (Erker and Romero, 1967; Bingham 

and Klein, 1973; Buckles and Watts, 1988; Watts, 1995); 

and (3) the Big Sandy Creek drainage (Coffin, 1962; Willard 

Owens Associates, 1971) and the Nussbaum Alluvium south 

of Big Sandy Creek (Scott, 1963c; Soister, 1967; Paschke, 

1992) (fig. A35). Eolian and colluvial deposits outside of 

stream channels were not included in this study because 

they generally are insufficiently saturated to form a productive aquifer. Unconsolidated, coarse-grained sand and gravel 

deposits composed of granitic and gneissic rock fragments, 

sedimentary rock fragments, quartz, and feldspar characterize 

alluvial deposits in the Denver Basin (Scott, 1963a). Interbedded clays are present in some areas (Scott, 1963a). Alluvial 

deposits along the main channel of the South Platte River 

and tributaries draining directly from the Front Range tend to 

be coarser grained than alluvial deposits in tributaries draining from the Palmer Divide because streams draining from 

the mountains receive coarser-grained source materials from 

steeper terrain than streams draining the sedimentary rocks of 

the Denver Basin. The Nussbaum Alluvium is a terrace gravel 

deposit of coarse-grained sand and gravel derived from erosion of the upper Dawson sequence to the north (Scott, 1963c; 

Soister, 1967; Paschke, 1992).
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 41

Figure A28. Altitude of the base and total thickness of the lower Dawson aquifer.

PALMER DIVIDE

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EL PASO

ELBERT

ADAMS

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TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

§ ̈¦25

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105° 104°30'

39°30'

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

!

Total thickness of the lower Dawson 

 aquifer, in feet

75 to 100

100 to 200

200 to 300

300 to 400

400 to 500

500 to 600

600 to 700

700 to 786

Lower Dawson aquifer extent

Denver aquifer extent

Lower Arapahoe aquifer extent

Laramie-Fox Hills aquifer extent

Line of equal base altitude, in feet. 

 Contour interval 100 feet

Base-altitude data point
42 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A29. Silt-plus-sand thickness of the lower Dawson aquifer.

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EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

PALMER DIVIDEPALMER DIVIDE

§ ̈¦25

50

100

150

0

200

250

300

350

0

0

0

0

300

100

150

150

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100

200

50

150

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100

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150

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105° 104°30'

39°30'

39°

0 5 10 MILES

0 5 10 KILOMETERS

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

EXPLANATION

Silt-plus-sand thickness of the lower

 Dawson aquifer, in feet

0 to 50

50 to 100

100 to 150

150 to 200

200 to 250

250 to 300

300 to 374

Lower Dawson aquifer extent

Denver aquifer extent

Lower Arapahoe aquifer extent

Laramie–Fox Hills aquifer extent

Line of equal silt-plus-sand thickness, 

 in feet. Contour interval 50 feet ! Silt-plus-sand data point
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 43

Figure A30. Simulated silt-plus-sand fraction of the lower Dawson aquifer.

PALMER

DIVIDEDIVIDE

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

!

! ! !

!

!

!

!

!

!

!

! !

!

!

!

!

!

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

§ ̈¦25

105° 104°30'

39°30'

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Simulated silt-plus-sand fraction 

 of total thickness

0.2 to 0.3

0.3 to 0.4

0.4 to 0.5

0.5 to 0.6

0.6 to 0.7

0.7 to 0.77

Laramie–Fox Hills aquifer simulated extent 

 (model layer 12)

Lower Arapahoe aquifer simulated extent 

 (model layer 10)

Denver aquifer simulated extent (model 

 layer 6)

Lower Dawson aquifer simulated extent 

 (model layer 4)
44 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A31. Altitude of the base and total thickness of the Dawson confining unit.

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EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

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PALMER

DIVIDEDIVIDE

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

§ ̈¦25

6,200 6,100

6,300

6,000

6,400

6,500

5,900

5,800

6,600

5,700

5,600

6,200 6,100

6,300

6,000

6,400

6,500

5,900

5,800

6,600

5,700

5,600

105° 104°30'

39°30'

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Total thickness of Dawson confining 

 unit, in feet

1 to 25

25 to 50

50 to 100

100 to 150

150 to 200

200 to 300

Dawson confining unit extent

Lower Dawson aquifer extent

Denver aquifer extent

Lower Arapahoe aquifer extent

Laramie-Fox Hills aquifer extent

Line of equal base altitude, in feet.

 Contour interval 100 feet ! Base-altitude data point
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 45

Figure A32. Altitude of the base and total thickness of the upper Dawson aquifer.

PALMER

DIVIDEDIVIDE

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EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

§ ̈¦25

6,250

6,050

6,400

6,200

6,350

6,100

6,300

6,450

6,500

6,550

6,000

5,950

5,900

6,650

5,800

6,700

5,700

6,250

6,050

6,400

6,200

6,350

6,100

6,300

6,450

6,500

6,550

6,000

5,950

5,900

6,650

5,800

6,700

5,700

105° 104°30'

39°30'

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Total thickness of upper 

 Dawson aquifer, in feet

3 to 200

200 to 400

400 to 600

600 to 840

Laramie–Fox Hills aquifer extent

Lower Arapahoe aquifer extent

Denver aquifer extent

Lower Dawson aquifer extent

Upper Dawson aquifer extent

Line of equal base altitude, in feet.

 Contour interval 100 feet

Base-altitude data point
46 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A33. Silt-plus-sand thickness of the upper Dawson aquifer.

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EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

PALMER

DIVIDE

PALMER

DIVIDE

§ ̈¦25

105° 104°30'

39°30'

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

EXPLANATION

Silt-plus-sand thickness of the upper 

 Dawson aquifer, in feet

3 to 25

25 to 50

50 to 75

75 to 100

100 to 125

125 to 150

150 to 175

175 to 200

200 to 225

225 to 250

250 to 275

Upper Dawson aquifer extent

Lower Dawson aquifer extent

Denver aquifer extent

Lower Arapahoe aquifer extent

Laramie-Fox Hills aquifer extent

Line of equal silt-plus-sand thickness, 

 in feet. Variable contour interval ! Silt-plus-sand data point

0 5 10 MILES

0 5 10 KILOMETERS
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 47

Figure A34. Simulated silt-plus-sand fraction of the upper Dawson aquifer.

PALMER

DIVIDEDIVIDE

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

!

! ! !

!

!

!

!

!

!

!

! !

!

!

!

!

!

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

§ ̈¦25

105° 104°30'

39°30'

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Simulated silt-plus-sand fraction 

 of total thickness

0.12 to 0.2

0.2 to 0.3

0.3 to 0.4

0.4 to 0.5

0.5 to 0.6

Laramie–Fox Hills aquifer simulated extent 

 (model layer 12)

Lower Arapahoe aquifer simulated extent 

 (model layer 10)

Denver aquifer simulated extent (model 

 layer 6)

Lower Dawson aquifer simulated extent 

 (model layer 4)

Upper Dawson aquifer simulated extent 

 (model layer 2)
48 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A35. Altitude of the base and total thickness of alluvial sand and gravel deposits in the 

Denver Basin.

South Platte

River

Cac he la Poudre R

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

Big Thompson R

PALMER

DIVIDEDIVIDE

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WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

6,000

4,400

4,500

6,100

5,900

6,200

5,800

6,300

6,400

4,600

4,300

4,900

5,100

4,700

6,500

4,800

5,000

5,700

6,600

5,200

5,300

5,400

5,600

6,700

5,500

7,000

6,900

4,800

5,000

5,800

5,700

5,700

5,700

6,000

4,500

5,600

5,900

5,000

4,700

4,700

5,800

5,800

4,600

5,200

5,300

4,600

5,200

4,900

5,800

6,100

5,900

5,100

4,700

5200

4,800

5,000

4,800

4,800

5,800

4,600

4,900

4,600

5,300

4,500

5,000

5,500

5,800

5,100

4,700

4,900

6,000

4,400

4,500

6,100

5,900

6,200

5,800

6,300

6,400

4,600

4,300

4,900

5,100

4,700

6,500

4,800

5,000

5,700

6,600

5,200

5,300

5,400

5,600

6,700

5,500

7,000

6,900

4,800

5,000

5,800

5,700

5,700

5,700

6,000

4,500

5,600

5,900

5,000

4,700

4,700

5,800

5,800

4,600

5,200

5,300

4,600

5,200

4,900

5,800

6,100

5,900

5,100

4,700

5200

4,800

5,000

4,800

4,800

5,800

4,600

4,900

4,600

5,300

4,500

5,000

5,500

5,800

5,100

4,700

4,900

105° 104°

40°

39°

Black Squirrel Creek 

alluvial aquifer

Nussbaum

alluvial aquifer

Big Sandy Creek

alluvial aquifer

South Platte River

and tributaries

alluvial aquifer

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Thickness of alluvial aquifer, in feet Alluvial aquifer extent

3 to 50

50 to 100

100 to 150

150 to 200

200 to 250

250 to 376 Stream

Perennial

Ephemeral

Laramie–Fox Hills aquifer extent

Equal base altitude of alluvial aquifer, 

 in feet. Contour interval 100 feet
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 49

In general, the base of the alluvial aquifer slopes 

outward in a radial fashion away from the Palmer Divide, 

reflecting paleo- and present-day topography (fig. A35). The 

base of alluvium in the South Platte River and its tributaries 

slopes northward, and the base of alluvium in Black Squirrel 

Creek slopes southward. The base of the Nussbaum Alluvium 

and Big Sandy Creek alluvial aquifers slopes southeast away 

from the Palmer Divide. Paleochannels are evident in the 

alluvial base configuration, and some present-day stream 

channels align with paleochannels, indicating renewed 

headward erosion along prehistoric drainages (Paschke, 

1992). Alluvial deposit thickness ranges from 3 to about 

376 ft (fig. A35). The thickest part of the South Platte alluvial aquifer (more than 250 ft) is located in the downstream 

part of the aquifer near Wiggins, Colorado (Hurr, Schneider, 

and others, 1972b); unconsolidated alluvial deposits over 

300 ft in thickness also are found in the Nussbaum Alluvium 

(Paschke, 1992).

Aquifer Hydraulic Properties

The ability of an aquifer to transmit and store water 

is a function of its thickness, hydraulic conductivity, and 

storage properties. Hydraulic conductivity (K) describes the 

capacity of a unit volume of permeable material to transmit 

water (Lohman, 1979). Transmissivity (T) is a measure of the 

capacity of a unit width of the aquifer to transmit water and 

is equal to the hydraulic conductivity multiplied by aquifer 

saturated thickness (b) (T = Kb) (Lohman, 1979). A greater 

thickness of water-yielding material of a given hydraulic 

conductivity allows larger volumes of water to move through 

the aquifer.

Storage properties of an aquifer, described in terms of 

storage coefficient or specific storage for confined aquifers and 

specific yield for unconfined aquifers, represent the volume of 

water released from or taken into aquifer storage as hydraulic 

head changes. These properties can vary substantially depending on whether the aquifer is under confined or unconfined 

conditions. The storage coefficient is the volume of water 

released from or taken into storage by an aquifer because of 

expansion of water and compression of the aquifer per unit 

surface area of the aquifer in response to a unit change in 

hydraulic head (Lohman, 1979). The capacity of a confined 

aquifer to release water from storage depends on the thickness 

of the aquifer, the porosity of the water-bearing material, and 

to a lesser extent, the compressibility of the water and rock 

(Lohman, 1979). If the potentiometric surface remains above 

the top of the water-bearing zone as for a confined aquifer, 

there is no physical draining of the aquifer when water is 

released from storage. Confined storage release is a result of 

the elastic properties of the water and the rock and is measured 

by the aquifer property of confined storage coefficient or specific storage (storage coefficient divided by aquifer thickness) 

(Lohman, 1979; Fetter, 1994). The specific yield is the ratio of 

the volume of water that will drain by gravity from a unit volume of the aquifer (Lohman, 1979). When the potentiometric 

surface of an aquifer drops below the top of the water-bearing 

zone, pore spaces in the rock are physically drained, and the 

aquifer at that location is considered unconfined. Specific yield 

is the aquifer parameter used to describe the capacity of an 

unconfined aquifer to release water as the water table is lowered and is defined as the ratio of the volume of water drained 

by gravity to the volume of drained rock (Lohman, 1979). The 

ratio of the volume of water not drained by gravity to the volume of drained rock is the specific retention. Porosity, which is 

the ratio of the volume of void spaces to the volume of rock, is 

the sum of specific yield and specific retention.

Hydraulic Conductivity and Transmissivity

Hydraulic-conductivity (K) values were derived from 

aquifer pumping tests, specific-capacity tests, and laboratory analyses. Hydraulic-conductivity values on which the 

discussion in this section is based are available in Hydrobase 

(Colorado Division of Water Resources, 2005; Colorado 

Water Conservation Board, 2006c), and the spatial distributions of hydraulic conductivity values are compared to modelcalibrated spatial distributions in the section “Calibrated 

Hydraulic-Conductivity Distribution” of Chapter C. 

Hydraulic-conductivity values from pumping tests for the 

upper Dawson aquifer range from 0.1 to about 6.2 ft/d, and 

hydraulic-conductivity values for the lower Dawson aquifer 

range from 0.01 to about 6.1 ft/d (fig. A36; table A5; Robson, 

1983). For the Denver aquifer, hydraulic-conductivity values 

from pumping tests range from a minimum of 0.03 ft/d to 

a maximum of 24 ft/d (fig. A36), and the maximum values 

are in the south Denver metropolitan area (fig. C6), similar 

to the hydraulic-conductivity distributions in the Arapahoe 

and Laramie–Fox Hills aquifers. For the Arapahoe aquifer, 

hydraulic-conductivity values from pumping tests range 

from a maximum of 9.9 ft/d south of Denver to a minimum 

of 0.06 ft/d in other areas (fig. A36). Hydraulic-conductivity 

values for the lower Arapahoe aquifer are greatest in the 

south Denver metropolitan area (fig. C7), but no pattern to 

hydraulic-conductivity values was discernible in the upper 

Arapahoe aquifer. For the Laramie–Fox Hills aquifer, Robson 

(1983) reported hydraulic-conductivity values ranging from 

about 0.05 ft/d along the northwest margin of the basin 

to about 6 ft/d south of Denver. The greatest hydraulicconductivity values from pumping tests (maximum of 7.2 ft/d) 

in the Laramie–Fox Hills aquifer (table A5; fig. A36) are 

observed in the south Denver metropolitan area, as noted by 

Robson (1983), and in the eastern part of the aquifer (fig. C8). 

The lowest hydraulic-conductivity values from pumping tests 

(minimum of 0.003 ft/d) in the Laramie–Fox Hills aquifer 

occur in the northwestern part of the aquifer, again consistent 

with results of Robson (1983). Few hydraulic-conductivity 

values are available for the Denver, Arapahoe, and Laramie–

Fox Hills aquifer in the areas overlain by the Dawson aquifer.
50 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Pumping

Specific capacity

Specific capacity

Specific capacity

Specific capacity

Laboratory

1E-5

1E-4

1E-3

0.01

0.1

1

10

100

1,000

10,000

1E-5

1E-4

1E-3

0.01

0.1

1

10

100

1,000

10,000

Hydraulic conductivity, in feet per day

Aquifer-test category

Pumping

Laboratory

Pumping

Laboratory

Pumping

Laboratory

90th percentile

EXPLANATION

25th percentile

50th percentile/mean

75th percentile

10th percentile

median

minimum

maximum

outliers

99th percentile

n=53 n=729 n=16 n=79 n=233 n=29 n=248 n=205 n=23 n=147 n=171 n=39

Dawson Denver Arapahoe Laramie–Fox Hills

Figure A36. Distribution of hydraulic-conductivity values from pumping tests for the Denver Basin bedrock aquifers.

A summary of hydraulic-conductivity values from 

pumping tests for the bedrock aquifers indicates the Arapahoe 

aquifer is the most permeable of the bedrock units, with a 

median hydraulic conductivity of 1.8 ft/d and geometric mean 

of 1.6 ft/d. The Dawson aquifer is the secondmost permeable 

bedrock unit, with a median hydraulic conductivity of 0.80 ft/d 

and a geometric mean of 0.71 ft/d (table A5; fig. A36). The 

Denver aquifer, with a median hydraulic conductivity of 

0.45 ft/d and a geometric mean of 0.42 ft/d, and the Laramie–

Fox Hills aquifer, with a median hydraulic conductivity of 

0.40 ft/d and a geometric mean of 0.40 ft/d, are nearly equal in 

hydraulic conductivity and are typically less permeable than 

either the Arapahoe or Dawson aquifers (fig. A36). Hydraulicconductivity values for the alluvial aquifer are two to more 

than three orders of magnitude greater than those of the bedrock aquifers and range from about 18 ft/d to about 2,560 ft/d 

with a median value of about 480 ft/d on the basis of pumpingtest results (table A5).

The median hydraulic-conductivity values derived from 

specific-capacity tests are generally similar to the medians 

of values from pumping tests for each aquifer (table A5). 

Hydraulic-conductivity values calculated from laboratory tests 

typically exhibit a larger range and have smaller geometricmean values than values from either pumping or specific 

capacity tests for all aquifers (table A5).

The transmissivity of the bedrock aquifers, as described 

by Robson (1983, 1987), ranged from zero at the limit of each 

of the aquifers to more than 1,000 ft2/d in the Laramie–Fox 

Hills aquifer, more than 2,100 ft2/d in the Arapahoe aquifer, 

more than 400 ft2/d in the Denver aquifer, and more than 

1,200 ft2/d in the Dawson aquifer. The Arapahoe aquifer was 

the most transmissive of the bedrock aquifers, followed by the 

Dawson and Laramie–Fox Hills aquifers (Robson, 1987). The 

Denver aquifer was considered the least transmissive of the 

bedrock aquifers (Robson, 1987). The alluvial aquifer is much 

more transmissive than the bedrock aquifers, as evidenced by 

an average transmissivity of about 13,000 ft2/d along the South 

Platte River downstream from Brighton (Hurr, Schneider, and 

others, 1972a). The difference in transmissivity between the 

alluvial and bedrock aquifers accounts for the larger yields of 

wells completed in the alluvial aquifer relative to the yields 

typical of wells completed in the bedrock aquifers (Robson, 

1989). The difference in hydraulic properties of the alluvial 

and bedrock aquifers is an important part of the Denver Basin 

conceptual model because it affects water movement and the 

water budget in the basin.

Storage Parameters

Storage-coefficient estimates for the Denver Basin 

bedrock aquifers were reported by Robson (1983), and 

additional storage-coefficient values based on subsequent 

aquifer tests were compiled as part of the SPDSS (Colorado 

Water Conservation Board, 2006c) with results reported 

in the CDWR Hydrobase database (Colorado Division of 
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 51

Water Resources, 2005). Reported storage-coefficient values 

ranged from 0.00002 to 0.004 for the Laramie–Fox Hills 

aquifer, from 0.0001 to 0.008 for the Arapahoe aquifer, and 

from 0.0002 to 0.0006 for the Denver and Dawson aquifers. 

In general, estimated storage-coefficient values are largest 

in the central and western parts of the basin (Robson, 1987; 

Colorado Water Conservation Board, 2006c). For this study, 

specific-storage values for the Denver Basin groundwater 

flow model were estimated separately for aquifers and 

confining units during model calibration. A specific-storage 

value of 5.2×10–7/ft was estimated for aquifers, and a value 

of 1.7×10–6 /ft was estimated for confining units as described 

in the “Specific Storage and Specific Yield” section of 

Chapter C.

Specific-yield estimates for the Denver Basin bedrock 

aquifers for this study tabulated from laboratory tests of hand 

and core samples (Robson, 1983; McConaghy and others, 

1964; Lapey, 2001; Robson and Banta, 1993; Raynolds and 

others, 2001) provided the basis for specific-yield values 

assigned in the groundwater flow model. Specific-yield values 

reported by Robson (1983) are from laboratory tests of hand 

and core samples, and specific-yield values reported by 

McConaghy and others (1964) are for hand samples collected 

from outcrops. Specific-yield values from Robson and Banta 

(1993) are for tests on core samples from the Castle Pines 

core hole located on the western margin of the basin near 

Castle Rock, and specific-yield values from Lapey (2001) are 

for tests on core samples from the Kiowa core hole located 

near the center of the Denver Basin near Kiowa. All four 

data sources classified specific-yield values as being from the 

Dawson, Denver, Arapahoe, or Laramie–Fox Hills aquifers; 

specific-yield values were not differentiated for the upper and 

lower Dawson or Arapahoe aquifer units.

Table A6 presents a summary of mean specific-yield 

values for bedrock aquifers tabulated from each of the 

original data sources and facilitates geographic and sampletype comparisons. Mean specific-yield values for the Dawson, 

Denver, and Arapahoe aquifers provided by McConaghy 

and others (1964) typically are greater than values provided 

by subsequent workers, probably owing to testing of hand 

samples from outcrops, which tend to be more weathered and 

porous than core samples. Mean specific-yield values for the 

Arapahoe and Laramie–Fox Hills aquifers from the Castle 

Pines core (Robson and Banta, 1993) are greater than mean 

specific-yield values for the Arapahoe and Laramie–Fox Hill 

aquifers from the Kiowa core hole (Lapey, 2001; Raynolds 

and others, 2001), likely owing to the eastward fining of sediment shed off the Front Range during the Late Cretaceous 

(Lapey-Woodard and others, 2002). Mean specific-yield 

values for the Dawson and Denver aquifers from the Castle 

Pines core (Robson and Banta, 1993) are less than mean 

specific-yield values for the Dawson and Denver aquifers 

from the Kiowa core hole (Lapey, 2001; Raynolds and others, 

2001), suggesting varying source areas and that the Dawson 

and Denver sandstones do not necessarily fine eastward 

between these two core holes. The Denver aquifer exhibits the 

smallest mean specific yield of the bedrock aquifers, which is 

consistent with the conceptualized depositional environment 

and lower hydraulic conductivity of the Denver aquifer.

Table A5. Summary of hydraulic-conductivity values calculated from pumping tests (adapted from Colorado Division of Water 

Resources [2005]).

[ft/d, feet per day]

Alluvial

aquifer

Upper

Dawson

aquifer

Lower

Dawson

aquifer

All

Dawson

aquifers

Denver

aquifer

Upper

Arapahoe

aquifer

Lower

Arapahoe

aquifer

All

Arapahoe

aquifers

Laramie–Fox

Hills aquifer

Hydraulic-conductivity values from pumping tests

Number of tests 132 22 52 53 79 45 244 248 147

Minimum, ft/d 18 0.1 0.01 0.01 0.03 0.06 0.06 0.06 0.003

Maximum, ft/d 2,558 6.2 6.2 6.2 24.0 4.7 9.9 9.9 7.2

Median, ft/d 479 1.2 0.78 0.80 0.45 1.2 1.8 1.8 0.40

Geometric mean, ft/d 1.1 0.69 0.71 0.42 0.9 1.6 1.6 0.40

Hydraulic-conductivity values for specific-capacity tests

Number of tests 490 265 464 729 233 46 159 205 171

Minimum, ft/d 0.67 0.06 0.04 0 0.01 0.07 0.02 0.02 0.03

Maximum, ft/d 7,194 32 191 191 430 6.7 42 42 262

Median, ft/d 290 1.40 0.88 0.98 0.71 0.69 0.79 0.75 0.54

Geometric mean, ft/d 1.75 1.08 1.3 0.71 0.78 0.68 0.70 0.58

Hydraulic conductivity values for laboratory tests

Number of tests 73 10 14 16 29 6 23 23 39

Minimum, ft/d 0.008 0.02 0.01 0.01 1.0E–04 0.01 3.0E–04 3.0E–04 4.0E–04

Maximum, ft/d 3,877 11 11 11 989 6.0 9.0 8.96 70

Median, ft/d 92.3 1.15 1.0 1 0.10 4.7 1.6 1.6 0.50

Geometric mean, ft/d 64.7 0.83 0.37 0.54 0.30 2.9 0.47 0.47 0.23
52 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Overall arithmetic mean values for specific yield calculated by this study from the original data sources are compared 

to specific-yield values assigned by the SB85–5 model of 

the Denver Basin aquifers in table A6. The SB85–5 model 

uses a constant specific-yield value for each aquifer as shown 

in table A6. For the Dawson and Denver aquifers, SB85–5 

specific-yield values are greater than arithmetic mean values 

calculated by this study. The Arapahoe SB85–5 specific-yield 

value of 17 percent is approximately equal to the overall 

arithmetic mean of 17.8 percent, and the Laramie–Fox Hills 

SB85–5 value of 15 percent is less than the overall arithmetic mean of 18.6 percent. Lapey-Woodard and others (2002) 

assumed a log-normal distribution to the specific-yield data, 

determined that geometric mean values from the Castle Pines 

and Kiowa core holes were less than SB85–5 specific-yield 

values, and concluded that previous estimates of specific yield 

may lead to overestimating the volume of recoverable water 

in the Denver Basin aquifers. However, the Shapiro-Wilks test 

for normality (Shapiro and Wilk, 1965) indicates the specificyield values for each aquifer are not log-normally distributed 

at a 95-percent confidence level.

This study assigned arithmetic mean specific-yield values 

(table A6) to model layers in the groundwater flow model as 

described in the “Specific Storage and Specific Yield” section 

of Chapter C. For bedrock aquifers, the mean specific-yield 

values from table A6 were multiplied by the fraction of siltplus-sand for the given aquifer (figs. A14, A20, A22, A27, 

A30, A34) to obtain an effective specific yield for the overall aquifer thickness for each model grid cell. The resulting 

spatial distributions of specific yield assigned to each bedrock 

aquifer (figs. A37–A42) thus reflect the spatial distributions 

of the silt-plus-sand fraction and assume that materials finer 

than silt sized provide a minimal contribution to specific yield. 

Because estimated specific-yield values were multiplied by 

the silt-plus-sand fraction, simulated specific-yield values 

for all bedrock aquifers are less than mean values reported in 

table 6. Specific yield for the alluvial aquifer ranges from less 

than 1 percent to about 37 percent based on pumping tests and 

laboratory analysis of samples from previous work (Bjorklund 

and Brown, 1957; McConaghy and others, 1964; Smith and 

others, 1964; and Wilson, 1965; Colorado Water Conservation 

Board, 2006c), and a specific yield of 0.165 was assigned to 

the simulated alluvial aquifer (model layer 1; table C13).

Predevelopment Groundwater Availability

Interpretations and results from the initial, steady-state 

stress period of the calibrated groundwater flow model 

(Chapter C) as well as previous studies form the basis for this 

description of the predevelopment (pre-1880) Denver Basin 

groundwater availability. Predevelopment conditions represent 

aquifer conditions at the end of 1879, prior to any groundwater 

withdrawals and are discussed in terms of the water budget, 

hydraulic heads, and groundwater flow directions.

Predevelopment Groundwater Budget

A groundwater budget accounts for all of the inflows and 

outflows for a hydrologic system. For predevelopment conditions in the Denver Basin, inflow components of the groundwater budget are recharge from precipitation plus irrigation 

return flow, recharge from streams, and interaquifer flow 

between hydrogeologic units. Predevelopment outflow components of the groundwater budget are discharge to evapotranspiration, streams, springs, and interaquifer flow. Discharge 

to pumping wells and associated changes in aquifer storage 

were assumed negligible before 1880 and are not included in 

the predevelopment groundwater budget. Both inflows and 

outflows exist for some budget components, and the difference between the inflow and the outflow is herein referred 

to as the “net” inflow or outflow. For example, net recharge 

equals recharge minus evapotranspiration, and the net flow 

to streams equals the inflow from streams minus the outflow 

to streams. The groundwater budgets presented herein uses 

the MODFLOW convention that positive values are inflows 

to, and negative values are outflows from, the groundwater 

system. The discussion is based on the simulated, cell-by-cell 

water budget for the initial (steady-state) model stress period, 

which represents hydrologic conditions at the end of 1879. 

Transient groundwater budget results from predevelopment to 

2003 are presented in section “Changes to the Groundwater 

Budget” in Chapter B. Groundwater budgets are presented for 

the entire model (sum of all model layers), the alluvial aquifer 

(model layer 1), and the bedrock units (layers 2 through 

12) and are discussed in terms of individual groundwater 

budget components.

Table A6. Summary of specific-yield values.

Aquifer

Specific yield

(percent)

Mean value

from McConaghy 

and others

(1964)

Mean value

from Robson 

(1983)

Mean value 

Castle Pines core 

(Robson and 

Banta, 1993)

Geometric mean

Kiowa core

(Raynolds and others, 

2001; Lapey, 2001)

Mean value

of all

available

data1

Senate

Bill 85–5

assigned

value

Percent difference

of mean values

from Senate

Bill 85–5

assigned values

Dawson 19.9 16.8 12.6 18.7 15.2 20 –27

Denver 33.7 13.8 11.9 14.4 13.3 17 –24

Arapahoe 20.8 17.9 18.3 10.8 17.8 17 5

Laramie–Fox Hills 17.3 21.2 22.0 12.9 18.6 15 21 1

Values used in U.S. Geological Survey Denver Basin groundwater flow model.
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 53

Figure A37. Simulated specific-yield distribution for the Laramie–Fox Hills aquifer.

PALMER

DIVIDEDIVIDE

!

!

!

!

!

!

!

! ! !

!

!

!

!

! !

!

!

!

!

!

!

!

!

!

!

!

!

!

!

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

§ ̈¦70

§ ̈¦25

§ ̈¦76

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Specific-yield value of 0.186 multiplied by 

 fraction silt-plus-sand, dimensionless

0.03 to 0.05

0.05 to 0.07

0.07 to 0.09

0.09 to 0.11

0.11 to 0.13

0.13 to 0.15

0.15 to 0.17

Laramie–Fox Hills aquifer simulated 

 extent (model layer 12)

Extent of active model cells
54 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A38. Simulated specific-yield distribution for the lower Arapahoe aquifer.

PALMER

DIVIDEDIVIDE

!

!

!

!

!

!

!

! ! !

!

!

!

!

! !

!

!

!

!

!

!

!

!

!

!

!

!

!

!

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

§ ̈¦70

§ ̈¦25

§ ̈¦76

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

105° 104°

40°

39°

0 10 20 MILES

0 10 20 KILOMETERS

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

EXPLANATION

Specific-yield value of 0.178 multiplied 

 fraction silt-plus-sand, dimensionless

0.014 to 0.02

0.02 to 0.04

0.04 to 0.05

0.05 to 0.06

0.06 to 0.07

0.07 to 0.08

0.08 to 0.09

0.09 to 0.11

0.11 to 0.13

0.13 to 0.15

Laramie–Fox Hills aquifer simulated extent 

 (model layer 12)

Lower Arapahoe aquifer simulated extent 

 (model layer 10)
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 55

Figure A39. Simulated specific-yield distribution for the upper Arapahoe aquifer.

!

!

!

! !

!

!

!

!

!

!

!

!

! !

!

!

!

!

!

! !

WELD

ELBERT

LARIMER

ADAMS

BOULDER

ARAPAHOE

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

WELD

ELBERT

LARIMER

ADAMS

BOULDER

ARAPAHOE

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Kiowa

Parker

Golden

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Fort

Lupton

Castle

Rock

Highlands

Ranch

Aurora

Littleton

Lafayette

Englewood

Kiowa

Parker

Golden

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Fort

Lupton

Castle

Rock

Highlands

Ranch

Aurora

Littleton

Lafayette

Englewood

§ ̈¦25

§ ̈¦76

105° 104°30'

40°

39°30'

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Specific-yield value of 0.178 multiplied by 

 fraction-silt-plus sand, dimensionless

0.028 to 0.04

0.04 to 0.05

0.05 to 0.06

0.06 to 0.07

0.07 to 0.08

0.08 to 0.09

0.09 to 0.1

0.1 to 0.11

0.11 to 0.12

0.12 to 0.137

Laramie–Fox Hills aquifer simulated extent 

 (model layer 12)

Lower Arapahoe aquifer simulated extent 

 (model layer 10)

Upper Arapahoe aquifer simulated extent 

 (model layer 8)
56 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A40. Simulated specific-yield distribution for the Denver aquifer.

PALMER

DIVIDEDIVIDE

!

!

!

!

!

!

!

! ! !

!

!

!

!

! !

!

!

!

!

!

!

!

!

!

!

!

!

!

!

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Specific-yield value of 0.133 multiplied by 

 fraction silt-plus-sand, dimensionless

0.008 to 0.02

0.02 to 0.03

0.03 to 0.04

0.04 to 0.05

0.05 to 0.06

0.06 to 0.07

0.07 to 0.08

0.08 to 0.1

Laramie–Fox Hills aquifer simulated 

 extent (model layer 12)

Lower Arapahoe aquifer simulated 

 extent (model layer 10)

Denver aquifer simulated extent 

 (model layer 6)
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 57

Figure A41. Simulated specific-yield distribution for the lower Dawson aquifer.

PALMER

DIVIDEDIVIDE

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

!

! ! !

!

!

!

!

!

!

!

! !

!

!

!

!

!

§ ̈¦25

105° 104°30'

39°30'

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Specific-yield value of 0.152 multiplied by 

 fraction silt-plus-sand, dimensionless

0.03 to 0.04

0.04 to 0.05

0.05 to 0.06

0.06 to 0.07

0.07 to 0.08

0.08 to 0.09

0.09 to 0.1

0.1 to 0.12 Laramie–Fox Hills aquifer simulated extent 

 (model layer 12)

Lower Arapahoe aquifer simulated extent 

 (model layer 10)

Denver aquifer simulated extent (model 

 layer 6)

Lower Dawson aquifer simulated extent 

 (model layer 4)
58 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A42. Simulated specific-yield distribution for the upper Dawson aquifer.

PALMER

DIVIDEDIVIDE

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

!

! ! !

!

!

!

!

!

!

!

! !

!

!

!

!

!

§ ̈¦25

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

105° 104°30'

39°30'

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Specific yield value of 0.152 multiplied by 

 fraction silt-plus-sand, dimensionless

0.019 to 0.03

0.03 to 0.04

0.04 to 0.05

0.05 to 0.06

0.06 to 0.07

0.07 to 0.08

0.08 to 0.1

Laramie–Fox Hills aquifer simulated extent 

 (model layer 12)

Lower Arapahoe aquifer simulated extent 

 (model layer 10)

Denver aquifer simulated extent (model 

 layer 6)

Lower Dawson aquifer simulated extent 

 (model layer 4)

Upper Dawson aquifer simulated extent 

 (model layer 2)
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 59

Groundwater Budget for the Entire Modeled Area

Precipitation plus irrigation recharge was the largest inflow 

component (630 ft3/s or 98 percent of inflow) for the predevelopment groundwater budget of the entire Denver Basin aquifer 

system (alluvial and bedrock units), and the primary outflow 

components were to evapotranspiration (442 ft3/s or 68 percent 

of outflow) and streams (182 ft3/s or 28 percent of outflow; 

table A7, figs. A43, A44). Stream inflow (16 ft3/s), spring 

outflow (4 ft3/s), and groundwater flow out of the basin through 

alluvial aquifers (19 ft3/s) were minor components of the predevelopment groundwater budget (table A7, figs. A43, A44). 

Groundwater flow out of the basin through the alluvial aquifer 

includes underflow to the alluvial aquifer and specified flux to 

the South Platte alluvial aquifer (table A7). Subtracting evapotranspiration from recharge results in a net recharge rate of 

189 ft3/s; net discharge to streams was about 166 ft3/s (table A7, 

figs. A43, A44). These results indicate that before development, 

precipitation plus irrigation recharge was the primary source 

of water to the entire Denver Basin aquifer system, and evapotranspiration and discharge to streams were the primary outflows from the system. There was no outflow to wells or inflow 

from aquifer storage for the predevelopment period. The total 

predevelopment water budget, defined as the total inflow or 

outflow, was about 650 ft3/s (table A7).

Groundwater Budget for the Alluvial Aquifer 

and Bedrock Units

Separating the water budget of the alluvial aquifer 

from that of the bedrock aquifers and confining units (herein 

referred to collectively as bedrock units) indicates that for 

predevelopment conditions, about three-fourths of the water 

moved in and out of the system through the alluvial aquifer 

(about 500 ft3/s), and about one-fourth of the water moved 

in and out of the system through the bedrock units (about 

187 ft3/s; table A7, fig. A45). This difference in water budgets between the alluvial and bedrock units is caused by the 

large difference in hydraulic-conductivity values between the 

unconsolidated and permeable alluvial materials as compared to the consolidated, less-permeable bedrock sandstones 

(Robson, 1989), which allows water to move more easily in 

and out of the alluvial aquifer. For the predevelopment period, 

the majority of the simulated recharge (72 percent), evapotranspiration (70 percent), and net recharge (78 percent) were 

directly to and from the alluvial aquifer, while 28 percent of 

recharge, 30 percent of evapotranspiration, and 22 percent of 

net recharge were directly to and from the bedrock aquifers 

(table A7). The majority of net outflow to streams also was 

from the alluvial aquifer (91 percent), and 9 percent of net 

outflow to streams was directly from bedrock units (table A7).

Precipitation plus irrigation recharge was the primary 

inflow groundwater budget component for the alluvial aquifer 

(454 ft3/s or 91 percent of alluvial aquifer inflow) and evapotranspiration was the primary outflow groundwater budget 

component for the alluvial aquifer (307 ft3/s or 61 percent 

of outflow) for the predevelopment period (fig. A45). The 

predevelopment net water budget for the alluvial aquifer 

indicates that 84 percent (147 ft3/s) of the net inflow was from 

precipitation plus irrigation recharge minus evapotranspiration and that the remaining 16 percent (26 ft3

/s) of inflow was 

from the bedrock aquifers (table A7; fig. A45). Net outflow 

from the alluvial aquifer was primarily to streams (151 ft3/s 

or 88 percent of net outflow). Groundwater flow out of the 

basin (19 ft3/s or 10 percent of net outflow) and flow to springs 

(2 percent of net outflow) were minor components of outflow 

from the alluvial aquifer (table A7; fig. A45).

Precipitation plus irrigation recharge was the primary 

inflow groundwater budget component for bedrock units 

(176 ft3/s or 94 percent of bedrock units inflow) (fig. A45), and 

evapotranspiration was the primary outflow groundwater budget component for the bedrock units (135 ft3

/s or 72 percent of 

outflow) for the predevelopment period (fig. A45). The predevelopment net water budget for the bedrock units (table A7; 

fig. A45) indicates that all of the net inflow was from precipitation plus irrigation recharge minus evapotranspiration 

(41 ft3/s) and that net outflow from the bedrock units was to 

the alluvial aquifer (26 ft3/s or 64 percent of net outflow) and 

streams (14 ft3/s or 34 percent of net outflow). There was no 

groundwater outflow out of the basin from bedrock units, and 

outflow to springs was a minor outflow component (2 percent 

of net outflow) for the bedrock units (figs. A1, A45).

Groundwater Budget Components

This discussion presents details of each groundwater budget component for the predevelopment Denver Basin groundwater system. Simulated inflow was from precipitation plus 

irrigation recharge, and simulated outflow was to evapotranspiration, springs, and model boundaries simulating groundwater 

flow out of the basin. Simulated streams were both sources and 

sinks of groundwater.

Recharge and Evapotranspiration

Sources of recharge to the predevelopment Denver 

Basin aquifer system included infiltration of incident precipitation and agricultural irrigation in excess of consumptive use 

(irrigation return flows). Precipitation infiltration and runoff 

is an important source of water in this semiarid region for 

streams and groundwater recharge. Mean annual precipitation 

in the basin supplies an estimated 6,900 ft3/s of water to the 

surface (Robson, 1987). However, most of this water runs off 

or is evapotranspired, and only a small fraction of precipitation infiltrates to the water table to provide recharge to the 

bedrock aquifers (Robson, 1987). In areas where bedrock 

crops out with little or no overlying surficial deposits, deep 

infiltration of precipitation provides direct recharge to the 

bedrock aquifers. Previous studies indicated that precipitation recharge is, in general, greatest over the upper Dawson 

aquifer because (1) precipitation is greatest at the higher 

elevations where the upper Dawson aquifer is located, 

(2) the Dawson aquifers have a larger outcrop area than the 

other bedrock aquifers, and (3) the upper Dawson aquifer 
60 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Table A7. Simulated predevelopment (pre-1880) groundwater budget for entire Denver Basin aquifer system, the alluvial aquifer, and 

the bedrock units.

[In some cases values do not sum to total because of rounding; ft3/s, cubic feet per second; --, not calculated]

Groundwater budget component

Entire model

flow rate

(ft3/s)

Alluvial aquifer Bedrock units

Flow rate

(ft3/s)

Percentage

of component

Flow rate

(ft3/s)

Percentage

of component

Inflow

Recharge (precipitation + irrigation) 630 454 72 176 28

Streams 16.2 12.7 78 3.5 22

Interaquifer flow -- 34.1 -- 7.8 --

Storage 0.0 0.0 -- 0.0 --

Total inflow

646 501 187

Outflow

Evapotranspiration –442 –307.1 70 –135 30

Streams –182 –164.2 90 –17.6 10

Springs –4.2 –3.2 76 –1.0 24

Underflow to alluvial aquifers –4.8 –4.8 100 0.0 0

Specified flux to South Platte alluvial aquifer –14.1 –14.1 100 0 0

Interaquifer flow -- –7.8 -- –34.1 --

Wells 0.0 0.0 -- 0.0 --

Storage 0.0 0.0 -- 0.0 --

Total outflow

–646 –501 –187

Net flows

Net recharge (recharge + evapotranspiration) 189 147 78 41.5 22

Net stream discharge (stream inflow + stream outflow) –166 –152 91 –14.2 9

Net interaquifer flow 0 26.3 -- –26.3 --

has a high hydraulic conductivity relative to the surrounding 

Denver aquifer (Robson, 1987). In areas overlain by alluvial 

aquifers, precipitation recharge is directly to permeable sand 

and gravel deposits.

Because agricultural irrigation, primarily by surfacewater diversions, began in the South Platte River valley prior 

to the 1880s (Nadler and Schumm, 1981), irrigation recharge 

is included in the predevelopment recharge estimates. The 

pre-1880 extent of irrigated agriculture was determined on the 

basis of irrigation ditch service areas, which were delimited as 

part of the SPDSS (Riverside Technology, Inc., 2005). Recharge 

to the pre-1880 irrigation ditch service areas downstream from 

Denver (fig. A46) were assigned a constant irrigation recharge 

rate of 10 in/yr on the basis of preliminary results from irrigation return-flow studies (L.R. Arnold, U.S. Geological Survey, 

oral commun., 2005). Total recharge in irrigated areas is equal 

to precipitation recharge plus the assigned irrigation recharge.

The simulated recharge distribution for predevelopment 

conditions (fig. A47) depicts the salient recharge features in 

the basin. The variation in permeability of geologic materials 

at the land surface, greater precipitation at higher altitudes, 

and the application of irrigation recharge are all factors that 

conceptually are expected to affect the spatial distribution 

of recharge in the Denver Basin and are represented in the 

groundwater flow model. Just as in the hydrologic system, 

simulated recharge is applied to the model layer that occurs 

at land surface, so that the variation in aquifer hydraulic conductivity at the land surface affects recharge rates. To represent this conceptual spatial variation of infiltration potential, 

the percentage of precipitation reaching the water table as 

recharge was an estimated model parameter for each bedrock 

aquifer during model calibration. The results indicate that of 

the bedrock aquifers, the Dawson aquifers and confining units 

receive the greatest percentage of precipitation (2 percent, 0.3 

to 0.5 in/yr), followed by the Arapahoe and Laramie–Fox Hills 

aquifers and confining units (1.4 percent, 0.2 to 0.4 in/yr), and 

the Denver aquifer and confining units (1.1 percent, 0.1 to 

0.3 in/yr). The model-estimated percentages and the resulting simulated distribution of recharge are consistent with the 

conceptual understanding of recharge in the basin. Recharge 

rates to the Dawson units are greater than for the other bedrock units because the Dawson units are composed of coarsegrained materials and crop out in the upland parts of the basin 

where precipitation is greatest and the overlying alluvial aquifer is sparse (allowing direct recharge to the bedrock units).

In the simulated system, the alluvial aquifer was assigned 

a recharge rate equal to 7 percent of precipitation, assuming alluvial aquifers are more permeable at the land surface 

than bedrock aquifers, which enables a larger percentage of 

precipitation to infiltrate the alluvial aquifer as compared to 

the bedrock aquifers. The resulting simulated recharge rates 

for the alluvial aquifer are thus greater than for the bedrock 

aquifers and range from 0.75 to 1.3 in/yr for predevelopment 

conditions outside the areas of irrigated agriculture (fig. A47). 

Irrigated agriculture areas in the South Platte River valley 

and the alluvial aquifer are located in proximity to streams 

such that recharge to the water table from agricultural return 

flows is primarily to the alluvial aquifer. Recharge to aquifers 
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 61

Figure A43. Predevelopment (pre-1880) groundwater budget for the Denver Basin aquifer system.

underlying irrigated agriculture is equal to the assigned 

recharge from irrigated recharge (10 in/yr) plus the percentage 

of precipitation recharge for the underlying units and ranges 

from 10 to 11.1 in/yr.

Evapotranspiration from groundwater is the primary 

process for natural discharge in the Denver Basin. Potential 

pan evaporation values near the Denver Basin range from 45 

to 48 in/yr (National Oceanic Atmospheric Administration 

[NOAA], 2004), greatly exceeding precipitation and estimated recharge rates. Measured pan evaporation data for three 

NOAA weather stations in eastern Colorado (National Oceanic 

Atmospheric Administration, 2004) indicate that evapotranspiration begins in March of each year, peaks in July at an average maximum value of approximately 10 inches per month, 

declines through the late summer and falls to zero, and remains 

at zero during the winter, when vegetation is dormant (fig. A48). 

Total average evaporation calculated on the basis of the three 

weather stations near the Denver Basin is 55.6 in/yr. These 

results indicate a potential for evapotranspiration from the 

Denver Basin aquifers in areas where the water table is shallow and phreatophytes grow. Because the climate is semiarid, 

potential also exists for evaporation to occur in nonriparian 

and nonirrigated areas, if the water table is sufficiently near 

land surface. Few evapotranspiration studies and data are 

available for native vegetation in the Denver Basin; however, 

studies from a similar climatic setting in the San Luis Valley 

of Colorado indicate evapotranspiration is a function of depth 

to water and suggest mathematical functions to describe the 

relation (David Groeneveld and Michael Prescott, HydroBio, 

Inc., written commun., 2006). Results from the San Luis Valley 

were used as a basis for the relation of groundwater evapotranspiration as a function of depth to water for the Denver Basin 

model (section “Hydrologic Stresses”, “Evapotranspiration” in 

Chapter C).

The simulated spatial distribution of groundwater 

evapotranspiration for predevelopment conditions (fig. A49) 

represents groundwater discharge from the water table to 

evapotranspiration in areas where the water table is less than 

30 ft below land surface. The map of evapotranspiration rates 

indicates small predevelopment evapotranspiration rates (less 

than 0.5 in/yr) over most of the basin (fig. A49). Evapotranspiration rates in the range of 25 to 45 in/yr were simulated 

for areas along stream valleys and in the areas of irrigated 

agriculture along the South Platte River (fig. A49). Although 

evapotranspiration rates are small over most of the basin, large 

volumes of water are discharged from the aquifers by evapotranspiration because of the large area over which evapotranspiration occurs, making evapotranspiration a primary outflow 

component of the groundwater budget.

The difference between recharge and evapotranspiration (net recharge) for predevelopment conditions is shown in 

figure A50. The predevelopment net recharge rate over much 

of the area where Denver Basin bedrock aquifers are exposed 

at land surface is less than 0.5 in/yr, while net recharge in 

most alluvial-aquifer areas is in the range of 0.5 to 2 in/yr 

(fig. A50). In areas of irrigated agriculture along the South 

Platte River, net recharge ranges from 10 to 11.1 in/yr. In 

Precipitation 

plus irrigation

recharge

(176 cubic feet

per second)

Evapotranspiration

(135 cubic feet

per second)

Stream 

and spring 

outflow

(19 cubic feet

per second)

Stream

inflow

(13 cubic feet

per second)

Flow from 

bedrock units

(34 cubic feet

per second)

Flow from

alluvial aquifer

(8 cubic feet

per second)

Bedrock

units

Precipitation 

plus irrigation

recharge

(454 cubic feet

per second)

Evapotranspiration

(307 cubic feet

per second)

Stream

inflow

(3 cubic feet 

per second)

Stream 

and spring

outflow

(167 cubic feet

per second) Groundwater flow 

out of basin

(19 cubic feet

per second)

Groundwater flow 

out of basin

(19 cubic feet

per second)

Precipitation 

plus irrigation

recharge

(630 cubic feet 

per second)

Evapotranspiration

(442 cubic feet

per second)

DENVER BASIN AQUIFER SYSTEM

Alluvial

aquifer

Stream

inflow

(16 cubic feet

per second)

Stream 

and spring

outflow

(186 cubic feet

per second)
62 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A44. Predevelopment (pre-1880) groundwater budget 

inflow and outflow components for the entire Denver Basin 

aquifer system.

some areas of the basin, primarily in agricultural recharge 

areas overlying the alluvial aquifer in the South Platte River 

valley, evapotranspiration exceeds recharge from precipitation 

plus irrigation such that net discharge results (represented as a 

negative net recharge value in figure A50).

Predevelopment recharge, evapotranspiration, and 

net recharge rates for individual aquifers (tables A7, A8; 

figs. A51A, A51B) indicate 78 percent of the net recharge was 

to the alluvial aquifer (147 ft3/s), while 22 percent of the net 

recharge was directly to bedrock units (41 ft3/s). Net recharge 

to individual bedrock aquifers and confining units was as follows: 9 percent (16 ft3

/s) to the Dawson aquifer and confining 

units, 7 percent (14 ft3/s) to the Denver units, 5 percent (9 ft3/s) 

to the Laramie–Fox Hills units, and 1 percent (2 ft3/s) to the 

Arapahoe units (fig. A51B). These values are generally consistent with previous studies (for example, Robson, 1987), which 

indicate that the Dawson units receive the greatest recharge 

because precipitation is greatest over their outcrop areas. The 

Arapahoe units receive the least recharge because of their limited outcrop area. However, because the present study includes 

the effects of predevelopment irrigation recharge in the South 

Platte River basin, and some of the irrigated areas overlie the 

Denver aquifer and confining units, results from the present 

study indicate predevelopment recharge to the Denver units 

was nearly equal to that for the Dawson units.

Groundwater/Surface-Water Interaction

Groundwater from bedrock aquifers and confining units 

interacts with streams and the alluvial aquifer. There also is 

hydraulic connection between streams and the alluvial aquifer 

where streams overlie alluvium. Surface water in the Denver 

Basin flows in perennial streams that originate as snowmelt 

runoff from the Front Range and in ephemeral and intermittent streams that originate on the plains east of the mountains. 

Conceptually, ephemeral streams that originate in the basin 

gain flow in the upland areas near the Palmer Divide where 

alluvium is thin or absent and bedrock groundwater discharges 

directly to streams. In downstream parts of the basin where 

the alluvial aquifer is present, ephemeral streams can lose 

water to the alluvial aquifer as topographic gradients flatten, 

and streambeds can be dry. Bedrock groundwater also can 

discharge to the overlying alluvial aquifer. Simulation results 

for predevelopment groundwater flow to and from streams 

(fig. A52) are consistent with this conceptual understanding. 

Negative flow values displayed in figure A52 (pale yellow and 

blue colors) represent areas where groundwater discharges to 

streams, and positive flow values (red colors) represent areas 

where groundwater receives streamflow (streams lose water 

to the groundwater system). Simulated rates of groundwater 

flow to streams are less than 0.5 ft3/s in upland areas near the 

Palmer Divide where the alluvial aquifer is absent (fig. A52), 

and groundwater discharge to streams is directly from bedrock units. Streamflow loss (maximum rate of 0.8 ft3

/s) to the 

groundwater system is evident in downstream areas underlain 

by the alluvial aquifer (fig. A52). There is little to no observed 

or simulated perennial streamflow in downstream reaches of 

Running/Box Elder, Kiowa, and Bijou Creeks (fig. A52). Predevelopment streamflow gains from groundwater flow also are 

simulated for the main stem of the South Platte River, again 

consistent with the conceptual understanding of historical and 

regional conditions (fig. A52).

The predevelopment net flow rate to streams from the 

bedrock aquifers and confining units (about 14 ft3/s or 9 percent 

of the net groundwater flow to streams) was small compared 

INFLOW

NETFLOW

OUTFLOW

Inflow

Outflow

Streams

16 cubic feet per second

(2 percent of inflow)

Recharge

630 cubic feet per second

(98 percent of inflow)

Springs 

4 cubic feet per second

(<1 percent of outflow)

Groundwater flow

out of basin

19 cubic feet per second

(3 percent of outflow)

Streams

182 cubic feet 

per second

(28 percent 

of outflow)

Evapotranspiration

442 cubic feet per second

(68 percent of outflow)

Net recharge

189 cubic feet per second

(100 percent of net inflow)

Groundwater flow

out of basin

19 cubic feet per second

(10 percent of net outflow)

Springs 

4 cubic feet per second

(2 percent of net outflow)

Net to streams

166 cubic feet per second

(88 percent of net outflow)

ALLUVIAL AQUIFER AND BEDROCK UNITS
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 63

Figure A45. Predevelopment (pre-1880) groundwater budget inflow and outflow components of the Denver 

Basin alluvial aquifer and bedrock units.

to discharge to streams from the alluvial aquifer (151 ft3/s or 

91 percent of net flow to streams; figs. A53A, A53B). About 

one-half of the net flow to streams directly from bedrock units 

was from the Dawson aquifer and confining units (7.6 ft3/s or 

53 percent of the bedrock net outflow to streams; fig. A53A) 

located where land-surface altitude and precipitation recharge 

are greatest. These results indicate that groundwater/surfacewater interaction is predominantly between the alluvial aquifer 

and streams, with lesser direct groundwater/surface-water interaction between the bedrock units and streams.

Discharge to Springs

Numerous springs and seeps occur in the Denver Basin 

where alluvial and bedrock groundwater discharges to surface 

water. Springs generally are contact springs located along topographic breaks in slope where coarse-grained materials overlie finer grained shales and(or) claystones (Richardson, 1915). 

Approximately 150 springs have been mapped in the Denver 

Basin, most of which are in the southern one-half of the basin 

and are associated with discharge from the bedrock aquifers 

Recharge

176 cubic feet per second

(94 percent of inflow)

Streams

13 cubic feet per second

(3 percent of inflow)

Streams

4 cubic feet per second

(2 percent of inflow)

Flow from 

bedrock units

34 cubic feet per second

(7 percent of inflow)

Flow from 

alluvial aquifer

8 cubic feet per second

(4 percent of inflow)

Streams

14 cubic feet per second

(34 percent of net outflow)

Streams

18 cubic feet per second

(10 percent of outflow)

Flow from 

bedrock units

26 cubic feet per second

(15 percent of net inflow)

Groundwater 

flow out of basin

19 cubic feet per second

(11 percent of net outflow)

Springs

3 cubic feet per second

(2 percent of net outflow)

Springs

3 cubic feet per second

(<1 percent of outflow)

Springs

1 cubic feet per second

(<1 percent of outflow)

Springs

1 cubic feet per second

(3 percent of net outflow)

Flow to

alluvial aquifer

26 cubic feet per second

(63 percent of net outflow)

Groundwater

flow out of basin

19 cubic feet per second

(4 percent of outflow)

Evapotranspiration

135 cubic feet per second

(72 percent of outflow)

Flow to

bedrock units

8 cubic feet per second

(2 percent of outflow)

Flow to

alluvial aquifer

34 cubic feet per second

(18 percent of outflow)

Net recharge

42 cubic feet per second

(100 percent of net inflow)

Recharge

454 cubic feet per second

(90 percent of inflow)

Streams

164 cubic feet per second

(33 percent of outflow)

Streams

151 cubic feet per second

(87 percent of net outflow)

Net recharge

147 cubic feet per second

(85 percent of net inflow)

Evapotranspiration

307 cubic feet per second

(61 percent of outflow)

INFLOW

NETFLOW

OUTFLOW

Inflow

Outflow

ALLUVIAL AQUIFER BEDROCK UNITS
64 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A46. Estimated areas of predevelopment (pre-1880) agricultural irrigation as simulated in 

the Denver Basin model.

South Platte

River

Cac he la Poudre R

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryC

P

r

lum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

Big Thompson R

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

PALMER

DIVIDEDIVIDE

!

!

!

!

!

!

!

! ! !

!

!

!

!

! !

!

!

!

!

!

!

!

!

!

!

!

!

!

!

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Area of simulated agricultural irrigation, pre-1880–1906

Agricultural ditch service areas, 1880

Alluvial aquifer extent

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Stream

Perennial

Ephemeral
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 65

Figure A47. Spatial distribution of simulated predevelopment (pre-1880) precipitation plus 

irrigation recharge for the Denver Basin modeled area.

PALMER

DIVIDEDIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

South Platte

River

Cac he la Poudre R

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

Big Thompson R

§ ̈¦70

§ ̈¦25

§ ̈¦76

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!

!

!

!

!

!

!

! ! !

!

!

!

!

! !

!

!

!

!

!

!

!

!

!

!

!

!

!

!

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Pre-1880 simulated precipitation plus

 irrigation recharge, in inches per year

0.13 to 0.2

0.2 to 0.3

0.3 to 0.4

0.4 to 0.5

0.5 to 0.75

0.75 to 1

1.0 to 1.3

10 to 11.1

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Alluvial aquifer simulated extent (model layer 1)

Stream

Perennial

Ephemeral
66 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A48. Monthly average measured evaporation for three 

NOAA weather stations near the Denver Basin.

(fig. A11). There are few historical flow measurements for 

springs, although Richardson (1915) reported flow of as much 

as 125 gallons per minute from a spring in the upper Cherry 

Creek basin. In general, simulated flow to springs was a small 

percentage (4 ft3/s or 2 percent of the net outflow; table A7) of 

the predevelopment outflow from the basin.

Interaquifer Flow

Interaquifer flow, the amount of flow between aquifers, 

is an important component of water exchange for confined 

portions of the Denver Basin aquifers because of their limited 

outcrop at the land surface and thus limited recharge (Robson, 

1987; this study). The lower potentiometric altitude in the 

underlying bedrock aquifers promotes downward water movement through bedrock aquifers and confining units. The rate of 

downward vertical movement is considered small compared to 

lateral movement in the bedrock aquifers because of horizontal 

bedding planes; however, the large area over which downward 

water movement occurs results in large volumes of water moving between aquifers (Robson, 1987; this study). An exception 

is the Laramie confining unit, which effectively separates the 

underlying Laramie–Fox Hills aquifer from the overlying layers because of its large thickness and small hydraulic conductivity (Robson, 1987; fig. A15). For predevelopment conditions, interaquifer flow between all bedrock units is downward 

with flow to underlying aquifers (table A8; fig. A54). The 

greatest downward flow is from the Denver aquifer (about 

14 ft3/s net flow) and Denver lower confining unit (about 

16 ft3/s net flow) into the Arapahoe aquifers (fig. A54) because 

the Denver lower confining unit is generally thin (less than 

50 ft thick) over much of its extent (fig. A25).

Groundwater Storage

The quantity of groundwater in storage can be calculated 

as the product of the specific yield of an aquifer and aquifer volume plus the confined storage available from aquifer 

and water compressibility. In the Denver Basin, the quantity 

of groundwater in unconfined bedrock-aquifer storage was 

previously estimated by multiplying the SB85–5 specific-yield 

values (table A9) times the volume of aquifer materials, and 

the result is an estimate of 295 million acre-ft of groundwater 

in storage (Colorado Division of Water Resources, 2004). An 

estimate of 259 million acre-ft of theoretically recoverable 

groundwater is cited by the South Metro Water Supply Study 

Board (written commun., 2004). However, many investigators, including Alley (2006, 2007), have pointed out the large 

uncertainty and possible misleading interpretations associated with estimating total recoverable groundwater in this 

manner because it is impossible to remove all groundwater 

from storage with pumping wells. While estimates of groundwater in storage are speculative, digital representation of the 

aquifer framework does facilitate storage calculations for the 

Denver Basin. This study estimated the volume of unconfined bedrock-aquifer storage as the product of aquifer area, 

simulated predevelopment (pre-1880) saturated thickness, 

and the spatial distribution of specific yield as presented in 

figures A37–A42. The calculation, which accounts for spatial 

heterogeneity of specific yield as a function of the silt-plussand aquifer fraction, results in about 247 million acre-ft of 

groundwater in unconfined storage, which is about 18 percent 

less than the SB85–5 estimate (table A9). About 45 million 

acre-ft of unconfined groundwater storage, or about 18 percent 

or the basin unconfined storage, underlies the south Denver 

metropolitan area (fig. B3). The section “Change in Aquifer 

Storage” in Chapter B discusses aquifer-storage depletion in 

terms of storage-loss rates and the cumulative amount of water 

removed from storage over the model-calibration period.

Predevelopment Hydraulic Heads and 

Groundwater Flow Directions

Potentiometric-surface maps illustrate the distribution of hydraulic heads in an aquifer using contour lines of 

equal hydraulic head. Groundwater flows from areas of high 

hydraulic head to areas of low hydraulic head, in a direction 

generally perpendicular to contours of equal hydraulic head 

on the potentiometric-surface maps. The groundwater flow 

model calculates heads at the center of every active model 

cell, which represent the average altitude of the potentiometric 

surface in the cell. Contour lines of equal hydraulic head 

prepared from simulated heads for each model cell compose 

a potentiometric-surface map for each aquifer layer in the 

Denver Basin model.

The extent, depth, thickness, and aquifer properties of the 

geologic units, the climate and resulting effects on the rate and 

location of recharge, and the location and altitude of surface 

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec

Average evapotranspiration, in inches

Month

Station AKRON 4 E

Station FORT COLLINS

Station WIGGINS 7 SW

Average of 3 stations

EXPLANATION
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 67

Figure A49. Spatial distribution of simulated predeveopment (pre-1880) evapotranspiration for the 

Denver Basin modeled area.

PALMER

DIVIDEDIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

South Platte

River

Cac he la Poudre R

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

Big Thompson R

§ ̈¦70

§ ̈¦25

§ ̈¦76

!

!

!

!

!

!

!

! ! !

!

!

!

!

! !

!

!

!

!

!

!

!

!

!

!

!

!

!

!

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Pre-1880 simulated evapotranspiration, 

 in inches per year

–45 to –25

–25 to –10

–10 to –5

–5 to –2

–2 to –1

–1 to –0.5

–0.5 to 0

0

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Alluvial aquifer simulated extent (model layer 1)

Stream

Perennial

Ephemeral
68 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A50. Spatial distribution of simulated predevelopment (pre-1880) recharge minus 

evapotranspiration for the Denver Basin modeled area.

PALMER

DIVIDEDIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

South Platte

River

Cac he la Poudre R

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryC

P

r

lum Creek

West P ul m Creek

Bear Creek

Running Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

Big Thompson R

§ ̈¦70

§ ̈¦25

§ ̈¦76

!

!

!

!

!

!

!

! ! !

!

!

!

!

! !

!

!

!

!

!

!

!

!

!

!

!

!

!

!

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Pre-1880 simulated recharge minus

 evapotranspiration, in inches per year

–44 to –25

–25 to –10

–10 to –3

–3 to 0

0

0 to 0.5

0.5 to 1

1 to 2

2 to 10

10 to 11

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Alluvial aquifer simulated extent (model layer 1)

Stream

Perennial

Ephemeral
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 69 Table A8. Simulated predevelopment (pre-1880) groundwater budget for individual bedrock aquifer and confining units in the Denver Basin. [In some cases values do not sum because of rounding; all flow rates are in cubic feet per second; positive values indicate inflow to groundwater; negative values indicate outflow from groundwater] Groundwater budget component Upper Dawson aquifer Dawson confining unit Lower Dawson aquifer Denver upper confining unit Denver aquifer Denver lower confining unit Upper Arapahoe aquifer Arapahoe confining unit Lower Arapahoe aquifer Laramie confining unit Laramie– Fox Hills aquifer Inflow Recharge (precipitation + irrigation) 18.3 1.3 14.9 2.1 18.3 8.7 9.6 2.4 10.6 37.4 52.6 Stream leakage 0.15 0.0 0.65 0.07 2.1 0.03 0.006 0.01 0.17 0.25 0.06 Inflow from alluvial aquifer 0.8 0.0 0.01 0.01 1.1 0.10 1.3 0.01 0.27 0.98 4.0 Inflow from overlying bedrock unit 0.0 3.4 3.7 5.8 6.4 14.2 16.1 1.9 2.2 2.5 7.2 Storage change 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Total inflow 19.3 6.4 20.3 8.5 31.1 29.8 35.9 14.3 18.6 42.4 64.8 Outflow Evapotranspiration –8.9 –0.5 –8.8 –1.1 –8.4 –5.9 –8.4 –2.0 –9.9 –33.1 –47.5 Stream leakage –4.3 –0.41 –3.7 –0.53 –3.0 –0.13 –2.1 –0.01 –0.32 –0.42 –2.6 Outflow to alluvial aquifer –1.6 –0.001 –0.6 0.0 –2.2 –0.80 –14.6 –0.02 –0.62 –0.36 –13.3 Outflow to underlying bedrock unit –3.4 –3.7 –5.8 –6.4 –14.2 –16.1 –1.9 –2.2 –2.5 –7.2 0.0 Springs –0.08 –0.08 –0.33 –0.02 –0.02 –0.05 –0.06 0.0 0.0 –0.003 –0.39 Wells 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Storage change 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Total outflow –19.3 –6.4 –20.3 –8.5 –31.1 –29.8 –35.9 –14.3 –18.6 –42.4 –64.8 Net flows Net recharge (recharge + evapotranspiration) 9.4 0.8 6.1 1.0 9.8 2.8 1.2 0.4 0.7 4.3 5.1 Net stream leakage (stream leakage inflow + stream leakage outflow) –4.2 –0.41 –3.0 –0.46 –0.9 –0.1 –2.2 0.0 –0.15 –0.17 –2.5 Net to alluvial aquifer –0.8 0.0 –0.6 0.0 –1.1 –0.7 –13.3 –0.01 –0.35 –0.11 –9.3
70 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A51. Simulated (A) predevelopment (pre-1880) recharge, evapotranspiration, and net recharge for the Denver Basin alluvial 

aquifer and individual bedrock units, and (B) net recharge for the Denver Basin alluvial aquifer and individual bedrock units.

drainages control the predevelopment distribution of hydraulic 

heads in the Denver Basin aquifers. Potentiometric-surface 

maps for predevelopment conditions for the seven aquifers 

show areas of high hydraulic head near the recharge area of the 

Palmer Divide and areas of low hydraulic head near discharge 

areas (figs. A55–A61). Groundwater flows downgradient from 

the Palmer Divide toward streams in all directions. Groundwater 

moves laterally through the permeable sandstones and alluvial 

454 176 34 29 23 90

–307 –134 –18 –15 –20 –81

147

42 16 14

3

9

–500

–400

–300

–200

–100

0

100

200

300

400

500

Alluvial

aquifer

Total for

bedrock units

Dawson

units

Denver

units

Arapahoe

units

Laramie−Fox Hills

units

–250

–200

–150

–100

–50

0

50

100

150

200

250

Flow rate, in cubic feet per second

Hydrogeologic unit

Net flow rate, in cubic feet per second

Recharge

Evapotranspiration

Net recharge

A

EXPLANATION

materials from areas of recharge toward areas of discharge on 

both a local and regional scale. On a local scale, water moves 

from upland recharge areas through the near-surface aquifer to 

discharge areas in nearby stream valleys. On a regional scale, 

bedrock groundwater moves laterally and downward from the 

topographic high of the Palmer Divide in the south-central part 

of the basin and ultimately discharges to alluvial aquifers or 

streams (Robson, 1987). 

Alluvial aquifer

147 cubic feet per second

(78 percent of net recharge)

Arapahoe units

3 cubic feet per second

(1 percent of net recharge)

Laramie–Fox Hills units

9 cubic feet per second

(5 percent of net recharge)

Denver units

14 cubic feet per second

(7 percent of net recharge) Dawson units

16 cubic feet per second

(9 percent of net recharge)

Total for bedrock units

42 cubic feet per second

(22 percent of net recharge)

B
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 71

Figure A52. Spatial distribution of simulated predevelopment (pre-1880) groundwater flow to and 

from streams for the Denver Basin modeled area.

PALMER

DIVIDEDIVIDE

!

!

!

!

!

!

!

! ! !

!

!

!

!

! !

!

!

!

!

!

!

!

!

!

!

!

!

!

!

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

South Platte

River

Cac he la Poudre R

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryC

P

r

lum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

Big Thompson R

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Pre-1880 groundwater flow to and from 

 streams, in cubic feet per second

–3.4 to –2

–2 to –1

–1 to –0.5

–0.5 to 0

0

0 to 0.5

0.5 to 0.8 Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Alluvial aquifer simulated extent (model layer 1)

Stream

Perennial

Ephemeral
72 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A53. Simulated (A) predevelopment (pre-1880) groundwater flow to and from streams for the Denver Basin alluvial aquifer and 

individual bedrock units, and (B) net flow to streams from the Denver Basin alluvial aquifer and individual bedrock units.

Groundwater flow in the alluvial aquifer is downvalley 

to the north and east in alluvium of the South Platte River 

and tributaries and to the south and southeast in alluvium of 

Arkansas River Basin tributaries. The simulated predevelopment potentiometric surface for the alluvial aquifer (fig. A55) 

generally follows topography and locally is controlled by 

stream-channel elevations.

Groundwater in the bedrock aquifers and confining units 

flows laterally away from the Palmer Divide and downward into 

underlying bedrock units (Robson, 1987). Flow in the Dawson 

and Denver aquifers away from the Palmer Divide recharge 

area is toward discharge areas of Plum and Cherry Creeks to 

the northwest, Monument and Black Squirrel Creeks to the 

south, and Box Elder, Bijou, Kiowa, and Big Sandy Creeks on 

A

12.7 3.5 0.8 2.2 0.2 0.3

–164.2 –17.6 –8.4 –3.7 –2.5 –3.1

–14.2

–7.6

–1.5 –2.3 –2.8

–151.5

Alluvial

aquifer

Total for 

bedrock units

Dawson

units

Denver

units

Arapahoe

units

Laramie−Fox Hills

units

Hydrogeologic unit

–200

–150

–100

–50

0

50

Flow rate, in cubic feet per second

–200

–150

–100

–50

0

50

Net flow rate, in cubic feet per second

Streams inflow

Streams outflow

Net to streams

EXPLANATION

Alluvial aquifer

–152 cubic feet per second

 (91 percent of net to streams)

Dawson units

–8 cubic feet per second

(5 percent of net to streams)

Denver units

–2 cubic feet per second

(1 percent of net to streams)

Arapahoe units

–2 cubic feet per second

(1 percent of net to streams) Total for bedrock units

–14 cubic feet per second

(9 percent of net to streams)

Laramie–Fox Hills units

–3 cubic feet per second

(2 percent of net to streams)

B
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 73

Figure A54. Simulated predevelopment (pre-1880) interaquifer flow for individual Denver Basin bedrock units.

the north and east (figs. A56–A58). Groundwater also moves 

downward to underlying bedrock aquifers from the Dawson and 

Denver aquifers because of the downward hydraulic gradients 

between aquifers (Robson, 1987; section “Interaquifer Flow” 

in this chapter). Predevelopment potentiometric surfaces for the 

Denver, upper Arapahoe, lower Arapahoe, and Laramie–Fox 

Hills aquifers (figs. A59–A61) depict low hydraulic head (potentiometric-surface troughs) along the South Platte River, Bijou 

Creek, Big Sandy Creek, Black Squirrel Creek, and Monument 

Creek, which are areas of regional discharge to streams or alluvial aquifers where the sandstones lie near land surface.

Prior to about 1885, wells completed in the Denver, 

Arapahoe, and Laramie–Fox Hills aquifers in the Denver area 

typically flowed at land surface (Robson, 1987; Cross and 

others 1884; Emmons and others, 1896). However, hydraulic 

heads rapidly declined within a few years of groundwater 

development. Emmons and others (1896) reported water levels 

20 to 50 ft below land surface in the Denver area by 1894, and 

Darton (1905) reported that heads in the Denver and Arapahoe 

aquifers were 50 to 200 ft below land surface in the Denver 

area by 1905, requiring that water be pumped to the surface 

(Robson, 1987). Outside of the Denver area, two flowing wells 

were reported in the Plum Creek drainage in the early 1900s 

(Richardson, 1915).

Groundwater in Denver Basin bedrock aquifers is, in general, confined where overlain by less-permeable claystone and 

shale confining units and unconfined in the near-surface parts 

of the bedrock aquifers and in the alluvial aquifer (Robson, 

1987). Predevelopment confined and unconfined conditions 

for the Denver (fig. A58), lower Arapahoe (fig. A60), and 

Laramie–Fox Hills aquifers (fig. A61) were tabulated from 

model results and generally are consistent with the conceptual 

understanding of conditions described by Robson (1987). 

Areas of confined groundwater were interpreted where the 

calculated potentiometric head was higher than the base 

altitude of the overlying confining layer. Areas of unconfined 

groundwater were interpreted where the calculated potentiometric head was lower than the base altitude of the overlying 

confining layer or where the overlying confining unit is absent. 

Unconfined parts of all three aquifers are located around the 

margins of the aquifer extents. Water released from storage in 

confined parts of the aquifer system is from elastic compressibility of the rocks and water and is expressed as the aquifer 

storage coefficient. Water released from storage in unconfined 

parts of the aquifer system is from that portion of the rock 

porosity drained by gravity flow and is represented by the 

specific yield. In general, greater volumes of water can be 

extracted from unconfined storage than from confined storage.

–25

–20

–15

–10

–5

0

5

10

15

Flow rate, in cubic feet per second

Upper

Dawson

aquifer 

Dawson

confining

unit

Lower

Dawson

aquifer 

Denver upper

confining

unit

Denver 

aquifer

Upper

Arapahoe

aquifer

Arapahoe

confining

unit

Lower

Arapahoe

aquifer

Laramie

confining

unit

Denver lower 

confining

unit

Hydrogeologic unit

–25

–20

–15

–10

–5

0

5

10

15

Net flow rate, in cubic feet per second

0.8 0.9 0.2 0.3 2.9 3.9 5.0 5.0 0.3 1.0

–4.2 –4.5 –6.1 –6.7

–17.1 20.0

–6.9 –7.3

–2.7

–8.2 –3.4 –3.7

–5.8 –6.4

–14.2

–16.1

–1.9 –2.3 –2.5

–7.2

Outflow to underlying unit

Inflow from underlying unit

Net to underlying unit

EXPLANATION
74 Groundwater Availability of the Denver Basin Aquifer System, Colorado Table A9. Estimated unconfined groundwater storage for individual bedrock aquifers in the Denver Basin. Aquifer Model layer Senate Bill 85–5 specific-yield assigned value Denver Basin model specific-yield assigned value (this study) Percent difference of Senate Bill 85–5 specific-yield assigned value from this study Senate Bill 85–5 estimated storage volume (millions of acre-feet) Denver Basin model estimated storage volume using spatial distribution of specific-yield values (figs. A37–A42; millions of acre-feet) Percent difference of Senate Bill 85–5 estimated storage volume from this study Denver Basin model estimated storage volume in the south Denver metropolitan area (millions of acre-feet) Percentage of storage volume in the south Denver metropolitan area Upper Dawson 2 20 15.2 –27 22 5 –121 1.9 35 Lower Dawson 4 20 15.2 –27 10 16 46 4.1 26 Denver 6 17 13.3 –24 71 44 –46 12.9 29 Upper Arapahoe 8 17 17.8 5 12 11 –12 2.1 20 Lower Arapahoe 10 17 17.8 5 78 46 –51 9.3 20

Laramie–Fox Hills 12 15 18.6 21 102 125 20 14.3 11Total 295 247 –18 45 18
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 75

Figure A55. Simulated predevelopment (pre-1880) potentiometric surface and groundwater flow 

directions for the alluvial aquifer (model layer 1).

PALMER

DIVIDEDIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

South Platte

River

Cac he la Poudre R

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr

Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryC

P

r

lum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

Big Thompson R

Black Squirrel Cr

§ ̈¦70

§ ̈¦25

§ ̈¦76

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!

!

!

!

!

!

!

! ! !

!

!

!

!

! !

!

!

!

!

!

!

!

!

!

!

!

!

!

!

6,100

5,900

6,200

6,000

6,300

6,500

6,400

4,500

4,700

5,800

4,800

4,400

5,000

5,700

4,900

4,600

5,200

5,100

4,900

6,200

5,000

4,900

5,100

4,600

4,800

4,600

5,800

6,000

5,900

4,800

6,400

6,000

4,600

6,300

4,700

5,000

4,700

4,900

6,100

5,900

6,200

6,000

6,300

6,500

6,400

4,500

4,700

5,800

4,800

4,400

5,000

5,700

4,900

4,600

5,200

5,100

4,900

6,200

5,000

4,900

5,100

4,600

4,800

4,600

5,800

6,000

5,900

4,800

6,400

6,000

4,600

6,300

4,700

5,000

4,700

4,900

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1879. 

 Datum NAVD88. Contour interval 100 feet

Perennial

Ephemeral

Stream

Generalized groundwater flow direction

Alluvial aquifer simulated extent (model layer 1)

EXPLANATION

Extent of active model cells
76 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A56. Simulated predevelopment (pre-1880) potentiometric surface and groundwater flow 

directions for the upper Dawson aquifer (model layer 2).

PALMER

DIVIDEDIVIDE

Coal Creek

Clear Creek

West Sand Creek

First Cree

Sa

k

nd Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Antelope Cr

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

! !

!

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

§ ̈¦25

6,700

6,600

6,800

6,900

6,400

6,300

7,000

6,100

6,000

6,200

7,100

5,900

6,800

6,700

6,600

6,800

6,900

6,400

6,300

7,000

6,100

6,000

6,200

7,100

5,900

6,800

105° 104°30'

39°30'

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1879.

 Datum NAVD88. Contour interval 100 feet

Generalized groundwater flow direction

EXPLANATION

Stream

Perennial

Ephemeral

Extent of active model cells

Upper Dawson aquifer simulated extent (model layer 2)
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 77

Figure A57. Simulated predevelopment (pre-1880) potentiometric surface and groundwater flow 

directions for the lower Dawson aquifer (model layer 4).

PALMER

DIVIDE

Coal Creek

Clear Creek

West Sand Creek

First Cree

Sa

k

nd Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Antelope Cr

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook Creek Dry Cr

§ ̈¦25

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

!

!

!

!

!

!

!

!

!

!

! !

!

!

!

! !

!

6,100

6,200

6,300

6,400

6,500

6,600

6,700

6,800

6,000

6,900

7,000

7,100

5,900

5,800

7,200

7,300

5,700

7,400

7,500

5,600

6,600

6,700

6,800

5,600

6,000

5,900

5,900

6,700

6,900

6,800

5,800

7,400

6,100

6,200

6,300

6,400

6,500

6,600

6,700

6,800

6,000

6,900

7,000

7,100

5,900

5,800

7,200

7,300

5,700

7,400

7,500

5,600

6,600

6,700

6,800

5,600

6,000

5,900

5,900

6,700

6,900

6,800

5,800

7,400

6,900

105° 104°30'

39°30'

39°

0 5 10 MILES

0 5 10 KILOMETERS

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1879.

 Datum NAVD88. Contour interval 100 feet

Generalized groundwater flow direction

EXPLANATION

Stream

Perennial

Ephemeral

Extent of active model cells

Lower Dawson aquifer simulated extent (model layer 4)
78 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A58. Simulated predevelopment (pre-1880) potentiometric surface, groundwater flow directions, 

and calculated areas of predevelopment confined and unconfined conditions for the Denver aquifer 

(model layer 6).

PALMER

DIVIDEDIVIDE

South Platte

River

Cac he la Poudre R

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

Big Thompson R

§ ̈¦70

§ ̈¦25

§ ̈¦76

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!

!

!

!

!

!

!

! ! !

!

!

!

!

! !

!

!

!

!

!

!

!

!

!

!

!

!

!

!

5,800

5,700

5,600

5,400

5,500

5,500

5,400

5,700

5,600

5,300

5,500

5,200

5,100

5,500

5,800 5,500

6,100

5,900 6,000

6,400

6,200

6,500

6,600

6,900

6,700

6,100

6,300

6,000

6,200

5,900 6,000

6,400

6,200

6,500

6,600

6,800

7,000

7,200

6,400

6,300

6,200

6,800

6,900

6,700

7,000

7,200

6,200

7,100

7,300

7,500

6,700

6,400 6,200

5,500

6,300

6,000

6,400

5,400

6,200

6,200

7,100

7,300

7,500

6,700

6,400

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1879.

 Datum NAVD88. Contour interval 100 feet

Generalized groundwater flow direction

EXPLANATION

Stream

Perennial

Ephemeral Extent of active model cells

Denver aquifer simulated extent (model layer 6)

Denver upper confining unit simulated extent (model layer 5)

Simulated extent of confined conditions

Simulated extent of unconfined conditions
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 79

Figure A59. Simulated predevelopment (pre-1880) potentiometric surface and groundwater flow 

directions for the upper Arapahoe aquifer (model layer 8).

PALMER

DIVIDEDIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

South Platte

River

Cac he la Poudre R

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryC

P

r

lum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

Big Thompson R

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!

!

!

!

!

!

!

! ! !

!

!

!

!

! !

!

!

!

!

!

!

!

!

!

!

!

!

!

!

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,300

5,200

5,100

5,400

5,000

5,5005,600

4,900

5,500

5,000

5,000

5,400

5,300

5,200

5,100

5,400

5,000

5,5005,600

4,900

5,500

5,000

5,000

5,400

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1879.

 Datum NAVD88. Contour interval 100 feet

Generalized groundwater flow direction

EXPLANATION

Stream

Perennial

Ephemeral

Extent of active model cells

Upper Arapahoe Dawson aquifer simulated extent (model layer 8)
80 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure A60. Simulated predevelopment (pre-1880) potentiometric surface, groundwater flow directions, 

and calculated areas of predevelopment confined and unconfined conditions for the lower Arapahoe 

aquifer (model layer 10).

South Platte

River

Cac he la Poudre R

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryC

P

r

lum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

Big Thompson R

§ ̈¦70

§ ̈¦25

§ ̈¦76

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

PALMER

DIVIDEDIVIDE

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!

!

!

!

!

!

! ! !

!

!

!

!

! !

!

!

!

!

!

!

!

!

!

!

!

!

!

! 5,400

6,000

5,300

5,900

5,600

5,800

6,100

5,200

5,500

5,700

6,200

5,100

6,300

6,400

6,500

6,600

5,000

6,700

6,800

6,900

7,000

4,900

7,100

7,200

7,300

4,800

7,400

6,000

6,000

5,000

6,200

5,000

5,700

5,600

5,600

5,900

5,500

5,700

5,900

6,100

6,300

5,000

5,900

4,900

5,400

6,000

5,300

5,900

5,600

5,800

6,100

5,200

5,500

5,700

6,200

5,100

6,300

6,400

6,500

6,600

5,000

6,700

6,800

6,900

7,000

4,900

7,100

7,200

7,300

4,800

7,400

6,000

6,000

5,000

6,200

5,000

5,700

5,600

5,600

5,900

5,500

5,700

5,900

6,100

6,300

5,000

5,900

4,900

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1879.

 Datum NAVD88. Contour interval 100 feet

Generalized groundwater flow direction

EXPLANATION

Stream

Perennial

Ephemeral Extent of active model cells

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver lower confining unit simulated extent (model layer 7)

Simulated extent of confined conditions

Simulated extent of unconfined conditions
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 81

Figure A61. Simulated predevelopment (pre-1880) potentiometric surface, groundwater flow directions, 

and calculated areas of predevelopment confined and unconfined conditions for the Laramie–Fox Hills 

aquifer (model layer 12).

South Platte

River

Cac he la Poudre R

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryC

P

r

lum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

Big Thompson R

PALMER

DIVIDEDIVIDE

§ ̈¦70

§ ̈¦25

§ ̈¦76

!

!

!

!

!

!

!

! ! !

!

!

!

!

! !

!

!

!

!

!

!

!

!

!

!

!

!

!

!

5,400

5,300

5,200

5,100

5,600

5,700

5,800

5,900

5,000

4,800

5,500

4,900

4,700

6,000

4,600

6,100

6,200

6,400

6,300

6,500

6,600

6,700

6,800

6,900

7,000

7,100

4,500

7,200

7,300

7,400

4,400

5,600

6,300

5,400

4,400

6,000

4,600

5,700

5,800

4,500

5,900

4,900

5,700

5,000

5,500

5,800

5,600

5,800

5,900

5,500

5,000

4,600

5,400

5,300

5,200

5,100

5,600

5,700

5,800

5,900

5,000

4,800

5,500

4,900

4,700

6,000

4,600

6,100

6,200

6,400

6,300

6,500

6,600

6,700

6,800

6,900

7,000

7,100

4,500

7,200

7,300

7,400

4,400

5,600

6,300

5,400

4,400

6,000

4,600

5,700

5,800

4,500

5,900

4,900

5,700

5,000

5,500

5,800

5,600

5,800

5,900

5,500

5,000

4,600

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1879.

 Datum NAVD88. Contour interval 100 feet

Generalized groundwater flow direction

EXPLANATION

Stream

Perennial

Extent of active model cells Ephemeral

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Laramie confining unit simulated extent (model layer 11)

Simulated extent of confined conditions

Simulated extent of unconfined conditions
82 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Summary

The Denver Basin aquifer system, located in eastcentral Colorado, is an important source of water supply for 

municipalities along the semiarid Front Range urban corridor, 

including suburbs of Denver and Colorado Springs. It also is 

an important resource for rural residents on the eastern plains 

of Colorado. Denver Basin groundwater is administratively 

recognized as nonrenewable because the aquifers are primarily confined and receive little precipitation recharge. Permitted 

pumping rates are based on a 100-year aquifer life in areas 

of the basin where groundwater is considered not tributary 

to surface water, and there are ongoing needs in the Denver 

Basin to understand and monitor groundwater availability as 

pumping and storage depletion continue.

In 2004, the U.S. Geological Survey initiated large-scale 

regional studies to provide updated groundwater availability 

assessments of important principle aquifers across the United 

States, including the Denver Basin. This study of the Denver 

Basin aquifer system evaluates the hydrologic effects of continued pumping and documents an updated groundwater flow 

model useful for appraisal of hydrologic conditions. Study 

results are presented as three chapters in this Professional 

Paper. This chapter, Chapter A, presents an introduction, 

previous work, study methods, the hydrogeologic framework 

of the aquifer system, and a description of predevelopment 

(pre-1880) water budgets and groundwater flow conditions 

based on modeling results. Chapter B describes the effects of 

development on groundwater availability including changes 

in land and water use, changes to the recharge, discharge, and 

storage components of the water budget, and effects of these 

changes on groundwater levels and flow directions from 1880 

through 2003. Chapter B also includes results from predictive 

simulations and a discussion of monitoring needs. Chapter C 

documents the groundwater flow model.

The Denver Basin is located in the Colorado Piedmont 

of the Great Plains physiographic province where rolling 

hills and dissected plains characterize the topography. The 

topographic high of about 8,000 ft is located in the southern 

one-third of the Denver Basin along the Palmer Divide, which 

is the drainage divide between the tributaries of the South 

Platte River to the north and those of the Arkansas River to 

the south. The topographic low of approximately 4,300 ft 

lies along the South Platte River on the northeast edge of 

the basin. Topography of the Rocky Mountain Front Range 

affects the semiarid climate and weather over the plains in the 

Denver Basin east of the Rocky Mountain front. The Rocky 

Mountains create an orographic effect on weather moving 

eastward across Colorado, causing a rain shadow and semiarid 

climate on the eastern slope of the mountains. Analysis of 

long-term mean annual precipitation data from 129 individual 

weather stations in and around the Denver Basin indicates 

mean annual precipitation over the basin ranges from approximately 11.5 to 20 inches for the period 1931–2003. The 

Palmer Divide creates a local orographic effect on storms in 

the Denver Basin, such that precipitation rates are greater at 

higher elevations near the divide. The long-term mean annual 

precipitation at the highest altitudes along the western basin 

margin and the Palmer Divide is about 20 inches per year, 

whereas the long-term average annual precipitation at lower 

elevations along the South Platte River and in the southernmost part of the basin is about 11 to 12 inches per year. The 

1930–2003 period of record for precipitation records exhibits 

several periods defined as exhibiting variable to dry (drought) 

conditions. Basinwide average precipitation was less than 

the long-term annual mean from 1931 to about 1940 (during 

the 1930s drought) and from 1948 to 1956 (during the 1950s 

drought). The period 1979–2001 had variable to wet precipitation conditions, which resulted in an overall upward trend for 

basinwide mean annual precipitation over the period of record. 

Variable to dry conditions existed from 2001 to 2003 when 

effects of a recent drought become apparent.

The Denver Basin contains perennial and ephemeral 

surface drainages. Streams originating in the Front Range 

enter the west side of the Denver Basin and are generally 

perennial because they receive water primarily from snowmelt runoff in the mountains. Perennial streams entering the 

western side of the basin include the main stem of the South 

Platte River and its major tributaries of Plum, Bear, Clear, 

Coal, and Boulder Creeks. The South Platte River flows 

east out of the mountains through Waterton Canyon and into 

Chatfield Reservoir, crosses the western part of the Denver 

Basin flowing north through Denver, and then flows northeast toward Greeley. Streams that originate on the semiarid 

plains within the Denver Basin are generally ephemeral and 

intermittent because they receive water primarily from local 

precipitation runoff and groundwater discharge from the 

Denver Basin aquifers. Drainage within the Denver Basin east 

of the mountains is radial to the north, east, and south away 

from the Palmer Divide. North of the Palmer Divide, streams 

drain toward the South Platte River, and south of the Palmer 

Divide, streams drain toward the Arkansas River. Ephemeral 

and intermittent streams that originate within the Denver Basin 

include the South Platte River tributaries of Cherry, Running/

Box Elder, Kiowa, Comanche, and Bijou Creeks. Ephemeral 

and intermittent tributaries that originate in the Denver Basin 

and drain south toward the Arkansas River include Monument, 

Black Squirrel, Adobe, and Big Sandy Creeks.

The Denver Basin aquifer system is composed of Upper 

Cretaceous- to Tertiary-age sandstone bedrock aquifers that 

occur in the uppermost layers of the structural Denver Basin 

above the Cretaceous Pierre Shale confining layer. From oldest to youngest, the four primary units are the Laramie–Fox 

Hills, Arapahoe, Denver, and Dawson aquifers. The Dawson 

and Arapahoe are further differentiated into upper and lower 

units in parts of the basin. The synclinal structure of the 

Denver Basin causes the bedrock aquifer units to crop out in a 

ring pattern where the oldest rocks of the Laramie–Fox Hills 

aquifer crop out around the outer margins of the basin and the 

youngest rocks of the Dawson aquifer crop out in the center 

of the basin. Confined groundwater conditions generally are 
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 83

found in the bedrock aquifers where they are overlain by 

younger units, and unconfined groundwater conditions are 

generally found in outcrop areas. Alluvial sand, gravel, and 

clay deposits overlie the bedrock formations primarily along 

stream channels, and these materials form an unconfined 

alluvial aquifer where saturated.

The Laramie–Fox Hills aquifer is the oldest, deepest, 

and most extensive of the bedrock aquifers underlying the 

area, and its extent defines the extent of the Denver Basin 

aquifer system. The Laramie–Fox Hills aquifer is composed 

of poorly to moderately consolidated sandstone units of the 

upper Cretaceous Fox Hills Sandstone and the lower Laramie 

Formation, and a base-altitude map of the Laramie–Fox 

Hills aquifer reflects the bowl shape and dipping margins 

of the Denver Basin geologic structure. The deepest part of 

the Laramie–Fox Hills aquifer base, and therefore also the 

deepest part of the Denver Basin aquifer system, occurs in 

Douglas County just north of Parker, Colorado, at an altitude 

of approximately 3,410 ft. Depth to the base of the Laramie–

Fox Hills aquifer near the structural center of the basin is 

approximately 2,200 to 2,300 ft below land surface, and the 

total thickness of the aquifer system reaches a maximum of 

approximately 3,200 ft beneath the topographic high of the 

Palmer Divide.

The Cretaceous upper Laramie Formation, composed 

of gray to black shale, coal seams, and minor amounts of siltstone and sandstone, overlies the Laramie–Fox Hills aquifer 

and forms a confining unit that separates the Arapahoe and 

Laramie–Fox Hills aquifers. Base elevation contours of the 

Laramie confining unit reflect the bowl shape and dipping 

margins of the Denver Basin similar to the base configuration 

of the Laramie–Fox Hills aquifer. The Laramie confining unit 

forms a wedge-shaped layer with a mountain-front thickness 

of as much as 700 ft that thins to less than 100 ft on the eastern 

margin of the basin.

The Arapahoe aquifer consists of a 400- to 600-ft-thick 

sequence of interbedded conglomerate, sandstone, siltstone, and shale of Cretaceous age. In the northern one-third 

of the basin, shale is more prevalent, and the Arapahoe is 

divided into upper and lower aquifers with an intervening 

shale confining unit. Predominant conglomerate and coarsegrained sandstone units in the lower Arapahoe aquifer represent erosion from the nearby Front Range Precambrian and 

Paleozoic rocks and deposition at the mountain front during 

the Laramide Orogeny. The coarse-grained sandstones of the 

lower Arapahoe aquifer are thickest and the most conductive 

in Douglas and El Paso Counties where they form a productive 

bedrock aquifer that is heavily used for municipal and domestic water supply. The base altitude ranges from 6,200 ft along 

the southwest basin margin to approximately 4,100 ft at the 

basin center just north of Parker, Colorado. Depth to the base 

of the lower Arapahoe aquifer near the structural center of the 

basin is approximately 1,700 ft below land surface, and the 

maximum depth to the base of the aquifer is approximately 

2,600 ft below land surface at the Palmer Divide.

The Denver aquifer and confining units consist of a 

600- to 1,200-ft-thick sequence of interbedded shale, claystone, siltstone, sandstone, coal, and volcanic ash deposits of 

Cretaceous to Tertiary age. The Arapahoe, Denver, and lower 

Dawson aquifers represent the synorogenic deposition of sediments in the Denver Basin during Laramide uplift of the Rocky 

Mountain Front Range. The prominent Wildcat Mountain alluvial fan mapped in the lower Arapahoe aquifer is also present 

in the Denver and lower Dawson portions of the sequence. The 

Cretaceous/Tertiary boundary occurs in the upper part of the 

Denver aquifer sequence and is closely established by vertebrate fossils. Away from the Wildcat Mountain alluvial fan, the 

Denver sequence is in general finer grained than the underlying 

Arapahoe aquifer sequence and is composed of isolated channel sandstones contained in extensive fine-grained deposits. 

Despite poor correlations between Denver aquifer sandstones, 

the base-altitude maps of the Denver aquifer and confining units 

depict the regional structure of the Denver Basin and provide reasonable representations of layering within the Denver 

sequence. Altitude of the Denver sequence base ranges from 

approximately 4,600 to 6,300 ft, and the maximum depth of the 

sequence is approximately 2,100 ft below land surface beneath 

the Palmer Divide. The greatest silt-plus-sand thickness in the 

Denver aquifer (400 to 600 ft) occurs along the western basin 

margin in southern Douglas County. The Denver confining units 

are thin (mean thicknesses of 50 ft) compared to the thickness 

of the Denver aquifer (mean thickness of 550 ft).

The Dawson aquifer sequence consists of a 100- to 

1,100-ft-thick interbedded sequence of Tertiary-age, fluvial 

conglomerate, sandstone, siltstone, and shale. In the northern 

two-thirds of the Dawson extent, a clay and shale confining 

layer is present, and the aquifer is separated into upper and 

lower aquifers. The lower Dawson aquifer forms the upper part 

of the D1 sequence defined by Raynolds (2002) and represents continued Laramide synorogenic fluvial deposition in an 

environment similar to that which existed during deposition 

of the Denver aquifer sequence. The base altitude of the lower 

Dawson aquifer ranges from 5,400 ft at the northern edge of 

its extent to 6,800 ft on the southern edge of its extent and is 

1,100 feet below land surface at the Palmer Divide. The greatest 

silt-plus-sand thickness (200 to 375 ft) is located in the westcentral part of the basin along the Douglas–El Paso County 

line similar to the Denver and Arapahoe aquifers. The Dawson 

confining unit consists of a shale-rich layer at the top of the 

lower Dawson sequence. The upper Dawson aquifer consists 

of arkosic, coarse-grained, poorly consolidated sandstones with 

some interbedded overbank mudstone deposits in a distribution 

pattern quite different from that of the underlying sediments. 

Sandstones of the upper Dawson aquifer are more uniform and 

less variable in composition than those from the underlying 

layers and were likely derived from the Pikes Peak area to 

the south rather than from the Front Range source area to the 

west. Paleochannels at the base of the lower Dawson aquifer are evident from the base-altitude configuration map, and 

one such paleochannel aligns with the present-day course of 

Cherry Creek.
84 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Quaternary alluvial, colluvial, and eolian deposits overlie 

of the Denver Basin bedrock aquifers, primarily along stream 

channels, forming an extensive and transmissive, unconfined 

alluvial aquifer where interconnected and saturated. Alluvial 

deposits along the main channel of the South Platte River and 

tributaries draining directly from the Front Range tend to be 

coarser grained than alluvial deposits along ephemeral tributaries draining from the Palmer Divide because the mountain 

streams receive coarser-grained source materials from steeper 

terrain than streams draining the sedimentary rocks of the 

Denver Basin. In general, the base of the alluvial aquifer slopes 

outward in a radial fashion away from the Palmer Divide, 

reflecting paleo and present-day topography. Alluvial deposit 

thickness ranges from 0 to approximately 300 ft, and the thickest part of the South Platte alluvial aquifer (more than 270 ft) is 

located in the downstream part of the aquifer near Wiggins.

Aquifer-property values for hydraulic conductivity, 

storage coefficient, and specific yield were compiled from 

previous Denver Basin studies. A summary of hydraulicconductivity values from pumping tests for the bedrock 

aquifers indicates the Arapahoe aquifer is the most permeable 

of the bedrock units (median of 1.8 ft/d; geometric mean of 

1.6 ft/d) followed by the Dawson aquifer (median of 0.80 ft/d; 

geometric mean of 0.7 ft/d), the Denver (median of 0.45 ft/d; 

geometric mean of 0.42 ft/d), and the Laramie–Fox Hills 

aquifers (median of 0.40 ft/d; geometric mean of 0.40 ft/d). 

Hydraulic-conductivity values for the alluvial aquifer are 

many orders of magnitude greater than those for the bedrock 

aquifers ranging from about 18 ft/d to about 2,560 ft/d with 

a median of about 480 ft/d based on pumping-test results. 

The difference in hydraulic conductivity between alluvial 

and bedrock aquifers is an important part of the Denver Basin 

conceptual model because it affects the water budget and 

water movement in the basin. Specific-storage values for this 

study were estimated during calibration of the groundwater 

flow model. A specific-storage value of 5.2×10–7/ft was estimated for aquifers, and a value of 1.7×10–6 /ft was estimated 

for confining units. Estimates of specific-yield values were 

compiled from previous studies, and the resulting mean values 

varied somewhat from values used for water administration. 

Mean specific-yield values of 15.2 percent for the Dawson 

aquifers, 13.3 percent for the Denver aquifer, 17.8 percent for 

the Arapahoe aquifers, and 18.6 percent for the Laramie–Fox 

Hills aquifer are reported by the current study and are used in 

the groundwater flow simulations.

Predevelopment groundwater availability discussions 

describe conditions prior to 1880 and are based on previous studies as well as interpretations and results from the 

steady-state stress period of the calibrated groundwater flow 

model. Predevelopment conditions are described in terms of 

groundwater budgets, hydraulic head, and groundwater flow 

directions. Groundwater inflow components are sources of 

water to the aquifer, and for predevelopment conditions in 

the Denver Basin, inflow was from precipitation plus irrigation recharge, streams, and interaquifer flow between hydrogeologic units. Because agricultural irrigation, primarily by 

surface-water diversions, began in the South Platte River 

valley prior to 1880, irrigation recharge was included as the 

predevelopment recharge estimates. Predevelopment outflow 

components of the water budget were discharge to evapotranspiration, streams, springs, and interaquifer flow. Discharge to 

pumping wells was assumed negligible before 1880 and was 

not included in the predevelopment groundwater budget. For 

some groundwater budget components such as streams, there 

are both inflows and outflows, and the difference between 

inflows and outflows is referred to as the “net.” For example, 

net recharge is calculated as the difference between inflow 

from recharge and outflow to evapotranspiration. Groundwater 

budgets are presented for the entire system (sum of all model 

layers), the alluvial aquifer (model layer 1), and the bedrock 

units (model layers 2 through 12) and are discussed in terms of 

individual groundwater budget components.

Precipitation plus irrigation recharge was the primary 

inflow component of the predevelopment groundwater 

budget for the entire system (630 ft3/s, 98 percent of inflow), 

the alluvial aquifer (454 ft3/s, 90 percent of inflow), and the 

bedrock aquifers (176 ft3/s, 94 percent of inflow) and is an 

important source of water in this semiarid region. However, 

much of the precipitation goes to surface-water runoff and 

evapotranspiration with only a small part of precipitation 

providing recharge to the bedrock aquifers. Simulated predevelopment net recharge (recharge minus evapotranspiration) 

to the alluvial aquifer was 147 ft3/s (84 percent of net inflow 

to the alluvial aquifer), and simulated predevelopment net 

recharge to the bedrock units was 41 ft3/s (100 percent of net 

inflow to the bedrock units). In areas where bedrock crops 

out with little to no overlying alluvium, deep infiltration of 

precipitation provides direct recharge to the bedrock aquifers. 

Inflow from streams and interaction between the alluvial 

aquifer and the bedrock units accounted for small percentages 

of groundwater inflow.

Evapotranspiration and streams were the primary outflow 

components of the predevelopment water budget. Simulated 

evapotranspiration was 442 ft3/s (68 percent of outflow) for 

the entire system, 307 ft3/s (61 percent of outflow) for the 

alluvial aquifer, and 135 ft3/s (72 percent of outflow) for the 

bedrock units. Streams accounted for 182 ft3/s (28 percent 

of the outflow) from the entire system, 164 ft3/s (33 percent 

of outflow) for the alluvial aquifer, and 18 ft3/s (10 percent 

of outflow) for the bedrock units. Streams provided inflow 

to and outflow from the system, but the net flow was from 

aquifers to streams. Simulated net outflow to streams from 

the alluvial aquifer was 151 ft3/s (88 percent of net outflow) 

and 14 ft3/s (34 percent of net outflow) from bedrock aquifers. 

In general, ephemeral streams that originate in the basin gain 

flow in upland areas near the Palmer Divide where alluvium is 

thin or absent and bedrock groundwater discharges directly to 

streams. In downstream parts of the basin where the alluvial 

aquifer is present, ephemeral streams can lose water to the 

alluvial aquifer as topographic gradients flatten, and streambeds can be dry.
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 85

In areas overlain by alluvial aquifers, groundwater 

moves between the alluvial aquifer and bedrock units. Simulated outflow from the bedrock units to the alluvial aquifer for 

predevelopment conditions was 34 ft3/s (7 percent of alluvial aquifer inflow), and simulated outflow from the alluvial 

aquifer to the bedrock units was 8 ft3/s (4 percent of bedrock 

inflow), resulting in a net outflow from the bedrock units to 

the alluvial aquifer of 26 ft3/s (64 percent of net outflow from 

the bedrock units and 16 percent of net inflow to the alluvial 

aquifer). In the center of the basin, downward movement of 

ground water from overlying bedrock layers is an important source of recharge to deeper confined bedrock aquifers. 

Although the rate of vertical movement is small compared to 

lateral movement in the bedrock aquifers, the large area over 

which downward movement occurs results in large volumes of 

water moving between aquifers. For predevelopment conditions, interaquifer flow between all bedrock units is downward 

with flow to underlying aquifers. The greatest predevelopment 

downward flow is from the Denver aquifer (about 14 ft3/s net 

flow) and Denver lower confining unit (about 16 ft3/s net flow) 

into the Arapahoe aquifers because the Denver lower confining 

unit is generally thin (less than 50 ft in thickness) over much 

of its extent.

The quantity of groundwater in storage can be calculated 

as the product of the specific yield of an aquifer and aquifer 

volume plus the confined storage available from aquifer and 

water compressibility. In the Denver Basin, the quantity of 

groundwater in unconfined bedrock-aquifer storage was previously estimated by multiplying constant specific-yield values 

defined for water administration times the volume of aquifer 

materials, and the result is an estimate of 295 million acre-ft 

of groundwater in storage. While estimates of groundwater in 

storage are speculative, digital representation of the aquifer 

framework does facilitate storage calculations for the Denver 

Basin. This study estimated the volume of unconfined bedrock-aquifer storage as the product of aquifer area, simulated 

predevelopment (pre-1880) saturated thickness, and the spatial 

distribution of specific yield derived for each aquifer. The calculation, which accounts for spatial heterogeneity of specific 

yield as a function of the silt-plus-sand aquifer fraction, results 

in an estimate of 247 million acre-ft of groundwater in unconfined storage, which is about 18 percent less than the previous 

administrative estimate.

The Denver Basin aquifers are confined over much of 

their area where overlain by less- permeable claystone and 

shale confining units. Unconfined, or water-table, conditions 

occur in the near-surface parts of the Denver Basin bedrock 

aquifers and in the alluvial aquifer. The extent, depth, thickness and aquifer properties of the geologic units; climate 

and the resulting effects on the rate and location of recharge; 

and the location and altitude of surface drainages control 

the predevelopment distribution of hydraulic heads in the 

Denver Basin aquifers. Potentiometric-surface maps for 

predevelopment conditions for the seven aquifers show areas 

of high hydraulic head near the recharge area of the Palmer 

Divide and areas of low hydraulic head near discharge areas. 

Groundwater flows downgradient from the Palmer Divide 

toward streams in all directions. Groundwater moves laterally 

through the permeable sandstones and alluvial materials from 

areas of recharge toward areas of discharge on both a local 

and regional scale. On a local scale, water moves from upland 

recharge areas through the near-surface aquifer to discharge 

areas in nearby stream valleys. On a regional scale, bedrock 

groundwater moves laterally and downward from the topographic high of the Palmer Divide in the south-central part of 

the basin and ultimately discharges to downgradient alluvial 

aquifers or streams. Groundwater also moves vertically down 

to underlying bedrock aquifers. The lower potentiometric 

altitude in the underlying bedrock aquifers promotes downward water movement, and although the low vertical hydraulic 

conductivities limit the rate of downward water movement, 

this vertical leakage is an important source of recharge to 

underlying bedrock aquifers.

References

Aikin, A.R., Anderman, E.R., Harmon, E., Paschke, S.S., 

Plazak, D., and Riemann, M., eds., 2000, Colorado groundwater atlas: Colorado Ground-Water Association, Lakewood, Colo., 127 p.

Alley, W.M., 2006, Tracking U.S. ground water reserves for 

the future: Environment, v. 48, no. 3, p. 10–25.

Alley, W.M., 2007, Another water budget myth—The significance of recoverable ground water in storage: Groundwater, 

v. 45, no. 3, p. 251.

Anderman, G.G., and Ackman, E.J., 1963, Structure of the 

Denver-Julesburg Basin and surrounding areas: Rocky 

Mountain Association of Geologists, Geology of the northern Denver Basin and adjacent uplifts, p. 170–175.

Anna, L.O., 1975, Map showing availability of hydrologic 

data published as of 1974 by the U.S. Environmental Data 

Service and by the U.S. Geological Survey and cooperating agencies, Colorado Springs-Castle Rock area, Front 

Range Urban Corridor, Colorado: U.S. Geological Survey Miscellaneous Investigations Series Map I–857–D, 

scale 1:100,000, 1 sheet.

Bader, J.W., Ehrenzeller, J.W., Bode, J.S., and Mars, K.L., 2007, 

Stratigraphic and depositional relationship, Late Cretaceous 

and Tertiary deposits, Centennial, Colorado—Implications 

for Eocene paleogeography and its control on shallow 

groundwater and contaminant flow: Geological Society of 

America Abstracts with Programs, v. 39, no. 6, p. 472.

Banta, E.R., 1989, Hydrologic effects of pumpage from the 

Denver Basin bedrock aquifers of northern El Paso County, 

Colorado: U.S. Geological Survey Water-Resources Investigations Report 88–4033, 81 p.
86 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Banta, E.R., 2000, MODFLOW-2000, the U.S. Geological 

Survey modular ground-water model—Documentation of 

packages for simulating evapotranspiration with a segmented function (ETS1) and drains with return flow (DRT1): 

U.S. Geological Survey Open-File Report 2000–466, 127 p.

Banta, E.R., 2006, Modifications to MODFLOW boundary 

conditions and an adaptive-damping scheme for Picard 

iterations for a highly nonlinear regional model, in Poeter, 

Eileen, Hill, Mary, and Zheng, Chunmiao, MODFLOW and 

More 2006—Managing groundwater systems: International 

Groundwater Modeling Center and Colorado School of 

Mines, 2006 [Proceedings, Golden, Colo.], p. 596–600.

Barclay, R.S., Johnson, K.R., Betterton, W.J., and Dilcher, 

D.L., 2003, Stratigraphy and megaflora of a K-T boundary section of the eastern Denver Basin, Colorado: Rocky 

Mountain Geology, v. 38, no. 1, p. 45–71.

Barkmann, P.E., 2004, Vertical hydraulic conductivity measurements in the Denver Basin, Colorado: The Mountain 

Geologist, v. 41, no. 4, p. 169–183.

Berman, A.E., Poleschook, D., and Dimelow, T.E., 1980, 

Jurassic and Cretaceous systems of Colorado, in Kent, H.C., 

and Porter, K.W., eds., Colorado Geology: Rocky Mountain 

Association of Geologists, p. 71–101.

Bingham, D.L., and Klein, J.M., 1973, Water-level declines 

and ground-water quality, upper Black Squirrel Creek 

basin, Colorado: U.S. Geological Survey, Colorado Water 

Resources Circular 23, 21 p., 2 sheets.

Bjorklund, L.J., and Brown, R.F., 1957, Geology and groundwater resources of the lower South Platte River valley between 

Hardin, Colorado, and Paxton, Nebraska: U.S. Geological 

Survey Water-Supply Paper 1378, 431 p.

Brand, K.E., 1980, Geophysical and lithological logs from 

the 1979 coal drilling and coring program, Denver East 

1/2°×1° quadrangle: Colorado Geological Survey OpenFile Report 80–1, 74 p.

Brand, K.E., and Caine, J.M., 1980, Geophysical and lithological logs from the 1980 coal drilling and coring program, 

Denver East 1/2°×1° quadrangle: Colorado Geological 

Survey Open-File Report 80–9, 42 p.

Britton, L.J., and Gaggiani, N.G., 1989, Northern Great Plains 

and Rocky Mountain Provinces—Denver and Raton Mesa 

region, in Britton, L.J., Anderson, C.L., Goolsby, D.A., and 

VanHaveren, B.P., eds., Summary of the U.S. Geological 

Survey and Bureau of Land Management National CoalHydrology Program, 1974–1981: U.S. Geological Survey 

Professional Paper 1464, p. 103–110.

Bryant, Bruce, McGrew, L.W., and Wobus, R.A., 1981, Geologic map of the Denver 1°×2° quadrangle, north-central 

Colorado: U.S. Geological Survey Miscellaneous Investigations Series Map I–1163, scale 1:250,000, 2 sheets.

Buckles, D.R., and Watts, K.R., 1988, Geohydrology, water 

quality, and preliminary simulations of ground-water flow 

of the alluvial aquifer in the upper Black Squirrel Creek 

basin, El Paso County, Colorado: U.S. Geological Survey 

Water-Resources Investigations Report 88–4017, 49 p.

Carpenter, Kenneth, and Young, D.B., 2002, Late Cretaceous 

dinosaurs from the Denver Basin, Colorado: Rocky Mountain Geology, v. 37, no. 2, p. 237–254.

Carroll, C.J., 2004, 2003 Summary of coal resources in Colorado: Colorado Geological Survey Special Publication 54, 

25 p.

Carroll, C.J., and Crawford, T.A., 2000, Geologic map of the 

Colorado Springs quadrangle, El Paso County, Colorado: 

Colorado Geological Survey Open-File Report 00–3, 17 p., 

scale 1:24,000, 1 sheet.

Chronic, Felicie, and Chronic, John, 1974, Bibliography and 

index of geology and hydrology, Front Range Urban Corridor, 

Colorado: U.S. Geological Survey Bulletin 1306, 102 p.

Coffin, D.L., 1962, Records, logs, and water-level measurements of selected wells and test holes, physical properties 

of unconsolidated materials, chemical analyses of ground 

water, and streamflow measurements in the Big Sandy 

Creek valley in Lincoln, Cheyenne, and Kiowa Counties, 

Colorado: U.S. Geological Survey, Colorado Groundwater 

Basic Data Report no. 12, 25 p., 2 sheets.

Colorado Division of Water Resources, 1998, Denver Basin 

and South Platte River Basin Technical Study, Final Report 

Senate Bill 96–074, variously paged.

Colorado Division of Water Resources, 2003, Ground water 

levels in the Denver Basin bedrock aquifers, 2003 annual 

report, 132 p.

Colorado Division of Water Resources, 2004, Ground water 

levels in the Denver Basin bedrock aquifers, 2004 annual 

report, 132 p.

Colorado Division of Water Resources, 2005, Hydrobase database, Analysis/query tools, Statewide, 07/01/2005: 1 DVD.

Colorado Water Conservation Board, 2004a, Statewide Water 

Supply Initiative Report, November 2004, variously paginated, accessed March 19, 2009, at http://cwcb.state.co.us/

IWMD/SWSITechnicalResources/SWSIPhaseIReport/

SWSIPhaseIReport.htm.
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 87

Colorado Water Conservation Board, 2004b, South Platte 

Decision Support System Ground-Water Component 

Phase 1, Task 44.2: Denver Basin region water level 

technical memorandum, July 30, 2004, 27 p.

Colorado Water Conservation Board, 2006a, South Platte 

Decision Support System Ground-Water Component 

Phase 3, Task 44.2: Denver Basin region water level technical memorandum, November 28, 2006, 65 p., accessed 

February 27, 2008, at ftp://dwrftp.state.co.us/cdss/gwm/tm/

SPDSS44-2_20061128.pdf.

Colorado Water Conservation Board, 2006b, South Platte Decision Support System Ground-Water Component Phase 3, 

Task 42.3: South Platte Alluvium region aquifer configuration final technical memorandum, November 30, 2006, 39 p., 

accessed February 27, 2008, at ftp://dwrftp.state.co.us/cdss/

gwm/tm/SPDSS42-3_20061130.pdf.

Colorado Water Conservation Board, 2006c, SPDSS 

Ground-Water Component Phase 2, Draft Final Task 43.2: 

Denver Basin region aquifer property technical memorandum, February 13, 2006, 67 p., accessed February 27, 2008, at ftp://dwrftp.state.co.us/cdss/gwm/tm/

SPDSS43-2_20060213.pdf.

Colton, R.B., and Lowrie, R.L., 1973, Map showing mined 

areas of the Boulder–Weld coal field, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF–513, 

1 sheet.

Crifasi, R.R., 1992, Alluvial architecture of Laramide orogenic 

sediments Denver Basin, Colorado: The Mountain Geologist, v. 29, p. 19–27.

Cross, C.W., Chisholm, F.F., Chauvenet, Regis, and Van Deist, 

P.H., 1884, The artesian wells of Denver: Colorado Scientific Society Proceedings, v. 1, p. 76–108.

Darton, N.H., 1905, Preliminary report on geology and 

underground water resources of the central Great Plains: 

U.S. Geological Survey Professional Paper 32, 433 p.

Davis, T.L., and Weimer, R.J., 1976, Late Cretaceous growth 

faulting, Denver Basin, Colorado, in Epis, R.C., and 

Weimer, R.J., eds., Professional Contributions of Colorado 

School of Mines Number 8: Studies in Colorado Field Geology, p. 280–300.

DeVoto, R.H., 1980, Pennsylvanian stratigraphy and history 

of Colorado, in Kent, H.C., and Porter, K.W., eds., Colorado Geology: Rocky Mountain Association of Geologists, 

p. 71–101.

Doherty, John, 2006, PEST—Model-independent parameter 

estimation user manual, 5th ed.: Watermark Numerical 

Computing, [Corinda, Australia], variously paged, accessed 

August 31, 2009, at http://www.pesthomepage.org/

Driscoll, L.B., 1974, Land-use classification map of the 

Boulder-Fort Collins-Greeley Area, Front Range urban corridor: U.S. Geological Survey Miscellaneous Investigations 

Series Map I–855–B, 1 sheet.

Driscoll, L.B., 1975, Land-use classification map of the Colorado Springs–Castle Rock Area, Front Range urban corridor: U.S. Geological Survey Miscellaneous Investigations 

Series Map I–857–B, 1 sheet.

Duke, H.R., and Longenbaugh, R.A., 1966, Evaluation of 

water resources in Kiowa and Bijou Creek basins, Colorado: prepared by Colorado State University for the Colorado Water Conservation Board, May 1966.

Eakins, Wynn, and Ellis, M.S., 1987, Coal resources of the 

Castle Rock 1/2°×1° quadrangle and adjacent area, Colorado: Colorado Geological Survey Resource Series 25, 

135 p.

Eberle, J.J., 2003, Puercan mammalian systematics and biostratigraphy in the Denver Formation, Denver Basin, Colorado: Rocky Mountain Geology, v. 38, no. 1, p. 143–169.

Ellis, Beth, Johnson, K.R., and Dunn, R.E., 2003, Evidence of 

an in-situ early Paleocene rainforest from Castle Rock, Colorado: Rocky Mountain Geology, v. 38, no. 1, p. 73–100.

Emmons, S.F., Cross, Whitman, and Eldridge, G.E., 1896, 

Geology of the Denver Basin in Colorado: U.S. Geological 

Survey Monograph 27, 526 p.

Environmental Systems Research Institute, Inc., 1999–2004, 

ArcGIS 9.2, accessed January 1, 2004 at http://www.esri.com/.

Epis, R.C., Scott, G.R., Taylor, R.B., and Chapin, C.E., 1976, 

Cenozoic volcanic, tectonic, and geomorphic features of 

central Colorado, in Epis, R.C., and Weimer, R.J., eds., 

Professional Contributions of Colorado School of Mines 

Number 8: Studies in Colorado Field Geology, p. 23–338.

Erker, H.W., and Romero, J.C., 1967, Ground-water resources 

of the upper Black Squirrel Creek Basin, El Paso County, 

Colorado: Prepared for the Colorado Groundwater Commission, January 1967.

Farnham, T.M., and Kraus, M.J., 2002, The stratigraphic and 

climatic significance of Paleogene alluvial paleosols in 

synorogenic strata of the Denver Basin, Colorado: Rocky 

Mountain Geology, v. 37, no. 2, p. 201–213.

Fenneman, N.M., 1931, Physiography of the western United 

States: New York, McGraw-Hill, 534 p.

Fetter, C.W., 1994, Applied hydrogeology: Third edition, 

MacMillan College Publishing Company, New York, 

New York, 691 p.

Gaggiani, N.G., Britton, L.J., Minges, D.R., and others, 

1987, Hydrology of Area 59, Northern Great Plains and 

Rocky Mountain coal provinces, Colorado and Wyoming: 

U.S. Geological Survey Open-File Report 83–153, 123 p.
88 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Graham, Glenn, and VanSlyke, George, 2004, Development 

of the regulatory framework for Denver Basin aquifers: The 

Mountain Geologist, v. 41, no. 4, p. 153–160.

Halford, K.J., and Hanson, R.T., 2002, User guide for the 

drawdown-limited, Multi-Node Well (MNW) package for the 

U.S. Geological Survey’s modular three-dimensional finitedifference ground-water flow model, versions MODFLOW-96 

and MODFLOW-2000: U.S. Geological Survey OpenFile Report 2002–293, 33 p., accessed August 31, 2009, at 

http://pubs.er.usgs.gov/usgspubs/ofr/ofr02293.

Hampton, E.R., 1975, Map showing availability of hydrologic 

data published by the U.S. Environmental Data Service and 

by the U.S. Geological Survey and cooperating agencies, 

Greater Denver area, Front Range Urban Corridor, Colorado: U.S. Geological Survey Miscellaneous Investigations 

Series Map I–856–C, scale 1:100,000, 1 sheet.

Hampton, E.R., Clark, G.A., and McNutt, M.H., 1974, Map 

showing availability of hydrologic data, Boulder-Fort 

Collins-Greeley area, Front Range Urban Corridor, Colorado: U.S. Geological Survey Miscellaneous Investigations 

Series Map I–855–C, scale 1:100,000, 1 sheet.

Hansen, W.R., Chronic, J., and Matelock, J., 1978, Climatography of the Front Range urban corridor and vicinity, 

Colorado: U.S. Geological Survey Professional Paper 1019, 

59 p.

Harbaugh, A.W., Banta, E.R., Hill, M.C., and McDonald, 

M.G., 2000, MODFLOW-2000, the U.S. Geological Survey 

modular ground-water model—User guide to modularization concepts and the groundwater flow process: U.S. Geological Survey Open-File Report 2000–92, 121 p.

Hicks, J.F., Johnson, K.R., Obradovich, J.D., Miggins, D.P., 

and Tauxe, Lisa, 2003, Magnetostratigraphy of upper Cretaceous (Maastrichtian) to lower Eocene strata of the Denver 

Basin, Colorado: Rocky Mountain Geology, v. 38, no. 1, 

p. 1–27.

Hill, M.C., Banta, E.R., Harbaugh, A.W., and Anderman, 

E.R., 2000, MODFLOW-2000, the U.S. Geological Survey 

modular ground-water model—User guide to the observation, sensitivity, and parameter-estimation processes and 

three post-processing programs: U.S. Geological Survey 

Open-File Report 2000–184, 209 p.

Hill, M.C., and Tiedeman, C.R., 2007, Effective groundwater model calibration, with analysis of data, sensitivities, 

predictions and uncertainty: New York, John Wiley & Sons, 

464 p.

Hillier, D.E., Brogden, R.E., and Schneider, P.A., Jr., 1978, 

Hydrology of the Arapahoe aquifer in the Englewood–

Castle Rock area south of Denver, Denver Basin, Colorado: 

U.S. Geological Survey Miscellaneous Investigations Series 

Map I–1043, 2 sheets.

Hunt, C.B., 1954, Pleistocene and recent deposits in the Denver area, Colorado: U.S. Geological Survey Bulletin 996–C, 

p. 91–139.

Hurr, R.T., and Schneider, P.A., Jr., and others, 1972a. Hydrogeologic characteristics of the valley-fill aquifer in the 

Brighton reach of the South Platte River valley, Colorado: 

U.S. Geological Survey Open-File Report, unnumbered.

Hurr, R.T., Schneider, P.A., Jr., and others, 1972b, Hydrogeologic characteristics of the valley-fill aquifer in the Greeley 

reach of the South Platte River valley, Colorado: U.S. Geological Survey Open-File Report, unnumbered.

Hurr, R.T., Schneider, P.A., Jr., and others, 1972c, Hydrogeologic characteristics of the valley-fill aquifer in the Weldona 

reach of the South Platte River valley, Colorado: U.S. Geological Survey Open-File Report, unnumbered.

Hurr, R.T., Schneider, P.A., Jr., and Minges, D.R., 1975, 

Hydrology of the South Platte River valley, northeastern 

Colorado: Colorado Water Resources Circular 28, 24 p.

Hutchinson, J.H., and Holroyd, P.A., 2003, Late Cretaceous 

and early Paleocene turtles of the Denver Basin, Colorado: 

Rocky Mountain Geology, v. 38, no. 1, p. 121–142.

Jenkins, E.D., 1961, Records, logs, and water-level measurements of selected wells and test holes and chemical analyses of ground water in Fountain, Jimmy Camp, and Black 

Squirrel valleys, El Paso County, Colorado: U.S. Geological 

Survey, Colorado Groundwater Basic-Data Report no. 3, 

25 p., 2 sheets.

Johnson, K.R., Reynolds, M.L., Werth, K.W., and Thomasson, J.R., 2003, Overview of the Late Cretaceous, early 

Paleocene and early Eocene megafloras of the Denver 

Basin, Colorado: Rocky Mountain Geology, v. 38, no. 1, 

p. 101–120.

Katich, P.J., and Bolyard, D.W., eds., 1963, Geology of the 

northern Denver Basin and adjacent uplifts: Rocky Mountain Association of Geologists, Denver, Colorado, 294 p.

Keith, J.R., and Maberry, J.O., 1973, Vegetation map of the 

Parker quadrangle, Arapahoe and Douglas Counties, Colorado: U.S. Geological Survey Folio of the Parker quadrangle, Colorado, Map I–770–N, 1 sheet.

Kelly, S.A., 2002, Unroofing of the southern Front Range, 

Colorado—A view from the Denver Basin: Rocky Mountain Geology, v. 37, no. 2, p. 189–200.

Kelly, S.A., and Blackwell, D.D., 2002, Subsurface temperatures in the southern Denver Basin, Colorado: Rocky 

Mountain Geology, v. 37, no. 2, p. 215–227.

Kent, H.C., and Porter, K.W., eds., 1980, Colorado geology: 

Rocky Mountain Association of Geologists, Denver, Colorado, 258 p.
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 89

Kirkham, R.M., 1978, Coal mines and coal analyses of the 

Denver and Cheyenne basins, Colorado: Colorado Geological Survey Open-File Report 78–9, 104 p.

Kirkham, R.M., and Ladwig, L.R., 1977, Preliminary investigation and feasibility study of environmental impact of 

energy resource development in the Denver Basin: Colorado 

Geological Survey Open-File Report 77–1, 30 p.

Kirkham, R.M., and Ladwig, L.R., 1979, Coal resources of the 

Denver and Cheyenne basins, Colorado: Colorado Geological Survey Resource Series 5, 70 p., 5 plates.

Kirkham, R.M., and Ladwig, L.R., 1980, Energy resources 

of the Denver and Cheyenne basins, Colorado: Colorado 

Geological Survey, Environmental Geology #12, 258 p., 

2 plates.

Kiteley, L.W., 1977, Shallow marine deposits in the upper 

Cretaceous Pierre Shale of the northern Denver Basin 

and their relation to hydrocarbon accumulation: Rocky 

Mountain Association of Geologists, 1977 Symposium, 

p. 197–211.

Kittleson, K.L., 2004, The effect of reverse faulting on the 

thickness, depth, and water quality of the Laramie–Fox 

Hills aquifer in the western Denver Basin, Colorado: The 

Mountain Geologist, v. 41, no. 4, p. 185–194.

Konikow, L.F., 1975, Hydrogeological maps of the alluvial 

aquifer in and adjacent to the Rocky Mountain Arsenal, 

Colorado: U.S. Geological Survey Open-File Report 74–342, 

1 sheet.

Lapey, L.A., 2001, Hydrogeologic parameters of the Kiowa 

research core, Kiowa, Colorado: Fort Collins, Colorado 

State University, Unpublished Master of Science thesis, 

67 p.

Lapey-Woodard, L.A., Sanford, W., and Raynolds, R.G., 2002, 

Stratigraphic variability of specific yield within bedrock 

aquifers of the Denver Basin, Colorado: Rocky Mountain 

Geology, v. 37, no. 2, p. 229–236.

Leake, S.A., and Lilly, M.R., 1997, Documentation of a computer program (FHB1) for assignment of transient specifiedflow and specified-head boundaries in applications of the 

modular finite-difference ground-water flow model (MODFLOW): U.S. Geological Suvey Open-File Report 97–571, 

50 p.

Livingston, R.K., Bingham, D.L., and Klein, J.M., 1975, 

Appraisal of water resources of northwestern El Paso County, 

Colorado: U.S. Geological Survey Colorado Water-Resources 

Circular no. 22, 74 p.

Livingston, R.K., Klein, J.M., and Bingham, D.L., 1976, 

Water resources of El Paso County, Colorado: U.S. Geological Survey Colorado Water-Resources Circular no. 32, 85 p.

Lohman, S.W., 1979, Ground-water hydraulics: U.S. Geological Survey Professional Paper 708, 70 p.

Madole, R.F., 2003, Geologic map of the Falcon NW quadrangle, El Paso County, Colorado: Colorado Geological Survey 

Open-File Report 03–9, 16 p., scale 1:24,000, 1 sheet.

Madole, R.F., and Thorson, J.P., 2003, Geologic map of the 

Elsmere quadrangle, El Paso County, Colorado: Colorado Geological Survey Open-File Report 02–2, 26 p., 

scale 1:24,000, 1 sheet.

Major, T.J., Robson, S.G., Romero, J.C., and Zawistowski, 

S., 1983, Hydrogeologic data from parts of the Denver 

Basin, Colorado: U.S. Geological Survey Open-File 

Report 83–274, 425 p.

McCabe, G.J., Palecki, M.A., and J.L. Betancourt, 2004, 

Pacific and Atlantic Ocean influences on multidecadal 

drought frequency in the United States: Proceedings of 

the National Academy of Sciences of the United States of 

America, v. 101, no. 12, p. 4136–4141.

McConaghy, J.A., Chase, G.H., Boettcher, A.J., and Major, 

T.J., 1964, Hydrogeologic data of the Denver Basin, 

Colorado: Colorado Water Conservation Board, Basic-Data 

Report no. 15, 224 p.

McDonald, M.G., and Harbaugh, A.W., 1988, A modular 

three-dimensional finite-difference ground-water flow 

model: U.S. Geological Survey Techniques of WaterResources Investigations, book 6, chap. A1, 586 p.

Moore, J.E., Raynolds, R.G., and Dechesne, M., 2007, Bedrock aquifers and population growth in the Denver Basin, 

Colorado, USA: Episodes, v. 30, no. 2, p. 115–118.

Morgan, M.L., McHarge, J.L., and Barkmann, P., 2005a, 

Geologic map of the Sedalia quadrangle, Douglas County, 

Colorado: Colorado Geological Survey Open-File 

Report 05–06, 19 p., scale 1:24,000, 1 sheet.

Morgan, M.L., Temple, J., Grizzell, M., and Barkmann, P., 

2005b, Geologic map of the Dawson Butte quadrangle, 

Douglas County, Colorado: Colorado Geological Survey 

Open-File Report 04–07, 19 p., scale 1:24,000, 1 sheet.

Morse, D.G., 1979, Paleogeography and tectonic implications of the late Cretaceous to middle Tertiary rocks of the 

southern Denver Basin, Colorado: Baltimore, Md., Johns 

Hopkins University, unpublished Ph.D. thesis, 344 p.

Murray, D.K., 1980, Coal in Colorado, in Colorado geology: 

Rocky Mountain Association of Geologists, p. 205–216.

Nadler, C.T., and Schumm, S.A., 1981, Metamorphosis of 

South Platte and Arkansas Rivers, eastern Colorado: Physical Geology, v. 2, no. 22, p. 95–115.

National Oceanic and Atmospheric Administration, 2004, 

1931–2003, Monthly surface data for Colorado, accessed 

October 29, 2004, at http://www.ncdc.noaa.gov/oa/ncdc.html.
90 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Nelson, Haley, Patterson, & Quirk, Inc., 1967, Ground-water 

resources of the Lost Creek drainage basin, Weld, Adams, 

and Arapahoe Counties, Colorado: Prepared for the Colorado Groundwater Commission by Nelson, Haley, Patterson, & Quirk, Inc., Consulting Engineers and Geologists, 

June 1967.

Nesse, W.D., 2006, Geometry and tectonics of the Laramide 

Front Range, Colorado: The Rocky Mountain Association of Geologists, The Mountain Geologist, v. 43, no. 1, 

p. 25–44.

Nichols, D.J., 1999, Summary of Tertiary coal resources of the 

Denver Basin, Colorado: U.S. Geological Survey Professional Paper 1625–A, Part V, Chapter SD, accessed February 24, 2009, at http://pubs.usgs.gov/pp/p1625a/Chapters/

SD.pdf.

Nichols, D.J., and Fleming, R.F, 2002, Palynology and palynostratigraphy of Maastrichtian, Paleocene, and Eocene 

strata in the Denver Basin, Colorado: Rocky Mountain 

Geology, v. 37, no. 2, p. 135–163.

Niswonger, R.G., and Prudic, D.E., 2005, Documentation of 

the streamflow-routing (SFR2) package to include unsaturated flow beneath streams—A modification to SFR1: 

U.S. Geological Survey Techniques and Methods, book 6, 

chap. A13, 47 p.

Norris, J.M., Robson, S.G., and Parker, R.S., 1983, Summary 

of hydrologic information for the Denver coal region, Colorado: U.S. Geological Survey Open-File Report 84–4337, 

68 p.

Nwangwu, Uka, 1977, Depositional environments, upper 

Pierre Shale, Denver Basin, Colorado: Rocky Mountain 

Association of Geologists, 1977 Symposium, p. 213–222.

Obradovich, J.D., 2002, Geochronology of Laramide synorogenic strata in the Denver Basin, Colorado: Rocky Mountain Geology, v. 37, no. 2, p. 165–171.

Paschke, S.S., 1992, Evaluating the hydrogeology of the 

Pleistocene Nussbaum Alluvium, Colorado, using vertical 

variability analysis and numerical modeling: Golden, Colorado School of Mines, Unpublished Master of Engineering 

report, 152 p.

Pearl, R.H., 1974, Geology of ground-water resources in Colorado, an introduction: Colorado Geological Survey Special 

Publication 4, 47 p.

Perry, M.J., and Mackun, P.J., 2002, Population change and 

distribution 1990 to 2000: U.S. Census Bureau, Census 

2000 Brief, C2KBR/01-2, 7 p., accessed February 15, 2009, 

at http://www.census.gov/prod/2001pubs/c2kbr01-2.pdf.

Poeter, E.P., Hill, M.C., Banta, E.R., Mehl, Steffen, and 

Christensen, Steen, 2005, UCODE_2005 and six other computer codes for universal sensitivity analysis, calibration, 

and uncertainty evaluation constructed using the JUPITER 

API: U.S. Geological Survey Techniques and Methods, 

book 6, chap. A11, 283 p., accessed August 31, 2009, at 

http://pubs.er.usgs.gov/usgspubs/tm/tm6A11.

Raforth, R.L., and Jehn, J.L., 1990, Preliminary results of the 

coring of the Denver Basin aquifers: Groundwater Engineering and Management Conference, 1990, Proceedings, 

p. 235–246.

Raynolds, R.G., 2002, Upper Cretaceous and Tertiary stratigraphy of the Denver Basin, Colorado: Rocky Mountain 

Geology, v. 37, no. 2, p. 111–134.

Raynolds, R.G., 2004, Stratigraphy and water levels in the 

Arapahoe aquifer, Douglas County area, Denver Basin, 

Colorado: The Mountain Geologist, v. 41, no. 4, p 195–210.

Raynolds, R.G., and Johnson, K.R., 2002, Drilling of the 

Kiowa core, Elbert County, Colorado: Rocky Mountain 

Geology, v. 37, no. 2, p. 105–109.

Raynolds, R.G., and Johnson, K.R., 2003, Synopsis of the 

stratigraphy and paleontology of the uppermost Cretaceous 

and lower Tertiary strata in the Denver Basin, Colorado: 

Rocky Mountain Geology, v. 38, no. 1, p. 171–181.

Raynolds, R.G., Johnson, K.R., Arnold, L.R., Farnham, 

T.M., Fleming, R.F., Hicks, J.F., Kelley, S.A., Lapey, L.A., 

Nichols, D.J., Obradovich, J.D., and Wilson, M.D., 2001, 

The Kiowa core—A continuous drill core through the Denver 

Basin bedrock aquifers at Kiowa, Elbert County, Colorado: 

U.S. Geological Survey Open-File Report 2001–0185, 72 p.

Reilly, T.E., 2005, Assessing the Nation’s groundwater 

resources: U.S. Geological Survey 125th anniversary articles, accessed August 31, 2009, at http://www.usgs.gov/125/

articles/groundwater.html.

Reilly, T.E., Dennehy, K.F., Alley, W.M., and Cunningham, 

W.L, 2008, Groundwater availability in the United States: 

U.S. Geological Survey Circular 1323, 70 p.

Richardson, G.B., 1915, Castle Rock folio, Colorado: U.S. Geological Survey Geologic Atlas of the United States, 14 p.

Riverside Technology, Inc., 2005, SPDSS 2001 Division 1 

ditch service areas: Online data accessed October 11, 2006, 

at http://cdss.state.co.us/DNN/GIS/tabid/67/Default.aspx.

Roberts, S.B., 2005, Coal in the Front Range urban corridor—

An overview of coal geology, coal production, and coal-bed 

methane potential in selected areas of the Denver Basin, 

Colorado, and the potential effects of historical coal mining on development and land-use planning, in Chapter F 

of Fishman, N.S., ed., Energy Resource Studies, Northern 

Front Range, Colorado, U.S. Geological Survey Professional Paper 1698, 170 p.
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 91

Robson, S.G., 1983, Hydraulic characteristics of the principal 

bedrock aquifers in the Denver Basin, Colorado: U.S. Geological Survey, Hydraulic Investigations Atlas HA–659, 

scale 1:500,000, 3 sheets.

Robson, S.G., 1987, Bedrock aquifers in the Denver Basin, 

Colorado—A quantitative water-resources appraisal: 

U.S. Geological Survey Professional Paper 1257, 73 p.

Robson, S.G., 1989, Alluvial and bedrock aquifers of the Denver Basin—Eastern Colorado’s dual groundwater resource: 

U.S. Geological Survey Water-Supply Paper 2302, 40 p.

Robson, S.G., 1995, Preparation of specific-yield logs for clastic bedrock aquifers: Groundwater, v. 33, n. 1, p. 4–10.

Robson, S.G., 1996, Geohydrology of the shallow aquifers 

in the Denver metropolitan area, Colorado: U.S. Geological Survey Hydraulic Investigations Atlas HA–736, 

scale 1:50,000, 5 sheets. 

Robson, S.G., Arnold, L.R., and Heiny, J.S., 2000a, Geohydrology of the shallow aquifers in the Greeley-Nunn area, 

Colorado: U.S. Geological Survey Hydrologic Investigations Atlas, HA–746A, scale 1:50,000, 5 sheets.

Robson, S.G., Arnold, L.R., and Heiny, J.S., 2000b, Geohydrology of the shallow aquifers in the Fort Collins-Loveland 

area, Colorado: U.S. Geological Survey Hydrologic Investigations Atlas, HA–746B, scale 1:50,000, 5 sheets.

Robson, S.G., and Banta, E.R., 1987, Geology and hydrology of the deep bedrock aquifers in eastern Colorado: 

U.S. Geological Survey Water-Resources Investigations 

Report 85–4240, 6 plates.

Robson, S.G., and Banta, E.R., 1990, Determination of specific storage by measurement of aquifer compression near a 

pumping well: Groundwater, v. 28, no. 6, p. 868–874.

Robson, S.G., and Banta, E.R., 1993, Data from core analysis, 

aquifer testing, and geophysical logging of Denver Basin 

bedrock aquifers at Castle Pines, Colorado: U.S. Geological 

Survey Open-File Report 93–442, 94 p.

Robson, S.G., Heiny, J.S., and Arnold, L.R., 2000a, Geohydrology of the shallow aquifers in the Fort LuptonGilcrest area, Colorado: U.S. Geological Survey Hydrologic 

Investigations Atlas, HA–746C, scale 1:50,000, 5 sheets.

Robson, S.G., Heiny, J.S., and Arnold, L.R., 2000b, Geohydrology of the shallow aquifers in the Boulder-Longmont 

area, Colorado: U.S. Geological Survey Hydrologic Investigations Atlas HA–746D, scale 1:50,000, 5 sheets.

Robson, S.G., and Romero, J.C., 1981a, Geologic structure, hydrology, and water quality of the Dawson aquifer 

in the Denver Basin, Colorado: U.S. Geological Survey 

Hydrologic Investigations Atlas HA–643, scale 1:500,000, 

3 sheets.

Robson, S.G., and Romero, J.C., 1981b, Geologic structure, hydrology, and water quality of the Denver aquifer 

in the Denver Basin, Colorado: U.S. Geological Survey 

Hydrologic Investigations Atlas HA–646, scale 1:500,000, 

3 sheets.

Robson, S.G., Romero, J.C., and Zawistowski, S., 1981, 

Geologic structure, hydrology, and water quality of the 

Arapahoe aquifer in the Denver Basin, Colorado: U.S. Geological Survey Hydrologic Investigations Atlas HA–646, 

scale 1:500,000, 3 sheets.

Robson, S.G., Van Slyke, G., and Graham, G., 1998, Structure, outcrop, and subcrop of the bedrock aquifers along the 

western margin of the Denver Basin, Colorado: U.S. Geological Survey Hydrologic Investigations Atlas HA–742, 

scale 1:50,000, 5 sheets.

Robson, S.G., Wacinski, A., Zawistowski, S., and Romero, 

J.C., 1981, Geologic structure, hydrology, and water quality 

of the Laramie–Fox Hills aquifer in the Denver Basin, Colorado: U.S. Geological Survey Hydrologic Investigations 

Atlas, HA–650, Scale 1:500,000, 3 sheets.

Rocky Mountain Association of Geologists, 1978, Energy 

resources of the Denver Basin: Rocky Mountain Association of Geologists, Denver, Colorado, 230 p.

Romero, J.C., 1976, Ground-water resources of the bedrock 

aquifers of the Denver Basin: Colorado Division of Water 

Resources Report, 109 p.

Romero, J.C., and Hampton, E.R., 1972, Maps showing 

the approximately configuration and depth to the top of 

the Laramie–Fox Hills aquifer, Denver Basin, Colorado: 

U.S. Geological Survey Miscellaneous Investigations 

Map I–791.

Rowley, P.D., Himmelreich, J.W., Kupfer, D.H., and Siddoway, 

C.S., 2003, Geologic map of the Cheyenne Mountain 

Quadrangle, El Paso County, Colorado: Colorado Geological 

Survey Open-File Report 02–5, 30 p., scale 1:24,000, 1 sheet.

Schneider, P.A., Jr., 1980, Water-supply assessment of the 

Laramie–Fox Hills aquifer in parts of Adams, Boulder, 

Jefferson, and Weld Counties, Colorado: U.S. Geological 

Survey Open-File Report 80–327, 21 p.

Scott, G.R., 1960, Subdivision of the Quaternary alluvium east 

of the Front Range near Denver, Colorado: Bulletin of the 

Geologic Society of America, v. 71, p. 1541–1544.

Scott, G.R., 1963a, Quaternary geology and geomorphic history of the Kassler quadrangle, Colorado: U.S. Geological 

Survey Professional Paper 421–A, 70 p.

Scott, G.R., 1963b, Bedrock geology of the Kassler quadrangle, Colorado: U.S. Geological Survey Professional 

Paper 421–B, 70 p.
92 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Scott, G.R., 1963c, Nussbaum Alluvium of Pleistocene (?) age 

at Pueblo, Colorado: U.S. Geological Survey Professional 

Paper 475–C, p. C49–C52.

Scott, G.R., Taylor, R.B., Epis, R.B., and Wobus, R.A., 1978, 

Geologic map of the Pueblo 1°×2° quadrangle, southcentral Colorado: U.S. Geological Survey Miscellaneous 

Investigations Series Map I–1022, scale 1:250,000, 2 sheets.

Shapiro, S.S., and Wilk, M.B., 1965, An analysis of variance 

test for normality (complete samples): Biometrika, v. 32, 

n. 3/4, p. 591–611.

Sharps, J.A., 1976, Geologic map of the Lamar quadrangle, 

Colorado and Kansas: U.S. Geological Survey Miscellaneous Investigations Series Map I–944, scale 1:250,000, 

2 sheets.

Sharps, J.A., 1980, Geologic map of the Limon 1°×2° quadrangle, Colorado and Kansas: U.S. Geological Survey Miscellaneous Investigations Series Map I–1250, 

scale 1:250,000, 2 sheets.

Smith, R.O., Schneider, P.A., Jr., and Petri, L.R., 1964, 

Ground-water resources of the South Platte River basin in 

western Adams and southwestern Weld Counties, Colorado: 

U.S. Geological Survey Water-Supply Paper 1658, 132 p.

Soister, P.E., 1967, Relation of the Nussbaum Alluvium 

(Pleistocene) to the Ogallala Formation (Pliocene) and to 

the Platte-Arkansas divide, southern Denver Basin, Colorado: U.S. Geological Survey Professional Paper 575–D, 

p. D39–D346.

Soister, P.E., 1972, Geologic map and lignite deposits of the 

Strasburg NW quadrangle, Arapahoe and Adams Counties, Colorado: U.S. Geological Survey Open-File Report, 

2 sheets.

Soister, P.E., 1974, A preliminary report on a zone containing 

thick lignite beds, Denver Basin, Colorado: U.S. Geological 

Survey Open-File Report 74–27, 48 p.

Soister, P.E., 1978a, Geologic setting of coal in Denver Basin: 

Rocky Mountain Association of Geologists 1978 Symposium, p. 183–185.

Soister, P.E., 1978b, Stratigraphy of uppermost Cretaceous and 

lower Tertiary rocks of the Denver Basin: Rocky Mountain 

Association of Geologists 1978 Symposium, p. 223–230.

Soister, P.E., and Tschudy, R.H., 1978, Eocene rocks in the 

Denver Basin: Rocky Mountain Association of Geologists 

1978 Symposium, p. 231–235.

Sterne, E.J., 2006, Stacked, “evolved” triangle zones along the 

southeastern flank of the Colorado Front Range: The Mountain Geologist, v. 43, no. 1, p. 65–92.

Taylor, C.J., and Alley, W.M., 2001, Ground-water-level 

monitoring and the importance of long-term water-level 

data: U.S. Geological Survey Circular 1217, 68 p.

Thorson, J.P., 2003, Geologic map of the Black Forest 

quadrangle, El Paso County, Colorado: Colorado Geological Survey Open-File Report 03–6, 19 p., scale 1:24,000, 

1 sheet.

Thorson, J.P., 2004a, Geologic map of the Castle Rock South 

7.5-minute quadrangle, Douglas County, Colorado: Colorado Geological Survey Open-File Report 04–05, 19 p., 

scale 1:24,000, 1 sheet.

Thorson, J.P., 2004b, Geologic map of the Cherry Valley 

School 7.5-minute 1uadrangle, Elbert, Douglas, and El Paso 

Counties, Colorado: Colorado Geological Survey Open-File 

Report 04–06, 19 p., scale 1:24,000, 1 sheet.

Thorson, J.P., 2005a, Geologic map of the Castle Rock 

North quadrangle, Douglas County, Colorado: Colorado 

Geological Survey Open-File Report 2005–02, 19 p., 

scale 1:24,000, 1 sheet.

Thorson, J.P., 2005b, Geologic map of the east half of the Larkspur quadrangle, Douglas and El Paso Counties, Colorado: 

Colorado Geological Survey Open-File Report 2005–07, 

19 p., scale 1:24,000, 1 sheet.

Thorson, J.P., 2006, Geologic map of the Russellville Gulch 

quadrangle, Douglas and Elbert Counties, Colorado: Colorado Geological Survey Open-File Report 2006–08, 19 p., 

scale 1:24,000, 1 sheet.

Thorson, J.P., 2007, Provenance and geochemistry of 

Laramide volcanic pebbles in the Denver Basin: Geological 

Society of America Abstracts with Programs, v. 39, no. 6, 

p. 26.

Thorson, J.P., 2008, Geologic map of the Ponderosa Park 

quadrangle, Douglas and Elbert Counties, Colorado: Colorado Geological Survey Open-File Report 2007–04, 19 p., 

scale 1:24,000, 1 sheet.

Thorson, J.P., Carroll, C.J., and Morgan, M.L., 2002, Geologic map of the Pikeview 7.5-minute quadrangle, El Paso 

County, Colorado: Colorado Geological Survey Open-File 

Report 2001–03, 19 p., scale 1:24,000, 1 sheet.

Thorson, J.P., and Himmelreich, J.W., 2004, Geologic map 

of the Greenland quadrangle, Douglas and El Paso Counties, Colorado: Colorado Geological Survey Open-File 

Report 2003–09, 19 p., scale 1:24,000, 1 sheet.

Thorson, J.P., and Madole, R.F., 2003, Geologic map of the 

Monument quadrangle, El Paso County, Colorado: Colorado Geological Survey Open-File Report 2002–4, 26 p., 

scale 1:24,000, 1 sheet.
Introduction, Conceptual Model, Framework, and Groundwater Availability of the Denver Basin Aquifer System 93

Topper, Ralf, Spray, K.L., Bellis, W.H., Hamilton, J.L., and 

Barkmann, P.E., 2003, Ground Water Atlas of Colorado: 

Colorado Geological Survey Special Publication 53, 210 p.

Trescott, P.C., 1975, Documentation of finite-difference model 

for simulation of three-dimensional ground-water flow: 

U.S. Geological Survey Open-File Report 75–438, 32 p.

Trescott, P.C., and Larson, S.P., 1976, Supplement to OpenFile Report 75–438, Documentation of finite-difference 

model of three-dimensional ground-water flow: U.S. Geological Survey Open-File Report 76–591, 21 p.

Trescott, P.C., Pinder, G.F., and Larson, S.P., 1976, Finite 

difference model for aquifer simulation in two dimensions 

with results of numerical experiments: U.S. Geological Survey Techniques of Water-Resources Investigations, book 7, 

chap. Cl, 116 p.

Trimble, D.E., 1980a, The geologic story of the Great Plains: 

U.S. Geological Survey Bulletin 1493, 55 p.

Trimble, D.E., 1980b, Cenozoic tectonic history of the Great 

Plains contrasted with that of the southern Rocky Mountains—A synthesis: The Mountain Geologist, v. 17, no. 3, 

p. 59–69.

Tweto, Ogden, 1979, Geologic map of Colorado: U.S. Geological Survey Special Geologic Map, 1 sheet.

Tweto, Ogden, 1980, Summary of Laramide orogeny in 

Colorado, in Kent, H.C., and Porter, K.W., eds., Colorado 

geology: Rocky Mountain Association of Geologists, 

p. 219–134.

U.S. Geological Survey, 1999, National elevation dataset: 

U.S. Geological Survey Fact Sheet 148–99, accessed 

August 31, 2009, at http://erg.usgs.gov/isb/pubs/factsheets/

fs14899.html.

VanSlyke, G., Romero, J.C., Moravec, G., and Wacinski, A, 

1988a, Geologic structure, sandstone/siltstone isolith, and 

location of non-tributary ground water for the Dawson aquifer, Denver Basin, Colorado: Colorado Division of Water 

Resources, Denver Basin Atlas no. 1 (DBA–1), 3 plates.

VanSlyke, G., Romero, J.C., Moravec, G., and Wacinski, A, 

1988b, Geologic structure, sandstone/siltstone isolith, and 

location of non-tributary ground water for the Denver aquifer, Denver Basin, Colorado: Colorado Division of Water 

Resources, Denver Basin Atlas no. 2 (DBA–2), 3 plates.

VanSlyke, G., Romero, J.C., Moravec, G., and Wacinski, 

A, 1988c, Geologic structure, sandstone/siltstone isolith, 

and location of non-tributary ground water for the Arapahoe aquifer, Denver Basin, Colorado: Colorado Division 

of Water Resources, Denver Basin Atlas no. 3 (DBA–3), 

3 plates.

VanSlyke, G., Romero, J.C., Moravec, G., and Wacinski, A, 

1988d, Geologic structure, sandstone/siltstone isolith, and 

location of non-tributary ground water for the Laramie–Fox 

Hills aquifer, Denver Basin, Colorado: Colorado Division 

of Water Resources, Denver Basin Atlas no. 4 (DBA–4), 

3 plates.

Wahl, K. L., and Wahl, T. L., 1988, Effects of regional 

groundwater declines on streamflows in the Oklahoma 

panhandle: Symposium on Water-Use Data for Water 

Resources Management, American Water Resources Association, Tucson, Arizona, p. 239–249.

Watts, K.R., 1995, Hydrogeology and simulation of flow 

between the alluvial and bedrock aquifers in the upper Black 

Squirrel Creek Basin, El Paso County, Colorado: U.S. Geological Survey Water-Resources Report 94–4238, 82 p.

Weimer, R.J, 1973, Guide to uppermost Cretaceous stratigraphy, Central Front Range, Colorado—Deltaic sedimentation, growth faulting and early Laramide crustal movement: 

The Mountain Geologist, v. 10, no. 3, p. 53–97.

Weimer, R.J., and LeRoy, L.W., 1987, Paleozoic-Mesozoic 

section—Red Rocks Park, I–70 road cut, and Rooney Road, 

Morrison area, Jefferson County, Colorado: Geological 

Society of America Centennial Field Guide, Rocky Mountain Section, p. 315–319.

Wheeler, E.A., and Michalski, T.C., 2003, Paleocene and 

early Eocene woods of the Denver Basin, Colorado: Rocky 

Mountain Geology, v. 38, no. 1, p. 29–43.

Willard Owens Associates, 1971, Groundwater resources of 

the Big Sandy Creek drainage area southeastern Colorado: 

Prepared for the Colorado Division of Water Resources, 

March 1971.

Wilson, W.W., 1965, Pumping tests in Colorado: U.S. Geological Survey Colorado Groundwater Series Circular no. 11, 

361 p.

Wilson, M.D., 2002, Petrographic provenance analysis of 

Kiowa core sandstone samples, Denver Basin, Colorado: 

Rocky Mountain Geology, v. 37, no. 2, p. 173–187.

Wilson, J.D., and Naff, R.L., 2004, The U.S. Geological 

Survey modular ground water model—GMG linear equation solver package documentation: U.S. Geological Survey 

Open-File Report 2004–1261, 47 p.

Wireman, Mike, and Romero, J.C., 1989, Bibliography of 

geology and ground water geology for the Denver Basin, 

Colorado: Colorado Division of Water Resources Office of 

the State Engineer, 12 p.

Wray, L.L., and Koenig, N.V., 2001, The coalbed methane 

potential in the Upper Cretaceous to Early Tertiary Laramie 

and Denver Formations, Denver Basin, Colorado: Colorado 

Geological Survey Open File Report 01–17, 2 compact disks.

Chapter B. Effects of Development on Groundwater 

Availability in the Denver Basin Aquifer System, Colorado

By Suzanne S. Paschke, Edward R. Banta, and David W. Litke

(Emmons and others, 1896; Darton, 1905), and most of the 

artesian wells were eventually abandoned. Since the 1950s, the 

Denver Basin bedrock aquifers have been used for domestic and 

municipal water supply, industrial and commercial uses, and to 

a lesser extent, for agricultural and urban irrigation. The Late 

Cretaceous- to Tertiary-age confined sandstone aquifers that 

compose the Denver Basin bedrock aquifer system are overlain 

by more permeable Quaternary sand and gravel alluvial deposits, primarily along present-day stream channels, that form a 

productive water-table aquifer where saturated. Since the 1950s, 

the alluvial aquifer has been used primarily for agricultural irrigation, while the bedrock aquifers have been used primarily for 

municipal and domestic water supplies in response to population growth as described in the section “Denver Basin Pumping 

History” in this chapter.

Changes in land use, water use, and climate have affected 

groundwater availability in the Denver Basin as described in the 

section “Effects of Development on Groundwater Availability 

in the Denver Basin” of this chapter. In areas of agricultural 

or urban land use, irrigation using local and imported surface 

water and pumped groundwater has increased water use on the 

landscape, which has generally increased recharge to, and thus 

groundwater availability in, the alluvial aquifer. Simultaneously, 

increased pumping from the bedrock aquifers has generally 

decreased discharge from the bedrock aquifers to the alluvial 

aquifer, increased downward interaquifer flow between bedrock 

units, decreased the amount of available groundwater in bedrock storage, and lowered hydraulic heads in bedrock aquifers. 

Climatic variation affects the amount of water available for 

precipitation recharge to the aquifer system, with less precipitation recharge in dry years and more precipitation recharge in 

wet years.

Land Use

Land use in the Denver Basin is changing from grasslands 

with sparse native shrubs and trees to land uses of agriculture, 

urbanized metropolitan areas, suburban residential housing, 

and rural residential. Present-day (2010) land use in the Denver 

Basin ranges from irrigated and nonirrigated agriculture along 

the South Platte River (fig. B1) to high-density urban development in downtown Denver (fig. B2). Based on year 2001 

National Land Cover data (U.S. Geological Survey, 2001a; 

Homer and others, 2004), 60 percent of the Denver Basin area 

is nonirrigated grassland and rangeland, 11 percent is irrigated 

agriculture, 16 percent is nonirrigated agriculture, 9 percent is 

Introduction

Population growth and associated land development for 

agricultural, commercial, and residential uses along the semiarid Colorado Front Range urban corridor have increased competition for limited water resources including Denver Basin 

groundwater. This study evaluated the effects of development 

and changing land use on the Denver Basin groundwater 

system by using a transient, three-dimensional groundwater 

flow model to represent conditions from predevelopment 

(pre-1880) through 2003 (Chapter C present details of the 

groundwater flow model). This Professional Paper chapter (Chapter B) describes the development of groundwater 

resources and the effects of that development on groundwater 

availability in the Denver Basin aquifer system on the basis of 

modeling results. This chapter presents the simulated spatial and temporal changes to the groundwater budget and its 

components including recharge, discharge, and aquifer storage 

for the entire aquifer system and separately for the alluvial 

and bedrock aquifers. The simulated effects of development 

on water levels and groundwater flow directions also are 

presented along with model predictions of future hypothetical 

conditions and a discussion of monitoring needs. The chapter 

concludes with implications for groundwater sustainability in 

the Denver Basin.

Development of the 

Denver Basin Aquifer System

The Denver Basin bedrock aquifers were discovered in the 

late 1800s when artesian groundwater conditions were encountered by exploration geologists drilling for coal near Denver 

in what are now recognized as sandstones of the Arapahoe 

and Laramie–Fox Hills aquifers (Cross and others, 1884; 

Emmons and others, 1896). At the time, downtown Denver 

was a bustling center of commerce and transportation for gold 

and silver mining in the Rocky Mountain Front Range and 

for agriculture (crops and cattle) along the South Platte River 

valley. The groundwater resource was heavily used in the city 

for steam baths, laundry facilities, public drinking fountains, 

public works, breweries, and even to power hotel elevators 

(Emmons and others, 1896). However, the large number and 

poor construction of wells during the late 1880s quickly dissipated the artesian pressure tapped by wells in downtown Denver 
96 Groundwater Availability of the Denver Basin Aquifer System, Colorado

developed urban and suburban land use, 3 percent is forested, 

and 1 percent is open water. Irrigated and nonirrigated agricultural land is primarily in the northern basin along the South 

Platte River valley with nonirrigated grassland covering much 

of the central and southern basin (fig. B3). Developed urban 

and suburban land use is primarily along the western side of the 

Denver Basin (fig. B3) and is associated with the metropolitan 

areas of Denver and Colorado Springs. The cities of Loveland 

and Fort Collins (about 50 miles north of Loveland) are considered part of the Front Range urban corridor, but they do not 

overlie the Denver Basin aquifer system or rely on the bedrock 

aquifers for water supply. Small towns, rural residences, and 

farms are spread across the less-populated parts of the basin, 

including forested areas at the higher elevations along the 

Palmer Divide northeast of Colorado Springs (fig. B3).

Population of the metropolitan areas over the Denver 

Basin aquifers has approximately doubled from 1.3 million 

in 1970 to about 2.7 million in 2005 (fig. B4) (T.L. Arnold, 

U.S. Geological Survey, written commun., 2009). Development has been especially rapid and extensive on the west side of 

the basin between Denver and Colorado Springs with Douglas 

County experiencing the fastest population and housing growth 

of any county in the United States in 2002 (Perry and Mackun, 

2002). Three general areas of recent development rely heavily 

on Denver Basin groundwater for municipal water supply. The 

area south of Littleton and encompassing Parker, Franktown, 

and Castle Rock (herein referred to as the south Denver metropolitan area; figs. B3 and B5) has undergone a transformation 

from rural residential land use to sprawling suburban land use 

(fig. B6) as part of this population increase. Land use for 2001 

in the southern half of the south Denver metropolitan area 

is largely shown as grassland and forest (fig. B3) rather than 

urban/suburban development because much of the development 

in this area occurred since compilation of the 2001 land-use 

datasets. Semiarid rangeland and rural-residential areas east 

of Monument and northeast of Colorado Springs have experienced similar rapid development (hereinafter referred to as the 

Monument area; fig. B3). A third area of suburban growth is 

developing north and northeast of Denver in Weld and Adams 

Counties (hereinafter referred to as the northern area; fig. B3). 

Rangeland and dryland farms in the northern area also are being 

converted to urban/suburban land use.

Water Use and Groundwater Administration

The State of Colorado and the Colorado Division of 

Water Resources (CDWR) administer State water law including groundwater withdrawal from the Denver Basin aquifers. 

Colorado water law is based on the prior-appropriation doctrine 

of first-in-time, first-in-right, which holds that older water rights 

are senior to more recent water rights (Graham and VanSlyke, 

2004). The doctrine applies to surface water and groundwater 

that is tributary to surface water (tributary groundwater), and, as 

a result of the administrative system, older municipalities such 

as Denver generally hold water rights senior to more recently 

established municipalities and suburbs. Public water supply is 

provided to Colorado residents by numerous local municipal 

utilities. For example, the Denver metropolitan area is serviced 

by the Denver Water Board, Colorado Springs is serviced by 

Colorado Springs Utilities, and Aurora is serviced by the City 

of Aurora. Smaller municipalities, suburbs, and rural towns are 

serviced by their respective municipal utilities. In rural areas, 

water is generally self-supplied from groundwater for domestic 

and irrigation purposes.

Public water suppliers rely on a combination of surface 

water from the mountains of the Front Range, groundwater 

from alluvial aquifers, and groundwater from Denver Basin 

bedrock aquifers (Colorado Water Conservation Board, 2004). 

Public water supply in the established municipal areas of 

Denver and Colorado Springs is primarily from surface-water 

sources. Much of the agricultural irrigation along the South 

Platte River and its tributaries also is supplied by surface water 

delivered through irrigation diversion ditches using water rights 

established as early as the 1860s (Colorado Water Conservation 

Board, 2004). Surface-water supplies are derived from inside 

and outside the basin. In-basin surface-water supplies, and 

the associated water rights, are derived from the South Platte 

River, the Arkansas River, and their tributaries. Transmountain 

diversions into the Denver Basin from drainages west of the 

Continental Divide are delivered to in-basin drainages by way 

of tunnels and pipelines through the Rocky Mountain Front 

Range. An estimated 480 ft3/s (345,000 acre-ft/yr) of water is 

transferred to the South Platte River basin, and an estimated 

Figure B1. An agricultural area in the South Platte River valley.

Figure B2. Urbanization along Cherry Creek in downtown Denver.
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 97

Figure B3. Land use in the Denver Basin for 2001.

!

!

South Platte River

Lost Creek

Box Elder Creek

Cache la Poudre R

Big Thompson River Little ThompsonR

BoulderCr

Coal Creek

Big Dry Cr

Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little Dry Cr

Plum Creek West P ul m Creek

Bear Creek

Runn ni g Cre ek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger Creek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Creek

Saint Vrain Creek

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§ ̈¦70

§ ̈¦25

§ ̈¦76

Northern

area

South Denver

metropolitan area

Monument

area

Northern

area

South Denver

metropolitan area

Monument area

(

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PALMER

DIVIDE

PALMER

DIVIDE

Barr

Lake

Aurora

Reservoir

Cherry Creek

Reservoir

Chatfield

Reservoir

Milton 

Reservoir

Barr

Lake

Aurora

Reservoir

Cherry Creek

Reservoir

Milton 

Reservoir

WELD

LARIMER

MORGAN

JEFFERSON

WASHINGTON

BROOMFIELD

LINCOLN

ADAMS

ARAPAHOE

TELLER

DOUGLAS

EL PASO

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DENVER

BOULDER

WELD

LARIMER

MORGAN

JEFFERSON

WASHINGTON

BROOMFIELD

LINCOLN

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ARAPAHOE

TELLER

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BOULDER

Greeley

Boulder

Loveland

Longmont

Brighton

Broomfield

Fort

Lupton

Lafayette

Golden

Lakewood Denver

Aurora

Bennett

Parker

Morrison

Franktown

Elizabeth

Castle

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Ranch

Littleton

Kiowa

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Fort

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Colorado

Springs

Greeley

Boulder

Loveland

Longmont

Brighton

Broomfield

Fort

Lupton

Lafayette

Golden

Lakewood Denver

Aurora

Bennett

Parker

Morrison

Franktown

Elizabeth

Castle

Rock

Highlands 

Ranch

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Kiowa

Engelwood

Fort

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Wiggins

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Monument

Colorado

Springs

105°

40°

39°

104°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

Land cover generalized from U.S. Geological Survey, 2001

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Land use category

Water

Urban/suburban development

Forest

Grassland

Irrigated pasture or row crops

Nonirrigated small grains or fallow

Urban recreational areas

Alluvial aquifer extent

Area of concentrated municipal pumping

Stream

Perennial

Ephemeral

# Bedrock municipal well
98 Groundwater Availability of the Denver Basin Aquifer System, Colorado

180 ft3/s (132,000 acre-ft/yr) of water is transferred to the 

Arkansas River basin from other basins, primarily from the 

Upper Colorado River Basin (Colorado Water Conservation 

Board, 2004).

Tributary groundwater pumped from the South Platte 

alluvial aquifer is mainly used for agricultural irrigation. Agricultural areas historically were located adjacent to streams, and 

thus also overlie alluvial aquifers. Both diverted surface water 

and pumped alluvial groundwater are sources of water for agricultural irrigation. Its large hydraulic conductivity and shallow 

depths to water compared to the bedrock aquifers also contribute to the beneficial use of the alluvial aquifer for agricultural 

irrigation (Hurr and others, 1975; Robson and Romero, 1981a, 

1981b; Robson, Romero, and Zawistowski, 1981, Robson, 

Wacinski, and others, 1981). The availability of South Platte 

River surface water made agriculture an important industry in 

the South Platte River valley beginning in the late 19th century 

(Nadler and Schumm, 1981). Crop irrigation from diversion 

ditches began in the 1880s, and by 1897, irrigation return flow 

had raised the alluvial-aquifer water table in late summer so that 

streamflow in the South Platte River changed from intermittent 

to perennial (Nadler and Schumm, 1981). Pumping from the 

alluvial aquifer for agricultural irrigation began and expanded 

in response to droughts of the 1930s and 1950s and the widespread availability of electricity (Hurr and others, 1975). By the 

1960s, State administration recognized the connection between 

groundwater and surface water, and regulation of pumping was 

considered necessary (Graham and VanSlyke, 2004). The Water 

Right Determination and Administration Act (Colorado Revised 

Statute (CRS) 37–92–101 to 37–92–602) recognized that prior 

appropriation also governs groundwater and regulated pumping 

Figure B4. Population for the areas overlying the Denver Basin aquifer system and for 

the fastest growing counties in the Denver Basin, 1970–2005.

of tributary groundwater, but application of the law was generally limited to the South Platte alluvial aquifer (Graham and 

VanSlyke, 2004).

Development of the bedrock aquifers began in the 1950s 

on the basis of well permits issued. In contrast to the alluvial 

aquifer, which is used mostly for agricultural irrigation, water 

from the bedrock aquifers is primarily used for municipal, 

commercial, industrial, and domestic purposes (Robson, 

1989; this study). In 1973, Senate Bill 73–113 (SB113, 

CRS 37–90–137(4)) was established to recognize the existence 

of nontributary groundwater in the Denver Basin and establish 

rules for its administration (Graham and VanSlyke, 2004). This 

law administers groundwater withdrawal based on ownership 

or control of the overlying land and limits annual withdrawal 

to 1 percent of the available water beneath the land in order 

to maintain a 100-year aquifer life for a given parcel of land 

(Graham and VanSlyke, 2004). By 1985, the continued increase 

in groundwater withdrawal from the Denver Basin prompted 

further study of the aquifers, and Colorado Senate Bill 85–5 

(SB85–5) was passed, which clarified nontributary groundwater 

definitions and established the Denver Basin Rules (Graham 

and Van Slyke, 2004). Senate Bill 85–5 adopted a 100-year 

aquifer life to administer pumping rates and accepted storage 

depletion by not protecting artesian head or aquifer water levels 

(Graham and VanSlyke, 2004). Because Denver Basin bedrock 

groundwater is considered mostly nontributary by SB85–5 and 

therefore is not subject to the prior-appropriation doctrine, it has 

been a readily available source of water to support growing and 

recently established municipalities in areas with limited surface 

water, limited tributary groundwater, or limited available water 

rights (Moore and others, 2007).

0

0.5

1.0

1.5

2.0

2.5

3.0

Population, in millions

El Paso County

Arapahoe County

Adams County

Weld County

DouglasCounty

Year

1970 1975 1980 1985 1990 1995 2000 2005

Weld County 69,500

AdamsCounty 177,057

Arapahoe County 151,424

El Paso County 168,602

DouglasCounty 5,881

DenverBasin total 1,299,860

84,446 96,072 102,270 102,596

208,516 234,385 252,581 254,425

205,458 273,905 344,629 365,632

209,992 221,083 264,561 283,667

10,353 17,595 27,173 42,244

1,498,537 1,661,830 1,864,405 1,899,595

115,187 140,822 176,572

287,777 346,756 381,023

417,390 455,712 492,423

332,082 369,346 405,918

69,870 122,948 172,383

2,145,263 2,468,846 2,669,768
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 99

Figure B5. Aerial photograph of suburban area in the south 

Denver metropolitan area.

Figure B6. A Denver Basin domestic well in a rural residential 

setting with new subdivision on the horizon.

Denver Basin Pumping History

In 1883, a well was drilled for coal exploration near 

downtown Denver but was abandoned because of the large, 

uncontrollable flow of water (Emmons and others, 1896). 

By 1884, about 80 wells had been drilled into what became 

later known as the Arapahoe and Laramie–Fox Hills aquifers, 

and by 1890, about 400 bedrock wells had been drilled in the 

downtown Denver area (fig. B7; Emmons and others, 1896; 

Robson, 1987). Flow from the uncapped wells was estimated at about 4.5 ft3

/s in 1884 (Cross and others, 1884), but 

decreasing heads in the aquifers and well interference caused 

the discharge to decrease to an estimated 2.3 ft3/s by 1894 

(Emmons and others, 1896; Robson, 1987).

Because pumping rates from the Denver Basin aquifer system are not monitored, various estimates of pumping have been 

made by previous work. In 1963, the U.S. Geological Survey 

compiled a preliminary tabulation of bedrock pumping in the 

Denver Basin, which included estimates of municipal, commercial, and industrial pumping (Robson, 1987). The 1963 pumping estimate indicated a total pumping rate of 12.5 ft3

/s from 

bedrock wells in the Denver Basin (Robson, 1987). Subsequent 

estimates indicated total pumping from bedrock aquifers ranged 

from about 15 ft3/s in 1958 to about 41 ft3/s in 1978 (Robson, 

1987). Previous pumping estimates indicated a substantial 

pumping increase between 1958 and 1962, relatively steady 

pumping from 1962 to 1975, and then another pumping increase 

between 1975 and 1978 (Robson, 1987). The 1975–78 pumping 

increase was attributed to the use of self-supplied groundwater 

for outdoor lawn watering in developing residential areas at a 

time when the Denver Water Department restricted the use of 

municipal water for lawn watering (Robson, 1987). In 1978, 

most of the pumping from bedrock aquifers was within a 30-mi 

radius of downtown Denver and had caused substantial waterlevel declines in the bedrock aquifers (Robson, 1987). Approximately one-half of the pumping from bedrock aquifers in 1978 

was from the Arapahoe aquifer (Robson, 1987).

Yield from bedrock wells is highly variable and can range 

from 2 to 700 gallons per minute (gal/min) depending on the 

transmissivity of the aquifer materials in which the well is 

completed (Robson, 1987). Large-capacity wells located in areas 

of high transmissivity can yield several hundred gallons per 

minute, but small discharges of only several gallons per minute 

are noted in areas of small transmissivity (Robson, 1987). More 

recently reported well yields exhibit similar variability because of 

aquifer heterogeneity, and well yields can decrease with time after 

well installation because of declining water levels in the bedrock 

aquifers (Frank Jaeger, City of Parker, oral commun., 2003). Well 

yields relate directly to hydraulic conductivity, such that wells 

in the Arapahoe aquifer generally have the greatest yields of the 

Denver Basin bedrock aquifers followed by wells in the Dawson, 

Laramie–Fox Hills, and Denver aquifers (Robson, 1987).

A well-permitting process through the CDWR administers installation of bedrock and alluvial wells in the Denver 

Basin, and permitted pumping rates for bedrock aquifers are 

determined based on SB85–5 requirements and the assumption 

of a 100-year aquifer life for a given parcel of land. However, 

systematic records of measured well pumping are not maintained for the entire basin. The most recent estimates of pumping from the Denver Basin aquifers were made by the CDWR 

(1998) in support of the SB96–74 groundwater flow model.

For this study, geographical information system (GIS) and 

database analysis were used to estimate pumping from a 2004 

version of the CDWR well-permit database (Brian Ahrens, 

Colorado Division of Water Resources, written commun., 

2004). Pumping from each of the alluvial and bedrock aquifers 

was estimated as the product of number of wells (derived from 

GIS and database analysis) and assigned pumping rates. For 

the period from 1880 to 2003, well locations and completioninterval depths listed in the well-permit database were compared 

to GIS files of aquifer extents and base altitude (presented in 

“Hydrogeologic Framework” section of Chapter A) and each 

well was assigned an aquifer designation. The analysis excluded 

nonproducing monitoring wells and wells with insufficient 

location or completion data. The previous well-permit database 

analysis by the CDWR assumed wells less 100 ft deep were 

completed in the alluvial aquifer, and these wells were excluded 

from the previous CDWR analysis because the alluvial aquifer 

was not explicitly represented in previous models (Colorado 
100 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B7. Locations of late 19th century artesian wells reported by Emmons and others (1896) in downtown Denver, Colorado.

76

6

70

6th

25

FEDERAL

8th

COLFAX

EVANS

38th

SHERIDAN

COLORADO

YORK

64TH

PECOS

ALAMEDA

70th

YALE

1st

26th

BROADWAY

VALLEY

FLORIDA

72nd

LOWELL

SANTA FE

44th

270

PARK

LINCOLN

58TH

UNIVERSITY

40th

32nd

DOWNING

SPEER

BRIGHTON

52nd

WASHINGTON

LARIMER

74TH

20th

IRVING

FOX

15th

IOWA

STEELE

LAWRENCE

KNOX

KALAMATH

ZUNI

TEJON

MORRISON

16th

JOSEPHINE

19th

E SPEER

29th

45th

VASQUEZ

23rd

AURARIA

22nd

48th

N SPEER

S PLATTE RIVER

BRYANT

47th

JEWELL

OSAGE

MARTIN LUTHER KING

AMHERST

WATER

RAMP

BLAKE

60th

8th AVENUE

SMITH

MARION

56th

OSCEOLA

25

KNOX

47th

FEDERAL

PARK

8th

WASHINGTON

6th

32nd

BLAKE

COLORADO

BRIGHTON

BROADWAY

44th

YORK

SPEER

SHERIDAN

COLORADO

SPEER

45th

YORK

SHERIDAN

44th

YALE

SPEER

26th

20th

SHERIDAN

IRVING

DENVER

DENVER BOULDER 76

6

70

6th

25

FEDERAL

8th

COLFAX

EVANS

38th

SHERIDAN

COLORADO

YORK

64TH

PECOS

ALAMEDA

70th

YALE

1st

26th

BROADWAY

VALLEY

FLORIDA

72nd

LOWELL

SANTA FE

44th

270

PARK

LINCOLN

58TH

UNIVERSITY

40th

32nd

DOWNING

SPEER

BRIGHTON

52nd

WASHINGTON

LARIMER

74TH

20th

IRVING

FOX

15th

IOWA

STEELE

LAWRENCE

KNOX

KALAMATH

ZUNI

TEJON

MORRISON

16th

JOSEPHINE

19th

E SPEER

29th

45th

VASQUEZ

23rd

AURARIA

22nd

48th

N SPEER

S PLATTE RIVER

BRYANT

47th

JEWELL

OSAGE

MARTIN LUTHER KING

AMHERST

WATER

RAMP

BLAKE

60th

8th AVENUE

SMITH

MARION

56th

OSCEOLA

25

KNOX

47th

FEDERAL

PARK

8th

WASHINGTON

6th

32nd

BLAKE

COLORADO

BRIGHTON

BROADWAY

44th

YORK

SPEER

SHERIDAN

COLORADO

SPEER

45th

YORK

SHERIDAN

44th

YALE

SPEER

26th

20th

SHERIDAN

IRVING

DENVER

DENVER BOULDER

Cherry Creek

South Platte River

Clear Cre ek

105°2' 105°00' 104°58'

39°48'

39°46'

39°44'

39°42'

39°40'

LARIMER

BOULDER

BROOMFIELD

DENVER

JEFFERSON

DOUGLAS

TELLER

FREMONT

EL PASO

ELBERT

ARAPAHOE

ADAMS

WELD

LOGAN

MORGANWASHINGTON

LINCOLN

105° 104°

40°

39°

EXPLANATION

Stream

Major street or highway

Estimated location of historical 

 flowing well from Emmons 

 and others (1896)

0 1 2 MILES

0 1 2 KILOMETERS

Division of Water Resources, 1998). For this study, alluvial 

wells were identified on the basis of their location within the 

limits of the simulated alluvial aquifer, well depth and yield 

criteria, or their classification as alluvial wells in the well-permit 

database. This study excluded alluvial wells if they were located 

outside the limits of the simulated alluvial aquifer. Uses of 

municipal, commercial/industrial, irrigation, or domestic and 

dates of use were assigned to each alluvial and bedrock well on 

the basis of information provided in the well-permit database. 

The number of wells was then totaled by aquifer of completion 

and water-use categories, and the results are described in the 

following discussion. The well-permit database analysis resulted 

in a count of about 52,000 pumped wells for the Denver Basin 

that were categorized by aquifer, use, and dates of use. Of the 

101,103 well records in the well-permit database, the analysis 

excluded about 23,340 records for non-producing monitoring 
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 101

wells. The remaining excluded well records (25,763) were 

either duplicate records or contained insufficient information 

for inclusion.

Pumping rates were assigned to individual wells on the 

basis of aquifer of completion and water use consistent with 

previous methodology (Colorado Division of Water Resources, 

1998). The previous methodology developed average annual 

pumping factors on the basis of actual pumping rates reported 

by municipal providers for 1996. Average annual pumping 

rates of 72, 104, 158, and 64 acre-ft per well were indicated for 

1996 for municipal wells completed in the Dawson, Denver, 

Arapahoe, and Laramie–Fox Hills aquifers, respectively 

(Colorado Division of Water Resources, 1998). Weighting factors for each aquifer (table B1) were calculated as the ratio of 

the average pumping rate for the aquifer divided by the overall average annual pumping rate for all wells (120 acre-ft/yr; 

Colorado Division of Water Resources, 1998). Categorized 

by water use, the following average pumping rates were 

assigned to each well by the CDWR (1998) and this study 

for all time periods: 0.6 acre-ft/yr for domestic and livestock 

wells, 0.3 acre-ft/yr for household-use only wells (a subset of 

domestic wells with no outdoor water use), and 9.0 acre-ft/yr 

for commercial and industrial wells (Colorado Division of 

Water Resources, 1998). Assigned pumping rates for domestic 

and livestock wells assume 50-percent consumptive use and 

50-percent return flow; assigned pumping rates for householduse only, commercial, and industrial wells assume 10-percent 

consumptive use and 90-percent return flow (Colorado Division 

of Water Resources, 1998). The assigned pumping rate for 

irrigation wells (41 acre-ft/yr for all time periods) assumes 

90-percent consumptive use and 10-percent return flow, and the 

rate is multiplied by the appropriate aquifer weighting factor to 

compute a per-well pumping rate depending on the aquifer of 

completion (table B1). The assigned pumping rate for municipal 

wells (32 acre-ft/yr in 1979) assumes 50-percent consumptive use, and the rate is multiplied by the appropriate aquifer 

weighting factor to compute a per-well pumping rate depending on the aquifer of completion (table B1). In addition, the 

assigned municipal pumping rate for this study was increased 

linearly from 32 acre-ft/yr in 1979 to 45 acre-ft/yr in 1996 

consistent with methods used by the Colorado Division of Water 

Resources (1998). The assigned municipal pumping rate for this 

study was held constant at 45 acre-ft/yr from 1997 to 2003.

About 52,000 permitted pumping wells with sufficient 

well-location and completion data are included in this analysis. 

About 8,000 wells (15 percent) were completed in the alluvial 

aquifer and about 44,000 wells (85 percent) were completed 

in bedrock aquifers by 2003 (fig. B8). The number of alluvial 

aquifer wells initially exceeded that for the bedrock aquifers 

from the 1930s through the 1950s, reflecting the early groundwater development of the alluvial-aquifer system. After 1960, 

the number of bedrock wells exceeded the number of alluvial 

wells as development of the bedrock aquifers proceeded, and 

the number of bedrock wells increased most rapidly after 1990 

(fig. B8).

The number of alluvial wells increased rapidly during 

the 1950s and 1960s (fig. B9A) as irrigation and domestic 

supplies from the alluvial aquifer were developed (Hurr and 

others, 1975). The rate of alluvial-well installation decreased 

and stabilized after 1969 in response to imposed regulation, 

although the number of alluvial wells increased again in the 

1990s in response to municipal- and domestic-well installation (fig. B9A). Categorization of alluvial wells by water 

use for 2003 indicates most were used for domestic purposes 

(4,386 wells, 56 percent of alluvial wells) and irrigation 

(2,956 wells, 38 percent of alluvial wells) (fig. B9B). Alluvial 

wells are located throughout the alluvial aquifer with concentrations of pumping noted along the main stem of the South 

Platte River between Denver and Greeley and in tributary 

valleys of Lost, Kiowa, Bijou, and Black Squirrel Creeks 

(fig. B10). Municipal wells also are pumped from the tributary 

alluvial aquifer in upper basins of Cherry and Plum Creeks 

south of Denver.

The total number of bedrock wells steadily increased 

after about 1955 (fig. B11A) with domestic wells (41,714 wells) 

accounting for the majority (94 percent) of bedrock wells 

in 2003 (fig. B11B). A count of bedrock wells by aquifer 

(figs. B12A, B12B) indicates that by 2003 most bedrock wells 

were completed in the Dawson aquifer (18,138 wells or 

41 percent of bedrock wells), followed by the Denver aquifer 

(11,488 wells or 26 percent of bedrock wells), the Arapahoe 

aquifer (9,118 wells or 21 percent of bedrock wells), and the 

Laramie–Fox Hills aquifer (5,405 wells or 12 percent of bedrock wells). Bedrock domestic wells are located throughout the 

basin and generally are completed in the bedrock aquifer nearest 

to the surface (fig. B13).

Bedrock municipal wells tend to be located on the west 

side of the basin near municipalities and are concentrated in the 

three identified areas of development (fig. B14). In the northern 

area, suburbs and municipalities in Boulder, Adams, and Weld 

Counties pump groundwater primarily from the Arapahoe and 

Laramie–Fox Hills aquifers. In the south Denver metropolitan 

Table B1. Estimated pumping rates assigned to wells in the Denver Basin model.

Aquifer in which well 

is completed

Aquifer

weighting

factor

Assigned pumping rate

(acre-feet per year)

Municipal Irrigation Commercial/ 

Industrial

Domestic

and livestock

Household

1880–1978 1979–1996 1997–2003 only

Alluvial aquifer 1.0 32.0 Linear increase to 45.0 45.0 41.0 9.0 0.6 0.3

Upper and lower Dawson aquifer 0.6 19.2 Linear increase to 27.0 27.0 24.6 9.0 0.6 0.3

Denver aquifer 0.87 27.8 Linear increase to 39.1 39.1 35.7 9.0 0.6 0.3

Upper and lower Arapahoe aquifer 1.32 42.2 Linear increase to 59.4 59.4 54.1 9.0 0.6 0.3

Laramie–Fox Hills aquifer 0.53 17.0 Linear increase to 23.8 23.8 21.7 9.0 0.6 0.3
102 Groundwater Availability of the Denver Basin Aquifer System, Colorado

area, a concentration of municipal wells supplies water to multiple municipalities and suburbs including Littleton, Parker, Castle Rock, Highlands Ranch, Castle Pines, Castle Pines North, 

Lone Tree, Stonegate, the Pinery, and other developments in 

Douglas and Arapahoe Counties. Municipal wells in the south 

Denver metropolitan area commonly are nested, with multiple 

wells at a given location, and each well completed in a different bedrock aquifer. Water pumped from various depths to meet 

demand commonly is blended to meet water-quality standards. 

Municipal water is used for lawn and garden irrigation in urban/

suburban areas, and water use peaks during the summer months 

to meet this irrigation demand. The extensive and conductive 

Cretaceous alluvial fans found in the Denver and Arapahoe 

aquifers provide a readily available source of nontributary 

water, and development in the south Denver metropolitan area 

relies on the availability of this water supply. In the Monument 

area, municipal wells completed in all of the bedrock aquifers 

are located near the southwestern margin of the basin, which 

is the regional discharge area of Monument Creek. Wells in 

the Monument area provide water supply to development east 

Figure B8. Total number of Denver Basin wells, 1880–2003.

Figure B9. Number of Denver Basin alluvial wells categorized by water use for (A) 1880–2003, and (B) 2003.

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Year

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

50,000

55,000

Number of wells

Alluvial wells

Total

Bedrock wells

EXPLANATION

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Year

A

Number of alluvial wells

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

EXPLANATION

Irrigation

Domestic/Household

Municipal

Commercial/Industrial

Total

Irrigation

2,956 wells

38 percent

Domestic

4,386 wells

56 percent

Municipal

189 wells

2 percent Commercial/Industrial

336 wells

4 percent

B
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 103

Figure B10. Locations of Denver Basin alluvial wells within limits of simulated alluvial aquifer, 2003.

South Platte

River

Lost Creek

Box Elder Creek

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C ree k

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

§ ̈¦70

§ ̈¦25

§ ̈¦76

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PALMER

DIVIDE

PALMER

DIVIDE

105° 104°

40°

39°

ADAMS

BOULDER

BROOMFIELD

JEFFERSON

DENVER

WELD

LARIMER

TELLER

DOUGLAS

ELBERT

ARAPAHOE

MORGAN

LINCOLN

EL PASO

WASHINGTON

ADAMS

BOULDER

BROOMFIELD

JEFFERSON

DENVER

WELD

LARIMER

TELLER

DOUGLAS

ELBERT

ARAPAHOE

MORGAN

LINCOLN

EL PASO

WASHINGTON

Golden

Denver

Brighton

Broomfield

Aurora

Engelwood

Littleton

Deer

Trail

Denver

Boulder

Lakewood

Longmont

Brighton

Broomfield

Fort

Lupton

Aurora

Lafayette

Engelwood

Morrison

Highlands 

Ranch

Littleton

Limon

Kiowa

Parker

Franktown

Elizabeth Castle

Rock

Deer

Trail

Simla

Monument Calhan

Colorado

Springs

Fort

Morgan

Greeley

Loveland

Bennett

Wiggins

Golden

Denver

Brighton

Broomfield

Aurora

Engelwood

Littleton

Deer

Trail

Denver

Boulder

Lakewood

Longmont

Brighton

Broomfield

Fort

Lupton

Aurora

Lafayette

Engelwood

Morrison

Highlands 

Ranch

Littleton

Limon

Kiowa

Parker

Franktown

Elizabeth Castle

Rock

Deer

Trail

Simla

Monument Calhan

Colorado

Springs

Fort

Morgan

Greeley

Loveland

Bennett

Wiggins

!(

!(

!(

!(

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!(

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!

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

Alluvial aquifer simulated extent (model layer 1)

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Stream

Perennial

Ephemeral ! Alluvial aquifer well, 2003

EXPLANATION
104 Groundwater Availability of the Denver Basin Aquifer System, Colorado

of Monument, and the City of Colorado Springs supplements 

its municipal supply by pumping from satellite well fields in 

this area (Cortney Brand, Colorado Springs Utilities, written 

commun., 2005).

Using the well counts presented previously and the 

assigned pumping rates listed in table B1, total pumping from 

Denver Basin alluvial and bedrock wells was estimated at 

about 305 ft3/s (221,100 acre-ft/yr) in 2003 (fig. B15A). About 

62 percent of the pumping was from alluvial wells (187 ft3/s; 

135,400 acre-ft/yr), and 38 percent of the pumping was from 

bedrock wells (118 ft3/s; 85,400 acre-ft/yr) in 2003 (fig. B15B) 

although most of the 52,000 wells (85 percent) are completed 

in the bedrock aquifers. Categorized by water use, total pumping from Denver Basin alluvial and bedrock aquifers was about 

62 percent irrigation, 20 percent municipal, 12 percent domestic, and 6 percent commercial/industrial in 2003 (fig. B16).

Figure B11. Number of Denver Basin bedrock wells categorized by water use for (A) 1880–2003, and (B) 2003.

Figure B12. Number of Denver Basin bedrock wells categorized by aquifer for (A) 1880–2003, and (B) 2003.

A

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

Number of bedrock wells

Year

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

UpperDawson

LowerDawson

Denver

UpperArapahoe

LowerArapahoe

Laramie–Fox Hills

EXPLANATION

Upper and lower

Dawson aquifer

18,138 wells

41 percent of 

bedrock wells

Denver aquifer

11,488 wells

26 percent of 

bedrock wells

Upper and lower

Arapahoe aquifer

9,118 wells

21 percent 

of bedrock 

wells

Laramie–Fox 

Hills aquifer

5,405 wells

12 percent 

of bedrock 

wells

B

A

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

50,000

Number of bedrock wells

Year 1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Domestic wells

Commercial/Industral wells

Municipal wells

Irrigation

Total bedrock wells

EXPLANATION Irrigation

458 wells

1 percent

Municipal

850 wells

2 percent

Commercial/Industrial

1,127 wells

3 percent

Domestic

41,714 wells

94 percent

B
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 105

Figure B13. Locations of Denver Basin bedrock domestic wells categorized by aquifer, 2003.

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WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

PALMER DIVIDE

DIVIDE

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

§ ̈¦70

§ ̈¦25

§ ̈¦76

105°

40°

39°

104°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Lower Dawson aquifer simulated extent (model layer 4)

Denver aquifer simulated extent (model layer 6)

Lower Arapahoe aquifer simulated extent (model layer 10)

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Extent of active model cells

! Upper or lower Dawson aquifer domestic well

! Denver aquifer domestic well

! Upper or lower Arapahoe aquifer domestic well

! Laramie–Fox Hills aquifer domestic well
106 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B14. Locations of Denver Basin bedrock municipal wells categorized by aquifer and areas 

of concentrated municipal pumping, 2003.

PALMER

DIVIDE

PALMER

DIVIDE

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EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

§ ̈¦70

§ ̈¦25

§ ̈¦76

Northern

area

South Denver

metropolitan area

Monument

area

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

105°

40°

39°

104°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Area of concentrated municipal pumping

Extent of active model cells

# Laramie–Fox Hills aquifer municipal well

# Upper or lower Arapahoe aquifer municipal well

# Denver aquifer municipal well

# Upper or lower Dawson aquifer municipal well
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 107

Figure B15. Total estimated pumping from Denver Basin alluvial and bedrock wells for (A) 1880–2003, and 

(B) 2003.

Pumping from alluvial wells increased steadily from 

less than 5 ft3/s (about 3,600 acre-ft/yr) in the 1920s to about 

150 ft3/s (109,000 acre-ft/yr) in 1969 (fig. B17A). Pumping 

from alluvial wells continued to increase, but at a lesser rate, 

after 1969 because of State laws that regulated pumping from 

the alluvial aquifer. Groundwater pumped from the alluvial 

aquifer has been primarily used for agricultural irrigation; 

however, there was an increase in alluvial aquifer pumping for 

municipal and domestic purposes in the 1990s (fig. B17A). In 

2003, estimated alluvial aquifer pumping was 90 percent irrigation, 6 percent municipal, 2 percent commercial/industrial, 

and 2 percent domestic (fig. B17B).

Development of the bedrock aquifers began in the 1950s, 

and bedrock pumping increased steadily to about 118 ft3/s 

(85,400 acre-ft/yr) by 2003 (fig. B18A). Groundwater pumped 

from the bedrock aquifers is used for municipal, domestic, 

irrigation, and commercial/industrial purposes, although 

municipal supply was the primary use of bedrock groundwater 

A

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Year

EXPLANATION

0

50

100

150

200

250

300

350

Estimated pumping, in cubic feet per second

Total

Alluvial wells

Bedrock wells

B

Alluvial aquifer

187 cubic feet 

per second

62 percent of pumping

Upper Arapahoe

8 cubic feet per second

3 percent of pumping

Upper Dawson

7 cubic feet per second

2 percent of pumping

Lower Arapahoe

40 cubic feet per second

13 percent of pumping

Laramie–Fox Hills

18 cubic feet per second

6 percent of pumping

Denver

29 cubic feet per second

9 percent of pumping

Lower Dawson

15 cubic feet per second

5 percent of pumping

Bedrock aquifers

118 cubic feet per second

38 percent of pumping
108 Groundwater Availability of the Denver Basin Aquifer System, Colorado

since about 1985 (fig. B18A). In 2003, estimated bedrock 

pumping was 41 percent municipal, 28 percent domestic, 

19 percent irrigation, and 12 percent commercial/industrial 

(fig. B18B). The lower Arapahoe and Denver aquifers were 

the most heavily used of the four major bedrock aquifers since 

the 1950s (fig. B19A). In 2003, the Arapahoe aquifer was the 

most heavily pumped of the bedrock aquifers (41 percent of 

bedrock pumping), followed by the Denver aquifer (24 percent of bedrock pumping), the Dawson aquifer (19 percent of 

bedrock pumping), and the Laramie–Fox Hills aquifer (16 percent of bedrock pumping) (fig. B19B). The Arapahoe and 

Laramie–Fox Hills aquifers primarily were used for municipal 

purposes, while the Dawson primarily was used for domestic 

purposes in 2003 (fig. B20). The Denver aquifer water use was 

split relatively equally among municipal, domestic, and irrigation uses in 2003 (fig. B20).

Analysis of pumping from the Denver Basin aquifers 

indicates that the greatest irrigation pumping is from the 

alluvial aquifer along the South Platte River and that the greatest municipal pumping is from bedrock aquifers in populated 

areas on the west side of the basin. The results are consistent 

with the conceptual understanding of conditions in the basin 

and compare reasonably well to previous estimates of bedrock pumping. For example, the Colorado Division of Water 

Resources (1998) estimated pumping from bedrock aquifers 

at about 81 ft3/s for 1996, and this study estimated pumping from bedrock aquifers for 1996 at about 89 ft3

/s. Robson 

(1987) estimated pumping from bedrock aquifers at about 

15 ft3/s in 1958 and about 41 ft3/s for 1978, and this study 

estimated bedrock pumping as about 12 ft3/s in 1958 and 

about 49 ft3/s in 1978. Accuracy of the pumping estimates is 

considered in the range of plus or minus 30 percent (Robson, 

1987; Colorado Division of Water Resources, 1998), and all 

of these estimates are considered plausible values for bedrock 

pumping. Future studies and management of Denver Basin 

groundwater would benefit from implementation of a metering and reporting system for pumping information to decrease 

the uncertainty and increase confidence in pumping estimates. 

Further discussion of data needs, including pumping records, 

is presented in the section “Monitoring the Hydrologic 

System” of this chapter.

Figure B16. Estimated pumping from Denver Basin alluvial 

and bedrock wells categorized by water use, 2003.

Estimated alluvial pumping, in cubic feet per second

Year

0

20

40

60

80

100

120

140

160

180

200

A

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

EXPLANATION

Total

Irrigation

Municipal

Domestic

Commercial/Industrial

Municipal

11.7 cubic feet per second

6 percent of pumping

Domestic

3.6 cubic feet per second

2 percent of pumping

Commercial/Industrial

4.1 cubic feet per second

2 percent of pumping

Irrigation

167 cubic feet per second

90 percent of pumping

B

Figure B17. Estimated pumping from Denver Basin alluvial wells categorized by water use for (A) 1880–2003, and (B) 2003.

Irrigation

190 cubic feet per second

62 percent of pumping

Municipal

60 cubic feet per second

20 percent of pumping

Domestic

37 cubic feet per second

12 percent of pumping

Commercial/Industrial

18 cubic feet per second

6 percent of pumping
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 109

Effects of Development on Groundwater 

Availability in the Denver Basin

This groundwater-availability analysis describes changes 

to the water budget, aquifer storage, and potentiometric surfaces 

from predevelopment (pre-1880) conditions through 2053. 

Water-budgets and hydraulic heads simulated by the Denver 

Basin groundwater flow model (Chapter C) for the transient 

model-calibration period (1880–2003) and the predictive-simulation period (2004–2053) form the basis for this description of 

changes to groundwater availability in the Denver Basin. The 

transient-calibration period of the model represents changing 

aquifer conditions from 1880 to 2003, and the predictive simulation period of the model (2004–2053) represents hypothetical 

predictions of future conditions.

Overview

Development of groundwater resources in the Denver 

Basin has altered the groundwater budget and flow directions as 

compared to predevelopment conditions by increasing water use 

on the land surface while removing water from deep, confined, 

bedrock aquifer storage. The groundwater flow model simulates 

the expanding area of urban/suburban land use and irrigated 

agriculture since the 1950s, and the results indicate increases in 

recharge, evapotranspiration, and the overall quantity of water 

moving in and out of the groundwater system in response to 

expanded development. Simultaneously, groundwater pumping 

from the deep and confined bedrock aquifers also has increased 

steadily since the 1950s, primarily in response to increased 

municipal water-supply needs in urban/suburban areas. The 

simulated increased pumping from the bedrock aquifers generally decreased discharge from the bedrock aquifers to the 

alluvial aquifer, increased downward interaquifer flow between 

bedrock units, decreased the amount of available groundwater 

in bedrock storage, and lowered hydraulic heads in bedrock 

aquifers (fig. B21) compared to predevelopment conditions. The 

groundwater flow model simulates precipitation recharge as a 

percentage of time-varying precipitation to represent the effects 

of climate variability and recent drought. Results indicate 

storage-depletion rates have increased substantially since 1999 

in response to decreased precipitation recharge during recent 

drought years (2000–2003), continued increases in bedrock 

pumping, and conversion of parts of the basin to unconfined 

conditions. Two predictive simulations that represent conditions from 2004–2053 indicate continued storage depletion in 

response to pumping and that a reduction in pumping could 

slow storage depletion rates to extend the usable aquifer life.

Differences between the alluvial and bedrock aquifers have 

important implications for groundwater resource management 

in the Denver Basin. This study focused on evaluating groundwater flow conditions in the Denver Basin bedrock aquifers, 

although the alluvial aquifer is an important part of the overall 

aquifer system and was included in the groundwater flow model 

to represent water exchange between the bedrock aquifers and 

the surficial system of alluvial aquifers and streams on a basinwide scale. The unconsolidated and permeable alluvial aquifer 

occurs at the land surface in direct hydraulic connection with 

streams, with shallow depths to water, and has no overlying 

confining unit such that most of the water moving in and out 

of the system is moving through the alluvial aquifer. Simulated 

recharge, evapotranspiration, and groundwater/surface-water 

interaction for the alluvial aquifer are greater than for bedrock 

0

20

40

60

80

100

120

140

Estimated bedrock pumping, in cubic feet per second

Year

A

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

EXPLANATION

Municipal

Domestic/Household

Irrigation

Commercial/Industrial

Total

B

Irrigation

23 cubic feet 

per second

19 percent of pumping

Municipal

48 cubic feet per second

41 percent of pumping

Domestic

34 cubic feet per second

28 percent of pumping

Commercial/Industrial

14 cubic feet per second

12 percent of pumping

Figure B18. Estimated pumping from Denver Basin bedrock wells categorized by water use for (A) 1880–2003, and (B) 2003.
110 Groundwater Availability of the Denver Basin Aquifer System, Colorado

aquifers because, in the model, the alluvial aquifer receives 

more agricultural and urban irrigation recharge and it receives a 

greater percentage or precipitation recharge (7 percent of annual 

precipitation) than the bedrock aquifers (2–4 percent of annual 

precipitation). These factors, combined with the large hydraulic 

conductivity of the alluvial aquifer, result in minimal changes 

to the alluvial-aquifer storage and potentiometric surface in 

response to pumping. In contrast, the bedrock aquifers receive 

little precipitation recharge because of overlying confining 

units, low precipitation rates, and high evapotranspiration rates. 

These factors, combined with low hydraulic-conductivity values 

as compared to the alluvial aquifer, result in reduced flow to 

the alluvial aquifer, removal of water from storage, substantial 

drawdown to potentiometric surfaces, and increased areas of 

unconfined conditions in response to pumping from the bedrock 

aquifers (fig. B22).

EXPLANATION

0

10

20

30

40

50

60

70

80

90

100

110

120

Upper

Dawson

Lower

Dawson

Denver Upper

Arapahoe

Lower

Arapahoe

Laramie–

Fox Hills

Total

Estimated pumping for 2003, in cubic feet per second

Aquifer

Total

Municipal

Domestic

Irrigation

Commercial/Industrial

Figure B20. Estimated pumping from individual Denver Basin bedrock aquifers 

categorized by aquifer and by water use, 2003.

A

0

5

10

15

20

25

30

35

40

45

50

Estimated bedrock pumping, in cubic feet per second

Year 1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

EXPLANATION

UpperDawson aquifer

LowerDawson aquifer

Denver aquifer

UpperArapahoe aquifer

LowerArapahoe aquifer

Laramie–Fox Hills aquifer

upper Arapahoe

8.2 cubic feet 

per second

7 percent of 

bedrock pumping

Denver

28.8 cubic feet 

per second

24 percent of 

bedrock pumping

upper Dawson

7.4 cubic feet 

per second

6 percent of 

bedrock pumping

lower Dawson

15.4 cubic feet 

per second

13 percent of 

bedrock pumping

B

lower Arapahoe

40.4 cubic feet 

per second

34 percent of 

bedrock pumping

Laramie–Fox Hills

18.2 cubic feet 

per second

16 percent of 

bedrock pumping

Figure B19. Estimated pumping from Denver Basin bedrock wells categorized by aquifer for (A) 1880–2003, and (B) 2003.
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 111

Figure B21. Conceptual block diagram of the Denver Basin aquifer system for developed conditions.

Figure B22. Groundwater budget for entire Denver Basin aquifer system, the alluvial aquifer, and bedrock units, 2003.

Groundwater flow 

out of basin

(19 cubic feet per second)

Precipitation plus 

irrigation recharge

(301 cubic feet 

per second)

ET

(218 cubic feet 

per second)

Stream and

spring

outflow

(21 cubic feet 

per second)

Stream and

reservoir inflow

(58 cubic feet 

per second)

Flow to 

alluvial aquifer

(27 cubic feet 

per second)

Flow from

alluvial aquifer

(12 cubic feet 

per second)

Bedrock

units

ET

(305 cubic feet 

per second)

Precipitation plus 

irrigation recharge

(593 cubic feet 

per second)

Stream and

reservoir inflow

(8 cubic feet 

per second)

Stream, 

reservoir,

and spring

outflow

(178 cubic feet 

per second)

Groundwater flow 

out of basin

(19 cubic feet per second)

Precipitation 

plus irrigation

recharge

(894 cubic feet 

per second)

Evapotranspiration (ET)

(523 cubic feet 

per second)

DENVER BASIN AQUIFER SYSTEM

Alluvial

aquifer

Stream and 

reservoir

inflow

(66 cubic feet 

per second) Stream, reservoir, 

spring outflow

(199 cubic feet 

per second)

Net storage loss 

(63 cubic feet per second)

Pumping 

(283 cubic feet 

per second)

Pumping 

(171 cubic feet 

per second)

Pumping 

(111 cubic feet 

per second)

Net storage loss 

(57 cubic feet per second)

Net storage loss 

(7 cubic feet per second)

Water

level

Denver aquifer

Dawson aquifer

Domestic well

Municipal wells

Laramie-Fox Hills aquifer

Arapahoe aquifer

Irrigation

well

South Platte River

Pierre Shale

Denver
112 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Changes to the Groundwater Budget

A groundwater budget accounts for all of the inflows and 

outflows for the hydrologic system. Inflow components of the 

developed Denver Basin groundwater budget are precipitation 

plus irrigation recharge, recharge from streams and reservoirs, 

interaquifer flow between hydrogeologic units, and changes in 

aquifer storage. Outflow components of the developed groundwater budget are evapotranspiration, discharge to springs, 

discharge to streams and reservoirs, pumping discharge to 

wells, interaquifer flow, and changes in aquifer storage. For 

some water-budget components, there are both inflows and 

outflows, and the difference between the inflow and outflow is 

herein referred to as the “net” inflow or outflow. For example, 

net recharge is calculated as the inflow from precipitation plus 

irrigation recharge minus evapotranspiration, and the net flow 

to streams and reservoirs is calculated as the inflow to aquifers 

from streams and reservoirs minus the outflow from aquifers 

to streams and reservoirs. For pumping, the MODFLOW Well 

(Harbaugh and others, 2000) and MNW Packages (Halford 

and Hanson, 2002) were used to simulate wells, and the net 

pumping presented in this water-budget discussion is the 

sum of outflow from the Well and MNW packages minus the 

interlayer inflow from MNW wells. For storage, MODFLOW 

assigns water removed from storage as an inflow and water 

returned to storage as an outflow. The groundwater budgets 

presented herein use the MODFLOW convention that positive 

values are inflows to the groundwater system and negative 

values are outflows from the groundwater system. Because 

MODFLOW simulates water removed from storage as an 

inflow to the groundwater flow system, positive net storage 

values indicate storage depletion (storage loss), and negative 

storage values indicate a return of water to storage (storage 

gain). Changes to aquifer storage are described in terms of 

storage-depletion rates and the cumulative volume of water 

removed from storage.

This discussion of transient groundwater budget results 

is based on the simulated, cell-by-cell water budget for the 

model-calibration period, which represents hydrologic conditions from predevelopment (pre-1880) to 2003. The predevelopment water budget, which is based on the initial (steadystate) model stress period, represents hydrologic conditions 

at the end of 1879 and is presented in section “Predevelopment 

Groundwater Budget” in Chapter A. Transient groundwater 

budgets are presented for the entire model (sum of all model 

layers), the alluvial aquifer (model layer 1), and the bedrock 

units (layers 2 through 12) and are discussed in terms of individual groundwater budget components.

Groundwater Budget for Entire Modeled Area

For the model-calibration period from pre-1880 (1879) to 

2003, recharge from precipitation plus irrigation was the largest inflow component (average of 90 percent of inflow) of the 

groundwater budget for the entire Denver Basin aquifer system 

(alluvial and bedrock units) (table B2; fig. B23A). The primary 

outflow components were to evapotranspiration, pumping, and 

streams. Stream inflow, spring outflow, and groundwater flow 

out of the basin though alluvial aquifers were minor components of the developed groundwater budget. Groundwater flow 

out of the basin includes underflow through the alluvial aquifer 

and specified flux to the South Platte alluvial aquifer. There is 

no groundwater flow out of the basin from bedrock aquifers.

Table B2. Simulated transient groundwater budget for the entire Denver Basin aquifer system during the model-calibration period, 

1879–2003.

[Positive values represent flow into the groundwater model; negative values represent flow out of the groundwater model; in some cases values do not sum 

because of rounding; ft3/s, cubic feet per second]

Stress 

period

Time 

step Year

Inflow component

(ft3/s)

Precipitation plus

irrigation recharge Streams Reservoirleakage

Wells completed

in multiple aquifers Storage Total

1 1 1879 630.3 16.2 0.0 0.0 0.0 647

2 6 1906 630.3 16.2 0.0 0.0 0.0 647

3 5 1919 630.3 16.2 22.5 0.0 0.9 670

4 5 1939 633.3 16.1 22.6 0.0 1.5 673

5 5 1953 639.9 16.5 38.1 0.0 6.9 701

6 5 1956 737.5 15.7 38.5 0.0 19.6 811

7 5 1961 758.1 16.4 38.5 0.0 17.1 830

8 5 1964 681.7 17.1 39.0 0.0 59.5 797

9 5 1971 741.4 17.3 38.9 0.1 27.3 825

10 5 1973 741.4 23.3 41.7 0.1 33.7 840

11 5 1978 700.6 23.3 41.8 0.1 58.7 825

12 5 1984 763.1 23.5 41.7 0.2 30.4 859

13 5 1986 763.1 23.7 41.7 0.3 37.6 866

14 5 1994 915.9 23.9 41.5 0.4 37.9 1,020

15 5 1999 939.4 24.1 41.6 0.5 43.9 1,050

16 5 2003 893.5 24.3 41.8 0.6 71.6 1,032
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 113

Table B2. Simulated transient groundwater budget for the entire Denver Basin aquifer system during the model-calibration period, 

1879–2003.—Continued

[Positive values represent flow into the groundwater model; negative values represent flow out of the groundwater model; in some cases values do not sum 

because of rounding; ft3/s, cubic feet per second]

Stress 

period

Time 

step Year

Outflow component 

(ft3/s)

Evapotranspiration

Streams Reservoir 

leakage Springs

Out of basin 

underflow 

through alluvial 

aquifers

Specified 

flux to South 

Platte alluvial 

aquifer

Wells 

completed 

in multiple 

aquifers

Wells Storage Total

1 1 1879 –441.6 –181.8 0.0 –4.2 –4.8 –14.1 0.0 0.0 0.0 –647

2 6 1906 –441.5 –181.8 0.0 –4.2 –4.8 –14.1 0.0 –0.1 –0.0 –647

3 5 1919 –462.3 –181.9 0.0 –4.2 –4.8 –14.1 0.0 –2.4 –0.1 –670

4 5 1939 –459.9 –180.3 0.0 –4.2 –4.8 –14.1 –0.0 –9.9 –0.2 –673

5 5 1953 –457.3 –175.0 –1.9 –4.2 –4.8 –14.1 –0.0 –43.9 –0.3 –701

6 5 1956 –470.4 –179.1 –1.9 –4.3 –4.8 –14.1 –0.1 –94.4 –42.1 –811

7 5 1961 –469.5 –183.0 –1.8 –4.4 –4.8 –14.1 –0.5 –120.8 –31.1 –830

8 5 1964 –436.7 –178.2 –1.6 –4.0 –4.8 –14.1 –0.8 –143.9 –13.3 –797

9 5 1971 –440.5 –179.8 –1.5 –4.1 –4.7 –14.1 –1.1 –171.0 –8.0 –825

10 5 1973 –436.7 –179.6 –10.4 –4.1 –4.7 –14.1 –1.4 –183.3 –5.9 –840

11 5 1978 –416.1 –176.1 –10.1 –3.8 –4.6 –14.1 –2.1 –195.7 –1.9 –825

12 5 1984 –427.7 –178.9 –9.9 –4.0 –4.5 –14.1 –2.6 –208.2 –9.0 –859

13 5 1986 –426.1 –178.4 –9.9 –3.9 –4.5 –14.1 –3.1 –219.0 –7.4 –866

14 5 1994 –527.3 –187.5 –11.3 –4.4 –4.6 –14.1 –4.0 –233.5 –32.7 –1,020

15 5 1999 –540.5 –188.5 –11.3 –4.5 –4.6 –14.1 –5.1 –255.3 –25.8 –1,050

16 5 2003 –523.0 –184.1 –11.0 –4.2 –4.5 –14.1 –6.3 –276.2 –8.3 –1,032

Stress 

period

Time 

step Year

Net flow for selected components

(ft3/s)

Net recharge (recharge 

plus evapotranspiration)

Net to streams 

(stream inflow plus 

stream outflow)

Net reservoir leakage 

(reservoir inflow plus 

reservoir outflow)

Wells

Change in storage

(positive value indicates loss, 

negative value indicates gain)

1 1 1879 188.8 –165.7 0.0 0.0 0.0

2 6 1906 188.9 –165.6 0.0 0.1 0.0

3 5 1919 168.0 –165.7 22.5 2.4 0.7

4 5 1939 173.4 –164.2 22.6 9.9 1.2

5 5 1953 182.6 –158.5 36.3 43.9 6.6

6 5 1956 267.0 –163.4 36.6 94.5 –22.5

7 5 1961 288.6 –166.6 36.7 121.4 –14.0

8 5 1964 245.1 –161.1 37.4 144.7 46.2

9 5 1971 300.9 –162.6 37.4 172.2 19.3

10 5 1973 304.8 –156.2 31.2 184.8 27.8

11 5 1978 284.4 –152.8 31.8 198.0 56.7

12 5 1984 335.4 –155.3 31.8 211.1 21.4

13 5 1986 337.0 –154.6 31.8 222.3 30.1

14 5 1994 388.5 –163.6 30.2 237.9 5.2

15 5 1999 399.0 –164.4 30.4 260.8 18.2

16 5 2003 370.4 –159.9 30.8 283.1 63.4

All of the groundwater budget components remained 

relatively constant until the 1950s when irrigated agriculture, urban development, and associated water use began 

increasing. After 1953, irrigation recharge and pumping both 

increased in response to development, causing the total inflow 

and outflow from the system to increase by about 60 percent from 650 ft3

/s for predevelopment (1879) conditions to 

1,030 ft3/s by 2003 (fig. B23A). Increases in the spatial extent 

of urban recharge are simulated for the periods 1954–1986 

and 1987–2003, and the additional water application results 

in step increases for simulated recharge and evapotranspiration in 1956 and 1994. Net recharge (recharge minus 

evapotranspiration) increased from about 190 ft3/s in 1953 to 

about 400 ft3/s in 1999 then decreased to about 370 ft3/s in 

2003 because of the less than average precipitation simulated 

from 2000 to 2003 to represent drought conditions (table B2). 

Inflow from streams to groundwater increased from about 

16 ft3/s for 1879 conditions to about 24 ft3/s in 2003, while 

outflow to streams for the entire modeled area remained 

relatively constant at about 180 ft3/s over the simulation period 

(table B2). Simulated total pumping steadily increased about 

sixfold from 44 ft3/s in 1953 to about 280 ft3/s in 2003 and was 

accompanied by a net storage-depletion rate of about 63 ft3/s 

in 2003 (table B2; fig. B23A).
114 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B23. Simulated transient groundwater budget for (A) the entire Denver Basin modeled area, 

(B) the alluvial aquifer, and (C) the bedrock aquifers and confining units, 1879–2003.

The water budget for the entire Denver Basin aquifer 

system at the end of the model-calibration period (2003) 

reflects the transient changes to recharge rates and pumping 

since the predevelopment condition. Precipitation plus irrigation recharge increased compared to predevelopment conditions because of an increase in the area of urban recharge, 

and recharge was the largest inflow component (894 ft3/s or 

87 percent of inflow) of the developed budget for the entire 

Denver Basin aquifer system (fig. B24). Inflow from streams 

and reservoirs (66 ft3/s or 6 percent of inflow) and storage 

(72 ft3/s or 7 percent of inflow) were other sources of inflow 

to the entire aquifer system in 2003 (fig. B24). Outflow from 

the entire aquifer system in 2003 was primarily to evapotranspiration (523 ft3

/s or 51 percent of outflow), wells (282 ft3/s 

or 27 percent of outflow), and streams (184 ft3/s or 18 percent 

of outflow). Net inflow was from precipitation and irrigation 

recharge (370 ft3/s or 85 percent of net inflow) and storage 

(63 ft3/s or 15 percent of net inflow). Most of the net outflow 

was to wells (282 ft3/s or 65 percent of net outflow) and 

streams (129 ft3/s or 30 percent of net outflow, fig. B24).

–1,200

–1,000

–800

–600

–400

–200

0

200

400

600

800

1,000

1,200

Flow rate, in cubic feet per second

Year

A

1880

1906

1919

1939

1953

1956

1961

1964

1971

1973

1978

1984

1986

1994

1999

2003

–1,200

–1,000

–800

–600

–400

–200

0

200

400

600

800

1,000

1,200

Flow rate, in cubic feet per second

Year

1880

1906

1919

1939

1953

1956

1961

1964

1971

1973

1978

1984

1986

1994

1999

2003

B
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 115

–1,200

–1,000

–800

–600

–400

–200

0

200

400

600

800

1,000

1,200

Flow rate, in cubic feet per second

Year

1880

1906

1919

1939

1953

1956

1961

1964

1971

1973

1978

1984

1986

1994

1999

2003

C

EXPLANATION

Storage change

Netflow from bedrock to alluvial aquifer

Stream and reservoir outflow

Evapotranspiration

Pumping

Springs and flow out of basin

Stream and reservoir inflow

Recharge

Figure B23. Simulated transient groundwater budget for (A) the entire Denver Basin modeled area, 

(B) the alluvial aquifer, and (C) the bedrock aquifers and confining units, 1879–2003.—Continued

Groundwater Budget for Alluvial 

and Bedrock Aquifers

Separating the water budget for the alluvial aquifer 

(table B3; fig. B23B) from that of the bedrock aquifers and 

confining units (herein referred to collectively as bedrock 

units) (table B4; fig. B23C) indicates that in 2003, about twothirds of the water moved in and out of the system through the 

alluvial aquifer (690 ft3/s), and about one-third of the water 

moved in and out of the system through the bedrock units 

(382 ft3/s). The fraction of total flow through the bedrock aquifers relative to flow through the alluvial aquifer increased from 

about one-quarter under predevelopment conditions to about 

one-third in 2003, reflecting the transient increase in bedrock 

aquifer water use relative to the alluvial aquifer. On average from 1879 to 2003, about 80 percent of the simulated net 

recharge was directly to the alluvial aquifer, while 20 percent 

of net recharge was directly to the bedrock aquifers. In 1956, 

simulated pumping from the alluvial aquifer (86 ft3/s) represented about 90 percent of the total pumping (about 95 ft3

/s), 

and pumping from bedrock aquifers (8 ft3/s) represented about 

10 percent of the total pumping. By 2003, pumping from the 

alluvial aquifer (about 170 ft3/s) represented about 60 percent 

of the total pumping (282 ft3/s), and pumping the bedrock 

aquifers (111 ft3/s) represented about 40 percent of the total 

pumping. The majority of net outflow to streams (90 percent 

on average) also was from the alluvial aquifer, while about 

10 percent of net outflow to streams was directly from bedrock 

aquifers from 1879 to 2003. The majority of net storage loss 

in 2003 (about 57 ft3/s or 90 percent) was from the bedrock 

aquifers (table B4).

Alluvial Aquifer Groundwater Budget

Inflow components of the developed alluvial aquifer 

water budget are recharge from infiltration of precipitation 

plus irrigation, inflow from underlying bedrock aquifers, 

and inflow from streams (table B3, fig. B25). Major outflow 

components from the alluvial aquifer are discharge to evapotranspiration, wells, and streams (table B3; fig. B23B, B25). 

Net recharge (recharge minus evapotranspiration) to the 

alluvial aquifer nearly doubled from a predevelopment (1879) 

flow rate of about 150 ft3/s to about 290 ft3/s in 2003 because 

of increases in the area of urban recharge. The maximum net 

recharge to the alluvial aquifer of about 308 ft3/s occurred in 

1999 before the onset of recent drought conditions (table B3). 

Simulated pumping from the alluvial aquifer increased 

approximately fourfold from about 40 ft3/s in 1953 to about 

144 ft3/s in 1971 and then more gradually to about 170 ft3/s in 

2003 (table B3). Outflow from the alluvial aquifer to streams 

remained relatively constant during the model-calibration 

period, but inflow to the alluvial aquifer from streams 

increased from a predevelopment flow rate of about 13 ft3/s 
116 Groundwater Availability of the Denver Basin Aquifer System, Colorado

to about 20 ft3/s in 2003 (table B3) and is attributed to the net 

increase in pumping through time. Recharge, evapotranspiration, and groundwater/surface-water interaction to and from 

the alluvial aquifer all increased from 1879 through 2003 

because of the increase in area of irrigation recharge overlying 

the alluvial aquifer and because of the increase in pumping 

from the alluvial aquifer. The alluvial aquifer is in hydraulic 

connection with the bedrock aquifers where bedrock sandstones are in direct contact with alluvial materials, and inflow 

from bedrock aquifers is a source of water to the alluvial aquifer. Net inflow from bedrock aquifers to the alluvial aquifer 

decreased from a predevelopment flow rate of about 26 ft3/s 

to a rate of about 15 ft3/s in 2003 (table B3), presumably in 

response to bedrock pumping, which has lowered hydraulic 

heads in the bedrock aquifers. Reservoir leakage also became 

a source of recharge to the alluvial aquifer through the modelcalibration period. Alluvial-aquifer storage gains and losses 

are related to net recharge rate and reflect climate variability. 

Storage loss (positive values of “net from storage”) is simulated during dry periods from 1964 through 1978 and from 

2000 through 2003, and storage gain (negative values of “net 

from storage”) is simulated during wet years from 1956 to 

1961 and from 1984 to 1999 (fig. B23B).

Bedrock Groundwater Budget

Recharge from precipitation plus irrigation is the primary 

inflow component of the bedrock water budget with inflow 

from streams and the overlying alluvial aquifer comprising 

minor inflow components (table B4; fig. B25). Inflow from 

storage became a contributing component of the bedrock 

water budget as pumping increased through time (table B4; 

fig. B23C). Primary outflow components from the bedrock 

aquifers and confining units are discharge to evapotranspiration, 

wells, the alluvial aquifer, and streams (table B4; fig. B23C, 

B25). Net recharge to the bedrock units approximately doubled 

from about 42 ft3/s in 1956 to about 83 ft3/s in 2003 because 

of increases in the area of urban recharge, and the maximum 

net recharge to the bedrock units of about 90 ft3/s occurred in 

1999 before the onset of recent drought conditions (table B4). 

Simulated pumping from the bedrock aquifers increased 

steadily from about 8 ft3/s in the 1956 to about 111 ft3/s in 

2003 (table B4). Net outflow to streams from the bedrock units 

increased slightly from a predevelopment flow rate of about 

14 ft3/s to about 16 ft3/s in 2003 (table B4). Net discharge 

from the bedrock units to the alluvial aquifer decreased from 

a predevelopment flow rate of about 26 ft3/s to about 15 ft3/s 

in 2003 (table B4), and the bedrock net storage-depletion rate 

increased from zero during predevelopment to about 57 ft3/s 

in 2003 (table B4, fig. B25) in response to pumping from the 

bedrock units.

Groundwater Budget Components

This discussion presents in-depth discussion of the changes 

to each groundwater budget component from 1879 to 2003. Simulated inflows were precipitation plus irrigation recharge, streams, 

reservoirs, interaquifer flow, and groundwater storage. Simulated 

outflows were evapotranspiration, wells, springs, interaquifer 

flow, groundwater storage, and model boundaries. The model 

represents streams, reservoirs, interaquifer flow, and groundwater 

storage such that they are both sources and sinks of groundwater.

INFLOW

NETFLOW

OUTFLOW

Inflow

Outflow

ALLUVIAL AQUIFER AND BEDROCK UNITS

Streams

24 cubic feet 

per second

(2 percent 

of inflow)

Recharge

894 cubic feet per second

(87 percent of inflow)

Reservoirs

42 cubic feet 

per second

(4 percent 

of inflow)

Storage loss

72 cubic feet per second

(7 percent of inflow)

Springs 

4 cubic feet 

per second

(<1 percent 

of outflow)

Groundwater 

flow out of basin

19 cubic feet 

per second

(2 percent 

of outflow)

Storage gain

8 cubic feet 

per second

(<1 percent 

of outflow)

Wells

282 cubic feet 

per second

(27 percent 

of outflow)

Streams

184 cubic feet 

per second

(18 percent 

of outflow)

Evapotranspiration

523 cubic feet per second 

(51 percent of outflow)

Reservoirs

11 cubic feet 

per second

(1 percent 

of inflow)

Groundwater flow

out of basin

19 cubic feet 

per second

(4 percent 

of net outflow)

Springs 

4 cubic feet 

per second

(1 percent 

of net outflow)

Wells

282 cubic feet 

per second

(65 percent of 

net outflow)

Net recharge

370 cubic feet per second

(85 percent of 

net inflow)

Net storage loss

63 cubic feet per second

(15 percent of net inflow)

Net to streams

129 cubic feet 

per second

(30 percent 

of net outflow)

Figure B24. Groundwater budget inflow and outflow components 

for the entire Denver Basin aquifer system at the end of the model 

calibration period, 2003.
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 117

Recharge and Evapotranspiration

Sources of recharge to the developed Denver Basin aquifer 

system include infiltration of incident precipitation and return 

flows in excess of consumptive use from agricultural irrigation and from urban applications (lawn irrigation and general 

water use). Simulated recharge from incident precipitation was 

applied to the land surface of the entire modeled area as a percentage of time-varying precipitation, and model stress periods 

were chosen so that climate variability, including recent drought 

conditions from 2000–2003, is represented in the model. 

Precipitation for a given model stress period was assigned as a 

spatial distribution (two-dimensional array) of average precipitation values for the given time period, and the percentage 

of incident precipitation assigned as recharge was estimated 

during model calibration. Model representation of precipitation 

recharge is described in section “Model-Calibration Results,” 

“Calibrated Recharge Parameters” in Chapter C.

Irrigated agricultural areas in the Denver Basin tend to 

overlie the alluvial aquifer along the South Platte River and 

its tributaries where surface water and alluvial groundwater 

Table B3. Simulated transient groundwater budget for the Denver Basin alluvial aquifer during the model-calibration period, 

1879–2003.

[Positive values represent flow into the groundwater model; negative values represent flow out of the groundwater model; in some cases values do not sum 

because of rounding; ft3/s, cubic feet per second]

Stress

period

Time

step Year

Inflow component

(ft3/s)

Precipitation plus

irrigation recharge Streams Reservoirleakage

Total from bedrock 

aquifers and 

confining units

Storage Total

1 1 1879 454.4 12.7 0.0 34.1 0.0 501

2 6 1906 454.4 12.7 0.0 34.1 0.0 501

3 5 1919 454.4 12.7 22.5 33.9 0.1 524

4 5 1939 454.4 12.6 22.6 33.8 0.6 524

5 5 1953 454.5 12.9 38.1 33.7 5.1 544

6 5 1956 511.4 12.5 38.3 33.8 17.1 613

7 5 1961 523.3 13.1 38.3 33.4 14.0 622

8 5 1964 476.6 13.4 38.9 32.5 42.6 604

9 5 1971 509.7 13.8 38.7 32.3 19.4 614

10 5 1973 509.6 19.8 41.5 31.8 21.3 624

11 5 1978 486.0 19.6 41.6 30.7 33.8 612

12 5 1984 528.7 19.9 41.5 29.9 8.9 629

13 5 1986 528.7 20.0 41.5 29.4 9.9 629

14 5 1994 604.7 20.1 37.9 29.4 6.9 699

15 5 1999 619.9 20.1 38.0 28.6 4.3 711

16 5 2003 592.7 20.1 38.1 27.2 11.4 690

Stress 

period

Time 

step Year

Outflow component

(ft3/s)

Evapotranspiration

Streams Reservoir 

leakage Springs

Out of basin 

underflow 

through 

alluvial 

aquifers

Specified 

flux to 

South Platte

alluvial 

aquifer

Wells 

completed 

in multiple 

aquifers

Wells

Total to 

bedrock 

aquifers and 

confining 

units

Storage Total

1 1 1879 –307.1 –164.2 0.0 –3.2 –4.8 –14.1 0.0 0.0 –7.8 0.0 –501

2 6 1906 –307.0 –164.2 0.0 –3.2 –4.8 –14.1 0.0 –0.0 –7.8 –0.0 –501

3 5 1919 –328.1 –164.3 0.0 –3.2 –4.8 –14.1 0.0 –1.1 –8.0 –0.1 –524

4 5 1939 –323.1 –162.7 0.0 –3.2 –4.8 –14.1 0.0 –7.8 –7.9 –0.2 –524

5 5 1953 –315.5 –157.1 –1.9 –3.1 –4.8 –14.1 0.0 –39.9 –7.7 –0.2 –544

6 5 1956 –303.1 –158.8 –1.9 –3.1 –4.8 –14.1 0.0 –86.1 –7.8 –33.5 –613

7 5 1961 –296.8 –162.1 –1.8 –3.1 –4.8 –14.1 –0.0 –106.8 –7.9 –24.7 –622

8 5 1964 –279.2 –159.2 –1.6 –3.0 –4.8 –14.1 –0.0 –123.7 –7.6 –10.8 –604

9 5 1971 –273.3 –159.4 –1.5 –2.9 –4.7 –14.1 –0.0 –143.6 –8.5 –5.9 –614

10 5 1973 –270.9 –159.2 –10.4 –2.9 –4.7 –14.1 –0.0 –148.5 –8.7 –4.5 –624

11 5 1978 –260.3 –157.1 –10.1 –2.9 –4.6 –14.1 –0.0 –152.4 –8.9 –1.5 –612

12 5 1984 –265.3 –159.3 –9.9 –2.9 –4.5 –14.1 –0.0 –155.9 –9.9 –7.0 –629

13 5 1986 –264.4 –158.9 –9.9 –2.9 –4.5 –14.1 –0.0 –158.7 –10.3 –5.7 –629

14 5 1994 –303.2 –166.1 –11.3 –3.0 –4.6 –14.1 –0.1 –162.1 –11.0 –23.7 –699

15 5 1999 –311.9 –167.0 –11.2 –3.0 –4.6 –14.1 –0.1 –168.1 –11.8 –19.3 –711

16 5 2003 –304.9 –164.3 –11.0 –2.9 –4.5 –14.1 –0.1 –170.8 –12.4 –4.5 –690
118 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Table B3. Simulated transient groundwater budget for the Denver Basin alluvial aquifer during the model-calibration period, 

1879–2003.—Continued

[Positive values represent flow into the groundwater model; negative values represent flow out of the groundwater model; in some cases values do not sum 

because of rounding; ft3/s, cubic feet per second]

Stress

period

Time

step Year

Net flow for selected components

(ft3

/s)

Net from recharge 

(recharge plus 

evapotranspiration)

Net to streams 

(stream inflow plus 

stream outflow)

Net to 

reservoir leakage

(reservoir inflow plus 

reservoir outflow)

Wells

Total to bedrock 

aquifers and 

confining units

Change in storage

(positive value indicates 

loss, negative value

indicates gain)

1 1 1879 147.3 –151.5 0.0 0.0 26.3 0.00

2 6 1906 147.4 –151.5 0.0 –0.0 26.3 0.01

3 5 1919 126.3 –151.6 22.5 –1.1 26.0 0.01

4 5 1939 131.2 –150.1 22.6 –7.8 25.9 0.38

5 5 1953 139.0 –144.2 36.3 –39.9 26.0 4.88

6 5 1956 208.3 –146.3 36.5 –86.1 26.0 –16.35

7 5 1961 226.5 –149.0 36.5 –106.8 25.6 –10.69

8 5 1964 197.3 –145.8 37.3 –123.7 24.9 31.84

9 5 1971 236.4 –145.7 37.2 –143.6 23.8 13.53

10 5 1973 238.8 –139.4 31.1 –148.5 23.0 16.80

11 5 1978 225.7 –137.5 31.6 –152.4 21.8 32.35

12 5 1984 263.4 –139.4 31.6 –155.9 19.9 1.97

13 5 1986 264.3 –138.9 31.6 –158.7 19.1 4.19

14 5 1994 301.5 –146.0 26.6 –162.2 18.4 –16.71

15 5 1999 308.0 –146.9 26.8 –168.1 16.8 –14.96

16 5 2003 287.8 –144.2 27.1 –170.9 14.8 6.93

Table B4. Simulated transient groundwater budget for the Denver Basin bedrock aquifers and confining units during the model-calibration

period, 1879–2003.

[Positive values represent flow into the groundwater model; negative values represent flow out of the groundwater model; in some cases values do not sum 

because of rounding; ft3/s, cubic feet per second]

Stress 

period

Time 

step Year

Inflow component

(ft3

/s)

Precipitation plus

irrigation recharge Streams Reservoir leakage

Wells completed

in multiple aquifers

Total from

alluvial aquifer Storage Total

1 1 1879 176.0 3.5 0.0 0.0 7.8 0.0 187

2 6 1906 176.0 3.5 0.0 0.0 7.8 0.0 187

3 5 1919 176.0 3.5 0.0 0.0 8.0 0.7 188

4 5 1939 178.9 3.5 0.0 0.0 7.9 0.8 191

5 5 1953 185.4 3.6 0.0 0.0 7.7 1.7 198

6 5 1956 226.1 3.2 0.1 0.0 7.8 2.5 240

7 5 1961 234.8 3.2 0.1 0.0 7.9 3.1 249

8 5 1964 205.1 3.7 0.1 0.0 7.6 16.9 233

9 5 1971 231.7 3.5 0.2 0.1 8.5 7.9 252

10 5 1973 231.8 3.5 0.2 0.1 8.7 12.4 257

11 5 1978 214.6 3.8 0.2 0.1 8.9 24.8 252

12 5 1984 234.4 3.7 0.2 0.2 9.9 21.4 270

13 5 1986 234.4 3.7 0.2 0.3 10.3 27.7 277

14 5 1994 311.1 3.8 3.6 0.4 11.0 30.9 361

15 5 1999 319.5 4.0 3.6 0.5 11.8 39.6 379

16 5 2003 300.8 4.2 3.7 0.6 12.4 60.2 382

are used as sources of irrigation water supply. Recharge from 

agricultural irrigation was applied as a constant rate to timevarying areas of irrigated agriculture determined from available 

GIS datasets and satellite images. Surface water used for irrigation is diverted from the South Platte River and its tributaries 

through irrigation ditches. Agricultural recharge in irrigation 

ditch service areas downstream from Denver was assigned 

a constant recharge rate of 10 in/yr on the basis of preliminary results from irrigation return-flow studies (L.R. Arnold, 

U.S. Geological Survey, oral commun., 2005). Irrigation ditch 

service areas delimited as part of the South Platte Decision 

Support System (Riverside Technology, Inc., 2005) were used 

to define the maximum area for agricultural irrigation recharge. 

The earliest available satellite imagery (U.S. Geological Survey, 

1973–1979) was used to identify irrigated areas in the 1970s, 

and for the simulated period from pre-1880 to 1953 (model 

stress periods 1 through 5), agricultural irrigation recharge 

was assumed to affect the 1973–1979 irrigated areas that also 
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 119

Table B4. Simulated transient groundwater budget for the Denver Basin bedrock aquifers and confining units during the modelcalibration period, 1879–2003.—Continued

[Positive values represent flow into the groundwater model; negative values represent flow out of the groundwater model; in some cases values do not sum 

because of rounding; ft3/s, cubic feet per second]

Stress 

period

Time 

step Year

Outflow component

(ft3/s)

Evapotranspiration

Streams Reservoir 

leakage Springs Wells completed in multiple aquifers Wells Total toalluvial aquifer Storage Total

1 1 1879 –134.5 –17.6 0.0 –1.0 0.0 0.0 –34.1 0.0 –187

2 6 1906 –134.5 –17.6 0.0 –1.1 0.0 –0.1 –34.1 –0.0 –187

3 5 1919 –134.3 –17.6 0.0 –1.0 0.0 –1.3 –33.9 –0.0 –188

4 5 1939 –136.8 –17.6 0.0 –1.0 –0.0 –2.0 –33.8 –0.0 –191

5 5 1953 –141.8 –17.9 0.0 –1.0 –0.0 –4.0 –33.7 –0.0 –198

6 5 1956 –167.3 –20.2 0.0 –1.2 –0.1 –8.4 –33.8 –8.6 –240

7 5 1961 –172.7 –20.8 0.0 –1.3 –0.5 –14.0 –33.4 –6.4 –249

8 5 1964 –157.4 –18.9 0.0 –1.0 –0.8 –20.2 –32.5 –2.5 –233

9 5 1971 –167.2 –20.4 0.0 –1.2 –1.1 –27.4 –32.3 –2.1 –252

10 5 1973 –165.8 –20.3 0.0 –1.1 –1.4 –34.9 –31.8 –1.4 –257

11 5 1978 –155.8 –19.1 0.0 –1.0 –2.1 –43.3 –30.7 –0.4 –252

12 5 1984 –162.4 –19.6 0.0 –1.0 –2.6 –52.4 –29.9 –2.0 –270

13 5 1986 –161.7 –19.5 0.0 –1.0 –3.0 –60.3 –29.4 –1.7 –277

14 5 1994 –224.1 –21.4 –0.010 –1.5 –4.0 –71.4 –29.4 –9.1 –361

15 5 1999 –228.6 –21.5 –0.011 –1.5 –5.0 –87.2 –28.6 –6.5 –379

16 5 2003 –218.1 –19.9 –0.008 –1.3 –6.2 –105.4 –27.2 –3.7 –382

Stress 

period

Time 

step Year

Net flow for selected components

(ft3/s)

Net from recharge 

(recharge plus 

evapotranspiration)

Net to streams 

(stream inflow plus 

stream outflow)

Net to reservoir leakage 

(reservoir inflow plus 

reservoir outflow)

Wells

Total to bedrock 

aquifers and

confining units

Change in storage

(positive value indicates 

loss, negative value 

indicates gain)

1 1 1879 41.5 –14.2 0.0 0 –26.3 0

2 6 1906 41.5 –14.2 0.0 –0.08 –26.3 0.04

3 5 1919 41.7 –14.1 0.0 –1.3 –26.0 0.7

4 5 1939 42.2 –14.1 0.0 –2.0 –25.9 0.8

5 5 1953 43.6 –14.3 0.0 –4.0 –26.0 1.7

6 5 1956 58.8 –17.1 0.1 –8.4 –26.0 –6.2

7 5 1961 62.1 –17.6 0.1 –14.5 –25.6 –3.3

8 5 1964 47.7 –15.3 0.1 –21.0 –24.9 14.4

9 5 1971 64.5 –16.9 0.2 –28.4 –23.8 5.8

10 5 1973 66.0 –16.8 0.2 –36.2 –23.0 11.0

11 5 1978 58.8 –15.3 0.2 –45.3 –21.8 24.4

12 5 1984 72.0 –15.9 0.2 –54.7 –19.9 19.4

13 5 1986 72.7 –15.7 0.2 –63.0 –19.1 25.9

14 5 1994 87.0 –17.6 3.6 –75.0 –18.4 21.9

15 5 1999 90.9 –17.5 3.6 –91.8 –16.8 33.1

16 5 2003 82.7 –15.7 3.7 –111.0 –14.8 56.5

are within the ditch service areas (fig. B26). For the simulated 

period 1954–1986 (model stress periods 6 though 13), polygons 

approximating the 1970s irrigated areas were used as zones 

of agricultural irrigation (fig. B27). For the simulation period 

1987–2003 (model stress periods 14 through 16), zones approximating irrigated areas were derived from satellite imagery from 

2000 (U.S. Geological Survey, 1999–2000) (fig. B28).

For urban recharge, a constant recharge rate was applied 

to time-varying urban areas also determined from available 

GIS datasets and satellite images. On the basis of recent lawnirrigation return-flow studies (Kevin Lusk, Colorado Springs 

Utilities, written commun., 2005), a constant water-application 

rate of 2.5 in/yr was applied to the mapped areas of urban 

recharge. While the urban recharge rate remained constant, 

the area over which urban recharge occurred increased 

through time on the basis of land-use mapping. Urban recharge 

is simulated beginning in 1920. For the simulation period 

1920–1939 (model stress period 4), the area for urban recharge 

application was delineated from “residential” land use in 

GIS data set LU30 (U.S. Geological Survey, 2001a). For the 

simulation period 1940–1953 (model stress period 5), the area 

for urban recharge application was delineated from residential 

land use in GIS dataset LU50 (U.S. Geological Survey, 2001b) 

(fig. B26). Satellite images were used to identify areas affected 
120 Groundwater Availability of the Denver Basin Aquifer System, Colorado

by urban recharge for the simulation period 1954–1986 (model 

stress periods 6 through 13; fig. B27) (U.S. Geological Survey, 

1973–1979) and for the simulation period 1987–2003 (model 

stress periods 14–16; fig. B28) (U.S. Geological Survey, 

1999–2000). The Denver aquifer underlies much of the area 

affected by urban recharge (fig. B28).

Simulated precipitation plus irrigation recharge to the 

entire aquifer system increased from a predevelopment 

(1879) flow rate of about 630 ft3/s to about 894 ft3/s in 2003 

(table B2). For the alluvial aquifer, simulated precipitation 

plus irrigation recharge increased from the 1879 flow rate of 

about 454 ft3/s to about 593 ft3/s in 2003, and for the bedrock 

aquifers, simulated precipitation plus irrigation recharge 

increased from the 1879 flow rate of about 176 ft3/s to about 

300 ft3/s in 2003 (fig. B29). Maximum recharge to the alluvial aquifer (about 620 ft3

/s) and to the bedrock aquifers 

(about 320 ft3/s) occurred in 1999 before the onset of recent 

drought conditions simulated from 2000–2003 (tables B2, 

B3; fig. B29). Recharge to the alluvial and bedrock aquifers 

showed step increases in 1956 and 1994 in response to the 

increase in the area of urban recharge simulated for the periods 

1954–1986 and 1987–2003 (fig. B29).

Figure B25. Groundwater budget inflow and outflow components for the Denver Basin alluvial aquifer 

and bedrock units at the end of the model calibration period, 2003.

Streams

4 cubic feet per second

(1 percent of inflow)

Flow from 

alluvial aquifer

12 cubic feet per second

(3 percent of inflow)

Recharge

301 cubic feet per second

(79 percent 

of inflow)

Storage loss

60 cubic feet per second

(16 percent of inflow)

Reservoirs

4 cubic feet per second

(1 percent of inflow)

ALLUVIAL AQUIFER BEDROCK UNITS

INFLOW

NETFLOW

OUTFLOW

Inflow

Outflow

Recharge

592 cubic feet per second

(86 percent of inflow)

Streams

20 cubic feet per second

(3 percent of inflow)

Flow from 

bedrock units

27 cubic feet per second

(4 percent of inflow)

Reservoirs

38 cubic feet per second

(6 percent 

of inflow)

Storage loss

12 cubic feet per second

(2 percent of inflow)

Net recharge

288 cubic feet per second

(93 percent of net inflow)

Springs

3 cubic feet per second

(1 percent of net outflow)

Groundwater flow

out of basin

19 cubic feet per second

(6 percent of net outflow)

Flow from bedrock units

15 cubic feet per second

(5 percent of net inflow)

Wells

171 cubic feet 

per second

(61 percent 

of net outflow)

Storage loss

7 cubic feet per second

(2 percent of net inflow)

Streams

117 cubic feet 

per second

(91 percent of 

net outflow)

Evapotranspiration

304 cubic feet per second

(44 percent of outflow)

Streams

164 cubic feet

per second

(24 percent 

of outflow)

Wells

171 cubic feet 

per second

(25 percent 

of outflow)

Flow to bedrock units

12 cubic feet per second

(2 percent of outflow)

Storage gain

5 cubic feet per second

(1 percent of outflow)

Reservoirs

11 cubic feet per second

(1 percent of outflow)

Springs

3 cubic feet 

per second

(<1 percent of

 outflow)

Groundwater flow out of basin

19 cubic feet per second

(3 percent of outflow)

Streams

20 cubic feet 

per second

(5 percent 

of outflow)

Evapotranspiration

218 cubic feet per second

(57 percent of outflow)

Flow to alluvial aquifer

27 cubic feet per second

(7 percent of outflow)

Wells

111 cubic feet per second

(29 percent of outflow)

Storage gain

4 cubic feet per second

(1 percent of outflow)

Streams

12 cubic feet per second

(9 percent of net outflow)

Net recharge

83 cubic feet per second

(59 percent of net inflow)

Flow to alluvial aquifer

15 cubic feet per second

(11 percent of net outflow)

Storage loss

57 cubic feet per second

(41 percent of net inflow)

Wells

111 cubic feet per second

(80 percent of net outflow)
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 121

Figure B26. Estimated areas of agricultural and urban irrigation as simulated by the Denver Basin 

model, 1940–1953.

South

Platte River

Lost Creek

Cache la Poudre R

Big Thompson R

Little ThompsonR

Boulder Cr

Coal Creek

Big Dry Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek WestP ul m Creek

Bear Creek

Running Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCreek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCr eek

Middle Ru sh Creek

Mustang Creek

Adobe Creek

Steels Fork Horse Creek

West Bijou Creek

Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Creek

S aint Vrain Creek

Box Elder Creek

PALMER

DIVIDE

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WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

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WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Greeley

Boulder

Bennett

Loveland

Morrison

Monument

Longmont

Brighton

Franktown

Elizabeth

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Colorado

Springs

Wiggins

Lafayette

Lakewood Denver

Broomfield

Highlands 

Ranch

Aurora

Littleton

Engelwood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Greeley

Boulder

Bennett

Loveland

Morrison

Monument

Longmont

Brighton

Franktown

Elizabeth

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Colorado

Springs

Wiggins

Lafayette

Lakewood Denver

Broomfield

Highlands 

Ranch

Aurora

Littleton

Engelwood

§ ̈¦70

§ ̈¦25

§ ̈¦76

105°

40°

39°

104°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Agricultural irrigation recharge, 1880–1953

Urban irrigation recharge, 1940–1953 Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Alluvial aquifer simulated extent (model layer 1) Stream

Perennial

Ephemeral
122 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B27. Estimated areas of agricultural and urban irrigation as simulated by the Denver Basin 

model, 1954–1986.

South

Platte River

Lost Creek

Box Elder Creek

Cache la Poudre R

Big Thompson Riv er

Little ThompsonR

Boulder Cr

Coal Creek

BigDry Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger Creek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East Bi oj uCr eek

Middle Ru sh Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Creek

Big Sandy Creek

Brac kett Cr

Black Squir rel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Creek Saint Vrain Creek

§ ̈¦70

§ ̈¦25

§ ̈¦76

PALMER

DIVIDE

PALMER

DIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

105°

40°

39°

104°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Agricultural irrigation recharge, 1954–1986

Urban irrigation recharge, 1954–1986

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Alluvial aquifer simulated extent (model layer 1) Stream

Perennial

Ephemeral
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 123

Figure B28. Estimated areas of agricultural and urban irrigation as simulated by the Denver Basin 

model, 1987–2003.

South

Platte

River

Lost Creek

Box Elder Creek

Cache la Poudre R

Big Thompson River Little Thompson R

BoulderCr

Coal Creek

Big Dry Cr

Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCreek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East Bi oj uCr eek

Middle Ru sh Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Creek

Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Creek

Saint Vrain Creek

PALMER

DIVIDE

PALMER

DIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

§ ̈¦70

§ ̈¦25

§ ̈¦76

105°

40°

39°

104°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Agricultural irrigation recharge, 1987–2003

Urban irrigation recharge, 1987–2003

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Alluvial aquifer simulated extent (model layer 1) Stream

Perennial

Ephemeral
124 Groundwater Availability of the Denver Basin Aquifer System, Colorado

The simulated spatial distribution of recharge for 2003 

shows that recharge rates were greatest (10 to 11.2 in/yr) in areas 

of agricultural irrigation overlying the alluvial aquifer (fig. B30). 

The effects of urban recharge in the Denver and Monument 

areas also are apparent in the 2003 recharge distribution map, 

where precipitation plus urban recharge rates ranged from 2.5 to 

3.8 in/yr (fig. B30). In areas not affected by agricultural or urban 

recharge, simulated precipitation recharge rates were greatest 

over the Dawson aquifers and confining unit, where recharge 

was estimated by model calibration as 2 percent of annual 

precipitation and ranged from 0.2 to 0.4 in/yr. The effects of 

recent drought are evident in the simulated recharge distribution 

for 2000–2003 (model stress period 16; fig. B30) which shows 

lower recharge rates to the northern part of the Dawson aquifer 

as compared to predevelopment conditions (fig. A47).

Of the bedrock units, the Denver aquifer received the 

greatest amount of precipitation plus irrigation recharge after 

1954 (table B5; fig. B31). The Denver aquifer underlies both 

of the areas receiving urban recharge (Denver and Monument) 

and therefore received greater amounts of recharge as 

urbanization proceeded. A large step increase in recharge to 

the Denver aquifer occurred in 1956, and step increases in 

recharge to all bedrock aquifers and confining units occurred 

in 1994 in response to increases in the area of urban recharge 

(fig. B31). Estimated precipitation recharge rates for the 

Dawson units are greater than to the other bedrock aquifers. 

However, simulation results indicate that the Laramie–Fox 

Hills aquifer and the Laramie confining unit received more 

Flow, in cubic feet per second

Year

–700

–500

–300

–100

100

300

500

700

EXPLANATION

Recharge to (positive flow) and evapotranspiration 

 from (negative flow) alluvial aquifer

Recharge to (positive flow) and evapotranspiration 

 from (negative flow) bedrock units

Recharge minus evapotranspiration for alluvial aquifer

Recharge minus evapotranspiration for bedrock units

1880

1906

1919

1939

1953

1956

1961

1964

1971

1973

1978

1984

1986

1994

1999

2003

Figure B29. Simulated transient recharge, evapotranspiration, and recharge minus 

evapotranspiration for the alluvial aquifer and bedrock units in the Denver Basin, 1879–2003.

total recharge than the combined Dawson units since predevelopment, likely because they receive agricultural irrigation 

recharge in the northern part of the basin.

The temporal distribution of recharge reflects climate variability and represents recent drought conditions. Dry conditions 

in the early 1960s resulted in decreased recharge rates to all bedrock aquifers and confining units in 1964 (fig. B31), and wetter 

conditions in the early 1970s resulted in increased recharge rates 

to all bedrock aquifers and confining units in 1971 and 1974 

(fig. B31). Recharge to almost all of the bedrock units increased 

substantially around 1990 in response to increased precipitation, and maximum recharge rates occurred in 1999 prior to the 

recent drought. The simulated decrease in precipitation recharge 

for the period 2000–2003 (fig. B31) represents the effects of 

recent drought conditions which began in 2000.

Evapotranspiration from groundwater is the primary 

process for natural discharge in the Denver Basin and was a 

simulated value based on a piecewise linear relation of evapotranspiration rate compared to depth to water as discussed 

in the sections “Hydrologic Stresses,” “Evapotranspiration” 

in Chapter C. A map of the predevelopment evapotranspiration distribution indicates small evapotranspiration rates (less 

than 0.5 in/yr) over much of the Denver Basin with greater 

evapotranspiration rates along stream channels and in areas 

of irrigated agriculture (fig. A49). The spatial distribution of 

evapotranspiration in 2003 (fig. B32) is similar to that for 

predevelopment conditions in that evapotranspiration rates 

are greatest from areas underlain by the alluvial aquifer along 
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 125

Figure B30. Spatial distribution of simulated precipitation plus irrigation recharge for the Denver 

Basin modeled area, 2003.

South Platte River

Cache la Poudre R

Big Thompson Riv er

Little ThompsonR

Boulder Cr

Coal Creek

BigDry Cr Clear Cre ek

West Sand Creek

First Cree k

Sand Cree

L

k

ittle Dry Cr

Plum Creek West P ul m Creek

Bear Creek

Running Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCreek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East Bi oj uCr eek

Middle Ru sh Creek

Mustang Creek

Adobe Cree

St

k

eels Fork

Horse Creek

West Bijou Creek

Big Sandy Creek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook C reek

Dry Cr

Fountain Creek

Saint Vrain Creek

Lost Creek

Box Elder Creek

PALMER

DIVIDE

PALMER

DIVIDE

§ ̈¦70

§ ̈¦25

§ ̈¦76

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

105°

40°

39°

104°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Simulated precipitation plus irrigation

 recharge, 2003, in inches per year

0.13 to 0.2

0.2 to 0.3

0.3 to 0.4

0.4 to 0.5

0.5 to 0.75

0.75 to 1.3

1.3 to 2.5

2.5 to 4

10.0 to 11.1 Stream

Perennial

Ephemeral

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Alluvial aquifer simulated extent (model layer 1)
126 Groundwater Availability of the Denver Basin Aquifer System, Colorado Table B5. Simulated groundwater budget for individual bedrock aquifers and confining units in the Denver Basin, 2003. [In some cases values do not sum because of rounding; all flow rates are in cubic feet per second (ft3/s); <, less than; blank, not applicable] Groundwater-budget component Upper Dawson aquifer Dawson confining unit Lower Dawson aquifer Denver upper confining unit Denver aquifer Denver lower confining unit Upper Arapahoe aquifer Arapahoe confining unit Lower Arapahoe aquifer Laramie confining unit Laramie–Fox Hills aquifer Inflow Recharge (precipitation + irrigation) 19.3 2.7 24.1 5.5 69.3 18.1 16.5 10.3 19.4 56.8 58.9 Streams 0.25 0.0 1.1 0.06 1.9 0.06 0.20 0.0 0.33 0.26 0.05 Reservoir leakage 0.0 3.4 0.0 0.0 0.27 0.0 0.0 0.0 0.0 0.0 0.0 From alluvial aquifer 0.04 0.008 0.28 0.0005 3.1 0.47 2.3 0.007 0.62 1.2 4.3 From overlying bedrock 0.0 6.8 7.4 12.5 13.6 41.6 53.3 36.9 38.0 4.1 15.1 From wells completed in multiple aquifers 0.0 0.0 0.36 0.0 0.44 0.0 0.04 0.0 0.12 0.0 0.03 Storage 4.3 0.11 10.3 0.25 26.1 0.64 2.6 0.17 1.6 6.2 8.0 Total inflow 24.3 13.4 44.2 19.0 116.9 63.9 78.1 50.5 63.0 69.6 86.4 Outflow Evapotranspiration –6.4 –5.1 –13.7 –3.9 –42.6 –6.9 –10.9 –9.3 –17.7 –50.0 –51.5 Streams –3.1 –0.39 –2.9 –0.59 –5.1 –0.31 –2.2 –0.10 –0.66 –1.2 –3.4 Reservoir leakage 0.0 0.008 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Springs –0.19 –0.07 –0.007 –0.17 –0.11 –0.22 –0.05 0.0 0.0 –0.003 –0.41 To alluvial aquifer –0.9 <–0.001 –0.35 –0.007 –1.1 –0.48 –10.4 –0.005 –0.58 –0.31 –13.2 To underlying bedrock –6.8 –7.4 –12.5 –13.6 –41.6 –53.3 –36.9 –38.0 –4.1 –15.1 0.0

To wells completed in multiple aquifers –0.5 0.0 –0.6 0.0 –0.04 0.0 –4.1 0.0 –0.96 0.0 –0.008Wells –6.5 0.0 –13.5 0.0 –25.3 0.0 –7.7 0.0 –35.7 0.0 –16.7Storage 0.0 –0.01 –0.05 0.0 –0.31 –0.003 –3.0 –0.003 –0.17 –0.004 –0.22

Total outflow

–24.3 –13.4 –44.2 –19.0 –116.9 –63.9 –78.1 –50.5 –63.0 –69.6 –86.4

Net flows

Net recharge (recharge + evapotranspiration) 12.9 –2.4 10.3 1.6 26.7 11.1 5.6 1.0 1.7 6.8 7.4Net stream discharge (stream inflow + stream outflow) –3.3 –0.40 –4.0 –0.65 –6.9 –0.37 –2.4 –0.1 –0.10 –1.4 –3.5Net from reservoirs 0.0 3.4 0.0 0.0 0.27 0.0 0.0 0.0 0.0 0.0 0.0Net to alluvial aquifer –0.9 0.008 –0.08 –0.002 2.0 –0.01 –8.0 0.06 0.04 –0.93 –8.8Net to wells –7.0 0.0 –13.8 0.0 –25.3 0.0 –11.7 0.0 –36.5 0.0 –16.7Net from storage 4.2 0.10 10.2 0.25 25.8 0.63 –0.41 0.17 1.5 6.2 7.8
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 127

stream channels and in areas of irrigated agriculture. However, 

in 2003, increased evapotranspiration is also evident in the areas 

of urban recharge near Denver and Monument (fig. B32).

Evapotranspiration from all of the bedrock units except the 

Denver aquifer remained relatively constant from predevelopment until the 1990s (fig. B33). Similar to recharge, a large step 

increase in evapotranspiration from the Denver aquifer occurred 

in 1956, and step increases in evapotranspiration from all bedrock 

aquifers and confining units occurred in 1994 in response to 

increases in the area of urban recharge (figs. B31, B33). Evapotranspiration from the bedrock units was greatest for the Laramie–

Fox Hills aquifer for the entire simulation period (table B5; 

fig. B33) likely because it crops out in the area of agricultural 

irrigation recharge in the northern part of the basin.

Net recharge is calculated as the difference between recharge 

and evapotranspiration. The simulated net recharge rates over 

undeveloped and nonirrigated areas of the Denver Basin represent 

recharge from precipitation only and were less than 0.5 in/yr for 

the entire model-calibration period changing only in response to 

climatic variations in precipitation recharge. Net recharge rates 

in the range of 0.5 to 2 in/yr were calculated for urban recharge 

areas overlying alluvial aquifers as 7 percent of precipitation plus 

2.5 in/yr for urban recharge minus model-calculated evapotranspiration. Net recharge rates in the range of 10 to 11.2 in/yr 

were calculated for agricultural recharge areas overlying alluvial 

aquifers for 2003 (fig. B34). In some areas of the basin, primarily in agricultural recharge areas overlying the alluvial aquifer 

in the South Platte River valley, simulated evapotranspiration 

exceeds recharge from precipitation plus irrigation such that a 

negative net recharge, or net discharge, results (fig. B34).

Of the bedrock units, the Denver aquifer received the 

greatest net recharge since predevelopment (table B5; fig. B35). 

Application of urban recharge near Denver and Monument 

accounts for the increase in net recharge to the Denver aquifer 

from the 1879 value of about 10 ft3/s to a 2003 value of about 

27 ft3/s. The upper Dawson aquifer received the second-greatest 

quantity of net recharge, which ranged from about 5 ft3/s in the 

1950s to about 13 ft3/s in 2003 (fig. B35). The Laramie–Fox Hills 

aquifer and Laramie confining units received large amounts of 

precipitation recharge (fig. B29), but evapotranspiration from 

these units also was large (fig. B33), which resulted in less net 

recharge to these units than to the Dawson and Denver units 

(fig. B35). From the mid-1980s to 1999, net recharge to all of 

the bedrock units increased in response to increased precipitation 

and urban recharge. However, net recharge to the bedrock units 

decreased after 1999 (figs. B29, B35) in response to regional 

drought, which is simulated by the model as reduced precipitation 

recharge from 2000 to 2003. These results indicate that variations 

in climate and thus precipitation directly affect recharge rates in 

the Denver Basin.

Increase in area of

urban recharge

Increase in area of

urban recharge

Year

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Flow, in cubic feet per second 0

10

20

30

40

50

60

70

80

Upper Dawson aquifer

Lower Dawson aquifer

Dawson confining unit

Variable to dry conditions

Variable to wet conditions

Upper Arapahoe aquifer

Lower Arapahoe aquifer

Laramie–Fox Hills aquifer

Arapahoe confining unit

Denver aquifer Laramie confining unit

Denver upperconfining unit

Denver lowerconfining unit

EXPLANATION

Figure B31. Simulated transient precipitation plus irrigation recharge for individual Denver Basin bedrock 

units, 1879–2003.
128 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B32. Spatial distribution of simulated evapotranspiration for the Denver Basin modeled 

area, 2003.

South Platte River

Cache la Poudre R

Big Thompson Rive r

Little Thompson R

Boulder Cr

Coal Creek

Big Dry Cr Clear Cre ek

West Sand Creek

First Creek

Sand Creek

Little Dry Cr

Plum Creek WestP ul m Creek

Bear Creek

Running Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCreek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East Bi oj uCr eek

Middle Ru sh Creek

Mustang Creek

Adobe Creek

Steels Fork Horse Creek

West Bijou Creek

Big Sandy Creek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook C reek

Dry Cr

Fountain Creek

Saint Vrain Creek

Lost Creek

Box Elder Creek

PALMER

DIVIDE

PALMER

DIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

105°

40°

39°

104°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Simulated evapotranspiration, 2003, 

 in inches per year

–45 to –25

–25 to –10

–10 to –5

–5 to –2

–2 to –1

–1 to –0.5

<–0.5

0 Stream

Perennial

Ephemeral

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Alluvial aquifer simulated extent (model layer 1)
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 129

Discharge to Wells

Simulated pumping increased steadily for the alluvial 

and bedrock aquifers since the 1950s consistent with assigned 

pumping rates and locations developed by this study (fig. B36). 

Simulated pumping for 2003 for the alluvial aquifer (170 ft3/s) 

was greater than that for the bedrock aquifers (111 ft3/s) consistent with the conceptual understanding that the alluvial aquifer 

is more conductive and more heavily pumped than the bedrock 

aquifers. Simulated pumping was slightly less than estimated 

pumping values of 187 ft3/s for alluvial wells and 118 ft3/s for 

bedrock wells because some model cells representing pumping 

wells were deactivated when simulated heads calculated during 

the iterative solution procedure dropped below the bottom of the 

model cell (dry model cells).

Simulated pumping also increased steadily since the 1950s 

for individual bedrock aquifers (fig. B37). The lower Arapahoe 

aquifer is considered the most transmissive and productive of 

the bedrock aquifers because of its relatively high hydraulic 

conductivity, large thickness, and extensive sandstones, and, of 

the bedrock aquifers, the greatest simulated pumping is from 

the lower Arapahoe aquifer (about 30 ft3/s in 2003, 31 percent 

of bedrock pumping). The remaining bedrock aquifers and their 

simulated pumping rates in 2003, in order of decreasing pumping, are the Denver aquifer (about 25 ft3

/s, 22 percent of bedrock 

pumping), the Laramie–Fox Hills aquifer (about 17 ft3/s, 14 percent of bedrock pumping), the lower Dawson aquifer (about 

14 ft3/s, 13 percent of bedrock pumping), the upper Arapahoe 

aquifer (about 12 ft3/s, 11 percent of bedrock pumping), and 

the upper Dawson aquifer (about 7 ft3/s, 6 percent of bedrock 

pumping) (table B5). The spatial distribution and quantities of 

simulated pumping are displayed on maps of simulated hydraulic heads for each model aquifer layer for 1956, 1978, and 

2003 in the section “Model Calibration Results,” “Simulated 

Hydraulic Heads” in Chapter C.

Groundwater/Surface-Water Interaction

Groundwater from the alluvial aquifer, bedrock aquifers, and confining units interacts with streams. There also is 

hydraulic connection between the bedrock units and the alluvial 

aquifer. Where alluvium is thin or absent, such as in higher 

altitude parts of the basin near the Palmer Divide, bedrock units 

discharge directly to streams that originate in the Denver Basin 

(as indicated by negative groundwater flow to streams) both for 

simulated predevelopment (fig. A52) and 2003 (fig. B38) conditions. In downstream parts of the basin where the topographic 

gradient flattens and the alluvial aquifer is present, flow is from 

streams to groundwater (as indicated by positive groundwater 

flow to streams on fig. B38) and streambeds can be dry for 

both predevelopment (fig. A52) and 2003 (fig. B38) conditions. 

Negative changes in groundwater flow to streams are simulated 

from 1880 to 2003 in the Denver and Monument areas affected 

by urban development (fig. B39) and indicate a transient 

increase in groundwater discharge to streams in urbanized areas 

resulting from the increase in urban recharge. Positive changes 

in groundwater flow to and from streams flow from 1880 to 

2003 represent a reduction in groundwater flow to streams and 

Figure B33. Simulated transient evapotranspiration for individual Denver Basin bedrock units, 1879–2003.

Increase in area 

of urban recharge

Increase in area 

of urban recharge

0

10

20

30

40

50

60

Flow, in cubic feet per second

Year

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Upper Dawson aquifer

Lower Dawson aquifer

Dawson confining unit

Variable to dry conditions

Variable to wet conditions

Upper Arapahoe aquifer

Lower Arapahoe aquifer

Laramie–Fox Hills aquifer

Arapahoe confining unit

Denver aquifer Laramie confining unit

Denver upper confining unit

Denver lower confining unit

EXPLANATION
130 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B34. Spatial distribution of simulated recharge minus evapotranspiration for the Denver 

Basin modeled area, 2003.

South

Platte River

Cache la Poudre R

Big Thompson R

Little Thompson R

Boulder Cr

Coal Creek

Big Dry Cr Clear Cre ek

West Sand Creek

First Creek

Sand Creek

Little Dry Cr

Plum Creek WestP ul m

Bear Creek

Running Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCreek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCr eek

Middle Ru sh Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Creek

Big Sandy Cre ek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook C reek

Dry Cr

Fountain Creek Saint Vrain Creek Lost Creek

Box Elder Creek

PALMER

DIVIDE

PALMER

DIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

105°

40°

39°

104°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Simulated recharge minus evapotranspiration, 

 2003, in inches per year

–45 to –25

–25 to –10

–10 to –3

–3 to 0

0

0 to 0.5

0.5 to 1

1.0 to 2.5

2.5 to 4

4.0 to 10

10.0 to 11.1

Stream

Perennial

Ephemeral

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Alluvial aquifer simulated extent (model layer 1)
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 131

Flow, in cubic feet per second

Year

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

–5

0

5

10

15

20

25

30

Increase in area of

urban recharge

Increase in area of

urban recharge

Upper Dawson aquifer

Lower Dawson aquifer

Dawson confining unit

Variable to dry conditions

Variable to wet conditions

Upper Arapahoe aquifer

Lower Arapahoe aquifer

Laramie–Fox Hills aquifer

Arapahoe confining unit

Denver aquifer Laramie confining unit

Denver upper confining unit

Denver lower confining unit

EXPLANATION

Figure B35. Simulated transient recharge minus evapotranspiration for individual Denver Basin 

bedrock units, 1879–2003.

Figure B36. Simulated transient pumping from Denver Basin alluvial and bedrock aquifers, 1879–2003.

Simulated pumping, in cubic feet per second 20

40

60

80

100

120

140

160

180

Year

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

0

Alluvial aquifer

Bedrock aquifers

EXPLANATION
132 Groundwater Availability of the Denver Basin Aquifer System, Colorado

are simulated in upland areas near the Palmer Divide (fig. B39) 

in response to decreased precipitation recharge and increased 

pumping for the bedrock aquifers. The overall transient pattern 

of increased groundwater discharge to streams in urbanized 

areas is consistent with the conceptual understanding of changes 

to the hydrologic system and previous studies that indicate 

increased irrigation in developed parts of the basin contributes 

to perennial surface-water flow in naturally ephemeral streams 

(Nadler and Schumm, 1981).

Groundwater/surface-water interaction is predominantly 

between the alluvial aquifer and streams on the basis of simulation results and is about 10 times greater than direct groundwater/surface-water interaction between the bedrock units and 

streams (fig. B40). Transient groundwater outflow to streams 

from the alluvial aquifer showed little variation ranging from a 

predevelopment value of about –164 ft3/s to a minimum value 

of about –157 ft3/s in 1953 and 1978, and to a maximum value 

of about –167 ft3/s in 1999 before recent drought conditions 

(table B2; fig. B40). Transient groundwater inflow (recharge) 

from streams to the alluvial aquifer increased from about 

13 ft3/s in 1956 to about 20 ft3/s in 2003 (table B3; fig. B40). 

The resulting transient net flow to streams from the alluvial 

aquifer decreased from about –150 ft3/s for predevelopment 

conditions to about –144 ft3/s for 2003 (table B2; fig. B40). For 

the bedrock aquifers and confining units, transient groundwater 

outflow to streams varied between about –18 and –20 ft3/s for 

the period 1879–2003, and the transient groundwater inflow 

from streams varied between about –3.5 and –4.2 ft3/s with a 

slight increase over time (table B3; fig. B40). The transient net 

flow to streams from bedrock units varied between –14 and 

–18 ft3/s with a slight increase over time (fig. B40).

For the individual bedrock units (fig. B41), net flow to 

streams before the 1950s was greatest from the upper and lower 

Dawson aquifers, which crop out beneath the Palmer Divide in 

the headwaters area of streams draining the Denver Basin. However, there was an overall decrease in net flow to streams for 

the upper and lower Dawson aquifers from 1880 through 2003. 

There was a substantial decrease in net flow to streams from 

both the upper and lower Dawson aquifers from 2000 to 2003 

(fig. B41) caused by a corresponding decrease in net recharge 

during recent drought conditions. Net flow to streams from the 

Denver aquifer increased over the model-calibration period in 

response to the increase in urban recharge. Simulated net flow 

to streams from the Denver aquifer increased from about –1 ft3/s 

prior to 1953 to about –3.3 ft3/s by 2003 (fig. B41).

The net flow to the alluvial aquifer from bedrock units 

decreased through time (fig. B42). Simulated flow from bedrock 

units to the alluvial aquifer decreased from about 34 ft3/s in 

1879 to 27 ft3/s in 2003, and simulated flow from the alluvial 

aquifer to the bedrock aquifer increased from about 8 ft3/s in 

1879 to 12 ft3/s in 2003 (table B3; fig. B42). The difference 

between bedrock flow to the alluvial aquifer and alluvial aquifer 

flow to the bedrock is the net flow from bedrock to alluvium, 

which has decreased from about 26 ft3/s in 1879 to about 15 ft3/s 

in 2003 (table B3; fig. B42). These flows translate to equivalent 

flux rates of 0.16 and 0.10 in/yr, for predevelopment and 2003, 

respectively, when the flow rates are divided by the alluvial 

aquifer area (2,121 mi2).

For individual bedrock units, net flow to the alluvial 

aquifer is greatest from the upper Arapahoe and Laramie–Fox 

Hills aquifers (fig. B43), which crop out in the northern parts 

of the Denver Basin where the alluvial aquifer is extensive. Net 

flow to the alluvial aquifer from the upper Arapahoe aquifer 

decreased from about 13 ft3/s before 1953 to about 8 ft3/s in 

2003, while there was little variation in the net flow to the 

alluvial aquifer from the Laramie–Fox Hills aquifer (table B5; 

fig. B43). Net flow to the alluvial aquifer from other bedrock 

aquifers was generally less than 2 ft3/s, and net flow to the 

Figure B37. Simulated transient pumping from individual Denver Basin bedrock aquifers, 1879–2003.

18801885

1890

1895

1900

1905

1910191519201925

193019351940

1945

1950

1955

19601965

1970

19751980

198519901995

2000

2005

Year

0

5

10

15

20

25

30

35

Flow, in cubic feet per second

Upper Dawson aquifer

Lower Dawson aquifer

Upper Arapahoe aquifer

Lower Arapahoe aquifer

Laramie–Fox Hills aquifer

Denver aquifer

EXPLANATION
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 133

Figure B38. Spatial distribution of simulated groundwater flow to and from streams for the Denver 

Basin modeled area, 2003.

South Platte River

Cache la Poudre R

Big Thompson R

Little Thompson R

Boulder Cr

Coal Creek

BigDry Cr

Clear Cre ek

West Sand Creek

First Creek

Sand Cree

L

k

ittle Dry Cr

Plum Creek West P ul m Creek

Bear Creek

Running Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCreek

Bijou Creek

Antelope Creek

Middle Bijou Creek

East BijouCr eek

Middle Ru sh Creek

Mustang Creek

Adobe Creek

Steels Fork Horse Creek

West Bijou Creek

Big Sandy Cre ek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook C reek

Dry Cr

Fountain Creek

Saint Vrain Creek

L ost Creek

Box Elder Creek

PALMER

DIVIDE

PALMER

DIVIDE

§ ̈¦70

§ ̈¦25

§ ̈¦76

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

105°

40°

39°

104°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Groundwater flow to and from streams, 

 2003, in cubic feet per second

–5.9 to –4

–4 to –2

–2 to –1

–1 to –0.25

–0.25 to 0

0

0 to 2

2 to 4

4 to 5.5

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Alluvial aquifer simulated extent (model layer 1)

Stream

Perennial

Ephemeral
134 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B39. Spatial distribution of change in sumulated groundwater flow to and from streams 

for the Denver Basin modeled area, 1880–2003.

Sout h Platte River

Cache la PoudreR

Big Thompson R

Little Thompson R

Boulder Cr

Coal Creek

Big Dry Cr Clear Creek

West Sand Creek

First Creek

Sand Creek

Little Dry Cr

Plum Creek WestPlu m

Bear Creek

Running Creek

Dry Creek Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCreek

Bijou Creek

Antelope Creek

Middle Bijou Creek

East BijouCreek

Middle R ush Creek

Mustang Creek

Adobe Creek

Steels Fork Horse Creek

West Bijou Cree k

Big Sandy Creek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek

Dry Cr

Fountain Creek

Saint Vrain Creek

Lost Creek

Box Elder Creek

PALMER

DIVIDE

PALMER

DIVIDE

§ ̈¦70

§ ̈¦25

§ ̈¦76

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

105°

40°

39°

104°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Change in groundwater flow to and 

 from streams, 1880–2003, in cubic 

 feet per second

–2.8 to –1

–1 to –0.25

–0.25 to 0

0

0 to 0.25

0.25 to 2

2 to 5 Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Alluvial aquifer simulated extent (model layer 1)

Stream

Perennial

Ephemeral
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 135

Year

1880

1906

1919

1939

1953

1956

1961

1964

1971

1973

1978

1984

1986

1994

1999

2003

0

50

–50

–100

–150

–200

Flow , in cubic feet per second

EXPLANATION

Net flow to streams from alluvial aquifer Net flow to streams from bedrock units

Inflow from streams to the alluvial aquifer 

(positive) or outflow to streams from 

the alluvial aquifer (negative)

Inflow from streams to the bedrock units 

(positive) or outflow to streams from 

the bedrock units (negative)

Figure B40. Simulated transient groundwater flow to and from streams from the alluvial aquifer and bedrock units 

for the Denver Basin modeled area, 1879–2003.

Year

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Flow, in cubic feet per second –5.0

–4.5

–4.0

–3.5

–3.0

–2.5

–2.0

–1.5

–1.0

–0.5

0

0.5

Increase in area

of urban recharge

Increase in area

of urban recharge

Upper Dawson aquifer

Lower Dawson aquifer

Dawson confining unit

Variable to dry conditions

Variable to wet conditions

Upper Arapahoe aquifer

Lower Arapahoe aquifer

Laramie–Fox Hills aquifer

Arapahoe confining unit

Denver aquifer Laramie confining unit

Denver upper confining unit

Denver lower confining unit

EXPLANATION

Figure B41. Simulated transient net groundwater flow to streams from individual bedrock aquifers in 

the Denver Basin modeled area, 1879–2003.
136 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B42. Simulated transient flow between the alluvial aquifer and bedrock units for the Denver Basin 

modeled area, 1879–2003.

Figure B43. Simulated transient net flow between the alluvial aquifer and individual bedrock aquifers 

for the Denver Basin modeled area, 1879–2003.

18801885

1890

1895

1900

1905

1910

19151920

1925

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Year

Flow, in cubic feet per second 0

5

10

15

20

25

30

35

40

1930

EXPLANATION

Flow to alluvial aquifer from bedrock units

Flow to bedrock units from alluvial aquifer

Net flow to alluvial aquifer from bedrock units

Increase in area 

of urban recharge

Increase in area 

of urban recharge

Year

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Flow, in cubic feet per second

Upper Dawson aquifer

Lower Dawson aquifer

Upper Arapahoe aquifer

Lower Arapahoe aquifer

Laramie–Fox Hills aquifer

Denver aquifer

EXPLANATION

Variable to dry conditions

Variable to wet conditions
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 137

alluvial aquifer from the bedrock confining units was less than 

1 ft3/s and is not shown in figure B43. Net flow to the alluvial 

aquifer from all bedrock aquifers decreased through time owing 

to increased pumping with the greatest capture of alluvial water 

occurring in the upper Arapahoe and Denver aquifers. Simulated net flow to the alluvial aquifer from the Denver aquifer 

before 1953 was about 1.0 ft3/s. By the mid-1970s, the Denver 

aquifer no longer discharged to the alluvial aquifer, and by 

2003, the Denver aquifer received about –2 ft3/s of net inflow 

(negative net flow) from the alluvial aquifer (fig. B43).

Flow to streams and the alluvial aquifer was a small 

percentage of the overall water budget for the Denver Basin 

bedrock aquifers (table B4). However, the simulated decrease 

in bedrock flow to streams and the alluvial aquifer, and in 

the case of the Denver aquifer, reversal of flow between the 

bedrock and alluvial aquifers, indicate pumping from the 

bedrock aquifers has reduced flow to the alluvial aquifer and 

streams that compose the surficial hydrologic system. The 

simulated increases in streamflow from the alluvial, Denver, 

and Laramie–Fox Hills aquifers represent the increase in nearsurface water use for urban and agricultural applications.

Discharge to springs was less than 1 percent of the overall 

groundwater budget for the Denver Basin bedrock aquifers, and 

similar to stream and alluvial aquifer discharge, simulated flow 

to springs has changed through time in response to changes in 

recharge and pumping rates. Flow to springs from the Laramie–

Fox Hills aquifer was greater than from other bedrock units and 

was relatively constant (about 0.4 ft3/s) for the entire modelcalibration period (table B5). Before 1953, flow to springs from 

the lower Dawson aquifer was about 0.33 ft3/s, but by 2003, 

flow to springs from the lower Dawson aquifer had decreased 

to less than 0.01 ft3/s, presumably because of a decrease in 

recharge and an increase in pumping. Flow to springs for the 

lower Denver confining unit was relatively constant before 1953 

(0.05 ft3/s) but then increased after 1953 to a relatively constant 

rate of 0.22 ft3/s in response to development and the associated 

increase in recharge. Flow to springs from the remaining hydrologic units (upper Dawson aquifer, upper Denver confining unit, 

Denver aquifer, and upper Arapahoe aquifer) was negligible 

(less than 0.2 ft3/s).

Interaquifer Flow

Interaquifer flow is flow between aquifers. For bedrock 

units with limited outcrop at the land surface and therefore limited recharge, interaquifer flow is an important source of water 

to wells. Similar to other water-budget components, interaquifer 

flow was relatively constant before 1953, and the net interaquifer flow between all bedrock units was downward as indicated 

by positive inflow values from overlying bedrock units in table 

B5. After 1953, as pumping and recharge increased, interaquifer 

flow also substantially increased from (1) the Denver aquifer to 

the lower Denver confining unit (from about 17 ft3/s in 1953 to 

about 42 ft3/s in 2003); (2) the lower Denver confining unit to 

the upper Arapahoe aquifer (from about 20 ft3/s in 1953 to about 

53 ft3/s in 2003); (3) the upper Arapahoe to the Arapahoe confining unit (from about 7 ft3

/s in 1953 to about 37 ft3/s in 2003); 

and (4) from the Arapahoe confining unit to the lower Arapahoe 

Figure B44. Simulated transient net flow between bedrock units in the Denver Basin modeled area, 

1879–2003.

–50

–45

–40

–35

–30

–25

–20

–15

–10

–5

0

Flow, in cubic feet per second

1880

–55

Year

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Upper Dawson aquifer

Lower Dawson aquifer

Denver aquifer

Upper Arapahoe aquifer

Lower Arapahoe aquifer

Laramie–Fox Hills aquifer

Denver upper confining unit

Denver lower confining unit

Arapahoe confining unit

Dawson confining unit Laramie confining unit

EXPLANATION
138 Groundwater Availability of the Denver Basin Aquifer System, Colorado

aquifer (from about 7 ft3/s in 1953 to about 38 ft3/s in 2003) 

(tables A7, B5; figs. B44, B45). From predevelopment to 2003 

conditions, there was a substantial increase of downward interaquifer flow from the Denver aquifer (about 24 ft3

/s), Denver 

lower confining unit (about 34 ft3/s), the upper Arapahoe aquifer 

(about 32 ft3/s) and the Arapahoe confining unit (about 33 ft3/s) 

to underlying bedrock units (fig. B45). These results indicate 

substantial simulated vertical connection between these layers 

and downward flow induced by the increase in pumping in the 

Arapahoe aquifers. Downward interaquifer flow from the lower 

Arapahoe aquifer to the Laramie confining unit was relatively 

constant and negligible (about 2 ft3/s) for the entire modelcalibration period of 1879–2003, indicating a lack of downward 

flow from the lower Arapahoe to the Laramie confining unit 

consistent with previous modeling results (Robson, 1987).

Change in Aquifer Storage

The simulated change in aquifer storage is the water 

removed from storage (storage inflow to the model) minus the 

water returned to storage (storage outflow from the model) so 

that a positive change in the storage value indicates removal 

of water from storage (storage depletion or storage loss). 

Simulated storage by MODFLOW is the total of confined 

aquifer storage from compressibility of the water and the rocks 

and unconfined aquifer storage from drainable porosity. Storage properties of an aquifer are commonly described in terms 

of specific storage for confined aquifers and specific yield 

for unconfined aquifers, and the volume of water released 

from or taken into aquifer storage as hydraulic head changes 

can vary substantially depending on whether the aquifer is 

under confined or unconfined conditions (Lohman, 1979). As 

the confined aquifer experiences drawdown and converts to 

unconfined conditions, the storage-depletion rate will theoretically increase because more water is released from drainable 

storage than from confined storage for a unit decrease in 

hydraulic head (Robson, 1987).

On the basis of simulation results for the model-calibration 

period 1879–2003, storage changes for the alluvial aquifer have 

varied depending on precipitation and pumping with storage 

being gained in wet years and depleted in dry years, while 

bedrock aquifer storage-depletion rates have increased since 

predevelopment (1879) because of pumping (fig. B46). In the 

1950s and early 1960s, simulated recharge increased in the 

Denver Basin as areas of urban recharge expanded, but pumping 

Figure B45. Change in simulated net flow between bedrock units in the Denver Basin modeled area, 

1880–2003.

Flow, in cubic feet per second –55

–50

–45

–40

–35

–30

–25

–20

–15

–10

–5

0

5

10

15

–1.3

–3.4 –3.7 –5.8 –6.4

–14.2

–3.2

–5.9 –6.5

–24.8

–6.3 –6.9

–11.7 –12.9

–38.9

–16.1

–1.9 –2.3

–34.1

–31.8 –32.5

–50.2

–33.7

–7.2

–7.0

–1.2

Hydrogeologic unit

Upper

Dawson

aquifer 

Dawson

confining

unit 

Lower

Dawson

aquifer 

Denver

upper

confining

unit 

Denver

aquifer

Denver

lower

confining

unit 

Upper

Arapahoe

aquifer 

Arapahoe

confining

unit 

Lower

Arapahoe

aquifer 

Laramie

confining

unit 

Change in net flow to underlying layer, 1880–2003

Predevelopment (pre-1880) net flow to underlying unit

Net flow to underlying layer, 2003

EXPLANATION

–2.9

–14.2

–34.8

–2.5
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 139

was not yet great enough to remove water from storage, so 

recharge contributed to alluvial and bedrock aquifer storage. As 

dry conditions ensued in the mid-1960s and pumping continued 

to increase, storage loss occurred in both the alluvial and bedrock aquifers (fig. B46). Wetter climatic conditions in the 1990s 

provided recharge that contributed storage to the alluvial aquifer, but in the bedrock aquifers, continued increases in pumping 

resulted in continued storage depletion (fig. B46). By 2003, dry 

climatic conditions, coupled with continued pumping, resulted 

in a storage-depletion rate for the alluvial aquifer of about 7 ft3/s 

(5,100 acre-ft/yr) (table B3) and a storage-depletion rate for the 

bedrock aquifers of about 57 ft3/s (41,300 acre-ft/yr) (table B4).

For individual Denver Basin bedrock aquifers, there 

was little change in storage inflow or outflow before 1953 

(fig. B47). From 1953 to 1961, storage was gained for the 

Denver and upper Arapahoe aquifers in response to the 

increase in area of urban recharge. There was a similar contribution to storage of the upper Arapahoe aquifer in response 

to increased urban recharge in the 1990s (fig. B47). However, 

except for the two mentioned increases, water was removed 

from storage for all of the bedrock aquifers after 1953. The 

greatest net storage-depletion rate was for the Denver aquifer, 

which reached a maximum of about 26 ft3/s in 2003 at the simulation end (table B5; fig. B47). Net storage-depletion rates for 

the lower Dawson and Laramie–Fox Hills aquifers were about 

10 and 8 ft3/s, respectively, by 2003. The net storage-depletion 

rate for all bedrock units increased exponentially after 1999 in 

response to drought conditions and the associated reduction in 

precipitation recharge combined with pumping increases.

The cumulative volumes of water removed from alluvial 

and bedrock aquifer storage reflect climatic and pumping 

conditions from 1880 to 2003 (fig. B48). Note that cumulative 

storage loss is plotted as a negative value in figure B48. The 

cumulative storage loss from the alluvial aquifer increased 

in response to pumping during the 1960s through the 1980s 

and reached a maximum cumulative storage loss of about 

326,000 acre-ft in 1986. After 1986, the simulated area of 

urban recharge increased in areas overlying the alluvial 

aquifer, which resulted in additional simulated recharge to 

the alluvial aquifer and about 200,000 acre-ft of storage gain 

(fig. B48). An estimated 25,000 acre-ft of cumulative storage was lost from the alluvial aquifer from 1999 to 2003 in 

response to drought conditions. The cumulative volume of 

water removed from bedrock units increased from zero under 

predevelopment (1879) conditions to about 690,000 acre-ft 

in 2003 (fig. B48). For context, Dillon Reservoir, a surface 

impoundment operated by Denver Water in the mountains 

west of Denver, has a storage volume of about 200,000 acre-ft 

(Robson, 1987). The amount of water removed from storage 

by pumping of the bedrock aquifers is thus about 3.5 times the 

volume of Dillon Reservoir. The simulated cumulative storage 

loss is about 0.28 percent of the total estimated amount of 

water in storage (247 million acre-ft). However, there is large 

uncertainty associated with estimates of total water in storage 

(Alley, 2006, 2007), especially in the Denver Basin where the 

fine-grained and heterogeneous aquifers exhibit spatially variable storage parameters.

Simulated flow, in cubic feet per second

Year

–40

–50

–60

–70

–30

–20

–10

0

10

20

30

EXPLANATION

1880

1906

1919

1939

1953

1956

1961

1964

1971

1973

1978

1984

1986

1994

1999

2003

Alluvial aquifer

Bedrock units

Figure B46. Simulated transient net storage loss (positive) and gain (negative) rates for the alluvial 

aquifer and bedrock units in the Denver Basin modeled area, 1879–2003.
140 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Flow, in cubic feet per second

Year 1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Increase in area

of urban recharge

Increase in area

of urban recharge

–30

–25

–20

–15

–10

–5

0

5

10

Upper Dawson aquifer

Lower Dawson aquifer

Dawson confining unit

Variable to dry conditions

Variable to wet conditions

Upper Arapahoe aquifer

Lower Arapahoe aquifer

Laramie–Fox Hills aquifer

Arapahoe confining unit

Denver aquifer Laramie confining unit

Denver upperconfining unit

Denver lowerconfining unit

EXPLANATION

Figure B47. Simulated transient net storage-depletion rates for individual bedrock units in the Denver 

Basin modeled area, 1879–2003.

Figure B48. Simulated transient cumulative volume of water removed from storage for bedrock units in the 

Denver Basin modeled area, 1880–2003.

Increase in area

of urban recharge

–800

–700

–600

–500

–400

–300

–200

–100

0

100

Cumulative change in bedrock groundwater storage,

in thousands of acre-feet 

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Year

Increase in area

of urban recharge

Variable to dry conditions

Variable to wet conditions

Total for alluvial aquifer

Total for bedrock units

Bedrock units in south Denver

 metropolitan area

Bedrock units in all other areas

EXPLANATION
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 141

While the overall percentage of storage loss is small 

compared to the estimated total water in storage, the temporal 

trend and spatial distribution of the storage loss lend insight to 

hydrologic processes controlling storage and warrant further 

consideration. Drought conditions, simulated in the model as 

reduced recharge from 2000 to 2003, coupled with continued 

pumping increases, caused an exponential increase in simulated cumulative storage loss from the bedrock aquifers since 

1999 (fig. B48). During dry years, less recharge is available 

than in wet years so that climate variability and the resulting recharge variability can directly affect aquifer storage. 

Because recharge and storage are the two primary sources of 

water to wells, a reduction in available recharge causes more 

storage loss during dry years. Storage-depletion rates also are 

expected to increase substantially as the confined aquifers 

experience drawdown and convert to unconfined conditions 

because more water is released from unconfined drainable storage than from confined storage for a unit decrease 

in hydraulic head (Robson, 1987). The increased storagedepletion rate simulated after 1999 is likely caused by a combination of factors including increased pumping, decreased 

recharge, and conversion to unconfined conditions. Spatially, 

50 percent of the 2003 storage loss from the bedrock units was 

from the 20 percent of the basin volume encompassed by the 

south Denver metropolitan area (fig. B48). The other 50 percent of storage loss was from remaining parts of the basin.

Changes in Hydraulic Heads 

and Groundwater Flow Directions

Changes in storage and hydraulic head in the alluvial 

aquifer are much less pronounced than those in bedrock 

aquifers because aquifer hydraulic conductivity and recharge 

rates for the alluvial aquifer are greater than those for the bedrock aquifers. Pumping and the removal of groundwater from 

storage have affected potentiometric conditions and regional 

groundwater flow directions in all of the Denver Basin bedrock aquifers.

Potentiometric-surface maps illustrate the distribution of hydraulic heads in an aquifer for a given time period. 

Groundwater flow directions are interpreted from potentiometric conditions with groundwater flow from areas of high 

hydraulic head to areas of low hydraulic head in a direction 

generally perpendicular to contours of equal hydraulic head on 

the potentiometric-surface maps. Potentiometric-surface maps 

can be generated from field measurements of depth to water or 

from groundwater flow simulations. Plots of water levels over 

time (hydrographs) also are useful for interpreting temporal changes in water levels. This section describes transient 

changes to hydraulic heads and groundwater flow directions 

in the Denver Basin aquifer system on the basis of existing 

water-level data and modeling results.

Water levels were routinely measured in a large number of Denver Basin wells during the 1970s and early 1980s, 

and potentiometric-surface maps developed from the data 

were published as a series of hydrologic atlases (Robson and 

Romero, 1981a, 1981b; Robson, Romero, and Zawistowski, 

1981; Robson, Wacinski, and others, 1981). Water-level 

data for Denver basin bedrock aquifers have been sparsely 

collected since the 1980s. The CDWR currently operates a water-level monitoring network of about 278 wells 

(fig. B49), which was established in the 1980s and includes 

some wells with water levels dating back to the 1950s and 

1960s (Colorado Division of Water Resources, 2003; 2004). 

The number of water levels measured annually in the CDWR 

network does not provide sufficient geographic coverage to 

prepare potentiometric-surface maps, and there are questions as to whether water levels measured in these wells are 

representative of ambient water-level conditions because of 

well-construction issues (issues associated with the CDWR 

water-level monitoring network are discussed in the section 

“Future Hydrologic Monitoring” in this chapter). Because 

of the limitations associated with the existing monitoring 

network, model calibration did not use water-level data from 

the CDWR network. However, hydrographs of simulated and 

observed hydraulic heads for selected wells in the CDWR 

network presented herein are useful for describing temporal 

water-level changes in the basin. The observed hydraulic 

heads are generally consistent with simulation results.

The Denver Basin groundwater flow model calculates 

heads at the center of every active model cell, and the head 

represents the average altitude of the potentiometric surface 

in the cell. The simulated heads from each cell were contoured 

to prepare a potentiometric-surface map for each aquifer layer 

in the Denver Basin model. Simulated potentiometric surfaces 

for the seven aquifer layers for 1956, 1978, and 2003 are presented in the section “Model-Calibration Results,” “Simulated 

Hydraulic Heads” in Chapter C and, when compared to each 

other, represent changes to the potentiometric surfaces over 

time as described in the following sections.

Alluvial Aquifer

For the alluvial aquifer, the water-level change between 

the simulated predevelopment potentiometric surface (fig. A55) 

and the simulated 2003 potentiometric surface (fig. B50) was 

less than plus or minus 10 ft over most of the affected area 

(fig. B50). The model simulated small drawdowns for the 

alluvial aquifer, despite increased groundwater development, 

because of large hydraulic conductivity values and recharge 

rates simulated for the alluvial aquifer relative to the bedrock 

aquifers. The greatest drawdowns in the alluvial aquifer were on 

the order of 40 ft in Black Squirrel Creek, which is not connected to a perennial stream, and in the upper reaches of Plum, 

Cherry, Box Elder, and Kiowa Creeks, where municipal and irrigation wells are active. Water-level rise on the order of 40 ft is 

noted in the northeast corner of the modeled area near Wiggins 

(fig. B50). These results are consistent with results from the 

CWCB and current modeling efforts of the SPDSS, which 

concluded that, despite local variation in water levels caused by 

pumping and irrigation return flows, the regional water table in 

the South Platte alluvial aquifer has remained relatively stable 

from 1968 to 2005 (Colorado Water Conservation Board, 2006).
142 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B49. Location of wells in the Colorado Division of Water Resources Denver Basin water-level 

monitoring network.

South

Platte River

Cache la Poudre R

Big Thompson R

Little Thomp son R

Boulder Cr

Coal Creek

Big Dry Cr Clear Creek

West Sand Creek

First Creek

Sand Creek

Li ttleD ry C

P

r

lum Creek West P ul m Creek

Bear Creek

Runn ni g

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCr eek

Bijou Creek

Antelope Creek

MiddleBijouCreek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Creek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek

Dry Cr

Fountain Creek

Saint Vrain Cr

Lost Creek

Box Elder Creek

PALMER

DIVIDEDIVIDE

!(

!(

!(

!(

!(

!(

!(

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!(

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!

§ ̈¦70

§ ̈¦25

§ ̈¦76

WELD

ELBERT

ADAMS

MORGAN

BOULDER

Golden

Greeley

Boulder

Loveland

Morrison

Longmont

Deer

Trail

Fort

Lupton

Fort

Morgan

Lafayette

WELD

EL PASO

LINCOLN

TELLER

Calhan

Colorado

Springs

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Kiowa

Limon

Simla

Parker

Denver

Bennett

Lakewood

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Aurora

Littleton

Englewood

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Kiowa

105°

40°

39°

104°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent

Lower Arapahoe aquifer simulated extent

Denver aquifer simulated extent

Lower Dawson aquifer simulated extent

Stream

Perennial

Ephemeral

Colorado Division of Water Resources 

 water-level monitoring site

! Laramie–Fox Hills aquifer

! Arapahoe aquifer undifferentiated

! Lower Arapahoe aquifer

! Upper Arapahoe aquifer

! Denver aquifer

! Dawson aquifer undifferentiated

! Lower Dawson aquifer

! Upper Dawson aquifer
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 143

Figure B50. Simulated 2003 potentiometric surface and hydraulic-head change from 1880 to 2003 

for the alluvial aquifer (model layer 1).

South Platt e River

Cac he la Poudre R

Big Thompson R

Little Thomps onR

Bould er Cr

Coal Creek

BigDryCr Clear Creek

West Sand Creek

First Creek

Sand Creek

Little Dry Cr

Plum Creek WestP ul m Creek

Bear Creek

Running Creek

Dry Creek Kiowa Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCre ek

Bijou Creek

Antelope Creek

Middle Bijou Creek

East Bi oj uCr eek

Middle Ru sh Creek

Mustang Creek

Adobe Creek

Steels Fork Horse Creek

West Bijou Creek

Big Sandy Creek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook C reek

Dry Cr

Fountain Creek

Saint Vrain Cr

Lost Creek

Box Elder Creek

PALMER

DIVIDE

PALMER

DIVIDE

§ ̈¦70

§ ̈¦25

§ ̈¦76

Barr 

Lake

Milton 

Reservoir

WELD

LARIMER

BOULDER

WASHINGTON

Golden

Greeley

Boulder

Loveland

Lakewood

Longmont

Lafayette

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir Aurora

Reservoir

Cherry Creek

Reservoir

ADAMS

MORGAN

Parker

Bennett

Morrison

Deer

Trail

Highlands

Ranch

Aurora

Reservoir

Cherry Creek

Reservoir

WELD

EL PASO

LINCOLN

TELLER

DOUGLAS

Colorado

Springs

EL PASO

ELBERT

ARAPAHOE

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

Denver

Brighton

Broomfield

Fort

Lupton

Aurora

Littleton

Englewood

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Calhan

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth Castle

Rock

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Wiggins

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

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!(

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!(

!(

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!(

!(

105°

40°

39°

104°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Alluvial aquifer simulated extent (model layer 1)

Extent of active model cells

Simulated potentiometric contour; shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 100 feet

Generalized groundwater flow direction

Stream

Perennial

Ephemeral

Simulated change in hydraulic head, 

 1880–2003, in feet

–44 to –20

–20 to –10

–10 to 0

Dry model cell

0 to 10

10 to 20

20 to 50

50 to 62
144 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Upper Dawson Aquifer

The changing potentiometric conditions in the upper 

Dawson aquifer reflect the increase in domestic and municipal pumping from the aquifer since 1956. Pumping from the 

upper Dawson aquifer in the south Denver metropolitan area 

increased between 1956 and 1978, lowering the potentiometric 

surface in the upper Dawson along Cherry Creek and shifting groundwater flow toward Cherry Creek. The area and rate 

of pumping from the upper Dawson continued to increase 

through 2003, which caused continued lowering of the potentiometric surface along Cherry Creek (fig. B51). By 2003, simulated drawdown in the upper Dawson potentiometric surface 

was as much as 277 ft in the northern part of the aquifer near 

Castle Rock and Parker, and a pattern indicative of regional 

discharge toward Cherry Creek developed (fig. B51) that was 

not present in the predevelopment potentiometric surface 

(fig. A56). Consistent with simulation results, water-level measurements from the CDWR network exhibit up to 89 feet of 

water-level declines in the northern part of the upper Dawson 

aquifer and very little change in hydraulic head in the southern 

part of the aquifer (fig. B52). The large simulated drawdown 

east of Parker was not observed in the CDWR water-level data 

(fig. B52) indicating additional refinement of the hydraulicconductivity distribution or pumping estimates might improve 

model fit in this area.

Lower Dawson Aquifer

Simulated hydraulic heads in the lower Dawson aquifer also decreased in response to pumping since 1956. The 

predevelopment potentiometric contours for the lower Dawson 

aquifer indicate discharge to Plum, Cherry, Kiowa, Bijou, 

Big Sandy, and Monument Creeks (fig. A57). In 1956, there 

was groundwater development near the northern and southern limits of the upper Dawson aquifer, but changes to the 

potentiometric surface from predevelopment conditions were 

limited in extent. By 1978, groundwater development had 

spread over much of the northwest part of the lower Dawson 

aquifer in the south Denver metropolitan area resulting in as 

much as 100 feet of drawdown since 1880. The potentiometric surface was further lowered by 2003 as the area and rate 

of pumping from the lower Dawson continued to increase. 

Drawdown in the potentiometric surface for 2003 as compared to predevelopment conditions was in the range of 100 

to 250 ft in the confined parts of lower Dawson aquifer in 

the Cherry Creek basin (fig. B53). The greatest drawdown 

was on the unconfined southwest margin of the aquifer in the 

Monument area (500 to 984 ft below the predevelopment surface, fig. B53). The extent of drawdown in the south Denver 

metropolitan area is more widespread than in the Monument 

area because of spatial variation in hydraulic conductivity. 

In the Monument area hydraulic conductivity is less than in 

the south Denver metropolitan area, which results in steeper 

and more isolated drawdown cones than in the south Denver 

metropolitan area. Urban recharge in the unconfined northwest 

part of the lower Dawson aquifer resulted in as much as 62 ft 

water-level rise in 2003 compared to predevelopment conditions (fig. B53).

Water-level data for the lower Dawson aquifer from the 

CDWR network in the Castle Rock area are consistent with the 

simulation results. In the Parker area, about 50 ft of water-level 

decline was measured and simulated at wells C119 and C145, 

while as much as 150 ft of water-level decline was measured 

at well C147 near Castle Rock since 1988 (water-level decline 

rate of as much as 23 ft/yr) (fig. B54). In the Monument area, 

CDWR water-level data indicate water-level decline of about 

215 ft since 1967 at well C200 with a water-level decline rate 

of about 6 ft/yr.

Denver Aquifer

Early groundwater development of the Denver aquifer took 

place in and around Denver during development of its western 

suburbs in the 1950s. By 1956, there was substantial drawdown 

in the Denver aquifer potentiometric surface in the Denver area 

compared to predevelopment conditions (fig. A58) (Robson, 

1987). In 1978, pumping from the Denver aquifer was more 

widespread with pumping increases in the south Denver metropolitan area and in the Monument area that resulted in substantial lowering of the simulated potentiometric surface along 

Cherry and Monument Creeks and shifting of groundwater flow 

toward these discharge areas. Pumping from the Denver aquifer 

in the Denver area decreased from 1956 to 1978, which resulted 

in aquifer recovery and contributed to the observed and simulated water-level rise on the northwest and southwest margins of 

the aquifer (Robson, 1987). From 1978 to 2003, pumping from 

the Denver aquifer increased, particularly in the south Denver 

metropolitan area around Castle Rock. In 2003, drawdown from 

predevelopment conditions was between 200 and 500 ft in the 

south Denver metropolitan area (fig. B55). In the Monument 

area, 2003 drawdown from predevelopment conditions was in 

the range of 500 to 924 ft (fig. B55). There was up to 442 ft 

of simulated water-level rise in the Denver aquifer on the 

unconfined northwest and southwest aquifer margins where the 

aquifer occurs near land surface and receives simulated urban 

recharge (fig. B55).

Hydrographs of water-level data from the CDWR are 

generally consistent with simulation results for the Denver 

aquifer. In the northern part of the aquifer near Bennett, 

measured water-level decline is about 40 ft at well C044 from 

1965 to 2003 (fig. B56). In the Castle Rock area, about 190 ft 

of water-level decline was observed at well C184 since 1991 

(fig. B56) where a water-level decline rate of about 16 ft/yr was 

observed since 1999. In the Monument area at well C217, about 

150 ft of water-level decline was observed since 1976 (waterlevel-decline rate of 35 ft/yr since 1999). East of Monument 

Creek water-level rise is observed at well C241 (fig. B56), and 

although there is not a good match between observed and simulated heads at this well, the model does simulate urban recharge 

and water-level rise south of Monument consistent with the 

observations (fig. B55).
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 145

Figure B51. Simulated 2003 potentiometric surface and hydraulic-head change from 1880 to 2003 for the upper Dawson aquifer (model 

layer 2).

Coal Creek

Clear Creek

Bear Creek

Little DryCreek

Plum Creek

West Plum

Creek

Cook Cree k

Dry Creek

Black Squirrel Creek

Brackett Creek

CherryCreek

Kettle Cre ek

We st K oi wa Creek

RunningCreek

Dry Creek

KiowaCreek

Sand Creek

Wolf Creek

West Sand Creek

Commanche Creek

Antelo peCreek

Rock Cr

First Creek

West Bijou Creek

Big Sandy Cree k

Horse Creek

Steals Fork

M di dl e Bijou Cr

6,600

6,500

6,900

6,400

6,300

7,000

6,700

6,800

6,600

6,500

6,900

6,200

6,100

5,900

6,400

6,300

7,000

6,000

5,800

6,100

7,100

7,200

6,800

5,900

5,800

6,700

6,800

§ ̈¦25

PALMER

DIVIDE

PALMER

DIVIDE

Barr 

Lake

Aurora

Reservoir

Cherry Creek

Reservoir

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

DOUGLAS

Kiowa

Golden

Calhan

Denver

Bennett

Lakewood

Monument

Broomfield

Highlands 

Ranch

Colorado

Springs

Barr 

Lake

Chatfield

Reservoir

Morrison

Aurora

Englewood

Aurora

Reservoir

Cherry Creek

Reservoir

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Kiowa

Parker

Franktown

Elizabeth

Castle

Rock

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

105°

39°30'

39°

104°30'

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Simulated change in hydraulic head,

 1880–2003, in feet

South Denver metropolitan area

Upper Dawson aquifer simulated extent (model layer 2)

Extent of active model cells

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased well, 2003. 

 Datum NAVD88. Contour interval 100 feet

Generalized groundwater flow direction

Stream

Perennial

Ephemeral

–38 to –25 

–25 to 0

Dry model cell

0 to 25 

25 to 50 

50 to 100 

100 to 200

200 to 277

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)
146 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B52. Hydrographs of measured and simulated hydraulic head for selected wells completed in the upper Dawson aquifer.

South Platte River

Cache la Poudre R

Big Thompson R

Little Thomp son R

Boulder Cr

Coal Creek

Big Dry Cr Clear Creek

West Sand Creek

First Creek

Sand Cree

L

k

i ttleDry Cr

Plum Creek

West P ul m Creek

Bear Creek

Runn ni g

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCr eek

Bijou Creek

Antelope Creek

MiddleBijouCreek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Creek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek

Dry Cr

Fountain Creek

Saint Vrain Cr

Lost Creek

Box Elder Creek

PALMER

DIVIDE

PALMER

DIVIDE

§ ̈¦70

§ ̈¦25

§ ̈¦76

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

!(

!(

!(

!(

!(

!( !(

!( !(

Limon

Kiowa

Parker

Golden

Calhan

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Deer

Trail

Castle

Rock

Highlands

Ranch

Aurora

Limon

Simla

Denver

Greeley

Boulder

Bennett

Loveland

Longmont

Brighton

Fort

Lupton

Fort

Morgan

Colorado

Springs

Wiggins

Lafayette

Englewood

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

105°

40°

39°

104°

0 10 20 MILES

0 10 20 KILOMETERS

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

EXPLANATION

Upper Dawson aquifer simulated extent (model layer 2)

Extent of active model cells

Stream

Perennial

Ephemeral

! Colorado Division of Water Resources water-level monitoring 

 site, upper Dawson aquifer

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

6,520

6,540

6,560

6,580

6,600

6,620

6,640

6,660

Summary for 'SiteID' C190 (17 detail records)

Identifier SC00906308BBD Layer 2 Simulated Observed

11/1/1973

11/1/1975

11/1/1977

11/1/1979

11/1/1981

11/1/1983

11/1/1985

11/1/1987

11/1/1989

11/1/1991

11/1/1993

11/1/1995

11/1/1997

11/1/1999

11/1/2001

8/1/1965

8/1/1968

8/1/1971

8/1/1974

8/1/1977

8/1/1980

8/1/1983

8/1/1986

8/1/1989

8/1/1992

8/1/1995

8/1/1998

8/1/2001

6,760

6,780

6,800

6,820

6,840

6,860

6,880

6,900

Summary for 'SiteID' = C193 (17 detail records)

Identifier SC00906525DBB Layer 2 Simulated Observed

5,700

5,750

5,800

5,850

5,900

5,950

Summary for 'SiteID' = C130 (3 detail records)

Identifier SC00606711CC Layer 2 Simulated Observed

8/1/1994

8/1/1995

8/1/1996

8/1/1997

8/1/19988/1/1999

8/1/2000

8/1/2001

8/1/2002

6,120

6,140

6,160

6,180

6,200

6,220

6,240

6,260

6,280

9/1/1971

9/1/1973

9/1/1975

9/1/1977

9/1/1979

9/1/1981

9/1/1983

9/1/1985

9/1/1987

9/1/1989

9/1/1991

9/1/1993

9/1/1995

9/1/1997

9/1/1999

9/1/2001

Identifier SC00706512AAA Layer 3 Simulated Observed

Summary for SiteID = C143 (18 detail records)
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 147

Figure B53. Simulated 2003 potentiometric surface and hydraulic-head change from 1880 to 2003 for the lower Dawson aquifer (model 

layer 4).

Coal Creek

Clear Creek

West Sand Creek

First Creek

Sand Creek

Li ttleDry Cr

Plum Creek

West P ul m Creek

Bear Creek

Runn ni g

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Antelope Creek

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Creek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook Creek

Dry Cr

§ ̈¦25

PALMER

DIVIDE

!(

!(

!( !( !(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

Simla

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

5,700

6,200

5,900

6,000

5,800

6,500

6,600

6,900

6,200

6,000

7,100

7,200

6,900

6,900

7,000

7,300

7,400

6,900

6,600

6,800

6,700

7,000

6,500

6,700

6,300

6,400

5,900

6,200

6,600

6,700

5,700

6,200

5,900

6,000

5,800

6,500

6,600

6,900

6,200

6,000

7,100

7,200

6,900

6,900

7,000

7,300

7,400

6,900

6,600

6,800

6,700

7,000

6,500

6,700

6,500

6,300

6,400

5,900

6,200

6,600

6,700

105°

39°30'

39°

104°30'

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

–62 to –25

–25 to 0

Simulated change in hydraulic head, 

 1880–2003, in feet

dry model cell

0 to 50

50 to 100

100 to 250

250 to 500

500 to 984

South Denver metropolitan area

Lower Dawson aquifer simulated extent

 (model layer 4)

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 100 feet

Generalized groundwater flow direction

Stream

Perennial

Ephemeral

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent 

 (model layer 12)

Lower Arapahoe aquifer simulated extent 

 (model layer 10)

Denver aquifer simulated extent 

 (model layer 6)

Dawson confining unit simulated extent

 (model layer 3)

EXPLANATION
148 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B54. Hydrographs of measured and simulated hydraulic head for selected wells completed in the lower Dawson aquifer.

South Platte River

Cache la Poudre R

Big Thompson R

Little Thomp son R

Boulder Cr

Coal Creek

Big Dry Cr Clear Creek

West Sand Creek

First Creek

Sand Creek

Li ttleDryC

P

r

lum Creek West P ul m Creek

Bear Creek

Runn ni g

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCr eek

Bijou Creek

Antelope Creek

MiddleBijouCreek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe

S

Creek

teels Fork

Horse Creek

West Bijou Cree k

Big Sandy Creek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek

Dry Cr

Fountain Creek

Saint Vrain Cr

Lost Creek

Box Elder Creek

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

PALMER

DIVIDEDIVIDE

!(

!( !(!(

!(!(!(

!( !( !(!(!(

!(!(

!(

!(!(!(!( !(

!( !(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(!( !(

!(!(

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

!

!(

!

!

!

!

!

! !( !(

!

!

!

!

! !

!(

!

!

!(

!

!

!

!

!

!

!

!

!

!

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

105°

40°

39°

104°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Lower Dawson aquifer simulated extent (model layer 4)

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Extent of active model cells

Stream

Perennial

Ephemeral

! Colorado Division of Water Resources water-

 level monitoring site, lower Dawson aquifer

6,800

6,850

6,900

6,950

7,000

7,050

7,100

7,150

7,200

7,250

7,300

7,350

Summary for 'SiteID' = C200 (18 detail records)

Identifier SC01006736ADB Layer 4 Simulated Observed

3/1/19673/1/19703/1/19733/1/19763/1/19793/1/19823/1/19853/1/19883/1/19913/1/19943/1/19973/1/20003/1/2003

Summary for 'SiteID' = C171 (17 detail records)

5,700

5,750

5,800

5,850

5,900

5,950

6,000

6,050

6,100

Identifier SC00806606ACC2 Layer 4 Simulated Observed

7/1/19847/1/19867/1/19887/1/19907/1/19927/1/19947/1/19967/1/19987/1/20007/1/2002

5,650

5,700

5,750

5,800

5,850

5,900

5,950

Identifier SC00606626CAD Layer 4 Simulated Observed

3/1/19633/1/19663/1/19693/1/19723/1/19753/1/19783/1/19813/1/19843/1/19873/1/19903/1/19933/1/19963/1/19993/1/2002

Summary for 'SiteID' = C119 (17 detail records)

5,830

5,840

5,850

5,860

5,870

5,880

5,890

5,900

5,910

5,920

Summary for 'SiteID' = C145 (17 detail records)

Identifier SC00706617BAB Layer 4 Simulated Observed

4/1/19844/1/19864/1/19884/1/19904/1/19924/1/19944/1/19964/1/19984/1/20004/1/2002

5,700

5,750

5,800

5,850

5,900

5,950

6,000

 Summary for 'SiteID' = C147 (16 detail records)

Identifier SC00706629AAC Layer 4 Simulated Observed

4/1/19884/1/19894/1/19904/1/19914/1/19924/1/19934/1/19944/1/19954/1/19964/1/19974/1/19984/1/19994/1/20004/1/20014/1/20024/1/2003
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 149

Figure B55. Simulated 2003 potentiometric surface and hydraulic-head change from 1880 to 2003 for the Denver aquifer (model layer 6).

South Platte River

Cache la Poudre R

Big Thompson R

Little Thomp son R

Boulder Cr

Coal Creek

Big Dry Cr Clear Creek

West Sand Creek

First Creek

Sand Creek

Li ttleD ry Cr

Plum Creek

West P ul m Creek

Bear Creek

Runn ni g

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCr eek

Bijou Creek

Antelope Cr

MiddleBijouCreek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Creek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek

Dry Cr

Fountain Creek

Saint Vrain Cr

Lost Creek

Box Elder Creek

PALMER

DIVIDEDIVIDE

§ ̈¦70

§ ̈¦25

§ ̈¦76

Barr

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir Cherry Creek

Reservoir

Barr

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir Cherry Creek

Reservoir

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

105°

40°

39°

104°

5,800

6,400

6,000 5,600

5,400

5,200

6,800

6,600

7,000

5,600

5,200

5,400

6,200

7,200

7,400

6,400

6,000

6,200

6,800

6,200

6,600

6,800

6,400

6,400

6,600

5,800

6,400

6,000 5,600

5,400

5,200

6,800

6,600

7,000

5,600

5,200

5,400

6,200

7,200

7,400

6,400

6,000

6,200

6,800

6,200

6,600

6,800

6,400

6,400

6,600

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

–442 to –100

–100 to 0

Simulated change in hydraulic head, 

 1880–2003, in feet

Dry model cell

0 to 50

50 to 100

100 to 250

250 to 500

500 to 924

South Denver metropolitan area

Denver aquifer simulated extent (model layer 6) Simulated potentiometric contour, shows altitude at which

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 200 feet

Generalized groundwater flow direction

Extent of active model cells

Stream Perennial

Ephemeral

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)
150 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B56. Hydrographs of measured and simulated hydraulic head for selected wells completed in the Denver aquifer.

South Platte River

Cache la Poudre R

Big Thompson R

Little Thomp son R

Boulder Cr

Coal Creek

BigDry C r

Clear Creek

West Sand Creek

First Creek

Sand Creek

Li ttleD ry Cr

Plum Creek West P ul m Creek

Bear Creek

Runn ni g

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

BadgerCr eek

Bijou Creek

Antelope Cr

MiddleBijouCreek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Creek

Brac kett C

B

r

lack Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook Creek

Dry Cr

Fountain Creek

Saint Vrain Cr

Lost Creek

Box Elder Creek

PALMER

DIVIDEDIVIDE

§ ̈¦70

§ ̈¦25

§ ̈¦76

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!

!

! !!

!

!

! !

! !

!

! ! !

!

!

!

!

!!

!

!

!

!

!

! !

!! ! ! ! !

!

! !

!

!!

! !

!

!!

! !

!

! ! ! !!

!

! !

! !

!

!

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

105°

40°

39°

104°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Extent of active model cells

Stream

Perennial

Ephemeral

! Colorado Division of Water Resources water-

 level monitoring site, Denver aquifer

Summary for 'SiteID' = C044 (18 detail records)

Identifier SC00306328ADA Simulated Observed

6/1/19656/1/19686/1/19716/1/19746/1/19776/1/19806/1/19836/1/19866/1/19896/1/19926/1/19956/1/19986/1/2001

Layer 6

5,310

5,320

5,330

5,340

5,350

5,360

5,370

5,380

5,390

5,400

Summary for 'SiteID' = C184 (8 detail records)

5,500

5,600

5,700

5,800

5,900

6,000

6,100

6,200

Identifier SC00806714DB2 Layer 6 Simulated Observed

4/1/19914/1/19924/1/19934/1/19944/1/19954/1/19964/1/19974/1/19984/1/19994/1/20004/1/20014/1/2002

6,200

6,300

6,400

6,500

6,600

6,700

6,800

6,900

7,000

Summary for 'SiteID' = C217 (15 detail records)

Identifier SC01106723AA1 Layer 6 Simulated Observed

11/1/197611/1/197811/1/198011/1/198211/1/198411/1/198611/1/198811/1/199011/1/199211/1/199411/1/199611/1/199811/1/200011/1/2002

Summary for 'SiteID' = C241 (11 detail records) 

5,900

6,000

6,100

6,200

6,300

6,400

6,500

6,600

6,700

Identifier SC01206701CCB Layer 6 Simulated Observed

2/1/19872/1/19892/1/19912/1/19932/1/19952/1/19972/1/19992/1/20012/1/2003
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 151

The area of unconfined conditions in the Denver aquifer for 2003 (fig. B57) increased substantially in the northern, western, and southern parts of the aquifer compared to 

predevelopment conditions (fig. A58). Drawdown in response 

to pumping converted confined parts of the Denver aquifer 

to unconfined conditions, which resulted in the accelerating storage-depletion rate simulated for the Denver aquifer 

since 1999 (fig. B47). As the confined aquifer experiences 

drawdown and converts to unconfined conditions, the storagedepletion rate increases because more water is released 

from drainable storage than from confined storage for a unit 

decrease in hydraulic head (Robson, 1987).

Arapahoe Aquifer

The Arapahoe aquifer is divided into upper and lower 

aquifers in the northern part of its extent by a recognizable 

claystone confining unit (Chapter A). The predevelopment 

potentiometric surface for the upper Arapahoe aquifer (model 

layer 8) depicts groundwater flow from the south and west 

toward a regional discharge area along the South Platte River 

(fig. A59). The 2003 drawdown from predevelopment conditions in the upper Arapahoe aquifer ranged from about 100 

to 400 ft south of Denver and Aurora (fig. B58). Drawdown 

in the northern parts of the upper Arapahoe along the South 

Platte River was generally less than 50 ft (fig. B58) because 

the aquifer is near land surface and receives direct recharge 

from the surface. As much as 105 ft of water-level rise was 

simulated in the upper Arapahoe aquifer on the northwest 

margin of the aquifer where it is near land surface, receives 

recharge from the land surface, and where pumping has 

decreased since 1956 (Robson, 1987; Colorado Division of 

Water Resources, 1998).

Development of the lower Arapahoe aquifer followed a 

pattern similar to that of the Denver aquifer. Initial development in the 1950s was in the northwest part of the aquifer 

and in the Monument area. By 1978, pumping from the 

lower Arapahoe had expanded in the northern area along the 

South Platte River, in the south Denver metropolitan area, 

and in the Monument area. In the northern area of development, drawdown from 1880 to 1978 was generally less than 

50 ft because the aquifer is near land surface in this area and 

receives recharge from the surface and overlying alluvial 

aquifer. In the south Denver metropolitan area, drawdown 

as much as 300 ft is simulated over a widespread area, and 

in the Monument area, steep drawdown cones as much as 

675 ft deep are simulated for 1978. Pumping from the lower 

Arapahoe aquifer continued to expand through 2003 to 

provide municipal water supply for continuing urban development. In the south Denver metropolitan area, where the 

aquifer is thickest and exhibits large transmissivity, a large 

coalescing area of drawdown (as much as 400 ft) is simulated for 2003 (fig. B59). In the Monument area, simulated 

drawdown was about 800 to 1,690 ft by 2003 (fig. B59). 

The difference in drawdown patterns between the two areas 

is caused by the contrast in simulated hydraulic conductivity. 

Hydraulic conductivity and thickness, the product of which 

is transmissivity, in the lower Arapahoe in the south Denver 

metropolitan area is simulated as greater than that in the 

Monument area to represent the Wildcat Mountain alluvial 

fan. Because hydraulic conductivity, and thus transmissivity, are less in the Monument area than in the south Denver 

metropolitan area, smaller, steeper, and more isolated cones 

of drawdown are simulated in the Monument area. Future 

studies should consider additional data collection, compilation, and model refinement of the hydraulic-conductivity 

contrast between the south Denver metropolitan area and the 

Monument area.

Comparisons between simulated and observed hydraulic 

heads for selected wells in the CDWR water-level monitoring network provide variable results with simulated heads 

being greater than measured water levels for several lower 

Arapahoe wells. In the northern area near Brighton, where the 

lower Arapahoe aquifer is unconfined, water-level data from 

well C018 indicate a total water-level decline of about 95 ft 

since 1973, whereas simulation results indicate less than 50 ft 

of water-level decline (fig. B60). Near Aurora, water-level 

data from well C050 indicate a total water-level decline of 

about 475 ft since 1964 and a water-level decline rate of about 

23 ft/yr since 1999 (fig. B60), whereas simulation results indicate about 200 ft of water-level decline since 1880 (fig. B59, 

B60). Similarly, in the south Denver metropolitan area, 

water-level data indicate water-level decline of about 540 ft 

since 1986 at well C088 (water-level decline rate of about 

28 ft since 1999) and about 420 ft since 1987 at well C157 

(water-level decline rate of 31 ft/yr), while simulated waterlevel decline was on the order of about 100 ft for the same 

time period (fig. B60). In the Monument area, simulated heads 

were again greater than measured water levels at well C214, 

although the simulated and measured water-level decline 

(about 530 ft since 1986) and water-level decline rates (about 

72 ft/yr) were similar (fig. B60). South of Monument waterlevel rise is observed at well well C239, and although there 

is not a good match between observed and simulated heads at 

this well, the model does simulate urban recharge and waterlevel rise south of Monument consistent with the observations 

(fig. B59).

The extent of unconfined conditions in the lower Arapahoe 

aquifer for 2003 (fig. B61) increased slightly in the northwestern and southern parts of the aquifer extent compared to 

predevelopment conditions (fig. A60). The area of simulated 

unconfined conditions for the lower Arapahoe aquifer did not 

increase substantially since 1880 as it did for the Denver aquifer, indicating storage removal from the lower Arapahoe aquifer 

was primarily from confined storage in 2003.

Laramie–Fox Hills Aquifer

As with the other bedrock aquifers, the potentiometric 

surface of the Laramie–Fox Hills aquifer has been lowered on 

the western margin of its extent where groundwater development was greatest. Numerous potentiometric-surface cones of 
152 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B57. Calculated areas of confined and unconfined conditions for the Denver aquifer (model 

layer 6), 2003.

South

Platte River

Cache la Poudre R

Big Thompson R

Little Thomp son R

Boulder Cr

Coal Creek

Big Dry Cr Clear Creek

West Sand Creek

First Creek

Sand Creek

Li ttleDry Cr

Plum Creek West P ul m Creek

Bear Creek

Runn ni g

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCr eek

Bijou Creek

Antelope Cr

MiddleBijouCreek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Creek

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek

Dry Cr

Fountain Creek

Saint Vrain Cr

Lost Creek

Box Elder Creek

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

PALMER

DIVIDEDIVIDE

§ ̈¦70

§ ̈¦25

§ ̈¦76

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

105°

40°

39°

104°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Simulated extent of confined conditions

Simulated extent of unconfined conditions

Simulated extent of change from confined to unconfined 

 conditions, 1880–2003

South Denver metropolitan area

Extent of active model cells

Denver aquifer simulated extent (model layer 6)

Lower Arapahoe aquifer simulated extent (model layer 10)

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Denver upper confining unit simulated extent (model layer 5)

Stream

Perennial

Ephemeral
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 153

Figure B58. Simulated 2003 potentiometric surface and hydraulic-head change from 1880 to 2003 for the upper Arapahoe aquifer 

(model layer 8).

South Platte

River

Box Elder Creek

Cache la Poudre R

Big Thompson River

Little Thompson R

Boulder Cr

Coal Creek

Big Dry Cr

Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little Dry Cr

Plum Creek West P ul m Creek

Bear Creek

Running Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCreek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCr eek

Middle Ru sh Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Creek

Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Creek Saint Vrain Cr

Lost Creek

§ ̈¦70

§ ̈¦25

§ ̈¦76

PALMER

DIVIDE

PALMER

DIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

5,100

5,200

5,300

5,400

5,000

5,000

5,300

5,000

5,100

5,200

5,300

5,400

5,000

5,000

5,300

5,000

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

105°

40°

39°

104°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

–105 to –50

–50 to 0

Simulated change in hydraulic head, 

 1880–2003, in feet

Dry model cell

0 to 50

50 to 100

100 to 200

200 to 300

300 to 403

Upper Arapahoe aquifer simulated extent (model layer 8) Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 100 feet

Generalized groundwater flow direction

Extent of active model cells

Stream Perennial

Ephemeral

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

EXPLANATION

Denver aquifer simulated extent (model layer 6)
154 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B59. Simulated 2003 potentiometric surface and hydraulic-head change from 1879 to 2003 

for the lower Arapahoe aquifer (model layer 10).

South Platte

River

Box Elder Creek

Cache la Poudre R

Big Thompson River

Little Thompson R

Boulder Cr

Coal Creek

Big Dry Cr

Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little Dry Cr

Plum Creek West P ul m Creek

Bear Creek

Running Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

BadgerCreek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCr eek

Middle Ru sh Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Creek

Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Creek Saint Vrain Cr

Lost Creek

6,000 6,200

6,400

6,600

6,800

7,000

7,200

7,400

6,800

7,000

6,400

6,800

7,200

6,600

6,400

6,200

6,200

6,800

6,000

6,000

6,4007,000

6,200

6,200

5,800

5,600

5,400

5,200

5,000

5,000

5,000

4,800

5,800

6,000 6,200

6,400

6,600

6,800

7,000

7,200

7,400

6,800

7,000

6,400

6,800

7,200

6,600

6,400

6,200

6,200

6,800

6,000

6,000

6,4007,000

6,200

6,200

5,800

5,600

5,400

5,200

5,000

5,000

5,000

4,800

5,800

PALMER

DIVIDEDIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

!

!

!

!

!

!

! ! !

!

!

!

!

! !

!

!(

!

!(

!(

!

!(

!(

!

!

!

!

!

!

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

105°

40°

39°

104°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

–104 to –50

–50 to 0

Simulated change in hydraulic head,

 1880–2003, in feet

Dry model cell

50 to 100

100 to 200

200 to 400

400 to 800

800 to 1,690

South Denver metropolitan area

Upper Arapahoe aquifer simulated extent (model layer 8)

Generalized groundwater flow direction

Extent of active model cells

Stream

Perennial

Ephemeral

Laramie–Fox Hills aquifer simulated extent (model layer 12)

0 to 50

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 200 feet
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 155

Figure B60. Hydrographs of measured and simulated hydraulic head for selected wells completed in the lower Arapahoe aquifer.

South Platte River

Cac he la Poudre R

Big Thompson River Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

PALMER

DIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(!(!(

!(

!(

!(

!

!((!(!(

!(!(!( !(

!( !( !(

!(

!(!(

!(

!(

!( !(

!(

!(!(!( !( !(!( !(!(!(

!(!(!(

!(

!(

!(

!( !(

!(

!(!(!( !(!(

!(

!(!(

!(

!(

!(!(!(!(

!(!(

!(

!( !(!(!( !(

!(

!( !(

!(

!(!(

!(!(

!(

!(

!(

!( !(

!(

!(

!( !(!(!(!(!(!(!(!(

!(

!( !( !(

!(

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

0 10 20 MILES

0 10 20 KILOMETERS

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

EXPLANATION

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

!( Colorado Division of Water Resources water-level 

 monitoring site, Araphaoe aquifer undifferentiated

Stream

Perennial

Ephemeral

Summary for 'SiteID' = C018 (18 detail records)

4,800

4,850

4,900

4,950

5,000

5,050

5,100

Identifier SC00106732DDA Layer 10 Simulated Observed

12/1/197312/1/197512/1/197712/1/197912/1/198112/1/198312/1/198512/1/198712/1/198912/1/199112/1/199312/1/199512/1/199712/1/199912/1/2001

4,300

4,400

4,500

4,600

4,700

4,800

4,900

5,000

5,100

5,200

5,300

Identifier SC00306631DCD Layer 10 Simulated Observed

6/1/19646/1/19676/1/19706/1/19736/1/19766/1/19796/1/19826/1/19856/1/19986/1/19916/1/19946/1/19976/1/2000

Summary for 'SiteID' = C050 (17 detail records)

Summary for 'SiteID' = C238 (12 detail records)

6,150

6,200

6,250

6,300

6,350

6,400

6,450

6,500

6,550

Identifier SC01206618DC Layer 10 Simulated Observed

2/1/19872/1/19892/1/1991

2/1/19932/1/19952/1/19972/1/19992/1/20012/1/2003

Summary for 'SiteID' = C157 (9 detail records)

4,400

4,600

4,800

5,000

5,200

5,400

5,600

5,800

6,000

Identifier SC00706709CA Layer 10 Simulated Observed

9/1/19879/1/19889/1/19899/1/19909/1/19919/1/19929/1/1993

9/1/1994

9/1/19959/1/19969/1/19979/1/1998

9/1/19999/1/20009/1/2001

Identifier SC00506709CDA Layer 10 Simulated Observed

4,200

4,300

4,400

4,500

4,600

4,700 4,800

4,900

5,000

5,100

5,200

5,300

Summary for 'SiteID' = C088 (18 detail records)

4/1/19864/1/1988

4/1/1990

4/1/19924/1/19944/1/19964/1/19984/1/2000

4/1/2002

Identified SC01106701DC Layer 10 Simulated

5/1/19865/1/19885/1/19905/1/19925/1/19945/1/19965/1/19985/1/20005/1/2002

Observed

Summary for 'SiteID' = C214 (14 detail records)

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

5,550

5,560

5,570

5,580

5,590

5,600

5,610

5,620

Summary for 'SiteID' = C138 (17 detail records)

Identifier SC00706009DBC Layer 10 Simulated Observed

8/1/19608/1/1963

8/1/19668/1/19698/1/19728/1/19758/1/1978

8/1/19818/1/19848/1/19878/1/19908/1/19938/1/1996

8/1/1999

8/1/2002
156 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B61. Calculated areas of confined and unconfined conditions for the lower Arapahoe 

aquifer (model layer 10), 2003.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Cre

M

ek

ustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

PALMER

DIVIDE

PALMER

DIVIDE

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Simulated extent of confined conditions

Stream

Perennial

Ephemeral

Simulated extent of unconfined conditions

Extent of active model cells

Lower Arapahoe aquifer simulated extent (model layer 10)

Arapahoe and Denver lower confining units combined 

 simulated extent (model layers 7 and 9)
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 157

depression developed along the western one-third of the aquifer 

in response to pumping from 1956 to 2003 (Colorado Division 

of Water Resources, 1998). In 1978, numerous drawdown cones 

are simulated in the northern area of development, in the south 

Denver metropolitan area, and in the Monument area. By 2003, 

simulated drawdown in the northern and south Denver metropolitan area had expanded over a larger area and had deepened 

to about 1,000 ft (fig. B62). The extent of simulated unconfined 

conditions in the Laramie–Fox Hills aquifer increased slightly, 

primarily along the northwestern and southern margins of the 

aquifer, from predevelopment conditions (fig. A61) to 2003 

(fig. B63).

There was relatively good agreement between simulated 

heads and measured water levels from the CDWR network 

for the Laramie–Fox Hills aquifer. In the northern area near 

Brighton and Broomfield, measured water-level decline 

ranged from about 220 ft since 1969 at well C001 (waterlevel decline rate of 7.5 ft/yr since 1999) to about 340 ft since 

1971 at well C004 (water-level decline rate of about 6.6 ft/yr 

since 1999) (fig. B64). Measured water-level decline was less 

east of 186 ft at well C043 (water-level decline rate of about 

33 ft/yr), and near Byers, a water-level decline of about 40 was 

measured since 1978 at well C081 (water-level decline rate of 

about 2 ft/yr) (fig. B64). In the south Denver metropolitan area, 

water-level decline of about 70 ft was measured from 1989 to 

1998 at well C072, and water-level decline of about 370 ft was 

measured from 1988 to 1996 at well C083 (fig. B64). Simulated water-level decline and water-level decline rates for the 

Laramie–Fox Hills aquifer at these locations were well represented in the model.

Simulated Predictions of Future Conditions

Predictive simulations use the calibrated Denver Basin 

model to calculate predictive model sensitivities and to demonstrate the possible effects of future pumping and precipitation 

variability on groundwater conditions. Predictive simulations 

were run 50 years into the future from the end of the modelcalibration period (December 31, 2003) to 2053. The predictive 

simulations demonstrate the effects of drought conditions and 

hypothetical temporal changes to pumping on bedrock flow to 

the alluvial aquifer, storage-depletion rates, aquifer drawdown, 

and conversion to unconfined conditions. The predictive simulations lend insight to long-term effects of continued pumping 

on the groundwater system, although they are not considered 

definitive predictions of future conditions.

The first predictive simulation was used to calculate predictive sensitivities and examines the effects of future pumping 

on the water budget and hydraulic heads in a simple fashion 

by continuing recharge and pumping conditions from 2003 

through 2053. This simulation addresses the effects of drought 

on recharge to the Denver Basin aquifers because precipitation 

recharge is assigned using the precipitation distribution from 

2000 to 2003, which represents recent drought conditions. The 

simulation assumes pumping and recharge are held constant, 

using the 2003 rates and spatial distributions, from 2004 to 

2053. All other model boundary conditions for simulation such 

as springs, reservoirs, and streams (head-dependent flux boundaries) are the same as in the calibrated model.

A second predictive simulation demonstrates the use of 

the model to evaluate possible future management strategies. 

The simulation predicts the effects of reducing pumping from 

the Denver Basin aquifers. This simulation uses continued 

2000–2003 drought conditions for precipitation recharge, as in 

the first predictive simulation, but without pumping from the 

lower Arapahoe aquifer (layer 10) in the south Denver metropolitan area (model cells in rows 57–81 and columns 9–35) 

beginning in 2009. The simulation is somewhat unrealistic 

in that pumping from the lower Arapahoe likely will not 

completely cease in the near future; however, the simulation was intended to demonstrate the potential for aquifer 

water-level recovery should storage depletion be reduced 

because of surface-water importation, reductions in pumping, 

or aquifer-storage-and-recovery projects.

Predictive Simulation Results

Predictive simulations can lend insight to the effects of 

varying input parameters such as recharge and pumping on 

other components of the water budget. Many different predictive simulations are possible, and future work should examine 

additional scenarios. For this study, the effects of pumping from 

the bedrock aquifer on discharge to streams, the alluvial aquifer, 

storage, and potentiometric surfaces were examined for the 

predictive simulations.

Discharge to Streams and the Alluvial Aquifer

Based on simulation results for the model-calibration 

period 1879–2003, discharge to streams was variable depending on precipitation recharge. Discharge from bedrock aquifers 

to the alluvial aquifer decreased, and storage loss increased 

because of pumping during the model-calibration period. 

Results from the first predictive simulation indicate continued 

pumping from the bedrock aquifers will continue to capture 

water discharging to the surficial system, reducing bedrock 

discharge to streams and the alluvial aquifer (fig. B65). The 

simulated net discharge to streams, reservoirs, and springs (all 

surface-water inflows minus all surface-water outflows) was 

reduced about 10 percent from 15.7 ft3/s in 2003 to 14.5 ft3/s in 

2053 for the first predictive simulation. As pumping continued 

at the 2003 rate, simulated inflow from the alluvial aquifer to the 

bedrock units increased from 12.4 ft3/s in 2003 to 14.0 ft3/s in 

2053 for the first predictive simulation, while discharge from the 

bedrock units to the alluvial aquifer decreased from 27.2 ft3/s in 

2003 to 26.1 ft3/s in 2053 (fig. B65). The result was a decrease 

in the net flow from bedrock units to the alluvial aquifer (inflow 

minus outflow) from 14.8 ft3/s in 2003 to 12.1 ft3/s in 2053 

for the first predictive simulation (fig. B65). Decreased pumping from the lower Arapahoe aquifer in the second predictive 

simulation resulted in a net discharge from bedrock units to the 

alluvial aquifer of 12.9 ft3/s (fig. B65).
158 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B62. Simulated 2003 potentiometric surface and hydraulic-head change from 1880 to 2003 

for the Laramie–Fox Hills aquifer (model layer 12).

South

Platte

River

Cac he la Poudre R

Big Thompson River

Little Thompson R

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Cre

M

ek

ustang Creek

Adobe Cree

Ste

k

els Fork Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,600

5,800

5,000

5,200

5,400

4,800

4,600

4,400

4,600

5,000

4,600

5,400

4,600

5,600

5,000

4,800

5,400

5,400

5,000

4,600

6,000

6,200

6,400

6,600

6,800

7,000

7,200

7,400

5,800

5,600

5,600

5,800

5,000

5,200

5,400

4,800

4,600

4,400

4,600

5,000

4,600

5,400

4,600

5,600

5,000

4,800

5,400

5,400

5,000

4,600

6,000

6,200

6,400

6,600

6,800

7,000

7,200

7,400

5,800

5,600

DIVIDE

PALMERPALMER DIVIDE

Barr 

Lake

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

–70 to –25

–25 to 0

Simulated change in hydraulic head,

 1880–2003, in feet

Dry model cell

100 to 200

200 to 400

800 to 1,000

1,000 to 1,200

1,200 to 1,975

South Denver metropolitan area

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Generalized groundwater flow direction

Extent of active model cells

Stream

Perennial

Ephemeral

0 to 100

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 200 feet
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 159

Figure B63. Calculated areas of confined and unconfined conditions for the Laramie–Fox Hills 

aquifer (model layer 12), 2003.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

§ ̈¦70

§ ̈¦25

§ ̈¦76

PALMER

DIVIDE

PALMER

DIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

105° 104°

40°

39°

0 10 20 MILES

0 10 20 KILOMETERS

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

Simulated extent of confined conditions

Simulated extent of unconfined conditions

Simulated extent of change from confined to unconfined conditions, 

 1880–2003

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Laramie confining unit simulated extent (model layer 11)

Stream

Perennial

Ephemeral

EXPLANATION
160 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B64. Hydrographs of measured and simulated hydraulic head for selected wells completed in the Laramie–Fox Hills aquifer.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

PALMER

DIVIDE

PALMER

DIVIDE

§ ̈¦70

§ ̈¦25

§ ̈¦76

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!( !(

!(!( !( !( !(!( !(

!(

!(!(

!(

!(!( !( !(!(

!( !( !(!( !(

!(

!( !(

!(

!( !(!(

!( !(

!( !( !(

!(

!(

!(

!(!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Stream

Perennial

Ephemeral

!( Colorado Division of Water Resources water-level monitoring 

 site, Laramie–Fox Hills aquifer

4,940

4,960

4,980

5,000

5,020

5,040

5,060

5,080

5,100

Identifier SC00406718BCA Layer 12 Simulated Observed

Summary for 'SiteID' = C072 (8 detail records)

5/1/19895/1/1990

5/1/19915/1/19925/1/1993

5/1/1994

5/1/19955/1/19965/1/19975/1/1998

Identifier SC00106935BBA Layer 12 Simulated Observed

4,600

4,700

4,800

4,900

5,000

5,100

5,200

5,300 Summary for 'SiteID' = C020 (17 detail records)

6/1/19586/1/1961

6/1/1964

6/1/19676/1/19706/1/19736/1/19766/1/19796/1/19826/1/19856/1/19886/1/19916/1/19946/1/19976/1/2000

Summary for 'SiteID' = C083 (11 detail records)

Identifier SC00506603AD Layer 12 Simulated Observed

4,200

4,400

4,600

4,800

5,000

5,200

5,400

1/1/19881/1/19891/1/19901/1/19911/1/19921/1/1993

1/1/19941/1/1995

1/1/19961/1/19971/1/19981/1/1999

Summary for 'SiteID' = C004 (18 detail records)

Identifier SB00106617DCC Layer 12 Simulated Observed

4,200

4,300

4,400

4,500

4,600

4,700

4,800

4,900

5,000

4/1/19714/1/19744/1/19774/1/19804/1/19834/1/19864/1/1989

4/1/19924/1/1995

4/1/1998

4/1/2001

Summary for 'SiteID' = C042 (16 detail records)

5,000

5,050

5,100

5,150

5,200

5,250

5,300

5,350

Identifier SC00306327BD Layer 12 Simulated Observed

4/1/19884/1/19894/1/19904/1/19914/1/19924/1/19934/1/19944/1/19954/1/19964/1/19974/1/1998

4/1/19994/1/20004/1/20014/1/2002

4/1/2003

Identifier SC00506123ABB Layer 12 Simulated Observed

5,160

5,170

5,180

5,190

5,200

5,210

5,220

5,230

Summary for 'SiteID' = C081 (17 detail records)

7/1/19787/1/19807/1/19827/1/1984

7/1/19867/1/19887/1/19907/1/19927/1/19947/1/19967/1/19987/1/20007/1/2002

Identifier SB00106529AAD Layer 12

4,600

4,650

4,700

4,750

4,800

4,850

4,900

4,950

5,000 Summary for 'SiteID' = C001 (18 detail records)

Simulated Observed

10/1/196910/1/197210/1/197510/1/197810/1/198110/1/198410/1/198710/1/199010/1/199310/1/1996

10/1/199910/1/2002
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 161

Figure B65. Simulated transient flow between the Denver Basin alluvial aquifer and bedrock units for 

model-calibration period and predictive simulations, 1879–2053.

0

5

10

15

20

25

30

35

40

Flow, in cubic feet per second

Year

1880

1906

1919

1939

1953

1956

1961

1964

1971

1973

1978

1984

1986

1994

1999

2003

2008

2013

2018

2023

2028

2033

2038

2043

2048

2053

Flow to alluvial aquifer from bedrock units for first

 predictive simulation 

Flow to bedrock units from alluvial aquiferfor first

 predictive simulation 

Net flow to alluvial aquife frombedrock units for

 first predictive simulation

Net flow to alluvial aquifer from bedrock units for

 second (reduced pumping) predictive simulation 

EXPLANATION

Storage

Predictive simulations to 2053 indicate continued storage 

loss as pumping continues. The rate of storage removal may be 

reduced by reducing pumping, but storage depletion will continue 

consistent with 100-year predictions simulated by the CDWR 

SB96–74 model (Colorado Division of Water Resources, 1998). 

The cumulative volume of water removed from bedrock storage 

was simulated to reach about 2.5 million acre-ft by 2053 with no 

increase in pumping over 2003 rates (fig. B66). About 50 percent 

of the storage loss for the first predictive simulation was from the 

south Denver metropolitan area, and about 50 percent of the storage loss was from the remaining areas of the basin. If pumping 

from the Arapahoe aquifer in the south Denver metropolitan area 

were reduced, as represented in the second predictive simulation, 

about 350,000 acre-ft of water would remain in storage for later 

use. These results demonstrate the relation between pumping and 

storage-depletion and indicate that reduction of pumping could 

slow the rate of storage depletion, at least while the aquifers are 

confined, to extend the usable aquifer life.

Changes in Predicted Hydraulic Heads

Model-simulation results for the calibration period 

1879–2003 indicate substantial drawdown in all of the Denver 

Basin bedrock aquifers compared to predevelopment conditions because of pumping from the confined aquifers. Pumping 

at the 2003 rate through 2053, as simulated in the first predictive simulation, shows continued drawdown of potentiometric 

surfaces in all model aquifer layers. Results from the second 

predictive simulation indicate some water-level recovery 

would occur in the Denver and lower Arapahoe aquifers if 

pumping from the lower Arapahoe aquifer was reduced.

Some cells became inactive during the predictive simulations. Inactive cells (shown in white on the drawdown figures) 

are considered artifacts of the model and do not indicate complete dewatering of the aquifer at the cell locations. Because of 

limitations of the model-solution procedure, model cells may 

become inactive when calculated heads are near the defined cell 

bottom. This problem typically arises when ambient hydraulic 

heads are near cell bottoms and the saturated thickness in the 

vicinity of the well cell is insufficient to support continued 

pumping at the specified withdrawal rate. Under actual field 

conditions, the well pumping rate would be limited by locally 

small transmissivity as the head approaches the aquifer bottom. 

However, the WEL Package does not adjust withdrawal rates 

as head approaches the cell bottom, and continued simulated 

pumping can result in cell deactivation. If a cell in which pumping is simulated by the WEL package deactivates, simulation of 

pumping at that cell ceases when the cell is made inactive.

For the upper Dawson aquifer, an additional 85 ft of 

drawdown is predicted from 2004 through 2053 with the maximum drawdown occurring in the Monument area and east of 
162 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Franktown (fig. B67). As pumping in the simulation lowered the 

upper Dawson potentiometric surface, groundwater flow directions shifted toward the Cherry Creek discharge area. An area 

of up to 28 ft of water-level rise was simulated in downgradient 

areas where urban recharge is applied (fig. B67).

For the lower Dawson aquifer, the first prediction simulates 

drawdown of less than 50 ft in much of the aquifer area, although 

as much as 200 ft of additional drawdown is simulated south 

and east of Franktown from 2004 to 2053 (fig. B68). Maximum 

predicted drawdown in the lower Dawson aquifer for the period 

2004–2053 is as much as 340 ft in the Monument area (fig. B68). 

Total predicted drawdown in the lower Dawson 2053 potentiometric surface from predevelopment conditions was about 100 

to 400 ft in the south Denver metropolitan area and about 400 to 

800 ft near the aquifer margin east of Monument.

Continued pumping in the Denver aquifer also will 

result in additional drawdown. Maximum drawdown from 

the first predictive simulation in the Denver aquifer for the 

period 2004–2053 will again occur east of Monument near the 

basin margin with simulated drawdowns of as much as 630 ft 

(fig. B69). In the south Denver metropolitan area as much as 

200 ft of drawdown was simulated south and east of Franktown 

for the predictive period 2004–2053 (fig. B69). Maximum 

predicted drawdown in the Denver aquifer 2053 potentiometric surface compared to predevelopment conditions was more 

than 800 ft in some parts of the south Denver metropolitan 

area and east of Monument, although less than 50 ft of regional 

drawdown is calculated for much of the aquifer. The extent of 

unconfined conditions in the Denver aquifer also increased from 

2004 to 2053 in response to pumping, primarily in the center of 

the basin (fig. B70).

Model-predicted heads for 2053 in the lower Arapahoe aquifer for the first predictive simulation reflect continued pumping in 

the south Denver metropolitan and Monument areas (fig. B71). 

An additional 100 to 200 ft of drawdown is predicted in the 

south Denver metropolitan area, and an additional 400 to 1,200 ft 

of drawdown is predicted in the area east of Monument from 

2004 to 2053 (fig. B71). Total predicted drawdown in the lower 

Arapahoe aquifer from predevelopment to 2053 was about 400 to 

800 in the south Denver metropolitan area and locally was about 

1,150 ft in the Monument area. The lower Arapahoe aquifer in the 

south Denver metropolitan area is heavily pumped for municipal 

purposes and has a large simulated transmissivity so that drawdown cones from individual wells have coalesced into a large 

area of regional drawdown. Drawdown in the lower Arapahoe 

aquifer in the Monument area was restricted to individual cones 

of depression with steep gradients surrounding pumping centers 

because the aquifer has a lower transmissivity. Some areas of 

water-level rise were simulated along the margins of the aquifer 

where it is unconfined and in hydrologic connection with the alluvial aquifer (fig. B71). The extent of unconfined conditions for 

the lower Arapahoe aquifer increased slightly in the northwestern 

and southern parts of the aquifer extent from predevelopment to 

2003, and additional conversion to unconfined conditions in the 

lower Arapahoe aquifer by 2053 is predicted for only a few model 

cells along the southern aquifer margin.

Figure B66. Simulated cumulative volume of water removed from storage for Denver Basin 

bedrock units, 1880–2053.

–3.0

–2.5

–2.0

–1.5

–1.0

0.5

0

0.5

Cumulative change in bedrock groundwater storage, 

In millions of acre-feet 

Year 1880

1890

1900

1910

1920

1930

1940

1950

1960

1970

1980

1990

2000

2010

2020

2030

2040

2050

2060

All bedrock units, calibration period

All bedrock units, first predictive simulation

All bedrock units, second (reduced pumping) 

 predictive simulation 

South Denver metropolitan area, 

 calibration period

South Denver metropolitan area, first 

 predictive simulation

South Denver metropolitan area, second 

 (reduced pumping) predictive simulation

Bedrock all other areas, calibration period

Bedrock other areas, first predictive simulation

Bedrock other areas, second (reduced pumping) 

predictive simulation 

EXPLANATION
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 163

Figure B67. Simulated 2053 potentiometric surface and hydraulic-head change from 2004 to 2053 for the upper Dawson aquifer (model 

layer 2) for predictive simulation 1.

Coal Creek

Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Antelope Cr

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

DIVIDE

PALMER

DIVIDE

!

!

! ! !

! !

!

!

!

!

!( ! !

!

!

!

!

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Barr 

Lake

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

§ ̈¦25

6,700

6,600

6,500

6,800

6,900

6,400

6,300

6,200

7,000

6,100

6,000

7,100

5,900

6,700

6,600

6,500

6,800

6,900

6,400

6,300

6,200

7,000

6,100

6,000

7,100

5,900

6,000

6,800

105° 104°30'

39°30'

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Simulated change in hydraulic head, 

 2004–2053, in feet

South Denver metropolitan area

Upper Dawson aquifer simulated extent (model layer 2) 

 

Generalized groundwater flow direction Extent of active model cells

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Lower Dawson aquifer simulated extent (model layer 4)

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2053. 

 Datum NAVD88. Contour interval 100 feet –28 to –10

–10 to 0

Dry model cell

0 to 10

10 to 20

20 to 40

40 to 60

60 to 85
164 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B68. Simulated 2053 potentiometric surface and hydraulic-head change from 2004 to 2053 for the lower Dawson 

aquifer (model layer 4) for predictive simulation 1.

Coal Creek

Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Antelope Cr

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

DIVIDE

PALMERPALMER DIVIDE

Barr 

Lake

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

!

!

! ! !

! !

!

!

!

!

! !

!

!

!

!

!

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

§ ̈¦25

6,100

6,200

6,300

6,000

6,400 6,500

6,600

6,800

6,700

6,900

5,900

5,800

7,000

7100

5,700

7,200

7,300

6,800

6,700

5,900

6,900

6,800

6,500

7,000

7,000

6,100

6,700

6,900

6,100

6,200

6,300

6,000

6,400 6,500

6,600

6,800

6,700

6,900

5,900

5,800

7,000

7100

5,700

7,200

7,300

6,800

6,700

5,900

6,900

6,800

6,500

7,000

7,000

6,100

6,700

6,900

105° 104°30'

39°30'

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Simulated change in hydraulic head, 

 2004–2053, in feet

South Denver metropolitan area

Lower Dawson aquifer simulated extent 

 (model layer 4)

Generalized groundwater flow direction

Extent of active model cells

Lower Arapahoe aquifer simulated extent

 (model layer 10)

Denver aquifer simulated extent 

 (model layer 6)

Laramie–Fox Hills aquifer simulated extent

 (model layer 12)

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

–110 to –50 Datum NAVD88. Contour interval 100 feet

–50 to 0

Dry model cell

0 to 50

50 to 100

100 to 200

200 to 300

300 to 328
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 165

Figure B69. Simulated 2053 potentiometric surface and hydraulic-head change from 2004 to 2053 for the Denver aquifer 

(model layer 6) for predictive simulation 1.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand

Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Cre

M

ek

ustang Creek

Adobe Cree

Ste

k

els Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

§ ̈¦70

§ ̈¦25

§ ̈¦76

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

PALMER

DIVIDE

PALMER

DIVIDE

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Simulated change in hydraulic head,

 2004–2053, in feet

South Denver metropolitan area

Denver aquifer simulated extent (model 

 layer 6) 

Generalized groundwater flow direction

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent

 (model layer 12)

Lower Arapahoe aquifer simulated extent

 (model layer 10) Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2053. 

–354 to –150 Datum NAVD88. Contour interval 200 feet

–150 to 0

Dry model cell

0 to 50

50 to 100

100 to 200

200 to 400

400 to 628

5,800

6,400 6,000

6,200

5,600

5,400

5,200

6,800

6,600

7,000

7,200

5,600

5,600

5,200

5,200

6,000

6,400

6,600

7,000

5,400

6,200

6,600

6,800

6,600

6,200 6,400

6,800

5,400

5,800

6,400 6,000

6,200

5,600

5,400

5,200

6,800

6,600

7,000

7,200

5,600

5,600

5,200

5,200

6,000

6,400

6,600

7,000

5,400

6,200

6,600

6,800

6,600

6,200 6,400

6,800

5,400
166 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B70. Calculated areas of confined and unconfined conditions for the Denver aquifer (model 

layer 6) in 2053 for predictive simulation 1.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East Bijou Creek

Middle Rush Cre

M

ek

ustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

PALMER

DIVIDE

PALMER

DIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Simulated extent of confined conditions

Stream

Perennial

Ephemeral

Simulated extent of unconfined conditions

Simulated extent of change from confined

 to unconfined conditions, 2004–2053

Simulated extent of change from confined

 to unconfined conditions, 1880–2003 South Denver metropolitan area

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Lower Arapahoe aquifer simulated extent (model layer 10)

Denver aquifer simulated extent (model layer 6)

Denver upper confining unit simulated extent (model layer 5)
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 167

Figure B71. Simulated 2053 potentiometric surface and hydraulic-head change from 2004 to 2053 

for the lower Arapahoe aquifer (model layer 10) for predictive simulation 1.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear

Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

5,400

6,000

5,200

5,600

5,800

6,200

6,400

5,000

6,600

6,800

7,000

7,200

4,800

7,000

6,200

5,000

6,600

6,200

6,200

5,800

6,400

6,600

6,000

5,000

6,600

5,000

5,400

6,000

5,200

5,600

5,800

6,200

6,400

5,000

6,600

6,800

7,000

7,200

4,800

7,000

6,200

5,000

6,600

6,200

6,200

5,800

6,400

6,600

6,000

5,000

6,600

5,000

PALMER DIVIDE

DIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

!

!

!

!

!

!

! ! !

!

!

!

!(

! !

!

!

!

!

!

!

!

!

!

!

!

!

!

!

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Simulated change in hydraulic head,

 2004–2053, in feet South Denver metropolitan area

Lower Arapahoe aquifer simulated extent (model layer 10) 

Generalized groundwater flow direction

Extent of active model cells

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2053. 

 Datum NAVD88. Contour interval 200 feet

–167 to –100

–100 to 0

Dry model cell

0 to 50

50 to 100

100 to 200

200 to 400

400 to 800

800 to 1,210
168 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Results for the Laramie–Fox Hills aquifer from the first 

predictive simulation indicate continued lowering of the potentiometric surface. From 2004 to 2053, as much as about 1,900 ft 

of drawdown is calculated for the south Denver metropolitan and 

Monument areas, while predicted regional drawdown over much 

of the aquifer extent is about 100 ft (fig. B72). Maximum predicted drawdown from predevelopment conditions was more than 

2,000 ft in the south Denver metropolitan and Monument areas. 

The area of unconfined conditions in the Laramie–Fox Hills 

aquifer expanded primarily along the northwestern and southern 

margins of the aquifer from predevelopment to 2003 (fig. B73). 

Some additional conversion to unconfined conditions is predicted 

near the northwestern and southern basin margins by the first 

predictive simulation, and a new area of unconfined conditions is 

predicted just north of Parker (fig. B73).

Results from the second predictive simulation indicate less 

drawdown of the lower Arapahoe potentiometric surface and less 

storage loss from 2004 to 2053 compared to the first predictive 

simulation, if pumping from the lower Arapahoe aquifer was 

ceased in south Denver metropolitan area (fig. B74). The predictive simulation of reduced pumping also indicates less drawdown 

of the Denver aquifer potentiometric surface by 2053 if pumping 

from the lower Arapahoe aquifer in the south Denver metropolitan area is ceased in 2009 (fig. B75) because of the hydraulic 

connection between the Denver and Arapahoe aquifers. In the 

south Denver metropolitan area, the second prediction simulated 

as much as 400 ft less drawdown for the lower Arapahoe aquifer 

(fig. B74) and as much as 100 ft less drawdown for the Denver 

aquifer (fig. B75) than for the first predictive simulation. Because 

of the large hydraulic-conductivity values simulated for the 

Denver and lower Arapahoe aquifers in this region, a difference in 

drawdown between the two predictive simulations of about 10 ft 

extends over a large area north toward the South Platte River, east 

to Bennett, and south toward the Palmer Divide (figs. B74, B75). 

These results indicate that pumping from the lower Arapahoe 

aquifer is affecting hydraulic heads and storage depletion in the 

northern two-thirds of the basin in the overlying Denver aquifer.

Monitoring the Hydrologic System

Sources of uncertainty related to hydrogeologic understanding and simulations of the Denver Basin aquifer system 

include system conceptualization and geologic framework, datameasurement uncertainty, and estimation or generalization uncertainty. Some sources of uncertainty, such as data-measurement 

and parameter estimation, can be quantified through statistical 

model analysis, and the results can be used to guide future data 

collection that could reduce model uncertainty as described in the 

section “Model-Based Statistical Analysis of Potential Monitoring 

Locations” in Chapter C. This ability to perform statistical 

analysis on model results is an important outcome from model 

construction. Other aspects of the model, such as spatial (cell 

size) and temporal discretization, aquifer top and bottom configurations, and values and distribution of sand-plus-silt fractions, 

are assigned (fixed) in the model input, and are not amenable to 

automated parameter estimation and sensitivity analysis. Errors 

associated with assigned parameters are more difficult to quantify, 

and suggestions for data collection related to assigned (fixed) 

parameters are thus more qualitative than the prediction sensitivity analysis presented in Chapter C for adjustable parameters.

Additional data-collection efforts are often appropriate to 

address sources of uncertainty and further future hydrogeologic 

analysis. The conceptual model and corresponding numerical 

simulations presented herein provide one realization of groundwater conditions in the Denver Basin. A reasonable and unique 

set of model parameters was developed by this study, although 

other conceptualizations of the flow system and different numerical results are possible. Future data-collection efforts are suggested to further improve the understanding of hydrogeologic 

conditions and the groundwater flow model. Future continued 

monitoring and refinements to the groundwater flow model also 

are needed to document future storage depletion in response to 

climate variability and continued groundwater pumping in the 

Denver Basin.

Geologic Framework and Aquifer Properties

The conceptualization of geologic layering used by this 

study is reasonable and provides model layering consistent with 

previous studies in the basin. Definitions of geologic layering 

implemented by the present model follow the Denver Basin Rules 

and Regulations (2CCR 410–1), which are defined on the basis of 

a combination of administrative and geologic factors. However, 

the Arapahoe, Denver, and lower Dawson aquifers are quite heterogeneous, and other conceptualizations of bedrock layering are 

possible. Aquifer-base altitudes in the geophysical database were 

assigned from geophysical logs by several workers over the years, 

and while a conscientious effort was made to pick geologic layers 

with consistency, aquifer heterogeneity causes inherent variability 

in the geologic database. Efforts are currently (2010) underway 

to reevaluate the continuity of well-defined sandstone layers 

and the layering definitions being applied to the Denver Basin 

(Peter Barkmann, Colorado Geological Survey, oral commun., 

2009). The groundwater flow model is constructed such that different base-altitude configurations could be substituted into the 

model framework and related to changes in model output.

The Parameter-Prediction statistical analysis in Chapter C 

indicates areas in the Denver Basin where additional hydraulicconductivity values would most effectively decrease prediction 

uncertainty for hydraulic heads in the lower Arapahoe aquifer. 

Additional information about parameter p12_10 (hydraulic 

conductivity of the Laramie–Fox Hills aquifer at pilot point 

p12_10) would reduce uncertainty of predicted heads in the 

lower Arapahoe aquifer in the eastern and southern parts of the 

basin (fig. C38). Additional information about parameter p12_09 

(hydraulic conductivity of the Laramie–Fox Hills aquifer at pilot 

point p12_09) would reduce uncertainty of predicted heads in 

the lower Arapahoe aquifer in the south-central part of the basin 

(fig. C39). Additional information about parameter pKa_11 

(hydraulic conductivity of the lower Arapahoe aquifer at pilot 

point pKa_11) would reduce uncertainty of predicted heads in the 

lower Arapahoe aquifer most in the eastern and northern parts of 

the basin (fig. C40).
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 169

Figure B72. Simulated 2053 potentiometric surface and hyraulic-head change from 2004 to 2053 

for the Laramie–Fox Hills aquifer (model layer 12) for predictive simulation 1.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

5,600

5,000

5,800

5,200

5,400

4,800

6,000

4,600

6,200

6,400

6,600

6,800

7,000

7,200

4,400

4,200

4,600

5,200

4,600

4,800

6,000

5,400

5,800

5,000

5,400

4,800

4,800

7,000

6,400

5,000

6,600

6,000

6,800

6,400

5,600

5,400

5,600

4,800

4,600

4,600

4,800

4,600

4,400

5,600

4,800

6,200

5,600

5,000

5,800

5,200

5,400

4,800

6,000

4,600

6,200

6,400

6,600

6,800

7,000

7,200

4,400

4,200

4,600

5,200

4,600

4,800

6,000

5,400

5,800

5,000

5,400

4,800

4,800

7,000

6,400

5,000

6,600

6,000

6,800

6,400

5,600

5,400

5,600

4,800

4,600

4,600

4,800

4,600

4,400

5,600

4,800

6,200

§ ̈¦70

§ ̈¦25

§ ̈¦76

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

DIVIDE

PALMERPALMER

DIVIDE

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!(

!

!

!(

!(

!

!(

! ! !(

!

!

!

!

!( !

!

!

!

!

!

!

!

!

!

!

!(

!

!

!

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Simulated change in hydraulic head, 

 2004–2053, in feet South Denver metropolitan area

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Generalized groundwater flow direction

Extent of active model cells

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 200 feet

–164 to –100

–100 to 0

Dry model cell

0 to 100

100 to 250

250 to 500

500 to 1,000

1,000 to 1,500

1,500 to 1,875
170 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B73. Calculated areas of confined and unconfined conditions for the Laramie–Fox Hills 

aquifer (model layer 12) in 2053 for predictive simulation 1.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Cre

M

ek

ustang Creek

Adobe Cree

St

k

eels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

PALMER

DIVIDE

PALMER

DIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Simulated extent of confined conditions

Stream

Perennial

Ephemeral

Simulated extent of unconfined conditions

Simulated extent of change from confined to 

 unconfined conditions, 1880–2003

Simulated extent of change from confined to 

 unconfined conditions, 2004–2053

South Denver metropolitan area

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Laramie confining unit simulated extent (model layer 11)
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 171

Figure B74. Simulated 2053 potentiometric surface for reduced pumping conditions and hydraulichead difference between predictive simulations 1 and 2 for the lower Arapahoe aquifer (model 

layer 10).

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

St

k

eels Fork Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

PALMER

DIVIDE

PALMER

DIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Simulated difference in hydraulic head

 between first and second predictive 

 simulations, 2053, in feet South Denver metropolitan area

Lower Arapahoe aquifer simulated extent 

 (model layer 10) 

Extent of active model cells

Stream

Perennial

Ephemeral

–400 to –200

–200 to –100

–100 to –50

–50 to –25

–25 to –10

–10 to 0

0
172 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure B75. Simulated 2053 potentiometric surface for reduced pumping conditions and 

hydraulic-head difference between predictive simulations 1 and 2 for the Denver aquifer (model 

layer 6).

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Cre

M

ek

ustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

PALMER

DIVIDE

PALMER

DIVIDE

§ ̈¦70

§ ̈¦25

§ ̈¦76

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Simulated difference in hydraulic head

 between first and second predictive 

 simulations, 2053, in feet South Denver metropolitan area

Denver aquifer simulated extent (model layer 6)

Extent of active model cells

Stream

Perennial

Ephemeral

Lower Arapahoe aquifer simulated extent (model layer 10)

–156 to –100

–100 to –50

–50 to –25

–25 to –10

–10 to –5

–5 to 0

0
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 173

Aquifer storage properties were fixed parameters in 

the groundwater flow model because there were insufficient 

measured values with which to compare an estimated spatial 

variation. However, the Denver Basin bedrock aquifers are 

heterogeneous, and there is spatial variability in storagecoefficient and specific-yield values. As drawdown continues 

and parts of the aquifer convert from confined to unconfined 

conditions, information on the spatial distribution of specific 

yield will become important to evaluating storage depletion especially for the Denver aquifer, which was simulated 

as having the most area converted to unconfined conditions. 

Continued collection of storage-coefficient and specific-yield 

estimates determined from aquifer testing or core analysis 

is encouraged, whenever the opportunity arises, to enhance 

the understanding of storage in the Denver Basin. Additional 

model realizations using expanded pilot-point configurations 

may improve the ability of the groundwater flow model to represent aquifer-property distributions in more detail (see section 

“Pilot-Point Approach to Hydraulic-Conductivity Estimation” 

in Chapter C for a description of the pilot-point methodology 

used to represent hydraulic-conductivity distributions for the 

present model).

Recharge and Discharge 

Recharge parameters were estimated in model calibration, 

and sensitivity analysis indicates model results are sensitive to 

recharge parameters, especially the percentage of precipitation 

that becomes recharge to the Dawson aquifer. Because recharge 

to the Dawson and to the Denver aquifers are two model 

parameters to which results are most sensitive (as discussed in 

the section “Parameter Sensitivity” in Chapter C), field efforts 

to better quantify precipitation recharge to these units would 

improve model and water-budget accuracy. More accurate 

estimates of agricultural and urban irrigation return flows also 

would increase model and water-budget accuracy. Unsaturatedzone monitoring of water content in both developed and undeveloped areas of the Dawson and Denver aquifers could provide 

estimates of recharge under varying land-use conditions that 

would be useful to estimating recharge.

Long-term streamflow records are sparse in undeveloped parts of the basin where they would be most useful 

for estimating base flow from groundwater. The site Cherry 

Creek near Franktown (06712000; fig. A6) is the only Denver 

Basin gaging station with a long-term record and minimal 

effects from upstream diversion and development. Monitoring 

streamflow in the headwaters of other tributaries in the basin 

could provide additional base-flow estimates of groundwater 

discharge from Denver Basin aquifers.

Pumping from the Denver Basin aquifers was estimated 

in this study by following methods used in previous studies. 

The resulting estimates are reasonable and consistent with the 

conceptual understanding of conditions in the basin, indicating 

that the greatest irrigation pumping is from the alluvial aquifer 

along the South Platte River and that the greatest municipal 

pumping is from bedrock aquifers in populated areas on 

the west side of the basin. However, because pumping is a 

large part of the water budget, model results for drawdown 

and storage depletion are sensitive to simulated pumping 

rates. Specifically, of the pumping parameters, the model 

was most sensitive to pumping rates from alluvial irrigation 

wells and pumping rates from irrigation, municipal and commercial/industrial bedrock wells as discussed in the section 

“Parameter Sensitivity” in Chapter C. If pumping information 

was collected from municipal water providers for irrigation, 

municipal, and commercial/industrial wells, simulated pumping estimates could be improved and thus model-prediction 

uncertainty would be reduced. Currently (2010), no centralized database or reporting system exists for pumping rates 

from the Denver Basin aquifers. Many individual municipal 

water providers meter and record pumping as part of daily 

operations, but these data are not compiled on a regional 

basis. Implementation of a metering and reporting system for 

pumping information would provide discharge information for 

the basin with which to better evaluate aquifer drawdown and 

storage depletion rates.

Water-Level Data

Water levels were periodically measured by the 

U.S. Geological Survey at more than 1,000 wells in the 

Denver Basin prior to the 1980s. Since the 1980s, the 

CDWR has operated a water-level monitoring network of 

about 278 wells (fig. B49). The network includes some wells 

with water levels dating back to the 1950s and 1960s (for 

example, Colorado Division of Water Resources, 2003, 2004). 

While the current network provides useful information, there 

are issues and concerns related to the present water-level 

monitoring network. Most of the wells in the present waterlevel monitoring network are active municipal, commercial, or 

domestic production wells, and, thus, are not solely dedicated 

to monitoring water levels. The network wells are constructed 

of various materials, some of which are not resistant to corrosion and plugging, and the screened intervals are not necessarily designed to appropriately monitor selected aquifer layers. 

For example, one domestic well in the network was logged 

with a televiewer tool, and substantial deterioration of the 

well screen was observed such that water levels measured in 

the well may not be representative of the static water level in 

the aquifer at this location (Courtney Hemenway, Hemenway 

Groundwater Engineering, oral commun., 2008). Water levels 

measured in wells with poor hydraulic connection to the 

aquifer likely do not reflect ambient water levels in the aquifer 

and should be considered for replacement or elimination from 

the network.

Questions also exist as to the pumping status of wells 

associated with the monitoring network at the time of waterlevel measurement. Because the water-level network wells are 

used for production, the water level recorded in the database 

may represent a pumping water level in the well, which would 
174 Groundwater Availability of the Denver Basin Aquifer System, Colorado

be lower than the ambient head in the aquifer. The pumping 

status of a well also is influenced by seasonal pumping variations. Many Denver Basin wells are more heavily pumped 

during the summer when lawn and garden watering occurs 

in urban and suburban areas. If water levels are measured 

during the summer and fall, the measurement is likely representative of pumping conditions and may indicate drawdown 

greater than what would be indicated by a winter water-level 

measurement. Water-level measurements in the CDWR 

Denver Basin network historically have been measured in 

the spring. In 2003, the CWCB and CDWR began collecting 

Denver Basin water-level data in the fall after the summer 

irrigation season and in the spring before irrigation season. 

Analysis of the data indicates summer and fall water-level 

measurements are substantially lower than spring water-level 

measurements, and measurements taken in the spring are 

considered most representative of ambient aquifer conditions 

(Brian Ahrens, Colorado Division of Water Resources, written 

commun., 2008).

The density and locations of wells in the current 

water-level monitoring network are insufficient to draw 

aquiferwide potentiometric-surface contours for the Denver 

Basin bedrock aquifers. An increased density of monitoring wells and additional measurements in areas identified by 

the model-sensitivity analysis would help evaluate regional 

water-level changes and reduce model uncertainty. For 

example, as discussed in the section “Model-Based Statistical 

Evaluation of Potential Monitoring Locations” in Chapter C, 

model-prediction statistical analysis indicates that additional 

observations in aquifer layers in the north-central and southcentral parts of the basin would likely reduce uncertainty 

in the model-calculated potentiometric surface of the lower 

Arapahoe aquifer.

Long-term water-level data from the CDWR database indicate water-level declines of as much as 500 ft and 

maximum water-level decline rates of 20 to 30 ft/yr for 

the Arapahoe and Laramie–Fox Hills aquifer in the south 

Denver metropolitan area (Colorado Division of Water 

Resources, 2004). Water-level decline in the Arapahoe and 

Laramie–Fox Hills aquifers is much less north of Denver in 

Adams County where the aquifers are near land surface and 

thus receive more recharge than areas near the center of the 

basin where confined conditions exist and there is little to 

no recharge. Recent review of well and pumping conditions 

for the network indicates regional drawdown for the Arapahoe aquifer in the south Denver metropolitan area is perhaps 

less than indicated by the CDWR network because of poor 

well construction in the network and the seasonal changes 

in pumping (Courtney Hemenway, Hemenway Groundwater 

Engineering, oral commun., 2008). Hydrographs of simulated 

heads generated by this study compared to observed heads 

for the CDWR water-level network wells indicate observed 

values were less than simulated values for wells completed 

in the lower Arapahoe aquifer. However, agreement between 

simulated heads and water levels measured in the CDWR 

water-level network was reasonable for the Dawson, Denver, 

and Laramie–Fox Hills aquifers.

The Observation-Parameter statistic discussed in 

Chapter C can be used to identify areas where parameter 

uncertainty would be decreased by adding head observations. 

Results indicate additional head observations in the northern 

part of the basin would decrease parameter uncertainty for 

all four of the highest ranked parameters (figs. C41–C44). 

Additional observations in the lower Arapahoe aquifer in 

the south Denver metropolitan area and the Monument area, 

where future development and drawdown are anticipated, also 

would reduce parameter uncertainty. Maps of the ObservationPrediction statistic discussed in Chapter C can be used to 

identify areas where additional head observations likely 

would be most beneficial in reducing the uncertainty in the 

simulated potentiometric surface and drawdown. Maps of the 

OPR statistic for the lower Arapahoe aquifer (fig. C45) and 

the Laramie–Fox Hills aquifer (fig. C46) indicate two general 

areas where additional head observations in the respective 

aquifer likely would reduce the uncertainty of the simulated 

potentiometric surface of the lower Arapahoe aquifer. One 

area is in the north-central part of the basin near the Adams 

and Weld County boundary, and the second area is in the 

south-central part of the basin where future development and 

drawdown are expected.

Future water-level monitoring efforts in the Denver Basin 

would benefit from dedicated monitoring wells constructed 

of material resistant to corrosion, such as polyvinylchloride 

(PVC) with screened intervals appropriately placed to monitor selected bedrock units. Because costs to install a dedicated 

monitoring-well network may be prohibitive, domestic and 

production wells will likely continue to be used for water-level 

measurements. The construction integrity of existing wells 

should be considered as additional wells are selected for a 

monitoring network. An ideal network would include wells 

located throughout the basin, perhaps with a concentration of 

monitoring wells on the west side of the basin where pumping 

is greatest. Based on analysis of the present network, waterlevel measurements collected in the spring represent ambient 

heads in the nonirrigation season while fall measurements are 

useful to evaluate the effects of summer irrigation pumping. 

Retaining existing wells in a long-term network should be 

considered if a long-term water-level record exists for the well 

and if the well condition and completion interval are appropriate for the inclusion in the network. Because model-sensitivity 

results indicate that the simulation results are sensitive to 

vertical hydraulic conductivity, vertical nesting of monitoring 

wells in the various bedrock aquifers also should be considered so that vertical head gradients between aquifers can be 

monitored. Vertical well nests also would facilitate field-scale 

aquifer testing from which vertical hydraulic-conductivity 

could be estimated.
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 175

Groundwater Sustainability 

and Management

Groundwater sustainability can be defined as the achievement of an acceptable tradeoff between groundwater use and 

the long-term effects of that use (Alley, 2006). In order to be 

sustainable, groundwater resources must be used and managed 

in a manner that can be maintained for an indefinite amount of 

time (Faunt, 2009). Sustainability requires iterations of monitoring, analysis, and application of management practices and 

is affected by physical, chemical, economic, environmental, 

legal, philosophical, and institutional factors (Faunt, 2009). 

The Denver Basin aquifer system is administrated as nonrenewable and nonsustainable because the aquifers are primarily 

confined and receive little precipitation recharge (Graham and 

VanSlyke, 2004). Groundwater storage is being depleted in the 

Denver Basin, and the present level of pumping is not considered sustainable over the next 50 years, especially in the south 

Denver metropolitan area (South Metro Water Supply Study 

Board, written commun., 2004). Recurring monitoring and 

analysis of groundwater availability is thus especially important to guide groundwater management and evaluate alternatives in areas such as the Denver Basin, where groundwater 

storage depletion is occurring.

This study developed a groundwater flow model to 

evaluate past and present groundwater availability in the 

Denver Basin, which could be useful for evaluating different 

management options in the future. Simulation results indicate 

changes in land and water use have altered the groundwater 

flow system compared to predevelopment conditions. The 

expansion of urban/suburban land use and irrigated agriculture since the 1950s has increased water use on the landscape, 

which has increased recharge, evapotranspiration, streamflow, 

and the overall groundwater budget in this semiarid region. 

Groundwater pumping from the bedrock aquifers also has 

increased steadily since the 1950s, primarily in response to 

increased municipal water-supply needs. The combination of 

these changing land- and water-use distributions has generally increased groundwater availability in the alluvial aquifer 

and shallow parts of the hydrologic system while removing 

water from storage and decreasing groundwater availability 

in the bedrock aquifers. Pumping from the bedrock aquifers 

also is capturing groundwater that would have discharged to 

evapotranspiration, streams and alluvial aquifers. This capture 

can result in a decline in groundwater discharge from bedrock 

aquifers to the surficial system, which could affect storage 

and groundwater availability in the overlying alluvial aquifer 

(Watts, 1995; Banta, 1989). Ecology of streams, wetlands, or 

riparian zones in discharge areas also could be affected.

While the estimated cumulative storage loss in the 

Denver Basin through 2003 is only a small percentage 

(0.3 percent) of the total estimated water in storage, the temporal trend and spatial distribution lend insight to hydrologic 

processes controlling storage. Drought conditions, simulated 

in the model as reduced recharge from 2000 to 2003, coupled 

with continued pumping increases, caused an exponential 

increase in simulated cumulative storage loss from the bedrock 

aquifers since 1999 (fig. B48). During drought years, less 

recharge is available and more water is removed from storage 

than in years with plentiful precipitation recharge such that climate variability and the resulting recharge variability directly 

affect aquifer storage.

Theoretically, storage loss would be expected to increase 

substantially as the confined aquifers experience drawdown 

and convert to unconfined conditions because more water is 

released from drainable (unconfined) storage than from confined storage for a unit decrease in hydraulic head (Robson, 

1987). The increased storage-depletion rate simulated after 

1999 is likely a combination of factors including increased 

pumping, decreased recharge, and conversion to unconfined 

conditions. Spatially, 50 percent of the 2003 storage loss 

from the bedrock units was from the south Denver metropolitan area where groundwater provides most of the municipal 

water supply. The other 50 percent of the loss was from 

remaining parts of the basin (fig. B48). These results suggest that storage depletion is most severe in the south Denver 

metropolitan area.

Water providers in the south Denver metropolitan area 

recognize the need to import additional renewable water supplies and are actively seeking alternative water supplies as the 

population continues to increase (South Metro Water Supply 

Board, written commun., 2004). After defeat of the Colorado 

and South Platte River Storage Agreement in 1989, which 

would have provided renewable water to the area from the 

proposed Two Forks reservoir along the upper South Platte 

River, growth in the south Denver metropolitan area developed limited surface-water and tributary groundwater rights on 

the South Platte River and Plum and Cherry Creeks in addition 

to nontributary Denver Basin bedrock groundwater (South 

Metro Water Supply Study Board, written commun., 2004). 

The Denver Basin aquifers provide an excellent source of 

water; however, well production rates from the Denver Basin 

aquifers vary widely and can be as low as 50 to 100 gallons 

per minute, requiring many wells to meet peak water demand 

(South Metro Water Supply Study Board, written commun., 

2004). Over the past 20 years, pumping from the confined 

aquifers has lowered hydraulic heads at rates of as much as 

30 ft/yr. As the head in the aquifer is lowered, larger pumps 

are needed to move water to the surface, increasing energy use 

and pumping costs (South Metro Water Supply Study Board, 

written commun., 2004). In 2004, a group of south Denver 

metropolitan area providers, partnered with State agencies and 

water-rights administrators from the Colorado River Basin and 

completed a study investigating alternatives for meeting watersupply needs of the South Denver Metropolitan area through 

2050 (South Metro Water Supply Study Board, written 

commun., 2004). Alternatives considered were the continued 
176 Groundwater Availability of the Denver Basin Aquifer System, Colorado

use of Denver Basin groundwater, importation of additional 

renewable water supplies, and better management of existing 

resources including conservation, reuse of nonpotable water, 

and aquifer-storage-and-recovery (ASR) (South Metro Water 

Supply Study Board, written commun., 2004). Providers 

continue to pursue renewable water supplies maximizing the 

development of available in-basin surface water and developing water-conservation and reuse programs.

Some providers, such as Centennial Water and Sanitation 

District, which serves the Highlands Ranch community, are 

successfully pursuing conjunctive-use projects that use excess 

surface water during spring runoff and other wet periods to 

artificially recharge the bedrock aquifer through injection 

wells (aquifer-storage-and-recovery, ASR). The stored water is 

later pumped from the bedrock aquifers to meet peak demands 

(Swithen Dick, Centennial Water and Sanitation District, oral 

commun., 2008). The City of Colorado Springs also has developed a conjunctive-use bedrock ASR project in the Monument 

area (Cortney Brand, Colorado Springs Utilities, oral commun., 2005), and the Consolidated Mutual Water Company 

in Lakewood has implemented a successful conjunctive-use 

bedrock ASR project injecting surface water into the Arapahoe 

aquifer west of Denver (Courtney Hemenway, Hemenway 

Groundwater Engineering, oral commun., 2005). The success of these projects may vary from year to year depending 

on available surface water for injection. In 2009, the Front 

Range experienced recordbreaking spring snowmelt runoff 

in addition to above-average summer precipitation, allowing 

the Centennial Water and Sanitation to inject up to 5 million gallons of water per day into the bedrock aquifers with 

no withdrawals needed for the year (Courtney Hemenway, 

Hemenway Groundwater Engineering, written commun., 

2009). Conjunctive-use and ASR projects such as these are 

promising solutions to storage depletion in the Denver Basin. 

Drawdown and unconfined conditions in the Denver and 

Arapahoe aquifers in particular may provide opportunity for 

additional ASR projects where sufficient surface water is 

available for injection.

There are other ongoing and planned water projects for 

municipalities and suburbs south of Denver to import surface 

water and to reduce the reliance on nonrenewable Denver 

Basin groundwater. For example, several municipal water 

suppliers including Parker Water and Sanitation, Castle Pines 

North, Town of Castle Rock, and Stonegate are partnering 

to store water in the Reuter-Hess Reservoir near Parker, 

Colorado (http://www.pwsd.org/rueter_hess_reservoir.php, 

accessed April 3, 2008). In addition, the East Cherry Creek 

Valley Water and Sanitation District in 2006 completed a 

new pipeline from the South Platte River to deliver surface 

water to its service area. The Chatfield reallocation project 

is a third effort to import surface water to the south Denver metropolitan area. Chatfield Reservoir, located at the 

mouth of Waterton Canyon on the South Platte River, was 

constructed beginning in 1967 as a flood-control reservoir. 

The reservoir also is used for water-supply storage by the 

Denver Water Board. In 2004, the CWCB began a process 

of reallocating water rights for 20,600 acre-ft of floodcontrol water storage in Chatfield Reservoir. The Chatfield 

Reservoir reallocation process is intended to provide additional surface water to several water providers in the south 

Denver metropolitan area who currently (2010) rely on 

groundwater for public water supply (http://cwcb.state.co.us/

WatershedProtectionFloodMitigation/ProgramsProjects/

ChatfieldReservoirReallocationProject/SiteInformation/, 

accessed April 3, 2008; http://www.douglas.co.us/community/

planning/documents/WorkSessiononWaterDCPC.pdf, accessed 

April 3, 2008). A Feasibility Study and Environmental Impact 

Statement (EIS) addressing engineering and environmental concerns was submitted to the U.S. Corps of Engineers 

in 2010, and public comment on the reallocation process 

will begin in 2011 (http://www.chatfieldstudy.org/faq.html, 

accessed January 14, 2011).

Like other natural resources, groundwater in storage 

(groundwater reserves) can be depleted (Alley, 2006). Water 

providers in the Denver Basin recognize that concentrated 

development and depletion of groundwater storage limits 

the ability to pump the aquifers in the future (South Metro 

Water Supply Study Board, written commun., 2004). While 

the length of time over which this resource may be available 

is uncertain, the conclusions of this and other studies indicate that pumping from the Denver Basin bedrock aquifers is 

not indefinitely sustainable and that renewable water supplies will be needed in the future. Conjunctive-use projects, 

conservation, water reuse, and importation of renewable 

water will enhance the prudent management of Denver Basin 

groundwater resources and can likely extend the practical 

usable life of the aquifers.

Summary

Groundwater development to support agriculture and 

urbanization in the Denver metropolitan area has affected 

groundwater availability in the Denver Basin aquifer system. 

This chapter discusses groundwater availability of the Denver 

Basin in terms of temporal changes to the groundwater budget, 

storage, and groundwater flow directions. Temporal changes 

are presented for the entire aquifer system and separately 

for the bedrock and alluvial systems on the basis of previous 

studies and results from the transient groundwater flow model 

developed by this study. Predictive simulations for hypothetical conditions from 2004 through 2053 were used to calculate 

model sensitivity, and results were used to evaluate which 

geographic areas of the system are most sensitive to additional 

data collection. Predictive simulations also demonstrate the 

utility of the model for evaluating future system response to 

continued pumping. Finally, the chapter presents a discussion 

of future monitoring needed to improve model calibration and 

to provide the necessary data for future and recurring hydrologic analysis.
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 177

Land-use data for the Denver Basin (2001) indicates the 

basin is 60 percent nonirrigated grassland and rangeland, 11 percent irrigated agriculture, 16 percent nonirrigated agriculture, 

9 percent developed urban and suburban land use, 3 percent 

forested, and 1 percent open water. Irrigated and nonirrigated 

agricultural land is located primarily along the South Platte 

River valley, and nonirrigated grassland and rangeland cover 

much of the central and southern basin. Developed urban and 

suburban land use is primarily along the western side of the 

basin along the Front Range urban corridor. Small towns, rural 

residences, and farms are spread across the less-populated parts 

of the basin including the forested areas at the higher elevations 

along the Palmer Divide. Population of the metropolitan areas 

overlying the Denver Basin aquifer system has approximately 

doubled from 1.3 million in 1970 to about 2.7 million in 2005. 

Development has been especially rapid and extensive on the 

west side of the basin between Denver and Colorado Springs. 

Three primary areas of development are identified that rely 

on groundwater for water supply: (1) the area north of Denver 

in Weld and Adams Counties; (2) the south Denver metropolitan area encompassing Littleton, Parker, Franktown, and 

Castle Rock; and (3) the Monument area northeast of Colorado 

Springs. Because groundwater in the Denver Basin bedrock 

aquifers is mostly considered nontributary and is not subject to 

the prior-appropriation doctrine, it has been a readily available 

source of water to support growing and recently established 

municipalities in areas with limited surface water, limited tributary alluvial groundwater, limited available water rights, or all 

of the above.

Because actual pumping in the Denver Basin is not monitored, this study estimated pumping from 1880 through 2003 

from the Colorado Division of Water Resources well-permit 

database following methods implemented in previous studies. Analysis results compare favorably to previous pumping 

estimates and were used as input to the groundwater flow 

model. About 52,000 permitted pumping wells with sufficient 

well-location and completion data were included in the analysis. About 8,000 wells (15 percent) were completed in the 

alluvial aquifer, and the remaining 44,000 wells (85 percent) 

were completed in the bedrock aquifers by 2003. Total pumping from the Denver Basin alluvial and bedrock wells was 

estimated at about 305 ft3/s (221,000 acre-ft/yr) in 2003. About 

62 percent of the pumping was from alluvial wells (187 ft3/s), 

and about 38 percent of the pumping was from bedrock wells 

(118 ft3/s). While most of the wells (85 percent) are completed in the bedrock aquifers, most of the estimated pumping (62 percent) is from the alluvial aquifer. These results are 

consistent with the conceptual understanding of the system 

and reflect the inherent difference in hydraulic conductivity 

between the more transmissive alluvial aquifer and the less 

transmissive bedrock aquifers.

Categorized by water use, total pumping from the entire 

system (alluvial plus bedrock aquifers) was about 62 percent 

irrigation, 20 percent municipal, 12 percent domestic, and 

6 percent commercial/industrial in 2003. For the alluvial aquifer, most of the wells were used for domestic (56 percent) and 

irrigation (38 percent) purposes, although most of the pumping 

(90 percent) was used for irrigation purposes in 2003. For the 

bedrock aquifers, most of wells also were used for domestic 

purposes (94 percent), and only 2 percent of the bedrock wells 

were used for municipal purposes in 2003. However, because 

assumed pumping rates for municipal wells are greater than 

those for domestic wells, estimated municipal pumping 

accounted for 41 percent and domestic pumping accounted 

for 28 percent of the bedrock pumping in 2003. The upper and 

lower Arapahoe aquifers were the most heavily pumped of the 

bedrock aquifers (41 percent of bedrock pumping) in 2003. 

Bedrock domestic wells are located throughout the basin and 

are generally completed in the bedrock aquifer nearest to the 

surface, while bedrock municipal wells are associated with 

development on the west side of the basin.

Changes in land and water use have altered the groundwater flow system compared to predevelopment conditions. 

The expansion of urban/suburban land use and(or) irrigated 

agriculture since the 1950s has increased water use on the 

landscape, which has increased recharge, evapotranspiration, 

streamflow, and the overall groundwater budget in this semiarid region. Groundwater pumping from the bedrock aquifers also has increased steadily since the 1950s, primarily in 

response to increased municipal water-supply needs. The combination of these changing land- and water-use distributions 

has increased groundwater availability in the alluvial aquifer 

and shallow parts of the hydrologic system while removing 

water from storage and decreasing groundwater availability in 

the bedrock aquifers.

The majority of water moving in and out of the groundwater system is moving through the alluvial aquifer. On 

average from 1880 through 2003, 80 percent of net recharge 

was directly to the alluvial aquifer, while 20 percent of net 

recharge was directly to the bedrock aquifers. The majority of 

net outflow to streams (90 percent on average) also was from 

the alluvial aquifer, while about 10 percent of net outflow to 

streams was directly from bedrock aquifers. Simulated pumping from the alluvial aquifer increased more than threefold 

from 40 ft3/s in 1953 to about 143 ft3/s in 1971 and then more 

gradually to about 170 ft3/s in 2003. Simulated pumping from 

the bedrock aquifers increased steadily from about 10 ft3/s in 

the 1950s to about 111 ft3/s in 2003. Flow from bedrock units 

to the alluvial aquifer decreased from about 34 ft3/s for predevelopment (1879) conditions to about 28 ft3

/s in 2003, and 

flow from the alluvial aquifer to the bedrock aquifer increased 

from about 8 ft3/s for predevelopment conditions to about 

12 ft3/s in 2003, indicating the net flux to the alluvial aquifer 

from bedrock units has decreased through time from about 

26 ft3/s to about 16 ft3/s from 1880 through 2003. Downward 

interaquifer flow between bedrock units increased substantially from the Denver aquifer and lower Denver confining 

unit into the upper and lower Arapahoe aquifer, indicating 

that vertical connection exists between these layers and that 

downward flow is induced by the increased pumping from the 

Arapahoe aquifers.
178 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Simulated bedrock aquifer storage responds to changes in 

pumping and net recharge. Based on simulation results for the 

model-calibration period 1879–2003, bedrock aquifer storagedepletion rates have increased since predevelopment because 

of pumping. Storage changes for the alluvial aquifer have 

varied depending on recharge and pumping with storage being 

gained in wet years and removed in dry years. In the 1950s 

and early 1960s, simulated recharge increased in the Denver 

Basin as urban areas expanded, but pumping was not yet sufficient to remove water from storage, so recharge contributed to 

alluvial and bedrock aquifer storage. As dry conditions ensued 

in the mid-1960s and pumping continued to increase, storage 

loss occurred in both the alluvial and bedrock aquifers. Wetter climatic conditions in the 1990s contributed precipitation 

recharge to storage in the alluvial aquifer, but in the bedrock 

aquifers, continued increases in pumping resulted in continued 

storage loss. By 2003, dry climatic conditions, coupled with 

continued pumping, resulted in a storage-depletion rate from 

the alluvial aquifer of about 7 ft3/s and a storage-depletion rate 

from the bedrock aquifers of about 57 ft3/s. All of the bedrock 

aquifers are experiencing storage depletion, although depletion 

is most severe in the Denver aquifer.

The cumulative storage loss from the alluvial aquifer 

increased in response to pumping during the 1960s through 

1980s and reached a maximum cumulative storage loss of 

about 326,000 acre-ft in 1986. After 1986, the simulated area 

of urban recharge increased in areas overlying the alluvial 

aquifer, which resulted in additional simulated recharge to the 

alluvial aquifer and about 200,000 acre-ft of storage recovery. There were about 25,000 acre-ft of cumulative storage 

loss from the alluvial aquifer simulated from 2000 to 2003 

in response to drought conditions. The simulated cumulative volume of water removed from bedrock aquifer storage 

increased from zero under predevelopment conditions to about 

690,000 acre-ft in 2003. While the overall amount of storage 

depletion is small compared to the estimated total water in 

storage, the spatial distribution and temporal trend of the storage loss warrant further consideration. Spatially, 50 percent 

of the 2003 storage loss from the bedrock units was from the 

south Denver metropolitan area where groundwater provides 

most of the municipal water supply to a growing population. 

The other 50 percent of the loss was from remaining parts of 

the basin. These results suggest that storage depletion is most 

severe in the south Denver metropolitan area. Drought conditions, simulated in the model from 2000 to 2003, coupled with 

continued pumping increases, caused an exponential increase 

in simulated cumulative storage loss from the bedrock aquifers 

since 1999. Storage depletion is expected to increase substantially as the confined aquifers experience drawdown and convert to unconfined conditions because more water is released 

from drainable storage than from confined storage for a unit 

decrease in hydraulic head.

The change in recharge patterns caused by development 

as well as pumping and the removal of groundwater from 

storage have lowered the potentiometric heads and altered 

groundwater flow directions in the Denver Basin aquifer 

system. Changes in hydraulic head in the alluvial aquifer 

are much less pronounced than those in the bedrock aquifers 

because of the alluvial aquifer’s connection to surface water 

and large hydraulic conductivity and recharge rates compared 

to the bedrock aquifers. Pumping from each of the bedrock 

aquifers resulted in substantial drawdown of their respective 

predevelopment potentiometric surfaces and an increase in 

unconfined conditions for some layers. For the upper Dawson 

aquifer, pumping south of the Denver metropolitan area near 

Castle Rock and Parker has lowered the potentiometric head 

up to 100 ft below predevelopment conditions in the Cherry 

Creek basin, creating a regional discharge area that was not 

present under predevelopment conditions. The greatest concentration of pumping wells in the Arapahoe aquifer occurs 

in the south Denver metropolitan area where the aquifer is 

thickest and most conductive. Simulated drawdown from 1880 

through 2003 for the lower Arapahoe aquifer is in the range of 

200–400 ft in the south Denver metropolitan area and in the 

range of 750–1,000 ft in the Monument area. In the northern 

part of the basin, drawdown in the Arapahoe aquifer was 

limited because the unit occurs near land surface and receives 

direct recharge from the surface and alluvial aquifer. Drawdown through 2003 was greatest in all bedrock aquifer model 

layers in the south Denver metropolitan and Monument areas, 

but the drawdown patterns were somewhat different between 

the two areas because of contrasts in hydraulic conductivity. In the south Denver metropolitan area, drawdown cones 

for individual wells in the lower Arapahoe aquifer coalesced 

into a large area of regional drawdown within an extensive 

lobe of transmissive sandstone. However, drawdown in the 

lower Arapahoe aquifer in the Monument area was restricted 

to individual cones of depression with steep hydraulic gradients surrounding pumping centers because the aquifer has a 

lower hydraulic conductivity. The spatial distribution of 1880 

through 2003 drawdown for the Laramie–Fox Hills aquifer is 

slightly different than that of the other bedrock aquifers with 

the greatest drawdown occurring in the northern Denver suburbs in addition to the south Denver metropolitan area.

Predictive simulations were used to calculate model 

predictive sensitivities and to demonstrate use of the model to 

evaluate future groundwater conditions. Predictive simulations 

were run 50 years into the future from the end of the model 

calibration period (December 31, 2003) to 2053. The first 

predictive simulation to 2053 assumes dry climatic conditions and that pumping continues at the 2003 rate. The second 

predictive simulation to 2053 demonstrates the use of the 

model to evaluate future conditions and simulates the effects 

of reducing pumping from municipal wells completed in the 

lower Arapahoe aquifer in the south Denver metropolitan area. 

As expected, results from the first predictive simulation indicate continued drawdown, an increase in unconfined areas, and 

continued storage loss in all bedrock aquifer layers. Results 

from the second predictive simulation indicate about 400 ft 

less drawdown for the lower Arapahoe potentiometric surface 

from 2009 to 2053 as compared to the first predictive simulation if pumping from the lower Arapahoe aquifer were to cease 

in the south Denver metropolitan area. Because of the hydraulic connection between the Denver and Arapahoe aquifers, 
Effects of Development on Groundwater Availability in the Denver Basin Aquifer System, Colorado 179

results from the second predictive simulation also predict as 

much as 150 ft less drawdown in the Denver aquifer potentiometric surface by 2053 if pumping were to cease in the lower 

Arapahoe aquifer. Results from predictive simulations indicate 

bedrock discharge to the alluvial aquifer will continue to 

decrease and storage loss will continue through 2053 if pumping is maintained at the 2003 rates. The storage-depletion rate 

may be reduced and the useful aquifer life extended by reducing pumping from the lower Arapahoe aquifer.

Further studies of the Denver Basin aquifers would benefit 

from additional and continued data collection and interpretation. 

The Colorado Division of Water Resources maintains centralized databases of well-permit records (with drilling logs) and 

geophysical logs. Maintenance and updating of these databases 

in a consistent manner is essential to further the availability of 

well and geologic data in the Denver Basin. As drilling and construction of water-supply wells continues in the basin, continued 

compilation of hydrogeologic data, such as geologic layering 

information, aquifer tests, and water levels, into a centralized 

database would allow more effective sharing of data among 

Federal, State, and local governments and scientists. Currently 

(2010) no centralized database exists for pumping records from 

the Denver Basin aquifers. Individual water providers meter and 

record pumping as part of daily operations, but these data are 

not compiled on a regional basis. Implementation of a metering 

and reporting system for pumping information would provide 

discharge information for the basin with which to better evaluate aquifer drawdown and storage depletion and reduce model 

uncertainty. Future water-level monitoring efforts in the Denver 

Basin would benefit from an expanded network of dedicated 

monitoring wells constructed of material resistant to corrosion 

with screened intervals placed to monitor selected bedrock 

units. Based on analysis of the present network, water-level 

measurements collected in the spring represent ambient heads 

in the nonirrigation season while fall measurements are useful 

to evaluate the effects of summer irrigation pumping. Retaining 

existing wells in a long-term network should be considered if 

there already is a long-term water-level record for the well and 

if the well condition and completion interval are appropriate for 

the inclusion in the network.

Bedrock groundwater storage is being depleted in the 

Denver Basin. While the length of time over which this resource 

may be available is uncertain, the conclusions of this and other 

studies indicate that pumping from the Denver Basin bedrock 

aquifers is not indefinitely sustainable and that renewable water 

supplies will be needed in the future. Water providers and 

administrators in the Denver Basin are working to develop and 

promote conservation, conjunctive-use projects, water reuse, 

and importation of renewable water to enhance the prudent 

management of Denver Basin groundwater resources, which 

can likely extend the practical usable life of the aquifers. Recurring monitoring and analysis of groundwater availability is 

especially important to guide groundwater management in areas 

such as the Denver Basin, where a growing population presently 

relies on this important and limited resource.

References

Alley, W.M., 2006, Tracking U.S. groundwater reserves for the 

future: Environment, v. 48, no. 3, p. 10–25.

Alley, W.M., 2007, Another water budget myth—The significance of recoverable groundwater in storage: Groundwater, 

v. 45, no. 3, p. 251.

Banta, E.R., 1989, Hydrologic effects of pumpage from the 

Denver Basin bedrock aquifers of northern El Paso County, 

Colorado: U.S. Geological Survey Water-Resources Investigations Report 88–4033, 81 p.

Colorado Division of Water Resources, 1998, Denver Basin 

and South Platte River Basin Technical Study, Final Report, 

Senate Bill 96–074, variously paged.

Colorado Division of Water Resources, 2003, Ground water 

levels in the Denver Basin bedrock aquifers, 2003 annual 

report, 132 p.

Colorado Division of Water Resources, 2004, Ground water 

levels in the Denver Basin bedrock aquifers, 2004 annual 

report, 132 p.

Colorado Water Conservation Board, 2004, Statewide Water 

Supply Initiative Report, November 2004, variously paginated, accessed March 19, 2009, at http://cwcb.state.co.us/

IWMD/SWSITechnicalResources/SWSIPhaseIReport/

SWSIPhaseIReport.htm.

Colorado Water Conservation Board, 2006, SPDSS 

Phase 3 Tasks 44.3 South Platte alluvium region water 

level technical memorandum, 46 p., accessed September 20, 2009, at ftp://dwrftp.state.co.us/cdss/gwm/tm/

SPDSS44-3_20061129.pdf.

Cross, C.W., Chisholm, F.F., Chauvenet, Regis, and Van Deist, 

P.H., 1884, The artesian wells of Denver: Colorado Scientific Society Proceedings, v. 1, p. 76–108.

Darton, N.H., 1905, Preliminary report on geology and 

underground water resources of the central Great Plains: 

U.S. Geological Survey Professional Paper 32, 433 p.

Emmons, S.F., Cross, Whitman, and Eldridge, G.E., 1896, 

Geology of the Denver Basin in Colorado: U.S. Geological 

Survey Monograph 27, 526 p.

Faunt, C.C., ed., 2009, Groundwater availability of the Central 

Valley aquifer, California: U.S. Geological Survey Professional Paper 1766, 225 p.

Graham, Glenn, and VanSlyke, George, 2004, Development 

of the regulatory framework for Denver Basin aquifers: The 

Mountain Geologist, v. 41, no. 4, p. 153–160.

Halford, K.J., and Hanson, R.T., 2002, User guide for the 

drawdown-limited, Multi-Node Well (MNW) package for the 

U.S. Geological Survey’s modular three-dimensional finitedifference ground-water flow model, versions MODFLOW-96 

and MODFLOW-2000: U.S. Geological Survey OpenFile Report 2002–293, 33 p., accessed August 31, 2009, at 

http://pubs.er.usgs.gov/usgspubs/ofr/ofr02293.
180 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Harbaugh, A.W., Banta, E.R., Hill, M.C., and McDonald, 

M.G., 2000, MODFLOW-2000, the U.S. Geological Survey 

modular ground-water model—User guide to modularization concepts and the Groundwater Flow Process: 

U.S. Geological Survey Open-File Report 2000–92, 121 p.

Homer, Collin, Huang, Chengquan, Yang, Limin, Wylle, Bruce, 

and Coan, Michael, 2004, Development of a 2001 National 

Land-Cover Database for the United States: Photogrammetric 

Engineering and Remote Sensing, July 2004, p. 829–840.

Hurr, R.T., Schneider, P.A., Jr., and Minges, D.R., 1975, 

Hydrology of the South Platte River valley, northeastern 

Colorado: Colorado Water Resources Circular 28.

Lohman, S.W., 1979, Ground-water hydraulics: U.S. Geological Survey Professional Paper 708, 70 p.

Moore, J.E., Raynolds, R.G., and Dechesne, M., 2007, Bedrock aquifers and population growth in the Denver Basin, 

Colorado, USA: Episodes, v. 30, no. 2, p. 115–118.

Nadler, C.T., and Schumm, S.A., 1981, Metamorphosis of 

South Platte and Arkansas Rivers, eastern Colorado: Physical Geology, v. 2, no. 22, p. 95–115.

Perry, M.J., and Mackun, P.J., 2002, Population change and 

distribution 1990 to 2000: U.S. Census Bureau, Census 

2000 Brief, C2KBR/01–2, 7 p., accessed February 15, 2009, 

at http://www.census.gov/prod/2001pubs/c2kbr01-2.pdf.

Riverside Technology, Inc., 2005, SPDSS 2001 Division 1 

ditch service areas: Online data accessed October 11, 2006, 

at http://cdss.state.co.us/DNN/GIS/tabid/67/Default.aspx.

Robson, S.G., 1987, Bedrock aquifers in the Denver Basin, 

Colorado—A quantitative water-resources appraisal: 

U.S. Geological Survey Professional Paper 1257, 73 p.

Robson, S.G., 1989, Alluvial and bedrock aquifers of the Denver Basin—Eastern Colorado’s dual ground-water resource: 

U.S. Geological Survey Water-Supply Paper 2302, 40 p.

Robson, S.G., and Romero, J.C., 1981a, Geologic structure, hydrology, and water quality of the Dawson aquifer 

in the Denver Basin, Colorado: U.S. Geological Survey 

Hydrologic Investigations Atlas HA–643, scale 1:500,000, 

3 sheets.

Robson, S.G., and Romero, J.C., 1981b, Geologic structure, hydrology, and water quality of the Denver aquifer 

in the Denver Basin, Colorado: U.S. Geological Survey 

Hydrologic Investigations Atlas HA–646, scale 1:500,000, 

3 sheets.

Robson, S.G., Romero, J.C., and Zawistowski, S., 1981, 

Geologic structure, hydrology, and water quality of the 

Arapahoe aquifer in the Denver Basin, Colorado: U.S. Geological Survey Hydrologic Investigations Atlas HA–646, 

scale 1:500,000, 3 sheets.

Robson, S.G., Wacinski, A., Zawistowski, S., and Romero, 

J.C., 1981, Geologic structure, hydrology, and water quality 

of the Laramie–Fox Hills aquifer in the Denver Basin, Colorado: U.S. Geological Survey Hydrologic Investigations 

Atlas, HA–650, scale 1: 500,000, 3 sheets.

U.S. Geological Survey, 1973–1979, Landsat MSS scenes, 

WRS–1, P35R32, P35R33, P36R32, P36R33, Sioux Falls, 

South Dakota.

U.S. Geological Survey, 1999–2000, Enhanced Landsat 

mosaic of Colorado, Sioux Falls, South Dakota.

U.S. Geological Survey, 2001a, National Land Cover Database 

2001, accessed December 2, 2009, at http://www.mrlc.gov/

nlcd.php.

U.S. Geological Survey, 2001b, Coverage LU30—Highresolution land use and land cover 1937/1938 Front 

Range Infrastructure Resources Project Demonstration 

Area, Version 1.0, April 5, 2001: U.S. Geological Survey Rocky Mountain Mapping Center, Lakewood, Colo., 

http://rockyweb.cr.usgs.gov/frontrange/NMD/data/lu30.html.

U.S. Geological Survey, 2001c, Coverage LU50—Highresolution land use and land cover 1953–1958 Front 

Range Infrastructure Resources Project Demonstration 

Area, Version 1.0, April 5, 2001: U.S. Geological Survey 

Rocky Mountain Mapping Center, Lakewood, Colo., 

http://rockyweb.cr.usgs.gov/frontrange/NMD/data/lu50.html.

Watts, K.R., 1995, Hydrogeology and simulation of flow 

between the alluvial and bedrock aquifers in the upper Black 

Squirrel Creek Basin, El Paso County, Colorado: U.S. Geological Survey Water-Resources Report 94–4238, 82 p.
Chapter C. Groundwater Flow Simulations of the Denver 

Basin Aquifer System, Colorado

By Edward R. Banta, Suzanne S. Paschke, and David W. Litke

the use of predictive sensitivity analysis to suggest monitoring locations; and (5) a discussion of appropriate model use 

and maintenance. Groundwater availability results from the 

Denver Basin model for predevelopment conditions are presented in Chapter A, and transient results describing temporal 

changes in recharge, discharge, aquifer storage, and groundwater flow directions are presented in Chapter B of this report.

The Denver Basin groundwater flow model includes 

several enhancements over previous modeling efforts because 

of the availability of additional data, improved modeling 

capabilities, and advanced computer technology. Additional 

data available for this study included updated geologic 

mapping of the extent of Denver Basin bedrock and alluvial 

aquifers (Chapter A); additional geophysical logs in the basin 

with which to better define the aquifer layering and geometry 

of the hydrogeologic framework for the model (Chapter A); 

additional water-level, streamflow, precipitation, and irrigation data collected since previous studies (Chapters A and B); 

and updated estimates of pumping from Denver Basin bedrock 

and alluvial aquifers (Chapter B). Modeling capabilities and 

computer technology also have advanced considerably since 

development of previous Denver Basin groundwater flow 

models such that additional features, hydrologic processes, 

and numerical techniques are included in the current model 

that were not possible in previous models. Updated modeling 

capabilities implemented by this study include:

• A fully three-dimensional representation of the 

aquifer system, which includes explicit definition of 

all Denver Basin aquifer and confining layers. Previous models used a quasi-three-dimensional approach, 

which represented confining layers by using a verticalconductance formulation.

• Explicit representation of the alluvial aquifer system 

as the uppermost layer in the model. Previous models 

simulated the alluvial aquifer as constant-head cells 

(Robson, 1987) or as head-dependent-flow boundaries using the MODFLOW River Package (Colorado 

Division of Water Resources, 1998).

• Use of streamflow-routing simulation capabilities 

(SFR2, Niswonger and Prudic, 2005), to represent 

stream systems. Previous models did not explicitly 

simulate streams.

Introduction

Groundwater flow in the Denver Basin bedrock aquifer system and overlying alluvial aquifer is simulated with 

the three-dimensional groundwater flow modeling program 

MODFLOW-2000 (Harbaugh and others, 2000; Hill and others, 2000). The calibrated Denver Basin model forms the basis 

for groundwater availability analysis presented in Chapters A 

and B of this report and provides a tool for analyzing temporal 

changes to the hydrologic system in response to changing climatic conditions and groundwater development. The Denver 

Basin groundwater flow model represents regional timevarying (transient) conditions prior to 1880 through 2003. A 

single steady-state model stress period represents predevelopment conditions prior to 1880. The 124-year transient modelcalibration period represents conditions from 1880 through 

2003 using 15 model stress periods ranging from 2 to 27 years 

in length. The model was calibrated by adjusting primarily 

hydraulic-conductivity and recharge parameters until a best 

fit was obtained between observed and simulated transient 

hydraulic heads and flows. The calibrated model represents 

a best fit of the numerical simulation to the observed data for 

the given model parameters and was attained using automated 

parameter-estimation techniques as implemented in PEST 

(Doherty, 2006). Sensitivity of the model results to estimated 

and assigned parameters was determined from PEST and 

UCODE_2005 (Poeter and others, 2005) sensitivity analysis, and the calibrated model was used in a predictive mode 

to estimate the hydrologic system response to two pumping 

scenarios for the period 2004 through 2053. Additional modelsensitivity calculations using Observation-Prediction (OPR) 

and Parameter-Prediction (PPR) statistics (Hill and Tiedeman, 

2007) were used to evaluate the benefits and locations of additional data collection.

This chapter, Chapter C, documents the groundwater 

flow model including model setup, calibration, and sensitivity analysis. Specifically this chapter includes information on 

the (1) development of input datasets for the transient threedimensional, finite-difference numerical model; (2) procedures 

and measures of model fit used to calibrate the flow model; 

(3) descriptions of the model sensitivity to estimated and 

assigned parameters; (4) descriptions of model predictions and 
182 Groundwater Availability of the Denver Basin Aquifer System, Colorado

• Inclusion of evapotranspiration as a boundary condition 

(ETS, Banta, 2000). Previous models did not explicitly 

include evapotranspiration as a hydrologic process.

• Use of recently developed software designed for 

parameter estimation and sensitivity analysis. In 

this report, the phrase “parameter estimation” refers 

to an automated inverse-modeling procedure such 

as those implemented in PEST (Doherty, 2006) or 

UCODE_2005 (Poeter and others, 2005). PEST 

was used to estimate model hydraulic parameters 

and guide transient model calibration. Model sensitivity to parameters was calculated with PEST and 

UCODE_2005 (Poeter and others, 2005). 

• A new MODFLOW numerical solver (GMG Package, 

Wilson and Naff, 2004; Banta, 2006). The Geometric 

MultiGrid (GMG) solver of MODFLOW-2000 provided improved model convergence for this highly 

nonlinear system.

• Parallel computing capabilities. Parameter estimation 

was accomplished with Parallel PEST (Doherty, 2006). 

Parallel simulations used multiple networked personal 

computers to simultaneously simulate various combinations of model parameters during model calibration.

Model Development

The three-dimensional, finite-difference, groundwater 

flow modeling program MODFLOW-2000 (Harbaugh and 

others, 2000; Hill and others, 2000) with modifications documented in McAda and Barroll (2002) and Banta (2006) was 

used to simulate the Denver Basin aquifer system. The summarized modifications are as follows:

1. The Layer Property Flow (LPF) Package was modified 

to eliminate the vertical flow correction (McAda and 

Barroll, 2002).

2. The Recharge (RCH) Package was modified to allow 

recharge to apply to the uppermost active cell connected 

by active cells to the lowermost active cell in a stack of 

cells (Banta, 2006).

3. The Evapotranspiration Segments (ETS) Package (Banta, 

2000) was modified to allow evapotranspiration to apply 

to the uppermost active cell connected by active cells to 

the lowermost active cell in a stack of cells (Banta, 2006).

4. The GMG solver was modified to support a new adaptivedamping option (Banta, 2006).

Geographic Information System (GIS) data containing 

the layer extent, layer top and base altitude values, geologic 

data, precipitation, and other hydrologic, geologic, and geographic data were stored and manipulated using ArcGIS version 9.0 (Environmental Systems Research Institute, 1999–

2004a). Input files for MODFLOW-2000 were generated 

from the GIS data by using ArcGIS (Environmental Systems 

Research Institute, 1999–2004a), ArcInfo (Environmental 

Systems Research Institute, 1982–2004b), and Argus Open 

Numerical Environments (Argus ONE, Argus Holdings, Ltd., 

1992–99) with the Graphical User Interface for MODFLOW 

(“MODFLOW-GUI”, Winston, 2000). The model-independent 

parameter-estimation program Parallel PEST (Doherty, 2006) 

was used for parameter estimation. Model results were processed using a series of utility computer programs (Banta and 

others, 2008) which translate the results into formats suitable 

for display as ArcGIS raster grids.

Model Conceptualization 

and Parameterization

Model parameterization consists of developing 

MODFLOW parameters and preparing model input files that 

represent various aspects of the conceptual hydrogeologic setting being simulated.

Model Area and Spatial Discretization

A model grid was defined to encompass the Denver 

Basin bedrock aquifer system and immediately adjacent areas 

of the alluvial aquifer of the South Platte River (fig. C1). The 

grid has 84 columns and 124 rows of square cells; each cell 

measures 1 mile by 1 mile (1-mi2). The grid was generated in 

the State Plane coordinate system (North American Datum 

of 1983, units: feet, zone: Colorado Central Zone). The grid 

origin is located at the northwest corner of the model area 

at easting 3,071,260 ft and northing 1,961,860 ft, such that 

row numbers increase from west to east and column numbers 

increase from north to south (fig. C1). The grid is aligned (not 

rotated) relative to the State Plane coordinate system.

MODFLOW-2000 provides two options for representation of confining units: “quasi-3D” and fully threedimensional. When a confining unit is represented as quasi3D, the confining unit does not occupy a layer in the model, 

vertical hydraulic connection across the confining unit is 

simulated by calculation or input of a vertical conductance, 

and lateral flow and storage changes in the confining unit are 

not simulated. In contrast, when the fully three-dimensional 

option is selected, the confining unit is explicitly represented as a model layer, lateral flow is simulated, and storage 

changes are simulated for transient stress periods. The fully 

three-dimensional approach was used in construction of the 

model described in this report primarily to allow simulation 

of storage changes in the confining units. Use of the fully 

three-dimensional approach also allows simulation of advective transport of particles. Table C1 lists each hydrogeologic 

unit and corresponding model layer; the section “Hydrologic 

Framework” in Chapter A presents detailed discussions of the 

aquifer-system stratigraphy.
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 183

Figure C1. Extent of Denver Basin model grid, active model cells, and uppermost model layer.

PALMER

DIVIDE

PALMER

DIVIDE

!(

!(

!(

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!(

!(

!(

!( !( !(

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!( !(

!(

!(

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!(

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!(

!(

!(

!(

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WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

105° 104°

40°

39°

1 10 20 30 40 50 60 70 80 84

COLUMN

124

120

100

110

90

70

80

60

50

40

30

20

10

1

ROW

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Extent of active model cells

Model grid

Alluvial aquifer (model layer 1)

Upper Dawson aquifer (model layer 2)

Lower Dawson aquifer (model layer 4)

Denver aquifer (model layer 6)

Upper Arapahoe aquifer (model layer 8)

Lower Arapahoe aquifer (model layer 10)

Laramie–Fox Hills aquifer (model layer 12)

Confining units (model layers 3, 5, 7, 9, 11)
184 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Table C1. Vertical discretization of Denver Basin aquifers 

and confining units (see table A3 for detailed explanations of 

hydrologic units).

Model layer Hydrogeologic unit

1 Alluvial aquifer

2 Upper Dawson aquifer

3 Dawson confining unit

4 Lower Dawson aquifer

5 Denver upper confining unit

6 Denver aquifer

7 Denver lower confining unit

8 Upper Arapahoe aquifer

9 Arapahoe confining unit

10 Lower Arapahoe aquifer

11 Laramie confining unit

12 Laramie–Fox Hills aquifer

The extents of the seven aquifers and five confining 

units represented in the Denver Basin model, and described in 

Chapter A, were used to define the initial active/inactive status 

of cells for each model layer. In general, cells were initially 

specified as active where a hydrogeologic unit is present and 

inactive where it is absent. The bowl-shaped structure of the 

basin results in a ringed outcrop pattern, and the distribution 

of uppermost active model layers exhibits a similar distribution for model layers representing bedrock units (model 

layers 2 through 12; fig. C1). The alluvial aquifer (represented by model layer 1) overlies all of the bedrock model 

layers (fig. C1). In areas where the alluvial aquifer overlies a 

hydrogeologic unit stratigraphically below the upper Dawson 

aquifer and intervening bedrock units are missing from the 

simulated stratigraphic column, cells in the intervening layers were specified as active to simulate vertical hydraulic 

connection between the alluvial aquifer and the underlying 

bedrock unit. The activated cells were assigned a thickness of 

0.1 ft, a base altitude 0.1 ft below that of the overlying layer, 

and hydraulic properties of the overlying alluvial aquifer, to 

maintain lateral and vertical continuity among interconnected 

active model cells.

The top of the aquifer system was specified as the landsurface altitude. The raster datasets of the base altitude of 

hydrogeologic units (model layers) were used with ArcGIS 

(Environmental Systems Research Institute, 1999–2004a) 

tools to generate arrays of model-layer base altitude. In areas 

where a model cell represents a hydrogeologic unit that is 

absent, the base altitude of the layer was defined to be 0.1 ft 

lower than the base altitude of the overlying layer. The top 

altitude was set equal to land-surface altitude where the hydrogeologic unit crops out, or the base altitude of the overlying 

hydrogeologic unit, where the unit does not crop out.

Hydraulic properties of the hydrogeologic units were 

specified using the Layer Property Flow (LPF) Package of 

MODFLOW-2000 (Harbaugh and others, 2000). In the LPF 

Package, each layer may be specified as either confined or 

convertible. Cells in layers specified as confined are assumed 

to have an unvarying saturated thickness, regardless of the 

calculated head, and do not become inactive if the calculated 

head is below the cell bottom. Cells in layers specified as 

convertible are simulated as having head-dependent saturated 

thickness when the calculated head is below the cell top, and 

these cells are deactivated if the head is below the cell bottom.

Each of the aquifers is unconfined in at least part of 

its extent, primarily where the unit crops out at or near land 

surface. Because continued pumping from the aquifers is 

expected to increase the area of unconfined conditions, and to 

allow more realistic simulation of hydrologic conditions in the 

aquifers with changing saturated thickness, the model layers 

representing aquifers (layers 1, 2, 4, 6, 8, 10, and 12; table C1) 

were specified as convertible between confined and unconfined conditions. The model layers representing confining 

units, which are composed primarily of fine-grained materials 

that are not expected to drain substantially as heads decline, 

were specified as confined. The “wetting” option, which 

allows cells to return to active status after being deactivated, 

was disabled to enhance numerical stability.

Temporal Discretization

Simulated time periods in MODFLOW-2000 (Harbaugh 

and others, 2000) are subdivided into “model stress periods” 

during which recharge, pumping, and other stresses are held 

constant. Stress periods are further subdivided into “time 

steps” during the MODFLOW simulation to facilitate numerical calculations. For the Denver Basin model, 16 model stress 

periods are used to represent the time period from prior to 

1880 through 2003. Hydrologic stresses and groundwater 

flow rates are assumed to have been constant (steady state) 

prior to 1880, and a single steady-state stress period is used to 

represent pre-1880 (predevelopment) conditions. Groundwater 

development from 1880 through 2003 is simulated as timevarying (transient), and the model was calibrated to hydrologic 

data collected during this period. Fifteen transient stress periods are used to simulate variable stresses during the 124-year 

calibration period, January 1, 1880, through December 31, 

2003. The timing and duration of transient stress periods were 

selected to allow approximation of historical precipitation and 

pumping stresses (fig. C2). The stress-period durations for the 

calibration period ranged from 2 to 27 years (table C2).

Hydrogeologic-Unit Properties

Intrinsic hydraulic-conductivity and storage properties of 

the aquifers and confining units are required inputs for the LPF 

Package of MODFLOW-2000 (Harbaugh and others, 2000). 

The input defines horizontal and vertical hydraulic conductivity and specific storage for all model layers. For the convertible layers, additional input defines specific yield. The following sections describe parameterization of these properties.
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 185

Figure C2. Temporal discretization of (A) annual precipitation from station data, and 

(B) simulated pumping.

5.0

10.0

15.0

20.0

25.0

Basinwide mean annual preciptation, in inches

Basinwide mean annual precipitation

Simulated basinwide precipitation

0

50

100

150

200

250

300

350

Pumping, in cubic feet per second

Year

Year

A

B

3

7 8

4 5 6

9 11 12

14 15 16

10

13

2

EXPLANATION

EXPLANATION

Transient stress-period number

Simulated total pumping

Simulated alluvial pumping

Simulated bedrock pumping

Estimated total pumping

Estimated alluvial pumping

Estimated bedrock pumping

4

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

1880

1885

1890

1895

1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
186 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Hydraulic Conductivity

Horizontal hydraulic-conductivity values for the hydrogeologic units of the Denver Basin were parameterized using 

several different approaches summarized in table C3. Note 

that the conceptualization schemes described in the table 

incorporate simplifying assumptions. Vertical hydraulic conductivity was assumed to equal horizontal hydraulic conductivity in all model layers representing bedrock; this assumption is represented in the model input by assigning vertical 

anisotropy of bedrock aquifers (ratio of horizontal to vertical 

hydraulic conductivity, parameter VANI_BR) a value of 1.0. 

In this conceptualization, resistance to vertical flow among the 

bedrock aquifers is assumed to be primarily controlled by the 

confining units. The parameter VANI_QPlat was used in the 

model to represent vertical anisotropy of the alluvial aquifer 

along the South Platte River main stem and tributaries and was 

estimated by parameter estimation (calibrated value of 9.9). 

The parameter VANI_Qbas was used in the model to represent 

vertical anisotropy of the alluvial aquifer in the Big Sandy and 

Black Squirrel Creek basins and was assigned a value of 10.

Parameterization of the hydraulic-conductivity distributions of the Denver, upper and lower Arapahoe, and 

Laramie–Fox Hills aquifers used the pilot-point approach 

(de Marsily and others, 1984; Certes and de Marsily, 1991; 

Doherty, 2001) as implemented in PEST and associated 

utilities (Doherty, 2003, 2006). Pilot points are locations in 

the model where a parameter, hydraulic conductivity in this 

study, is estimated by the parameter estimation. The estimated 

parameter values at pilot points are then interpolated between 

locations within a model layer to assign a parameter distribution to the layer. The pilot-point approach allows the estimated 

parameter values to vary gradationally between the pilot 

points and contrasts with a MODFLOW zoned parameterization of hydraulic conductivity where hydraulic-conductivity 

parameters are used for various spatial zones of a simulated 

aquifer. For the Denver Basin, the pilot-point approach worked 

well because it allowed the model to represent gradational, 

rather than abrupt, hydraulic-conductivity distributions across 

the basin consistent with the sedimentary deposits that fine 

eastward from the mountain front.

Selection of the number of pilot points applied the 

principal of parsimony. A large number of model parameters 

increases the required number of parameter-estimation 

simulations, and a model parameter is required by PEST for 

each pilot point. The pilot-point locations were thus selected 

to provide reasonably uniform coverage over the aquifer 

domain, to provide a reasonable but least-complex representation of observed hydraulic-conductivity distributions, and to 

simplify the numerical calculations. To ensure that excessive 

extrapolation would not be required to populate the hydraulicconductivity arrays, some pilot points were located near the 

margins of the aquifers. The locations of pilot points used for 

the Denver, upper Arapahoe, lower Arapahoe, and Laramie–

Fox Hills aquifers are shown in figure C3.

Interpolation to populate the hydraulic-conductivity 

arrays from the pilot-point values implemented the geostatistical interpolation method ordinary kriging (Davis, 1986). For 

the kriging analysis, hydraulic-conductivity values (in ft/d) 

from aquifer pumping tests discussed in the section “Aquifer 

Hydraulic Properties” in Chapter A (table A4; Colorado 

Division of Water Resources, 2005) were transformed to 

base-10 logarithms to account for the tendency of hydraulic 

conductivity to have a log-normal distribution. Semivariograms of log hydraulic-conductivity data were prepared for 

the Denver, the upper and lower Arapahoe, and the Laramie–

Fox Hills aquifers. Records of aquifer tests of the Arapahoe 

aquifers generally did not distinguish between the upper and 

lower aquifers; therefore, the data were assumed to apply to 

both aquifers, and a single semivariogram was prepared for the 

Table C2. Temporal discretization for the Denver Basin model.

[--, not applicable]

Stress period Stress-period length

(days)

Stress-period length

(years) Time period simulated

1 -- -- Predevelopment through December 31, 1879

2 9,861 27 January 1, 1880 through December 31, 1906

3 4,748 13 January 1, 1907 through December 31, 1919

4 7,305 20 January 1, 1920 through December 31, 1939

5 5,114 14 January 1, 1940 through December 31, 1953

6 1,096 3 January 1, 1954 through December 31, 1956

7 1,826 5 January 1, 1957 through December 31, 1961

8 1,096 3 January 1, 1962 through December 31, 1964

9 2,556 7 January 1, 1965 through December 31, 1971

10 731 2 January 1, 1972 through December 31, 1973

11 1,826 5 January 1, 1974 through December 31, 1978

12 2,192 6 January 1, 1979 through December 31, 1984

13 730 2 January 1, 1985 through December 31, 1986

14 2,922 8 January 1, 1987 through December 31, 1994

15 1,826 5 January 1, 1995 through December 31, 1999

16 1,461 4 January 1, 2000 through December 31, 2003
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 187

Table C3. Hydraulic-conductivity conceptualization and parameterization.—Continued

[ft/d, feet per day]

Hydrogeologic unit Parameter names and definitions

(ft/d except where noted) Hydraulic-conductivity conceptualization

Alluvial aquifer K_Q_Platte—Hydraulic conductivity of alluvial aquifer 

adjacent to South Platte River and its tributaries.

Aquifer area is divided into zones. Assumption: 

Hydraulic conductivity within each zone is 

homogeneous and isotropic in the lateral dimensions. 

Parameters represent hydraulic conductivity of entire 

unit thickness or vertical anisotropy.

K_Q_bas—Hydraulic conductivity of alluvial aquifer 

in Big Sandy and Black Squirrel basins.

VANI_QPlat—Vertical anisotropy1 of alluvial aquifer 

adjacent to South Platte River and its tributaries. 

Unit: dimensionless.

VANI_Qbas—Vertical anisotropy1 of alluvial 

aquifer in Big Sandy and Black Squirrel basins. 

Unit: dimensionless.

Upper Dawson aquifer K_utdw—Hydraulic conductivity of the silt-plus-sand 

fraction of upper Dawson aquifer.

Assumptions: (1) Hydraulic conductivity of aquifer 

is attributable to materials with grain size reported 

as silt-sized or coarser; (2) contribution of finer 

grained material to transmissivity is negligible; and 

(3) hydraulic conductivity of silt-sized and coarser 

fraction is uniform. Parameter represents hydraulic 

conductivity of the silt-plus-sand fraction.

Dawson confining unit K_tdwc—Hydraulic conductivity of Dawson 

confining unit.

Assumption: Hydraulic conductivity is homogeneous 

and isotropic. Parameter represents hydraulic 

conductivity of entire unit thickness.

Lower Dawson aquifer K_ltdw—Hydraulic conductivity of the silt-plus-sand 

fraction of lower Dawson aquifer.

Assumptions: (1) Hydraulic conductivity of aquifer 

is attributable to materials with grain size reported 

as silt-sized or coarser; (2) contribution of finer 

grained material to transmissivity is negligible; and 

(3) hydraulic conductivity of silt-sized and coarser 

fraction is uniform. Parameter represents hydraulic 

conductivity of the silt-plus-sand fraction.

Denver upper confining unit K_tkduc—Hydraulic conductivity of Denver upper 

confining unit.

Assumption: Hydraulic conductivity is homogeneous 

and isotropic. Parameter represents hydraulic 

conductivity of entire unit thickness.

Denver aquifer p6_01, p6_02, p6_03, ... p6_08—Hydraulic conductivity 

of the silt-plus-sand fraction of Denver aquifer. Each 

parameter is associated with a pilot-point location 

(fig. C3; hydraulic-conductivity field is determined by 

interpolation from the point values.

Assumptions: (1) Hydraulic conductivity of aquifer 

is attributable to materials with grain size reported 

as silt-sized or coarser; (2) contribution of finer 

grained material to transmissivity is negligible; and 

(3) spatial variation of hydraulic conductivity of 

silt-sized and coarser fraction is represented by a 

small number of point values interpolated to aquifer 

domain. Parameters represent hydraulic conductivity 

of the silt-plus-sand fraction.

Denver lower confining unit K_tkdlc—Hydraulic conductivity of Denver lower 

confining unit.

Assumption: Hydraulic conductivity is homogeneous 

and isotropic. Parameter represents hydraulic 

conductivity of entire unit thickness.

Upper Arapahoe aquifer pKa_02, pKa_07, pKa_08, pKa_09, pKa_10, 

pKa_11, pKa_12, p8_01, p8_03, p8_04, p8_05, 

and p8_06—Hydraulic conductivity of the siltplus-sand fraction of upper Arapahoe aquifer. Each 

parameter is associated with a pilot-point location 

(fig. C3); hydraulic-conductivity field is determined 

by interpolation from the point values. Pilot points 

associated with parameters pKa_02, pKa_07, 

pKa_08, pKa_09, pKa_10, pKa_11, and pKa_12 are 

in locations where the Arapahoe confining unit is 

absent; these parameters accordingly apply to both 

upper and lower Arapahoe aquifers.

Assumptions: (1) Hydraulic conductivity of aquifer 

is attributable to materials with grain size reported 

as silt-sized or coarser; (2) contribution of finer 

grained material to transmissivity is negligible; and 

(3) spatial variation of hydraulic conductivity of 

silt-sized and coarser fraction is represented by a 

small number of point values interpolated to aquifer 

domain. Parameters represent hydraulic conductivity 

of the silt-plus-sand fraction.
188 Groundwater Availability of the Denver Basin Aquifer System, Colorado

undifferentiated Arapahoe aquifer. An exponential model was 

fitted to each semivariogram. The fitted model parameters are 

shown in table C4. These kriging models, in combination with 

parameter values for each of the pilot-point locations shown in 

figure C3, were then used with PEST utilities to generate, over 

the active domain of each aquifer, values of hydraulic conductivity of the silt-sized and coarser aquifer materials (siltplus-sand fraction). The hydraulic-conductivity values were 

multiplied by the fraction of silt-plus-sand materials to obtain 

an equivalent hydraulic conductivity for the overall aquifer 

thickness represented by each cell.

Specific Storage and Specific Yield

The capacity of each hydrogeologic unit to yield water was 

represented in the model by the parameters specific storage and 

specific yield. Hydrogeologic units represented as confined were 

assigned values of specific storage; units represented as convertible from confined to unconfined conditions were assigned 

values of both specific storage and specific yield. Specific-storage values were estimated separately for aquifers and confining units during model calibration. A specific-storage value of 

5.2 ×10–7/ft was estimated by PEST for aquifers (parameter 

SS_coarse in model input), and a value of 1.7 ×10–6 /ft was estimated by PEST for confining units (parameter SS_fine in model 

input). These aquifer specific-storage values are in the range of 

values computed by various methods for a well completed in the 

Arapahoe aquifer at Castle Pines, Colorado (Robson and Banta, 

1990), and the confining-unit specific-storage value is within 

the range of values reported for confining units by Konikow and 

Neuzil (2007).

Specific-yield values assigned to all aquifer units in the 

model (model layers 1, 2, 4, 6, 8, 10, and 12) allowed for the 

simulation of unconfined conditions and(or) conversion from 

confined to unconfined conditions. Mean specific-yield values 

for each aquifer unit were determined from laboratory and 

aquifer tests (see section “Storage Parameters” in Chapter A; 

table A6) and a spatial distribution of specific yield was 

determined for each bedrock aquifer model layer as described 

herein. For the bedrock aquifers, four specific-yield model 

parameters were defined for the bedrock aquifers (table C5), 

and a constant specific-yield value (equal to the mean values in table A6) was assigned to each model parameter. The 

silt-plus-sand fraction of aquifer materials for each grid 

cell (figs. A14, A20, A22, A27, A30, A34) were input to the 

model as multiplier arrays and multiplied by the constant 

Table C3. Hydraulic-conductivity conceptualization and parameterization.—Continued

[ft/d, feet per day]

Hydrogeologic unit Parameter names and definitions

(ft/d except where noted) Hydraulic-conductivity conceptualization

Arapahoe confining unit K_kac—Hydraulic conductivity of Arapahoe 

confining unit.

Assumption: Hydraulic conductivity is homogeneous 

and isotropic. Parameter represents hydraulic 

conductivity of entire unit thickness.

Lower Arapahoe aquifer pKa_02, pKa_07, pKa_08, pKa_09, pKa_10, 

pKa_11, pKa_12, p10_01, p10_03, p10_04, p10_05, 

and p10_06—Hydraulic conductivity of the siltplus-sand fraction of lower Arapahoe aquifer. Each 

parameter is associated with a pilot-point location 

(fig. C3); hydraulic-conductivity field is determined 

by interpolation from the point values. Pilot points 

associated with parameters pKa_02, pKa_07, pKa_08, 

pKa_09, pKa_10, pKa_11, and pKa_12 are in 

locations where the Arapahoe confining unit is absent; 

these parameters accordingly apply to both upper and 

lower Arapahoe aquifers.

Assumptions: (1) Hydraulic conductivity of aquifer 

is attributable to materials with grain size reported 

as silt-sized or coarser; (2) contribution of finer 

grained material to transmissivity is negligible; 

and (3) spatial variation of hydraulic conductivity 

of silt-sized and coarser fraction is represented 

by a small number of point values interpolated to 

aquifer domain. Parameters represent hydraulic 

conductivity of the silt-plus-sand fraction.

Laramie confining unit K_klc—Hydraulic conductivity of Laramie 

confining unit.

Assumption: Hydraulic conductivity is homogeneous 

and isotropic. Parameter represents hydraulic 

conductivity of entire unit thickness.

Laramie–Fox Hills aquifer p12_01, p12_02, p12_03, ... p12_11—Hydraulic 

conductivity of the silt-plus-sand fraction of 

Laramie–Fox Hills aquifer. Each parameter is 

associated with a pilot-point location (fig. C3); 

hydraulic-conductivity field is determined by 

interpolation from the point values.

Assumptions: (1) Hydraulic conductivity of aquifer 

is attributable to materials with grain size reported 

as silt-sized or coarser; (2) contribution of finer 

grained material to transmissivity is negligible; 

and (3) spatial variation of hydraulic conductivity 

of silt-sized and coarser fraction is represented 

by a small number of point values interpolated to 

aquifer domain. Parameters represent hydraulic 

conductivity of the silt-plus-sand fraction. 1

Vertical anisotropy is defined in Layer Property Flow Package as ratio of horizontal to vertical hydraulic conductivity.
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 189

Figure C3. Location of pilot points for estimating hydraulic-conductivity distributions for model 

layers 6 (Denver aquifer), 8 and 10 (upper and lower Arapahoe aquifers undifferentiated), and 12 

(Laramie–Fox Hills aquifer).

PALMER

DIVIDE

PALMER

DIVIDE

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

§ ̈¦70

§ ̈¦25

§ ̈¦76

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

South Platte River

Coal Creek

Big Dry Cr

Clear Creek

First Cree k

Sand Creek

West P ul m Creek

Running

Creek

Kiow a Creek

Comanche Creek

Muddy Creek

Bijou Creek

Middle Bijou Creek

Adobe Creek

West Bijou Creek Big Sandy Cree k

Cherry Cr

Cook Creek

Box Elder Creek

Lo st Creek

Boulder Creek

Indian Cr

Monument Cr

Crow Creek pKa_09

pKa_12

pKa_11

pKa_10

pKa_07

pKa_02

p10_01

p10_03

p10_04

p10_05

p10_06

p12_03

p12_08

p12_11

p12_10

p12_09

p12_06

p12_04

p12_05

p12_01 p12_02

p6_08

p6_04

p6_06

p6_07

p6_05

p6_03

p6_01

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Denver aquifer simulated extent Extent of active model cells

 (model layer 6)

Laramie–Fox Hills aquifer simulated 

 extent (model layer 12)

Lower Arapahoe aquifer simulated 

 extent (model layer 10)

Simulated streams

!( Layers 8 and 10 pilot points

!( Layer 12 pilot points

!( Layer 6 pilot points
190 Groundwater Availability of the Denver Basin Aquifer System, Colorado

specific-yield values during model execution to obtain an 

equivalent specific yield for the overall aquifer thickness 

represented by each cell (figs. A37, A38, A39, A40, A41, and 

A42). This calculation assumes that materials finer than silt 

sized provide minimal contribution to specific yield of the 

bedrock aquifers. A uniform mean specific yield of 0.165 was 

assigned to the alluvial aquifer (model layer 1; see table C13).

Hydrologic Stresses

Hydrologic stresses on the groundwater system include 

any processes that cause recharge to, or discharge from, the 

aquifers or confining units. Stresses simulated by the model 

include recharge from precipitation plus irrigation return 

flows, evapotranspiration, interaction with streams and reservoirs, spring discharge, and pumping from wells. Interaquifer 

flow in wells, many of which are no longer in use, also is simulated. The groundwater budget calculated by the flow model 

represents the hydrologic stresses discussed in this section.

Recharge

Two sources of water, infiltration of incident precipitation and irrigation in excess of consumptive use (irrigation 

return flow), are simulated as recharging the groundwater 

system. The entire groundwater system domain is assumed 

to be affected by recharge from precipitation. Recharge from 

irrigation return flow is simulated for areas affected by urban 

or agricultural irrigation as described in this section. Total 

recharge in irrigated areas is equal to precipitation recharge 

plus irrigation recharge.

Monthly precipitation data for the period 1931–2003 

for 129 climate-monitoring stations (National Oceanic and 

Atmospheric Administration, 2004) in and adjacent to the 

Denver Basin (fig. A4) were used to develop a series of data 

arrays representing the time-varying spatial distribution of 

precipitation in the model area. The number of active stations 

in a given year ranges from 27 in 1935 and 1936 to 54 in 1965 

and 1996 because of activation and deactivation of individual 

stations or periods of missing record. The interval 1957–2003 

was divided into eight 2- to 8-year stress periods (table C2, 

fig. C2), and the spatial distribution of precipitation, determined by cokriging precipitation data for the stress period 

with land-surface altitude, was held constant during each 

stress period. Stress periods were chosen on the basis of similarities in mean annual precipitation and to include data from 

a large number of climate-monitoring stations in each period. 

For each of the eight stress periods, the set of stations used to 

define the precipitation distribution included all stations with 

complete record for all years in the period.

A long-term mean annual precipitation distribution for 

1931–2003 was interpolated for stations with complete record 

for at least one year (fig. A4) and was applied to the model 

stress periods representing predevelopment through 1956. 

The method for developing the long-term distribution differed from the method used for the 2- to 8-year stress periods 

previously described. For the long-term distribution, a mean 

annual value was determined for each station, and those values 

were cokriged with land-surface altitude to generate a spatial 

precipitation distribution (fig. A4).

Recharge from agricultural irrigation return flows 

(agricultural recharge) was simulated during all stress periods. 

Because agricultural irrigation, primarily by surface-water 

diversions, began in the South Platte River valley prior to 

the 1880s (Nadler and Schumm, 1981), irrigation recharge 

is included in the predevelopment recharge estimates. The 

recharge rate attributed to agriculture, in terms of depth of 

water per unit time, was spatially uniform within an affected 

zone, but the area over which it applied was time varying. 

Irrigation ditch service areas delimited as part of the South 

Platte Decision Support System (Riverside Technology, Inc., 

2005) were used to define the maximum area for agricultural 

Table C4. Parameters of exponential models fitted to semivariograms of log hydraulic-conductivity data from aquifer tests.

Aquifer

Variogram

range

(feet)

Variogram

sill

Denver aquifer 40,416 0.21793

Upper and lower Arapahoe aquifers 118,530 0.31954

Laramie–Fox Hills aquifer 87,420 0.35665

Table C5. Specific-yield conceptualization and parameterization.

Aquifer Parameter name and definition

(units dimensionless) Specific-yield conceptualization

Alluvial aquifer SY_Qal—Specific yield of the alluvial aquifer. Assumption: Specific yield of aquifer is uniform.

Upper and lower Dawson aquifers SY_TDW—Specific yield of the silt-plussand fraction of the upper and lower 

Dawson aquifers.

Denver aquifer SY_TKD—Specific yield of the silt-plussand fraction of the Denver aquifer.Assumptions: (1) Specific yield of aquifer is attributable 

to materials with grain size reported as silt-sized or 

coarser; (2) contribution of finer grained material to 

specific yield is negligible; and (3) specific yield of 

silt-sized and coarser fraction is constant. Parameters 

represent specific yield of the silt-plus-sand fraction.

Upper and lower Arapahoe aquifers SY_KA— Specific yield of the silt-plussand fraction of the upper and lower 

Arapahoe aquifers

Laramie–Fox Hills aquifer SY_KLF—Specific yield of the silt-plus-sand 

fraction of the Laramie–Fox Hills aquifer.
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 191

irrigation recharge from 1880 to 1953. The earliest available satellite imagery (U.S. Geological Survey, 1973–1979) 

was used to identify irrigated areas in the 1970s, and for the 

simulated period from pre-1880 to 1953 (model stress periods 

1 through 5), agricultural irrigation recharge was assumed 

to affect the 1973–1979 irrigated areas that also are within 

the ditch service areas (fig. B26). For the simulated period 

1954–1986 (model stress periods 6 though 13), polygons 

approximating the 1970s irrigated areas were used as zones 

of agricultural irrigation (fig. B27). For the simulation period 

1987–2003 (model stress periods 14 through 16), zones 

approximating irrigated areas were derived from satellite 

imagery from 2000 (U.S. Geological Survey, 1999–2000) 

(fig. B28).

Recharge from urban return flows was simulated starting in 1920. The recharge rate attributed to urban return 

flows, in terms of depth of water per unit time, was spatially 

uniform within an affected zone, but the area over which it 

was applied was time varying. Areas of urbanization were 

based on GIS datasets and satellite images. For the simulation 

period 1920–1939 (model stress period 4), the area for urban 

recharge application was delineated from “residential” land 

use in GIS data set LU30 (U.S. Geological Survey, 2001a). 

For the simulation period 1940–1953 (model stress period 5), 

the area for urban recharge application was delineated from 

residential land use in GIS data set LU50 (U.S. Geological 

Survey, 2001b) (fig. B26). Satellite images were used to identify areas affected by urban recharge for the simulation period 

1954-1986 (model stress periods 6 through 13; fig. B27) 

(U.S. Geological Survey, 1973–1979) and for the simulation 

period 1987–2003 (model stress periods 14–16; fig. B28) 

(U.S. Geological Survey, 1999–2000).

Model parameters representing recharge from precipitation and agricultural and urban irrigation return flows 

were defined as previously described and are summarized 

in table C6. Recharge was simulated using the NRCHOP=4 

option of the MODFLOW Recharge Package (Banta, 2006). 

This option specifies that recharge is applied to the uppermost 

active cell connected by active cells to the lowermost active 

cell in a stack of cells. The use of this option avoids unrealistic 

mounding of simulated heads in areas of thin, low-transmissivity cells in confined layers where cells in overlying and 

underlying convertible layers go dry during the simulation.

Evapotranspiration

To ensure that evapotranspiration (ET) was simulated 

at the same cells in which recharge was simulated, a new 

option for specifying the layer to which evapotranspiration 

applies was added to the Evapotranspiration Segments (ETS) 

Package (Banta, 2000). The modifications support a new 

NETSOP=4 option, which works identically to the NEVTOP=4 

option described by Banta (2006). The simulations described 

in this report use the MODFLOW ETS package with the 

NETSOP=4 option.

Land-surface altitude was used as the “evapotranspiration 

surface” of the ETS Package. When the calculated head in a 

cell affected by evapotranspiration is at or above the evapotranspiration surface altitude, simulated evapotranspiration 

is assigned as the maximum evapotranspiration flux. When 

the head is below the extinction depth, evapotranspiration 

is assigned as zero. When the calculated head is below the 

evapotranspiration surface altitude but above the extinction 

depth, the evapotranspiration rate is defined by a segmented 

Table C6. Recharge conceptualization and parameterization.

Water source Parameter name and definition Recharge conceptualization Areas affected

Precipitation RCH_Qal—Fraction of precipitation 

in affected area that becomes 

recharge. Unit: dimensionless.

Assumptions: (1) Recharge (or 

recharge component, in areas 

also affected by irrigation) is a 

uniform fraction of precipitation; 

and (2) precipitation is accurately 

represented by interpolated distribution generated by cokriging 

observed precipation values for 

selected time intervals with landsurface elevation.

Areas where alluvial aquifer is the 

uppermost hydrogeologic unit.

RCH_Tdw—Fraction of precipitation 

in affected area that becomes 

recharge. Unit: dimensionless.

Areas where upper or lower Dawson 

aquifer or Dawson confining unit is 

the uppermost hydrogeologic unit.

RCH_TKd—Fraction of precipitation 

in affected area that becomes 

recharge. Unit: dimensionless.

Areas where Denver aquifer or upper 

or lower Denver confining unit is 

the uppermost hydrogeologic unit.

RCH_Ka—Fraction of precipitation 

in affected area that becomes 

recharge. Unit: dimensionless.

Areas where upper or lower Arapahoe 

aquifer or Arapahoe confining unit is 

the uppermost hydrogeologic unit.

RCH_Klf—Fraction of precipitation 

in affected area that becomes 

recharge. Unit: dimensionless.

Areas where Laramie confining unit 

or Laramie–Fox Hills aquifer is the 

uppermost hydrogeologic unit.

Agricultural irrigation RCH_AgIrr—Recharge from 

agricultural in affected area. 

Unit: inch per year, in/yr.

Recharge component is that part 

of applied irrigation water that 

reaches the water table. This 

component supplements recharge 

from precipitation.

Agricultural areas irrigated by flood, 

furrow, and sprinkler irrigation. 

The affected areas are time-varying.

Residential irrigation RCH_Resid—Recharge flux from 

residential irrigation in affected 

area. Unit: inch per year, in/yr.

Urban and suburban areas primarily in 

and adjacent to Denver and Colorado 

Springs. The affected areas are 

time-varying.
192 Groundwater Availability of the Denver Basin Aquifer System, Colorado

function of depth below the evapotranspiration surface. The 

segment ends are defined in terms of proportions of maximum 

evapotranspiration rate and of extinction depth. The maximum evapotranspiration rate used for the Denver Basin model 

was based on analysis described by David Groeneveld and 

Michael Prescott (HydroBio, Inc., written commun., 2006) 

who list 10-year average annual “grass-reference ET” rates for 

several stations in eastern Colorado; two of the stations are in 

the Denver Basin model area. The average of the rates for the 

two stations, 45 inches per year, was used as the maximum 

evapotranspiration rate (parameter ET_MAX in model input) 

for the Denver Basin model area. The function developed for 

the San Luis Valley of Colorado, which defines evapotranspiration rate for depths to water between land surface and an 

extinction depth of 30 ft (David Cooper, written commun., 

2005) was applied in the Denver Basin model (fig. C4).

Streams

Streams including the South Platte River, its tributaries, and streams in the Arkansas River Basin were simulated 

using the Streamflow Routing (SFR2) Package (Niswonger 

and Prudic, 2005, version 2.6, June 29, 2006). Locations of 

streams in the study area were obtained as Digital Line Graph 

(DLG) data (U.S. Geological Survey, 1989). This dataset was 

manually edited to convert streams represented as two lines to 

be represented instead as single lines. Ponds and small lakes 

were replaced with single lines, and lines were digitized to 

represent dry wash areas shown on 1:100,000 scale Digital 

Raster Graphic (DRG) images (Bailey, Castle Rock, Colorado 

Springs, Denver East, Denver West, Fort Morgan, Greeley, 

Karval, Last Chance, and Limon quadrangles, U.S. Geological 

Survey, 1999b). The digitized streams were divided into segments with segment lengths less than or equal to 25,000 ft. A 

raster dataset representing land-surface altitude at a horizontal resolution of 30 meters (U.S. Geological Survey, 1999a) 

was used to assign streambed top altitude of the upstream 

and downstream ends of each segment. The stream data 

were imported into the MODFLOW graphical user interface 

(Winston, 2000), which was then used to prepare model-input 

files in which streams were discretized as specified cells in the 

model grid (fig. C5). For all segments, the streambed thickness was assigned as 30 ft, and depth of water in the channel 

was assigned as 1.0 ft. Two streamflow routing parameters 

(table C7) were defined to represent the hydraulic conductivity 

of the streambed materials.

Streams simulated in the Denver Basin model include 

those that originate within the basin and those that originate 

outside the basin. Most of the basin is drained by streams 

that originate within the basin. Along the west and northwest 

margin of the basin, many of the streams originate in the Front 

Range west and outside of the basin.

To ensure that simulated leakage from streams that 

originate within the basin would not exceed the amount of 

water physically available, it was important to track simulated 

flows in those streams and allow them to behave in the model 

as many of them physically do, that is, as intermittent and 

ephemeral streams. Input to the SFR2 Package specified zero 

inflow at the headwaters of these streams. With inflow specified as zero, surface-water flow is limited to reaches where the 

simulated water table in the uppermost aquifer is above the top 

of the stream bed or surface-water flow from upstream reaches 

exceeds loss to groundwater. SFR2 was used to track streamflow rates, but it was not used to calculated stream stage; stage 

was assumed one foot above the streambed top wherever 

streamflow was simulated.

A number of perennial streams and rivers enter the 

Denver Basin from the west and north. Because these streams 

are perennial, tracking of streamflow was not important. 

However, for consistency with the streams originating within 

the basin, the streams originating outside the basin also were 

simulated with the SFR2 Package. Again, SFR2 was not used 

to calculate stream stage. To ensure that these streams behaved 

in the model as perennial streams, it was necessary to specify 

inflow at the upstream ends of the simulated reaches such that 

flow was great enough to supply downstream losses to groundwater as needed. Data from Boulder Creek (Murphy and 

others, 2003) indicated a base flow of 50 ft3/s would be typical 

and reasonable. This inflow rate was used for all streams and 

rivers originating outside the basin and was sufficient to maintain flow in the simulated streams. These assumptions and 

generalizations are suitable for the purpose of groundwater 

modeling, but the model-computed surface-water flow rates 

for these streams are not meaningful products of the model 

and were not included in the model calibration.

Reservoirs

Five reservoirs in the Denver Basin were simulated using 

the MODFLOW River (RIV) Package (Harbaugh and others, 

2000) (fig. C5). Table C8 lists the reservoirs and corresponding 

properties as simulated. One parameter (RIV_Lakes) was defined 

to control the hydraulic conductance of materials between the 

reservoirs and the underlying aquifer. The stress period chosen for 

the start of simulation of each reservoir was the one nearest the 

year of reservoir construction or filling. The purpose of reservoir 

0

5

10

15

20

25

30

35

40

45

50

0 5 10 15 20 25 30

Evapotranspiration rate,

in inches per year

Depth to water,

in feet

Figure C4. Evapotranspiration as a function of depth to water 

used for the Denver Basin model.
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 193

Figure C5. Locations of boundary condition cells for the Denver Basin model.

PALMER

DIVIDE

PALMER

DIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Extent of active model cells

Alluvial aquifer simulated extent Stream (SFR) cell

Spring (DRN) cell

Pre-1880 flowing well (DRN) cell

Reservoir (RIV) cell

General-head boundary (GHB) cell

Laramie–Fox Hills aquifer simulated extent Specified-flux (FHB) cell

Lower Arapahoe aquifer simulated extent

Denver aquifer simulated extent

Lower Dawson aquifer simulated extent

Simulated stream
194 Groundwater Availability of the Denver Basin Aquifer System, Colorado

simulation was to include the effects of the reservoirs on groundwater levels, and the RIV Package was used to simulate reservoirs 

as a simple head-dependent boundary.

Springs

All spring locations within the Denver Basin area that are 

shown on the 1:100,000 scale DRG images were digitized for 

representation in the model (fig. A11). The MODFLOW Drain 

(DRN) Package (Harbaugh and others, 2000) was used to 

simulate all springs (fig. C5). Drain cells were located at grid 

cells encompassing each spring location, and drain altitudes 

were assigned from land-surface altitudes (U.S. Geological 

Survey, 1999a). The hydrogeologic unit at land surface at each 

spring location determined the model layer for each drain feature. One DRN parameter, named DRN_COND, was defined 

to control the hydraulic conductance applied to all drains.

Groundwater Flow Across Basin Boundaries

The model domain approximately conforms to the extent 

of the Denver Basin bedrock units, and groundwater flow 

in the aquifer system is largely constrained to the extent of 

bedrock units. However, groundwater flow crosses the extent 

of bedrock units where saturated materials of the alluvial 

aquifer extend beyond the bedrock units, such as in the areas 

of the Black Squirrel Creek basin (Buckles and Watts, 1988) 

and the Nussbaum Alluvium (Paschke, 1992). These areas of 

alluvial aquifer overlap the southern and southeastern parts of 

the model boundary. Model cells in areas where groundwater 

flow crosses the model boundary were simulated as headdependent flow boundaries using the MODFLOW GeneralHead Boundary (GHB) Package (fig. C5).

Groundwater flow out of the model domain in the South 

Platte alluvial aquifer near Wiggins, Colorado, was simulated 

using specified flow boundaries with the MODFLOW Flow 

and Head Boundary (FHB) Package. Detailed information on 

water levels, transmissivity, and saturated thickness in this 

area (Hurr, Schneider, and others, 1972) was used to estimate 

groundwater flow parallel to the South Platte River in the 

alluvial aquifer. A 7-mile cross section of the alluvial aquifer — drawn approximately perpendicular to the South Platte 

River through the northeast corner of section 13 in Township 4 

North, Range 59 West and the northeast corner of section 8 

in Township 3 North, Range 59 West — was considered in 

intervals of 0.25 mile. Transmissivity, saturated thickness, 

and cross-sectional area for each interval were estimated from 

maps in Hurr, Schneider, and others (1972). Hydraulic gradient was estimated as 0.0014. Flow was computed for each 

interval and summed to obtain a total estimated underflow 

for the alluvial cross section of 14.1 ft3/s. Seven FHB cells 

were specified at the downgradient alluvial aquifer boundary 

(fig. C5) with a specified total withdrawal of 14.1 ft3/s.

Historical Flowing Wells

As discussed in Chapters A and B, many of the bedrock wells constructed in the late 19th century flowed at 

land surface upon installation. Emmons and others (1896, 

p. 422) inventoried 394 wells completed in the Arapahoe and 

Laramie–Fox Hills aquifers of the Platte Valley from 1883 to 

1890. A data table (Emmons and others, 1896, p. 433–447) 

explicitly lists 209 wells inventoried in Denver, and 185 wells 

were referenced as having locations in “the country” (Emmons 

and others, 1896). Well location information for the 209 wells 

was provided in the form of street addresses or major cross 

streets. To generate latitude and longitude coordinates and 

land-surface altitudes for the historical wells, well addresses 

were located on Sanborn Fire Insurance street maps from 

1887, 1890, 1893, 1897, 1903, and 1904 (accessed at the 

Denver Public Library), the locations were manually plotted 

on electronic street and topographic maps, and the latitude 

and longitude coordinates were generated by the map software (Garmin Ltd., 2004) (table C9). The wells were poorly 

constructed by modern-day standards, and many wells were 

Table C7. Properties assigned to Denver Basin model features representing the South Platte River and streams.

Stream or river Stream width

(feet)

Streambed

thickness

(feet)

Depth of water

in channel

(feet)

Parameter name

and definition

South Platte River 150 30 1 SFR_PLATTE—Hydraulic conductivity of riverbed 

materials, in feet per day.

All other streams 50 30 1 SFR_TRIBS—Hydraulic conductivity of streambed 

materials, in feet per day.

Table C8. Properties assigned to Denver Basin model features representing reservoirs.

Reservoir Year of reservoir

construction or filling

Stress period in

which reservoir is

first simulated

Model

layer

Bottom altitude

(feet)

Stage

(feet)

Area

(acres)

Barr Lake 1908 3 1 5,050 5,096 1,733

Milton Reservoir Prior to 1950 5 1 4,770 4,810 1,622

Cherry Creek Reservoir 1950 6 6 5,500 5,548 860

Chatfield Reservoir 1972 10 1 5,400 5,426 1,407

Aurora Reservoir 1990 14 3 5,810 5,930 638
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 195

constructed with multiple completion intervals (Emmons 

and others, 1896). For each well, the model layer or layers, 

row, and column were assigned on the basis of well location 

and depth. Locations could not be determined for 12 of the 

209 wells reported by Emmons and others (1896), resulting 

in 197 wells with estimated locations (table C9).

The 197 late-19th century (pre-1900) flowing wells for 

which locations could be determined were represented as 

drain features in 37 cells in model layers 6, 8, and 10 using 

the MODFLOW Drain Package (Harbaugh and others, 2000) 

(fig. C5). Most of the wells had stopped flowing by 1905 

(Darton, 1905), so they were simulated as drains only in stress 

period 2, which represents 1880 through 1906. Land-surface 

altitudes from the U.S. Geological Survey (1999a) at the well 

locations were assigned as the drain altitudes, and each drain 

feature was assigned hydraulic conductance based on the 

appropriate model layer or layers. The conductance of all drain 

cells representing flowing wells was controlled by a parameter 

named “FLWG_WELLS.”

Pumping

Pumping from wells completed in the alluvial and bedrock 

aquifers was simulated using the MODFLOW Well (WEL) 

Package (Harbaugh and others, 2000). No pumping was assigned 

to confining units. As described in the section “Denver Basin 

Pumping History” of Chapter B, the number and locations of 

domestic, irrigation, commercial/industrial, and municipal wells 

were tabulated for each year from 1880 to 2003 based on the 

CDWR well-permit database. Pumping rates were then assigned 

to each well type for each aquifer, and pumping was summed 

for each model grid cell (layer, row, and column) for each year. 

Annual pumping volumes for each grid cell were summed and 

averaged over each stress period for input to the WEL Package. 

Simulated pumping for 2003 for the alluvial aquifer (169 ft3/s) 

and the bedrock aquifers (111 ft3/s) was slightly less than the estimated pumping values of 187 ft3

/s for alluvial wells and 118 ft3/s 

for bedrock wells because some model cells representing pumping wells were deactivated during the iterative solution procedure 

of the simulation. In general, pumping increased in volume and 

geographic extent for each aquifer model layer through time. The 

spatial distribution of pumping is displayed along with simulated 

potentiometric surfaces for 1956, 1978, and 2003 for each aquifer 

model layer (layers 1, 2, 4, 6, 8, 10, and 12, respectively) in the 

section “Simulated Hydraulic Heads” of this chapter.

Multiaquifer Wells

Wells that allow hydraulic communication among 

geohydrologic units were simulated using the Multi-Node 

Well (MNW) Package (Halford and Hanson, 2002) for 

MODFLOW. The well-loss coefficient was assumed to be 

linear and was defined using the “skin” model of Halford and 

Hanson (2002, equation 3). The skin value was assigned a typical value of 2.0 (dimensionless) (Halford and Hansen, 2002).

Solver

The presence of seven convertible model layers and 

numerous nonlinear boundary conditions described in the 

previous sections produces a highly nonlinear system of finitedifference equations, which can be difficult to solve. Also, 

deactivation of cells due to approximations of hydraulic head 

being below cell-bottom altitudes during the iterative solution procedure was a common problem. The GMG Package 

(Wilson and Naff, 2004) for MODFLOW was selected to 

solve the system of equations because of its speed and efficiency. Damping of the head changes by specifying a constant 

damping value lessened the problem of cell deactivation, but 

at the expense of longer execution times. Use of Cooley’s 

adaptive damping method (Mehl and Hill, 2001) caused instability in the solution procedure. Use of an alternative adaptive 

damping method described by Banta (2006) was found to 

provide a solution in a reasonable execution time and with a 

relatively small number of deactivated cells.

Model Calibration

Model calibration is the process by which model parameter 

values are adjusted within reasonable limits to minimize the 

difference between model-computed and measured heads and 

flows. Calibration of the Denver Basin model used nonlinearregression methods implemented in PEST (Doherty, 2006) in 

combination with manual assignment of parameters that proved 

resistant to calibration by automated methods.

Model fit was evaluated by comparing model-simulated 

values to head or flow values observed in the field or derived 

by analysis of field data. For each observed value and corresponding model-simulated value, a residual was defined by 

subtracting the simulated value from the observed value. Each 

observation was assigned a weight based on an estimate of the 

standard deviation or coefficient of variation associated with 

the observation. For this study, the definition of weight follows 

the convention used in PEST, where weight is calculated as the 

inverse of the (estimated) standard deviation associated with 

an observation or item of prior information. A measurementobjective function (Sm) was defined as (Doherty, 2006):

S wr m i i

i

m

= =

∑( )2

1

(1)

where

wi is the weight associated with observation i,

ri is the residual for observation i,

and

m is the number of observations.

The value of Sm is an indicator of the fit of the model to observations; in general, a smaller value of Sm indicates a better 

fit than does a larger value of Sm. One of the goals of model 

calibration is to minimize Sm while maintaining physically 

reasonable parameter values.
196 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[1, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Well

name1

Original head,

in feet above land 

surface or pressure

(pounds per 

square inch)

Calculated

original head

altitude

(feet)

Original reported

discharge

(gallons per day)

December 1890

reported head

(feet above land 

surface) or pressure

(pounds per

square inch)

Calculated

December 1890

head altitude

(feet)

December 1890

reported discharge

(gallons per day)

1 1 Anderson -- -- 200,000 -- -- 0

2 2 Carico 50 ft 5,268 -- -- -- pumping

3 3 Collins -- -- 51,000 -- -- --

4 4 Ester 40 ft 5,260 40,000 –25 ft 5,195 24,000

5 5 Oakes -- -- 34,560 -- -- 0

6 6 Eckhart 32 psi 5,298 -- -- -- 0

7 7 The Rink -- -- -- -- -- 0

8 8 County Court House 50 ft 5,280 60,000 0 ft 5,230 pumping

9 9 Kinsey 30 ft 5,254 86,400 –25 ft 5,199 0

10 10 Albany Hotel 50 ft 5,273 50,000 –20 ft 5,203 pumping

11 11 Timerman -- -- -- –20 ft 5,201 0

12 12 Cowell -- -- 40,000 -- -- 0

13 13 Charles 80 psi 5,405 -- –20 ft 5,200 pumping

14 14 St. James Hotel -- -- 45,000 –27 ft 5,193 0

15 15 Tritch 25 ft 5,242 -- -- -- 0

16 16 Tabor Opera House 36 psi 5,301 -- –12 ft 5,206 pumping

17 17 Welker 50 ft 5,267 120,000 -- -- pumping

18 18 Daniels & Fisher 78 ft 5,290 40,000 -- -- pumping

19 19 McClelland 75 ft 5,287 -- –50 ft 5,162 pumping

20 20 Goode 75 ft 5,277 85,000 –25 ft 5,177 pumping

21 21 Metropolitan 70 psi 5,360 -- -- -- 0

22 22 Lothrop -- -- 21,600 -- -- 0

23 23 Barkley Block -- -- 76,320 –15 ft 5,195 pumping - 72,000

24 24 Windsor 50 psi 5,325 300,000 –92 ft 5,118 pumping

25 25 Stacy 35 psi 5,276 -- -- -- 0

26 26 Union Depot 20 psi 5,231 180,000 –200 ft 5,985 0

27 27 Mars, Middleton 

& Hunter

20 ft 5,205 -- -- -- 0

28 28 American House 25 psi 5,249 -- -- -- pumping

29 29 Columbus House 

(Watkins Bldg)

-- -- 17,280 -- -- 0

30 30 Tremont House 20 ft 5,215 -- –15 ft 5,180 pumping

31 31 Anheuser-Busch -- -- 100,000 -- -- 10,000

32 32 Mullen -- -- -- –15 ft 5,170 pumping

33 33 Mayer -- -- -- -- -- pumping

34 34 D&RG No. 1 38 ft 5,223 -- -- -- pumping - 20,000

35 35 Wagner 4 ft 5,199 -- –3 ft 5,192 pumping

36 36 Lindell Hotel 30 ft 5,225 86,400 –10 ft 5,185 pumping

37 37 Milwaukee Brewery 27 ft 5,222 -- –6 ft 5,189 pumping

38 38 Spitzer -- -- 43,200 -- -- 0

39 39 Western Hotel -- -- 150,000 –18 ft 5,180 pumping

40 40 Knight -- -- 60,000 -- -- 0

41 41 Denver Brewing Co -- -- 100,000 –28 ft 5,177 27,000

42 42 Lion Brewery 40 ft 5,235 26,448 –8 ft 5,187 pumping

43 43 Chase 8 ft 5,212 -- -- -- 0

44 44 Bomblitz 40 ft 5,235 -- –4 ft 5,191 0

45 45 Waterworks -- -- 40,000 -- -- 0

46 46 Waterworks -- -- 40,000 -- -- 0

47 47 Waterworks -- -- 40,000 -- -- 0

48 48 Waterworks -- -- 40,000 -- -- 0

49 49 Waterworks -- -- 40,000 -- -- 0

50 50 D&RG No. 2 30 ft 5,255 -- -- -- 0
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 197

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[1, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Assigned

well depth

(feet 

below land 

surface)

Sanborn Fire

Insurance

Map used

 Assigned

landsurface

altitude

(feet)

Assigned

latitude

(decimal

degrees,

NAD83)

Assigned

longitude

(decimal

degrees,

NAD83)

Model

layer

Model

row

Model 

column Comments

1 1 375 1887 39.740 –104.998 8 51 14

2 2 375 1887 5,218 39.740 –104.995 8 51 14 S 12th St = Fox St south of Colfax

3 3 375 1887 39.742 –104.998 8 51 14

4 4 600 1887 5,220 39.737 –104.995 10 51 14 65 S 12th St = Fox St = approximate location south 

of 14th Ave

5 5 365 1887 39.744 –105.000 8 51 14

6 6 375 1887 5,224 39.745 –104.994 8 51 14

7 7 627 1887 39.745 –104.992 10 51 14

8 8 600 1887 sheet 22 5,230 39.743 –104.989 10 51 14 Arapahoe County Court House

9 9 615 1887 5,224 39.747 –104.990 10 51 14

10 10 700 1887 5,223 39.747 –104.992 10 51 14

11 11 600 1887 5,221 39.748 –104.993 10 51 14

12 12 580 1887 39.749 –104.992 10 50 14

13 13 564 1887 5,220 39.746 –104.996 8 51 14

14 14 670 1887 sheet 24 5,220 39.746 –104.995 10 51 14

15 15 650 1887 sheet 19 5,217 39.748 –104.994 10 50 14

16 16 375 1887 sheet 25 5,218 39.747 –104.995 8 51 14

17 17 650 1887 5,217 39.748 –104.994 10 51 14

18 18 669 1887 5,212 39.748 –104.996 10 50 14

19 19 607 1887 5,212 39.748 –104.997 10 51 14

20 20 680 1887 5,202 39.749 –104.998 10 50 14

21 21 545 1887 5,198 39.750 –104.998 8 50 14

22 22 473 1887 39.750 –104.994 8 50 14

23 23 602 1887 sheet 18 5,210 39.751 –104.995 10 50 14

24 24 530 1887 sheet 14 5,210 39.751 –104.995 8 50 14

25 25 600 1887 sheet 7 5,195 39.755 –104.992 10 50 14

26 26 506 1887 sheet17 5,185 39.753 –105.000 8 50 14

27 27 520 1887 sheet 18 5,185 39.753 –104.998 8 50 14

28 28 545 1887 sheet 18 5,191 39.751 –104.999 8 50 14

29 29 356 1887 sheet 27 39.751 –105.001 8 50 14

30 30 325 1887 sheet 32 5,195 39.748 –105.003 8 51 13

31 31 314 1887 sheet 36,

1890 volume 1

sheet 9a

39.748 –105.006 8 51 13

32 32 360 1887 sheet 35 5,185 39.746 –105.009 8 51 13

33 33 333 1887 sheet 35 39.746 –105.009 8 51 13

34 34 350 1887 sheet 36 5,185 39.745 –105.011 8 51 13

35 35 330 1887 sheet 33 5,195 39.744 –105.006 8 51 13

36 36 360 1887 sheet 33 5,195 39.745 –105.004 8 51 13 11th and Larimer

37 37 354 1887 sheet 33 5,195 39.745 –105.005 8 51 13

38 38 333 1887 sheet 32 39.746 –105.004 8 51 13

39 39 585 1887 sheet 32 5,198 39.746 –105.003 10 51 13

40 40 340 1887 sheet 28 5,198 39.746 –105.002 8 51 14

41 41 600 1887 sheet 31 5,205 39.743 –105.005 10 51 13 Artesian well shown on map

42 42 294 1887 sheet 34 5,195 39.744 –105.007 8 51 13

43 43 366 1887 sheet 31 5,204 39.744 –105.003 8 51 13

44 44 315 1887 sheet 1 5,195 39.740 –105.011 8 51 13 4th and Colfax

45 45 600 1887 sheet 1 39.735 –105.009 10 51 13 Approx location from 1887 Sanborn south of 12th St

46 46 600 1887 sheet 1 39.734 –105.009 10 51 13 Approx location from 1887 Sanborn south of 12th St

47 47 600 1887 sheet 1 39.734 –105.009 10 51 13 Approx location from 1887 Sanborn south of 12th St

48 48 600 1887 sheet 1 39.735 –105.009 10 51 13 Approx location from 1887 Sanborn south of 12th St

49 49 600 1887 sheet 1 39.734 –105.009 10 51 13 Approx location from 1887 Sanborn south of 12th St

50 50 800 1890 volume 1

sheet 24a

5,225 39.730 –105.006 10 52 13 Burnham shops at 9th Ave and S 7th (south of 

Lincoln Park)
198 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[1, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Well

name1

Original head,

in feet above land 

surface or pressure

(pounds per 

square inch)

Calculated

original head

altitude

(feet)

Original reported

discharge

(gallons per day)

December 1890

reported head

(feet above land 

surface) or pressure

(pounds per

square inch)

Calculated

December 1890

head altitude

(feet)

December 1890

reported discharge

(gallons per day)

51 51 A.E. Pierce 30 psi 5,335 100,000 -- -- 0

52 52 Brown -- -- -- -- -- 0

53 53 Fleming -- -- 165,375 -- -- 0

54 54 Miles -- -- -- -- -- 0

55 55 Bonesteel -- -- 21,600 -- -- 0

56 56 Buergy -- -- -- -- -- 0

57 57 Cemetery 35 psi 5,239 500,000 -- -- 0

58 58 Waverly -- -- 140,000 -- -- 0

59 59 Cowan -- -- 147,000 -- -- 0

60 60 Knox 24 psi 5,274 -- -- -- 0

61 61 Stevens -- -- 80,000 -- -- 0

62 62 Home Artesian Well -- -- 45,000 -- -- 0

63 63 Gas Works 20 ft 5,205 300,000 –25 ft 5,160 pumping

64 64 Germania House -- -- 36,000 –12 ft 5,173 0

65 65 Steam Heating Co 20 ft 5,203 200,000 –25 ft 5,158 0

66 66 Freund 25 ft 5,207 -- -- -- 0

67 67 Tierman -- -- 41,760 –55 ft 5,130 pumping

68 68 Jerome 15 ft 5,200 -- –8 ft 5,177 pumping

69 69 Nahring 25 ft 5,210 -- -- -- 0

70 70 Bareslaux -- -- 34,560 -- -- 0

71 71 McVeigh 20 ft -- -- –25 ft -- 0

72 72 Mazza -- -- -- -- -- 0

73 73 Electric Light Co. 30 psi 5,259 -- -- -- pumping

74 74 Schindelhotz 40 ft 5,225 -- -- -- 0

75 75 Belisle -- -- 14,400 -- -- pumping

76 76 City Laundry 19 psi 5,247 -- –27 ft 5,177 pumping

77 77 Universal 

Sampling Works

140 ft 5,335 547,200 –6 ft 5,189 pumping

78 78 Swift -- -- -- -- -- 0

79 79 Bennett -- -- 108,000 –20 ft 5,190 pumping

80 80 30th and 

Arapahoe Sts

-- -- 130,000 -- -- 0

81 81 Savage 50 ft 5,242 -- –25 ft 5,167 pumping

82 82 Walker -- -- 125,000 -- -- 0

83 83 Colorado

Iron Works

35 psi 5,266 -- –8 ft 5,177 pumping

84 84 Adair -- -- 72,000 –6 ft 5,189 pumping

85 85 Nichols 40 psi 5,287 -- -- -- pumping

86 86 Morrison Bros 30 ft 5,225 -- -- -- 0

87 87 U.P. Hospital 40 psi 5,287 90,000 -- -- 0

88 88 Grant Smelter 45 psi 5,289 500,000 -- -- pumping
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 199

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[1, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Assigned

well depth

(feet 

below land 

surface)

Sanborn Fire

Insurance

Map used

 Assigned

landsurface

altitude

(feet)

Assigned

latitude

(decimal

degrees,

NAD83)

Assigned

longitude

(decimal

degrees,

NAD83)

Model

layer

Model

row

Model 

column Comments

51 51 720 1890 volume 1

sheet 1

5,266 39.716 –104.986 10 53 14

52 52 995 1890 volume 1

sheet 1

5,268 39.716 –104.985 10 53 14

53 53 670 1890 volume 2 

sheet 56a

39.757 –105.005 10 50 13 Approx location Exposition bldg at Riverside Park?/

Text says southernmost of Denver wells south of 

old Exposition bldg

54 54 610 1893 volume 3 

sheet 111a

39.737 –104.989 10 51 14 Approx location, 1893 S 15th = 2006 Acoma south 

of Colfax—Deer and Moose still not found

55 55 850 1893 volume 3 

sheet 111a

39.737 –104.975 10 51 15 Approx location, 1893 Alta = 2006 Ogden south of 

Colfax—Deer and Moose still not found

56 56 550 1893 volume 3 

sheet 111b

39.736 –104.973 8 51 15 Approx location,1893 Hallett = 2006 Downing south 

of Colfax—Pine still not found

57 57 525 5,158 39.792 –104.962 10 48 16

58 58 860 1890 volume 1

sheet 8a

5,200 39.745 –105.005 10 51 13 Waverly Hotel—10th and Larimer

59 59 670 1887 sheet 9 5,220 39.751 –104.987 10 50 14 Not sure which corner

60 60 700 1887 sheet 1 5,219 39.753 –104.985 10 50 14

61 61 750 1887 sheet 1 39.755 –104.984 10 50 15

62 62 685 39.732 –104.967 10 52 15

63 63 610 1887 sheet 15 5,185 39.755 –104.998 10 50 14

64 64 341 1887 sheet 15 5,185 39.755 –104.998 8 50 14 On 19th south of gas works

65 65 325 1887 sheet 15 5,183 39.756 –104.999 8 50 14 On 19th north of gas works

66 66 309 1887 sheet 15 5,182 39.756 –104.998 8 50 14

67 67 535 1887 sheet 15 5,185 39.756 –104.997 8 50 14

68 68 325 5,185 39.756 –104.997 8 50 14 Approx location near Wewetta and 20th—can’t find 

Cottage Ln

69 69 300 1887 sheet 1 5,185 39.759 –104.997 8 50 14 Approx corner of Huron and 29th now

70 70 304 1887 sheet 1 5,185 39.760 –104.997 8 50 14 Approx Huron Ave

71 71 320 1887 sheet 1 39.759 –104.997 8 50 14 Approx Huron Ave

72 72 300 8

73 73 330 1887 sheet 39 5,190 39.758 –104.994 8 50 14

74 74 416 1887 sheet 5 5,185 39.759 –104.986 8 50 14 Schindelhotz Terrace

75 75 420 1887 sheet 5 -- 39.757 –104.985 8 50 14

76 76 406 1887 sheet 4 5,204 39.759 –104.984 8 50 15

77 77 400 1887 sheet 4 5,195 39.762 –104.985 8 50 14 Artesian well on map

78 78 457 1887 sheet 1 -- 39.758 –104.979 8 50 15

79 79 450 1887 sheet 1 5,210 39.759 –104.974 8 50 15

80 80 620 1887 sheet 1 -- 39.761 –104.979 10 50 15

81 81 400 1887 sheet 1 5,192 39.768 –104.975 8 49 15

82 82 587 1887 sheet 1 -- 39.763 –104.977 8 49 15

83 83 420 1887 sheet 38, 

1890 volume 2 

sheet 83a

5,185 39.768 –104.980 8 49 15 Well shown on map

84 84 392 1887 sheet 1 5,195 39.769 –104.976 8 49 15

85 85 366 1887 sheet 38 5,195 39.770 –104.976 8 49 15 Artesian well on map

86 86 400 1887 sheet 1 5,195 39.769 –104.974 8 49 15

87 87 675 1903 volume 2 

sheet 261, |

1903 volume 3 

sheet 112b

5,195 39.773 –104.967 10 49 15 North of 40th between Franklin and Gilpin

88 88 620 1903 volume 2 

sheet 261

5,185 39.778 –104.969 10 48 15
200 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[

1

, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Well

name1

Original head,

in feet above land 

surface or pressure

(pounds per 

square inch)

Calculated

original head

altitude

(feet)

Original reported

discharge

(gallons per day)

December 1890

reported head

(feet above land 

surface) or pressure

(pounds per

square inch)

Calculated

December 1890

head altitude

(feet)

December 1890

reported discharge

(gallons per day)

89 89 McNassor 23 ft -- -- -- -- 0

90 90 Morrison Bros -- -- -- –60 ft -- pumping

91 91 D.U and P.R.R. 25 ft 5,210 -- -- -- pumping

92 92 Smedley -- -- 216,000 –76 ft -- pumping

93 93 John Mullen -- -- 21,600 -- -- pumping

94 94 Doyle & White 20 ft 5,215 -- -- -- 0

95 95 Sanderson 30 psi 5,292 -- –25 ft 5,198 pumping

96 96 Green 30 ft 5,240 -- -- -- 0

97 97 Hanson -- -- -- -- -- --

98 98 Hecker 16 ft 5,219 -- –12 ft 5,191 pumping

99 99 Poole 35 ft 5,238 -- –28 ft 5,175 --

100 100 Granton 22.5 psi 5,227 -- –15 ft 5,160 0

101 101 Marquis 40 ft 5,218 -- -- -- pumping

102 102 Scanlon 20 ft 5,205 25,920 –8 ft 5,177 pumping

103 103 Oppenlander 31 psi 5,272 -- –8 ft 5,192 pumping

104 104 Frey & Hoelzle 25 ft 5,213 -- -- -- --

105 105 Spitzer -- -- 4,514,400 –20 ft 5,170 0

106 106 Highland House 70 ft 5,262 -- –12 ft 5,180 pumping

107 107 Crisman 40 ft 5,225 -- –5 ft 5,180 0

108 108 Shannon -- -- 86,400 –30 ft 5,258 0

109 109 Clark & Killison -- -- -- -- -- 0

110 110 Montague -8 ft 5,272 pumping –100 ft 5,180 --

111 111 Ashland

School House

-- -- pumping -- -- 0

112 112 Meanea 25 ft 5,225 -- –10 ft 5,190 0

113 113 Swenson 14 ft 5,224 8,640 –20 ft 5,190 pumping

114 114 Norton 30 ft 5,240 21,600 -- -- 0

115 115 Eckhart well No. 1 35 psi 5,384 -- -- -- 0

116 116 Eckhart well No. 2 -- -- -- -- -- 0

117 117 Quayle 35 ft 5,306 -- –50 ft 5,221 pumping

118 118 Zang No. 1 20 psi 5,246 -- -- -- 0

119 119 Zang No.2 25 psi 5,258 400,000 –40 ft 5,160 0

120 120 Gurley Bros 30 psi 5,264 -- -- -- 0

121 121 Weeber -- -- 1,800 -- -- 0

122 122 Myer 20 ft 5,280 -- –72 ft 5,188 pumping

123 123 Tegeler 32 ft 5,232 -- –2 ft 5,198 pumping

124 124 Higgins -- -- -- -- -- pumping
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 201

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[1, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Assigned

well depth

(feet 

below land 

surface)

Sanborn Fire

Insurance

Map used

 Assigned

landsurface

altitude

(feet)

Assigned

latitude

(decimal

degrees,

NAD83)

Assigned

longitude

(decimal

degrees,

NAD83)

Model

layer

Model

row

Model 

column Comments

89 89 300 -- 8

90 90 400 -- 8

91 91 306 1887 sheet 16 5,185 39.756 –104.999 8 50 14 South of Hartford btwn 19th and Division

92 92 647 -- 10 Approx location—Clear Creek = Pecos, can’t find 

Backus

93 93 300 1890 volume 2 

sheet 0

-- 39.764 –105.005 8 49 13 Osage between 33 and 34th

94 94 320 1887 sheet 1 5,195 39.761 –105.006 8 50 13

95 95 579 1887 sheet 1 5,223 39.761 –105.008 10 50 13

96 96 500 1887 sheet 1 5,210 39.761 –105.007 8 50 13

97 97 600 1887 sheet 1 5,210 39.761 –105.008 10 50 13

98 98 316 1887 sheet 1 5,203 39.760 –105.007 8 50 13

99 99 371 1887 sheet 1 5,203 39.761 –105.008 8 50 13

100 100 238 1887 sheet 1 5,175 39.759 –105.006 8 50 13

101 101 290 1887 sheet 37 5,178 39.758 –105.007 8 50 13 Marquis canned goods

102 102 251 1887 sheet 37 5,185 39.758 –105.008 8 50 13

103 103 515 1887 sheet 37 5,200 39.758 –105.009 8 50 13 Oppenlander City Brewery—artesian well shown 

on map

104 104 312 1887 sheet 37 5,187 39.757 –105.008 8 50 13

105 105 270 1887 sheet 37 5,190 39.756 –105.009 8 50 13

106 106 512 1887 sheet 37 5,192 39.756 –105.009 8 50 13

107 107 296 1887 sheet 37 5,185 39.756 –105.008 8 50 13

108 108 364 1890 volume 2 

sheet 91b

5,288 39.760 –105.013 8 50 13 Corner 30th and Vallejo

109 109 371 1890 volume 2 

sheet 91b

5,260 39.758 –105.013 8 50 13 Corner 29th and Vallejo

110 110 370 1890 volume 2 

sheet 91a

5,280 39.759 –105.016 8 50 13 Ashland = 29th, Gallup = Zuni

111 111 711 1890 volume 2 

sheet 91a

5,290 39.759 –105.017 10 50 13 29th and Zuni

112 112 185 1890 volume 2 

sheet 0

5,200 39.755 –105.011 6 50 13

113 113 293 1890 volume 2 

sheet 0

5,210 39.755 –105.013 8 50 13 Highland = 26th

114 114 509 1890 volume 2 

sheet 0

5,210 39.754 –105.014 8 50 13

115 115 665 1890 volume 2 

sheet 0

5,303 39.755 –105.021 10 50 13

116 116 840 1890 volume 2 

sheet 0

5,303 39.755 –105.022 10 50 12

117 117 565 1890 volume 2 

sheet 0

5,271 39.753 –105.018 8 50 13 Emerald = 25th

118 118 300 1887 sheet 35 5,200 39.752 –105.015 8 50 13 Rocky Mountain Brewery—artesian well on map

119 119 480 1887 sheet 35 5,200 39.752 –105.015 8 50 13 Rocky Mountain Brewery—artesian well on map

120 120 775 1890 volume 2 

sheet 0

5,195 39.748 –105.017 10 51 13

121 121 214 5,282 39.749 –105.025 6 50 12 Federal and 21st?

122 122 600 5,260 39.746 –104.980 10 51 15 St Lukes = 19th and Pearl

123 123 270 1890 volume 2 

sheet 0

5,200 39.746 –105.021 8 51 13 19th and Clay—under old Mile High Stadium

124 124 525 1893 volume 3 

index

5,200 39.740 –105.022 8 51 12 Morrison Rd and Colfax (Golden = Colfax)
202 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[1, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Well

name1

Original head,

in feet above land 

surface or pressure

(pounds per 

square inch)

Calculated

original head

altitude

(feet)

Original reported

discharge

(gallons per day)

December 1890

reported head

(feet above land 

surface) or pressure

(pounds per

square inch)

Calculated

December 1890

head altitude

(feet)

December 1890

reported discharge

(gallons per day)

125 125 Agerer 30 ft 5,230 -- –16 ft 5,184 pumping

126 126 Snively -- -- -- –15 ft 5,185 pumping

127 127 Heidrer 40 ft 5,240 -- –12 ft 5,188 pumping

128 128 Villa Park No. 1 -- -- -- –30 ft 5,230 pumping

129 129 Villa Park No. 2 -- -- -- –50 ft 5,210 pumping

130 130 Weir No. 1 -- -- 45,360 -- -- 0

131 131 Weir No. 2 55 psi 5,377 -- –12 ft 5,238 pumping

132 132 County Hospital -- -- 12,000 -- -- pumping

133 133 Sloan Lake -- -- 0 -- --

134 134 Reeves 18 psi 5,302 -- –60 ft 5,200 pumping

135 135 Alkire -- -- -- -- -- --

136 136 Standard

Bottling Works

30 ft 5,227 -- -- -- 0

137 137 United Oil Co -- -- -- –28 ft 5,157 0

138 138 Union Brewing Co -- -- -- –16 ft 5,171 pumping

139 139 Hungarian Mills -- -- -- –12 ft 5,173 pumping

140 140 United Oil Co -- -- -- –28 ft 5,157 0

141 141 Sanderson -- -- -- –25 ft 5,198 pumping

142 142 Highland House 70 ft 5,262 -- –12 ft 5,180 pumping

143 143 Denver Brick Co No. 1 -- -- -- 4 ft 5,184 flowing

144 144 Denver Brick Co No. 2 -- -- -- at land surface 5,220 flowing

145 145 Haverly -- -- -- –16 ft 5,181 pumping

146 E Evans -- -- -- -- -- --

147 401 Cliff -- -- 172,800 -- -- --

148 402 Symes -- -- 28,800 -- -- --

149 403 Smith -- -- 43,200 -- -- --

150 404 Segnor -- -- 25,920 -- -- --

151 405 Lightburn -- -- 57,600 -- -- --

152 406 Sanquinette -- -- -- -- -- --

153 301 A.J. Konzie -- -- -- -- -- pumping

154 302 Broadway Theatre -- -- 108,000 -- -- pumping

155 303 Wall & Purcell 12 ft 5,200 -- –4 ft 5,184 pumping

156 304 Armusson 35 ft 5,228 -- –12 ft 5,181 pumping

157 305 Haller -- -- -- -- -- pumping

158 306 Electric Light Co. 11 ft 5,208 72,000 -- -- pumping

159 307 Denver and South 

Park Shops

-1.5 ft 5,195 -- –14 ft 5,181 pumping

160 308 Tramway, Electric 

Power House

-12 ft 5,183 16,800 -- -- pumping
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 203

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[1, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Assigned

well depth

(feet 

below land 

surface)

Sanborn Fire

Insurance

Map used

 Assigned

landsurface

altitude

(feet)

Assigned

latitude

(decimal

degrees,

NAD83)

Assigned

longitude

(decimal

degrees,

NAD83)

Model

layer

Model

row

Model 

column Comments

125 125 280 1890 volume 1

sheet 41ab

5,200 39.740 –105.021 8 51 12 Morrison Rd and Colfax (Golden = Colfax)

126 126 280 1890 volume 1

sheet 41ab

5,200 39.740 –105.021 8 51 13

127 127 280 1890 volume 1

sheet 41ab

5,200 39.740 –105.020 8 51 13

128 128 100 1893 volume 3 

index

5,260 39.724 –105.026 6 52 12 Approx location, Barnum’s Sub

129 129 763 1893 volume 3 

index

5,260 39.724 –105.025 10 52 12 Approx location, Barnum’s Sub

130 130 365 1893 volume 3 

sheet 120a

5,250 39.727 –105.026 8 52 12 Approx location, Weir = 7th Ave west of 

S. Platte River

131 131 658 1893 volume 3 

sheet 120a

5,250 39.727 –105.025 10 52 12 Approx location, Weir = 7th Ave west of 

S. Platte River

132 132 635 1893 volume 1

sheet 30a

-- 39.726 –104.992 10 52 14 Arapahoe Co Hospital—Evans and W 6th Ave—

now 6th and Cherokee NE corner

133 133 400 1893 volume 3 

index

5,350 39.756 –105.048 8 50 11 Eckhart Place is north of Sloans Lake

134 134 541 5,260 39.746 –104.980 8 51 15 St Lukes = 19th and Pearl

135 135 700 1893 volume 1 

sheet 38

-- 39.717 –104.987 10 53 14

136 136 350 1887 sheet 33 5,197 39.746 –105.004 8 51 13 Standard Bottle Works next to Lindell Hotel (#36)

137 137 331 1887 sheet 1 5,185 39.757 –104.996 8 50 14

138 138 515 1887 sheet 1 5,187 39.757 –105.008 8 50 13

139 139 375 1887 sheet 35 5,185 39.746 –105.009 8 51 13

140 140 331 1887 sheet 1 5,185 8 Same as 137—assume this is a duplicate data entry 

and ignore

141 141 679 5,223 39.761 –105.008 10 50 13 Same as 95—no different depth 

142 142 516 1887 sheet 37 5,192 10 Same as 106—yes, assume this is a duplicate data 

entry and ignore

143 143 325 1890 volume 1

sheet 10a

5,180 39.748 –105.011 8 51 13 South side of Wewetta between 7th and 8th

144 144 325 1893 volume 3 

sheet 121a

5,220 39.714 –105.003 8 53 13 Shows Valverde location—never found brick co—

approx location = Valverde Park (near Bayaud 

and Osage (S 8th on old maps)

145 145 680 1887 sheet 33 5,197 39.745 –105.004 10 51 13

146 E 1140 1887 sheets 

25, 28

-- 39.746 –104.998 10 51 14

147 401 300 5,155 39.784 –104.981 8 48 15

148 402 300 5,155 39.783 –104.982 8 48 15

149 403 360 5,155 39.783 –104.982 8 48 15

150 404 340 5,155 39.784 –104.982 8 48 15

151 405 360 5,155 39.783 –104.982 8 48 15

152 406 -- 5,155 39.782 –104.982 8 48 15

153 301 605 1887 sheet 27 -- 39.751 –105.002 10 50 14

154 302 653 1890 volume 2 

sheet 60b

-- 39.744 –104.986 10 51 14 West of Lincoln and south of 18th

155 303 340 1887 sheet 27 5,188 39.751 –105.002 8 50 14

156 304 536 1887 sheet 36 5,193 39.748 –105.004 8 50 13

157 305 1100 1887 sheet 36 -- 39.746 –105.002 10 51 14

158 306 630 1887 sheet 34 5,197 39.742 –105.008 10 51 13 Check this 6th?

159 307 610.5 1890 volume 1

sheet 15a

5,195 39.741 –105.010 10 51 13 North side Colfax—DRG shops?

160 308 629 1890 volume 1

sheet 15a

5,195 39.740 –105.012 10 51 13 South side Colfax at 3rd
204 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[1, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Well

name1

Original head,

in feet above land 

surface or pressure

(pounds per 

square inch)

Calculated

original head

altitude

(feet)

Original reported

discharge

(gallons per day)

December 1890

reported head

(feet above land 

surface) or pressure

(pounds per

square inch)

Calculated

December 1890

head altitude

(feet)

December 1890

reported discharge

(gallons per day)

161 309 Harman 20 ft 5,215 -- –4 ft 5,191 pumping

162 310 McClelland 30 ft 5,225 -- –6 ft 5,189 pumping

163 311 Hanson 30 ft 5,225 -- –7 ft 5,188 pumping

164 312 Browne 11 ft 5,206 -- –4 ft 5,191 pumping

165 313 Artesian Ice Co at land surface 5,195 -- –5 ft 5,190 pumping

166 314 Crisman 4 ft 5,194 -- -- -- pumping

167 315 Excelsior Laundry 20 ft 5,222 -- –9 ft 5,193 pumping

168 316 West Denver

Gas Works

25 ft 5,205 -- -- -- pumping

169 317 Zang Brewery No. 3 4 ft 5,204 -- -- -- pumping

170 318 New Mining

Exchange

-- -- -- -- -- --

171 319 Denver City

Cable Co.

-- -- -- –60 ft 5,143 pumping

172 320 Mack Building -- -- -- –45 ft 5,180 --

173 321 Equitable Building -- -- -- –50 ft 5,173 pumping

174 322 McPhee Block -- -- -- –13 ft 5,215 pumping

175 323 Kittridge Block -- -- -- –20 ft 5,208 pumping

176 324 Railroad Building -- -- -- at land surface 5,206 pumping

177 325 Denver 

Tramway Co No. 1

-- -- -- –30 ft 5,210 pumping

178 326 Denver

Tramway Co No. 2

-- -- -- –10 ft 5,185 pumping

179 327 Stacy No. 2 30 ft 5,232 -- -- -- 0

180 328 Windsor Hotel No. 2 -- -- -- -- -- pumping

181 329 Crescent Mills -- -- -- –10 ft 5,170 pumping

182 330 United Oil Co No. 2 28 psi 5,250 129,600 –30 ft 5,155 pumping

183 331 Steam Heating Co -- -- -- –20 ft 5,163 pumping

184 332 Monat No. 1 -- -- -- –18 ft 5,167 pumping

185 333 Monat No. 2 -- -- -- –18 ft 5,167 pumping

186 334 Harris -- -- -- –12 ft 5,173 pumping

187 335 Welch -- -- -- –20 ft 5,183 pumping

188 336 Sewell -- -- -- –60 ft 5,205 pumping

189 337 Trowbridge -- -- -- –60 ft 5,200 pumping

190 338 Kountz –5 ft 5,195 -- –18 ft 5,182 pumping

191 339 Wightman –60 ft 5,170 -- –60 ft 5,170 pumping

192 340 Hurd -- -- -- –4 ft 5,201 pumping

193 341 Peabody -- -- -- –24 ft 5,191 pumping

194 342 Denver Brick Co No. 3 -- -- -- 1 ft 5,251 flowing

195 343 Denver Brick Co No. 4 -- -- -- –16 ft 5,204 pumping

196 344 Grand and 6th Ave 8 ft 5,208 -- -- -- pumping

197 345 Villa Park No. 3 -- -- -- –30 ft 5,230 pumping

198 346 Fletcher -- -- 945 12 ft 5,162 flowing

199 347 Boivier -- -- 472 12 ft 5,167 flowing

200 348 Morrison -- -- -- –60 ft -- pumping
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 205

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[1, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Assigned

well depth

(feet 

below land 

surface)

Sanborn Fire

Insurance

Map used

 Assigned

landsurface

altitude

(feet)

Assigned

latitude

(decimal

degrees,

NAD83)

Assigned

longitude

(decimal

degrees,

NAD83)

Model

layer

Model

row

Model 

column Comments

161 309 350 5,195 39.740 –105.011 8 51 13 Approx location—Grand Ave near Larimer

162 310 336 5,195 39.740 –105.012 8 51 13 Approx location—Grand Ave near Larimer

163 311 350 5,195 39.740 –105.012 8 51 13 Approx location—Grand Ave near Larimer

164 312 310 5,195 39.740 –105.013 8 51 13 Approx location—Grand Ave near Larimer

165 313 618 1890 volume 1

sheet 15

5,195 39.740 –105.010 10 51 13 South side Colfax between 3rd and Cottonwood

166 314 435 1887 sheet 1 5,190 39.753 –105.011 8 50 13

167 315 607 1890 volume 1

sheet 3a

5,202 39.745 –105.000 10 51 14 SW corner Arapahoe and 12th next to creek—

had 2 -315s need to recheck

168 316 650 1890 volume 1

sheet 10a

5,180 39.749 –105.011 10 50 13

169 317 660 1887 sheet 35 5,200 39.752 –105.015 10 50 13 Rocky Mountain Brewery—artesian well on map

170 318 608 1887 sheet 25 5,215 39.747 –104.997 10 51 14

171 319 650 5,203 39.751 –104.994 10 50 14

172 320 621 5,225 39.745 –104.992 10 51 14

173 321 610 5,223 39.747 –104.992 10 51 14

174 322 750 5,228 39.744 –104.990 10 51 14

175 323 650 5,228 39.744 –104.990 10 51 14

176 324 600 5,206 39.748 –104.999 10 51 14

177 325 600 5,240 39.740 –104.987 10 51 14

178 326 600 5,195 39.740 –105.012 10 51 13 2nd well at Tramway shop

179 327 600 5,202 39.754 –104.992 10 50 14

180 328 530 1887 sheet 14 -- 39.751 –104.995 8 50 14

181 329 393 1890 volume 2 

sheet 65a

5,180 39.759 –105.002 8 50 14 29th and 19th east of rr tracks

182 330 668 5,185 39.757 –104.996 10 50 14

183 331 340 5,183 39.756 –104.999 8 50 14 This well replaced Emmons65 and never flowed

184 332 400 5,185 39.760 –104.987 8 50 14

185 333 400 5,185 39.760 –104.987 8 50 14

186 334 100 1887 5,185 39.756 –104.999 6 50 14

187 335 463 5,203 39.760 –105.007 8 50 13

188 336 425 1893 volume 3 

index

5,265 39.764 –105.008 8 49 13

189 337 473 1893 volume 3 

index

5,260 39.764 –105.008 8 49 13 34th and Quivas

190 338 900 1890 volume 2 

sheet 0

5,200 39.766 –105.003 10 49 13 35th and Mariposa

191 339 340 1890 volume 2 

sheet 0

5,230 39.756 –105.013 8 50 13 27th and Vallejo

192 340 440 5,205 39.738 –105.022 8 51 12

193 341 530 5,215 39.738 –105.024 8 51 12

194 342 325 1893 volume 3 

sheet 117b

5,250 39.750 –105.019 8 50 13 Denver white lead just east of Cresent Dr and Zuni 

(Gallup)

195 343 480 1904 volume 4 

sheet 521

5,220 39.738 –105.024 8 51 12 AE Epleys brick yard not in operation 1904—well 

water noted on map

196 344 100 5,200 39.740 –105.008 6 51 13

197 345 300 1893 volume 3 

index

5,260 39.724 –105.026 8 52 12

198 346 500 5,150 39.777 –104.987 8 49 14

199 347 500 1893 volume 3 

index

5,155 39.778 –104.986 8 48 14 5th and Central in Argo = Lincoln and 45th

200 348 400 -- -- Look in 1890 v3
206 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Pilot-Point Approach to 

Hydraulic-Conductivity Estimation

Widely varying values of hydraulic conductivity for 

similar materials in different areas of a given aquifer can be 

considered unrealistic. Regularization, in combination with 

the pilot-point approach as applied to the parameterization of 

hydraulic conductivity of the Denver, Arapahoe, and Laramie–

Fox Hills aquifers, was used to impose a penalty on widely 

varying hydraulic-conductivity parameter values in a given 

aquifer. For each pair of points in a given aquifer, the penalty 

is formulated as prior information that the difference in parameter values is zero. The penalty takes the form of a regularization objective function (Sr

) (Doherty, 2006):

S F wr r r jj

j

p

= ⎛

⎝

⎜

⎞

⎠

⎟ =

∑( )2

1

(2)

where

rj is the difference in hydraulic-conductivity estimates 

for each pair of pilot points in a given aquifer,

wj is a weight applicable to the pair of pilot points,

p is the total number of pairs of pilot points for all 

layers,

and

Fr is a regularization weight factor.

During calibration, parameter values were adjusted in 

an attempt to minimize an objective function (Φ) defined as 

(Doherty, 2006):

Φ = Sm + Sr (3)

Adjustments to Fr (eq. 2) increase or decrease the effect of 

the regularization term of this objective function. When Fr is 

assigned a relatively large value, the penalty for widely varying estimates of parameters that control hydraulic conductivity of a particular aquifer (such as the set of pilot points that 

define the hydraulic conductivity of the Laramie–Fox Hills 

aquifer) is larger than when Fr (eq. 2) is assigned a relatively 

small value. By manipulating Fr, the regression algorithm 

attempts to find a set of parameters that achieves an acceptably small value of Sm while maintaining a reasonably uniform 

distribution of hydraulic conductivity in each aquifer where 

pilot points are used.

Calibration Targets

Two types of observations were used in calibrating the 

model: hydraulic heads and flows. The head observations 

were based on water-level measurements made in wells. The 

flow observations included estimates of base flow at select 

locations and estimates of the production rates of historical 

flowing wells based on information in Emmons and others 

(1896). The regression algorithm used for model calibration 

requires a weight be assigned to each observation, to allow 

inclusion of observations differing in type and units of measurement and to allow observations having different levels of 

uncertainty to be emphasized accordingly. The following sections include discussions of the calibration datasets and assignment of observation weights. The weights used in the regression are based on estimates of the errors associated with the 

observations. Use of estimated, reasonable weights is suitable 

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[

1

, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Well

name1

Original head,

in feet above land 

surface or pressure

(pounds per 

square inch)

Calculated

original head

altitude

(feet)

Original reported

discharge

(gallons per day)

December 1890

reported head

(feet above land 

surface) or pressure

(pounds per

square inch)

Calculated

December 1890

head altitude

(feet)

December 1890

reported discharge

(gallons per day)

201 349 Anderson -- -- -- –90 ft -- pumping

202 350 Norber Ice Co -- -- -- –60 ft -- pumping

203 351 Gunter -- -- -- –60 ft -- pumping

204 352 Boston and 

Colorado Smelting Co

-- -- -- -- -- pumping

205 353 Fisher -- -- -- –30 ft 5,248 pumping

206 354 Davis -- -- -- –80 ft 5,195 pumping

207 355 Richardson No. 1 -- -- -- –30 ft -- pumping

208 356 Richardson No. 2 -- -- -- –20 ft -- pumping

209 357 Globe Smelter -- -- -- -- -- pumping
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 207

Table C9. Tabulation of well locations, depths, head, discharge, and assigned model locations for late 19th century wells listed in 

Emmons and others (1896).—Continued

[1, Data from Emmons and others (1896); --, no data; blank, not estimated; ft, feet; psi, pounds per square inch; pumping, well reported as pumping but no 

rate provided; flowing, well reported as flowing; NAD83, North American Datum 1983; Sanborn Fire Insurance Maps, Environmental Data Resources, Inc., 

available online through the Denver Public Library, http://history.denverlibrary.org/collections/access.html, accessed March 9, 2006 and May 31, 2006]

Count

of wells

Well

number1

Assigned

well depth

(feet 

below land 

surface)

Sanborn Fire

Insurance

Map used

 Assigned

landsurface

altitude

(feet)

Assigned

latitude

(decimal

degrees,

NAD83)

Assigned

longitude

(decimal

degrees,

NAD83)

Model

layer

Model

row

Model 

column Comments

201 349 200 -- --

202 350 275 -- --

203 351 580 -- --

204 352 800 1887 sheet 40,

1890 volume 2 

sheet 93b,

1904 volume 4 

sheet 547

5,210 39.782 –104.995 10 48 14 47th and Fox (Argo on old maps) from 1904 

vol 4 index

205 353 700 1893 volume 3 

index

5,278 39.769 –105.011 10 49 13 38th and Tejon

206 354 557 1893 volume 3 

index

5,275 39.772 –105.011 8 49 13 40th and Tejon

207 355 540 --

208 356 540 --

209 357 505 5,180 39.794 –104.980 8 47 15

for calibration of the model because regression results generally are insensitive to moderate variation in the weighting (Hill 

and Tiedeman, 2007, p. 299).

Hydraulic Head

A total of 4,984 water-level measurements for 1,131 sites 

were used as observations of hydraulic head (Appendix C1, 

http://pubs.usgs.gov/pp/1770/). Water-level measurement 

dates ranged from 1883 through 2003. Because the earliest 

water-level measurements occurred during the calibration time 

period, model-simulated equivalents for all head observations 

were generated during transient-stress periods. No predevelopment water-level measurements were available. However, 

the long-term history of observations, which extends through 

nearly the entire period of development, provides useful information on stress conditions similar to those existing during the 

predevelopment period.

Head observations for the late 19th century were derived 

from the historical well inventory data (Emmons and others, 

1896; table C9). Initial head or pressure estimates at the 

time of well drilling were used as head observations for 91 

of the 197 wells for which locations were determined. Head 

or pressure estimates from 1890 were used as head observations for 103 of the 197 wells for which locations were 

determined (table C10). A total of 194 head observations at 

142 sites were derived from the 19th-century well inventory 

(Emmons and others, 1896).

Head observations for the alluvial and bedrock 

aquifer systems were primarily acquired from the USGS 

National Water Information System (NWIS) database 

(http://waterdata.usgs.gov/co/nwis/). A total of 4,672 waterlevel measurements for 875 sites were retrieved from the 

NWIS database. For the alluvial aquifer, 190 head observations were retrieved for 8 sites, and for the bedrock aquifers, 

4,482 head observations were retrieved for 867 sites. For 

the Nussbaum Alluvium, 113 head observations (one-time 

measurements at 113 sites) were obtained from CDWR 

well-permit records as compiled by Paschke (1992).

Water-level data for Denver Basin bedrock aquifers have 

been sparsely collected since the 1980s. The CDWR currently 

operates a water-level monitoring network of approximately 

278 wells (fig. B49), which was established in the 1980s, and 

water-level records for some wells date back to the 1950s and 

1960s (for example, Colorado Division of Water Resources, 

2003, 2004). Wells in the CDWR monitoring network are 

domestic, commercial, and municipal wells and are not solely 

dedicated monitoring wells. Water levels measured in these 

wells might not be representative of ambient water-level 

conditions because the completion intervals of some wells are 

unknown or not appropriate for monitoring water levels and 

because water levels in some wells appear affected by pumping at the time of the measurement (Courtney Hemenway, 

Hemenway Groundwater Consulting, written commun., 2008). 

Model calibration did not utilize the CDWR water-level data 

because of uncertainty related to well-completion intervals 

and pumping status. However, selected data from the CDWR 

water-level network are compared to simulation results in the 

section “Changes in Hydraulic Heads and Groundwater Flow 

Directions” in Chapter B.
208 Groundwater Availability of the Denver Basin Aquifer System, Colorado Table C10. Historical head observations derived from Emmons and others (1896).—Continued Well number Observation name Observation date Model layer Model row Model column Reference stress period to which observation time is referenced Time offset from beginning of reference stress period to time of observation (days) Relative row offset used to locate the observation within a finite-difference cell (dimensionless) Relative column offset used to locate the observation within a finite-difference cell (dimensionless) Head altitude (feet)

2 E00218841115 11/15/1884 8 51 14 2 1,780 –0.082 –0.112 5,2682 E00218901215 12/15/1890 8 51 14 2 4,001 –0.082 –0.112 5,2184 E00418901215 12/15/1890 10 51 14 2 4,001 –0.300 –0.113 5,1956 E00618831115 11/15/1883 8 51 14 2 1,414 0.268 –0.061 5,2986 E00618901215 12/15/1890 8 51 14 2 4,001 0.268 –0.061 5,2248 E00818901215 12/15/1890 10 51 14 2 4,001 0.134 0.193 5,2309 E00918901215 12/15/1890 10 51 14 2 4,001 0.411 0.179 5,199

10 E01018901215 12/15/1890 10 51 14 2 4,001 0.391 0.078 5,203

11 E01118901215 12/15/1890 10 51 14 2 4,001 0.449 0.020 5,201

13 E01318831101 11/1/1883 8 51 14 2 1,400 0.340 –0.156 5,40513 E01318901215 12/15/1890 8 51 14 2 4,001 0.340 –0.156 5,20014 E01418901215 12/15/1890 10 51 14 2 4,001 0.371 –0.121 5,19315 E01518840515 5/15/1884 10 50 14 2 1,596 –0.498 –0.053 5,24216 E01618830701 7/1/1883 8 51 14 2 1,277 0.420 –0.110 5,30116 E01618901215 12/15/1890 8 51 14 2 4,001 0.420 –0.110 5,20617 E01718841101 11/1/1884 10 51 14 2 1,766 0.480 –0.046 5,26718 E01818840701 7/1/1884 10 50 14 2 1,643 –0.491 –0.166 5,29019 E01918840815 8/15/1884 10 51 14 2 1,688 0.448 –0.228 5,28719 E01918901215 12/15/1890 10 51 14 2 4,001 0.448 –0.228 5,16220 E02018850101 1/1/1885 10 50 14 2 1,827 –0.421 –0.243 5,27720 E02018901215 12/15/1890 10 50 14 2 4,001 –0.421 –0.243 5,17721 E02118831115 11/15/1883 8 50 14 2 1,414 –0.398 –0.267 5,35923 E02318901215 12/15/1890 10 50 14 2 4,001 –0.303 –0.120 5,19524 E02418830830 8/30/1883 8 50 14 2 1,337 –0.296 –0.098 5,32524 E02418901215 12/15/1890 8 50 14 2 4,001 –0.296 –0.098 5,11825 E02518840415 4/15/1884 10 50 14 2 1,566 –0.072 0.048 5,27626 E02618831215 12/15/1883 8 50 14 2 1,444 –0.182 –0.362 5,23126 E02618901215 12/15/1890 8 50 14 2 4,001 –0.182 –0.362 4,98527 E02718840715 7/15/1884 8 50 14 2 1,657 –0.211 –0.268 5,20528 E02818840815 8/15/1884 8 50 14 2 1,688 –0.339 –0.325 5,24930 E03018850215 2/15/1885 8 51 13 2 1,872 0.488 0.475 5,21530 E03018901215 12/15/1890 8 51 13 2 4,001 0.488 0.475 5,18032 E03218901215 12/15/1890 8 51 13 2 4,001 0.366 0.153 5,17034 E03418831101 11/1/1883 8 51 13 2 1,400 0.291 0.045 5,22335 E03518841007 10/7/1884 8 51 13 2 1,741 0.229 0.306 5,19935 E03518901215 12/15/1890 8 51 13 2 4,001 0.229 0.306 5,19236 E03618830915 9/15/1883 8 51 13 2 1,353 0.300 0.429 5,22036 E03618901215 12/15/1890 8 51 13 2 4,001 0.300 0.429 5,18537 E03718830915 9/15/1883 8 51 13 2 1,353 0.272 0.376 5,22237 E03718901215 12/15/1890 8 51 13 2 4,001 0.272 0.376 5,18939 E03918901215 12/15/1890 10 51 13 2 4,001 0.334 0.484 5,18041 E04118901215 12/15/1890 10 51 13 2 4,001 0.142 0.381 5,177
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 209

Table C10. Historical head observations derived from Emmons and others (1896).—Continued

Well

number

Observation

name

Observation

date

Model

layer

Model

row

Model

column

Reference stress

period to which

observation time

is referenced 

Time offset

from beginning

of reference stress 

period to time

of observation

(days)

Relative row

offset used to locate 

the observation within 

a finite-difference cell 

(dimensionless)

Relative column

offset used to locate 

the observation within 

a finite-difference cell 

(dimensionless)

Head

altitude

(feet)

42 E04218830701 7/1/1883 8 51 13 2 1,277 0.186 0.265 5,23542 E04218901215 12/15/1890 8 51 13 2 4,001 0.186 0.265 5,18743 E04218850115 1/15/1885 8 51 13 2 1,841 0.218 0.482 5,21244 E04318850215 2/15/1885 8 51 13 2 1,872 –0.096 0.072 5,23544 E04318901215 12/15/1890 8 51 13 2 4,001 –0.096 0.072 5,19150 E05018830701 7/1/1883 10 52 13 2 1,277 0.227 0.307 5,25551 E05118841101 11/1/1884 10 53 14 2 1,766 0.304 0.383 5,33552 E05218831101 11/1/1883 10 53 14 2 1,400 0.304 0.443 5,26857 E05718850615 6/15/1885 10 48 16 2 1,992 0.490 –0.366 5,23959 E05918840315 3/15/1884 10 50 14 2 1,535 –0.346 0.323 5,22060 E06018840815 8/15/1884 10 50 14 2 1,688 –0.172 0.406 5,27463 E06318840615 6/15/1884 10 50 14 2 1,627 –0.011 –0.287 5,20563 E06318901215 12/15/1890 10 50 14 2 4,001 –0.011 –0.287 5,16064 E06418901215 12/15/1890 8 50 14 2 4,001 –0.030 –0.272 5,17365 E06518831215 12/15/1883 8 50 14 2 1,444 0.006 –0.304 5,20365 E06518901215 12/15/1890 8 50 14 2 4,001 0.006 –0.304 5,15866 E06618831215 12/15/1883 8 50 14 2 1,444 0.037 –0.268 5,20767 E06718901215 12/15/1890 8 50 14 2 4,001 0.017 –0.230 5,13068 E06818851115 11/15/1885 8 50 14 2 2,145 0.040 –0.209 5,20068 E06818901215 12/15/1890 8 50 14 2 4,001 0.040 –0.209 5,17769 E06918830101 1/1/1883 8 50 14 2 1,096 0.206 –0.229 5,21073 E07318830715 7/15/1883 8 50 14 2 1,291 0.144 –0.057 5,25974 E07418831115 11/15/1883 8 50 14 2 1,414 0.242 0.364 5,22576 E07618841015 10/15/1884 8 50 15 2 1,749 0.253 –0.497 5,24876 E07618901215 12/15/1890 8 50 15 2 4,001 0.253 –0.497 5,17777 E07718830101 1/1/1883 8 50 14 2 1,096 0.442 0.445 5,33577 E07718901215 12/15/1890 8 50 14 2 4,001 0.442 0.445 5,18979 E07918901215 12/15/1890 8 50 15 2 4,001 0.256 0.007 5,19081 E08118840315 3/15/1884 8 49 15 2 1,535 –0.167 –0.064 5,24281 E08118901215 12/15/1890 8 49 15 2 4,001 –0.167 –0.064 5,16783 E08318831215 12/15/1883 8 49 15 2 1,444 –0.113 –0.293 5,26683 E08318901215 12/15/1890 8 49 15 2 4,001 –0.113 –0.293 5,17784 E08418901215 12/15/1890 8 49 15 2 4,001 –0.083 –0.082 5,18985 E08518840815 8/15/1884 8 49 15 2 1,688 –0.007 –0.116 5,28786 E08618840215 2/15/1884 8 49 15 2 1,506 –0.066 0.025 5,22587 E08718841101 11/1/1884 10 49 15 2 1,766 0.228 0.355 5,28788 E08818830701 7/1/1883 10 48 15 2 1,277 –0.422 0.271 5,28991 E09118851215 12/15/1885 8 50 14 2 2,175 0.040 –0.297 5,21094 E09418850915 9/15/1885 8 50 13 2 2,084 0.373 0.325 5,21595 E09518840215 2/15/1884 10 50 13 2 1,506 0.373 0.199 5,29295 E09518901215 12/15/1890 10 50 13 2 4,001 0.373 0.199 5,19896 E09618840115 1/15/1884 8 50 13 2 1,475 0.337 0.232 5,240
210 Groundwater Availability of the Denver Basin Aquifer System, Colorado Table C10. Historical head observations derived from Emmons and others (1896).—Continued Well number Observation name Observation date Model layer Model row Model column Reference stress period to which observation time is referenced Time offset from beginning of reference stress period to time of observation (days) Relative row offset used to locate the observation within a finite-difference cell (dimensionless) Relative column offset used to locate the observation within a finite-difference cell (dimensionless) Head altitude (feet) 98 E09818850215 2/15/1885 8 50 13 2 1,872 0.318 0.270 5,219 98 E09818901215 12/15/1890 8 50 13 2 4,001 0.318 0.270 5,191 99 E09918831115 11/15/1883 8 50 13 2 1,414 0.363 0.206 5,238 99 E09918901215 12/15/1890 8 50 13 2 4,001 0.363 0.206 5,175 100 E10018840215 2/15/1884 8 50 13 2 1,506 0.224 0.291 5,227 100 E10018901215 12/15/1890 8 50 13 2 4,001 0.224 0.291 5,160 101 E10118840215 2/15/1884 8 50 13 2 1,506 0.173 0.262 5,218 102 E10218840315 3/15/1884 8 50 13 2 1,535 0.146 0.219 5,205 102 E10218901215 12/15/1890 8 50 13 2 4,001 0.146 0.219 5,177 103 E10318830701 7/1/1883 8 50 13 2 1,277 0.171 0.152 5,272 103 E10318901215 12/15/1890 8 50 13 2 4,001 0.171 0.152 5,192 104 E10418851115 11/15/1885 8 50 13 2 2,145 0.120 0.200 5,212 105 E10518901215 12/15/1890 8 50 13 2 4,001 0.053 0.128 5,170 106 E10618830615 6/15/1883 8 50 13 2 1,261 0.045 0.137 5,262 106 E10618901215 12/15/1890 8 50 13 2 4,001 0.045 0.137 5,180 107 E10718831015 10/15/1883 8 50 13 2 1,383 0.013 0.183 5,225 107 E10718901215 12/15/1890 8 50 13 2 4,001 0.013 0.183 5,180 108 E10818901215 12/15/1890 8 50 13 2 4,001 0.279 –0.075 5,258 110 E11018831101 11/1/1883 8 50 13 2 1,400 0.196 –0.225 5,272 110 E11018901215 12/15/1890 8 50 13 2 4,001 0.196 –0.225 5,180 112 E11218830815 8/15/1883 6 50 13 2 1,322 –0.057 0.049 5,225 112 E11218901215 12/15/1890 6 50 13 2 4,001 –0.057 0.049 5,190 113 E11318840515 5/15/1884 8 50 13 2 1,596 –0.080 –0.080 5,224

113 E11318901215 12/15/1890 8 50 13 2 4,001 –0.080 –0.080 5,190114 E11418840615 6/15/1884 8 50 13 2 1,627 –0.112 –0.141 5,240115 E11518830401 4/1/1883 10 50 13 2 1,186 –0.066 –0.485 5,384117 E11718840401 4/1/1884 8 50 13 2 1,552 –0.157 –0.332 5,306117 E11718901215 12/15/1890 8 50 13 2 4,001 –0.157 –0.332 5,221118 E11818830401 4/1/1883 8 50 13 2 1,186 –0.275 –0.164 5,246119 E11918830615 6/15/1883 8 50 13 2 1,261 –0.270 –0.157 5,258119 E11918901215 12/15/1890 8 50 13 2 4,001 –0.270 –0.157 5,160

120 E12018831101 11/1/1883 10 51 13 2 1,400 0.451 –0.275 5,264122 E12218901215 12/15/1890 10 51 15 2 4,001 0.362 –0.281 5,188123 E12318850101 1/1/1885 8 51 13 2 1,827 0.364 –0.462 5,232123 E12318901215 12/15/1890 8 51 13 2 4,001 0.364 –0.462 5,198125 E12518850215 2/15/1885 8 51 12 2 1,872 –0.083 0.500 5,230125 E12518901215 12/15/1890 8 51 12 2 4,001 –0.083 0.500 5,184126 E12618901215 12/15/1890 8 51 13 2 4,001 –0.084 –0.477 5,185127 E12718830815 8/15/1883 8 51 13 2 1,322 –0.085 –0.453 5,240127 E12718901215 12/15/1890 8 51 13 2 4,001 –0.085 –0.453 5,188128 E12818901215 12/15/1890 6 52 12 2 4,001 –0.196 0.281 5,230129 E12918901215 12/15/1890 10 52 12 2 4,001 –0.214 0.283 5,210
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 211

Table C10. Historical head observations derived from Emmons and others (1896).—Continued

Well

number

Observation

name

Observation

date

Model

layer

Model

row

Model

column

Reference stress

period to which

observation time

is referenced 

Time offset

from beginning

of reference stress 

period to time

of observation

(days)

Relative row

offset used to locate 

the observation within 

a finite-difference cell 

(dimensionless)

Relative column

offset used to locate 

the observation within 

a finite-difference cell 

(dimensionless)

Head

altitude

(feet)

131 E13118850215 2/15/1885 10 52 12 2 1,872 0.033 0.288 5,377131 E13118901215 12/15/1890 10 52 12 2 4,001 0.033 0.288 5,238134 E13418840701 7/1/1884 8 51 15 2 1,643 0.332 –0.303 5,302134 E13418901215 12/15/1890 8 51 15 2 4,001 0.332 –0.303 5,200136 E13618830701 7/1/1883 8 51 13 2 1,277 0.309 0.425 5,227137 E13718901215 12/15/1890 8 50 14 2 4,001 0.094 –0.156 5,157138 E13818901215 12/15/1890 8 50 13 2 4,001 0.109 0.198 5,171139 E13918901215 12/15/1890 8 51 13 2 4,001 0.363 0.157 5,173141 E14118901215 12/15/1890 10 50 13 2 4,001 0.370 0.192 5,198143 E14318901215 12/15/1890 8 51 13 2 4,001 0.476 0.062 5,184144 E14418901215 12/15/1890 8 53 13 2 4,001 0.146 0.472 5,220145 E14518901215 12/15/1890 10 51 13 2 4,001 0.281 0.406 5,181303 E30318880701 7/1/1888 8 50 14 2 3,104 –0.349 –0.459 5,200303 E30318901215 12/15/1890 8 50 14 2 4,001 –0.349 –0.459 5,184304 E30418870701 7/1/1887 8 50 13 2 2,738 –0.496 0.392 5,228304 E30418901215 12/15/1890 8 50 13 2 4,001 –0.496 0.392 5,181306 E30618891015 10/15/1889 10 51 13 2 3,575 0.048 0.183 5,208307 E30718900315 3/15/1890 10 51 13 2 3,726 –0.038 0.089 5,194307 E30718901215 12/15/1890 10 51 13 2 4,001 –0.038 0.089 5,181308 E30818900415 4/15/1890 10 51 13 2 3,757 –0.112 0.016 5,183309 E30918870701 7/1/1887 8 51 13 2 2,738 –0.098 0.037 5,215309 E30918901215 12/15/1890 8 51 13 2 4,001 –0.098 0.037 5,191310 E31018870315 3/15/1887 8 51 13 2 2,630 –0.098 0.005 5,225310 E31018901215 12/15/1890 8 51 13 2 4,001 –0.098 0.005 5,195

311 E31118870415 4/15/1887 8 51 13 2 2,661 –0.101 –0.017 5,225311 E31118901215 12/15/1890 8 51 13 2 4,001 –0.101 –0.017 5,188

312 E31218870701 7/1/1887 8 51 13 2 2,738 –0.101 –0.038 5,206312 E31218901215 12/15/1890 8 51 13 2 4,001 –0.101 –0.038 5,191313 E31318890215 2/15/1889 10 51 13 2 3,333 –0.114 0.087 5,195313 E31318901215 12/15/1890 10 51 13 2 4,001 –0.114 0.087 5,190314 E31418890715 7/15/1889 8 50 13 2 3,483 –0.157 0.031 5,194315 E31518860415 4/15/1886 10 51 14 2 2,296 0.267 –0.368 5,222315 E31518901215 12/15/1890 10 51 14 2 4,001 0.267 –0.368 5,193316 E31618860415 4/15/1886 10 50 13 2 2,296 –0.481 0.065 5,205317 E31718900815 8/15/1890 10 50 13 2 3,879 –0.272 –0.162 5,204319 E31918901215 12/15/1890 10 50 14 2 4,001 –0.349 –0.052 5,143320 E32018901215 12/15/1890 10 51 14 2 4,001 0.272 0.051 5,180321 E32118901215 12/15/1890 10 51 14 2 4,001 0.380 0.068 5,173322 E32218901215 12/15/1890 10 51 14 2 4,001 0.191 0.145 5,215323 E32318901215 12/15/1890 10 51 14 2 4,001 0.176 0.145 5,208324 E32418901215 12/15/1890 10 51 14 2 4,001 0.492 –0.295 5,206325 E32518901215 12/15/1890 10 51 14 2 4,001 –0.102 0.309 5,210
212 Groundwater Availability of the Denver Basin Aquifer System, Colorado Table C10. Historical head observations derived from Emmons and others (1896).—Continued Well number Observation name Observation date Model layer Model row Model column Reference stress period to which observation time is referenced Time offset from beginning of reference stress period to time of observation (days) Relative row offset used to locate the observation within a finite-difference cell (dimensionless) Relative column offset used to locate the observation within a finite-difference cell (dimensionless) Head altitude (feet) 326 E32618901215 12/15/1890 10 51 13 2 4,001 –0.114 0.011 5,185 327 E32718870701 7/1/1887 10 50 14 2 2,738 –0.084 0.042 5,232 329 E32918901215 12/15/1890 8 50 14 2 4,001 0.204 –0.467 5,170 330 E33018870701 7/1/1887 10 50 14 2 2,738 0.083 –0.164 5,250 330 E33018901215 12/15/1890 10 50 14 2 4,001 0.083 –0.164 5,155 331 E33118901215 12/15/1890 8 50 14 2 4,001 0.002 –0.303 5,163 332 E33218901215 12/15/1890 8 50 14 2 4,001 0.300 0.313 5,167 333 E33318901215 12/15/1890 8 50 14 2 4,001 0.305 0.321 5,167 334 E33418901215 12/15/1890 6 50 14 2 4,001 0.021 –0.323 5,173 335 E33518901215 12/15/1890 8 50 13 2 4,001 0.308 0.260 5,183 336 E33618901215 12/15/1890 8 49 13 2 4,001 –0.402 0.186 5,205 337 E33718901215 12/15/1890 8 49 13 2 4,001 –0.399 0.214 5,200 338 E33818890701 7/1/1889 10 49 13 2 3,469 –0.316 0.467 5,195 338 E33818901215 12/15/1890 10 49 13 2 4,001 –0.316 0.467 5,182 339 E33918890701 7/1/1889 8 50 13 2 3,469 0.022 –0.076 5,170

339 E33918901215 12/15/1890 8 50 13 2 4,001 0.022 –0.076 5,170340 E34018901215 12/15/1890 8 51 12 2 4,001 –0.207 0.468 5,201341 E34118901215 12/15/1890 8 51 12 2 4,001 –0.215 0.381 5,191342 E34218901215 12/15/1890 8 50 13 2 4,001 –0.423 –0.360 5,251343 E34318901215 12/15/1890 8 51 12 2 4,001 –0.246 0.353 5,201344 E34418890701 7/1/1889 6 51 13 2 3,469 –0.056 0.216 5,208345 E34518901215 12/15/1890 8 52 12 2 4,001 –0.171 0.281 5,230346 E34618901215 12/15/1890 8 49 14 2 4,001 0.487 0.338 5,162347 E34718901215 12/15/1890 8 48 14 2 4,001 –0.417 0.378 5,167353 E35318901215 12/15/1890 10 49 13 2 4,001 –0.051 0.027 5,248354 E35418901215 12/15/1890 8 49 13 2 4,001 0.109 0.024 5,195
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 213

The weight for a head observation based on a depth to 

water relative to a measuring-point altitude was calculated as 

(Doherty, 2006):

Weight SD SD = + ( ) mst mp

− 2 2 0 5.

(4)

where

SDmst is the estimated standard deviation of the depthto-water measurement

and

SDmp is the estimated standard deviation of the 

measuring-point altitude.

The value of SDmst was assumed to equal 1.0 ft, and SDmp was 

assigned as the estimated measuring-point altitude accuracy 

from the source data base. For the water-level observations 

from Emmons and others (1896), the standard deviation of 

the measurement was assumed to be 25 ft, and the weight was 

assigned as 0.04 ft–1.

Stream Base Flow

Streamflow records for eight sites in the Denver Basin 

(fig. A6) were used to estimate base flow from groundwater. 

The base-flow analysis generated 153 observations for the 

eight sites (table C11), with observation dates ranging from 

1939 to 2003. Most of the stream base-flow observations 

(61 percent) are for Cherry Creek (63 observations for Cherry 

Creek near Franktown, 1939–2003, and 31 observations for 

Cherry Creek near Melvin, 1939–1969 and 1985). Twelve 

observations are for First Creek at Rocky Mountain Arsenal 

(1992–2003), 10 observations are for Kiowa Creek at Elbert 

(1955–1965), 10 observations are for Kiowa Creek at Kiowa 

(1955–1965), 4 observations are for Kiowa Creek at Bennett 

(1961–1964), 6 observations are for Bijou Creek near Wiggins 

(1950–1956), and 17 observations are for Cottonwood Creek 

at mouth, at Pikeview, CO (1985–2003). Observation weights 

for the base-flow observations were calculated for each mean 

annual observation from either the annual standard deviation 

or the coefficient of variation.

Historical Flowing Wells

Flow from model cells representing the 197 historical flowing wells for which locations were determined was 

estimated from information provided by Emmons and others (1896). Emmons and others (1896, p. 426) estimated 

a daily yield from the Denver wells of approximately 

1,500,000 gallons per day, which they reported is a “little 

more than one-seventh of the original rate of discharge.” 

Multiplying the estimate by 7, and assuming the original 

rate applied to the year 1883 when well installation began in 

Denver, results in a discharge estimate of 10,500,000 gallons 

per day for 1883. Emmons and others (1896) also stated that 

the flow in 1886 was approximately one-fourth of the original, 

which would be an estimated 2,625,000 gallons per day.

In the model, the historical flowing wells are represented using the Drain Package, which simulates continuous 

discharge when the head in a model cell is above the drain 

altitude. The drain altitude is assigned as the land-surface 

altitude at the well location. It is unknown to what extent 

discharge from these wells was controlled by valves. It is 

assumed that the reported discharge values (table C9) represent rates measured at a time when discharge from the well 

was not controlled and that the wells were shut in when not 

needed. Observations of flow for the drain cells representing the historical wells were included in the model to ensure 

that cumulative flows simulated from the drain cells were 

reasonable. For lack of information on well discharges, and 

based on initial model simulations that indicated flow rates 

less than those reported, the flow rates used as observations 

in calibration were assigned as one-half the reported flow rate 

(table C12). Weights for the flowing-well observations were 

based on a coefficient of variation of 0.5 to indicate a relatively large amount of uncertainty.

Model-Calibration Results

Parameters used in the simulation were adjusted within 

reasonable limits until the objective function and mean head 

residuals were minimized. Seventy-seven parameters were 

included in the model, 52 of which were adjusted during 

parameter estimation and 25 of which had assigned values. 

Estimated parameters included hydraulic conductivity and 

recharge parameters. The groundwater flow model was considered calibrated when the following criteria were satisfied:

1. Incremental changes in model parameters did not substantially reduce the objective function, root mean squared 

error (RMSE) (Hill and others, 2000), or other calibration 

statistics.

2. The RMSE of heads over the entire model was less than 

approximately 5 percent of the total head change in the 

study area.

3. Hydraulic-conductivity values and distributions provided 

reasonable representations of aquifer properties as compared to aquifer-testing results on a regional scale.

To evaluate the model-calibration process, model-estimated parameters (table C13) were compared to measured and 

estimated values, and model-computed heads and flows were 

compared to measured (observed) water levels and estimated 

discharges.
214 Groundwater Availability of the Denver Basin Aquifer System, Colorado Table C11. Summay of stream base-flow observations for eight surface-water gaging stations in the Denver Basin. [USGS site ID, U.S. Geological Survey site identification number; ft3/s, cubic feet per second] Site name USGS site ID Observation name prefix Period of record Number of annual observations Base flow (ft3/s) Total flow (ft3/s) Mean for period of record Standard deviation Coefficient of variation Mean for period of record Standard deviation Coefficient of variation Cherry Creek near Franktown 06712000 BF06712000 1939–2003 63 5.36 3.73 0.70 9.49 6.67 0.70 Cherry Creek near Melvin 06712500 BF06712500 1939–1969, 1985 31 3.40 4.83 1.42 12.33 12.13 0.98 First Creek below Buckley Road, at Rocky Mountain Arsenal 06720460 BF06720460 1992–2003 12 0.47 0.72 1.52 0.91 1.02 1.13 Kiowa Creek at Elbert 06758000 BF06758000 1955–1965 10 0.01 0.02 1.89 0.89 2.35 2.64 Kiowa Creek at Kiowa 06758200 BF06758200 1955–1965 10 0.74 0.61 0.82 3.81 3.29 0.86 Kiowa Creek at Bennett 06758300 BF06758300 1961–1964 4 0.52 0.45 0.87 3.23 0.96 0.30 Bijou Creek near Wiggins 06759000 BF06759000 1950–1956 6 0.01 0.03 2.45 9.21 12.01 1.30 Cottonwood Creek at mouth, at Pikeview 07103990 BF07103990 1985–2003 17 4.38 1.46 0.33 6.91 2.87 0.42 Table C12. Drain observations derived from historical data provided by Emmons and others (1896). [ft3/d, cubic feet per day] Observation name Reference stress period to which observation time is referenced Time offset from beginning of reference stress period to time of observation (days) Model layer Model row Model column Estimated discharge (ft3/d) Observation, one-half of estimated discharge (ft3/d) Basis for estimated discharge E12118840701 2 1,643 6 50 12 241 120 Well 121 flow for 1884.

E40118851101 2 2,114 8 48 15 43,893 21,947 Sum of flow for wells 401, 402, 403, 404, and 405 for 1885.E34618891115 2 3,606 8 49 14 126 63 Well 346 flow for 1889.E09918831115 2 1,414 8 50 13 71,091 35,545 Sum of flow for wells 105, 108, and 119 for 1883.

E06918840101 2 1,461 8 50 14 172,535 86,267 Sum of flow for wells 22, 24, 26, 65, 67, and 77 for 1883.E07918830815 2 1,322 8 50 15 14,439 7,219 Well 79 flow for 1883.

E03418831101 2 1,400 8 51 13 34,231 17,116 Sum of flow for wells 31, 36, 38, and 42 for 1883.E13018831101 2 1,400 8 52 12 6,064 3,032 Well 130 flow for 1883.

E08818830701 2 1,277 10 48 15 66,845 33,422 Well 88 flow for 1883.E05718850615 2 1,992 10 48 16 66,845 33,422 Well 57 flow for 1885.

E08718841101 2 1,766 10 49 15 12,032 6,016 Well 87 flow for 1884.

E05318840315 2 1,535 10 50 13 22,109 11,054 Well 53 flow for 1884.E02318830804 2 1,311 10 50 14 10,203 5,102 Well 23 flow for 1883.E08018830804 2 1,657 10 50 15 17,380 8,690 Well 80 flow for 1884.E04618830701 2 1,277 10 51 13 40,107 20,053 Sum of flow for wells 41,45, 46, 47, 48, 49 for 1883.

E01718841101 2 1,766 10 51 14 41,631 20,816 Sum of flow for wells 8, 9, 14, and 19 for 1884.

E05518840615 2 1,627 10 51 15 2,888 1,444 Well 55 flow for 1884.E13218840315 2 1,535 10 52 14 1,604 802 Well 132 flow for 1884.E06218850515 2 1,961 10 52 15 6,016 3,008 Well 62 flow for 1885.

E05118841101 2 1,766 10 53 14 13,369 6,684 Well 51 flow for 1884.
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 215

Table C13. Calibrated Denver Basin model parameter values.—Continued[ft/d, feet per day; in/yr, inches per year; ft–1, per foot; ft3/d, cubic feet per day; ft2/d, square feet per day]

Parameter

name Parameter description

Parameter

value

(units)

Composite scaled

sensitivity to

all head and flow

observations

(dimensionless)

Composite scaled

sensitivity to

flow observations

(dimensionless)

Composite scaled

sensitivity to

head observations

(dimensionless)

Estimated

using

automated

methods

Hydraulic-conductivity parameters

K_Q_Platte Hydraulic conductivity of alluvial aquifer adjacent to South Platte River 

and its tributaries.

200 (ft/d) 9.42 1.16 9.58 No

K_Q_bas Hydraulic conductivity of alluvial aquifer in Big Sandy and Black 

Squirrel basins.

5.0 (ft/d) 4.02 0.025 4.09 No

K_utdw Hydraulic conductivity of silt-plus-sand fraction of upper Dawson aquifer. 4.739 (ft/d) 1.35 3.89 1.17 YesK_tdwc Hydraulic conductivity of Dawson confining unit. 1.423×10–5 (ft/d) 1.69 0.057 1.72 YesK_ltdw Hydraulic conductivity of silt-plus-sand fraction of lower Dawson aquifer. 0.2662 (ft/d) 3.59 0.23 3.65 YesK_tkduc Hydraulic conductivity of Denver upper confining unit. 1.597×10–5 (ft/d) 3.94 0.09 4.01 Yesp6_01 Hydraulic conductivity of silt-plus-sand fraction of the Denver aquifer at a 

pilot point location (fig. C3). Simulated hydraulic-conductivity distribution is determined from kriging of the point values.

3.943×10–4 (ft/d) 3.23 0.009 3.28 Yes

p6_02 6.317×10–5 (ft/d) 3.09 0.052 3.14 Yesp6_03 9.683×10–4 (ft/d) 4.57 0.022 4.65 Yesp6_04 8.815×10–5 (ft/d) 1.24 0.041 1.26 Yesp6_05 2.220×10–2 (ft/d) 4.59 0.019 4.67 Yesp6_06 8.396×10–5 (ft/d) 5.48 0.006 5.57 Yesp6_07 4.258×10–3 (ft/d) 1.25 0.027 1.27 Yesp6_08 2.618×10–5 (ft/d) 1.0 0.044 1.02 YesK_tkdlc Hydraulic conductivity of Denver lower confining unit. 9.731×10–5 (ft/d) 4.65 0.12 4.73 YespKa_02 Hydraulic conductivity of silt-plus-sand fraction of the upper Arapahoe 

aquifers at a pilot point location (fig. C3). Simulated hydraulic-conductivity distribution is determined from kriging of the point values.

1.635×10–2 (ft/d) 0.86 0.013 0.88 Yes

pKa_07 21.83 (ft/d) 4.53 0.045 4.60 YespKa_08 3.172 (ft/d) 4.43 0.19 4.51 YespKa_09 2.387×10–4 (ft/d) 0.97 0.075 0.98 YespKa_10 0.8549 (ft/d) 5.32 0.030 5.41 YespKa_11 1.469×10–3 (ft/d) 1.23 0.017 1.25 YespKa_12 1.000×10–4 (ft/d) 3.69 0.029 3.75 Yesp8_01 95.90 (ft/d) 2.12 0.27 2.16 Yesp8_03 3.305 (ft/d) 2.67 0.14 2.71 Yesp8_04 619.7 (ft/d) 5.46 0.93 5.55 Yesp8_05 0.2236 (ft/d) 4.09 0.25 4.16 Yesp8_06 8.732 (ft/d) 6.76 0.22 6.88 YesK_kac Hydraulic conductivity of Arapahoe confining unit. 1.285×10–3 (ft/d) 3.03 0.044 3.08 Yesp10_01 Hydraulic conductivity of silt-plus-sand fraction of the lower Arapahoe 

aquifers at a pilot point location (fig. C3). Simulated hydraulic-conductivity distribution is determined from kriging of the point values.

4.013×10–4 (ft/d) 1.19 1.21 Yes
216 Groundwater Availability of the Denver Basin Aquifer System, Colorado Table C13. Calibrated Denver Basin model parameter values.—Continued [ft/d, feet per day; in/yr, inches per year; ft–1, per foot; ft3/d, cubic feet per day; ft2/d, square feet per day] Parameter name Parameter description Parameter value (units) Composite scaled sensitivity to all head and flow observations (dimensionless) Composite scaled sensitivity to flow observations (dimensionless) Composite scaled sensitivity to head observations (dimensionless) Estimated using automated methods Hydraulic-conductivity parameters—Continued p10_03 7.698×10–3 (ft/d) 2.70 2.75 Yes p10_04 5.923 (ft/d) 0.98 1.00 Yes p10_05 5.434×10–4 (ft/d) 4.30 4.38 Yes p10_06 4.425 (ft/d) 5.56 5.65 Yes K_klc Hydraulic conductivity of Laramie confining unit. 1.314×10–5 (ft/d) 9.40 9.56 Yes p12_01 Hydraulic conductivity of silt-plus-sand fraction of the Laramie–Fox Hills aquifer at a pilot point location (fig. C3). Simulated hydraulic-conductivity distribution is determined from kriging of the point values. 52.18 (ft/d) 0.94 0.007 0.96 Yes p12_02 44.60 (ft/d) 2.31 0.026 2.34 Yes p12_03 2.586 (ft/d) 3.01 0.033 3.06 Yes p12_04 3.054×10–4 (ft/d) 1.77 0.002 1.80 Yes p12_05 6.177×10–2 (ft/d) 10.4 0.011 10.6 Yes p12_06 9.489 (ft/d) 2.89 0.028 2.94 Yes p12_07 4.530×10–2 (ft/d) 4.62 0.038 4.70 Yes p12_08 9.480×10–5 (ft/d) 2.98 0.038 3.03 Yes p12_09 40.39 (ft/d) 0.99 0.017 1.00 Yes p12_10 1.150×10–5 (ft/d) 1.87 0.003 1.91 Yes p12_11 3.001×10–3 (ft/d) 6.67 0.001 6.79 Yes Vertical-anisotropy parameters VANI_QPlat Ratio of horizontal to vertical hydraulic conductivity for alluvial aquifer adjacent to the South Platte River and its tributaries. 9.927 (dimensionless) 0.50 0.0013 0.51 Yes

VANI_Qbas Ratio of horizontal to vertical hydraulic conductivity of alluvial aquifer in 

Black Squirrel and Big Sandy basins.

10.0 (dimensionless) 4.34 0.003 4.42 No

VANI_BR Ratio of horizontal to vertical hydraulic conductivity for bedrock aquifers 

and confining units.

1.0 (dimensionless) 19.8 0.58 20.2 No

Recharge parameters

RCH_Qal Fraction of precipitation in area overlying the alluvial aquifer that 

becomes recharge.

7.0 (percent) 14.9 0.84 15.1 No

RCH_Tdw Fraction of precipitation in area overlying the upper and lower Dawson 

aquifers that becomes recharge.

2.026 (percent) 21.8 7.55 22.1 Yes

RCH_TKd Fraction of precipitation in area overlying the Denver aquifer that 

becomes recharge.

1.086 (percent) 6.87 0.82 6.99 Yes

RCH_Ka Fraction of precipitation in area overlying the upper and lower Arapahoe 

aquifer that becomes recharge.

1.367 (percent) 1.60 0.097 1.63 Yes

RCH_Klf Fraction of precipitation in area overlying the Laramie–Fox Hills aquifer 

that becomes recharge.

1.367 (percent) 4.32 0.006 4.39 Yes
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 217

Table C13. Calibrated Denver Basin model parameter values.—Continued[ft/d, feet per day; in/yr, inches per year; ft–1, per foot; ft3/d, cubic feet per day; ft2/d, square feet per day]

Parameter

name Parameter description

Parameter

value

(units)

Composite scaled

sensitivity to

all head and flow

observations

(dimensionless)

Composite scaled

sensitivity to

flow observations

(dimensionless)

Composite scaled

sensitivity to

head observations

(dimensionless)

Estimated

using

automated

methods

Recharge parameters—Continued

RCH_Resid Recharge rate from urban irrigation in affected areas. 2.5 (in/yr) 0.57 0.30 0.58 NoRCH_AgIrr Recharge rate from agricultural irrigation in affected areas. 10.0 (in/yr) 4.58 0.076 4.66 No

Storage parameters

SY_Qal Specific yield of the alluvial aquifer. 16.5 (percent) 6.14 0.46 6.24 NoSY_TDW Specific yield of the upper and lower Dawson aquifers. 15.2 (percent) 0.50 0.030 0.51 NoSY_TKD Specific yield of the Denver aquifer. 13.3 (percent) 2.54 0.030 2.58 NoSY_KA Specific yield of the upper and lower Arapahoe aquifers. 17.8 (percent) 0.11 0.0004 0.11 NoSY_KLF Specific yield of the Laramie–Fox Hills aquifer. 18.6 (percent) 0.25 0.0006 0.25 NoSS_coarse Specific storage of bedrock aquifers. 5.2×10–7 (ft–1) 7.85 0.071 7.99 YesSS_fine Specific storage of bedrock confining units. 1.7×10–6 (ft–1) 3.14 0.028 3.19 Yes

Pumping parameters

Q_Qal_IR Pumping rate of alluvial irrigation well. (ft3/d) 9.97 0.85 10.1 NoQ_Qal_MU Pumping rate of alluvial municipal well. (ft3/d) 0.50 0.040 0.51 NoQ_QAL_CI Pumping rate of alluvial commercial/industrial well. (ft3/d) 0.098 0.004 0.10 NoQ_BR_IR Pumping rate of bedrock irrigation well. (ft3/d) 8.60 0.170 8.75 NoQ_BR_MU Pumping rate of bedrock municipal well. (ft3/d) 8.14 0.085 8.28 NoQ_BR_CI Pumping rate of bedrock commercial/irrigation well. (ft3/d) 7.77 0.048 7.91 No

Head-dependent boundary parameters

ET_MAX Maximum allowed evapotranspiration rate. 45.0 (in/yr) 2.44 1.05 2.47 NoDRN_COND Drain conductance for springs and flowing wells. 1500 (ft2/d) 2.90 0.040 2.95 NoRIV_LAKES Conductance for River cells. 2.25 (d–1) 0.008 0.0006 0.008 NoGHB_BS_CK General-head-boundary conductance along southern model boundary represents underflow out of basin through Black Squirrel Creek alluvial aquifer. 113 (ft/d) 4.54 0.0009 4.62 NoGHB_Nuss General-head-boundary conductance along southeastern model boundary 

represents underflow out of basin through Nussbaum Alluvium.

10 (ft/d) 0.88 0.011 0.89 No

SFR_PLATTE Hydraulic conductivity of streambed materials for the South Platte River. 0.76 (ft/d) 4.20 0.026 4.27 NoSFR_TRIBS Hydraulic conductivity of streambed materials. 2.06×10–2 (ft/d) 1.38 3.25 1.27 YesSkin Well-loss coefficient for multinode wells. 2.0 (dimensionless) 0.018 0.0007 0.018 NoFLWG_WELLS Conductance. 14.00 (ft2/d) 0.042 0.21 0.016 Yes
218 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Calibrated Hydraulic-Conductivity Distribution

The calibrated hydraulic-conductivity (K) values listed 

in table C13 provide reasonable representations of the alluvial and bedrock aquifers with values in relative proportion 

to each other that are consistent with the hydrogeologic 

conceptual model presented in Chapter A. The hydraulicconductivity parameters for the alluvial aquifer were assigned 

values of 200 ft/d in the main stem of the South Platte River 

(K_Q_Platte) and 5 ft/d in the Big Sandy and Black Squirrel 

Creek Basins, such that the alluvial aquifer is one of the most 

conductive parts of the model domain. Although hydraulicconductivity parameters of the alluvial aquifer were assigned 

during parameter estimation, their values were manually 

adjusted during model calibration to obtain the final values 

and resulted in an improved model fit.

Hydraulic conductivity for the bedrock confining units 

was systematically adjusted during parameter estimation, and 

the resulting values are representative of low-conductivity 

claystone bedrock of the Denver Basin. Calibrated hydraulicconductivity values for the Dawson (K_tdwc), upper Denver 

(K_tkduc), lower Denver (K_tkdlc), and Laramie (K_klc) 

confining units were 1.4×10–5, 1.6×10–5, 9.7×10–5, and 

1.3×10–5 ft/d, respectively. The largest calibrated hydraulicconductivity value for confining units was 1.3X10–3 ft/d for 

the Arapahoe (K_kac) confining unit. The calibrated confining unit hydraulic-conductivity values are in general, several 

orders of magnitude less than hydraulic-conductivity values 

for the aquifers (table C13).

For the bedrock aquifers, hydraulic conductivity also 

was systematically adjusted during parameter estimation, 

and the resulting calibrated hydraulic-conductivity values for 

the upper and lower Dawson aquifers (K_utdw and K_ltdw, 

respectively) fit within the hydraulic-conductivity values 

estimated from aquifer tests (fig. A36). The upper Dawson 

aquifer consists of coarse-grained arkosic sand and gravel 

deposits eroded from the nearby Rocky Mountain Front Range 

and forms the D2 depositional sequence of Raynolds (2004), 

while the lower Dawson aquifer is generally considered less 

conductive than the upper Dawson (Robson, 1987) and forms 

the upper part of the D1 sequence (Raynolds, 2004). The 

calibrated hydraulic-conductivity value for the upper Dawson 

aquifer (4.7 ft/d) is in the upper 90th percentile of hydraulicconductivity values estimated from aquifer tests for the Dawson aquifer (fig. A36) and is nearly equal to that of the tributary alluvial sediments. The calibrated hydraulic-conductivity 

value for the lower Dawson aquifer (0.27 ft/d) is in the lower 

25th percentile of hydraulic-conductivity values estimated for 

the Dawson aquifer (fig. A36). The calibrated hydraulic-conductivity values for the Dawson aquifers are within the range 

of the data and fit within the conceptual understanding that 

the lower Dawson aquifer is less conductive than the upper 

Dawson aquifer.

Parameter estimation of hydraulic conductivity for the 

Denver, upper Arapahoe, lower Arapahoe, and Laramie–Fox 

Hills aquifers used pilot points and regularization. 

For the Denver aquifer, calibrated hydraulicconductivity values at the pilot points ranged from 

2.6×10–5 ft/d (logK = –4.6) at pilot point p6_08 to 2.2×10–2 ft/d 

(logK = –1.7) at pilot point p6_05 (table C13), which is in the 

lower 10th percentile of hydraulic-conductivity values estimated from aquifer tests (fig. A36). The spatial distribution of 

hydraulic conductivity derived by kriging the estimated pilotpoint values for the Denver aquifer is generally consistent with 

the spatial distribution of hydraulic conductivity estimated 

from aquifer-test results and is a reasonable representation 

of hydraulic-conductivity distribution for the Denver aquifer 

(fig. C6). The locations of maximum simulated hydraulic 

conductivity values (logK = –2.3) for the Denver aquifer in the 

western and central parts of the basin correspond to the area 

with the greatest silt-plus-sand thickness (fig. A26) and with 

the location of the Wildcat Mountain fan in the D1 synorogenic deposition sequence (Raynolds, 2004).

Calibrated hydraulic-conductivity at the pilot points 

for the upper Arapahoe ranged from 0.2 ft/d (logK = –0.7) 

at pilot point p8_05 to about 620 ft/d (logK = 2.8) at pilot 

point p8_04 (table C13). For the lower Arapahoe, calibrated 

hydraulic conductivity at the pilot points ranged from 4.0×10–4

(logK = –3.4) at pilot point p10_01 to 5.9 ft/d (logK = 0.77 at 

pilot point p10_04, and the values generally encompass the 

full range of hydraulic-conductivity values estimated from 

aquifer tests for the Arapahoe aquifers (fig. A36). Spatially, the 

greatest hydraulic-conductivity values for the lower Arapahoe 

aquifer were for the south Denver metropolitan area (fig. C7) 

and correspond to the location of the Wildcat Mountain fan 

in the D1 sequence (Raynolds, 2004). There was close correspondence between the calibrated and estimated hydraulicconductivity values in the south Denver metropolitan area and 

the northern area, although in the Monument area, the calibrated hydraulic-conductivity values were less than the values 

estimated from aquifer tests (fig. C7). 

Calibrated hydraulic conductivity at the pilot points 

for the Laramie–Fox Hills aquifer ranged from 1.2×10–5

(logK = –4.9) at pilot point p12_10 to 52 ft/d (logK = 1.7) 

at pilot point p12_01 (table C13), and the values generally 

encompass the full range of values estimated from aquifer 

tests. Spatially, the greatest calibrated hydraulic-conductivity 

values were in the eastern part of the Laramie–Fox Hills 

aquifer where there was close correspondence between the 

calibrated and estimated values (fig. C8). The correspondence 

between calibrated hydraulic-conductivity values and values 

estimated from aquifer tests for the Laramie–Fox Hills aquifer 

in the south Denver metropolitan area was variable, but in 

general, the calibrated values in this area were less than the 

values estimated from aquifer tests.
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 219

Figure C6. Calibrated hydraulic-conductivity distribution and hydraulic-conductivity values estimated 

from aquifer tests for the Denver aquifer.

DIVIDE

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Wiggins

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Lafayette

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p6_08

p6_04

p6_02

p6_06

p6_07

p6_05

p6_03

p6_01

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

Hydraulic conductivity data from Colorado Water Conservation Board, 2006

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Extent of active model cells

Logarithm of simulated hydraulic-conductivity 

 value, in feet per day

–5.3 to –5

–5 to –4.75

–4.75 to –4.5

–4.5 to –4.25

–4.25 to –4

–4 to –3.75

–3.75 to –3.5

–3.5 to –3.25

–3.25 to –3

–3 to –2.75

–2.75 to –2.5

–2.5 to –2.3

Denver aquifer simulated extent 

 (model layer 6)

Logarithm of hydraulic-conductivity 

 value from pumping, specific capacity 

 or laboratory test, in feet per day

–4 to –3

–3 to –2

–2 to –1

–1 to –0.5

–0.5 to 0

0 to 0.5

0.5 to 1

1. to 2

2 to 3

# Layer 6 pilot point
220 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C7. Calibrated hydraulic-conductivity distribution and hydraulic-conductivity values estimated 

from aquifer tests for the lower Arapahoe aquifer.

PALMER

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p10_01

p10_03

p10_04

p10_05

p10_06

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

Hydraulic conductivity data from Colorado Water Conservation Board, 2006

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Extent of active model cells

Logarithm of simulated hydraulic-conductivity 

 value, in feet per day

–4.38 to –4

–4 to –3.5

–3.5 to –3

–3 to –2.5

–2.5 to –2

–2 to –1.5

–1.5 to –1

–1 to –0.5

–0.5 to 0

0 to 0.5

0.5 to 0.902

Lower Arapahoe aquifer simulated 

 extent (model layer 10)

Logarithm of hydraulic-conductivity 

 value from pumping, specific capacity 

 or laboratory test, in feet per day

–3.5 to –3

–2.7 to –2.5

–2.0

–2.0 to –1.5

–1.5 to –1

–1 to –0.5

–0.5 to 0

0.0 to 0.5

0.5 to 1

1 to 1.6

# Layer 10 pilot point
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 221

Figure C8. Calibrated hydraulic-conductivity distribution and hydraulic-conductivity values estimated 

from aquifer tests for the Laramie–Fox Hills aquifer.

PALMER

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BROOMFIELD

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105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

Hydraulic conductivity data from Colorado Water Conservation Board, 2006

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Extent of active model cells

Logarithm of simulated hydraulic-conductivity 

 value, in feet per day

–4.373 to –4

–4 to –3.5

–3.5 to –3

–3 to –2.5

–2.5 to –2

–2 to –1.5

–1.5 to –1

–1 to –0.5

–0.5 to 0

0 to 0.5

0.5 to 0.9

Laramie–Fox Hills aquifer simulated 

 extent (model layer 12)

Logarithm of hydraulic-conductivity 

 value from pumping, specific capacity 

 or laboratory test, in feet per day

–3.4 to –3 –3 to –2.5 –2.5 to –2 –2 to –1.5 –1.5 to –1 –1 to –0.5

–0.5 to 0

0 to 0.5

0.5 to 1

1. to 1.5

1.5 to 2.4

# Layer 12 pilot point
222 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Calibrated Recharge Parameters

Some recharge parameter values were assigned while others 

were determined by parameter estimation. Assigned recharge 

parameters included the percentage of precipitation that is 

recharged to alluvial aquifers (RCH_Qal, 7 percent), the agricultural irrigation recharge rate (RCH_AgIrr, 10 in/yr), and the urban 

recharge rate (RCH_Resid, 2.5 in/yr) (table C13). Four recharge 

parameters were estimated (RCH_Tdw, RCH_TKd, RCH_Ka, 

and RCH_Klf), representing the percentage of precipitation 

that is recharged to the surface-exposed areas of the Dawson, 

Denver, Arapahoe, and Laramie–Fox Hills aquifers, respectively. 

Parameter-estimation results indicate 2 percent of precipitation 

becomes recharge for the Dawson aquifers, 1.1 percent for the 

Denver aquifer, and 1.4 percent for the Arapahoe and Laramie–

Fox Hills aquifers. The relative percentages are consistent in that 

the upper and lower Dawson aquifers are believed to receive 

greater recharge than the other bedrock aquifers because they 

are exposed at higher altitudes in the basin where precipitation is 

greatest and because they are coarser grained than the underlying 

Denver aquifer.

The spatial distribution of simulated recharge rates changed 

through time, depending on the precipitation and irrigation 

distributions for the selected stress period. The predevelopment 

recharge distribution, which includes the effects of agricultural 

recharge, is shown in figure A47 and is discussed in the section 

“Recharge and Evapotranspiration” of “Groundwater-Budget 

Components” in Chapter A of this report. The recharge distribution for 2003 at the end of the model calibration period is shown 

in figure B28, and the changes in recharge through time are 

discussed in the section “Recharge and Evapotranspiration” of 

“Groundwater-Budget Components” in Chapter B of this report.

Comparison of Simulated and 

Observed Hydraulic Heads

The overall goodness of fit of the model-computed hydraulic heads to the observation data was evaluated using summary measures and graphical analyses. The root-mean-squared 

error (RMSE), the range of head and residuals, the mean and 

distribution of residuals, the standard deviation, and the spatial 

distribution of residuals were used to evaluate the model calibration. The RMSE is a measure of the variation of the residuals 

and was calculated as (Anderson and Woessner, 1992):

RMSE

h h

N

meas sim i

i

N

=

− =

∑( ) 2

1 (5)

where

hmeas is the measured (observed) hydraulic head,

hsim is the model-computed (simulated) hydraulic 

head,

(hmeas – hsim) is the head residual,

and

N is the number of observations used in the 

computation.

Positive head residual values indicate that the simulated heads 

are lower than the observed heads, and negative head residual 

values indicate that the simulated heads are higher than the 

observed heads. If the ratio of the RMSE to the total range of 

head observations in the modeled area is small, then the error 

in the head calculations is a small part of the overall model 

response (Anderson and Woessner, 1992).

The mean residual (Rmean) is computed as:

R

h h

N mean

meas sim i

i

n

=

− =

∑( )

1 (6)

and the positive or negative sign of the mean residual indicates 

whether simulated hydraulic heads were higher or lower than 

observed hydraulic heads, respectively.

The model-computed hydraulic heads in all model 

layers were in good agreement with groundwater flow directions indicated by previous regional investigations. A simple 

method of assessing model fit is to plot the model-computed 

hydraulic head values in relation to the measured observations. 

For a perfect fit, all points should fall on the 1:1 diagonal line. 

Figure C9 presents a graph of the head observations plotted 

in relation to simulated heads for the Denver Basin model 

area and indicates reasonable model fit. The mean residual 

for the entire model is –16 ft, the median residual is –13 ft, 

and residuals range from –477 ft to 399 ft (range of 875 ft) 

(fig. C10). The residuals are biased slightly low, which indicates that simulated heads are, on average, slightly higher than 

the head observations. The standard deviation of the residuals is 82 ft, and the standard error of the mean is 1.2 ft. The 

RMSE for the entire model is 85 ft, which is about 2.8 percent 

of the 3,024-ft range of head observations in the model, and 

the head residuals appear to be independent of head observations (fig. C11).

Weighted residuals also are considered when evaluating 

model fit. Observations are weighted to convert various types 

of observations (such as heads and flows) to consistent units 

Figure C9. Head observations in relation to simulated heads for 

the Denver Basin model.

1:1 line

R2

 = 0.993

4,000

4,500

5,000

5,500

6,000

6,500

7,000

7,500

8,000

Simulated head equivalent, in feet

4,000 4,500 5,000 5,500 6,000 6,500 7,000 7,500 8,000

Observed head, in feet
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 223

Figure C10. Distribution of head residuals for the Denver Basin model.

Figure C11. Head observations in relation to head residuals for 

the Denver Basin model.

that can be squared and summed, to increase the influence of 

more accurate observations, and to decrease the influence of 

less accurate observations (Hill, 1998). For the Denver Basin 

model, head observations were weighted based on the accuracy of land-surface altitude as reported in the original data 

source. Similar to unweighted observations, when weighted 

observations are plotted in relation to weighted simulated 

values, the points should fall close to a line with slope equal to 

1.0, an intercept of zero, and a correlation coefficient near 1.0 

for a well-calibrated model (Hill, 1998). For the Denver Basin, 

a plot of weighted observations in relation to weighted-simulated equivalents (fig. C12) shows the points do fall close to 

the 1:1 line with an R-squared of 0.999. The correlation coefficient between the weighted head observations and normal 

order statistics is 0.993 (which is greater than the 5-percent 

significance level of 0.946), indicating the hypothesis that the 

weighted residuals are independent and normally distributed at 

the 5-percent significance level is valid (Hill, 1998).

The spatial distribution of head residuals for a given time 

can lend insight to any spatial bias in model calibration. In 

order to plot the spatial distribution of head residuals, head 

observations from a single time period need to be available 

for the entire modeled area. For the Denver Basin, 1978 is the 

Distribution of head residuals

–500

–400

–300

–200

–100

100

200

300

400

500

0 200 400 600 800 1,000 1,200

 Head residual, in feet

Number of residuals

–600

–500

–400

–300

–200

–100

0

100

200

300

400

500

600

Head residual, in feet

25 percent

75 percent

50 percent

90 percent

10 percent

Mean = –16 feet

Median = –13 feet

99 percent

1 percent

Minimum

Maximum

0

only time for which widespread and numerous water-level 

measurements are available, so a map of head residuals is plotted only for 1978 (fig. C13). The residual map for 1978 show 

that head residuals are randomly distributed across the study 

area with no apparent spatial bias.

100

200

300

400

500

600

4,000 4,500 5,000 5,500 6,000 6,500 7,000 7,500 8,000

Head residual, in feet

Observed head, in feet

–500

–400

–300

–200

–100

0
224 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C12. Weighted head observations in relation to simulated head for the Denver 

Basin model.

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

5,000

5,500

6,000

6,500

7,000

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 6,000 6,500 7,000

Weighted simulated head equivalent, in feet

Weighted observed head, in feet

1:1 line

R2

 = 0.999

Plots of simulated water levels over time (hydrographs) 

compared to observed values at specific sites can indicate 

how well the model represents temporal changes in hydraulic 

heads, and the results can guide future model refinements by 

identifying areas where the model did not achieve a good fit 

between simulated and observed values. Model calibration 

did not utilize water-level data from the CDWR water-level 

monitoring network (as described in the “Calibration Targets” 

section of this chapter). However, hydrographs of simulated 

and observed hydraulic heads are presented for selected wells 

in the CDWR network in the section “Changes in Hydraulic 

Heads and Groundwater Flow Directions” of Chapter B. 

There generally is good agreement between simulated and 

observed hydraulic heads for the lower Dawson (fig. B54), 

Denver (fig. B56), and Laramie–Fox Hills (fig. B64) There is 

opportunity for improvement in the match between transient 

simulated and observed hydraulic heads at selected sites for 

the lower Arapahoe aquifer (fig. B60). For the upper Dawson 

aquifer, simulation results indicate water-level declines of 

up to about 90 ft in the northern part of the aquifer and very 

little change in head for the southern part of the aquifer 

consistent with observed hydraulic-head changes. However, 

large simulated drawdown in the upper Dawson aquifer east 

of Parker was not observed in the CDWR water-level data 

(fig. B52). For the lower Arapahoe aquifer, comparisons 

between simulated and observed hydraulic heads for selected 

wells in the CDWR water-level monitoring network provide 

variable results with simulated heads being generally greater 

than measured water levels for several lower Arapahoe wells 

(fig. B60). The model appears to underestimate drawdown in 

the lower Arapahoe aquifer compared to the CDWR waterlevel data, indicating that further refinement of the hydraulicconductivity or pumping estimates might improve model 

fit for this aquifer. In an area south of Monument, observed 

water-level rise for wells completed in the Denver and lower 

Arapahoe aquifers, presumably in response to increased 

urban recharge, is not well represented in the model. Future 

modeling efforts should consider additional water-level 

data collection or refinement of model parameters in areas 

where the model did not achieve a good fit between transient simulated and observed hydraulic heads. For example, 

decreasing simulated hydraulic conductivity or increasing simulated pumping might improve the match between 

simulated and observed water-level measurements in the 

affected areas.

Comparison of Simulated and 

Observed Stream Base Flow

The simulated flows to streams and drains also were 

considered during model calibration, although the drain 

observations developed for the historical flowing wells are 

not considered accurate and were assigned small weights 

in the regression. In general, the Denver Basin simulated 

stream base-flow rates are less than those estimated from 

the streamflow data, and as with the flow estimates for 

historical flowing wells, low weights were assigned to 

the streamflow observations in the regression. A plot of 

flow observations in relation to simulated flow (fig. C14) 

indicates there is not a close 1:1 correspondence between 

observations and simulated flows. Weighted flow residuals 

are biased positively (fig. C15), the mean flow residual is 

2.83 ft3/s, and the median flow residual is 2.3 ft3/s, indicating that simulated flows are in general less than the estimated 

flow observations.
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 225

Figure C13. Spatial distribution of head residuals for the Denver Basin model, 1978.

Parameter Sensitivity

Insight into the relations among model parameters and 

simulated equivalents of observed values can be gained by 

sensitivity analysis of a calibrated model. The sensitivity analysis 

included both estimated and assigned (nonestimated) parameters 

to investigate the degree to which the model results were sensitive to parameter values. Sensitivities were quantified by using 

UCODE_2005 (Poeter and others, 2005) to calculate composite 

scaled sensitivity (CSS) (Hill and Tiedeman, 2007, p. 50) of simulated values with respect to each estimated parameter. Values of 

CSS were computed for all observations (fig. C16A) and separately for head (fig. C16B) and flow (fig. C16C) observations 

(table C13). Prior information was not considered in calculation 

of the CSS values to eliminate the effect of the regularization 

scheme on parameter sensitivities. Composite scaled sensitivity values can be interpreted as indicating the relative degree to 

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WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

!(

!(

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Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Extent of active model cells

Upper Dawson aquifer 

 head residuals, in feet

" –169 to –160.0

" –159.9 to –100.0

" –99.9 to –50.0

" –49.9 to –25.0

" –24.9 to 25.0

" 25.0 to 50.0

" 50.0 to 100.0

" 100.0 to 160.0

Lower Dawson aquifer 

 head residuals, in feet

X –332.0 to –100.0

X –99.9 to –25.0

X –24.99 to 25.0

X 25.01 to 100.0

X 100.01 to 200.0

X 200.000001 to 470.000000

Denver aquifer head 

 residuals, in feet

$ –476.6 to –300.0

$ –299.9 to –200.0

$ –199.9 to –100.0

$ –99.9 to –25.0

$ –24.9 to 25.0

$ 25.01 to 100.0

$ 100.01 to 200.0

$ 200.01 to 304.0

Lower Arapahoe aquifer 

 head residuals, in feet

# –315.0 to –200.0

# –199.9 to –100.0

# –99.9 to –25.0

# –24.9 to 25.0

# 25.01 to 100.0

# 100.01 to 226.0

Laramie–Fox Hills aquifer 

 head residuals, in feet

! –417 to –200.0

! –199.9 to –100.0

! –99.9 to –25.0

! –24.9 to 25.0

! 25.01 to 100.0

! 100.01 to 200.0

! 200.01 to 277.0
226 Groundwater Availability of the Denver Basin Aquifer System, Colorado

which information contained in the observations is useful in estimating values of individual parameters (Hill, 1998). Large CSS 

values indicate that the simulated equivalents of observations 

are sensitive to that parameter and that the observations contain 

much information for estimating a parameter. Small CSS values 

indicate that the simulated equivalents of observations are less 

sensitive to that parameter and that little information is available 

for estimating a parameter.

Simulation results are most sensitive to parameters 

representing the percentage of precipitation recharge to the 

Dawson aquifer (RCH_Tdw, estimated as 2 percent), the 

ratio of horizontal to vertical conductivity for bedrock units 

(VANI_BR, assigned a value of 1.0), and the percentage 

of precipitation recharge to the alluvial aquifer (RCH_Qal, 

assigned a value of 7 percent) on the basis of CSS values for 

all head and flow observations (fig. C16A, table C13). Other 

parameters to which the overall simulation results are sensitive, 

in decreasing order, include the hydraulic conductivity at pilot 

point p12_05 in the Laramie–Fox Hills aquifer (p12_05), irrigation pumping from the alluvial aquifer (Q_Qal_IR), hydraulic 

conductivity of the alluvial aquifer adjacent to the South Platte 

River and its tributaries (K_Q_Platte), hydraulic conductivity 

of the Laramie confining bed (K_klc), irrigation (Q_BR_IR) 

and municipal (Q_BR_MU) pumping rates for the bedrock 

aquifers, specific storage of the bedrock aquifers (SS_coarse), 

and the commercial/industrial pumping rate from the bedrock 

aquifers (Q_BR_CI) (fig. C16A, table C13). Simulation results 

are least sensitive to the urban recharge rate (RCH_Resid), 

specific yield of the Dawson aquifer (SY_TDW), the pumping 

rate for alluvial aquifer municipal wells (Q_Qal_MU), the ratio 

of horizontal to vertical hydraulic conductivity in the alluvial 

aquifer (VANI_QPlat), specific yield of the Laramie–Fox Hills 

(SY_KLF) and Arapahoe aquifers (SY_KA), the pumping rate 

for alluvial aquifer commercial/industrial wells (Q_Qal_CI), 

and conductance values for the historical flowing wells 

(FLWG_WELLS) and reservoirs (RIV_LAKES) (fig. C16A, 

table C13).

Sensitivity-analysis results indicate that simulated heads and 

flows are most sensitive to recharge rates to the Dawson and alluvial aquifers, vertical anisotropy within the bedrock units, specific 

storage of the bedrock aquifers, and pumping rates for wells with 

the greatest assigned production. Composite scaled sensitivity 

values computed from the head observations only (fig. C16B) 

exhibit a similar ranking to those computed from head and flow 

observations, reflecting the predominance of head observations 

used in model calibration. Composite scaled sensitivity values 

computed from the flow observations only (fig. C16C) indicate 

that the simulated flows are most sensitive to parameters representing the percentage of precipitation recharge to the Dawson 

aquifer (RCH_Tdw), hydraulic conductivity of the upper Dawson 

aquifer (K_utdw), and the hydraulic conductivity of streambed 

materials in tributaries (SFR_TRIBS). Additional data collection 

or refinement of these parameter values might improve the model 

fit to the observed flows.

The presence of large parameter correlation coefficients (values close to 1.0 or –1.0), generated by PEST or UCODE_2005 

for pairs of model parameters, generally indicates difficulty in 

estimating a unique set of parameter values (Hill and Tiedeman, 

2007, p. 51). Hill and Tiedeman (2007) indicate that if all correlation coefficients are less than 0.95, then it is likely that all parameter values can be estimated uniquely. The final PEST parameterestimation model execution, which involved only the estimated 

parameters values, showed that the largest parameter correlation 

coefficient is less than 0.90, which is well below the 0.95 value at 

which parameter correlation may result in nonuniqueness in the 

set of estimated parameters.

Simulated Groundwater Budgets

A groundwater flow model is a useful tool for quantifying water budgets in complex hydrologic systems such as the 

Denver Basin where hand calculations are intractable. A water 

budget calculated by any groundwater flow model that uses a 

discretized approximation of the aquifer system depends, to 

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000

Observed flow,

in thousands of cubic feet per day

–20

20

40

60

80

100

120

140

160

180

200

Simulated flow equivalent, in thousands of cubic feet per day

0

Stream base-flow observations

Historical flowing well observations

EXPLANATION

Figure C14. Flow observations in relation to simulated flows for 

the Denver Basin model.

Figure C15. Simulated equivalents in relation to weighted flow 

residuals for the Denver Basin model.

–20

–15

–10

0

5

10

15

Weighted flow residual,

in cubic feet per day –5

–20 0 20 40 60 80 100 120 140 160 180

Simulated flow equivalent,

in thousands of cubic feet per day

Stream base-flow observations

Historical flowing well observations

EXPLANATION
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 227

a certain extent, on the resolution captured in the spatial and 

temporal discretization scheme used to represent the system 

and stresses. Flow processes that cycle water between the 

groundwater system and streams on a highly localized spatial 

scale (less than about 1 mile), for example, cannot be captured 

by a system discretized into 1-mi2 cells. Similarly, seasonal 

recharge and discharge processes cannot be fully captured by 

a temporal discretization scheme in which the shortest stress 

period is 2 years. Despite these limitations, useful inferences 

can be based on the simulated groundwater budget.

For the sake of model stability and accuracy, each transient 

stress period is subdivided into multiple time steps during model 

execution; simulated stresses are constant for all time steps in 

a given stress period. The initial steady-state stress period has 

a single time step. The model-calibration period uses a total of 

77 time steps in 16 stress periods. A water budget for the entire 

groundwater system is calculated for every time step in every 

stress period of the simulation. Simulated groundwater budgets at the end of each stress period were tabulated from model 

results using the programs ZONEBUDGET (Harbaugh, 1990) 

and GW_Chart (Winston, 2000). Table C14 lists the inflows, 

table C15 lists the outflows, and table C16 lists the net flows for 

the entire model (all model layers), the alluvial aquifer (model 

layer 1), and the bedrock aquifers and confining units combined 

(model layers 2–12 combined). The water budget for the initial 

steady-state stress period represents predevelopment (pre-1880) 

conditions as discussed in the section “Predevelopment Groundwater Budget” in Chapter A. Changes to the groundwater budget 

from predevelopment through 2003 are described in the section 

“Changes to the Groundwater Budget” in Chapter B.

Simulated Hydraulic Heads

MODFLOW calculates hydraulic head at the center of 

each active cell in the model grid, and the simulated heads can 

be contoured to prepare potentiometric-surface maps for each 

aquifer model layer. Potentiometric-surface maps illustrate 

the distribution of hydraulic heads in an aquifer using contour lines of equal hydraulic head. Groundwater flows from 

areas of high hydraulic head to areas of low hydraulic head, 

in a direction generally perpendicular to contours of equal 

hydraulic head on the potentiometric-surface maps. Potentiometric-surface maps for the Denver Basin were prepared 

0

5

10

15

20

RCH_Tdw

VANI_BR

RCH_Qal

p12_05

Q_Qal_IR

K_Q_Platte

K_klc

Q_BR_IR

Q_BR_MU

SS_coarse

Q_BR_CI

RCH_TKd

p8_06

p12_11

SY_Qal

p10_06

p6_06p8_04

pKa_10

K_tkdlc

p12_07

p6_05

RCH_AgIrr

p6_03

GHB_BS_CK

pKa_07pKa_08

VANI_Qbas

RCH_Klf

p10_05

SFR_PLATTE

p8_05

K_Q_bas

K_tkduc

pKa_12

K_ltdw

p6_01

SS_fine

p6_02

K_kac

p12_03p12_08

DRN_COND

p12_06p10_03

p8_03

SY_TKD

ET_MAX

p12_02

p8_01

p12_10p12_04

K_tdwc

RCH_Ka

SFR_TRIBS

K_utdw

p6_07p6_04

pKa_11

p10_01

p6_08

p12_09p10_04

pKa_09

p12_01

GHB_Nuss

pKa_02

RCH_Resid

SY_TDW

Q_Qal_MU

VANI_QPlat

SY_KLF

SY_KA

Q_Qal_CI

FLWG_WELLS

Skin

RIV_LAKES

Composite scaled sensitivity, dimensionless 25

A

Parameter name

Parameter groups

Storage properties

EXPLANATION

Recharge

Hydraulic conductivity

Vertical anisotropy 

Head-dependent boundaries

Pumping

Figure C16. Composite scaled sensitivities for the parameters of the final calibrated Denver Basin model for (A) all head and flow 

observations; (B) head observations only; and (C) flow observations only.
228 Groundwater Availability of the Denver Basin Aquifer System, Colorado

0

5

10

15

20

25

Composite scaled sensitivity, dimensionless

RCH_Tdw

VANI_BR

RCH_Qal

p12_05

Q_Qal_IR

K_Q_Platte

K_klc

Q_BR_IR

Q_BR_MU

SS_coarse

Q_BR_CI

RCH_TKd

p8_06

p12_11

SY_Qal

p10_06

p6_06p8_04

pKa_10

K_tkdlc

p12_07

p6_05

RCH_AgIrr

p6_03

GHB_BS_CK

pKa_07pKa_08

VANI_Qbas

RCH_Klf

p10_05

SFR_PLATTE

p8_05

K_Q_bas

K_tkduc

pKa_12

K_ltdw

p6_01

SS_fine

p6_02

K_kac

p12_03p12_08

DRN_COND

p12_06p10_03

p8_03

SY_TKD

ET_MAX

p12_02

p8_01

p12_10p12_04

K_tdwc

RCH_Ka

p6_07

SFR_TRIBS

p6_04

pKa_11

p10_01

K_utdw

p6_08

p12_09p10_04

pKa_09

p12_01

GHB_Nuss

pKa_02

RCH_Resid

SY_TDW

Q_Qal_MU

VANI_QPlat

SY_KLF

SY_KA

Q_Qal_CI

FLWG_WELLS

RIV_LAKES

Parameter name

B

Skin

Parameter groups

Storage properties

EXPLANATION

Recharge

Hydraulic conductivity

Vertical anisotropy 

Head-dependent boundaries

Pumping

Figure C16. Composite scaled sensitivities for the parameters of the final calibrated Denver Basin model for (A) all head and flow 

observations; (B) head observations only; and (C) flow observations only.—Continued

for each model aquifer layer (layers 1, 2, 4, 6, 8, 10, and 12) 

for predevelopment (pre-1880), 1956, 1978, and 2003 conditions. The predevelopment (pre-1880) potentiometric-surface 

maps are presented in the section “Predevelopment Hydraulic 

Heads and Groundwater Flow Directions” in Chapter A. 

Potentiometric-surface maps for each model layer are presented for 1956, 1978, and 2003 (figs. C17–C37) and include 

the distribution of simulated cell-by-cell pumping for the 

corresponding time. Drawdown of potentiometric surfaces and 

changes in groundwater flow directions caused by development are described in the section “Changes in Hydraulic 

Heads and Groundwater Flow Directions” in Chapter B.

Predictive Simulations

Two predictive scenarios were simulated with the 

calibrated Denver Basin model to calculate predictive model 

sensitivities and to demonstrate use of the model for predictive analysis. Predictive simulations were run 50 years 

into the future from the end of the model calibration period 

(December 31, 2003) to 2053 and were divided into ten 5-year 

stress periods (table C17). The predictive simulations lend 

insight to long-term effects of continued pumping on the 

groundwater system, although they are not considered definitive predictions of future conditions. Detailed discussion of the 

prediction results including water budget, hydraulic head, and 

predictive sensitivity are presented in the section “Simulated

Predictions of Future Conditions” in Chapter B.

Model-Based Statistical Evaluation 

of Potential Monitoring Locations

Model parameters, which can be readily adjusted during 

calibration, are subject to uncertainty that can be quantified 

with model statistics. These parameters include hydraulicconductivity values assigned to aquifers and pilot points, rates 

of recharge and discharge (precipitation, irrigation, withdrawal 

from wells), and degree of hydraulic connection between the 

groundwater system and surface water. Observed values used 
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 229

0

1

2

3

4

5

6

7

8

RCH_Tdw

K_utdw

SFR_TRIBS

K_Q_Platte

ET_MAX

p8_04

Q_Qal_IR

RCH_Qal

RCH_TKd

VANI_BR

SY_Qal

RCH_Resid

p8_01p8_05

K_ltdw

p8_06

FLWG_WELLS

pKa_08

Q_BR_IR

p10_06

p8_03

K_tkdlc

RCH_Ka

K_tkduc

Q_BR_MU

RCH_AgIrr

pKa_09

SS_coarse

K_tdwc

p10_03

p6_02

Q_BR_CI

pKa_07

K_kac

p6_08p6_04

DRN_COND

Q_Qal_MU

p12_08p12_07p12_03

SY_TKD

SY_TDW

pKa_10pKa_12

p12_06

SS_fine

p6_07

SFR_PLATTE

p12_02

K_Q_bas

p6_03

p10_05

p6_05

p10_04

pKa_11

p12_09

K_klc

pKa_02

p12_05

GHB_Nuss

p6_01

p12_01

p6_06

RCH_Klf

Q_Qal_CI

p12_10p10_01

VANI_Qbas

p12_04p12_11

VANI_QPlat

GHB_BS_CK

Skin

SY_KLF

RIV_LAKES

SY_KA

Composite scaled sensitivity, dimensionless

Parameter name

C

Parameter groups

Storage properties

EXPLANATION

Recharge

Hydraulic conductivity

Vertical anisotropy 

Head-dependent boundaries

Pumping

Figure C16. Composite scaled sensitivities for the parameters of the final calibrated Denver Basin model for (A) all head and flow 

observations; (B) head observations only; and (C) flow observations only.—Continued

as calibration targets also have associated uncertainties, which 

are characterized by observation weights. Estimated uncertainties related to model parameters and observed values can be 

used to evaluate the part of prediction uncertainty not associated with the conceptual model and model discretization.

One benefit of the automated techniques used to calibrate 

the Denver Basin model is that the results can be used in an 

analysis of the relations among uncertainties in parameters, 

observations, and predictions. Hill and Tiedeman (2007) 

describe the Observation-Prediction (OPR) and ParameterPrediction (PPR) statistics, which quantify these relations. The 

OPR statistic quantifies the decrease in prediction uncertainty 

caused by addition or omission of an observation. The PPR 

statistic quantifies the decrease in prediction uncertainty 

caused by improved information for a parameter. The program 

OPR-PPR (Tonkin and others, 2007) is a model-analysis tool 

designed to calculate the OPR and PPR statistics. OPR-PPR 

also calculates the Observation-Parameter (OPA) statistic, which quantifies the relation of observations and their 

uncertainties to parameter uncertainty. OPR-PPR uses existing 

and potential additional observations and their assigned 

weights, sensitivities of simulated equivalents to observations 

with respect to parameters, sensitivities of predictions with 

respect to parameters, and other information to calculate 

these statistics.

When OPR-PPR calculates OPR statistics, it evaluates 

one potential observation at a time to determine its effect on 

reducing the uncertainty of each prediction or each group of 

predictions. The OPR statistic, which is calculated for each 

potential observation, is the percent reduction in uncertainty 

that would be expected due to the addition of the potential 

observation. The PPR statistic is an indicator of the value 

of improved information about a selected parameter with 

respect to a prediction or prediction group. PPR is defined as 

the percent change in prediction standard deviation resulting 

from decreasing the standard deviation of the parameter value 

by 10 percent. OPR-PPR calculates the PPR statistic for each 

prediction for each parameter. The OPA statistic is defined as 

the percent change in parameter standard deviation caused by 

omitting or adding an observation.
230 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Alluvial aquifer Inflows (ft3/s)

Stress period Time step Year Recharge Streams Reservoirs Multinode 

wells

Flow from 

bedrock units Storage Total inflow

1 1 1879 454.4 12.69 0.0 0.0 34.1 0.0 501.1

2 6 1906 454.4 12.69 0.0 0.0 34.1 0.0 501.1

3 5 1919 454.4 12.72 22.5 0.0 33.9 0.1 523.7

4 5 1939 454.4 12.59 22.6 0.0 33.8 0.6 523.9

5 5 1953 454.5 12.92 38.1 0.0 33.7 5.1 544.5

6 5 1956 511.4 12.47 38.3 0.0 33.8 17.1 613.1

7 5 1961 523.3 13.14 38.3 0.0 33.4 14.0 622.2

8 5 1964 476.6 13.41 38.9 0.0 32.5 42.6 604.0

9 5 1971 509.7 13.77 38.7 0.0 32.3 19.4 614.0

10 5 1973 509.6 19.79 41.5 0.0 31.8 21.3 623.9

11 5 1978 486.0 19.56 41.6 0.0 30.7 33.8 611.8

12 5 1984 528.7 19.86 41.5 0.0 29.9 8.9 628.8

13 5 1986 528.7 19.98 41.5 0.0 29.4 9.9 629.4

14 5 1994 604.7 20.09 37.9 0.0 29.4 6.9 699.1

15 5 1999 619.9 20.12 38.0 0.0 28.6 4.3 711.0

16 5 2003 592.7 20.05 38.1 0.0 27.2 11.4 689.6

Bedrock units Inflows (ft3/s)

Stress period Time step Year Recharge Streams Reservoirs Multinode

wells

Flow from 

alluvial aquifer Storage Total inflow

1 1 1879 176.0 3.49 0.0 0.0 7.8 0.0 187.3

2 6 1906 176.0 3.49 0.0 0.0 7.8 0.0 187.3

3 5 1919 176.0 3.50 0.0 0.0 8.0 0.7 188.2

4 5 1939 178.9 3.51 0.0 7.1E-6 7.9 0.8 191.2

5 5 1953 185.4 3.55 0.0 1.0E-5 7.7 1.7 198.4

6 5 1956 226.1 3.19 0.11 3.4E-4 7.8 2.5 239.6

7 5 1961 234.8 3.21 0.13 7.6E-3 7.9 3.1 249.2

8 5 1964 205.1 3.66 0.14 0.03 7.6 16.9 233.5

9 5 1971 231.7 3.48 0.15 0.08 8.5 7.9 251.8

10 5 1973 231.8 3.52 0.16 0.09 8.7 12.4 256.7

11 5 1978 214.6 3.78 0.20 0.14 8.9 24.8 252.4

12 5 1984 234.4 3.68 0.22 0.24 9.9 21.4 269.9

13 5 1986 234.4 3.73 0.23 0.26 10.3 27.7 276.6

14 5 1994 311.1 3.80 3.61 0.36 11.0 30.9 360.8

15 5 1999 319.5 3.96 3.62 0.45 11.8 39.6 378.9

16 5 2003 300.8 4.20 3.66 0.59 12.4 60.2 381.8

Table C14. Simulated transient inflows for the Denver Basin entire modeled area, alluvial aquifer, and bedrock units, 1879–2003.

[ft3/s, cubic feet per second]

Entire modeled area Inflows (ft3/s)

Stress period Time step Year Recharge Streams Reservoirs Multinode

wells Storage Total inflow

1 1 1879 630.3 16.18 0.0 0.0 0.0 646.5

2 6 1906 630.3 16.18 0.0 0.0 0.0 646.6

3 5 1919 630.3 16.22 22.5 0.0 0.9 670.0

4 5 1939 633.3 16.11 22.6 7.1E-6 1.5 673.4

5 5 1953 639.9 16.48 38.1 1.0E-5 6.9 701.4

6 5 1956 737.5 15.66 38.5 3.4E-4 19.6 811.1

7 5 1961 758.1 16.36 38.5 7.6E-3 17.1 830.1

8 5 1964 681.7 17.07 39.0 0.03 59.5 797.3

9 5 1971 741.4 17.25 38.9 0.08 27.3 824.9

10 5 1973 741.4 23.31 41.7 0.09 33.7 840.2

11 5 1978 700.6 23.34 41.8 0.14 58.7 824.6

12 5 1984 763.1 23.54 41.7 0.24 30.4 859.0

13 5 1986 763.1 23.71 41.7 0.26 37.6 866.3

14 5 1994 915.9 23.89 41.5 0.36 37.9 1019.5

15 5 1999 939.4 24.08 41.6 0.45 43.9 1049.5

16 5 2003 893.5 24.25 41.8 0.59 71.6 1031.7
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 231

Table C15. Simulated transient outflows for the Denver Basin entire modeled area, alluvial aquifer, and bedrock units, 1879–2003.

[ft3/s, cubic feet per second; ET, evapotranspiration]

Entire modeled area Outflows (ft3/s)

Stress

period

Time

step Year ET Streams Reservoirs Springs

Head

dependent

boundaries

Specified

flow Wells

Multinode

wells

Storage Total

outflow

1 1 1879 441.6 181.8 0.00 4.21 4.80 14.11 0.0 0.0 0.0 646.5

2 6 1906 441.5 181.8 0.00 4.23 4.80 14.11 0.1 0.0 0.0 646.6

3 5 1919 462.3 181.9 0.00 4.20 4.80 14.11 2.4 0.0 0.1 670.0

4 5 1939 459.9 180.3 0.00 4.19 4.80 14.11 9.9 3.8E-4 0.2 673.4

5 5 1953 457.3 175.0 1.88 4.17 4.80 14.11 43.9 2.2E-2 0.3 701.4

6 5 1956 470.4 179.1 1.85 4.32 4.80 14.11 94.4 6.6E-2 42.1 811.1

7 5 1961 469.5 183.0 1.80 4.41 4.83 14.11 120.8 0.50 31.1 830.1

8 5 1964 436.7 178.2 1.62 4.02 4.77 14.11 143.9 0.84 13.3 797.3

9 5 1971 440.5 179.8 1.48 4.13 4.71 14.11 171.0 1.10 8.0 824.9

10 5 1973 436.7 179.6 10.4 4.08 4.68 14.11 183.3 1.44 5.9 840.2

11 5 1978 416.1 176.1 10.1 3.82 4.57 14.11 195.7 2.13 1.9 824.6

12 5 1984 427.7 178.9 9.9 3.95 4.53 14.11 208.2 2.65 9.0 859.0

13 5 1986 426.1 178.4 9.9 3.93 4.52 14.11 219.0 3.06 7.4 866.3

14 5 1994 527.3 187.5 11.3 4.44 4.55 14.11 233.5 4.01 32.7 1019.5

15 5 1999 540.5 188.5 11.3 4.48 4.58 14.11 255.3 5.07 25.8 1049.5

16 5 2003 523.0 184.1 11.0 4.22 4.48 14.11 276.2 6.30 8.3 1031.7

Alluvial aquifer Outflows (ft3/s)

Stress

period

Time

step Year ET Streams Reservoirs Springs

Head

dependent

boundaries

Specified

flow Wells

Multinode

wells

Flow to

bedrock

units

Storage Total

outflow

1 1 1879 307.1 164.2 0.0 3.18 4.80 14.11 0.0 0.0 7.79 0.0 501.1

2 6 1906 307.0 164.2 0.0 3.18 4.80 14.11 4.9E-2 0.0 7.80 0.0 501.1

3 5 1919 328.1 164.3 0.0 3.18 4.80 14.11 1.1 0.0 7.96 0.1 523.7

4 5 1939 323.1 162.7 0.0 3.17 4.80 14.11 7.8 0.0 7.95 0.2 523.9

5 5 1953 315.5 157.1 1.9 3.15 4.80 14.11 39.9 0.0 7.75 0.2 544.5

6 5 1956 303.1 158.8 1.9 3.12 4.80 14.11 86.1 0.0 7.76 33.5 613.1

7 5 1961 296.8 162.1 1.8 3.12 4.83 14.11 106.8 6.7E-4 7.86 24.7 622.2

8 5 1964 279.2 159.2 1.6 3.02 4.77 14.11 123.7 8.3E-4 7.62 10.8 604.0

9 5 1971 273.3 159.4 1.5 2.95 4.71 14.11 143.6 8.3E-4 8.50 5.9 614.0

10 5 1973 270.9 159.2 10.4 2.94 4.68 14.11 148.5 8.3E-4 8.75 4.5 623.9

11 5 1978 260.3 157.1 10.1 2.87 4.57 14.11 152.4 3.5E-2 8.87 1.5 611.8

12 5 1984 265.3 159.3 9.9 2.91 4.53 14.11 155.9 4.5E-2 9.92 7.0 628.8

13 5 1986 264.4 158.9 9.9 2.91 4.52 14.11 158.7 4.8E-2 10.30 5.7 629.4

14 5 1994 303.2 166.1 11.3 2.96 4.55 14.11 162.1 5.1E-2 10.96 23.7 699.1

15 5 1999 311.9 167.0 11.2 3.00 4.58 14.11 168.1 5.6E-2 11.78 19.3 711.0

16 5 2003 304.9 164.3 11.0 2.95 4.48 14.11 170.8 6.0E-2 12.43 4.5 689.6

Bedrock units Outflows (ft3/s)

Stress

period

Time

step Year ET Streams Reservoirs Springs

Head

dependent

boundaries

Specified

flow Wells

Multinode

wells

Flow to

alluvial

aquifer

Storage Total

outflow

1 1 1879 134.5 17.65 0.0 1.03 0.0 0.00 0.0 0.0 34.1 0.0 187.3

2 6 1906 134.5 17.64 0.0 1.06 0.0 0.00 7.82E-2 0.0 34.1 0.0 187.3

3 5 1919 134.3 17.61 0.0 1.02 0.0 0.00 1.3 0.0 33.9 0.0 188.2

4 5 1939 136.8 17.57 0.0 1.02 0.0 0.00 2.0 3.8E-4 33.8 0.0 191.2

5 5 1953 141.8 17.88 0.0 1.02 0.0 0.00 4.0 2.2E-2 33.7 0.0 198.4

6 5 1956 167.3 20.24 0.0 1.20 0.0 0.00 8.4 6.6E-2 33.8 8.6 239.6

7 5 1961 172.7 20.82 0.0 1.28 0.0 0.00 14.0 0.50 33.4 6.4 249.2

8 5 1964 157.4 18.95 0.0 1.00 0.0 0.00 20.2 0.84 32.5 2.5 233.5

9 5 1971 167.2 20.41 0.0 1.18 0.0 0.00 27.4 1.10 32.3 2.1 251.8

10 5 1973 165.8 20.33 0.0 1.14 0.0 0.00 34.9 1.44 31.8 1.4 256.7

11 5 1978 155.8 19.06 0.0 0.95 0.0 0.00 43.3 2.09 30.7 0.4 252.4

12 5 1984 162.4 19.57 0.0 1.04 0.0 0.00 52.4 2.60 29.9 2.0 269.9

13 5 1986 161.7 19.47 0.0 1.02 0.0 0.00 60.3 3.01 29.4 1.7 276.6

14 5 1994 224.1 21.37 1.0E-2 1.48 0.0 0.00 71.4 3.96 29.4 9.1 360.8

15 5 1999 228.6 21.51 1.1E-2 1.48 0.0 0.00 87.2 5.02 28.6 6.5 378.9

16 5 2003 218.1 19.86 8.4E-3 1.28 0.0 0.00 105.4 6.24 27.2 3.7 381.8
232 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Alluvial aquifer Net flows (ft3/s)

Stress period Time step Year Net

recharge

Net

reservoir inflow

Net

stream outflow

Net

well outflow

Change

in storage

1 1 1879 147.3 0.0 –151.5 0.0 26.31 0.0

2 6 1906 147.4 0.0 –151.5 –0.0 26.28 0.0

3 5 1919 126.3 22.5 –151.6 –1.1 25.97 0.0

4 5 1939 131.2 22.6 –150.1 –7.8 25.89 0.4

5 5 1953 139.0 36.3 –144.2 –39.9 25.97 4.9

6 5 1956 208.3 36.5 –146.3 –86.1 26.02 –16.4

7 5 1961 226.5 36.5 –149.0 –106.8 25.56 –10.7

8 5 1964 197.3 37.3 –145.8 –123.7 24.92 31.8

9 5 1971 236.4 37.2 –145.7 –143.6 23.85 13.5

10 5 1973 238.8 31.1 –139.4 –148.5 23.01 16.8

11 5 1978 225.7 31.6 –137.5 –152.4 21.84 32.3

12 5 1984 263.4 31.6 –139.4 –155.9 19.94 2.0

13 5 1986 264.3 31.6 –138.9 –158.7 19.09 4.2

14 5 1994 301.5 26.6 –146.0 –162.2 18.44 –16.7

15 5 1999 308.0 26.8 –146.9 –168.1 16.85 –15.0

16 5 2003 287.8 27.1 –144.2 –170.9 14.80 6.9

Bedrock units Net flows (ft3/s)

Stress period Time step Year Net

recharge

Net

reservoir inflow

Net

stream outflow

Net

well outflow

Change

in storage

1 1 1880 41.5 0.0 –14.16 0.0 –26.31 0.0

2 6 1906 41.5 0.0 –14.15 –0.1 –26.28 0.0

3 5 1919 41.7 0.0 –14.11 –1.3 –25.97 0.7

4 5 1939 42.2 0.0 –14.05 –2.0 –25.89 0.8

5 5 1953 43.6 0.0 –14.33 –4.0 –25.97 1.7

6 5 1956 58.8 0.1 –17.05 –8.4 –26.02 –6.2

7 5 1961 62.1 0.1 –17.61 –14.5 –25.56 –3.3

8 5 1964 47.7 0.1 –15.29 –21.0 –24.92 14.4

9 5 1971 64.5 0.2 –16.93 –28.4 –23.85 5.8

10 5 1973 66.0 0.2 –16.81 –36.2 –23.01 11.0

11 5 1978 58.8 0.2 –15.28 –45.3 –21.84 24.4

12 5 1984 72.0 0.2 –15.89 –54.7 –19.94 19.4

13 5 1986 72.7 0.2 –15.73 –63.0 –19.09 25.9

14 5 1994 87.0 3.6 –17.57 –75.0 –18.44 21.9

15 5 1999 90.9 3.6 –17.55 –91.8 –16.85 33.1

16 5 2003 82.7 3.6 –15.66 –111.0 –14.80 56.5

Table C16. Simulated transient net water budget for the Denver Basin entire modeled area, alluvial aquifer, and bedrock units, 1879–2003.

[ft3/s, cubic feet per second]

Entire modeled area Net flows (ft3/s)

Stress period Time step Year Net

recharge

Net

reservoir inflow

Net

stream outflow

Net

well outflow

Change

in storage

1 1 1879 188.8 0.0 –165.7 0.0 0.0

2 6 1906 188.9 0.0 –165.6 –0.1 0.0

3 5 1919 168.0 22.5 –165.7 –2.4 0.7

4 5 1939 173.4 22.6 –164.2 –9.9 1.2

5 5 1953 182.6 36.3 –158.5 –43.9 6.6

6 5 1956 267.0 36.6 –163.4 –94.5 –22.5

7 5 1961 288.6 36.7 –166.6 –121.3 –14.0

8 5 1964 245.1 37.4 –161.1 –144.7 46.2

9 5 1971 300.9 37.4 –162.6 –172.0 19.3

10 5 1973 304.8 31.2 –156.2 –184.7 27.8

11 5 1978 284.4 31.8 –152.8 –197.7 56.7

12 5 1984 335.4 31.8 –155.3 –210.6 21.4

13 5 1986 337.0 31.8 –154.6 –221.7 30.1

14 5 1994 388.5 30.2 –163.6 –237.2 5.2

15 5 1999 399.0 30.4 –164.4 –259.9 18.2

16 5 2003 370.4 30.8 –159.9 –281.9 63.4
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 233

Figure C17. Simulated 1956 potentiometric surface and pumping rates for the alluvial aquifer 

(model layer 1).

South Platte River

Cac he la Poudre R

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand

Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

Middle Rush Creek

Mustang Creek

Adobe Cree

St

k

eels Fork

Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

Bi g Thompson River

PALMER

DIVIDE

PALMER

DIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

6,100

5,900

6,200

6,000

6,300

6,400

6,500

5,800

5,700

6,000

5,900

6,300

6,100

5,900

6,200

6,000

6,300

6,400

6,500

5,800

4,700

4,800

4,400

5,000

4,900

4,600

4,700

4,800

4,700

4,800

4,400

5,000

5,700

4,900

4,600

5,100

5,200

4,900

4,800

4,900

4,600

4,900

4,600

5,000

4,700

5,000

5,000

4,900

5,100

5,200

4,600

5,700

5,800

6,000

6,300

6,200

4,900

6,000

4,800

4,900

5,900

4,600

6,000

4,900

4,600

4,700

6,300

5,000

4,800

6,300

4,700

5,000

5,000

4,900

6,200

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1956. 

 Datum NAVD88. Contour interval 100 feet

Perennial

Ephemeral

Stream

Alluvial aquifer simulated extent (model layer 1)

Extent of active model cells

Alluvial aquifer simulated pumping, 

 1956, in cubic feet per second

EXPLANATION

–0.89 to –0.75

–0.75 to –0.5

–0.5 to –0.25

–0.25 to –0.1

0

<–0.1
234 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C18. Simulated 1978 potentiometric surface and pumping rates for the alluvial aquifer 

(model layer 1).

South Platte River

Cac he la Poudre R

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brackett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

Big Thompso n River

PALMER

DIVIDE

PALMER

DIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

6,100

5,900

6,200

6,000

6,300 6,400

6,500

5,800

5,700

6,000

5,900

6,300

6,100

5,900

6,200

6,000

6,300 6,400

6,500

5,800

4,700

4,800

4,400

5,000

4,900

4,600

4,800

4,700

4,800

4,400

5,000

5,700

4,900

4,600

5,100

4,600

4,600

4,700

5,200

4,600

4,900

4,800

4,900 4,900

4,700

5,000

5,000

4,900

5,200

4,600

5,700

5,800

6,000

6,300

6,200

4,900

6,000

4,800

4,900

5,900

4,600

6,000

4,900

4,600

4,700

6,300

5,000 4,800

6,300

4,700

5,000

5,000

4,900

6,200

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1978. 

 Datum NAVD88. Contour interval 100 feet

Perennial

Ephemeral

Stream

Alluvial aquifer simulated extent (model layer 1)

Extent of active model cells

Alluvial aquifer simulated pumping, 

 1978, in cubic feet per second

–1.2 to –1

–1 to –0.75

–0.75 to –0.5

–0.5 to –0.25

<–0.25

0
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 235

Figure C19. Simulated 2003 potentiometric surface and pumping rates for the alluvial aquifer 

(model layer 1).

PALMER

DIVIDE

PALMER

DIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

South Platte River

Cac he la Poudre R

Big Thompson Riv er

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

Middle Rush Creek

Mustang Creek

Adobe Cree

St

k

eels Fork

Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

6,100

5,900

6,200

6,000

6,300

6,400

6,500

5,800

5,700

6,000

6,300

5,900

6,100

5,900

6,200

6,000

6,300

6,400

6,500

4,700

4,800

5,000

4,900

4,600

4,700

4,800

4,700

5,800

4,800

5,000

5,700

4,900

4,600

5,100

5,200

4,600

4,900 4,900

4,900

4,600

4,600

5,000

4,900

4,800

4,700

5,200

4,600

5,700

6,000

6,300

5,800

6,000

4,900

6,300

4,900

4,900

4,600

6,000

4,600

5,000

4,700

4,800

4,900

5,900

4,800

4,700

5,000

6,300

5,800

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 100 feet

Alluvial aquifer simulated extent (model layer 1)

Extent of active model cells

Alluvial aquifer simulated pumping, 2003, 

 in cubic feet per second

EXPLANATION

–1.6 to –1.25

–1.25 to –1

–1.0 to –0.75

–0.75 to –0.5

–0.5 to –0.25

<–0.25

0
236 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C20. Simulated 1956 potentiometric surface and pumping rates for the upper Dawson aquifer 

(model layer 2).

PALMER

DIVIDE

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Coal Creek

Clear Creek

West Sand Creek

First Cree

Sa

k

nd Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Cr

Antelope Cr

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

§ ̈¦25

6,700

6,600

6,800

6,500

6,900

6,400

6,100

6,300

7,000

6,200

6,000

7,100

5,900

6,700

6,600

6,800

6,500

6,900

6,400

6,100

6,300

7,000

6,200

6,000

7,100

5,900

6,800

105° 104°30'

39°30'

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1956. 

 Datum NAVD88. Contour interval 100 feet

Extent of active model cells

Layer 2 simulated pumping, Upper Dawson aquifer simulated extent (model layer 2)

 1956, in cubic feet per second

–0.035 to –0.025

–0.025 to –0.01

<–0.01

0

0 5 10 MILES

0 5 10 KILOMETERS
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 237

Figure C21. Simulated 1978 potentiometric surface and pumping rates for the upper Dawson aquifer 

(model layer 2).

PALMER

DIVIDE

PALMER

DIVIDE

Coal Creek

Clear Creek

West Sand Creek

First Cree

S

k

and Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Cr

Antelope Cr

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr

Cherry Cr

Kettle Cr

Cook Creek Dry Cr

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

§ ̈¦25

6,700

6,600

6,800

6,500

6,900

6,200

6,400

6,300

7,000

6,100

6,000

7,100

5,900

7,200

5,800

6,800

6,700

6,600

6,800

6,500

6,900

6,200

6,400

6,300

7,000

6,100

6,000

7,100

5,900

7,200

5,800

6,800

105° 104°30'

39°30'

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

EXPLANATION

Layer 2 simulated pumping, 

 1978, in cubic feet per second

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1978. 

 Datum NAVD88. Contour interval 100 feet

–0.17 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Upper Dawson aquifer simulated extent (model layer 2)

0 5 10 MILES

0 5 10 KILOMETERS
238 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C22. Simulated 2003 potentiometric surface and pumping rates for the upper Dawson aquifer 

(model layer 2).

DIVIDE

PALMERPALMER DIVIDE

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Coal Creek

Wolf Creek

Clear Creek

We st Sand Creek

First Creek

Sand Creek

Little Dry Creek

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Comanche Creek

Rock Cr

Antelope Cr

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brac kett Creek

Black Squirrel Creek

West Kiowa Creek

Cherry Creek

Kettle Creek

Cook Creek Dry Cr

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

§ ̈¦25

6,700

6,600

6,800

6,500

6,900

6,200

6,400

6,300

7,000

6,100

6,000

7,100

5,900

7,200

5,800

6,800

6,700

6,600

6,800

6,500

6,900

6,200

6,400

6,300

7,000

6,100

6,000

7,100

5,900

7,200

5,800

6,800

105° 104°30'

39°30'

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 100 feet

–0.19 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Layer 2 simulated pumping, Upper Dawson aquifer simulated extent (model layer 2)

 2003, in cubic feet per second

0 5 10 MILES

0 5 10 KILOMETERS
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 239

Figure C23. Simulated 1956 potentiometric surface and pumping rates for the lower Dawson 

aquifer (model layer 4).

PALMER DIVIDE

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Coal Creek

Wolf Creek

Clear Creek

We st Sand Creek

First Creek

Sand Creek

Little Dry Creek

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiowa Creek

Comanche Creek

Rock Cr

Antelope Cr

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brac kett Creek

Black Squirrel Creek

West Kiowa Creek

Cherry Creek

Kettle Creek

Cook Creek Dry Cr

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

§ ̈¦25

6,100

6,200

6,400

6,500

6,600

6,700

6,800

6,000

6,900

7,000

7,100

5,900

5,800

7,200

5,700

7,300

7,400

5,600

6,800

5,900

6,500

6,900

6,000

6,700

6,100

6,200

6,400

6,500

6,600

6,700

6,800

6,000

6,900

7,000

7,100

5,900

5,800

7,200

5,700

7,300

7,400

5,600

6,800

5,900

6,500

6,900

6,900

5,900

6,000

6,700

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1956. 

 Datum NAVD88. Contour interval 100 feet

–0.11 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Lower Dawson aquifer simulated extent (model layer 4)

Layer 4 simulated pumping, 

 1956, in cubic feet per second

Dawson confining unit simulated extent (model layer 3)
240 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C24. Simulated 1978 potentiometric surface and pumping rates for the lower Dawson 

aquifer (model layer 4).

PALMER DIVIDEPALMER DIVIDE

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Coal Creek

Wolf Creek

Clear Creek

We st Sand Creek

First Cree

S

k

and Creek

Little Dry Creek

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiowa Creek

Comanche Creek

Rock Cr

Antelope Cr

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brac kett Creek

Black Squirrel Creek

West Kiowa Creek

Cherry Creek

Kettle Creek

Cook Creek Dry Cr

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

§ ̈¦25 6,100

6,200

6,400

6,500

6,000

6,600

6,800

6,700

6,900

7,000

7,100

5,900

5,800

7,200

5,700

7,300

7,400

5,600

6,900

6,500

6,600

6,700

6,100

6,200

6,400

6,500

6,000

6,600

6,800

6,700

6,900

7,000

7,100

5,900

5,800

7,200

5,700

7,300

7,400

5,600

6,900

6,500

6,600

6,700

6,900

6,700

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1978. 

 Datum NAVD88. Contour interval 100 feet

–0.25 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Lower Dawson aquifer simulated extent (model layer 4)

Layer 4 simulated pumping, 

 1978, in cubic feet per second 

Dawson confining unit simulated extent (model layer 3)
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 241

Figure C25. Simulated 2003 potentiometric surface and pumping rates for the lower Dawson aquifer 

(model layer 4).

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

EL PASO

ELBERT

ADAMS

ARAPAHOE

TELLER

JEFFERSON

DENVER

BROOMFIELD

DOUGLAS

Coal Creek

Wolf Creek

Clear Creek

We st Sand Creek

First Cree

S

k

and Creek

Little Dry Creek

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry Creek

Kiowa Creek

Comanche Creek

Rock Cr

Antelope Cr

Steels Fork

Horse Creek

West Bijou Cree k

Big Sandy Cree k

Brac kett Creek

Black Squirrel Creek

West Kiowa Creek

Cherry Creek

Kettle Creek

Cook Creek Dry Cr

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

Kiowa

Parker

Golden

Calhan

Denver

Bennett

Morrison

Lakewood

Monument

Franktown

Elizabeth

Broomfield

Castle

Rock

Highlands

Ranch

Colorado

Springs

Aurora

Littleton

Englewood

§ ̈¦25

6,200

6,000

6,400

6,500

6,600

6,800

6,700

7,000

6,900

5,800

5,900

7,100

7,200

5,700

7,300

7,400

5,600

6,000

6,700

5,900

7,200

6,900

6,600

5,600

6,900

6,800

6,900

6,500

6,200

6,000

6,400

6,500

6,600

6,800

6,700

7,000

6,900

5,800

5,900

7,100

7,200

5,700

7,300

7,400

5,600

6,000

6,700

5,900

7,200

6,900

6,600

5,600

6,900

6,800

6,900

6,500

DIVIDE

PALMERPALMER

DIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 100 feet

–0.37 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Lower Dawson aquifer simulated extent (model layer 4)

Layer 4 simulated pumping, 

 2003, in cubic feet per second

Dawson confining unit simulated extent (model layer 3)
242 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C26. Simulated 1956 potentiometric surface and pumping rates for the Denver aquifer 

(model layer 6).

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

6,100

6,300

5,900

6,000

6,400

5,800

5,400

6,200

5,700 5,600

5,300

5,500

5,200

6,500 6,600

6,900

6,800

6,700

7,000

5,100

7,100

7,200

7,300

7,400

6,700

5,500

5,500

5,500

5,100

5,500

6,600

6,500

5,400

6,000

6,300

6,200

6,400

6,200

5,500

6,100

6,300

5,900

6,000

6,400

5,800

5,400

6,200

5,700 5,600

5,300

5,500

5,200

6,500 6,600

6,900

6,800

6,700

7,000

5,100

7,100

7,200

7,300

7,400

6,700

5,500

5,500

5,500

5,100

5,500

6,600

6,500

5,400

6,000

6,300

6,200

6,400

6,200

5,500

PALMER

DIVIDE

PALMER

DIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1956. 

 Datum NAVD88. Contour interval 100 feet

–0.25 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Denver aquifer simulated extent (model layer 6)

Layer 6 simulated pumping, 

 1956, in cubic feet per second

Denver upper confining unit simulated extent (model layer 5)
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 243

Figure C27. Simulated 1978 potentiometric surface and pumping rates for the Denver aquifer 

(model layer 6).

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

South Platte River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou Creek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

6,100

6,300

5,900

6,400

6,000

5,800

5,400

5,700

6,200

5,600

5,500

5,300

6,500

5,200

6,600

5,100

6,900

6,800

6,700

7,000 7,100

7,200

7,300

7,400

5,100

6,700

5,200

6,800

5,500

5,500

5,500

6,300

6,200

6,200

5,300

6,500

6,800

6,700

6,000

6,400

5,500

6,000

5,400

5,500

6,100

6,300

5,900

6,400

6,000

5,800

5,400

5,700

6,200

5,600

5,500

5,300

6,500

5,200

6,600

5,100

6,900

6,800

6,700

7,000 7,100

7,200

7,300

7,400

5,100

6,700

5,200

6,800

5,500

5,500

5,500

6,300

6,200

6,200

5,300

6,500

6,800

6,700

6,000

6,400

5,500

6,000

5,400

5,500

PALMER

DIVIDE

PALMER

DIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1978. 

 Datum NAVD88. Contour interval 100 feet

–0.31 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Denver aquifer simulated extent (model layer 6)

Layer 6 simulated pumping, 

 1978, in cubic feet per second

Denver upper confining unit simulated extent (model layer 5)
244 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C28. Simulated 2003 potentiometric surface and pumping rates for the Denver aquifer 

(model layer 6).

PALMER

DIVIDE

PALMER

DIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

South Platte River

Cac he la Poudre R

Big Thompson River Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

6,300

6,100

5,900

6,000

5,800

6,400

5,700

6,200

5,600

5,400

5,500

5,300

5,200

6,500

5,100

6,900

6,600

7,000

6,800

6,700

7,100

7,200

6,200

6,700

6,600

5,500

5,600

7,000

6,300

6,500

6,200

6,400

6,700

6,200

6,900

6,700

6,000

5,200

6,700

5,500

5,400

6,500

6,700

6,300

6,100

5,900

6,000

5,800

6,400

5,700

6,200

5,600

5,400

5,500

5,300

5,200

6,500

5,100

6,900

6,600

7,000

6,800

6,700

7,100

7,200

6,200

6,700

6,600

5,500

5,600

7,000

6,300

6,500

6,200

6,400

6,700

6,200

6,900

6,700

6,000

5,200

6,700

5,500

5,400

6,500

6,700

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 100 feet

–0.31 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Denver aquifer simulated extent (model layer 6)

Layer 6 simulated pumping, 

 2003, in cubic feet per second

Denver upper confining unit simulated extent (model layer 5)
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 245

Figure C29. Simulated 1956 potentiometric surface and pumping rates for the upper Arapahoe 

aquifer (model layer 8).

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

PALMER

DIVIDEDIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,300

5,200

5,100

5,400

5,000

5,600

5,000

5,400

5,000

5,300

5,200

5,100

5,400

5,000

5,600

5,000

5,400

5,000

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1956. 

 Datum NAVD88. Contour interval 100 feet

–0.175 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Layer 8 simulated pumping, Upper Arapahoe aquifer simulated extent (model layer 8)

 1956, in cubic feet per second
246 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C30. Simulated 1978 potentiometric surface and pumping rates for the upper Arapahoe 

aquifer (model layer 8).

South Platte River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryC

P

r

lum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

PALMER

DIVIDEDIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,200

5,100

5,300

5,400

5,000

5,300

5,000

5,000

5,200

5,100

5,300

5,400

5,000

5,300

5,000

5,000

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1978. 

 Datum NAVD88. Contour interval 100 feet

–0.24 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Layer 8 simulated pumping, Upper Arapahoe aquifer simulated extent (model layer 8)

 1978, in cubic feet per second
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 247

Figure C31. Simulated 2003 potentiometric surface and pumping rates for the upper Arapahoe 

aquifer (model layer 8).

South Platte

River

Cac he la Poudre R

Big Thompson River Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

PALMER

DIVIDEDIVIDE

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,200

5,100

5,300

5,400

5,000

5,300

5,000

5,000

5,200

5,100

5,300

5,400

5,000

5,300

5,000

5,000

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 100 feet

–0.31 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Layer 8 simulated pumping, Upper Arapahoe aquifer simulated extent (model layer 8)

 2003, in cubic feet per second
248 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C32. Simulated 1956 potentiometric surface and pumping rates for the lower Arapahoe 

aquifer (model layer 10).

South Platte

River

Cac he la Poudre R

Big Thompson River Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

PALMER

DIVIDEDIVIDE

5,400

6,000

5,300

5,900

5,600

5,800

5,200

6,100

5,500

5,700

6,200

5,100

6,300

6,400

6,500

6,600

5,000

6,700

6,800

6,900

7,000

4,900

7,100

7,200

7,300

4,800

7,400

5,700

6,200

4,900

6,000

5,000

6,000

5,900

5,000

6,100

5,500

5,900

5,500

5,900

5,700

5,000

5,400

6,000

5,300

5,900

5,600

5,800

5,200

6,100

5,500

5,700

6,200

5,100

6,300

6,400

6,500

6,600

5,000

6,700

6,800

6,900

7,000

4,900

7,100

7,200

7,300

4,800

7,400

5,700

6,200

4,900

6,000

5,000

6,000

5,900

5,000

6,100

5,500

5,900

5,500

5,900

5,700

5,000

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands 

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1956. 

 Datum NAVD88. Contour interval 100 feet

–0.31 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Lower Arapahoe aquifer simulated extent (model layer 8)

Layer 8 simulated pumping, 

 1956, in cubic feet per second

Overlying confining units simulated extent (model layers 7 and 9)
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 249

Figure C33. Simulated 1978 potentiometric surface and pumping rates for the lower Arapahoe 

aquifer (model layer 10).

South Platte

River

Cac he la Poudre R

Big Thompson River Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryC

P

r

lum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,300

6,000

5,400

5,600

5,900

5,200

5,800

6,100

5,500

5,700

6,200

5,100

6,300

6,400

6,500

6,600

5,000

6,700

6,800

7,000

6,900

4,900

7,100

7,200

7,300

4,800

5,700

5,900

5,700

6,200

5,500

5,500

6,000

5,900

4,900

6,000

5,000

5,000

5,900

6,100

5,000

5,300

6,000

5,400

5,600

5,900

5,200

5,800

6,100

5,500

5,700

6,200

5,100

6,300

6,400

6,500

6,600

5,000

6,700

6,800

7,000

6,900

4,900

7,100

7,200

7,300

4,800

5,700

5,900

5,700

6,200

5,500

5,500

6,000

5,900

4,900

6,000

5,000

5,000

5,900

6,100

5,000

PALMER

DIVIDEDIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1978. 

 Datum NAVD88. Contour interval 100 feet

–0.25 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Lower Arapahoe aquifer (model layer 10) simulated extent

Layer 10 simulated pumping, Overlying confining units (model layers 7 and 9) simulated extent

 1978, in cubic feet per second
250 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C34. Simulated 2003 potentiometric surface and pumping rates for the lower Arapahoe 

aquifer (model layer 10).

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,300

5,400

6,000

5,600

5,900

5,200

5,500

5,800

6,100

5,700

6,200

5,100

6,300

6,400

5,000

6,500

6,600

6,700

6,900

6,800

7,000

4,900

7,100

7,200

7,300

4,800

7,400

5,700

5,500

4,900

5,000

5,400

5,900

6,900

6,200

5,700

5,900

6,000

5,000

5,900

6,100

5,900

5,300

5,400

6,000

5,600

5,900

5,200

5,500

5,800

6,100

5,700

6,200

5,100

6,300

6,400

5,000

6,500

6,600

6,700

6,900

6,800

7,000

4,900

7,100

7,200

7,300

4,800

7,400

5,700

5,500

4,900

5,000

5,400

5,900

6,900

6,200

5,700

5,900

6,000

5,000

5,900

6,100

5,900

PALMER

DIVIDEDIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 100 feet

–0.41 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Lower Arapahoe aquifer simulated extent (model layer 10)

Layer 10 simulated pumping, Overlying confining units simulated extent (model layers 7 and 9)

 2003, in cubic feet per second
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 251

Figure C35. Simulated 1956 potentiometric surface and pumping rates for the Laramie–Fox Hills 

aquifer (model layer 12).

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,400

5,300

5,200

5,100

5,600

5,700

5,800

5,900

5,000

4,800

5,500

4,900

4,700

6,000

4,600

6,100

6,200

6,400

6,300

6,500 6,600

6,700

6,800

6,900

7,000 7,100

4,500

7,200

7,300

7,400

4,400

5,600

5,700

6,000

4,900

5,600

6,300

5,800

4,400

5,400

4,600

5,000

5,700

5,700

5,900

5,500

4,600

5,500

5,900

5,400

5,300

5,200

5,100

5,600

5,700

5,800

5,900

5,000

4,800

5,500

4,900

4,700

6,000

4,600

6,100

6,200

6,400

6,300

6,500 6,600

6,700

6,800

6,900

7,000 7,100

4,500

7,200

7,300

7,400

4,400

5,600

5,700

6,000

4,900

5,600

6,300

5,800

4,400

5,400

4,600

5,000

5,700

5,700

5,900

5,500

4,600

5,500

5,900

PALMER

DIVIDEDIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1956. 

 Datum NAVD88. Contour interval 100 feet

–0.06 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Layer 12 simulated pumping, Laramie confining units simulated extent (model layer 11)

 1956, in cubic feet per second
252 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C36. Simulated 1978 potentiometric surface and pumping rates for the Laramie–Fox Hills 

aquifer (model layer 12).

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

Broomfield

Lafayette

DOUGLAS

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,300

5,200

5,100

5,600

5,700

5,400

5,800

5,900

5,000

4,800

5,500

4,900

4,700

6,000

4,600

6,100

6,300

6,200

6,400

6,500

6,600

6,700

6,800

6,900

7,000

7,100

4,500

7,200

7,300

7,400

5,800

4,600

5,900

5,000

5,000

5,600

6,000

4,800

4,900

5,900

5,800

5,700

5,500

5,500

5,000

6,200

6,600

5,800 5,700

5,700

4,600

5,300

5,200

5,100

5,600

5,700

5,400

5,800

5,900

5,000

4,800

5,500

4,900

4,700

6,000

4,600

6,100

6,300

6,200

6,400

6,500

6,600

6,700

6,800

6,900

7,000

7,100

4,500

7,200

7,300

7,400

5,800

4,600

5,900

5,000

5,000

5,600

6,000

4,800

4,900

5,900

5,800

5,700

5,500

5,500

5,000

6,200

6,600

5,800 5,700

5,700

4,600

PALMER

DIVIDEDIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 1978. 

 Datum NAVD88. Contour interval 100 feet

–0.14 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Layer 12 simulated pumping, Laramie confining units simulated extent (model layer 11)

 1978, in cubic feet per second
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 253

Figure C37. Simulated 2003 potentiometric surface and pumping rates for the Laramie–Fox Hills 

aquifer (model layer 12).

South Platte River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Lafayette

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

§ ̈¦70

§ ̈¦25

§ ̈¦76

5,100

5,200

5,600

5,700

5,800

5,900

5,300

5,000

5,400

4,800

4,900

5,500

4,700

6,000

4,600

6,200 6,100

6,300

6,400

6,500

6,600

6,700

6,800

6,900

7,000

4,500

7,100

7,200

7,300

7,400

4,800

4,900

5,400

6,000

4,900

6,800

4,600

5,000

7,000

6,600

5,400

5,900

5,800

5,700

5,600

4,600

4,600

5,100

5,000

6,700

5,500

5,200

5,900

5,700

5,100

5,200

5,600

5,700

5,800

5,900

5,300

5,000

5,400

4,800

4,900

5,500

4,700

6,000

4,600

6,200 6,100

6,300

6,400

6,500

6,600

6,700

6,800

6,900

7,000

4,500

7,100

7,200

7,300

7,400

4,800

4,900

5,400

6,000

4,900

6,800

4,600

5,000

7,000

6,600

5,400

5,900

5,800

5,700

5,600

4,600

4,600

5,100

5,000

6,700

5,500

5,200

5,900

5,700

PALMER

DIVIDEDIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

Simulated potentiometric contour, shows altitude at which 

 water level would have stood in tightly cased wells, 2003. 

 Datum NAVD88. Contour interval 100 feet

–0.18 to –0.1

–0.1 to –0.05

–0.05 to –0.025

–0.025 to –0.01

<–0.01

0

Extent of active model cells

Laramie–Fox Hills aquifer simulated extent (model layer 12)

Layer 12 simulated pumping, Laramie confining units simulated extent (model layer 11)

 2003, in cubic feet per second
254 Groundwater Availability of the Denver Basin Aquifer System, Colorado

For the Denver Basin model, the potentiometric surface 

for the lower Arapahoe aquifer at the end of the prediction 

period (2053) was identified as being of predictive interest. To 

characterize the simulated potentiometric surface, a subset of 

the model layer representing the lower Arapahoe aquifer was 

selected for analysis (layer 10). A uniformly distributed subset 

of cells was established by selecting all cells for which row and 

column indices are evenly divisible by 5. Head predictions at 

the resulting 184 cells were defined as a prediction group in 

OPR-PPR. Potential head observations were defined for the end 

of the calibration period at all active cells in the seven layers 

representing aquifers (layers 1, 2, 4, 6, 8, 10, and 12). Maps of 

the PPR statistic values for a selected parameter can be used 

to identify areas where prediction uncertainty would be most 

effectively decreased as a result of improved information about 

the parameter. The PPR values for all parameters in the Denver 

Basin model were averaged over all 184 predictions, and the 

resulting averages were used to rank the parameters. The 10 

parameters with the highest PPR statistic values (out of a total 

of 75 parameters) are listed in table C18, and maps of PPR 

statistic values for the four highest-ranked parameters (p12_10, 

p12_09, and pKa_11 ) are presented in figures C38–C40. The 

darkest colors on the maps of PPR statistics identify areas where 

additional information about the indicated parameter would 

most effectively decrease prediction uncertainty for hydraulic 

heads in the lower Arapahoe aquifer. Additional information about parameter p12_10 (hydraulic conductivity of the 

Laramie–Fox Hills aquifer at pilot point p12_10) would most 

reduce uncertainty of predicted heads in the lower Arapahoe 

aquifer in the eastern and southern parts of the basin (fig. C38). 

Additional information about parameter p12_09 (hydraulic 

conductivity of the Laramie–Fox Hills aquifer at pilot point 

p12_09) would most reduce uncertainty of predicted heads in 

the lower Arapahoe aquifer in the south-central part of the basin 

(fig. C39). Additional information about parameter pKa_11 

(hydraulic conductivity of the lower Arapahoe aquifer at pilot 

point pKa_11) would most reduce uncertainty of predicted 

heads in the lower Arapahoe aquifer in the eastern and northern 

parts of the basin (fig. C40).

Maps of the OPA statistic values for a selected parameter 

can be used to identify areas where parameter uncertainty 

would be most effectively decreased by adding an observation 

(in this case, a head observation). Figures C41–C44 illustrate 

OPA statistic values for the four highest-ranked parameters for 

potential additional head observations in the lower Arapahoe 

aquifer. The darkest colors on these maps identify areas where 

the standard deviation of the specified parameter would be most 

effectively decreased by an additional head observation. Results 

indicate additional head observations in the northern part of the 

basin would decrease parameter uncertainty for all four of the 

highest-ranked parameters. Additional observations in the lower 

Arapahoe aquifer in the south Denver metropolitan area and the 

Monument area, where future development and drawdown are 

anticipated, also would reduce parameter uncertainty.

Table C17. Denver Basin model predictive simulation stress periods.

Predictive

stress period

number

Beginning of 

stress period

End of 

stress period

Stress period 

length

(days)

1 January 1, 2004 December 31, 2008 1,826

2 January 1, 2009 December 31, 2013 1,826

3 January 1, 2014 December 31, 2018 1,826

4 January 1, 2019 December 31, 2023 1,826

5 January 1, 2024 December 31, 2028 1,826

6 January 1, 2029 December 31, 2033 1,826

7 January 1, 2034 December 31, 2038 1,826

8 January 1, 2039 December 31, 2043 1,826

9 January 1, 2044 December 31, 2048 1,826

10 January 1, 2049 December 31, 2053 1,826

Table C18. Parameters with the highest ranking parameter-prediction (PPR) statistic values from the Denver Basin model.

Rank Parameter 

name Parameter description

 Parameter-prediction 

statistic average value

(percent)

1 p12_10 Hydraulic conductivity of silt-plus-sand sized fraction of the Laramie–Fox Hills aquifer 

(model layer 12) at pilot point 10.

2.99

2 p12_11 Hydraulic conductivity of silt-plus-sand sized fraction of the Laramie–Fox Hills aquifer 

(model layer 12) at pilot point 9.

2.44

3 p12_09 Hydraulic conductivity of silt-plus-sand sized fraction of the Laramie–Fox Hills aquifer 

(model layer 12) at pilot point 11.

1.86

4 pKa_11 Hydraulic conductivity of silt-plus-sand sized fraction of the upper and lower Arapahoe 

aquifer (model layers 8 and 10) at pilot point 11.

1.74

5 SS_all Specific storage of bedrock aquifers. 1.03

6 Q_BR_MU Pumping-rate factor for bedrock municipal wells. 0.93

7 RCH_Qal Fraction of precipitation in areas where alluvial aquifer is the uppermost hydrogeologic 

unit that becomes recharge.

0.81

8 p6_04 Hydraulic conductivity of silt-sized and coarser fraction of Denver aquifer (model layer 6) 

at pilot point 4.

0.81

9 RCH_Resid Recharge rate applied for urban/suburban irrigation return flow. 0.51

10 p10_03 Hydraulic conductivity of silt-sized and coarser fraction of lower Arapahoe aquifer (model 

layer 10) at pilot point 3.

0.49
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 255

Figure C38. Parameter-prediction statistic (PPR) distribution for parameter p12_10.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

§ ̈¦70

§ ̈¦25

§ ̈¦76

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

6 8

4

2

0

10

0

2

0

2 8

0

8

6

4

2

0

0

4

0

4

2

0 2

2

6

4

0

0

6 8

4

2

0

10

0

2

0

2 8

0

8

6

4

2

0

0

4

0

4

2

0 2

2

6

4

0

0

PALMER

DIVIDEDIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Line of equal Prediction-Parameter (PPR) statistic for pilot 

 point P_12_10, in percent. Contour interval 2 percent

Stream

Perennial

Ephemeral

Extent of active model cells

Lower Arapahoe aquifer simulated extent (model layer 10)
256 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C39. Parameter-prediction statistic (PPR) distribution for parameter p12_09.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryC

P

r

lum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

4

2

8

6

0

-2

10

–2

0

6

0

2 0

8 4

0

0

2

0

–2

4

2

8

6

0

-2

10

–2

0

6

0

2 0

8 4

0

0

2

0

–2

PALMER

DIVIDEDIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Line of equal Prediction-Parameter (PPR) statistic for pilot 

 point P12_09, in percent. Contour interval 2 percent

Stream

Perennial

Ephemeral

Extent of active model cells

Lower Arapahoe aquifer simulated extent (model layer 10)
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 257

Figure C40. Parameter-prediction statistic (PPR) distribution for parameter pKa_11.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Engelwood

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

2

4

0

0

2

0

0

0

2

0

2

4

0

0

2

4

0

0

2

0

0

0

2

0

2

4

0

0

PALMER

DIVIDEDIVIDE

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Line of equal Prediction-Parameter (PPR) statistic for pilot 

 point pKa_11, in percent. Contour interval 2 percent

Stream

Perennial

Ephemeral

Extent of active model cells

Lower Arapahoe aquifer simulated extent (model layer 10)
258 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C41. Observation-parameter (OPA) statistic distribution for parameter p12_10.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryC

P

r

lum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

Muddy Creek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

PALMER

DIVIDEDIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

–2.4 to –2

–2 to –1.5

–1.5 to –1

–1 to –0.5

–0.5 to –0.2

–0.2 to –0.1

–0.1 to –0.05

–0.05 to –0.01

–0.01 to 0

Extent of active model cells

Lower Arapahoe aquifer simulated extent 

 (model layer 10) 

Observation parameter (OPA) statistic

 in model layer 10 for pilot point P12_10,

 in percent
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 259

Figure C42. Observation-parameter (OPA) statistic distribution for parameter p12_09.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lo st Creek

PALMER

DIVIDEDIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton 

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

–11.5 to –10

–10 to –8

–8 to –6

–6 to –4

–4 to –2

–2 to –1

–1 to –0.5

–0.5 to –0.2

–0.2 to –0.1

–0.1 to –0.01

–0.01 to 0

Extent of active model cells

Lower Arapahoe aquifer simulated extent 

 (model layer 10)

Observation parameter (OPA) statistic

 in model layer 10 for pilot point P12_09,

 in percent
260 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C43. Observation-parameter (OPA) statistic distribution for parameter pKa_11.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryCr

Plum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

PALMER

DIVIDEDIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

–2.2 to –2

–2 to –1.5

–1.5 to –1

–1 to –0.5

–0.5 to –0.1

–0.1 to –0.05

–0.05 to –0.01

–0.01 to 0

Extent of active model cells

Lower Arapahoe aquifer simulated extent 

 (model layer 10)

Observation parameter (OPA) statistic

 in model layer 10 for pilot point pKa_11,

 in percent
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 261

Figure C44. Observation-parameter (OPA) statistic distribution for parameter p10_03.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryC

P

r

lum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

PALMER

DIVIDEDIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

–38 to –20

–20 to –10

–10 to –5

–5 to –2.5

–2.5 to –1

–1 to –0.5

–0.5 to –0.01

–0.01 to 0

Extent of active model cells

Lower Arapahoe aquifer simulated extent 

 (model layer 10)

Observation parameter (OPA) statistic

 in model layer 10 for pilot point P10_03,

 in percent
262 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Maps of the OPR statistic values can be used to identify 

areas where additional head observations likely would be most 

beneficial in reducing the uncertainty in the simulated potentiometric surface and drawdown. The OPR statistic values 

in the analysis were averaged over all 184 predictions, and a 

map of the values was prepared on a cell-by-cell basis for each 

model layer. Maps of the OPR statistic for the lower Arapahoe 

aquifer (fig. C45) and the Laramie–Fox Hills aquifer (fig. C46) 

indicate two general areas where additional head observations 

in the respective aquifer likely would reduce the uncertainty 

of the simulated potentiometric surface of the lower Arapahoe 

aquifer. One area is in the north-central part of the basin near 

the Adams and Weld County boundary, and the second area 

is in the south-central part of the basin where future development and drawdown are expected. Maps of OPR statistics for 

layers overlying the lower Arapahoe aquifer tend to have areas 

of high and low values in the same locations as for the lower 

Arapahoe (fig. C45).

Interpretation of the OPR statistic maps is aided by considering maps of the other statistics calculated by OPR-PPR. 

The OPR statistic combines uncertainty information about all 

parameters and all existing and potential observations. Reduction of uncertainty for a parameter with large areas of large 

PPR values (for example, fig. C38) will reduce the uncertainty 

of the predictions more than will reduction of uncertainty for 

a parameter with smaller PPR values. If comparing the OPA 

and PPR maps for a given parameter, no spatial correlation 

between areas of large OPA statistic and areas of large PPR 

statistic is apparent. However, the PPR maps do provide an 

indication of the degree to which the corresponding OPA distribution contributes to the OPR map; that is, parameters with 

large areas of large PPR values will cause the corresponding 

OPA distributions to be represented more prominently in the 

OPR distribution. For example, the area of large OPA values along the border between Adams and Weld Counties in 

figures C41–C44 is important to several parameters that rank 

high in PPR statistic value; as a result, this area shows up as 

the most prominent feature on the OPR map for the lower 

Arapahoe aquifer (fig. C45).

The maps resulting from the OPR analysis (figs. C45, 

C46) can be interpreted as showing areas where additional 

data would be most valuable in terms of reducing uncertainty 

of predicted heads in the Arapahoe aquifer; to use a common 

term, these are “data gap” areas. The largest and most prominent of these features is along the border between Adams and 

Weld Counties; less prominent features are in central Adams 

and north-central Elbert Counties. Each of these features of 

elevated OPR statistics is in or immediately adjacent to an 

area overlain by the alluvial aquifer. The elevated-OPR feature 

along the Adams-Weld border is closely associated with the 

alluvium of Box Elder Creek. The feature in central Adams 

County is at a location where the alluvium of the Lost Creek 

Basin connects with the alluvium of the Kiowa Creek Basin. 

The feature in north-central Elbert County is in and adjacent 

to the alluvium of West Bijou Creek. The association of large 

OPR statistic values with the alluvial aquifer in these areas is 

interpreted as an indication of uncertainty in the simulation of 

conditions at and adjacent to the bedrock/alluvium interface in 

these areas. Future modeling efforts likely would benefit from 

additional hydraulic-head data collection and more detailed 

characterization of hydraulic connection between alluvial and 

bedrock aquifers in these areas.

Comparisons Between Current 

and Previous Models

Differences in methods used to represent the hydrogeologic framework and hydrologic stresses complicate 

comparisons between the current Denver Basin model and 

previous models. However, some comparisons of the methods and results are warranted as general measures of how 

well the model fits the current conceptual understanding of 

the hydrologic system. Major refinements used in the current model compared to previous models included (1) a fully 

three-dimensional representation of the aquifer system, which 

includes explicit definition of all Denver Basin aquifer and 

confining layers; (2) explicit representation of the alluvial 

aquifer system as the uppermost layer in the model; (3) use of 

streamflow-routing simulation capabilities (SFR2, Niswonger 

and Prudic, 2005) to represent streams; (4) inclusion of 

evapotranspiration as a boundary condition (ETS, Banta, 

2000); and (5) updated pumping estimates to include pumping 

from the alluvial aquifer. In addition, recharge from urban and 

agricultural irrigation return flows is included in the current 

model, whereas previous models simulated only precipitation 

recharge.

The current 12-layer model explicitly represents the 

alluvial aquifer (model layer 1) and each of bedrock aquifers 

(6 model layers) and confining units (5 model layers). Previous models used a quasi-three-dimensional approach, which 

represented confining layers by using a vertical-conductance 

formulation. The current model assumes no vertical anisotropy 

within bedrock model layers, such that hydraulic conductivity of confining units controls vertical flow between model 

layers. Previous models used vertical-conductance variables 

to control vertical flow between bedrock aquifers. For the 

current study, the geometric mean of calibrated horizontal 

hydraulic-conductivity values (equal to vertical hydraulicconductivity values) for the Dawson and Denver confining 

units is about 3×10–5 ft/d (about 1.0×10–8 cm/s), and the 

values are in the range of values used by previous models 

(Robson, 1987; Colorado Division of Water Resources, 1998; 

table C19). The confining-unit hydraulic-conductivity values used in the present study also are in the range of vertical 

hydraulic conductivities reported by Barkmann (2004) and 

are considered reasonable values of low-conductivity materials for the current model. For the Laramie confining unit, 

Robson (1987) assumed zero vertical flow from the Arapahoe 
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 263

Figure C45. Observation-prediction (OPR) statistic distribution for the lower Arapahoe aquifer.

South Platte

River

Cac he la Poudre R

Big Thompson River

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Cree

L

k

ittle DryC

P

r

lum Creek West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Creek

Steels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

PALMER

DIVIDEDIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

0 to 0.005

0.005 to 0.01

0.01 to 0.02

0.02 to 0.05

0.05 to 0.075

0.075 to 0.1

0.1 to 0.125

0.125 to 0.145

Extent of active model cells

Observation prediction (OPR) statistic for

 model layer 10, in percent

Lower Arapahoe aquifer simulated extent 

 (model layer 10)
264 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Figure C46. Observation-prediction (OPR) statistic distribution for the Laramie–Fox Hills aquifer.

South Platte

River

Cac he la Poudre R

Little ThompsonR

Boulder C r Coal Creek

Big D ry

Cr Clear Creek

West Sand Creek

First Cree k

Sand Creek

Little DryC

P

r

lum Creek

West P ul m Creek

Bear Creek

Running

Creek

Dry

Creek

Kiow a Creek

Wolf Creek

Comanche Creek

Rock Creek

MuddyCreek

Badger C reek

Bijou C reek

Antelope Cr

Middle Bijou Creek

East BijouCreek

Middle Rush Creek

Mustang Creek

Adobe Cree

S

k

teels Fork

Horse Creek

West Bijou Cree k Big Sandy Cree k

Brac kett Cr

Black Squirrel Creek

West Kiowa Cr Cherry Cr

Kettle Cr

Cook Creek Dry Cr

Fountain Cree k

Saint Vrain Creek

Box Elder Creek

Lost Creek

Big Thompson R

PALMER

DIVIDEDIVIDE

!(

!(

!(

!(

!(

!(

!(

!( !( !(

!(

!(

!(

!(

!( !(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

WELD

EL PASO

ELBERT

LINCOLN

LARIMER

ADAMS

MORGAN

BOULDER

ARAPAHOE

TELLER

JEFFERSON

WASHINGTON

DENVER

BROOMFIELD

DOUGLAS

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Limon

Simla

Kiowa

Parker

Golden

Calhan

Denver

Greeley

Boulder

Bennett

Loveland

Morrison

Lakewood

Monument

Longmont

Brighton

Franktown

Elizabeth

Broomfield

Deer

Trail

Fort

Lupton

Fort

Morgan

Castle

Rock

Highlands

Ranch

Colorado

Springs

Wiggins

Aurora

Littleton

Lafayette

Englewood

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

Barr 

Lake

Milton

Reservoir

Chatfield

Reservoir

Aurora

Reservoir

Cherry Creek

Reservoir

§ ̈¦70

§ ̈¦25

§ ̈¦76

105° 104°

40°

39°

Base from U.S. Geological Survey digital data, 2009, 1:100,000

Lambert Conformal Conic projection (Colorado State Plane Central)

Standard parallels 38°27'N and 37°45'N, central meridian 105°00'W

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Stream

Perennial

Ephemeral

0 to 0.001

0.001 to 0.0025

0.0025 to 0.005

0.005 to 0.01

0.01 to 0.025

0.025 to 0.05

0.05 to 0.075

0.075 to 0.1

Laramie–Fox Hills aquifer simulated extent

 (model layer 12)

Extent of active model cells

Observation prediction (OPR) statistic for model

 layer 12, in percent
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 265

Table C19. Comparison of vertical hydraulic-conductivity values between the current and previous Denver Basin models.

[NA, not applicable – parameter not included in model; ft/d, feet per day; CDWR, Colorado Division of Water Resources]

Between aquifers

(confining unit in current model)

Current model 

calibrated values

(ft/d)

Robson (1987)

(ft/d)

Banta (1989)

(ft/d)

CDWR (1998)

(ft/d)

Upper Dawson–lower Dawson (Dawson confining unit) 1.4×10–5 NA NA 5.0×10–3

Dawson–Denver (Denver upper confining unit) 1.6×10–5 3.5×10–5 4.1×10–5 5.0×10–5

Denver–upper Arapahoe (Denver lower confining unit) 9.7×10–5 2.6×10–5 1.3×10–5 5.0×10–5

Upper Arapahoe–lower Arapahoe (Arapahoe confining unit) 1.3×10–3 NA NA 5.0×10–4

Arapahoe–Laramie–Fox Hills (Laramie confining unit 1.3×10–5 0 6.2×10–7 6.2×10–8

to the underlying Laramie–Fox Hills aquifer, while the 

CDWR SB96–74 model used a small, but non-zero, vertical 

hydraulic conductivity of 6.2×10–8 ft/d (Colorado Division of 

Water Resources, 1998). The calibrated hydraulic conductivity for the Laramie confining unit in the current model was 

1.3×10–5 ft/d, which allows a reasonable amount of downward 

flow of downward flow from the Laramie confining bed to the 

Laramie–Fox Hills aquifer (about 7 ft3/s for predevelopment 

conditions; fig. A54).

The differences among vertical hydraulic-conductivity 

values used by the various models, combined with variation 

in the methods used to simulate predevelopment recharge 

and evapotranspiration, affect the groundwater budget and 

interaquifer flow calculated by each model (table C20). For 

the Dawson aquifers and confining units, predevelopment 

inflow from the surficial system (precipitation recharge, 

streams, and the alluvial aquifer) recharge simulated by the 

current study (35.3 ft3/s) was about 14 percent less than the 

value of 40.6 ft3/s simulated by the Robson (1987) model and 

about 30 percent less than the values of 47.7 ft3/s simulated by 

the CDWR SB96–74 model; table C20). However, a revised 

model calibration of the CDWR SB96–74 model resulted in 

an inflow rate to the Dawson aquifers of 37 ft3/s (Colorado 

Division of Water Resources, 1998), which is within 5 percent 

of the current calibrated model. Predevelopment interaquifer 

flow from the Dawson aquifers and confining unit to the 

underlying Denver units computed by the current model was 

5.8 ft3/s, which is about 20 percent less than the value computed by the Robson model (7.2 ft3

/s) and about 50 percent 

less than the value computed by the CDWR SB96–74 model 

(9.4 ft3/s) (table C20). The water budget and interaquifer flow 

simulated by the current model for the Denver aquifer and 

confining units are about five times greater than the water budget and interaquifer flow simulated by previous models (table 

C20) because the current model simulates recharge from precipitation and historical agricultural irrigation return flows to 

the Denver aquifer and confining units. Previous models simulated only precipitation recharge. The increased recharge in the 

current model results in increased outflow to the surficial system and increased downward interaquifer flow from the Denver aquifer as compared to previous models. Unlike previous 

models, the current model also simulates evapotranspiration 

from the water table. The combination of increased recharge 

in historically irrigated areas and the associated increased discharge to evapotranspiration simulated by the current model 

results in a much larger total water budget for the current study 

(187 ft3/s) compared to the range for previous models (54.7 

to 60.9 ft3/s) (Colorado Division of Water Resources, 1998) 

(table C20). Furthermore, the increased recharge to the Denver 

aquifer simulated by the current model, in addition to the differences in vertical hydraulic conductivities, results in greater 

simulated downward interaquifer flow from the Denver to the 

Arapahoe aquifers in the current model than previous models 

for predevelopment conditions (table C20).

The representation and simulated interaction between 

bedrock groundwater, streams, and the alluvial aquifer is 

another substantial difference between the current and previous models. Previous models represented the alluvial aquifer 

as constant-head cells (Robson, 1987) or as head-dependentflow boundaries using the MODFLOW River Package 

(Harbaugh and others, 2000; Colorado Division of Water 

Resources, 1998); streams were not represented in previous 

models. The current model simulates the alluvial aquifer as the 

uppermost layer in the model and simulates streams using the 

MODFLOW Streamflow-Routing Package SFR2 (Niswonger 

and Prudic, 2005). The current model thus represents the 

surficial system of streams and the alluvial aquifer in a more 

detailed manner than previous bedrock-modeling studies. 

The current model simulates outflow to the surficial system 

of 52.8 ft3/s compared to outflow values of 54.7 ft3/s (Robson, 

1987) and 60.9 ft3/s (Colorado Division of Water Resources, 

1998) from previous models (table C21). Results from a 

second calibration of the CDWR SB96–74 model indicated 

outflow as low as 36.6 ft3/s (table C21). In addition to simulating a predevelopment outflow about 14 percent less than that 

by the CDWR SB96–74 first calibration model, the current 

model also simulates a different spatial distribution of outflow 

than previous models. The current model simulates about 

70 percent less outflow from the Dawson aquifers and confining unit and 70–75 percent more outflow from the Arapahoe 

and Laramie–Fox Hills aquifers and confining units than was 

simulated by the CDWR SB96–74 first calibration model 

(table C21).
266 Groundwater Availability of the Denver Basin Aquifer System, Colorado Table C20. Comparison of predevelopment groundwater budget for current and previous Denver Basin models. [For the current model, inflow equals flow from precipitation plus irrigation recharge, streams, and the alluvial aquifer; outflow equals flow to evapotranspiration, streams, springs, and the alluvial aquifer; see table A7 for the current model results. For previous models, inflow equals flow from precipitation recharge and the alluvial aquifer; outflow equals flow to the alluvial aquifer; ft3/s, cubic feet per second; CDWR, Colorado Division of Water Resources; negative interaquifer flow indicates outflow to underlying units; positive interaquifer flow indicates inflow from overlying units] Dawson aquifers and confining units Denver aquifer and confining units Arapahoe aquifers and confining units Laramie confining unit and Laramie–Fox Hills aquifer Total Current model Robson (1987) CDWR (1998) Current model Robson (1987) CDWR (1998) Current model Robson (1987) CDWR (1998) Current model Robson (1987) CDWR (1998) Current model Robson (1987) CDWR (1998) Inflow (ft3/s) 35.3 40.6 47.7 32.5 5.5 6.9 24.3 2.8 3.3 90.0 5.8 3.1 187 54.7 60.9 Outflow (ft3/s) 29.4 33.4 38.3 22.2 7.4 9.8 37.9 8.1 9.4 97.7 5.8 3.5 187 54.7 60.9 Outflow minus Inflow = Interaquifer flow (ft3/s) –5.8 –7.2 –9.4 –10.3 1.9 2.9 13.6 5.3 6.1 7.7 0 0.4 0 0 0
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 267

Model Uncertainty and Limitations 

The Denver Basin groundwater flow model simulates a 

reasonable conceptual understanding of regional hydrogeologic conditions to calculate temporal changes in groundwater 

availability since predevelopment. The present model represents the salient features of the Denver Basin aquifer system 

and provides an updated understanding of the flow system at 

a regional scale that is relevant to regional water-management 

decisions. However, as with any groundwater model, the 

Denver Basin simulations are subject to sources of uncertainty, 

which can include the temporal and spatial discretization of 

the model domain, representation of aquifer heterogeneity, and 

uncertainty in the data used to develop boundary conditions 

and calibration targets. Though the Denver Basin model used 

current modeling methods and software available at the time 

of the study, limitations of modeling software, data limitations, 

and assumptions made during model development and calibrations are all factors that may constrain appropriate use of this 

and all models (Bredehoeft, 2005).

The Denver Basin groundwater flow model simulates 

transient flow in the Denver Basin bedrock and alluvial 

aquifers using a temporal discretization designed to represent 

large-scale changes in hydrologic stresses from predevelopment (pre-1880) to 2003. Model stress periods range from 

2 to 27 years in length and were defined so as to represent 

large-scale temporal changes in precipitation, land use, and 

total pumping. The longer stress periods at the beginning 

of the simulation are considered adequate to represent early 

withdrawals because temporal changes in pumping were 

small. However, the model may not accurately represent 

detailed changes in precipitation before 1957 because the average annual precipitation distribution from 1930 to 2003 was 

applied to all pre-1957 stress periods. The model uses average 

annual rates for recharge, evapotranspiration, and well pumping and provides a reasonable representation of groundwater 

flows through time consistent with the current conceptual 

understanding of groundwater flow and with previous groundwater flow models of the basin. However, the use of multiyear 

stress periods does not allow simulation of seasonal changes in 

water use. Future model applications addressing issues related 

to seasonal groundwater flow conditions in the Denver Basin 

should consider more detailed temporal discretization because 

recharge, evapotranspiration, and well pumping do exhibit 

seasonality, reaching peak values during the summer irrigation 

season and minimal values during the winter.

Modeled areas are discretized into finite-difference grid 

cells for solution of the three-dimensional groundwater flow 

equation. For the Denver Basin model, the modeled area was 

divided into 1-mi2 grid cells in the horizontal direction. The 

1-mile grid spacing is consistent with previous modeling 

studies in the basin and was deemed necessary to expedite 

model computations. The 1-mile grid provides sufficient detail 

over most of the study area for this regional study but may 

not accurately represent the steep bedrock dip along some 

parts of the western basin margin or may not provide adequate 

spatial resolution for future site-specific modeling efforts. A 

finer spatial discretization using local grid-refinement (LGR) 

techniques (Mehl and Hill, 2005) could be used in areas where 

finer resolution of the model domain is needed.

The Denver Basin was subdivided into 11 bedrock layers 

and 1 overlying alluvial aquifer layer. The vertical discretization used by the current model is more detailed than previous 

models and is considered a substantial improvement over 

previous efforts because the entire volume of the groundwater system is explicitly represented in the model. The base 

altitude and thickness of each model layer were determined 

from an existing database of geophysical logs (Brian Ahrens, 

Colorado Division of Water Resources, written commun., 

2003). Sources of error in the geophysical log database include 

inaccurate land-surface altitudes, anomalous aquifer base 

altitudes, and variation in aquifer base altitude “picks” from 

the geophysical logs by the original interpretation. Geophysical logs were not reinterpreted for this study, although entries 

in the geophysical log database were examined for anomalies 

through geographic analysis. Aquifer-base altitudes were plotted and contoured using an inverse-distance-weighted method, 

which highlighted anomalous values. Altitudes considered 

anomalous were removed from the dataset before final contouring of the surfaces. The contoured aquifer-base altitudes 

were subsequently converted to a raster dataset, which was 

then processed using an area-weighted averaging scheme to 

derive a value for each 1-mi2 grid cell. While the methods used 

do not guarantee an error-free dataset, the resulting aquiferbase-altitude maps provide reasonable representations of the 

aquifer layering in the Denver Basin consistent with the conceptual understanding of geologic structure and stratigraphy.

The Denver Basin bedrock aquifers consist of a sequence 

of heterogeneous sandstones, siltstones, and claystones. The 

layering used in the present groundwater flow model represents some, but not all, of the heterogeneity inherent in the 

Denver Basin. Heterogeneity within each bedrock aquifer is 

represented by a varying hydraulic conductivity within the 

corresponding model layer. Hydraulic conductivity is varied 

in two ways for the bedrock aquifers. For the upper and lower 

Dawson aquifers, a constant value of hydraulic conductivity, 

Table C21. Comparison of predevelopment outflow to the surficial 

system (streams, springs, and the alluvial aquifer) from bedrock 

aquifers and confining units for the current and previous Denver 

Basin models.

[For the current model, outflow is the sum of outflow to streams, springs, and 

the alluvial aquifer. For previous models, outflow is to the alluvial aquifer; 

CDWR, Colorado Division of Water Resources; ft3/s, cubic feet per second]

Aquifer

Current

model

(ft3/s)

Robson

(1987)

(ft3/s)

CDWR

(1998), first 

calibration

(ft3/s)

CDWR

(1998), second

calibration

(ft3/s)

Dawson 11.1 33.4 38.3 20.7

Denver 6.8 7.4 9.8 5.2

Arapahoe 17.7 8.1 9.4 7.9

Laramie–Fox Hills 17.1 5.8 3.5 2.8

Total 52.8 54.7 60.9 36.6
268 Groundwater Availability of the Denver Basin Aquifer System, Colorado

derived from model calibration, is multiplied by an array of 

the silt-plus-sand fraction for the layer. The resulting distribution of hydraulic conductivity represents the conductive part 

of each bedrock aquifer (silt-plus-sand fraction). The silt-plussand fraction was calculated as the silt-plus-sand thickness 

values taken from the geophysical log database divided by 

aquifer thickness from the same geophysical log. Silt-plussand fractions were contoured, converted to a raster grid, and 

averaged onto the 1-mi2 grid cells to form a multiplier array in 

the groundwater flow model. For the Denver, Arapahoe, and 

Laramie–Fox Hills aquifers, a spatial distribution of hydraulic 

conductivity was developed by kriging hydraulic-conductivity 

values at pilot points that were derived from model calibration. 

The spatially variable hydraulic-conductivity distribution was 

then multiplied by the silt-plus-sand fraction for the layer to 

represent the conductive parts of the aquifers. Bedrock confining units were each assigned a single hydraulic-conductivity 

value based on model calibration and were assumed 

homogeneous.

While there are many possible ways to represent heterogeneity in the Denver Basin groundwater flow model, the 

methods used in this effort utilize the available lithologic 

and aquifer-testing data to the extent possible and provide a 

more detailed representation of aquifer properties than previous efforts. The current groundwater flow model in general 

provides reasonable representations of Denver Basin aquifer 

properties and stratigraphic features. For example, the Arapahoe aquifer in the south Denver metropolitan area has a greater 

thickness and hydraulic conductivity than in other parts of the 

basin owing to the presence of the subsurface Wildcat Mountain alluvial fan (Raynolds, 2002, 2004). The features representing the Wildcat Mountain alluvial fan are evident on maps 

of the Denver and lower Arapahoe aquifers, and the current 

model represents the fan as areas of high hydraulic conductivity in the Denver and lower Arapahoe aquifers consistent with 

the conceptual understanding of the system. Similarly, the 

model appropriately represents high hydraulic-conductivity 

zones in the Laramie–Fox Hills aquifer observed on the 

eastern edge of the basin. Future modeling efforts should 

consider additional data collection or refinement of model 

parameters in areas where the model did not achieve a good 

fit between transient simulated and observed hydraulic heads. 

For example, large simulated drawdown in the upper Dawson 

aquifer east of Parker was not observed in the CDWR waterlevel data, and the model appears to underestimate drawdown 

in the lower Arapahoe aquifer compared to the CDWR waterlevel data. South of Monument, observed water-level rise for 

wells completed in the Denver and lower Arapahoe aquifers, 

presumably in response to increased urban recharge, is not 

well represented in the model. These discrepancies between 

simulated and observed hydraulic heads indicate the need 

for additional water-level data collection or refinement of the 

hydraulic-conductivity distribution and pumping estimates for 

the affected areas.

Various data types were used to develop boundary 

conditions for the Denver Basin model and some uncertainty 

is inherent in these data. Estimates of recharge are based on 

precipitation data, land-use data, and recharge estimates from 

previous studies. Estimates of recharge from precipitation 

are reasonable and consistent with previous studies. However, additional field studies on agricultural and urban irrigation return-flow rates could improve estimates of irrigation 

recharge. Evapotranspiration is a simulated value based on 

a piecewise linear function relating evapotranspiration rate 

to depth to the water table, and while the simulation results 

are considered reasonable. Estimates of discharge from wells 

are made on the basis of well permits on file in the Colorado 

Division of Water Resources well-permit database. The location, depth, type, and dates of use for each well in the database 

were used to locate the well within the model grid, and pumping rates were assigned using methods from previous studies. 

This study followed methodology used by previous Denver 

Basin modeling studies to develop the pumping estimates, and 

the results are considered accurate to plus or minus 30 percent 

(Colorado Division of Water Resources, 1998). Sources of 

error in the pumping estimates include inadequacies in the 

well-permit database as well as assumptions regarding perwell pumping rates.

The data used to develop model-calibration targets are 

another source of uncertainty in the Denver Basin model. Two 

data types were used as calibration targets—water-level measurements and flow estimates from stream base-flow determinations and historical flowing wells. The water-level data are, 

in general, accurate to the accuracy level of the land-surface 

altitude determination and were most heavily relied upon in 

model calibration. All flow observations are estimated values, 

and are not considered accurate. In order to maximize the 

influence of head observations and minimize the influence of 

flow observations on parameter values, assigned observation 

weights were greater for the head observations than for the 

flow observations.

The Denver Basin model was designed to primarily 

evaluate groundwater availability in the bedrock aquifer system. The alluvial aquifer system was included as the uppermost model boundary to represent interaction between the 

bedrock system and the surficial hydrologic system. While this 

representation provides more detailed analysis of groundwater/

surface-water interaction than previous models, representation of the alluvial aquifer is generalized in the Denver Basin 

model, and the model may not be suitable for detailed modeling investigations of the alluvial aquifer. For example, because 

a 1-mile grid spacing was used in the model, the area of the 

alluvial aquifer included in the model was limited to the extent 

of alluvium in present-day stream channels where the alluvium width is greater than one-half mile. In addition, detailed 

representations of surficial water features and flow such as 

streamflow routing, wastewater discharge, irrigation return 

flows, and irrigation ditches were not explicitly included in the 

Denver Basin model. Instead, estimates of water derived from 

these surficial sources were included as urban and agricultural 

recharge to the model. A detailed groundwater flow model of 

the South Platte alluvial aquifer and its tributaries is currently 

(2010) being developed by the CWCB as part of the South 

Platte Decision Support System, which does include detailed 
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 269

groundwater/surface-water interaction between the alluvial 

aquifer and surface-water delivery systems (Colorado Water 

Conservation Board, 2008).

The Denver Basin groundwater flow model provides 

an updated representation of groundwater flow conditions in 

the study area from predevelopment through 2003 by using 

justifiable aquifer properties and boundary conditions. The 

current model is considered an improvement over previous 

models because, unlike previous models, it explicitly represents confining layers and the alluvial aquifer. The current 

model also represents temporal changes in pumping, recharge, 

and evapotranspiration in a more detailed manner and includes 

more calibration targets than previous models. A good model 

fit was achieved to the head observations, although the fit to 

estimates of stream base flow and historical flowing wells was 

less satisfactory. The Denver Basin model is a data-analysis 

tool well suited for evaluating temporal changes to regional 

groundwater flow conditions and directions, making predictions of changing conditions into the near future, and guiding 

future detailed investigations in the study area. The use of 

parameter-estimation techniques facilitated statistical evaluation of the model calibration and predictions.

Future Model Maintenance 

and Applications

The refinements of the present Denver Basin model over 

previous models and areas for improvement in the current 

model highlight the need for recurring model maintenance and 

updates. As additional data, modeling techniques, and conceptual understanding develop, the Denver Basin model and the 

groundwater availability conclusions made from the results 

will require updates and revision. The underlying data and 

supporting computer programs can be refreshed on a regular 

basis to update groundwater availability results with sufficient 

frequency so that water-management decisions can respond to 

changing climatic and anthropogenic conditions.

The ability of the Denver Basin model to represent 

realistic hydrologic conditions could be improved upon in 

several ways related to the model calibration and the availability of modeling tools. As additional geologic, hydrologic, and 

aquifer property data are compiled, further refinement of the 

model layering, parameterization of aquifer properties, and the 

resulting effects on model calibration may need reconsideration. For example, additional parameter estimation techniques 

such as more detailed pilot-point analysis might be useful to 

further refine hydraulic-conductivity distributions and improve 

model fit between transient simulated and observed hydraulic 

heads in parts of the aquifer system. Refined pumping estimates from measured discharge would produce more accurate 

model results, and additional monitoring observations could 

be used to refine the model calibration. While the match 

between simulated and observed hydraulic heads was quite 

good, the match between simulated and observed flows was 

less satisfactory. Parameter sensitivity results indicate that the 

simulated flows are most sensitive to parameters representing 

the percentage of precipitation recharge to the Dawson aquifer 

(RCH_Tdw), hydraulic conductivity of the upper Dawson 

aquifer (K_utdw), and the hydraulic conductivity of streambed materials in tributaries (SFR_TRIBS). Because the flow 

observations were derived from a limited set of streamflow 

measurements, additional streamflow data and(or) refinement 

of the parameters affecting streamflow calculations might 

improve the model fit to the observed flows.

Improved modeling tools, which could separate individual water-budget components, would be beneficial to refine 

interpretations of modeling results. For example, the ability 

to separate recharge sources in model input and output would 

support calculations separating precipitation and irrigation 

return-flow recharge in the water budget. Similarly, the ability 

to separate calculations of confined and unconfined storage 

depletion in model output would further the understanding of 

storage depletion rates in the basin. Further temporal discretization could be used to examine seasonal patterns of pumping, 

precipitation, and irrigation, and a finer spatial discretization 

using local grid-refinement (LGR) techniques (Mehl and Hill, 

2005) could be used in areas where finer resolution of the 

model domain is needed.

The Denver Basin model is designed to evaluate longterm regional changes in groundwater availability and thus is 

well suited for future regional applications such as optimization modeling, particle-tracking simulations of groundwater 

age, and coupling with more detailed models of the surficial 

system. Optimization modeling involves evaluating watermanagement strategies to meet optimization criteria such as 

maximizing pumping while minimizing drawdown or storage 

depletion (Ahlfeld and others, 2005). Optimization modeling 

is an appropriate use of the Denver Basin model because the 

effects of changing pumping conditions can be evaluated on 

a regional scale. Optimization modeling also can incorporate 

the effects of conjunctive-use projects such as aquifer-storageand-recovery (ASR) efforts. Particle-tracking simulations using 

MODPATH (Pollack, 1994) and related tools could be used for 

calculating advective traveltimes from recharge to discharge 

areas and for delineating zones of capture for wells of interest 

(for example, Paschke, 2007). Coupling of the Denver Basin 

model with a surface-water or watershed model such as the 

Precipitation-Runoff Modeling System (Leavesley and others, 

1983) could allow more detailed analysis of groundwater/surface-water interaction and precipitation recharge. The Colorado 

Water Conservation Board is currently (2010) calibrating a 

groundwater flow model of the alluvial aquifer of the South 

Platte River and its tributaries (Colorado Water Conservation Board, 2008). Software utilities were developed for this 

study (Banta and others, 2008), which allow flows for bedrock 

discharge to alluvial aquifers calculated by the Denver Basin 

model to be imported to the South Platte alluvial-aquifer model. 

However, formal linking of the Denver Basin model with a 

detailed model of the South Platte alluvial aquifer and streams 

could provide a more refined representation of groundwater/

surface-water interaction in the basin.
270 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Summary

Groundwater flow in the Denver Basin bedrock aquifers and overlying alluvial aquifer is simulated with a threedimensional groundwater flow model to provide a framework 

for analysis of aquifer and confining bed materials, hydrologic 

stresses, field observations of past hydrologic conditions, and 

predictions of future hydrologic conditions. The model uses 

the U.S. Geological Survey (USGS) modular finite-difference 

groundwater flow modeling program MODFLOW-2000 and 

includes several enhancements over previous modeling efforts 

because of additional data availability, improved modeling 

capabilities, and improved computer technology.

The Denver Basin model grid encompasses the Denver Basin bedrock aquifer system and immediately adjacent 

areas of the alluvial aquifer of the South Platte River with 

84 columns and 124 rows of square cells; each cell measures 

1 mile by 1 mile. A fully three-dimensional approach was used 

to simulate lateral and vertical flow and storage changes in 

all hydrogeologic units of the aquifer system. Each of the six 

bedrock aquifers, five bedrock confining units, and the alluvial 

aquifer are explicitly represented in the model with aquifer 

base altitudes defined from geophysical logs and geologic 

mapping from previous work. The alluvial aquifer is simulated 

as unconfined, the bedrock aquifers are simulated as convertible from confined to unconfined, and the bedrock confining 

units are simulated as confined. The model simulates steadystate conditions prior to 1880 and transient groundwater 

conditions from 1880 through 2003 using 16 stress periods of 

durations ranging from 2 to 27 years.

Horizontal hydraulic conductivity for the bedrock units is 

represented in the model by using several adjustable parameters whose values were calibrated through parameter estimation. Vertical hydraulic conductivity was assumed equal to 

horizontal hydraulic conductivity in the bedrock units, such 

that resistance to vertical flow among the bedrock aquifers is 

primarily controlled by the hydraulic conductivity of the confining units. For model layers representing the Denver, Arapahoe, and Laramie–Fox Hills aquifers, hydraulic-conductivity 

parameterization used the pilot-point approach. Pilot points are 

locations in the model where a parameter, hydraulic conductivity in this study, is calibrated by parameter estimation. The 

estimated parameter values at pilot points are then interpolated 

between locations within a model layer to assign a parameter 

(hydraulic conductivity) distribution to the layer. Finally, the 

calibrated hydraulic-conductivity values for each layer were 

multiplied by the percent of coarse-grained materials (siltplus-sand fraction) for each model cell to obtain an equivalent hydraulic conductivity for the overall aquifer thickness 

represented by each cell. For the Denver Basin, the pilot-point 

approach worked well because it allowed the model to represent gradational, rather than abrupt hydraulic-conductivity 

distributions across the basin consistent with basin stratigraphy. For the alluvial aquifer, horizontal hydraulic conductivity 

was assigned a value of 200 ft/d for the alluvial aquifer in the 

South Platte River Basin and a value of 5 ft/d for the alluvial 

aquifer in the Big Sandy and Black Squirrel Creek Basins. 

The ratio of horizontal to vertical hydraulic conductivity 

for the alluvial aquifer in the South Platte River Basin was 

represented by an adjustable parameter whose final value (9.9) 

was determined through model calibration. A fixed parameter 

value of 10 was assigned to the ratio of horizontal to vertical 

hydraulic conductivity for the alluvial aquifer in the Big Sandy 

and Black Squirrel Creek Basins.

Aquifer storage properties of specific storage for confined 

units and specific yield for unconfined units were represented 

in the model by using several estimated and assigned 

parameters. Specific storage was represented by using two 

adjustable parameters. One specific-storage parameter was 

estimated for the model layers representing aquifers, and one 

specific-storage parameter was estimated for the model layers 

representing confining units. The final calibrated specificstorage values of 5.2×10–7/ft for aquifers and 1.7×10–6/ft for 

confining units are in the range of reasonable values for materials in the Denver Basin. Specific-yield values were assigned 

for each aquifer unit based on previous field studies in the 

basin and were multiplied by the percentage of coarse-grained 

materials (silt-plus-sand fraction) for each model cell to obtain 

an equivalent specific yield for the overall aquifer thickness 

represented by each cell.

Hydrologic stresses simulated by the model include 

recharge from precipitation plus irrigation return flows, evapotranspiration, streams, springs, reservoirs, pumping wells, 

interaquifer flow, flow across basin boundaries, and storage. 

The percentage of precipitation becoming recharge was represented in the model by using several adjustable parameters 

whose values were calibrated through parameter estimation. 

Model-calibration results indicate about 1 to 2 percent of 

precipitation becomes recharge to the bedrock aquifers, and 

an estimated 7 percent of precipitation becomes recharge to 

the alluvial aquifer. Recharge rates in irrigated areas were 

assigned values of 2.5 in/yr for urban irrigation return flows 

(urban recharge) and 10 in/yr for agricultural irrigation return 

flows. The recharge rates attributed to urban and agricultural 

return flows were uniformly applied within an affected zone, 

but the areas of urbanization and irrigated agriculture over 

which they were applied increased over time, as defined by 

satellite imagery and land-use maps. Evapotranspiration was 

simulated using a piecewise linear function in which evapotranspiration decreased as depth to groundwater increased 

over the entire modeled area. Streamflow was simulated using 

the SFR2 Package, reservoirs were represented using the RIV 

Package, and springs were simulated with the DRN Package. 

Flow across the southern basin boundary was simulated using 

the GHB Package and across the northeast basin boundary 

using the FHB Package. Pumping was simulated using the 

WEL and MNW Packages and was estimated for each aquifer 

model layer on the basis of well locations, depths, and water 
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 271

use taken from the Colorado Division of Water Resources 

well-permit database as described in Chapter B. The GMG 

Package and an alternative adaptive damping method were 

used to solve the highly nonlinear system of finite-difference 

equations, which provided a solution in a reasonable execution 

time and with a relatively small number of deactivated cells.

The Denver Basin model was calibrated using nonlinear 

regression methods as implemented in the parameter estimation program PEST in combination with manual adjustments 

to parameters that proved resistant to calibration by automated 

methods. Seventy-seven parameters were included in the 

model, 52 of which were adjusted during parameter estimation 

and 25 of which had assigned values. Estimated parameters 

included hydraulic conductivity and recharge parameters. The 

model-calibrated distributions of aquifer hydraulic conductivity and recharge are consistent with previous data, previous 

modeling efforts, and the hydrogeologic conceptual model. 

Calibrated hydraulic-conductivity values for various model 

layers also are in appropriate relative proportion to each 

other, which is consistent with the hydrogeologic conceptual 

understanding.

Model fit was evaluated by comparing model-computed 

heads and flows to observed values. A total of 4,984 transient 

head observations from 1883 through 2003, 147 base-flow 

observations from 1941 through 2003, and 20 flow observations from historical flowing wells were used to calibrate the 

model. The model is well calibrated to the transient heads 

with a mean head residual of –16 ft and a RMSE of 85 ft, 

which is approximately 3 percent of the 3,024-ft range of 

head observations in the model. The head residuals appear 

to be independent of measured head and do not appear to be 

spatially correlated across the study area. Plots of simulated 

water levels over time (hydrographs) compared to observed 

values from the CDWR water-level network indicate a good 

match between transient simulated hydraulic heads for the 

lower Dawson, Denver, and Laramie–Fox Hills aquifer. The 

poor match between transient simulated hydraulic heads 

and observed heads for CDWR water-level monitoring sites 

in the northeastern part of the upper Dawson aquifer, the 

lower Arapahoe aquifer, and the Denver and lower Arapahoe 

aquifers south of Monument indicates areas where additional 

water-level data collection and(or) model parameter refinement might improve model fit. The weighted-flow residuals are biased positively, indicating simulated flows are, in 

general, less than the observations. Flow observations were 

assigned small weights in the nonlinear regression to minimize the effects of inaccurate flow observations on estimated 

model parameters.

Composite scaled sensitivities indicate simulated 

equivalents of observations were most sensitive to estimated 

parameters that control percent precipitation recharged to the 

Dawson and alluvial aquifers, vertical anisotropy within the 

bedrock units, specific storage of the bedrock aquifers, and 

pumping rates for wells with the greatest assigned production. 

Composite scaled sensitivity values computed from the flow 

observations indicate that the simulated flows are most sensitive to parameters representing the percentage of precipitation 

recharge to the Dawson aquifer, hydraulic conductivity of 

the upper Dawson aquifer, and the hydraulic conductivity of 

streambed materials in tributaries. Additional data collection 

or refinement of these parameter values might improve the 

model fit to the observed flows.

Two predictive scenarios were simulated with the 

calibrated Denver Basin model to calculate predictive model 

sensitivities and to demonstrate use of the model for predictive analysis. Predictive simulations were run 50 years 

into the future from the end of the model calibration period 

(December 31, 2003) to 2053 and were divided into ten 5-year 

stress periods. The predictive simulations lend insight to longterm effects of continued pumping on the groundwater system, 

although they are not considered definitive predictions of 

future conditions.

One benefit of the automated techniques used to calibrate 

the Denver Basin model is that the results can be used in an 

analysis of the relations among uncertainties in parameters, 

observations, and predictions. For the Denver Basin model, 

the potentiometric surface for the lower Arapahoe aquifer at 

the end of the prediction period (2053) is of particular predictive interest because of its importance as a water supply. 

The Observation-Prediction (OPR) and Parameter-Prediction 

(PPR) statistics were calculated for a subset of cells in this 

model layer (10) to identify prediction uncertainty and the 

effects of additional observations on predictions. Maps of 

the PPR statistic values for a selected parameter were used 

to identify areas where prediction uncertainty would be most 

effectively decreased as a result of improved information 

about the parameter. Maps of the OPA statistic values for a 

selected parameter were used to identify areas where parameter uncertainty would be most effectively decreased by adding 

observations (in this case, head observation). Maps of the OPR 

statistic values were used to identify areas where additional 

head observations likely would be most beneficial in reducing 

the uncertainty in the model-calculated potentiometric surface 

and drawdown. An OPR statistic map for the lower Arapahoe 

aquifer indicates additional observations in aquifer layers in 

the north-central and south-central parts of the basin would 

likely reduce uncertainty in the model-calculated potentiometric surface of the lower Arapahoe aquifer.

Comparisons between the current and previous Denver 

Basin models highlight the differences and similarities among 

the models. Major refinements used in the present model 

compared to previous models included (1) a fully threedimensional representation of the aquifer system, (2) explicit 

representation of the alluvial aquifer, (3) use of streamflowrouting capabilities, (4) inclusion of evapotranspiration as a 

boundary condition, (5) updated pumping estimates to include 

pumping from the alluvial aquifer, and (6) recharge from 

urban and agricultural irrigation. The current model is considered an improvement over previous models because it includes 

these model refinements.
272 Groundwater Availability of the Denver Basin Aquifer System, Colorado

The Denver Basin groundwater flow model developed for 

this study provides an updated representation of groundwater 

flow conditions from 1880 through 2003 by using reasonable 

aquifer properties and boundary conditions. The current model 

also represents temporal changes in recharge, evapotranspiration, and well pumping in a more detailed manner and 

includes more calibration targets than previous models. The 

model is well suited for evaluating changing regional groundwater flow directions and water budgets through time in the 

Denver Basin, making predictions of changing conditions into 

the near future, and guiding future detailed investigations in 

the study area. The refinements of the present Denver Basin 

model over previous models highlight the need for recurring 

model maintenance and updates. As additional data, modeling techniques, and conceptual understanding develop, the 

Denver Basin model and the groundwater availability conclusions made from the results will require updates and revision 

to support water-management decisions made in response to 

changing climatic and anthropogenic conditions.

References

Ahlfeld, D.P., Barlow, P.M., and Mulligan, A.E., 2005, GWM—

A ground-water management process for the U.S. Geological 

Survey modular ground-water model (MODFLOW-2000): 

U.S. Geological Survey Open-File Report 2005–1072, 124 p.

Anderson, M.P., and Woessner, W.W., 1992, Applied groundwater modeling: San Diego, Calif., Academic Press, Inc., 

381 p.

Argus Holdings, Ltd., 1992–99, Argus One user’s guide, 

Argus Open Numerical Environments—A GIS modeling 

system, version 4.0: Jericho, New York, Argues Interware, 

Inc., variously paginated.

Banta, E.R., 2000, MODFLOW-2000, the U.S. Geological 

Survey modular ground-water model—Documentation 

of packages for simulating evapotranspiration with a segmented function (ETS1) and drains with return flow (DRT1): 

U.S. Geological Survey Open-File Report 2000–466, 127 p.

Banta, E.R., 2006, Modifications to MODFLOW boundary conditions and an adaptive-damping scheme for 

Picard iterations for a highly nonlinear regional model, 

in Poeter, Eileen, Hill, Mary, and Zheng, Chunmiao, eds., 

MODFLOW and more, 2006—Managing ground-water 

systems: International Groundwater Modeling Center and 

Colorado School of Mines, 2006 [Proceedings, Golden, 

Colo.], p. 596–600.

Banta, E.R., Paschke, S.S., and Litke, D.W., 2008, User guide 

and documentation for five MODFLOW ground-water modeling utility programs: U.S. Geological Survey Techniques 

and Methods 6–A28, 24 p.

Barkmann, P.E., 2004, Vertical hydraulic conductivity measurements in the Denver Basin, Colorado: The Mountain 

Geologist, v. 41, no. 4, p. 169–183.

Bredehoeft, John, 2005, The conceptualization model problem 

– surprise: Hydrogeology Journal, v. 13, p. 37–46.

Buckles, D.R., and Watts, K.R., 1988, Geohydrology, water 

quality, and preliminary simulations of ground-water flow 

of the alluvial aquifer in the upper Black Squirrel Creek 

basin, El Paso County, Colorado: U.S. Geological Survey 

Water-Resources Investigations Report 88–4017, 49 p.

Certes, Catherine, and deMarsily, G., 1991, Application of the 

pilot point method to the identification of aquifer transmissivities: Advances in Water Resources, v. 14, no. 5. p. 

284–300.

Colorado Division of Water Resources, 1998, Denver Basin 

and South Platte River Basin Technical Study, Final Report, 

Colorado Senate Bill 96–074, variously paged.

Colorado Division of Water Resources, 2003, Ground water 

levels in the Denver Basin bedrock aquifers: Colorado Division of Water Resources 2003 annual report, 132 p.

Colorado Division of Water Resources, 2004, Ground water 

levels in the Denver Basin bedrock aquifers: Colorado Division of Water Resources 2004 annual report, 132 p.

Colorado Division of Water Resources, 2005, Hydrobase data 

set: Analysis/query tools, Statewide, 07/01/2005: 1 DVD.

Colorado Water Conservation Board, 2008, SPDSS Phase 4, 

Task 48.2 Development of calibration targets and criteria 

– final, 31 p., accessed September 20, 2009, at ftp://dwrftp.

state.co.us/cdss/gwm/tm/SPDSS_48_2_20081008.pdf.

Darton, N.H., 1905, Preliminary report on geology and underground water resources of the central Great Plains: U.S. 

Geological Survey Professional Paper 32, 433 p.

Davis, J.C., 1986, Statistics and data analysis in geology: New 

York, John Wiley and Sons, Inc., 646 p.

de Marsily, G., Lavedan, G., Boucher, M., and Fasanino, G., 

1984, Interpretation of interference tests in a well field using 

geostatistical techniques to fit the permeability distribution 

in a reservoir model, in Verly, G., and others, eds., Geostatistics for natural resources characterization, part 2: Dordrecht, Holland, Reidel Publishing Company, p. 831–849.

Doherty, John, 2001, Using pilot points and regularization in ground-water model calibration, in Seo, H.S., 

Poeter, Eileen, Zheng, Chunmiao, and Poeter, Onna, eds., 

MODFLOW 2001 and other modeling odysseys, 2001, 

Proceedings: [Golden, Colo.], International Groundwater 

Modeling Center, Colorado School of Mines, and 

U.S. Geological Survey, p. 181–187.

Doherty, John, 2003, Ground-water model calibration using 

pilot points and regularization: Groundwater, v. 41, no. 2, 

p. 170–177.
Groundwater Flow Simulations of the Denver Basin Aquifer System, Colorado 273

Doherty, John, 2006, PEST—Model-independent parameter 

estimation user manual, 5th ed.: Corinda, Australia, Watermark Numerical Computing, variously paginated, accessed 

September 17, 2010, at http://www.pesthomepage.org/.

Emmons, S.F., Cross, Whitman, and Eldridge, G.H., 1896, 

Geology of the Denver Basin: U.S. Geological Survey 

Monograph 27, 556 p., 31 pls.

Environmental Systems Research Institute, Inc., 1999–2004a, 

ArcGIS 9.2, accessed January 1, 2004, at http://www.esri.com/.

Environmental Systems Research Institute, Inc., 1999–2004b, 

ArcInfo 9.0, accessed January 1, 2004, at http://www.esri.com/.

Garmin Ltd., 2004, MapSource trip and waypoint manager, version 6.0: Olathe, Kansas, Garmin Ltd., accessed January 1, 

2004, at http://www.garmin.com/garmin/cms/site/us.

Halford, K.J., and Hanson, R.T., 2002, User guide for the 

drawdown-limited, Multi-Node Well (MNW) package for the 

U.S. Geological Survey’s modular three-dimensional finitedifference ground-water flow model, versions MODFLOW-96 

and MODFLOW-2000: U.S. Geological Survey OpenFile Report 2002–293, 33 p., accessed August 31, 2009, 

at http://pubs.er.usgs.gov/usgspubs/ofr/ofr02293.

Harbaugh, A.W., 1990, A computer program for calculating subregional water budgets using results from the 

U.S. Geological Survey modular three-dimensional groundwater flow model: U.S. Geological Survey Open-File 

Report 90–392, 46 p.

Harbaugh, A.W., Banta, E.R., Hill, M.C., and McDonald, 

M.G., 2000, MODFLOW-2000, the U.S. Geological Survey 

modular ground-water model—User guide to modularization concepts and the groundwater flow process: U.S. Geological Survey Open-File Report 2000–92, 121 p.

Hill, M.C., 1998, Methods and guidelines for effective model 

calibration: U.S. Geological Survey Water-Resources Investigations Report 98–4005, 90 p.

Hill, M.C., Banta, E.R., Harbaugh, A.W., and Anderman, 

E.R., 2000, MODFLOW-2000, the U.S. Geological Survey 

modular ground-water model—User guide to the observation, sensitivity, and parameter-estimation processes and 

three post-processing programs: U.S. Geological Survey 

Open-File Report 2000–184, 209 p. 

Hill, M.C., and Tiedeman, C.R., 2007, Effective groundwater model calibration, with analysis of data, sensitivities, 

predictions, and uncertainty: Hoboken, New Jersey, Wiley, 

455 p.

Hurr, R.T., Schneider, P.A., and others, 1972, Hydrogeologic 

characteristics of the valley-fill aquifer in the Greeley reach 

of the South Platte River Valley, Colorado: U.S. Geological 

Survey Open-File Report 73–124, 2 p.

Konikow, L.F., and Neuzil, C.E., 2007, A method to estimate groundwater depletion from confining layers: Water 

Resources Research, v. 43, W07417, 15 p.

Leavesley, G.H., Lichty, R.W., Troutman, B.M., and Saindon, 

L.G., 1983, Precipitation-Runoff Modeling System—User’s 

manual: U.S. Geological Survey Water-Resources Investigations 83–4238, 207 p.

McAda, D.P., and Barroll, Peggy, 2002, Simulation of groundwater flow in the middle Rio Grande basin between Cochiti 

and San Acacia, New Mexico: U.S. Geological Survey 

Water-Resources Investigations Report 2002–4200, 81 p.

Mehl, S.W., and Hill, M.C., 2001, MODFLOW-2000, The 

U.S. Geological Survey modular ground-water model—

User guide to the Link-AMG (LMG) package for solving 

matrix equations using an algebraic multigrid solver: 

U.S. Geological Survey Open-File Report 2001–177, 33 p.

Mehl, S.W., and Hill, M.C., 2005, MODFLOW-2005, the 

U.S. Geological Survey modular ground-water model—

Documentation of shared node Local Grid Refinement 

(LGR) and the Boundary Flow and Head (BFH) Package: 

U.S. Geological Survey Techniques and Methods 6–A12, 

68 p.

Murphy, S.F., Barber, L.B., Verplanck, P.L., and Kinner, D.A., 

2003, Chapter 1 – Environmental setting and hydrology of 

the Boulder Creek watershed, Colorado, in Murphy, S.F., 

Verplanck, P.L., and Barber. L.B., eds., Comprehensive water 

quality of the Boulder Creek watershed, Colorado, during 

high-flow and low-flow conditions, 2000: U.S. Geological 

Survey Water-Resources Investigations Report 2003–4045, 

p. 5–26.

Nadler, C.T., and Schumm, S.A., 1981, Metamorphosis of 

South Platte and Arkansas Rivers, eastern Colorado: Physical Geology, v. 2, no. 22, p. 95–115.

National Oceanic and Atmospheric Administration, 2004, 

1931–2003, Monthly surface data for Colorado, accessed 

October 29, 2004, at http://www.ncdc.noaa.gov/oa/ncdc.html.

Niswonger, R.G., and Prudic, D.E., 2005, Documentation 

of the Streamflow-Routing (SFR2) package to include 

unsaturated flow beneath streams—A modification to SFR1: 

U.S. Geological Survey Techniques and Methods 6–A13, 

48 p.

Paschke, S.S., 1992, Evaluating the hydrogeology of the 

Pleistocene Nussbaum Alluvium, Colorado, using vertical 

variability analysis and numerical modeling: Golden, Colorado School of Mines, Unpublished Master of Engineering 

Report, 152 p.

Paschke, S.S., ed., 2007, Hydrogeologic settings and groundwater flow simulations for regional studies of the transport 

of anthropogenic and natural contaminants to public-supply 

wells—Studies begun in 2001: U.S. Geological Survey 

Professional Paper 1737–A, 244 p.
274 Groundwater Availability of the Denver Basin Aquifer System, Colorado

Poeter, E.P., Hill, M.C., Banta, E.R., Mehl, Steffen, and 

Christensen, Steen, 2005, UCODE_2005 and six other 

computer codes for universal sensitivity analysis, calibration, and uncertainty evaluation: U.S. Geological Survey 

Techniques and Methods 6–A11, 283 p.

Pollock, D.W., 1994, User’s guide for MODPATH/MODPATHPLOT, version 3—A particle tracking post-processing package 

for MODFLOW, the U.S. Geological Survey finite-difference 

ground-water flow model: U.S. Geological Survey Open-File 

Report 94–464, 6 chaps.

Raynolds, R.G., 2002, Upper Cretaceous and Tertiary stratigraphy of the Denver Basin, Colorado: Rocky Mountain 

Geology, v. 37, no. 2, p. 111–134.

Raynolds, R.G., 2004, Stratigraphy and water levels in the 

Arapahoe aquifer, Douglas County area, Denver Basin, Colorado: Rocky Mountain Geologist, v. 41, no. 4, p. 195–210.

Riverside Technology, Inc., 2005, SPDSS 2001 Division 1 

ditch service areas: Online data accessed October 11, 2006, 

at http://cdss.state.co.us/DNN/GIS/tabid/67/Default.aspx.

Robson, S.G., 1987, Bedrock aquifers in the Denver Basin, 

Colorado—A quantitative water-resources appraisal: 

U.S. Geological Survey Professional Paper 1257, 73 p.

Robson, S.G., and Banta, E.R., 1990, Determination of specific storage by measurement of aquifer compression near a 

pumping well: Groundwater, v. 28, no. 6, p. 868–874.

Tonkin, M.J., Tiedeman, C.R., Ely, D.M., and Hill, M.C., 2007, 

OPR–PPR, a computer program for assessing data importance to model predictions using linear statistics: U.S. Geological Survey Techniques and Methods 6–E2, 115 p.

U.S. Geological Survey, 1973–1979, Landsat MSS scenes, 

WRS-1, P35R32, P35R33, P36R32, P36R33: Sioux Falls, 

South Dakota.

U.S. Geological Survey, 1989, Digital line graphs from 

1:100,000 scale maps: Data Users Guide #2, Reston, Va.

U.S. Geological Survey, 1999a, National altitude dataset: 

U.S. Geological Survey Fact Sheet 148–99, http://erg.usgs.gov/

isb/pubs/factsheets/fs14899.html.

U.S. Geological Survey, 1999b, USGS digital raster graphics: 

accessed November 23, 2004, at http://topomaps.usgs.gov/drg/.

U.S. Geological Survey, 1999–2000, Enhanced Landsat 

mosaic of Colorado: Sioux Falls, South Dakota.

U.S. Geological Survey, 2001a, Coverage LU30—Highresolution land use and land cover 1937/1938 Front Range 

Infrastructure Resources Project Demonstration Area, 

Version 1.0, April 5, 2001: U.S. Geological Survey Rocky 

Mountain Mapping Center, Lakewood, Colo., accessed 

November 23, 2004, http://rockyweb.cr.usgs.gov/frontrange/

NMD/data/lu30.html.

U.S. Geological Survey, 2001b, Coverage LU50—Highresolution land use and land cover 1953–1958 Front Range 

Infrastructure Resources Project Demonstration Area, 

Version 1.0, April 5, 2001: U.S. Geological Survey Rocky 

Mountain Mapping Center, Lakewood, Colo., accessed 

November 23, 2004, http://rockyweb.cr.usgs.gov/frontrange/

NMD/data/lu50.html.

Wilson, J.D., and Naff, R.L., 2004, The U.S. Geological Survey modular ground-water model—GMG Linear Equation 

Solver package documentation: U.S. Geological Survey 

Open-File Report 2004–1261, 47 p.

Winston, R.B., 2000, Graphical User Interface for 

MODFLOW, version 4: U.S. Geological Survey OpenFile Report 2000–315, 27 p., accessed June 1, 2004, 

at http://water.usgs.gov/nrp/gwsoftware/mfgui4/

modflow-gui.html.

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Groundwater Availability of 

the Denver Basin Aquifer System, Colorado

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Denver 

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