U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2020–5076

Prepared in cooperation with the Rural Water Authority of Douglas County

Groundwater Levels in the Denver Basin Bedrock Aquifers of 

Douglas County, Colorado, 2011–19
Cover Photograph showing a domestic water well in the foreground and Pikes Peak in the 

background, taken near Franktown, Colorado, on February 5, 2020, by Helen Malenda, 

U.S. Geological Survey.
Groundwater Levels in the Denver Basin 

Bedrock Aquifers of Douglas County, 

Colorado, 2011–19

By Helen F. Malenda and Colin A. Penn

Prepared in cooperation with the Rural Water Authority of Douglas County

Scientific Investigations Report 2020–5076

U.S. Department of the Interior

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

DAVID BERNHARDT, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2020

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Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Malenda, H.F., and Penn, C.A., 2020, Groundwater levels in the Denver Basin bedrock aquifers of Douglas County, 

Colorado, 2011–19: U.S. Geological Survey Scientific Investigations Report 2020–5076, 44 p., https://doi.org/10.3133/

sir20205076.

Associated data for this publication:

U.S. Geological Survey, 2020, USGS water data for the Nation: U.S. Geological Survey National Water Information 

System database, https://doi.org/10.5066/F7P55KJN.

ISSN 2328-0328 (online)
iii

Acknowledgments

The authors would like to thank the residents of Douglas County, especially the well owners 

who allowed access to their property. The authors also acknowledge the participation of the 

Rural Water Authority of Douglas County and former County Commissioner Steve Boand who 

assisted in the selection of sites and collection of data. The U.S. Geological Survey and Rural 

Water Authority of Douglas County acknowledge the Colorado Water Conservation Board 

for partially funding the study through grants from the Water Supply Reserve Account and 

Severance Tax Trust Fund Operational Account.

The authors also acknowledge U.S. Geological Survey colleagues Teresa Krizman, Jeannette 

Oden, Alisa Mast, Rhett Everett, Evan Gohring, Emily Baker, and William McDermott for assistance with collecting, processing, and presenting data related to this study.

v

Contents

Acknowledgments........................................................................................................................................iii

Abstract...........................................................................................................................................................1

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

Purpose and Scope ..............................................................................................................................2

Previous Studies ...................................................................................................................................2

Description of Study Area ...................................................................................................................5

Description of the Denver Basin Aquifer System ............................................................................5

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

Groundwater-Level Measurements and Groundwater-Level Elevations ....................................6

Discrete Groundwater-Level Measurements and Groundwater-Level Elevations ..........7

Time-Series Groundwater-Level Measurements and Groundwater-Level Elevations ...........8

Accessing Data ............................................................................................................................8

Groundwater-Level Elevation Temporal Trend Analysis and Mapping ......................................10

Groundwater-Level Elevations in the Denver Basin Bedrock Aquifers of Douglas County ............12

Seasonal Patterns in Discrete and Time-Series Groundwater-Level Elevation Data .............12

Long-Term Trends in Discrete Groundwater-Level Elevations ....................................................12

Long-Term Trends in Time-Series Groundwater-Level Elevations .............................................15

Potentiometric-Surface and Trend Maps .......................................................................................15

Future Research Needs .....................................................................................................................20

Summary........................................................................................................................................................20

References Cited..........................................................................................................................................21

Appendix 1 Groundwater-Well Measurement Diagram ....................................................................24

Appendix 2 Hydrographs Showing Groundwater-Level Elevation Through Time for 

Wells in the Douglas County Groundwater-Level Monitoring Network ................................25

Appendix 3 Descriptions and Equations of Mann-Kendall Test, Seasonal Mann-Kendall 

Test, and Sen Slope Estimate .......................................................................................................44

Figures

1. Map showing location of the Denver Basin aquifer system and geologic lines of 

section A, A–A’ and B, B–B’ near Douglas County, Colorado ...............................................3

2. Map showing location of groundwater-level monitoring network wells and 

producing aquifer, Douglas County, Colorado .........................................................................4

3. Generalized geologic cross-sections A, A–A’, west to east, and B, B–B’, south 

to north, through the Denver Basin aquifer system ................................................................6

4. Map showing the distribution of significant trends in discrete 

groundwater-level elevation, by aquifer, Douglas County, Colorado .................................14

5. Maps showing estimates of potentiometric-surface elevations and 

groundwater-level elevation trends for the upper Dawson aquifer, Douglas 

County, Colorado .........................................................................................................................17

6. Maps showing estimates of potentiometric-surface elevations and 

groundwater-level elevation trends for the lower Dawson aquifer, Douglas 

County, Colorado .........................................................................................................................18

7. Maps showing estimates of potentiometric-surface elevations and 

groundwater-level elevation trends for the Denver aquifer, Douglas County, Colorado .......19
vi

Tables

1. Physical characteristics of bedrock aquifers in the Denver Basin aquifer system ..........7

2. Well identification and location information and a summary of discrete 

groundwater-level measurements, April 2011 through June 2019, Douglas 

County, Colorado ...........................................................................................................................9

3. Trend analysis summary of discrete and time-series groundwater-level 

elevation data, January 2012 through June 2019, Douglas County, Colorado ..................11

4. Statistically significant trends in discrete static groundwater-level elevations, 

February 2012 through February 2019, Douglas County, Colorado .....................................13

5. Values and differences in static discrete groundwater-level elevations, 

February 2012 and 2019, Douglas County, Colorado .............................................................16

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2)

Flow Rate

foot per year (ft/yr) 0.3048 meter per year (m/yr)

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.

Datum

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Elevation, as used in this report, refers to distance above the vertical datum.
vii

Abbreviations

ARAP Arapahoe aquifer well, used in the well common names

CDWR Colorado Division of Water Resources

DENV Denver aquifer well, used in the well common names

GRNDAW Grandview Estates, lower Dawson aquifer well, used in the well common names

GRNDEV Grandview Estates, Denver aquifer well, used in the well common names

LARA Laramie-Fox Hills aquifer well, used in the well common names

LDAW lower Dawson aquifer well, used in the well common names

LSD land-surface datum

M–K Mann-Kendall

MP measuring point

NAD 83 North American Datum of 1983

NAVD 88 North American Vertical Datum of 1988

NWIS National Water Information System

RWADC Rural Water Authority of Douglas County

sM–K seasonal Mann-Kendall

SMWSA South Metro Water Supply Authority

UDAW upper Dawson aquifer well, used in the well common names

USGS U.S. Geological Survey

Groundwater Levels in the Denver Basin Bedrock Aquifers 

of Douglas County, Colorado, 2011–19

By Helen F. Malenda and Colin A. Penn

Abstract

Municipal and domestic water users in Douglas County, 

Colorado, rely on groundwater from the bedrock aquifers in 

the Denver Basin aquifer system as part of their water supply. 

The four principal Denver Basin bedrock aquifers are, from 

shallowest to deepest, the Dawson aquifer (divided administratively into “upper” and “lower” Dawson aquifers in Douglas 

County), the Denver aquifer, the Arapahoe aquifer, and the 

Laramie-Fox Hills aquifer. Increased groundwater pumping 

in response to rapid population growth and development has 

led to declining groundwater levels in Douglas County, where 

groundwater is a primary water source for densely populated 

and rural communities. The U.S. Geological Survey, in cooperation with the Rural Water Authority of Douglas County, began 

a study in 2011 to assess the groundwater resources of the 

Denver Basin bedrock aquifers within the county. The primary 

purpose of this report is to present a summary of groundwater 

levels measured during the study period (2011–19) and present 

results from statistical analyses of changes in groundwater-level 

elevations, reported above the land-surface datum, North 

American Vertical Datum of 1988, through time. During the 

study period, January 2011 through June 2019, discrete 

groundwater levels were routinely measured at 36 wells producing from Denver Basin bedrock aquifers within Douglas 

County. Of the 36 wells, 15 are instrumented with pressure 

transducers that record groundwater-level measurements at 

hourly intervals, and these data were temporally aggregated 

into time-series records. During 2011, wells were added to 

the monitoring network in phases, so that the start dates of 

the well records are noncontemporaneous. To keep temporal 

analysis among wells consistent, the periods of record used 

in statistical analyses were from February 2012 through 

February 2019 for the discrete data and from January 2012 

through June 2019 for the time-series data.

The upper Dawson, lower Dawson, Denver, and 

Arapahoe aquifers had some wells with rises in calculated 

groundwater-level elevations, but most wells showed declines 

on the basis of statistically significant trends and the relative 

differences in static groundwater-level elevations between the 

February 2012 and February 2019 measurements. Neither of 

the two wells in the Laramie-Fox Hills aquifer showed significant trends in groundwater-level elevations, and these wells 

had few static discrete measurements, precluding a comparison 

between 2012 and 2019 static groundwater-level elevations. 

Of the 13 wells in the upper Dawson, lower Dawson, Denver, 

and Arapahoe aquifers with significant trends in discrete 

groundwater-level elevation measurements, the records of 

12 wells demonstrated negative trends during the study period. 

The upper Dawson, lower Dawson, Denver, and Arapahoe 

aquifers had median significant trends of −0.23, −0.31, −0.92, 

and −2.26 feet per year, respectively. Although the Arapahoe 

aquifer had the greatest negative median trend, this median 

only represents one well with significant trends. Otherwise, 

the Denver aquifer had the next greatest negative trend, with 

a median trend of −0.92 foot per year. Significant trends in 

time-series groundwater-level elevations agreed with significant trends in discrete groundwater-level elevations; for all 

wells with statistically significant trends in discrete and in 

time-series groundwater-level elevation data, trend estimates 

from the two records were within 0.1 foot per year of each 

other. Potentiometric-surface maps of the upper Dawson, 

lower Dawson, and Denver aquifers, created using discrete 

static groundwater levels measured in February 2019, show 

that groundwater flow direction for the upper Dawson, lower 

Dawson, and Denver aquifers is generally from south to north. 

Results of this study could guide future groundwater monitoring 

in the county and aid in long-term planning of water resources.

Introduction

Douglas County is a rapidly urbanizing county to the 

south of Denver, Colorado, along the foothills of the Colorado 

Front Range Mountains, and the county relies on groundwater 

withdrawals from the bedrock aquifers in the Denver Basin 

aquifer system (also referred to as the Denver Basin bedrock 

aquifers) (fig. 1). Douglas County is one of the fastest growing 

counties in Colorado, according to the U.S. Census Bureau. 

In 1990, the population of Douglas County was more than 

60,000 people (U.S. Census Bureau, 1995). Between 2000 

and 2019, the population increased by more than 100 percent 

from 175,766 to approximately 358,000 residents, and the 

Douglas County Planning Commission estimates the population will grow to more than 418,000 by 2030 (Douglas County 

Demographic Summary, 2019; Douglas County Department of 

Community Development, 2019).
2 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

Development of groundwater resources is necessary to 

meet the growing water needs of Douglas County. Although 

some water providers in the county have surface-water rights, 

their allocations do not provide enough water to satisfy the 

renewable supplies necessary to fulfill the existing water 

demands of the county (Douglas County, 2019). Therefore, 

groundwater from the Denver Basin aquifer system, which 

underlies the northeastern two-thirds of Douglas County (fig. 1), 

provides a critical component to water supply in the county.

Despite the recent growth of Douglas County, the county 

retains a mixture of rural and suburban land use, and municipal 

and domestic (private) water users rely on groundwater from 

Denver Basin bedrock aquifers. In 2004, 13 local municipalities’ 

water authorities in the south Denver metropolitan area 

combined to form the South Metro Water Supply Authority 

(SMWSA). Approximately 80 percent of Douglas County is 

served by SMWSA (SMWSA, undated), and although domestic 

groundwater use is less than municipal use, residents in rural 

parts of the county depend solely on self-supplied groundwater (Paschke, 2011). In October 2008, the Rural Water 

Authority of Douglas County (RWADC) was created to assist 

county residents in developing water resources and systems 

for the benefit of all water users and landowners within 

the county. The RWADC mission is to assist the more than 

8,000 rural water users and local water districts in the county 

by evaluating current and future water supplies and demand 

(RWADC, 2019a).

In the late 2000s, SMWSA recognized that regional 

demand on groundwater resources from the Denver Basin 

bedrock aquifers was outpacing recharge and, thus, the reliance 

on groundwater by local municipalities was unsustainable 

(SMWSA, undated). However, almost one-half of the municipal 

water supply in the south Denver metropolitan area was 

still provided by the Denver Basin aquifer system in 2019 

(SMWSA, 2020).

In 2011, the U.S. Geological Survey (USGS), in 

cooperation with the RWADC, began a study to assess the 

groundwater resources of the Denver Basin bedrock aquifers 

within the county by establishing and maintaining a groundwater 

monitoring network (fig. 2) and by analyzing the groundwater 

levels of the Denver Basin bedrock aquifers throughout 

Douglas County (Everett, 2014). The establishment of a 

monitoring network allowed for assessment of the current 

groundwater resource and provided the basis from which 

to monitor long-term changes of the hydrologic system. In 

subsequent years, with cooperation from the RWADC, the 

USGS has continued routine discrete (manual) measurements 

of groundwater levels and with additional funding from the 

Colorado Water Conservation Board equipped and maintained 

instruments in 15 wells that record groundwater levels on an 

hourly basis. Continued monitoring improves the ability to 

assess short- and long-term changes in the groundwater-level 

elevations and can aid communities in water-resource 

management.

Purpose and Scope

This report builds upon initial observations made by 

Everett (2014), who examined groundwater-level elevations 

measured in Douglas County from 2011 through 2013. This 

report uses data from a network of 36 groundwater wells 

where discrete measurements of groundwater levels were 

made bimonthly from 2012 through 2014 and annually from 

2015 through 2019. There were at least two wells in each of 

the Denver Basin bedrock aquifers. The purpose of this report 

is to summarize groundwater levels measured during the study 

period and present results from statistical analyses of changes 

in groundwater-level elevations through time (trends) in the 

Denver Basin bedrock aquifers in Douglas County, Colorado, 

from January 2012 through June 2019. During 2011, wells were 

added to the monitoring network in phases, so that the start dates 

of the well records are noncontemporaneous. For this reason, 

the study period, including summarized groundwater levels, 

covers 2011–19, whereas the statistical analysis period covers 

2012–19. Of the wells added to the monitoring network, 15 

were instrumented with pressure transducers that measure 

and record groundwater-level data on an hourly basis, herein 

referred to as time-series data (fig. 2). To keep temporal 

trend analysis among wells consistent, the periods of record 

used in statistical analyses were from February 2012 through 

February 2019 for the discrete data and from January 2012 

through June 2019 for the time-series data.

Previous Studies

Since the late 1800s, the Denver Basin aquifer system 

has been the subject of numerous studies examining the geology, structure, and hydrogeology of the basin and its bedrock 

aquifers. Systematic hydrogeologic characterization of the 

Denver Basin bedrock aquifers began in the 1970s as part of 

the development of nontributary groundwater rules established 

by Colorado Senate Bill 213 (Graham and Van Slyke, 2004). 

The Colorado Division of Water Resources (CDWR) and the 

USGS collaborated through the 1970s and 1980s by mapping 

and characterizing the primary aquifers of the Denver Basin 

aquifer system. These studies, listed or summarized in Wireman 

and Romero (1989) and Paschke (2011), were crucial to the 

development of a groundwater flow model (Robson, 1987) and 

a fully three-dimensional MODFLOW–2000 groundwater 

flow model (Paschke, 2011) of the Denver Basin aquifer system. 

Everett (2014) and Penn and Everett (2019) summarized 

findings from recent groundwater monitoring in Douglas and 

Elbert Counties, respectively, and included descriptions of 

the characterization studies, and Everett (2014) described the 

principal aquifers’ geology in detail. Additional studies have 

investigated the hydrology and water quality of the Arapahoe 

aquifer (Hillier and others, 1978) and the Denver Basin aquifer 

system (Bauch and others, 2014).
Introduction 3

South Platte River

Plum 

Creek

25

25

76

70

A A' B'

B

WELD

COUNTY

MORGAN

COUNTY

WASHINGTON COUNTY

LINCOLN

COUNTY

ELBERT

COUNTY

EL PASO

COUNTY

TELLER

COUNTY

DOUGLAS

COUNTY

JEFFERSON

COUNTY

BOULDER

COUNTY

LARIMER

COUNTY

PARK

COUNTY

ADAMS COUNTY

ARAPAHOE COUNTY

DENVER

COUNTY

FREMONT

COUNTY COLORADO FRONT RANGE MOUNTAINS

Palmer Divide

Cherry Creek

EXPLANATION

Upper Dawson 

Lower Dawson 

Denver 

Arapahoe 

Laramie-Fox Hills 

Aquifer extent Douglas County study

 area boundary

Line of section A A'

Base from U.S. Geological Survey digital data, 2014

Universal Transverse Mercator, Zone 13

North American Datum of 1983

Denver Basin aquifer system extent from Paschke, 2011

0 5 10 15 20 KILOMETERS

0 5 10 15 20 MILES

105°30' 104°30'

39°30'

105°00' 104°00'

40°00'

39°00'

"

"

Boulder

Denver

Parker

Castle

Rock

Colorado Springs

Limon

Greeley

Fort Morgan

Denver Basin 

aquifer system

extent

DOUGLAS

COUNTY

COLORADO

Figure 1. Location of the Denver Basin aquifer system and geologic lines of section A, A–A’ and B, B–B’ near Douglas 

County, Colorado. 
4 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

Base from U.S. Geological Survey digital data, 2014

Universal Transverse Mercator, Zone 13

North American Datum of 1983

§ ̈¦25

£¤85

Parker

Franktown

Larkspur

Castle Rock

Louviers

Highlands

Ranch

Deckers

Sedalia

DOUGLAS

COUNTY

JEFFERSON

COUNTY

ARAPAHOE COUNTY

ELBERT COUNTY

TELLER COUNTY EL PASO COUNTY

PARK

COUNTY

DENV 8 LDAW 2

LDAW 3

LDAW 6

DENV 7 UDAW 1

DENV 3

LDAW 11

LDAW 7

DENV 1

UDAW 7

DENV 2

DENV 10

DENV 4 UDAW 5

DENV 5

LDAW 4

UDAW 3

UDAW 6

LARA 1

LARA 2

LDAW 5

ARAP 1

UDAW 2

UDAW 10 UDAW 4

LDAW10

DENV 6

ARAP 2 UDAW 9

LDAW 9 UDAW 8 GRNDEV 3

GRNDAW 4 DENV 11

LDAW 8

39°30'

39°20'

39°10'

105°20' 105°10' 105°00' 104°50' 104°40'

EXPLANATION

Aquifer extent

Upper Dawson

Lower Dawson

Denver

Arapahoe

Laramie-Fox Hills

Alluvial

Well location and 

producing aquifer

Upper Dawson

Lower Dawson 

Denver

Arapahoe

Laramie-Fox Hills

Well with pressure transducer

Douglas County 

study area boundary

UDAW 1 Well common name

 Well common name abbreviations

UDAW upper Dawson aquifer well

LDAW lower Dawson aquifer well

GRNDAW Grandview Estates lower Dawson 

aquifer well 

DENV Denver aquifer well

GRNDEV Grandview Estates Denver 

aquifer well 

ARAP Arapahoe aquifer well 

LARA Laramie-Fox Hills aquifer well

0 5 10 KILOMETERS

0 5 10 MILES

DOUGLAS

COUNTY

COLORADO

Figure 2. Location of groundwater-level monitoring network wells and producing aquifer, Douglas County, Colorado.
Introduction 5

Historically, monitoring of groundwater levels in the 

Denver Basin bedrock aquifers has been intermittent (Colorado 

Water Conservation Board, 2004, 2006), with contributions from 

several entities—the USGS (McConaghy and others, 1964), the 

Colorado Water Conservation Board (McConaghy and others, 1964), the CDWR (Pottorff and Horn, 2013; Flor, 2017), 

and local municipalities (Flor, 2017). As of 2017, the CDWR 

groundwater network monitors groundwater levels in about 

89 municipal and domestic wells within the Denver Basin aquifer 

system on an annual basis (Pottorff and Horn, 2013; Flor, 2017). 

Recently, Moore and others (2007) assessed groundwater use 

and population growth and summarized problems associated 

with groundwater development in Douglas County, an ongoing 

topic of interest for residents and municipal leaders. In neighboring Elbert County (fig. 1), a groundwater-level monitoring 

network similar to the Douglas County network presented in 

this report, has been operating since 2015 (Penn and Everett, 

2019). This report builds upon initial observations made by 

Everett (2014), who summarized groundwater-level elevations 

measured in Douglas County from 2011 through 2013.

Description of Study Area

Douglas County encompasses an 842-square-mile area 

at the base of the Colorado Front Range Mountains, midway 

between Denver and Colorado Springs (fig. 1). The county is 

bounded by the South Platte River and Jefferson County to the 

west, Arapahoe County to the north, Elbert County to the east, 

and Teller and El Paso Counties to the south (fig. 1). Douglas 

County is mostly rural, although the area is experiencing rapid 

residential and commercial development (Douglas County 

Department of Community Development, 2019), expanding outward from the Denver metropolitan area and along Interstate 25 

(fig. 1). However, parts of the southeast plains and the mountainous southwest corner of the county, largely designated as 

national forest, remain relatively unpopulated (Douglas County 

Department of Community Development, 2019). The topography 

of the county is varied and includes mountains, foothills, ridgelines, mesas, and plains. Vegetation changes with topography. 

The mountains are characterized by pine, spruce, and fir trees; the 

foothills by gamble oak, mountain mahogany, and chokecherry; 

the riparian zones by cottonwood trees, willows, and lush grasses; 

and the plains by blue grama, switch grass, and winter wheat 

grasses (Douglas County Department of Community Development, 

2019). The South Platte River and its tributaries, Cherry and 

Plum Creeks, flow north through the county (fig. 1).

Description of the Denver Basin Aquifer System

The western edge of the Denver Basin aquifer system 

borders the base of the Colorado Front Range Mountains and 

extends into the eastern plains of Colorado, covering an area 

of approximately 7,000 square miles (Bauch and others, 2014) 

(fig. 1). The northernmost extent ends near the city of Greeley 

in Weld County, and the southern extent passes under the 

topographic Palmer Divide and ends southeast of Colorado 

Springs in El Paso County. The eastern edge runs parallel with 

the eastern borders of Adams, Arapahoe, and Elbert Counties. 

The basin’s western extent bisects Douglas County, along the 

base of the Colorado Front Range Mountains (fig. 1). The 

northeastern two-thirds of the county are underlain by the 

Denver Basin aquifer system, and private well owners draw 

from one of the principal bedrock aquifers or the surficial 

alluvial aquifers (Paschke, 2011). Approximately one-third of 

Douglas County is west of the Denver Basin aquifer system’s 

western edge, outside the study area, and is underlain by granitic 

bedrock of the mountains (Tweto, 1979).

The bedrock aquifers in the Denver Basin aquifer system 

have a synorogenic, bowl-like structure composed of Late 

Cretaceous to Tertiary-age sandstone bedrock separated 

by unnamed claystone confining units (Fenneman, 1931; 

Robson, 1987; Paschke, 2011) and bounded at the base by the 

Cretaceous-age Pierre Shale (fig. 3, table 1). The four principal bedrock aquifers, from youngest (shallowest) to oldest 

(deepest), are the Dawson aquifer in the Dawson Formation, 

Denver aquifer in the Denver Formation, Arapahoe aquifer in 

the Arapahoe Formation, and Laramie-Fox Hills aquifer in the 

Laramie Formation and Fox Hills Sandstone (fig. 3). The consolidated sediments comprising these aquifers were deposited 

during different periods of mountain-building and have physical properties (sediment grain size, porosity, specific yield, and 

hydraulic conductivity) that differ among aquifers and across 

the basin. Parts of the basin are overlain by unconsolidated 

alluvial aquifers (fig. 2). In parts of the Denver Basin aquifer 

system, the Arapahoe and Dawson aquifers are divided by 

discontinuous confining units into upper and lower aquifers. 

Across Douglas County, the Arapahoe aquifer is undivided. 

The Dawson aquifer is divided into upper and lower aquifers 

in the northeast part of the county (fig. 1). Outcrops of each 

bedrock formation are along the outer edge of the associated 

aquifer extent where the aquifers are generally considered 

unconfined, whereas confined conditions exist towards the 

interior of the basin in each aquifer where deeper bedrock 

aquifers are overlain by younger confining units (fig. 3) 

(Paschke, 2011).

Many studies have previously investigated the extent, 

thickness, age, and physical properties of each aquifer. The 

physical characteristics of the Denver Basin bedrock aquifers 

are summarized in table 1. Studies from which the information in table 1 was acquired are Romero (1976), Kirkham and 

Ladwig (1979), Schneider (1980), Robson and others (1981a), 

Robson and others (1981b), Robson (1987), Crifasi (1992), 

Raynolds and others (2001), Raynolds (2002, 2004), and 

Paschke (2011). The reader is referred to Everett (2014) for 

synopsis of the work completed by the aforementioned authors 

and descriptions of the hydrostratigraphy and depositional 

conditions of the aquifers.
6 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

Study Methods

This section describes how groundwater-level measurements were made and processed, how to access data, the statistical tools used to analyze trends in groundwater-level elevations 

throughout the county, and how potentiometric-surface and trend 

maps were created from static groundwater-level elevations.

The Douglas County groundwater monitoring network 

described in this study was established in the 2011, and the 

methods related to establishing a groundwater monitoring 

network—how target areas were identified, study wells were 

selected, and land-surface elevations were surveyed using a 

real-time kinetic global positioning system—were described 

by Everett (2014). All survey data were collected with a 

common coordinate system, geoid, ellipsoid, and datum. The 

coordinate system used was Universal Transverse Mercator, 

zone 13 north, using the horizontal datum North American 

Datum of 1983 (NAD 83), and the vertical datum North 

American Vertical Datum of 1988 (NAVD 88), Geoid 03, 

ellipsoid World Geodetic System.

Groundwater-Level Measurements and 

Groundwater-Level Elevations

This section presents the methods used for measuring 

and processing the discrete and time-series groundwater levels 

analyzed in this study. Groundwater levels are presented as 

depth to groundwater in feet below land-surface datum (LSD). 

Calculated groundwater-level elevations are presented in feet 

above NAVD 88. This report presents data from 36 wells 

across Douglas County, with at least 2 wells in each of the 

Denver Basin bedrock aquifers. Well common names include 

the following abbreviations: UDAW, upper Dawson aquifer 

well; LDAW, lower Dawson aquifer well; DENV, Denver 

aquifer well; ARAP, Arapahoe aquifer well; LARA, LaramieFox Hills aquifer well; GRNDAW, Grandview Estates Lower 

Dawson aquifer well; GRNDEV, Grandview Estates, Denver 

aquifer well.

DENVER Watkins

South Platte River

Pierre Shale

Denver Formation Arapahoe Formation

Laramie Formation

Fox Hills Sandstone

Colorado

Springs

Watkins

South Platte River

Pierre Shale

Denver Formation

Arapahoe Formation

Laramie Formation Fox Hills Sandstone

Castle Rock Conglomerate

Dawson Formation

Greeley

0 10 20 30 KILOMETERS

0 10 20 30 MILES

7,000

6,000

5,000

4,000

3,000

A'

FEET FEET

7,000

6,000

5,000

4,000

3,000

A

FEET

SOUTH NORTH

WEST EAST

7,000

6,000

5,000

4,000

3,000

B'

8,000

FEET

7,000

6,000

5,000

4,000

3,000

B

8,000

VERTICAL EXAGGERATION × 32

NORTH AMERICAN VERTICAL DATUM OF 1988

Modified from Robson, 1987

B

A

Figure 3. Generalized geologic cross-sections A, A–A', west to east, and B, B–B', south to north, through the Denver Basin aquifer 

system. See figure 1 for cross-section locations and table 1 for bedrock aquifer descriptions within each geologic unit.
Study Methods 7

Discrete Groundwater-Level Measurements and 

Groundwater-Level Elevations

Groundwater levels were routinely measured in 36 wells 

during the study period, beginning in April 2011 through 

June 2019 (table 2). Because of access issues, routine measurements were discontinued recently at three wells (UDAW 1, 

UDAW 7, and UDAW 8), including one well outfitted with a 

pressure transducer (UDAW 1) (table 2). For calendar years 

2011–14, discrete measurements were made approximately 

bimonthly (in February, April, June, August, October, and 

December). Beginning in 2015, measurement frequency was 

reduced to one measurement per year in February at all wells. 

The measurement timing in late winter reduces the likelihood 

of pumping for lawn or garden irrigation. Although this timing 

does not prevent domestic use, the reduced water use generally decreases stress on the hydraulic system and can provide 

groundwater-level measurements that are more representative of 

the system’s static conditions. Additional manual measurements 

were made at 15 wells instrumented with pressure transducers during routine service visits (table 2). The procedures for 

making discrete groundwater-level measurements are outlined 

in Cunningham and Schalk (2011), with the exception that a 

break-away weight was not used because of concerns that the 

weight could get entangled with pump wiring or piping.

A measuring point (MP) was established on the casing of 

each well as a consistent point from which to make measurements (fig. 1.1). The height of each MP above the land surface 

was manually measured. The elevation of each well’s MP was 

determined using the real-time kinetic global positioning system 

survey, described by Everett (2014). The LSD of each well 

was calculated by subtracting the well MP height from the MP 

elevation determined by the survey. Coordinates and elevation 

of LSD for each well are summarized in table 2. By computing 

the elevation of LSD for each well with a consistent coordinate 

system, horizontal datum, and vertical datum, groundwater-level 

elevations can be calculated and accurately compared across 

Douglas County.

For most discrete measurements, a calibrated steel tape 

was lowered down the well to record the depth to groundwater 

from the well MP (fig. 1.1). In instances where a steel tape 

could not be used (such as excessive moisture causing fouled 

Table 1. Physical characteristics of bedrock aquifers in the Denver Basin aquifer system.

[See figure 1 for extent and location of aquifers and extent and location of Douglas County. mi2, square mile; ft, foot; N/A, not applicable]

Bedrock 

aquifer

Total 

surface 

area 

(mi2)

Area 

within 

Douglas 

County 

(mi2)

Minimum 

thickness 

(ft)

Maximum 

thickness 

(ft)

Mean 

water-yielding 

thickness 

(ft)

Composition Age Top confining 

layers

Upper 

Dawson1

600 298 100 1,100 100–400 Dawson Formation: interbedded 

fluvial conglomerate, sandstone, 

siltstone, shale

Tertiary N/A—unconfined

Lower 

Dawson1

1,400 488 100 1,100 100–40 Dawson Formation: interbedded 

fluvial conglomerate, sandstone, 

siltstone, shale

Tertiary Clay and shale

Denver2 3,200 532 600 1,200 100–300 Denver Formation: interbedded 

shale, claystone, siltstone, 

sandstone, coal, and volcanic 

ash and rocks

Late 

Cretaceous 

to early 

Tertiary

Heterogeneous 

claystone and shale

Arapahoe3 4,700 540 400 700 200–300 Arapahoe Formation: interbedded 

conglomerate, sandstone, 

siltstone, shale

Late 

Cretaceous

Upper Arapahoe 

Formation 

fine-grained 

deposits

Laramie-Fox 

Hills4

7,000 532 10 400 150 Laramie Formation: very fine- to 

medium-grained sandstone with 

interstitial silt and clay; Fox 

Hills Sandstone: very fine-grained 

silty sandstone and shaly siltstone 

with interbedded shale

Late 

Cretaceous

Upper Laramie 

Formation gray to 

black shale, coal 

seams, siltstone, 

sandstone

1Romero, 1976; Robson and others, 1981b; Robson, 1987; Raynolds and others, 2001; Raynolds, 2002; Paschke, 2011.

2Romero, 1976; Kirkham and Ladwig, 1979; Robson and others, 1981b; Robson, 1987; Crifasi, 1992; Raynolds and others, 2001; Raynolds, 2002; Paschke, 2011.

3Romero, 1976; Robson and others, 1981a; Robson, 1987; Raynolds and others, 2001; Raynolds, 2002; Raynolds, 2004; Paschke, 2011.

4Romero, 1976; Schneider, 1980; Robson and others, 1981b; Robson, 1987; Raynolds and others, 2001; Raynolds, 2002; Paschke, 2011.
8 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

readings, erratic levels because of pumping, or difficulties 

with a well access port), a calibrated electrical tape was used 

(fig. 1.1). In each instance, the depth to groundwater from the 

MP was recorded to the nearest 0.01 foot (ft) and corrected 

for the height of the MP above LSD to give a final reading of 

measured depth to groundwater below LSD. To determine if 

the groundwater level measured in the well was static and to 

follow USGS protocol as a quality-control measure, a second 

check measurement was made, typically 3–5 minutes after the 

first measurement. Measurements that differed by 0.02 ft or 

less were considered static and a reliable measurement.

When the check measurement did not agree with the 

original measurement, additional measurements were made until 

the reason for lack of agreement was determined, or results 

were determined to be reliably representative of field conditions. 

Subsequent measurements were made to document the status of the 

groundwater level in the well. If consecutive measurements indicated a rising groundwater level (decreasing depth to groundwater), 

the well was considered to be recovering from recent pumping, 

and the highest groundwater level (smallest depth to groundwater) 

measured during the field visit was assigned a status of “R,” 

indicating recently pumped. Typical reasons for recently pumped 

wells include water use for lawn irrigation systems, washing 

machines, or flushing toilets. If consecutive measurements indicated a slowly decreasing groundwater level (increasing depth 

to groundwater), the well was considered to be affected by one 

or more wells pumping nearby from the same aquifer, and the 

highest groundwater level measured during the field visit was 

assigned a status of “S,” indicating nearby pumping. Typical 

reasons for nearby pumping include agricultural operations or 

domestic use. If the pump in the well was cycling on and off, the 

measured depth to groundwater was usually erratic and did not 

follow a pattern. If the well owners were available, they were 

asked to temporarily suspend water use during the field visit 

so that an “R” status could be obtained. If the pump could not 

be turned off, the highest groundwater level (smallest depth to 

groundwater) measured during the field visit was given the status 

of “P,” indicating pumping. Static measurements, which were 

made approximately 80 percent of the time, are ideal for assessing 

changes and estimating temporal trends— quantified changes 

through time— in aquifer groundwater levels (appendix 2).

In this report, groundwater-level elevation is calculated 

from groundwater level below LSD according to the following 

equation:

Groundwater-level elevation = 

LSD – Water level below LSD (1)

where

Groundwater-level 

elevation

is groundwater-level elevation, in feet 

above NAVD 88;

LSD is land-surface datum, in feet above 

NAVD 88; and

Groundwater level 

below LSD

is measured depth, in feet, to groundwater 

below land-surface datum.

Time-Series Groundwater-Level Measurements 

and Groundwater-Level Elevations

Of the 36 wells in the monitoring network, 15 were 

instrumented with a pressure transducer containing an internal 

data logger (table 2) (fig. 2). The pressure transducers are 

vented and rated for a 69-ft range in a freshwater-water 

column, with a manufacturer accuracy of plus or minus (±) 

0.05 percent at 59 degrees Fahrenheit (15 degrees Celsius) 

(In Situ, Inc., 2020). The transducers are suspended in the 

well on a vented communication cable that allows the user to 

download data from the instrument while the transducer remains 

in place and to use the data directly to calculate depth to water, 

without needing to correct for barometric pressure. The internal 

data logger was programmed to record depth to groundwater 

below LSD every hour, calibrated using a concurrent, static 

discrete groundwater-level measurement, following the methods 

described in Cunningham and Schalk (2011).

Each transducer was downloaded, serviced, and 

calibrated during each site visit. At the time of each discrete 

groundwater-level measurement, a concurrent instantaneous 

transducer groundwater-level measurement was recorded. In 

instances where the transducer measurement had drifted greater 

than 0.10 ft from the concurrent discrete groundwater-level 

measurement, the transducer was reset to match the discrete value 

for depth to groundwater. However, if the groundwater-levels 

were not static, no attempt was made to reset the transducer. 

Hourly data were uploaded to the USGS National Water 

Information System (NWIS) database and processed following 

USGS guidelines (Freeman and others, 2004). To account for 

instrument drift, time-series groundwater-level records were 

corrected to match discrete groundwater-level measurements. 

To more accurately compare data from different wells, discrete 

and time-series groundwater-level measurements were 

converted to groundwater-level elevation using equation 1. 

Daily mean, minimum, and maximum groundwater-level 

elevations were computed from the hourly groundwater-level 

elevation values.

Accessing Data

All discrete and time-series groundwater levels summarized 

in this report are publicly available through the NWIS database 

at https://doi.org/10.5066/F7P55KJN (U.S. Geological Survey, 

2020) by using the site identification numbers in table 2. 

The NWIS website provides an interface for accessing site 

information and data collected by the USGS and is regularly 

updated to reflect the most current data. Users of the interface 

can retrieve USGS data by category, region, site number, or 

many other criteria and can produce tables and graphs for 

web viewing or export. Data accessible from NWIS can be 

downloaded in the R statistical software (R Core Team, 2018) 

using the USGS “dataRetrieval” package (Hirsch and De 

Cicco, 2015).
Table 2. Well identification and location information and a summary of discrete groundwater-level measurements, April 2011 through June 2019, Do[Well data can be downloaded using the site identification numbers in the U.S. Geological Survey National Water Information System (NWIS) database https://doi.org/10.5066

well locations. Bold indicates site instrumented with a pressure transducer. NAD 83, North American Datum of 1983; LSD, land-surface datum; ft, foot; NAVD 88, North Amebls, below land surface; “R,” recently pumped; “S,” nearby pumping; “P,” pumping; UDAW, upper Dawson aquifer well;°, degrees; ′, minutes; ′′, seconds; LDAW, lower Daws

Grandview Estates, lower Dawson aquifer well; DENV, Denver aquifer well; GRNDEV, Grandview Estates, Denver aquifer well; ARAP, Arapahoe aquifer well; LARA, Laram

Site identification 

number

Well 

common 

name

Latitude 

(NAD 83) 

(degrees, minutes, 

seconds)

Longitude 

(NAD 83) 

(degrees, minutes, 

seconds)

Elevation of 

LSD (ft above 

NAVD 88)

Well 

depth 

(ft bls)

Total 

measurements

Number 

of static 

measurements

Number of 

measurements 

with status 

“R”

Number of 

measurements 

with status 

“S”

Number of 

measurements 

with status 

“P”

Me

gr

b

391229104421901 UDAW 1a 39°12′22.40′′ −104°42′18.79′′ 6,934.52 320 43 35 7 0 1 

392856104424101 UDAW 2 39°28′51.1′′ −104°42′41.81′′ 6,284.27 310 24 18 5 1 0 392412104434201 UDAW 3 39°24′00.07′′ −104°43′41.47′′ 6,414.87 283 40 34 6 0 0 392934104414901 UDAW 4 39°29′28.68′′ −104°41′45.98′′ 6,267.98 300 41 35 4 2 0 392149104415501 UDAW 5 39°21′42.84′′ −104°41′53.47′′ 6,501.66 350 40 22 17 1 0 392441104394901 UDAW 6 39°24′35.49′′ −104°39′46.81′′ 6,590.31 400 24 24 0 0 0 

391658104453101 UDAW7b 39°16′51.02′′ −104°45′25.37′′ 6,808.79 302 22 19 3 0 0 

393252104434701 UDAW 8c 39°32′44.61′′ −104°43′40.56′′ 6,195.89 213 22 19 3 0 0 393226104394401 UDAW 9 39°32′18.18′′ −104°40′09.34′′ 6,285.29 314 43 35 8 0 0 392916104423601 UDAW10 39°29′10.65′′ −104°42′34.58′′ 6,288.97 320 42 37 5 0 0 390756104453801 LDAW 2 39°07′50.15′′ −104°45′35.11′′ 7,278.15 180 39 39 0 0 0 390811104453801 LDAW 3 39°08′05.45′′ −104°45′36.86′′ 7,308.07 300 24 18 6 0 0 392318104424601 LDAW 4 39°23′13.64′′ −104°42′46.06′′ 6,501.52 723 24 12 12 0 0 392851104450101 LDAW 5 39°28′44.38′′ −104°45′02.28′′ 6,021.79 530 24 14 10 0 0 391143104482501 LDAW 6 39°11′37.67′′ −104°48′22.89′′ 7,085.07 205 37 30 7 0 0 391654104464501 LDAW 7 39°16′48.55′′ −104°46′46.54′′ 6,676.78 345 50 45 3 2 0 392949104523401 LDAW 8 39°29′41.31′′ −104°52′33.56′′ 6,235.80 468 23 19 4 0 0 393239104452901 LDAW 9 39°32′34.88′′ −104°45′33.98′′ 5,908.71 285 24 21 3 0 0 393021104533101 LDAW 10 39°30′14.61′′ −104°53′30.83′′ 6,324.88 620 24 22 1 1 0 391257104530201 LDAW 11 39°12′49.86′′ −104°53′00.55′′ 6,799.61 240 17 15 2 0 0 393259104491001 GRNDAW 4 39°32′25′′ −104°48′49′′ 5,816.50 280 47 42 1 4 0 391656104473001 DENV 1 39°16′43.87′′ −104°47′28.54′′ 6,783.59 600 46 42 4 0 0 391929104574101 DENV 2 39°19′22.18′′ −104°57′40.27′′ 6,268.94 300 45 29 13 3 0 391245104525501 DENV 3 39°12′38.72′′ −104°52′56.68′′ 6,822.46 665 22 22 0 0 0 392115104553501 DENV 4 39°21′09.46′′ −104°55′32.44′′ 6,376.53 480 25 16 9 0 0 392235105003001 DENV 5 39°22′29.42′′ −105°00′30.46′′ 6,317.29 380 46 19 27 0 0 393040105003201 DENV 6 39°30′32.91′′ −105°00′32.78′′ 5,716.55 320 40 31 9 0 0 391212104473801 DENV 7 39°12′02.73′′ −104°47′39.07′′ 7,003.66 900 24 14 10 0 0 390755104454001 DENV 8 39°07′50.14′′ −104°45′40.26′′ 7,265.13 1,300 23 22 1 0 0 391936104570101 DENV 10 39°19′31.13′′ −104°57′00.44′′ 6,410.74 404 24 23 1 0 0 393330104450701 DENV 11 39°33′22.42′′ −104°45′07.66′′ 6,058.29 610 24 22 2 0 0 393252104492101 GRNDEV 3 39°32′51.83′′ −104°49′23.15′′ 5,864.18 463 48 40 8 0 0 392853105015001 ARAP 1 39°28′46.00′′ −105°01′48.83′′ 5,789.08 730 23 22 1 0 0 393120105003101 ARAP 2 39°31′12.83′′ −105°00′30.08′′ 5,750.03 735 23 18 5 0 0 392522105015001 LARA 1 39°25′15.92′′ −105°01′49.28′′ 6,169.43 601 27 8 19 0 0 392522105015401 LARA 2 39°25′15.20′′ −105°01′53.18′′ 6,155.85 480 24 10 14 0 0 

aWell dropped from routine monitoring in April 2019.bWell dropped from routine monitoring in February 2018.cWell dropped from routine monitoring in February 2017.
10 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

Groundwater-Level Elevation Temporal Trend 

Analysis and Mapping

To evaluate the presence of temporal trends in discrete and 

time-series groundwater-level elevation data, nonparametric 

Mann-Kendall (M–K) and nonparametric seasonal Mann-Kendall 

(sM–K) trend tests were used (Helsel and others, 2020), respectively, using the R statistical software and the “smwrStats” 

package (Lorenz, 2014) (appendix 3). Trends, quantified changes 

in groundwater-level elevations through time, were calculated 

using the Sen slope estimate (Sen, 1968; Hirsch and others, 1982) 

(appendix 3) with the “smwrStats” package (Lorenz, 2014). 

These nonparametric statistical methods were chosen because 

the methods require no assumptions of sample distribution, trend 

shape, or data continuity when measuring the strength of trends. 

The reader is referred to appendix 3 for a more detailed description of the statistical methods and the respective equations.

The M–K test (Mann, 1945; Kendall, 1975; Helsel and 

others, 2020) was applied to discrete winter groundwater-level 

elevations, manually measured each February at all 36 wells 

between 2012 and 2019, for a maximum of 8 measurements per 

site. Only the discrete February measurements were used, herein 

referred to as “winter measurements,” because measurement 

frequency at noninstrumented sites (21 out of 36) was reduced 

to once per year starting in 2015. The measurement timing in 

late winter reduces the likelihood of pumping for lawn or garden irrigation. Although this timing does not prevent domestic 

use, the reduced water use generally decreases stress on the 

hydraulic system and can provide groundwater-level measurements that are more representative of the system’s static state. 

To reduce bias from recent or nearby pumping, the test was 

applied to discrete measurements that were determined to be 

static. Although all 36 wells were measured each winter, some 

measurements were affected by pumping, which reduced the 

number of static measurements (n) used in the test (table 3). In 

two cases, wells LDAW 4 and LARA 1, an insufficient number 

of static measurements were available to conduct the analysis; 

therefore, groundwater-level elevations marked with “recently 

pumped” field notes were included in the trend analysis and 

noted in the results table (table 3). The Sen slope estimate is 

referred to as the “trend estimate” or “trend” in groundwaterlevel elevations (the change in groundwater-level elevations 

through time) and is reported in feet per year.

Hydrographs (appendix 2) provide a graphical representation of groundwater-level elevations through time. The 

groundwater-level elevations are denoted by measurement 

status (static, recently pumped, and pumping) and can be 

used as a visual comparison to the calculated trends. For the 

time-series data, the daily maximum elevations were used 

for reporting (appendix 2), and monthly mean values of these 

daily maxima were used for trend analysis. The daily maximum groundwater-level elevations were chosen because these 

elevations tend to best represent periods during the day when 

pumping is not occurring and has not occurred recently at the 

well or at nearby wells.

For the time-series measurements, the sM–K test (Hirsch 

and others, 1982; Helsel and others, 2020) (appendix 3) was 

utilized to account for seasonal variability in groundwater levels, 

at the 15 instrumented sites. The sM–K test was applied to the 

monthly mean values of daily maximum groundwater-level 

elevations, derived from the time-series data. The sM–K tests 

account for temporal correlation caused by seasonality by 

comparing data from a user-defined season only to data from 

the same season (appendix 3). For the sM–K test, seasons 

were defined as individual months to minimize effects of 

temporal correlation among months (for example, January 

data from one year are only compared to January data from 

the following years), and the period used in the analysis was 

January 2012 through June 2019. Trends in time-series data 

were calculated using seasonal Sen slope estimate, which 

follows a similar approach to the sM–K test to account for 

seasonality and was applied to the monthly mean values of 

groundwater-level elevations.

In addition to statistical tests and estimates of trends in 

groundwater-level elevations, relative changes in groundwaterlevel elevations were computed as the difference between the 

February 2012 and February 2019 groundwater-level elevations 

for sites with static discrete measurements in both years. 

These relative differences are not necessarily representative 

of trends, but the differences indicate relative changes at wells 

between the beginning and end of the study period and offer a 

comparison to trend estimates at each well.

For visualization, trend estimates for the upper Dawson, 

lower Dawson, and Denver aquifers were mapped in the study 

area by interpolating the trend estimates among wells completed 

in the same aquifer. These maps are generated solely from the 

reported data and calculations. An inverse distance weighting 

function from the Geostatistical Analyst toolbox in ArcMap 

was applied to interpolate the data (Esri, Inc., variously dated) 

using default inputs and adding a weight field of (1−p-value)2

to graphically emphasize statistically significant trends. The 

trend estimate for well LDAW 4 was not included in the interpolation because not enough static measurements were available to calculate a trend estimate reflecting static conditions. 

Maps of the groundwater-level elevation, also known as 

potentiometric-surface maps, were created to show the hydraulic 

head distribution of the different aquifers in the study area. To 

remove effects of local pumping, only static winter measurements from 2019 were used to produce the maps. The Topo 

to Raster (default options) and Contour functions in ArcMap 

Spatial Analyst Toolbox (Esri, Inc., variously dated) were used 

to derive the hydraulic head distribution and contour lines of 

equal hydraulic head, respectively.
Study Methods 11

Table 3. Trend analysis summary of discrete and time-series groundwater-level elevation data, January 2012 through June 2019, 

Douglas County, Colorado.

[See table 2 and figure 2 for well locations. The discrete data record analyzed was from February 2012 through February 2019, and the time-series data analyzed were 

from January 2012 through June 2019. Only static measurements were used in the discrete dataset, unless noted otherwise. Mann-Kendall trend tests evaluates the 

significance of a monotonic trend in the data (Mann, 1945; Kendall, 1975; Helsel and others, 2020), whereas the Sen slope estimator (Sen, 1968; Hirsch and others, 

1982) calculates the trend, or change in groundwater-level elevations through time. Statistically significant trends—trends were considered significant if the p-value is 

less than the defined alpha of 0.1. See “Methods” section and appendix 3 for details of field measurement and statistical methods used. Bold, italicized font indicates 

trend is significant. n, number of observations used in the analysis; tau, rank correlation coefficient, also known as “Kendall's tau” (Kendall, 1975), which measures 

the strength of the correlation between time and groundwater-level elevations; p-value, probability value, which indicates the level of significance; ft/yr, foot per 

year; UDAW, upper Dawson aquifer well; --, not calculated; LDAW, lower Dawson aquifer well; GRNDAW, Grandview Estates, lower Dawson aquifer well; DENV, 

Denver aquifer well; GRNDEV, Grandview Estates, Denver aquifer well; ARAP, Arapahoe aquifer well; LARA, Laramie-Fox Hills aquifer well]

Well common 

name

Hydrograph appendix 

figure number

Discrete data Time-series data

Mann-Kendall 

trend test

Sen slope 

estimator

Seasonal Mann-Kendall 

trend test

Seasonal Sen slope 

estimator

n tau p-value Trend (ft/yr) tau p-value Trend (ft/yr)

Upper Dawson aquifer

UDAW 1 2.1 7 −0.05 1.000 0.00 0.29 0.204 0.10

UDAW 2 2.2 7 0.43 0.230 0.23 -- -- --

UDAW 3 2.3 8 −0.96 0.001 −0.25 −0.89 0.001 −0.26

UDAW 4 2.4 7 0.43 0.230 0.20 0.27 0.163 0.30

UDAW 5 2.5 5 −0.50 0.312 −0.32 −0.06 0.597 −0.02

UDAW 6 2.6 8 −0.50 0.105 −0.09 -- -- --

UDAW 7 2.7 4 0.50 0.470 0.06 -- -- --

UDAW 8 2.8 5 −0.20 0.806 −0.13 -- -- --

UDAW 9 2.9 6 −0.80 0.035 −0.21 −0.87 0.001 −0.26

UDAW 10 2.10 6 0.40 0.339 0.43 0.61 0.024 0.57

Lower Dawson aquifer

LDAW 2 2.11 8 0.11 0.803 0.23 0.19 0.457 0.41

LDAW 3 2.12 6 0.07 1.000 0.20 -- -- --

LDAW 4a 2.13 8 −0.50 0.108 −8.55 -- -- --

LDAW 5 2.14 5 −0.40 0.462 −0.44 -- -- --

LDAW 6 2.15 7 −0.14 0.764 −0.08 0.06 0.824 0.04

LDAW 7 2.16 8 −0.75 0.013 −0.31 −0.46 0.030

LDAW 8 2.17 5 −0.60 0.221 −0.50 -- --

LDAW 9 2.18 5 0.60 0.221 0.45 -- --

LDAW 10 2.19 7 −1.00 0.003 −0.85 -- --

LDAW 11 2.20 6 1.00 0.009 0.71 -- --

GRNDAW 4 2.21 8 0.43 0.174 0.65 0.29 0.239

−0.23

--

--

--

--

–0.64

Denver aquifer

DENV 1 2.22 6 −0.87 0.024 −1.11 −0.60 0.022 −1.06

DENV 2 2.23 7 −1.00 0.003 −0.73 −0.93 0.001 −0.67

DENV 3 2.24 7 −0.86 0.009 −0.15 -- -- --

DENV 4 2.25 5 −1.00 0.027 −0.92 -- -- --

DENV 5 2.26 6 0.33 0.452 0.77 0.56 0.017 1.42

DENV 6 2.27 7 −1.00 0.003 −0.48 −1.00 0.001 −0.57

DENV 7 2.28 4 0.33 0.734 0.38 -- -- --

DENV 8 2.29 7 −1.00 0.003 −5.51 -- -- --

DENV 10 2.30 7 −1.00 0.003 −0.92 -- -- --

DENV 11 2.31 8 0.29 0.386 0.87 -- -- --

GRNDEV 3 2.32 8 −0.32 0.319 −1.12 −0.09 0.705 −0.59

Arapahoe aquifer

ARAP 1 2.33 8 −1.00 0.001 −2.26 -- -- --

ARAP 2 2.34 7 0.14 0.764 0.73 -- -- --

Laramie-Fox Hills aquifer

LARA 1a 2.35 8 −0.14 0.711 −0.66 -- -- --

LARA 2 2.36 3 −1.00 0.296 −2.03 -- -- --

aInsufficient number of static discrete measurements; both measurements determined to be static and affected by recent pumping used in the trend analysis.
12 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

Groundwater-Level Elevations in the 

Denver Basin Bedrock Aquifers of 

Douglas County

From April 2011 through June 2019, more than 1,100 discrete and 41,000 time-series groundwater-level measurements 

were made in the Douglas County groundwater monitoring 

network. Hydrographs showing groundwater-level elevations 

through time for each well in the network are provided in 

appendix 2.

Seasonal Patterns in Discrete and Time-Series 

Groundwater-Level Elevation Data

In general, groundwater-level elevations were lowest 

during summer and fall and recovered to higher elevations 

in winter and spring (appendix 2). Seasonal patterns were 

clearest in wells with pressure transducers and time-series 

data, but even wells with only discrete measurements showed 

seasonal fluctuations in groundwater-level elevations in the 

early years of the study, when discrete measurements were 

made bimonthly (for example, well UDAW 2, fig. 2.2). Some 

wells showed strong seasonal fluctuations of several feet 

(for example, well DENV 1, fig. 2.22), whereas other wells 

showed minimal seasonality with fluctuations less than 1 ft 

during the year (for example, well DENV 6, fig. 2.27). In 

time-series data, groundwater-level elevations generally were 

highest during winter and spring and lowest during summer 

and fall, except for well LDAW 6 (fig. 2.15), which did not 

have strong seasonal patterns. Seasonal variations are caused 

by natural processes connected to the land surface, including 

precipitation and evapotranspiration, which affect timing 

and amount of aquifer recharge in unconfined aquifer zones 

(Paschke, 2011). Human activities, such as increased irrigation 

for agriculture (during the growing season) and domestic 

pumping (for lawns and gardens), also can affect seasonal 

variations.

Long-Term Trends in Discrete 

Groundwater-Level Elevations

For the discrete groundwater-level elevations, the 

significance of trends between 2012 and 2019 were tested 

using the M–K test, and trend estimates were calculated using 

the Sen slope estimator (table 3). A negative trend indicates 

generally declining groundwater-level elevations in the well 

through time, and a positive trend indicates generally rising 

groundwater-level elevations in the well through time. Results 

of the M–K trend test for the winter static groundwater-level 

elevations indicate that 13 of the 36 wells exhibited statistically 

significant temporal trends (table 3). Wells LDAW 4 and 

LARA 1 had insufficient static measurements to assess trend 

significance, so recently pumped values were included in the 

analysis (table 3). Of the 13 wells with significant trends, 

12 wells had negative trends in groundwater-level elevations. 

Only well LDAW 11, in the lower Dawson aquifer, had a 

significant positive trend of +0.71 foot per year (ft/yr). For all 

aquifers with significant trends in discrete groundwater-level 

elevations, the median trends for each aquifer were negative, 

indicating generally declining groundwater-level elevations in 

each aquifer (table 4).

The upper Dawson aquifer had significant negative trends 

at two wells (UDAW 3 and 9), with a median trend of −0.23 ft/yr

and a maximum negative trend of −0.25 ft/yr. The lower 

Dawson aquifer had significant trends at three wells (LDAW 7, 

LDAW 10, and LDAW 11), with a median trend of −0.31 ft/yr, 

a maximum negative trend of −0.85 ft/yr, and a maximum 

positive trend of +0.71 ft/yr. Significant negative trends were 

present at wells LDAW 7 and LDAW 10, whereas a positive 

trend was present at LDAW 11. The negative trends for wells 

LDAW 7 and LDAW 10 exceeded −0.30 ft/yr (table 3). The 

Denver aquifer had 7 wells with significant negative trends 

(DENV 1, DENV 2, DENV 3, DENV 4, DENV 6, DENV 8, 

and DENV 10), with a median trend of −0.92 ft/yr and a 

maximum negative trend of −5.51 ft/yr. In the Arapahoe 

aquifer, ARAP 1 had a significant trend of −2.26 ft/yr, and the 

Laramie-Fox Hills aquifer had no wells with significant trends. 

Of the 12 wells that had significant negative trends in static 

groundwater-level elevations, 9 wells had negative trends that 

were less than 1 ft/yr (for example, well UDAW 3 had a negative

trend of −0.25 ft/yr). Only three wells, DENV 1 (−1.11 ft/yr), 

ARAP 1 (−2.26 ft/yr), and DENV 8 (−5.51 ft/yr), showed negative trends exceeding 1 ft/yr (table 4). In the Denver aquifer, 

the magnitude of negative groundwater-level elevation trends 

had a larger range than the other aquifers, ranging from −0.15 

to −5.51 ft/yr, with five of the seven negative trends exceeding 

−0.50 ft/yr (table 4).

The magnitude of significant trends is relatively consistent, 

considering the producing aquifer and well locations throughout Douglas County (fig. 4). An exception is well LDAW 11 

along the western edge of the Denver Basin aquifer system, 

(fig. 4), which had the only positive trend. Otherwise, wells 

in proximity and producing from the same aquifer generally 

agree in trend significance and direction. For example, in 

the Denver aquifer wells DENV 2, DENV 4, and DENV 10, 

which are less than 3 miles apart, displayed trends of −0.73, 

−0.92, and −0.92 ft/yr, respectively. Additionally, in the 

upper Dawson aquifer wells UDAW 3 and UDAW 9, which 

are 10 miles apart, displayed trends of −0.25 and −0.21 ft/yr, 

respectively. Both sets of wells show negative trends (with 

medians of −0.92 and −0.23 ft/yr, respectively) and are in 

relatively low-density residential areas covered by the 

RWADC (RWADC, 2019b). The three Denver aquifer wells 

represent confined aquifer conditions, whereas the upper 

Dawson aquifer wells represent unconfined aquifer conditions; 
Groundwater-Level Elevations in the Denver Basin Bedrock Aquifers of Douglas County 13

although both sets of wells exhibit statistically significant 

negative trends in groundwater-level elevations. The one 

Arapahoe well (ARAP 1) with a statistically significant trend 

(−2.26 ft/yr) is under confined conditions and is in the northwest corner of the county (fig. 4).

Differences in the hydraulic head distribution from 

two or more points in time can highlight areas where 

groundwater-level elevations are rising or declining but may or 

may not have trends that are statistically significant. Relative 

changes in discrete groundwater-level elevations between the 

February 2012 and February 2019 static measurements are 

presented in table 5. The negative changes at 16 wells represent 

a relative decline in groundwater-level elevation between the 

two measurements, whereas the 8 wells with a positive change 

represent a rise in groundwater-level elevation. The largest 

groundwater-level elevation decline between the 2 years was 

at well ARAP 1 (−15.61 ft) in the Arapahoe aquifer, but the 

lower Dawson and the Denver aquifers also had multiple wells 

with declines in groundwater-level elevation exceeding 

−5.0 ft. The largest rise between static groundwater-level 

elevations (+3.26 ft) was at well DENV 5, along the western 

edge of the Denver aquifer (fig. 2).

Of the four aquifers that had wells with static measurements in February 2012 and February 2019, three aquifers had 

wells with increases in groundwater-level elevation (upper 

Dawson, lower Dawson, and Denver aquifers). In each of 

these aquifers, at least two wells had a positive change and 

at least three wells had a negative change between the 2012 

and 2019 groundwater-level elevations. Both wells in the 

Arapahoe aquifer had declines in the discrete groundwaterlevel elevations (table 5). Changes were not computed for 

wells in the Laramie-Fox Hills aquifer because two static 

measurements for 2012 and 2019 were not available. Relative 

changes do not represent statistically significant trends in 

groundwater-level elevation at a given well but offer a point of 

comparison for trend results.

Table 4. Statistically significant trends in discrete static groundwater-level elevations, February 2012 through 

February 2019, Douglas County, Colorado.

[See table 2 and figure 2 for well locations. Only statistically significant trends and results are listed in this table. Mann-Kendall trend 

tests evaluates the significance of a monotonic trend in the data (Mann, 1945; Kendall, 1975; Helsel and others, 2020), whereas the 

Sen slope estimator (Sen, 1968; Hirsch and others, 1982) calculates the trend, or change in groundwater-level elevations through time. 

Trends were considered significant if the p-value is less than the defined alpha of 0.1. See “Methods” section and appendix 3 for details 

of statistical methods used. tau, rank correlation coefficient, also known as “Kendall's tau” (Kendall, 1975; Helsel and others, 2020), 

which measures the strength of the correlation between time and groundwater-level elevations; p-value, probability value, which 

indicates the level of significance; ft/yr, foot per year; UDAW, upper Dawson aquifer well; LDAW, lower Dawson aquifer well; DENV, 

Denver aquifer well; ARAP, Arapahoe aquifer well]

Well common name

Mann-Kendall test Sen slope estimator

tau p-value Trend (ft/yr)

Upper Dawson aquifer (significant trend median, −0.23)

UDAW 3 −0.96 0.001 −0.25

UDAW 9 −0.80 0.035 −0.21

Lower Dawson aquifer (significant trend median, −0.31)

LDAW 7 −0.75 0.013 −0.31

LDAW 10 −1.00 0.003 −0.85

LDAW 11 1.00 0.009 0.71

Denver aquifer (significant trend median, −0.92)

DENV 1 −0.87 0.024 −1.11

DENV 2 −1.00 0.003 −0.73

DENV 3 −0.86 0.009 −0.15

DENV 4 −1.00 0.027 −0.92

DENV 6 −1.00 0.003 −0.48

DENV 8 −1.00 0.003 −5.51

DENV 10 −1.00 0.003 −0.92

Arapahoe aquifer (significant trend median, −2.26)

ARAP 1 −1.00 0.001 −2.26
14 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

DOUGLAS

COUNTY

Parker

Franktown

Larkspur

Castle Rock

Louviers

Highlands

Ranch

Deckers

Sedalia

JEFFERSON

COUNTY

ARAPAHOE COUNTY

ELBERT COUNTY

TELLER COUNTY EL PASO COUNTY

PARK

COUNTY

£¤85

§ ̈¦25

"

"

"

"

"

"

Base from U.S. Geological Survey digital data, 2014

Universal Transverse Mercator, Zone 13

North American Datum of 1983

DOUGLAS

COUNTY

COLORADO

ARAP 1

DENV 6

UDAW 9

LDAW10

UDAW3

UDAW 5

LDAW 4

UDAW 6

DENV 10 DENV 2

DENV 4

LDAW 11

DENV 3

DENV 8

DENV 1

LDAW 2 LDAW 3

LDAW 6

DENV 7

UDAW 1

UDAW 7

LDAW 7

DENV 5

LARA 1

LARA 2

LDAW 5

UDAW 2

UDAW 10 UDAW 4

ARAP 2

LDAW 9

GRNDEV 3

GRNDAW 4 DENV 11

LDAW 8

UDAW 8

105°20' 105°10' 104°50' 104°40'

39°30'

39°20'

39°10'

105°00'

EXPLANATION

Aquifer extent

Upper Dawson

Lower Dawson

Denver

Arapahoe

Laramie-Fox Hills

Alluvial

Well location and 

producing aquifer

Upper Dawson

Lower Dawson 

Denver

Arapahoe

Laramie-Fox Hills

No significant trend

Positive significant trend

Negative significant trend

UDAW 1 Well common name

Well common name 

abbreviations

UDAW Upper Dawson aquifer well

LDAW Lower Dawson aquifer well

GRNDAW Grandview Estates lower 

Dawson aquifer well 

DENV Denver aquifer well

GRNDEV Grandview Estates Denver 

aquifer well 

ARAP Arapahoe aquifer well 

LARA Laramie-Fox Hills 

aquifer well 

Significant trends in discrete 

groundwater-level elevations, 

in feet per year

> 5.0

< 1.0 to 5.0

< 0.5 to 1.0

0.0 to 0.5

Douglas County 

study area boundary

0 5 10 KILOMETERS

0 5 10 MILES

Figure 4. Distribution of significant trends in discrete groundwater-level elevation, by aquifer, Douglas County, Colorado.
Groundwater-Level Elevations in the Denver Basin Bedrock Aquifers of Douglas County 15

Long-Term Trends in Time-Series 

Groundwater-Level Elevations

Hydrographs of time-series groundwater-level elevations 

from the 15 instrumented wells were in general agreement with 

discrete groundwater-level elevations measured at the same well 

(see hydrograph appendix figure number listed in table 3).

The sM–K test results of the time-series data are compared 

with the M–K test results from the discrete groundwater-level 

elevations in table 3, and discrete and time-series measurements 

are displayed on hydrographs in appendix 2. Significant trends 

in the time-series groundwater-level elevation data agreed with 

the significant trends’ direction and magnitude calculated from 

discrete data. If significant trends were indicated in the discrete and in the time-series data for a well, the trend estimates 

for the two datasets differed by less than 0.1 ft/yr (table 3). 

Some wells displayed significant trends in the time-series 

data but not the discrete data (wells UDAW 10 and DENV 5) 

(table 3). Continued monitoring and more static measurements 

at these wells may increase the likelihood of significant trend 

occurrence in discrete datasets at these wells in the future.

Three wells screened in the upper Dawson aquifer had 

significant trends in the time-series groundwater-level elevation data (wells UDAW 3, UDAW 9, and UDAW 10). Wells 

UDAW 3 and UDAW 9 had the same trend estimate, −0.26 ft/yr, 

for time-series data. A spike observed in daily data for UDAW 

3 (appendix figure 2.3) in May 2014 was caused by days of 

continuous pumping but did not greatly affect the monthly 

mean used in the trend calculation, and thus did not affect the 

trend’s significance or estimate. In contrast, well UDAW 10 

had a significant positive trend in the time-series data 

(+0.57 ft/yr), although the discrete data positive trend for well 

UDAW 10 was not significant. Only one well screened in the 

lower Dawson aquifer, LDAW 7, had a statistically significant 

trend in the time-series data of −0.23 ft/yr. Of the five wells 

screened in the Denver aquifer with available time-series 

measurements, four wells displayed significant trends (wells 

DENV 1, DENV 2, DENV 5, and DENV 6), with the three 

negative trend estimates exceeding 0.5 ft decline per year 

(wells DENV 1, DENV 2, and DENV 6) (table 3). Only one 

well screened in the Denver aquifer (well DENV 5) had a significant positive trend (+1.42 ft/yr) in the time-series data and 

is approximately 0.5 mile from the western edge of the Denver 

Basin aquifer system (fig. 2). The discrete data trend at well 

DENV 5 was also positive but was not statistically significant. 

No wells in the Arapahoe or Laramie-Fox Hills aquifers have 

pressure transducers and time-series data (table 3).

Potentiometric-Surface and Trend Maps

Maps of the groundwater-level elevation, also known as the 

potentiometric-surface maps, were derived from static discrete 

groundwater levels measured in February 2019 in the upper 

Dawson, lower Dawson, and Denver aquifers (figs. 5, 6, and 7, 

respectively). The potentiometric surface can be used to show the 

general direction of groundwater flow. Groundwater flow is from 

areas of high hydraulic head (higher groundwater-level elevation) 

to areas of low hydraulic head (lower groundwater-level elevation); flow direction is assumed to be generally perpendicular to 

the contours. The February 2019 potentiometric surfaces for the 

three aquifers are displayed using 100-ft contour intervals, and 

groundwater-level elevation trends in each aquifer are mapped 

with spatial weighting that takes trend significance into account.

Based on the derived static potentiometric-surface maps 

for February 2019, groundwater-level elevations in the upper 

Dawson aquifer are highest east of Franktown (fig. 5A) along 

the eastern edge of the county, and lower groundwater-level 

elevations are east of Parker. From the 2019 data, groundwater flow is generally from south to north in the upper Dawson 

aquifer. In the lower Dawson aquifer, groundwater flow is generally from south to north (fig. 6A). Groundwater elevations 

are highest in the southeast and lowest in the northwest in the 

Denver aquifer, and groundwater flow is from the southeast to 

the northwest (fig. 7A). General flow direction patterns across 

the three aquifers are similar to earlier observations across 

Douglas County (Everett, 2014).

The trends in discrete groundwater-level elevations 

(2012–19) were mapped for the upper Dawson, lower 

Dawson, and Denver aquifers (figs. 5, 6, and 7, respectively). 

Trends of the upper Dawson aquifer show slight negative 

changes (groundwater-level elevation declines) of less than 

0.5 ft/yr to the east of Franktown and slight positive trends of 

less than 0.5 ft/yr southeast of the town of Parker (fig. 5B). 

These changes show similar patterns to difference maps 

derived in western Elbert County (Penn and Everett, 2019), 

which showed relative increases and decreases between 

April 2015 and 2018 in upper Dawson groundwater levels of 

less than 1 ft. However, the two sets of derived maps represent 

different periods of record and times of the year, and the two 

sets do not overlap in spatial coverage. Trends mapped in the 

lower Dawson aquifer varied within the county, with the greatest negative trends southeast of Highlands Ranch (fig. 6B). 

Slightly upward trends are indicated at wells in the northern 

edge of the county and the southwestern edge of the county. 

The only well with a statistically significant positive trend 

is in the southwestern edge of the aquifer. Unlike the other 

wells with positive trends to the north, this well (LDAW 11) 

is within the unconfined part of the lower Dawson aquifer 

(fig. 4), and recharge might contribute to the statistically significant upward trend. In the Denver aquifer, negative trends 

were observed across the county with greater negative trends 

to the southeast, although the significant negative trend in well 

DENV 8 has a large effect on the interpolation (fig. 7B).

Across Douglas County, proximal locations of wells with 

and without significant trends may indicate local influences 

on groundwater-level elevations, such as local water use and 

management or the presence of localized recharge zones, 

especially in areas where the aquifers are unconfined and 

receive greater recharge (Paschke, 2011). For example, three 

wells with statistically significant positive trends in either 

the discrete data (LDAW 11) (fig. 4) or the time-series data 

(DENV 5 and UDAW 10) (table 3) are in areas of potential 

recharge. Wells LDAW 11 and UDAW 10 are wells producing 

from unconfined aquifers, and well DENV 5 is less than 1 mile 

from the western edge of the basin (fig. 2).
16 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

Table 5. Values and differences in static discrete groundwater-level elevations, February 2012 and 2019, Douglas County, Colorado.

[See table 2 and figure 2 for well locations. Only static groundwater-level elevations listed. GW–L, groundwater-level; ft, foot; NAVD 88, North American 

Vertical Datum of 1988; UDAW, upper Dawson aquifer; --, data not available or unable to be calculated; LDAW, lower Dawson aquifer well; GRNDAW, 

Grandview Estates lower Dawson aquifer well; DENV, Denver aquifer well; GRNDEV, Grandview Estates, Denver aquifer well; ARAP, Arapahoe aquifer 

well; LARA, Laramie-Fox Hills aquifer well]

Well common name

2012 2019

Difference (ft) Date GW–L elevation 

(ft above NAVD 88) Date GW–L elevation (ft above NAVD 88)

Upper Dawson aquifer

UDAW 1 2/1/2012 6,843.96 -- -- --

UDAW 2 2/10/2012 6,147.56 2/22/2019 6,148.10 0.54

UDAW 3 2/2/2012 6,260.24 2/22/2019 6,258.43 −1.81

UDAW 4 2/2/2012 6,153.61 2/22/2019 6,153.89 0.28

UDAW 5 2/1/2012 6,374.94 2/22/2019 6,372.65 −2.29

UDAW 6 2/2/2012 6,375.05 2/22/2019 6,373.92 −1.13

UDAW 7 2/2/2012 6,654.72 -- -- --

UDAW 8 2/10/2012 6,028.30 -- -- --

UDAW 9 -- -- 2/22/2019 6,073.95 --

UDAW 10 2/10/2012 6,176.39 2/22/2019 6,178.19 1.80

Lower Dawson aquifer

LDAW 2 2/1/2012 7,210.93 2/21/2019 7,210.63 −0.30

LDAW 3 2/1/2012 7,184.53 -- -- --

LDAW 4 2/2/2012 5,921.82 -- -- --

LDAW 5 -- -- 2/22/2019 5,823.55 --

LDAW 6 2/1/2012 7,044.88 2/21/2019 7,043.54 −1.34

LDAW 7 2/2/2012 6,592.36 2/21/2019 6,590.12 −2.24

LDAW 8 2/9/2012 5,855.51 2/21/2019 5,844.77 −10.74

LDAW 9 2/10/2012 5,748.35 2/22/2019 5,750.25 1.90

LDAW 10 2/9/2012 5,849.38 2/21/2019 5,842.30 −7.08

LDAW 11 -- -- 2/20/2019 6,713.69 --

GRNDAW 4 2/10/2012 5,766.63 2/25/2019 5,768.40 1.77

Denver aquifer

DENV 1 2/2/2012 6,636.26 2/21/2019 6,629.20 −7.06

DENV 2 2/9/2012 6,167.41 2/20/2019 6,161.98 −5.43

DENV 3 2/1/2012 6,379.57 2/25/2019 6,378.60 −0.97

DENV 4 2/9/2012 6,151.95 2/20/2019 6,145.44 −6.51

DENV 5 2/9/2012 6,134.28 2/20/2019 6,137.54 3.26

DENV 6 2/9/2012 5,492.98 2/20/2019 5,489.69 −3.29

DENV 7 2/1/2012 6,600.99 2/21/2019 6,601.74 0.75

DENV 8 -- -- 2/21/2019 6,978.23 --

DENV 10 -- -- 2/20/2019 6,171.80 --

DENV 11 2/10/2012 5,719.52 2/22/2019 5,722.24 2.72

GRNDEV 3 2/10/2012 5,741.82 2/25/2019 5,733.06 −8.76

Arapahoe aquifer

ARAP 1 2/9/2012 5,247.00 2/20/2019 5,231.39 −15.61

ARAP 2 2/9/2012 5,389.08 2/20/2019 5,388.28 −0.80

Laramie-Fox Hills aquifer

LARA 1 2/9/2012 6,066.15 -- -- --

LARA 2 2/9/2012 6,068.89 -- -- --
Groundwater-Level Elevations in the Denver Basin Bedrock Aquifers of Douglas County 17

£¤85 £¤85

83

25 25

86

83

86

Parker

Franktown

Larkspur

Castle

Rock

Louviers

Highlands

Ranch

Sedalia

Parker

Franktown

Larkspur

Castle

Rock

Louviers

Highlands

Ranch

Sedalia

ARAPAHOE COUNTY

ELBERT COUNTY

EL PASO COUNTY

ARAPAHOE COUNTY

ELBERT COUNTY

EL PASO COUNTY

DOUGLAS

COUNTY

DOUGLAS

COUNTY

!

!

!

!

!

!

!

! !

!

!

!

#*

!

!

!

!

! #*

!

UDAW 8 UDAW 9

UDAW 10

UDAW 2

UDAW 4

UDAW 6

UDAW 3

UDAW 5

UDAW 7

UDAW 1

−0.21 ft/yr

UDAW 8 UDAW 9

UDAW 10

UDAW 2

UDAW 4

UDAW 6 UDAW 3

UDAW 5

UDAW 7

UDAW 1

−0.25 ft/yr

6,200

6,200

6,300

6,100

105°0' 104°50' 104°40'

39°30'

39°20'

39°10'

105°0' 104°50' 104°40'

39°30'

39°20'

39°10'

A B

EXPLANATION

Upper Dawson aquifer boundary

Douglas County boundary

Estimated potentiometric contour 

February 2019, in feet, contour 

interval 100 feet

No significant trend

Groundwater-level elevation trend

Positive significant trend

Negative significant trend

Groundwater-level elevation trend 

estimate, in feet per year

> +0.5 to +1.0

> +0.1 to +0.5

> −0.1 to +0.1

> −0.5 to −0.1

> −1.0 to −0.5

> −2.0 to −1.0

> −3.0 to −2.0

 −5.0 to −3.0

< −5.0

Groundwater-level elevation, in feet above 

North American Vertical Datum of 1988

6,450

6,000

6,225

UDAW 1 Well common name

 Well common name abbreviations

UDAW Upper Dawson aquifer well

DOUGLAS

COUNTY

COLORADO

0 5 10 KILOMETERS

0 5 10 MILES

Base from U.S. Geological Survey digital data, 2014

Universal Transverse Mercator, Zone 13

North American Datum of 1983

Figure 5. Estimates of potentiometric-surface elevations and groundwater-level elevation trends for the upper Dawson aquifer, 

Douglas County, Colorado. A, estimated potentiometric surface of the upper Dawson aquifer, February 2019. B, groundwater-level 

elevation trend estimates for the upper Dawson aquifer, 2012–19.
18 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

¬«86

¬«83

25 25

£¤85

¬«86

¬«83

£¤85

Parker

Franktown

Larkspur

Castle

Rock

Louviers

Highlands

Ranch

Sedalia

Parker

Franktown

Larkspur

Castle

Rock

Louviers

Highlands

Ranch

Sedalia

LDAW 9

GRNDAW 4

LDAW 11

LDAW 7

LDAW 10

LDAW 2

LDAW 3

LDAW 4

LDAW 6

LDAW 8

LDAW 2

LDAW 3

LDAW 4

LDAW 5 LDAW 5

LDAW 6

LDAW 8

LDAW 9

GRNDAW 4

LDAW 11

LDAW 7

LDAW 10

0.71 ft/yr

−0.31 ft/yr

−0.85 ft/yr 5,800

5,900

5,900

6,000

6,200

6,300

6,400

6,900

7,200

6,100

6,500

6,700

7,100

ARAPAHOE COUNTY

ELBERT COUNTY

EL PASO COUNTY

ARAPAHOE COUNTY

ELBERT COUNTY

EL PASO COUNTY

DOUGLAS

COUNTY

DOUGLAS

COUNTY

105°0' 104°50' 104°40'

39°20'

39°10'

105°0' 104°50' 104°40'

39°30' 39°30'

39°20'

39°10'

A B

EXPLANATION

Lower Dawson aquifer boundary

Douglas County boundary

Estimated potentiometric contour 

February 2019, in feet, contour 

interval 100 feet

No significant trend

Groundwater-level elevation trend

* Positive significant trend

Negative significant trend *

Groundwater-level elevation trend 

estimate, in feet per year

> +0.5 to +1.0

> +0.1 to +0.5

> −0.1 to +0.1

> −0.5 to −0.1

> −1.0 to −0.5

> −2.0 to −1.0

> −3.0 to −2.0

 −5.0 to −3.0

< −5.0

Groundwater-level elevation, in feet above 

North American Vertical Datum of 1988

7,280

5,700

6,500

LDAW 2 Well common name

 Well common name abbreviations

LDAW Lower Dawson aquifer well

GRNDAW Grandview Estates lower Dawson 

aquifer well 

DOUGLAS

COUNTY

COLORADO

0 5 10 KILOMETERS

0 5 10 MILES

Base from U.S. Geological Survey digital data, 2014

Universal Transverse Mercator, Zone 13

North American Datum of 1983

Figure 6. Estimates of potentiometric-surface elevations and groundwater-level elevation trends for the lower Dawson aquifer, 

Douglas County, Colorado. A, estimated potentiometric surface of the lower Dawson aquifer, February 2019. B, groundwater-level 

elevation trend estimates for the lower Dawson aquifer, 2012–19.
Groundwater-Level Elevations in the Denver Basin Bedrock Aquifers of Douglas County 19

86

83

25

£¤85

83

86

25

ARAPAHOE COUNTY

EL PASO COUNTY

ARAPAHOE COUNTY

EL PASO COUNTY

DOUGLAS

COUNTY

DOUGLAS

COUNTY

JEFFERSON COUNTYJEFFERSON COUNTY

TELLER 

COUNTY

TELLER 

COUNTY

Parker

Franktown

Larkspur

Castle

Rock

Louviers

Parker

Franktown

Larkspur

Castle

Rock

Louviers

Highlands

Ranch

Sedalia Sedalia

Highlands

Ranch

!

DENV 11 GRNDEV 3

DENV 6

DENV 5

DENV 4

DENV 2

DENV 10

DENV 3

DENV 1

DENV 7

DENV 8

GRNDEV 3 DENV 11

DENV 6

DENV 5 DENV 4

DENV 10

DENV 1

DENV 3

DENV 7

DENV 8

DENV 2

#

#

!

#

!

!

!

!

!

!

!

!

!

!

!

!

!

!

5,400

5,700

5,600

6,100

5,800

6,000

5,900

6,300

6,400

6,500

6,600

6,700

6,800

−0.48 ft/yr

−0.92 ft/yr

−0.73 ft/yr

−0.92 ft/yr

−1.11 ft/yr

−0.15 ft/yr

−5.51 ft/yr

105°0' 104°50' 105°0' 104°50'

39°30'

39°20'

39°10'

39°30'

39°20'

39°10'

EXPLANATION

Denver aquifer boundary

Douglas County boundary

Estimated potentiometric contour 

February 2019, in feet, contour 

interval 100 feet

No significant trend

Groundwater-level elevation trend

Positive significant trend

Negative significant trend

Groundwater-level elevation trend 

estimate, in feet per year

> +0.5 to +1.0

> +0.1 to +0.5

> −0.1 to +0.1

> −0.5 to −0.1

> −1.0 to −0.5

> −2.0 to −1.0

> −3.0 to −2.0

 −5.0 to −3.0

< −5.0

Groundwater-level elevation, in feet above 

North American Vertical Datum of 1988

7,200

5,300

6,150

DENV 1 Well common name

 Well common name abbreviations

DENV Denver aquifer well

GRNDEV Grandview Estates Denver aquifer well

A B

DOUGLAS

COUNTY

COLORADO

0 5 10 KILOMETERS

0 5 10 MILES

Base from U.S. Geological Survey digital data, 2014

Universal Transverse Mercator, Zone 13

North American Datum of 1983

Figure 7. Estimates of potentiometric-surface elevations and groundwater-level elevation trends for the Denver aquifer, Douglas 

County, Colorado. A, estimated potentiometric surface of the Denver aquifer, February 2019. B, groundwater-level elevation trend 

estimates for the Denver aquifer, 2012–19.
20 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

Future Research Needs

Changes and trends in groundwater-level elevations are 

important for informing local water-resource managers and 

for guiding future monitoring efforts. Continued monitoring 

and additional static measurements at wells with no significant trends in this study would provide more data points for 

the trend analysis and may increase the number of wells with 

statistically significant trends in the future. Additionally, continued monitoring and future analyses of measurements would 

help elucidate if trends are consistent and persist beyond 

the study period. Groundwater levels in several wells in this 

study exhibit interannual periods of rise and decline outside 

of the normal seasonal variation, for example well LDAW 2 

(fig. 2.11). Long-term monitoring at these wells and additional 

comparisons with water use and recharge patterns may provide 

insight on the cause of these patterns and if the patterns persist 

beyond the study period.

A regional study and analysis that combines data from 

groundwater monitoring networks of the Denver Basin aquifer 

system in Douglas and Elbert Counties could provide a better 

understanding of how groundwater levels are changing regionally 

beyond the Douglas County border. Both counties have had 

a recent increase in development and have rural areas where 

residents are reliant on domestic wells. According to the CDWR 

well permit database (Colorado Division of Water Resources, 

2019), from January 2012 through June 2019, within Douglas 

and Elbert Counties, 626 new domestic water-supply wells were 

constructed in the upper and lower Dawson aquifers, 264 wells 

were constructed in the Denver aquifer, 71 wells were constructed 

in the Arapahoe aquifer, and 23 wells were constructed in the 

Laramie-Fox Hills aquifer. Continued groundwater monitoring 

is key to understanding the effect of former and future water-use 

on aquifer response, recovery, and long-term sustainability 

(Ruybal and others, 2019a, b). The regional study could produce 

regional groundwater-level trend maps focusing on monitoring networks with overlapping periods of record. Regional 

potentiometric-surface and hydraulic-head difference maps 

from wells with common data collection periods would be 

more comparable across county boundaries and may provide 

more insight into the relations among population increase, 

development, groundwater use, and groundwater-level elevation changes. A regional study and consolidation of available 

well data could provide additional calibration data to update and 

improve the Denver Basin groundwater model.

Summary

Douglas County is one of the fastest growing counties in 

Colorado, and the development of the county, as well as the 

rapid development of neighboring counties, have generated 

increased demand on groundwater resources. Groundwater in 

Douglas County is withdrawn from the four principal Denver 

Basin bedrock, from shallowest to deepest, the Dawson 

aquifer (divided administratively into “upper” and “lower” 

Dawson aquifers in Douglas County), the Denver aquifer, 

the Arapahoe aquifer, and the Laramie-Fox Hills aquifer. 

Increases in demand have raised questions about groundwater 

availability and sustainability. Municipal and domestic water 

users in Douglas County rely on groundwater from the bedrock aquifers in the Denver Basin aquifer system as part of 

their water supply. The U.S. Geological Survey, in cooperation with the Rural Water Authority of Douglas County, began 

a study in 2011 to assess the groundwater resources of the 

Denver Basin bedrock aquifers within the county. The purpose 

of the study is to assess the groundwater resources of the 

Denver Basin bedrock aquifers within the county by establishing and maintaining a groundwater monitoring network and by 

analyzing the groundwater levels of the Denver Basin bedrock 

aquifers throughout Douglas County.

The primary purpose of this report is to present a summary 

of groundwater levels measured during the study period 

(2011–19) and present results from statistical analyses of 

changes in groundwater-level elevations, reported above the 

land-surface datum, North American Vertical Datum of 1988, 

through time. This report presents data from 36 wells across 

Douglas County, with at least 2 wells in each of the Denver 

Basin bedrock aquifers. Of the 36 wells, 15 were instrumented 

with pressure transducers that record groundwater-level measurements at hourly intervals, and these data were temporally 

aggregated into time-series records. During 2011, wells were 

added to the monitoring network in phases, so that the start 

dates of the well records were noncontemporaneous. To keep 

temporal analysis among wells consistent, the periods of 

record used in statistical analyses were from February 2012 

through February 2019 for the discrete data and from 

January 2012 through June 2019 for the time-series data.

Groundwater levels were routinely measured in 36 wells 

between April 2011 and June 2019. During the analysis 

period, January 2012 through June 2019, changes and trends 

in groundwater-level elevations in each well and aquifer were 

evaluated using a variety of metrics. Trends in static discrete 

groundwater-level elevations measured in February of each year 

and monthly mean values of daily maximum groundwater-level 

elevations in time-series data were tested for significance using 

the nonparametric Mann-Kendall trend test and seasonal 

Mann-Kendall trend test, respectively. Trends were calculated 

in feet per year using the nonparametric Sen slope estimate. In 

addition to statistical tests, relative changes in groundwater-level 

elevations were computed as the difference between the 

February 2012 and February 2019 groundwater-level elevations 

for sites with static discrete measurements in each period. 

Maps of the groundwater-level elevation, also known as the 

potentiometric-surface maps, were derived from static discrete 

groundwater levels measured in February 2019 in the upper 

Dawson, lower Dawson, and Denver aquifers.

Four aquifers, the upper Dawson, lower Dawson, Denver, 

and Arapahoe, had some wells with rises in calculated 

groundwater-level elevations, but most wells showed 

water-level declines on the basis of statistically significant 

trends and the relative differences in static groundwater-level 

elevations between the February 2012 and February 2019 
References Cited 21

measurements. Neither of the two wells in the Laramie-Fox 

Hills aquifer showed significant trends in groundwater-level 

elevations, and these wells had few static discrete measurements, 

precluding a comparison between 2012 and 2019 static 

groundwater-level elevations. Of the 13 wells in the upper 

Dawson, lower Dawson, Denver, and Arapahoe aquifers with 

significant trends in discrete groundwater-level elevation 

measurements, 12 wells demonstrated negative trends during 

the study period. The upper Dawson, lower Dawson, Denver, 

and Arapahoe aquifers had median significant trends of −0.23, 

−0.31, −0.92, and −2.26 feet per year (ft/yr), respectively, 

in the discrete groundwater-level elevations. Although the 

Arapahoe aquifer had the greatest negative median trend, 

this median only represents one well with significant trends. 

Otherwise, the Denver aquifer had the next greatest negative 

trend, with a median trend of −0.92 ft/yr. The magnitudes of 

negative groundwater-level elevation trends were greatest in 

the Denver aquifer, with one well having a trend of −5.51 ft/yr, 

and five of the seven wells having significant negative trends 

greater than −0.50 ft/yr. Significant trends observed in upper 

Dawson wells indicated declines that were less than −0.30 ft/yr. 

In the lower Dawson aquifer, two wells had negative trends, and 

both negative trends exceeded −0.30 ft/yr. However, the only 

statistically significant positive trend in discrete groundwater-level 

elevations was observed in the lower Dawson well near the 

southwest edge of the extent of the aquifer, and this well is under 

unconfined conditions.

Significant trends in time-series groundwater-level elevations agreed with significant trends in discrete groundwater-level 

elevations; for all wells with statistically significant trends in 

discrete and in time-series of groundwater-level elevation data, 

trend estimates from the two records were within 0.1 ft/yr of 

each other. However, two wells exhibited significant trends in 

time-series data but not in static discrete data. A longer study 

period and more static discrete measurements could increase 

the frequency of statistically significant trends in discrete data.

Potentiometric-surface maps of the upper Dawson, lower 

Dawson, and Denver aquifers for February 2019 indicate that 

groundwater flow is generally from south to north in each 

aquifer. Relative changes among static groundwater elevations 

measured in February 2012 and February 2019 were calculated 

by taking the difference between the two measurements. Of 

the four aquifers that had wells with static measurements in 

February 2012 and February 2019, three aquifers had at least 

two wells with an increase and three wells with a decrease in 

groundwater-level elevation (upper Dawson, lower Dawson, 

and Denver aquifers). The two wells in the Arapahoe aquifer 

showed decreases in groundwater-level elevation, and neither 

of the two wells in the Laramie-Fox Hills aquifer had enough 

static measurements to compute a difference. However, relative 

differences between two measurements are not necessarily 

representative of trends but, instead, offer a point of comparison 

to calculated trends.

Results of this study could guide future groundwater 

monitoring in the county and aid in long-term planning of 

water resources. Results also could be used for a regional 

study of groundwater-level elevations in the Denver Basin 

aquifer system to provide additional calibration data for the 

Denver Basin groundwater flow model.

References Cited

Bauch, N.J., Musgrove, M., Mahler, B.J., and Paschke, S.S., 

2014, The quality of our Nation’s waters—Water quality 

in the Denver Basin aquifer system, Colorado, 2003–05: 

U.S. Geological Survey Circular 1357, 100 p., accessed 

September 2019 at https://dx.doi.org/10.3133/cir1357.

Colorado Division of Water Resources, 2019, Colorado Division of 

Water Resources permit search website, accessed September 30, 

2019, at https://dwr.state.co.us/Tools/WellPermits.

Colorado Water Conservation Board, 2004, South Platte Decision 

Support System ground-water component phase 1, task 44.2—

Denver Basin region water level technical memorandum, 

July 30, 2004: Colorado Water Conservation Board, 27 p.

Colorado Water Conservation Board, 2006, South Platte 

Decision Support System ground-water component phase 3, 

task 44.2—Denver Basin region water level technical memorandum, November 28, 2006: Colorado Water Conservation Board, 

65 p., accessed April 2, 2020, at https://dnrftp.state.co.us/DWR/

HydroGeology/Denver_Basin_Atlases_Complete/SPDSS/

spdss44-2_20061128.pdf.

Crifasi, R.R., 1992, Alluvial architecture of Laramide orogenic sediments Denver Basin, Colorado: The Mountain 

Geologist, v. 29, p. 19–27.

Cunningham, W.L., and Schalk, C.W., comps., 2011, 

Groundwater technical procedures of the U.S. Geological 

Survey: U.S. Geological Survey Techniques and Methods, 

book 1, chap. A1, 151 p., accessed September 2019 at 

https://doi.org/10.3133/tm1A1.

Douglas County, 2019, Water Supply: Douglas County 

water supply website, accessed September 27, 2019, at 

https://www.douglas.co.us/water/water-supply/.

Douglas County Demographic Summary, 2019, Douglas 

County Community Development Department, accessed 

September 27, 2019, at https://www.douglas.co.us/

documents/douglas-county-demographics-summary.pdf/.

Douglas County Department of Community Development, 

2019, Douglas County 2040 Comprehensive Master Plan: 

Douglas County, Colo., Douglas County Department 

of Community Development, Planning Services 

Division, 141 p., accessed September 27, 2019, at 

https://www.douglas.co.us/land/comprehensive-master-plan/.

Esri, Inc., variously dated, ArcGIS desktop 10.5, version 

10.5.0.6491: Redlands, Calif., Esri, Inc.

Everett, R.R., 2014, Groundwater levels in the Denver Basin 

bedrock aquifers of Douglas County, Colorado, 2011–2013: 

U.S. Geological Survey Scientific Investigations Report 

2014–5172, 45 p. [Also available at https://doi.org/10.3133/

sir20145172.]
22 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

Fenneman, N.M., 1931, Physiography of the western United 

States: New York, McGraw Hill, 534 p.

Flor, A.D., 2017, Groundwater levels in the Denver Basin 

bedrock aquifers: Colorado Division of Water Resources, 

Department of Natural Resources, 10 p., accessed 

September 27, 2019, at https://dwr.state.co.us/Tools/

GroundWater/RunBasinReport?pub=DENVER%20BASIN.

Freeman, L.A., Carpenter, M.C., Rosenberry, D.O., Rousseau, 

J.P., Unger, R., and McLean, J.C. 2004, Use of submersible pressure transducers in water-resources investigations: U.S. Geological Survey Techniques of WaterResources Investigations, book 8, chap. A3, 52 p., accessed 

October 29, 2019, at https://doi.org/10.3133/twri08A3.

Graham, G., and Van Slyke, G., 2004, Development of the 

regulatory framework for Denver Basin aquifers: The 

Mountain Geologist, v. 41, no. 4, p. 153–160.

Helsel, D.R., Hirsch, R.M., Ryberg, K.R., Archfield, S.A., and 

Gilroy, E.J., 2020, Statistical methods in water resources: 

U.S. Geological Survey Techniques and Methods, book 4, 

chapter A3, 458 p., accessed June 2020 at https://doi.org/

10.3133/tm4a3. [Supersedes USGS Techniques of WaterResources Investigations, book 4, chapter A3, version 1.1]

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, accessed September 2019 at 

https://doi.org/10.3133/i1043.

Hirsch, R.M., and De Cicco, L.A., 2015, User guide to 

exploration and graphics for RivEr Trends (EGRET) and 

data retrieval—R packages for hydrologic data (version 

2.0, February 2015): U.S. Geological Survey Techniques 

and Methods, book 4, chap. A10, 93 p. [Also available at 

https://doi.org/10.3133/tm4A10.]

Hirsch, R.M., Slack, J.R., and Smith, R.A., 1982, Techniques 

of trend analysis for monthly water quality data: Water 

Resources Research, v. 18, no. 1, p. 107–121. [Also available at https://doi.org/10.1029/WR018i001p00107.]

In-Situ, Inc., 2020, Level TROLL® 400, 500 & 700 Data 

Loggers spec sheet: Fort Collins, Colo., In-Situ, Inc., 2 p., 

accessed June 2, 2020, at https://in-situ.com/pub/media/

support/documents/LevelTROLL_SS.pdf.

Kendall, M.G., 1975, Rank correlation methods, 4th ed.: 

London, Charles Griffen, p. 272.

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 pls.

Lorenz, D.L., 2014, General tools for hydrologic data and trend 

analysis: U.S. Geological Survey, accessed October 29, 2019, 

at https://github.com/USGS-R/smwrStats.

Mann, H.B., 1945, Nonparametric tests against trend: 

Econometrica, v. 13, no. 3, p. 245–259. [Also available at 

https://doi.org/10.2307/1907187.]

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.

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. 

[Also available at https://doi.org/10.18814/epiiugs/2007/

v30i2/006.]

Paschke, S.S., ed., 2011, Groundwater availability of the 

Denver Basin aquifer system, Colorado, U.S. Geological 

Survey Professional Paper 1770, 274 p. [Also available at 

https://doi.org/10.3133/pp1770.]

Penn, C.A., and Everett, R.R., 2019, Groundwater-level 

elevations in the Denver Basin bedrock aquifers of Elbert 

County, Colorado, 2015–18: U.S. Geological Survey 

Scientific Investigations Report 2019–5014, 50 p. [Also 

available at https://doi.org/10.3133/sir20195014.]

Pottorff, E.T., and Horn, A., 2013, Groundwater levels in the 

Denver Basin bedrock aquifers, 2013: Colorado Division 

of Water Resources, 198 p, accessed June 2, 2020, at 

https://dnrweblink.state.co.us/dwr/ElectronicFile.aspx?

docid=2769885&dbid=0.

R Core Team, 2018, R—A language and environment for 

statistical computing: Vienna, Austria, R Foundation 

for Statistical Computing, accessed August 1, 2018, at 

https://www.R-project.org/.

Raynolds, R.G., 2002, Upper Cretaceous and Tertiary stratigraphy of the Denver Basin, Colorado: Rocky Mountain 

Geology, v. 37, no. 2, p. 111–134. [Also available at https://

doi.org/10.2113/gsrocky.37.2.111.]

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., 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 01–0185, 72 p. [Also 

available at https://doi.org/10.3133/ofr01185.]
References Cited 23

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. [Also 

available at https://doi.org/10.3133/pp1257.]

Robson, S.G., Romero, J.C., and Zawistowski, S., 1981a, 

Geologic structure, hydrology, and water quality of the 

Arapahoe aquifer in the Denver Basin, Colorado: U.S. 

Geological Survey Hydrologic Investigations Atlas 

HA–647, scale 1:500,000, 3 sheets. [Also available at 

https://doi.org/10.3133/ha647.]

Robson, S.G., Wacinski, A., Zawistowski, S., and Romero, 

J.C., 1981b, 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. 

[Also available at https://doi.org/10.3133/ha650.]

Romero, J.C., 1976, Ground-water resources of the bedrock 

aquifers of the Denver Basin: Denver, Colo., Colorado 

Division of Water Resources Report, 109 p.

Rural Water Authority of Douglas County [RWADC], 2019a, 

Rural Water Authority of Douglas County mission: Rural 

Water Authority of Douglas County, Colorado, web page, 

accessed September 30, 2019, at http://www.rwadc.org/.

Rural Water Authority of Douglas County [RWADC], 2019b, 

Rural water authority of Douglas County service area, water 

providers and wells: Rural Water Authority of Douglas County, 

Colorado, web page, accessed September 30, 2019, at http://

www.rwadc.org/images/Rural-Water-Providers-Esize.2.pdf.

Ruybal, C.J., Hogue, T.S., and McCray, J.E., 2019a, 

Evaluation of groundwater levels in the Arapahoe aquifer 

using spatiotemporal regression kriging: Water Resources 

Research, v. 55, no. 4, p. 2820–2837. [Also available at 

https://doi.org/10.1029/2018WR023437.]

Ruybal, C.J., Hogue, T.S., and McCray, J.E., 2019b, 

Assessment of groundwater depletion and implications for 

management in the Denver Basin Aquifer System: Journal 

of the American Water Resources Association, v. 55, no. 5, 

p. 1130–1148. [Also available at https://doi.org/10.1111/

1752-1688.12755.]

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. [Also available at 

https://doi.org/10.3133/ofr80327.]

Sen, P.K., 1968, Estimate of the regression coefficient based 

on Kendall’s tau: Journal of the American Statistical 

Association, v. 63, no. 324, p. 1379–1389. [Also available at 

https://doi.org/10.1080/01621459.1968.10480934.]

South Metro Water Supply Authority [SMWSA], undated, 

Master plan overview—2016 regional master plan update: 

South Metro Water Supply Authority, 20 p., accessed 

September 27, 2019, at https://southmetrowater.org/

application/files/9615/7867/2371/MP-Publication-Final.pdf.

South Metro Water Supply Authority [SMWSA], 2020, 

Strength through partnerships: South Metro Water 

Supply Authority web page, accessed April 2, 2020, at 

https://southmetrowater.org/.

Tweto, O., 1979, MI–16 Geologic Map of Colorado: 

Denver, Colo., Miscellaneous Investigations, 

Colorado Geological Survey, Department of Natural 

Resources, Scale 1:500,000, 1 sheet. [Also available at 

https://coloradogeologicalsurvey.org/publications/twetogeologic-map-colorado-1979.]

U.S. Census Bureau, 1995, Population of Counties by 

Decennial Census: 1900 to 1990. U.S. Census Bureau, 

accessed June 2, 2020, at https://www.census.gov/

population/cencounts/co190090.txt.

U.S. Geological Survey, 2020, USGS water data for 

the Nation: U.S. Geological Survey National Water 

Information System database, accessed January 8, 2020, at 

https://doi.org/10.5066/F7P55KJN.

Wireman, M., and Romero, J.C., 1989, Bibliography of 

geology and ground water geology for the Denver Basin, 

Colorado: Denver, Colo., Colorado Division of Water 

Resources Office of the State Engineer, 12 p.
24 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

Appendix 1. Groundwater-Well Measurement Diagram

Measuring

point (MP)

MP hold

0.85

Water level

1.28

(Wetted

chalk mark)

Well

casing

Land-surface

datum (LSD)

12.86 (Depth to water corrected for LSD)

14.99

13.71 (Depth to water from MP)

1’

Measuring

point (MP)

MP hold

0.85

Water level

Well

casing

Land-surface

datum (LSD)

12.86 (Depth to water corrected for LSD)

13.71 (Depth to water from MP)

A B

Figure 1.1. Diagram showing example measurement point and groundwater-level measurement using A, a calibrated steel tape with 

chalk, and B, a calibrated electrical tape. Modified from Cunningham and Schalk, 2011 (values are in feet).

Reference Cited

Cunningham, W., and Schalk, C.W. comps., 2011, 

Groundwater technical procedures of the U.S. Geological 

Survey: U.S. Geological Survey Techniques and Methods, 

book 1, chap. A1, 151 p., accessed September 2019 at 

https://doi.org/10.3133/tm1A1.
Appendix 2 25

Appendix 2. Hydrographs Showing Groundwater-Level Elevation Through Time 

for Wells in the Douglas County Groundwater-Level Monitoring Network

Hydrographs showing groundwater-level elevation 

through time for each well in this study are presented in this 

appendix (figs. 2.1 through 2.36). Measurement periods differ but are generally from April 2011 through June 2019 for 

discrete measurements and are during summer or fall 2011 

through June 2019 for time-series measurements. Daily 

maximum groundwater-level elevation, in feet above North 

American Vertical Datum of 1988, is plotted for time-series 

measurements. Daily median and minimum values were 

not plotted, but data are available; see the “Accessing Data” 

section. Discrete measurement symbols differ by measurement status; see “Study Methods” section for a description of 

the status codes. Well common names include the following 

abbreviations: UDAW, upper Dawson aquifer well; LDAW, 

lower Dawson aquifer well; DENV, Denver aquifer well; 

ARAP, Arapahoe aquifer well; LARA, Laramie-Fox Hills 

aquifer well; GRNDAW, Grandview Estates lower Dawson 

aquifer well; GRNDEV, Grandview Estates, Denver aquifer 

well.

●

●

●

●

●

●●●

●

●

●

●●

●

●

●

●● ● ●

●

●

●

●

●

● ●

●

●

●

6,834

6,836

6,838

6,840

6,842

6,844

6,846

6,848

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Groundwater-level status

EXPLANATION

Pumping

Recently pumped

Static

Continuous record

Daily maximum

Figure 2.1. Groundwater-level hydrograph for well UDAW 1, U.S. Geological Survey site number 391229104421901, Douglas 

County, Colorado.
26 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

● ●

6,129

6,131

6,133

6,135

6,137

6,139

6,141

6,143

6,145

6,147

6,149

6,151

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Groundwater-level status

EXPLANATION

Nearby pumping

Recently pumped

Static

Figure 2.2. Groundwater-level hydrograph for well UDAW 2, U.S. Geological Survey site number 392856104424101, Douglas 

County, Colorado.

Figure 2.3. Groundwater-level hydrograph for well UDAW 3, U.S. Geological Survey site number 392412104434201, Douglas 

County, Colorado.

●

●●●●

●●

● ●●●

●●●●

● ●● ●

●

● ●

●

●

●

●

●●

● ●

6,239

6,241

6,243

6,245

6,247

6,249

6,251

6,253

6,255

6,257

6,259

6,261

6,263

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

EXPLANATION

Groundwater-level status

Recently pumped

Static

Continuous record

Represents a 2-day 

period of extended 

pumping in the well

Daily maximum

*

* 
Appendix 2 27

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●

●

●

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●

●

●●

●

●

●

●

●●

●

●

●

● ●

●

●

●

●

● ●

●

●

6,131

6,133

6,135

6,137

6,139

6,141

6,143

6,145

6,147

6,149

6,151

6,153

6,155

6,157

6,159

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

EXPLANATION

Groundwater-level status

Nearby pumping

Recently pumped

Static

Continuous record

Daily maximum

Figure 2.4. Groundwater-level hydrograph for well UDAW 4, U.S. Geological Survey site number 392934104414901, Douglas 

County, Colorado.

●

●

●

●

●

●

●

●

●●● ●●

●

●

● ● ●

● ●

6,326

6,331

6,336

6,341

6,346

6,351

6,356

6,361

6,366

6,371

6,376

6,381

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Groundwater-level status

EXPLANATION

Nearby pumping

Recently pumped

Static

Continuous record

Daily maximum

Figure 2.5. Groundwater-level hydrograph for well UDAW 5, U.S. Geological Survey site number 392149104415501, Douglas 

County, Colorado.
28 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

●

●

●

●

●

●

●

●

●

●

●●

●

●

●

●

●

●

●

● ● ●

● ●

6,371

6,372

6,373

6,374

6,375

6,376

6,377

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Groundwater-level status

EXPLANATION

Static

Figure 2.6. Groundwater-level hydrograph for well UDAW 6, U.S. Geological Survey site number 392441104394901, Douglas 

County, Colorado.

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Groundwater-level status

EXPLANATION

Recently pumped

Static

●

●●

● ●

●

●

●

●●

●

●

●●

●

●

●

● ●

6,652

6,653

6,654

6,655

6,656

Figure 2.7. Groundwater-level hydrograph for well UDAW 7, U.S. Geological Survey site number 391658104453101, Douglas 

County, Colorado.
Appendix 2 29

6,024

6,025

6,026

6,027

6,028

6,029

6,030

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Groundwater-level status

EXPLANATION

Recently pumped

Static

Figure 2.8. Groundwater-level hydrograph for well UDAW 8, U.S. Geological Survey site number 393252104434701, Douglas 

County, Colorado.

●

●

●●

●

●

●

●

●

●

●

●

●

●●●

●

● ●

●

●

●

●

●●

●

●

●

●

●

6,068

6,070

6,072

6,074

6,076

6,078

6,080

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Groundwater-level status

EXPLANATION

Recently pumped

Static

Continuous record

Daily maximum

Figure 2.9. Groundwater-level hydrograph for well UDAW 9, U.S. Geological Survey site number 393226104394401, Douglas 

County, Colorado.
30 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

●

●

●

●●●

●

●●

●●

●●

●

●●

●

●● ●

●

●

● ●

●

●

●

●

●

●

●

6,163

6,165

6,167

6,169

6,171

6,173

6,175

6,177

6,179

6,181

6,183

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Groundwater-level status

EXPLANATION

Recently pumped

Static

Continuous record

Daily maximum

Figure 2.10. Groundwater-level hydrograph for well UDAW 10, U.S. Geological Survey site number 392916104423601, Douglas 

County, Colorado.

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

EXPLANATION

Groundwater-level status

Static

Continuous record

Daily maximum

●

●●●

●●

●

●

●●

●●●

●

●●

●●●

●

●●

●

●

● ●

● ●

●

● ●

●●

●

●

7,204

7,202

7,206

7,208

7,210

7,212

7,214

7,216

7,218

Figure 2.11. Groundwater-level hydrograph for well LDAW 2, U.S. Geological Survey site number 390756104453801, Douglas 

County, Colorado.
Appendix 2 31

7,178

7,180

7,182

7,184

7,186

7,188

7,190

7,192

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

EXPLANATION

Groundwater-level status

Recently pumped

Static

Figure 2.12. Groundwater-level hydrograph for well LDAW 3, U.S. Geological Survey site number 390811104453801, Douglas 

County, Colorado.

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Groundwater-level status

EXPLANATION

Recently pumped

Static

●●

●

●

●

●

●●

● ● ●

●

5,860

5,865

5,870

5,875

5,880

5,885

5,890

5,895

5,900

5,905

5,910

5,915

5,920

5,925

5,930

5,935

5,940

5,945

5,950

5,955

5,960

Figure 2.13. Groundwater-level hydrograph for well LDAW 4, U.S. Geological Survey site number 392318104424601, Douglas 

County, Colorado.
32 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

●

●

●

●

●

●

●

●

●

●

● ● ●

●

5,783

5,788

5,793

5,798

5,803

5,808

5,813

5,818

5,823

5,828

5,833

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Groundwater-level status

EXPLANATION

Recently pumped

Static

Figure 2.14. Groundwater-level hydrograph for well LDAW 5, U.S. Geological Survey site number 391924104374101, Douglas 

County, Colorado.

7,041

7,042

7,043

7,044

7,045

7,046

7,047

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

7,040

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Date

Continuous record

Daily maximum

Groundwater-level status

EXPLANATION

Recently pumped

Static

Figure 2.15. Groundwater-level hydrograph for well LDAW 6, U.S. Geological Survey site number 391143104482501, Douglas 

County, Colorado.
Appendix 2 33

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●●

●

● ●

●

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●

●

●

●

●

●

● ●

6,581

6,583

6,585

6,587

6,589

6,591

6,593

6,595

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Groundwater-level status

EXPLANATION

Nearby pumping

Recently pumped

Static

Continuous record

Daily maximum

Figure 2.16. Groundwater-level hydrograph for well LDAW 7, U.S. Geological Survey site number 391654104464501, Douglas 

County, Colorado.

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Groundwater-level status

EXPLANATION

Recently pumped

Static

●

●

●

●

●

●

●●

●

●

●

●

●

●

●

●

● ●

●

5,838

5,840

5,842

5,844

5,846

5,848

5,850

5,852

5,854

5,856

5,858

Figure 2.17. Groundwater-level hydrograph for well LDAW 8, U.S. Geological Survey site number 392949104523401, Douglas 

County, Colorado.
34 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

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●

●

●

●

●

●

●

●

●

●

● ●

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

5,721

5,723

5,725

5,727

5,729

5,731

5,733

5,735

5,737

5,739

5,741

5,743

5,745

5,747

5,749

5,751

5,753

Groundwater-level status

EXPLANATION

Recently pumped

Static

Figure 2.18. Groundwater-level hydrograph for well LDAW 9, U.S. Geological Survey site number 393239104452901, Douglas 

County, Colorado.

●

●

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●

● ●

●

●

5,836

5,838

5,840

5,842

5,844

5,846

5,848

5,850

5,852

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Groundwater-level status

EXPLANATION

Nearby pumping

Recently pumped

Static

Figure 2.19. Groundwater-level hydrograph for well LDAW 10, U.S. Geological Survey site number 393021104533101, Douglas 

County, Colorado.
Appendix 2 35

6,706

6,708

6,710

6,712

6,714

6,716

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Groundwater-level status

EXPLANATION

Recently pumped

Static

Figure 2.20. Groundwater-level hydrograph for well LDAW 11, U.S. Geological Survey site number 391257104530201, Douglas 

County, Colorado.

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●

●

●

●

●

5,741

5,746

5,751

5,756

5,761

5,766

5,771

5,776

5,781

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Groundwater-level status

EXPLANATION

Nearby pumping

Recently pumped

Static

Continuous record

Daily maximum

Figure 2.21. Groundwater-level hydrograph for well GRNDAW 4, U.S. Geological Survey site number 393259104491001, Douglas 

County, Colorado.
36 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

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●

● ●

6,620

6,622

6,624

6,626

6,628

6,630

6,632

6,634

6,636

6,638

6,640

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Groundwater-level status

EXPLANATION

Recently pumped

Static

Continuous record

Daily maximum

Figure 2.22. Groundwater-level hydrograph for well DENV 1, U.S. Geological Survey site number 391656104473001, Douglas 

County, Colorado.

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●

6,154

6,156

6,158

6,160

6,162

6,164

6,166

6,168

6,170

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Groundwater-level status

EXPLANATION

Nearby pumping

Recently pumped

Static

Continuous record

Daily maximum

Figure 2.23. Groundwater-level hydrograph for well DENV 2, U.S. Geological Survey site number 391929104574101, Douglas 

County, Colorado.
Appendix 2 37

6,377

6,378

6,379

6,380

6,381

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

EXPLANATION

Groundwater-level status

Static

Figure 2.24. Groundwater-level hydrograph for well DENV 3, U.S. Geological Survey site number 391245104525501, Douglas 

County, Colorado.

●

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●●

●

●

●

● ●

6,138

6,140

6,142

6,144

6,146

6,148

6,150

6,152

6,154

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

EXPLANATION

Groundwater-level status

Recently pumped

Static

Figure 2.25. Groundwater-level hydrograph for well DENV 4, U.S. Geological Survey site number 392115104553501, Douglas 

County, Colorado.
38 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

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● ●

● ●

6,087

6,092

6,097

6,102

6,107

6,112

6,117

6,122

6,127

6,132

6,137

6,142

6,147

6,152

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Continuous record

Daily maximum

EXPLANATION

Groundwater-level status

Recently pumped

Static

Figure 2.26. Groundwater-level hydrograph for well DENV 5, U.S. Geological Survey site number 392235105003001, Douglas 

County, Colorado.

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●

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●

●

5,486

5,488

5,490

5,492

5,494

5,496

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Continuous record

Daily maximum

EXPLANATION

Groundwater-level status

Recently pumped

Static

Figure 2.27. Groundwater-level hydrograph for well DENV 6, U.S. Geological Survey site number 393040105003201, Douglas 

County, Colorado.
Appendix 2 39

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●

●

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●

●

●

●

●

6,582

6,584

6,586

6,588

6,590

6,592

6,594

6,596

6,598

6,600

6,602

6,604

6,606

6,608

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

EXPLANATION

Groundwater-level status

Recently pumped

Static

Figure 2.28. Groundwater-level hydrograph for well DENV 7, U.S. Geological Survey site number 391212104473801, Douglas 

County, Colorado.

● ●● ●●●●●●●●●●●●● ● ● ●

●

●

●

6,945

6,950

6,955

6,960

6,965

6,970

6,975

6,980

6,985

6,990

6,995

7,000

7,005

7,010

7,015

7,020

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

EXPLANATION

Groundwater-level status

Recently pumped

Static

Figure 2.29. Groundwater-level hydrograph for well DENV 8, U.S. Geological Survey site number 390755104454001, Douglas 

County, Colorado.
40 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

●

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●●

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● ●

●

●●

● ●

●

● ●

●

6,169

6,171

6,173

6,175

6,177

6,179

6,181

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

EXPLANATION

Groundwater-level status

Recently pumped

Static

Figure 2.30. Groundwater-level hydrograph for well DENV 10, U.S. Geological Survey site number 391936104570101, Douglas 

County, Colorado.

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● ●

●

● ●

5,668

5,673

5,678

5,683

5,688

5,693

5,698

5,703

5,708

5,713

5,718

5,723

5,728

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

EXPLANATION

Groundwater-level status

Recently pumped

Static

Figure 2.31. Groundwater-level hydrograph for well DENV 11, U.S. Geological Survey site number 393330104450701, Douglas 

County, Colorado.
Appendix 2 41

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●●

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●

●●●

● ●

●

●

●

●

5,229

5,231

5,233

5,235

5,237

5,239

5,241

5,243

5,245

5,247

5,249

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

EXPLANATION

Groundwater-level status

Recently pumped

Static

Figure 2.33. Groundwater-level hydrograph for well ARAP 1, U.S. Geological Survey site number 392853105015001, Douglas 

County, Colorado.

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●

●

●

5,699

5,704

5,709

5,714

5,719

5,724

5,729

5,734

5,739

5,744

5,749

5,754

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Continuous record

Daily maximum

EXPLANATION

Groundwater-level status

Recently pumped

Static

Figure 2.32. Groundwater-level hydrograph for well GRNDEV 3, U.S. Geological Survey site number 393252104492101, Douglas 

County, Colorado.
42 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

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●●

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●

●

●

●

5,375

5,377

5,379

5,381

5,383

5,385

5,387

5,389

5,391

5,393

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

EXPLANATION

Groundwater-level status

Recently pumped

Static

Figure 2.34. Groundwater-level hydrograph for well ARAP 2, U.S. Geological Survey site number 393120105003101, Douglas 

County, Colorado.

●

●●

●

●

●

●●

5,982

5,987

5,992

5,997

6,002

6,007

6,012

6,017

6,022

6,027

6,032

6,037

6,042

6,047

6,052

6,057

6,062

6,067

6,072

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

EXPLANATION

Groundwater-level status

Recently pumped

Static

Figure 2.35. Groundwater-level hydrograph for well LARA 1, U.S. Geological Survey site number 392522105015001, Douglas 

County, Colorado.
Appendix 2 43

●

●

●●

●

●

●

● ●●

6,021

6,026

6,031

6,036

6,041

6,046

6,051

6,056

6,061

6,066

6,071

Groundwater elevation above North American 

Vertical Datum of 1988, in feet

Date

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

EXPLANATION

Groundwater-level status

Recently pumped

Static

Figure 2.36. Groundwater-level hydrograph for well LARA 2, U.S. Geological Survey site number 392522105015401, Douglas 

County, Colorado.
44 Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19

Appendix 3. Descriptions and Equations of Mann-Kendall Test, Seasonal 

Mann-Kendall Test, and Sen Slope Estimate

The Mann-Kendall (M–K) trend test evaluates the 

strength of the monotonic association between two vectors, in 

this case groundwater-level elevations (y) and time (x). The 

nonparametric M–K test requires no assumptions of sample 

distribution, trend shape, or data continuity when measuring 

the strength of the relation. The M–K test compares the number of times y decreases as x increases (“discordant” pairs) to 

the number of times y increases as x increases (“concordant” 

pairs) (Helsel and others, 2020):

 S=∑

i<j

(sign(xj −

xi)*sign(yj −yi)) (3.1)

where

S is the test statistic, which estimates the 

monotonic dependence of y on x;

x is the rank of time variable, from least to most 

recent; and

y is the measured groundwater-level elevation, 

in feet above North American Vertical 

Datum of 1988.

The strength of the correlation is then estimated by 

Kendall’s tau (τ), also known as the rank correlation coefficient (Helsel and others, 2020). Kendall’s tau is analogous 

to the linear correlation coefficient and compares the S test 

statistic to the maximum possible value of S:

 τ = _S n(n − 1) / 2 (3.2)

where

τ is the rank correlation coefficient and

n is the number of data pairs.

The range of τ is from –1 (where all y values decrease 

with increasing x values) to +1 (where all y values increase 

with increasing x values). A τ value close to zero indicates a 

weak dependence of y on x, or lack of trend. Absolute τ values 

greater than 0.7 are considered to indicate strong correlation 

(Helsel and others, 2020). A probability value (p-value) can 

be calculated or estimated (depending on the sample size) 

using the S statistic and its distribution (Helsel and others, 

2020). Although the M–K test is preferred rather than parametric methods in scenarios where residuals’ distributions 

are nonnormal or the correlation between x and y is nonlinear 

(Hirsch and others, 1991), the M–K test evaluates monotonic (consistently negative or positive) trends. Datasets with 

repeated negative and positive correlations will result in a 

nonsignificant trend. This condition means that standard M–K 

tests are not suitable for data with cyclical seasonality, unless 

the applied method accounts for periodicity.

To account for seasonality, the seasonal Mann-Kendall 

(sM–K) test was used, which conducts M–K tests for each 

season separately (for example, January data are compared 

only to January data in other years). The S test statistics are 

calculated for each month (eq. 3.1), and then the individual 

months’ S statistics are summed for an overall S test statistic 

(Sk) (Helsel and others, 2020). Subsequently, an overall τ and 

the p-value can be calculated from Sk values for each record.

To evaluate trend significance, a hypothesis test and the 

derived p-value were used. The null hypothesis of no monotonic trend and an alpha (α) of 0.10 were used. Therefore, 

when the p-value was less than or equal to 0.10, the null 

hypothesis was rejected, and a trend in groundwater-level 

elevations was considered statistically significant.

The Sen slope estimate is referred to as the “trend estimate” or “trend” in groundwater-level elevations in the report 

(tables 3 and 4). The Sen slope estimate was used to calculate 

the trend in groundwater-level elevations by using the same 

pairs of x and y data used to compute S in the Mann-Kendall 

test. The Sen slope is calculated by taking the median of the 

slope of each pair as follows:

βss = median (

y

_j −

yi

xj −xi) (3.3)

where

βss is the Sen slope estimate, in feet per year.

References Cited

Helsel, D.R., Hirsch, R.M., Ryberg, K.R., Archfield, S.A., and 

Gilroy, E.J., 2020, Statistical methods in water resources: 

U.S. Geological Survey Techniques and Methods, book 4, 

chapter A3, 458 p., accessed June 2020 at https://doi.org/

10.3133/tm4a3. [Supersedes USGS Techniques of WaterResources Investigations, book 4, chapter A3, version 1.1]

Hirsch, R.M., Alexander, R.B., and Smith, R.A., 1991, 

Selection of methods for the detection and estimation of 

trends in water quality: Water Resources Research, v. 27, 

no. 5, p. 803–813. [Also available at https://doi.org/10.1029/

91WR00259.]
For more information about this publication, contact:

Director, USGS Colorado Water Science Center

Box 25046, Mail Stop 415

Denver, CO 80225

(303) 236–4882

Or visit the Colorado Water Science Center website at

https://co.water.usgs.gov/

Publishing support provided by the Denver and Rolla 

Publishing Service Centers
Malenda and Penn—Groundwater Levels in the Denver Basin Bedrock Aquifers of Douglas County, Colorado, 2011–19—SIR 2020–5076

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20205076