Cover description:

Landsat thematic mapper mosaic of the Middle Rio Grande Basin. The four scenes used in the image were acquired in September 1993. 

Bands 1, 4, and 7 are displayed through blue, green, and red filters, respectively. The image has been output at 30-meter resolution by cubic 

convolution resampling to fit the North American Datum of 1983 (NAD83) in a Universal Transverse Mercator (UTM) projection. A terrain 

correction was included in the processing using USGS 1:24,000-scale Digital Elevation Model (DEM) data. Image compiled by the USGS 

Astrogeology Program, Flagstaff Field Center. See Mullins and Hare (1999) for a more complete description of the image.

Mullins, K.F., and Hare, T.M., 1999, Calibration, processing, and production of a Landsat thematic mapper mosaic of the Middle Rio 

Grande Basin Study area, in Bartolino, J.R., ed., U.S. Geological Survey Middle Rio Grande Basin Study—Proceedings of the 

Third Annual Workshop, Albuquerque, New Mexico, February 24–25, 1999: U.S. Geological Survey Open-File Report 99–203, 

p. 15–17.

Additional photograph credits, clockwise from upper right:

1. J.R. Bartolino

2. J.R. Bartolino

3. K.A. Winfield

4. C.E. Heywood

5. J.R. Bartolino

6. F.E. Gebhardt
GROUND-WATER RESOURCES OF THE

MIDDLE RIO GRANDE BASIN

By

James R. Bartolino and James C. Cole

U.S. Geological Survey

Circular 1222

2002
U.S. DEPARTMENT OF THE INTERIOR

Gale A. Norton

Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat

Director

Reston, Virginia 2002

The use of firm, trade, and brand names in this report is for identification purposes only and does not 

constitute endorsement by the U.S. Government.

Free on application to the

U.S. Geological Survey

Denver Federal Center

Information Services

Box 25286

Denver CO 80225

Library of Congress Cataloging-in-Publication Data
In 1995, the agency primarily responsible for managing water resources in New Mexico, the Office of the 

State Engineer, declared the Middle Rio Grande Basin a “critical basin”; that is, a ground-water basin faced 

with rapid economic and population growth for which there is less than adequate technical information about 

the available water supply. This declaration was largely the result of studies of the ground-water resources of 

the Middle Rio Grande Basin by the New Mexico Bureau of Geology and Mineral Resources (formerly the 

New Mexico Bureau of Mines and Mineral Resources) and U.S. Geological Survey (USGS) in cooperation 

with the City of Albuquerque that showed conclusively that many aspects of the popular understanding of 

water resources of the basin were incorrect. The two most important conclusions of these studies were that 

there is significantly less ground water available for supply than previously thought and that the Rio Grande 

contributes less water to the Santa Fe Group aquifer system than was previously believed. Both conclusions 

have had and will continue to have major impacts on how water is used, allocated, and managed in the basin. 

However, these studies also revealed gaps in the understanding of the water resources of the basin. In an effort 

to fill some of these gaps, the USGS and other agencies began the Middle Rio Grande Basin Study, a 6-year 

effort to improve the understanding of the hydrology, geology, and land-surface characteristics of the Middle 

Rio Grande Basin.

An important aspect of the USGS mission is to provide information that describes the Earth, its resources, and 

the processes that govern the availability and quality of those resources. With reports such as this Circular, the 

USGS seeks to broaden public understanding of water resources and the processes that affect those resources. 

Our hope is that this improved understanding will contribute to another goal of the USGS: the use of this scientific information to enhance and protect our quality of life.

This Circular presents an overview of our current understanding of the water resources of the Middle Rio 

Grande Basin, with an emphasis on ground water. This report is written for a wide audience of people interested or involved in the use of water resources in the Middle Rio Grande Basin. It is intended to serve as a 

general educational document rather than a report of new scientific findings, though much of the information 

it contains is the result of new studies performed as part of the Middle Rio Grande Basin Study. This Circular, 

coupled with ongoing data collection and research, is the USGS contribution toward a sound scientific basis 

for water managers and policy makers to make informed decisions about the water resources of the basin with 

the goal of meeting current needs and assuring a sustainable supply for future generations.

Foreword

Charles G. Groat

Director, U.S. Geological Survey
This report is not only the culmination of the 6-year Middle Rio Grande Basin Study, but also of 

the work of many preceding scientists and engineers. Some of the most notable scientists in the 

fields of geology and hydrology have worked in the Middle Rio Grande Basin at some point in 

their careers, including Kirk Bryan and C.V. Theis. The authors wish to acknowledge the contribution of all those who have contributed to the current understanding of the hydrogeology of the 

basin. The oft-quoted remark of Lucan (Marcus Annaeus Lucanus, A.D. 39–65) applies: 

“Pigmies placed on the shoulders of giants see more than the giants themselves.”

Technical assistance (in the form of discussions and suggestions) was provided by S.K. Anderholm, J.W. Hawley, D.P. McAda, D.G. Woodward, and all the scientists who worked on the 

Middle Rio Grande Basin Study. Other nontechnical assistance was provided by L.V. Beal, 

R.A. Durall, and D.E. Straka.

Primary editorial and technical review of this Circular was provided by H.R. Allen, L.M. 

Bexfield, P.R. Bowman, J.V. Flager, D.J. Hester, R.J. Olmstead, T.E. Reilly, Seymour Subitzky, 

and D.G. Woodward of the U.S. Geological Survey; S.D. Connell and Peggy Johnson of the New 

Mexico Bureau of Geology and Mineral Resources (formerly the New Mexico Bureau of Mines 

and Mineral Resources); L.M. Logan and Jess Ward of the New Mexico Office of the State 

Engineer; J.M. Stomp of the City of Albuquerque; and L.A. Bartolino. These reviewers made 

many excellent suggestions, and any errors that may remain are the sole responsibility of the 

authors.

In addition to the U.S. Geological Survey, many other Federal, State, and local governments and 

agencies contributed resources to or cooperated in the characterization of the water resources, 

geology, and land surface of the Middle Rio Grande Basin. These governments and agencies 

include the City of Albuquerque, New Mexico Office of the State Engineer, New Mexico Bureau 

of Geology and Mineral Resources, Albuquerque Metropolitan Arroyo Flood Control Authority, 

Middle Rio Grande Council of Governments, Middle Rio Grande Conservancy District, Bureau 

of Reclamation, Pueblo of Cochiti, Pueblo of Isleta, Pueblo of Jemez, Pueblo of Laguna, Pueblo 

of San Felipe, Pueblo of Sandia, Pueblo of Santa Ana, Pueblo of Santo Domingo, Pueblo of Zia, 

City of Santa Fe, Village of Los Lunas, Bernalillo County, Santa Fe County, New Mexico Environment Department, Sandia National Laboratories, Los Alamos National Laboratory, U.S. 

Environmental Protection Agency, and the U.S. Army Corps of Engineers.

Final layout was prepared by A.J. Brogan with design input from R.J. Olmstead, illustration support from J.M. Evans and S.P. Clendening, and editorial review by M.A. Kidd, all of the U.S. 

Geological Survey, Denver, Colorado. Final versions of all figures were prepared by Alice and 

J.T. Springfield of Springfield and Springfield, Fort Collins, Colorado. All photographs are by 

J.R. Bartolino except as noted.

Acknowledgments
Contents

Executive Summary 1

Characteristics of the Middle Rio Grande Basin 1

Geology 1

Surface Water 2

Ground Water 3

Ground-Water Chemistry 3

Ground-Water-Flow Modeling 4

Chapter 1: Common questions about water resources in the Middle Rio Grande Basin 5

How much water do we have? 5

How much water do we use? 5

How long will our supplies last? 6

How effective are water conservation efforts in the area? 6

How rapidly are ground-water levels declining? 6

Is municipal and(or) industrial pumping lowering ground-water levels outside major metropolitan areas? 7

Have ground-water-level declines triggered land subsidence? 7

How will water chemistry affect the use of ground water? 7

How much water in the basin is appropriated? 7

How much water can be pumped from the aquifer system using the present infrastructure? 8

How interrelated are the ground-water and surface-water systems? 8

Chapter 2: The Middle Rio Grande Basin 9

Physical characteristics 9

Climate 9

Major vegetation types 14

Human activities and water resources 16

Chapter 3: Geology of the Santa Fe Group aquifer system 23

The Rio Grande Rift 23

Geologic processes that shaped the aquifer system 29

How the basin has changed over geologic time 31

Three-dimensional form of the aquifer system today 33

Effect of faults on the aquifer system 34

Contribution of geophysical data to understanding the aquifer system 35

How the geologic model represents current interpretation of basin structure and stratigraphy 40

Chapter 4: The hydrologic system of the Middle Rio Grande Basin 41

Surface-water system 41

Surface-water quantity 44

Ground-water system 47

Ground-water-level declines 47

Aquifer productivity 58

Ground-water quantity 60

Water use in the basin 60

Water budgets 63

Major legal and institutional controls on water in the basin 65

Rio Grande Compact 66

San Juan-Chama Transmountain Diversion Project 67

Endangered species 67

Water appropriation 69
Chapter 5: How water moves through the aquifer system 71

Recharge and underflow—How ground water enters the aquifer system 71

Mountain-front recharge 71

Tributary recharge 73

Rio Grande and inner-valley recharge 76

Subsurface recharge or underflow 77

Flow paths—How ground water moves through the aquifer system 80

Discharge—How ground water leaves the aquifer system 81

Pumpage 81

Seepage to drains and the Rio Grande and springs 81

Evapotranspiration 84

Underflow 85

Effects of ground-water withdrawals 85

Deterioration of water quality 85

Water-well problems 86

Subsidence 86

Chapter 6: Chemical characteristics of water in the aquifer system 91

General quality of ground water and what it reveals about the ground-water system 91

Naturally occurring substances that limit the use of ground water 94

Contaminants of human origin and ground water 99

Chapter 7: Computer simulations of the aquifer system 101

Ground-water-flow model of the basin 101

Information used in the ground-water-flow model 106

What the ground-water-flow model tells us about the hydrologic system of the basin 110

What the ground-water-flow model tells us about future conditions 114

Chapter 8: Important questions that remain about water resources of the Middle Rio Grande Basin 115

How much water is pumped where and by whom? 115

What are the availability and quality of water in deeper parts of the aquifer? 115

How much water does vegetation in the bosque use? 116

How is the aquifer responding to pumping over the long term? 116

Is septic-system effluent contaminating ground water? 116

How will the more stringent arsenic standard affect water supplies? 116

Are pharmaceuticals present in ground or surface water? 117

Chapter 9: Key points regarding water resources of the Middle Rio Grande Basin 119

References Cited 121

Abbreviations and Chemical Notation 132

Prefixes for Abbreviations for Multiples and Submultiples 133
FIGURES

2.1–2.3. Maps showing:

2.1. Major physiographic features of the Middle Rio Grande Basin 10

2.2. Average monthly temperatures for selected National Weather Service stations in and near the 

Middle Rio Grande Basin 12

2.3. Average monthly precipitation for selected National Weather Service stations in and near the 

Middle Rio Grande Basin 13

2.4. Photographs looking west across the Rio Grande toward the Albuquerque volcanoes 15

2.5–3.2. Maps showing:

2.5. Generalized land use and land cover in the Middle Rio Grande Basin in the early 1980’s 19

3.1. Location of the Middle Rio Grande Basin and the Rio Grande Rift 28

3.2. Simplified structural features of the Middle Rio Grande Basin 29

3.3. Section showing east-west geologic section through the Calabacillas subbasin illustrating general 

relation of faults and sedimentary units 30

3.4. Graph showing variation of oxygen isotope composition of shells from bottom-dwelling micro-organisms 

in the Pacific and Atlantic Oceans during the last 25 million years 32

4.1. Map showing major surface-water features of the Middle Rio Grande Basin 42

4.2. Diagram of the inner valley irrigation network in the Middle Rio Grande Basin 43

4.3–4.7. Maps showing:

4.3. Current and discontinued streamflow-gaging stations in and adjacent to the Middle Rio Grande Basin 45

4.4. Ground-water levels that represent predevelopment conditions in the Santa Fe Group aquifer system 

in the Middle Rio Grande Basin 50

4.5. Ground-water levels that represent 1960–61 conditions in the Santa Fe Group aquifer system in the 

Middle Rio Grande Basin 51

4.6. Ground-water levels that represent winter 1994–95 conditions in the Santa Fe Group aquifer system 

in the Middle Rio Grande Basin 52

4.7. Location of selected wells in the Middle Rio Grande Basin 53

4.8. Graphs showing water levels in selected wells in the Middle Rio Grande Basin 55

4.9. Map showing distribution of east-west horizontal hydraulic conductivity in the upper part of the Santa Fe Group 

aquifer system in the ground-water-flow model of McAda and Barroll (2002) 59

4.10. Diagram showing water withdrawal estimates by category for surface and ground water during 1995 for 

counties in the Middle Rio Grande Basin. See table 4.2 for the data by county 62

4.11–6.1. Maps showing:

4.11. Middle Rio Grande water budget for the reach from the Otowi stream-gaging station to Elephant Butte 

Dam as prepared by the Action Committee of the Middle Rio Grande Water Assembly 64

4.12. Diversion dams and tunnels of the San Juan-Chama Transmountain Diversion Project 68

6.1. Hydrochemical regions of the Middle Rio Grande Basin 95

7.1. Section showing generalized configuration of ground-water-flow model layers used by McAda and 

Barroll (2002) along model row 80 104

7.2. Map showing active cells in the ground-water-flow model grid (layer 1) of McAda and Barroll (2002) 105

TABLES

2.1. National Weather Service weather stations in the Middle Rio Grande Basin and Sandia Crest station 11

2.2. Population in New Mexico, Albuquerque, and the Middle Rio Grande Basin, 1900–2000 18

4.1. Mean annual surface-water inflows into and outflows from the Middle Rio Grande Basin 46

4.2. Water withdrawal estimates during 1995 for counties in the Middle Rio Grande Basin 61

6.1. Median values of selected parameters of the 13 hydrochemical zones delineated for the Santa Fe Group 

aquifer system of the Middle Rio Grande Basin 96

6.2. Current drinking-water standards and significance of constituents commonly found in ground water in 

the Middle Rio Grande Basin 97

7.1. Simulated annual water budget for the ground-water-flow model of McAda and Barroll (2002) 111
 

 A Landscape change modeling 20

 B Structural, sedimentologic, and climatic effects on the Middle Rio Grande Basin aquifer system 24

 C How well information is used to understand the hydrogeology of the basin 26

 D How geophysical methods have been used to understand the subsurface 36

 E Knowledge gained from the 98th Street well core 38

 F Ground-water-level maps and how they are used to understand the aquifer 48

 G How mountain-front recharge is studied 74

 H How ground-water/surface-water interaction of the Rio Grande has been studied 78

 I Environmental tracers and how they are used to understand the aquifer 82

 J Land subsidence and how it is being studied in the basin 88

 K How ground-water chemistry helps us understand the aquifer 92

 L Ground-water-flow models and how they are used to study the basin 102

 M How the geologic framework is translated into a ground-water-flow model 108

 N How carbon-14 data were used to improve the ground-water-flow model 112 

 FIGURES

A.1. Graph showing changes in urban characteristics for Albuquerque, 1940–2050 20

A.2. Diagram showing urban area in the vicinity of Albuquerque in 1935, 1991, and 2050 projected using 

the SLEUTH model 21

B.1. Generalized section showing substantial thickening of the Atrisco silt- and clay-rich beds in the downthrown fault 

block east of the 98th Street well location and index map 24

B.2. Oblique aerial photograph of outcrops in the upper Santa Fe Group sediment adjacent to the Zia fault in the 

northern Calabacillas subbasin. The prominent whitish zone is a buried calcareous soil that was buried by yellowish, 

windblown silt deposited following downdropping on the Zia fault 25

 C.1. Section showing hypothetical responses of various borehole geophysical tools to alluvial deposits of 

contrasting texture and saturation and to volcanic rock units 26

 C.2. Graph showing correlation of electrical conductivity logs among Albuquerque well fields west of the 

Rio Grande 27

D.1. Map showing gravity data for the entire Middle Rio Grande Basin and surrounding area 36

 D.2. Map showing area south of Albuquerque and simplified map of important hydrogeologic features 37

E.1. Graph showing lithology and geophysical logs of the 98th Street well 39

F.1. Map showing information needed to determine water-table elevations and to calculate hydraulic gradients 48

F.2. Section showing hypothetical well locations, water-table elevations, water-table contours, and 

approximate directions of ground-water flow 48

F.3. Diagram showing examples of water-table contours and directions of ground-water flow in the vicinity of 

losing and gaining streams 49

G.1. Map showing locations of study sites for mountain-front recharge and water temperature in the 

Middle Rio Grande Basin 74

 G.2. Diagram showing temperature compared to time at two depths in an ephemeral streambed during 

periods of no flow and flow 75

Boxes
 

H.1. Map showing locations of study sites on the Rio Grande for water temperature and flood pulses 78

H.2. Graph showing thermographs from Paseo del Norte section showing Rio Grande temperature and 

ground-water temperatures measured in wells P06, P07, and P08 79

I.1. Graph showing concentrations of tritium (3H) in precipitation, chlorofluorocarbons (CFC-11, CFC-12, 

and CFC-113) in air, and sulfur hexafluoride (SF6) in air over North America, 1940–97 82

J.1. Photograph showing surface instrumentation of the Montaño extensometer 89

 J.2. Map showing Interferometric Synthetic Aperture Radar (InSAR) image of the Albuquerque area, 

July 2, 1993–September 3, 1995 89

L.1–L.3. Diagrams showing:

L.1. Part of a hypothetical basin-fill ground-water system 102

L.2. Part of a hypothetical basin-fill ground-water system with some model cells shown superimposed 103

L.3. Subset of the model cells that represent an aquifer, indicating that flow is calculated between adjacent cells 103

M.1. Section showing representation of an aquifer in a finite-difference ground-water-flow model 108

M.2. Section showing representation of ground-water flow-model cells related to sedimentary deposits 109

N.1. Map showing traveltimes and ground-water flow paths predicted by a preliminary version of the current 

revision of the ground-water-flow model of the Middle Rio Grande Basin 113

 TABLES

A.1. Urban growth in Albuquerque, 1935–2050. Projections for 2050 are based on SLEUTH model output 20

D.1. Brief description of the geophysical methods used and the hydrogeologic features delineated by each 37
Conversions

This Circular uses both inch/pound (U.S. customary) and International System of Units (SI metric) 

units. The conversion factors listed below are provided to convert between inch/pound and SI metric units, 

or different units in the same systems.

Electrical conductivity units are given in siemens (S), which is the preferred unit name under the 

International System of Units. It is numerically equivalent to the older term mhos.

Electrical resistivity can be converted to electrical conductivity (siemens per meter) by taking its 

inverse.

Measurement Multiply By To Obtain

Length inch 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area square mile (mi2

) 2.590 square kilometer (km2)

acre (acre) 0.4047 hectare (ha)

Volume acre-foot (acre-ft) 1,233 cubic meter (m3

)

gallon 0.003785 cubic meter (m3

)

cubic foot (ft3) 0.02832 cubic meter (m3)

Flow rate cubic foot per second (ft3/s) 0.2832 cubic meter per second (m3/s)

cubic foot per second (ft3/s) 723.97 acre-foot per year (acre-ft/yr)

cubic foot per second (ft3/s) 448.83 gallon per minute (gal/min)

Hydraulic conductivity foot per day (ft/d) 0.3048 meter per day (m/d)

Temperature degree Fahrenheit (°F) (°F–32)/1.8 degree Celsius (°C)

Tritium activity tritium unit (TU) 3.24 picocuries per liter (pCi/L)

Magnetism Tesla (T) 1 weber per square meter (Wb/m2)

Gravity gal (Gal) 1 centimeter per second squared (cm/s2

)
Vertical Datum

In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD of 

1929)—a geodetic datum derived from a general adjustment of the first-order level nets of the United States 

and Canada, formerly called Sea Level Datum of 1929.

Base Credits

All maps of the Middle Rio Grande Basin in this report are in Lambert Conformal Conic projection 

with standard parallels 33°00' and 45°00' north latitude, and central meridian 106°00' west longitude. The 

base for figure 3.1 was compiled from U.S. Department of Commerce, Bureau of Census TIGER/line 

Precensus Files, 1990, scale 1:100,000. 

The base for the maps of the Middle Rio Grande Basin was compiled from several sources. The 

hydrography is from 1977–78 U.S. Geological Survey digital data, scale 1:100,000. Cultural features are 

from 1992 City of Albuquerque digital data, scale 1:2,400, and digitized from 1977–78 U.S. Geological 

Survey maps, scale 1:100,000. Other sources are noted on the maps themselves.
131
1

Executive Summary

The Middle Rio Grande Basin covers approximately 3,060 square miles in central New Mexico, encompassing parts 

of Santa Fe, Sandoval, Bernalillo, Valencia, Socorro, Torrance, and Cibola Counties. In this report, “Middle Rio 

Grande Basin” refers to the geologic basin defined by the extent of deposits of Cenozoic age along the Rio Grande 

from about Cochiti Dam to about San Acacia. In 2000, the population of the Middle Rio Grande Basin was about 

690,000, or about 38 percent of the population of New Mexico (U.S. Census Bureau, 2001a, 2001b).

In 1995, the New Mexico Office of the State Engineer declared the Middle Rio Grande Basin a “critical basin”; that is, 

a ground-water basin faced with rapid economic and population growth for which there is less than adequate technical 

information about the available water supply. Though the basin had been intensively studied for a number of years, 

important gaps remained in the understanding of the water resources of the basin. In an effort to fill some of these 

gaps, the U.S. Geological Survey (USGS) and other Federal, State, and local agencies began the Middle 

Rio Grande Basin Study, a 6-year effort to improve the understanding of the hydrology, geology, and land-surface 

characteristics of the basin.

Characteristics of the Middle Rio Grande Basin

Much of the Middle Rio Grande Basin is classified as desert, with mean annual precipitation ranging from 7.6 inches 

at Belen to 12.7 inches at Cochiti Dam. Mean annual temperatures range from 54.0° F at Corrales to 56.5° F at Albuquerque and Belen (National Weather Service, 2002).

Scurlock (1998) listed eight main plant communities in the present-day Middle Rio Grande Basin and bordering 

mountains. They are, in a progression from near the Rio Grande to the mountaintops: riparian, desert grassland, plainsmesa grassland, scrublands, juniper savanna, pinyon-juniper woodlands, ponderosa pine, and subalpine and mixed 

coniferous forest. The vegetation of the riparian woodland (or bosque) has evolved significantly since the introduction 

of exotic species prior to 1900 and the construction of flood-control and bank-stabilization projects. During the last 60 

to 70 years, the bosque has developed in an area that was formerly semibarren flood plain.

The Albuquerque area began to grow significantly during and after the Second World War. Postwar growth expanded 

the economic base of the area and led to a population increase in Albuquerque from about 35,000 to about 200,000 

people between 1940 and 1960 (Reeve, 1961). This population growth led to increased pumping of ground water.

Geology

The Middle Rio Grande Basin lies in the Rio Grande rift valley, a zone of faults and basins that stretches from Mexico 

north to approximately Leadville, Colorado (about 150 miles north of the New Mexico border)—the modern Rio 

Grande follows this rift valley. The rift formed more than 25 million years ago and initially consisted of a succession 

of topographically closed basins. These closed basins filled with sediment from the adjacent mountain ranges, dune 

deposits from windblown sand, and volcanic deposits from local volcanic areas such as the Jemez Mountains. Flowing 

southward into and through the successive basins in the rift, the Rio Grande deposited river-borne sediment and established the through-flowing river seen today. About 3 million years ago the Rio Grande began to erode into sediment 

that it had deposited previously, suggesting that the river drained all the way to the Gulf of Mexico. Basin-fill deposits 

derived from all these sources (deposited in both open- and closed-basin conditions) are known as the Santa Fe Group 

and range from about 1,400 feet thick at the basin margins to approximately 14,000 feet in the deepest parts of the 

Middle Rio Grande Basin. The Santa Fe Group, in addition to younger alluvial deposits along the Rio Grande, makes 

up the Santa Fe Group aquifer system.
2

Each of the different settings in which sediment was deposited in the Middle Rio Grande Basin (such as mountainfront alluvial fans, rivers and streams, or sand dunes) resulted in a unique type of sedimentary deposit. These deposits 

are a complex mixture of different sediment types and grain sizes that change rapidly in the vertical and horizontal 

directions. Some of these deposits make better aquifer material than others, resulting in variations in the quantity and 

quality of water produced from wells installed in different locations.

Faults throughout the basin further increase the complexity of the aquifer system. Ground-water flow can be restricted 

across faults by offsetting units of different permeability or enhanced along faults by the presence of fractured rock. 

Over time, such fractures may become barriers to flow because of the precipitation of chemical cements in the fractures.

Surface, airborne, and borehole-geophysical techniques have been used to improve the understanding of the geologic 

framework of the Santa Fe Group aquifer system. Such properties as magnetism, gravity, electrical properties, and 

natural radioactivity have allowed scientists to better define the boundaries of the aquifer system, faults, and areas 

underlain by a more permeable aquifer material.

Geologic information collected for the Middle Rio Grande Basin Study has been incorporated into a new conceptualization of the composition of the aquifer system. This improved understanding has been formalized into a three-dimensional geologic model that is the basis for a new ground-water-flow model of the basin.

Surface Water

In the Middle Rio Grande Basin, the surface- and ground-water systems are intimately linked through a series of 

complex interactions. These interactions can make it difficult to recognize the boundary between the two systems, and 

changes in one often affect the other. The most prominent hydrologic feature in the basin is the Rio Grande, which 

flows through the entire length of the basin, generally from north to south. The fifth longest river in North America, its 

headwaters are in the mountains of southern Colorado. Flow in the Rio Grande is currently (2002) regulated by a series 

of dams and storage reservoirs. The greatest flows occur in late spring as a result of snowmelt and for shorter periods 

during the summer in response to rainfall. Historically, the Rio Grande has flowed year-round through much of the 

basin, except during severe drought. Within the basin, tributary steams, wastewater-treatment plants, flood-diversion 

channels from urban areas, and a large number of arroyos and washes contribute flow to the river. 

The inner valley of the Rio Grande contains a complex network of irrigation canals, ditches, and drains. During irrigation season, water is diverted from the river at four locations in the basin and flows through the Rio Grande inner 

valley in a series of irrigation canals and smaller ditches for application to fields. This water recharges ground water, is 

lost to evaporation, is transpired by plants, or is intercepted by interior drains and returned to the river. Besides the Rio 

Grande, the inner-valley surface-water system also contains a system of riverside drains, which are deep canals that 

parallel the river immediately outside the levees. The drains are designed to intercept lateral ground-water flow from 

the river, thus preventing waterlogged conditions in the inner valley. The drains then carry this ground water back to 

the Rio Grande.

Estimated and measured annual surface-water inflow into the Middle Rio Grande Basin is about 1,330,000 acre-feet 

(for water years 1974–2000) and measured annual surface-water outflow is about 1,050,000 acre-feet (for water years 

1974–2000). Currently (2002), the primary consumptive use by humans of surface water in the Middle Rio Grande 

Basin is irrigation in the inner valley of the Rio Grande. Other water is consumed by reservoir evaporation, recharge to 

ground water, and evapotranspiration by riparian vegetation. Other nonconsumptive uses include recreation, esthetics, 

and ceremonial use by Native Americans. 
3

Ground Water

The Santa Fe Group aquifer system is divided into three parts: the upper (from less than 1,000 to 1,500 feet thick), 

middle (from 250 to 9,000 feet thick), and lower (from less than 1,000 to 3,500 feet thick). In places, the upper part 

and(or) the middle part of the aquifer has eroded away. Much of the lower part may have low permeability and poor 

water chemistry; thus, ground water is mostly withdrawn from the upper and middle parts of the aquifer. Only about 

the upper 2,000 feet of the aquifer is typically used for ground-water withdrawal. Ground water from the Santa Fe 

Group aquifer system is currently the sole source of water for municipal supply, domestic, commercial, and industrial 

use in the Middle Rio Grande Basin.

The depth to water in the Santa Fe Group aquifer system varies widely, ranging from less than 2 feet near the Rio 

Grande to about 1,180 feet in an area west of the river beneath the West Mesa. Effects of ground-water pumping are 

not evident on the earliest ground-water-level maps of the Middle Rio Grande Basin (1936 conditions). However, a 

ground-water-level map showing more recent conditions (winter 1994–95) shows well-defined cones of depression in 

the Albuquerque and Rio Rancho areas and marked distortion of water-level contours across the Albuquerque area. 

Water levels in a network of 255 wells are being measured to monitor further water-level changes. 

Water enters the Santa Fe Group aquifer system in four main settings: mountain fronts and tributaries to the Rio 

Grande, the inner valley of the Rio Grande, the Rio Grande, and subsurface basin margins. Water entering the aquifer 

in the first three settings is usually termed recharge, whereas water entering the basin in the subsurface is typically 

termed underflow.

Ground water discharges from the Santa Fe Group aquifer system in several ways: pumpage from wells, seepage into 

the Rio Grande and riverside drains, springs, evapotranspiration, and subsurface outflow to the Socorro Basin. If 

ground-water pumpage from an aquifer exceeds recharge, water levels in the aquifer decline, as has been observed in 

the Middle Rio Grande Basin. These declining water levels can have adverse effects that influence the long-term use 

of the aquifer, including deterioration of water quality, water-well problems, and land subsidence.

Ground-Water Chemistry

A useful approach to characterizing ground-water chemistry in the Middle Rio Grande Basin is to divide the basin into 

13 zones, or regions, of different water-chemistry characteristics. The median concentrations of two constituents 

(chloride and sulfate) exceed the U.S. Environmental Protection Agency (USEPA) secondary standards for drinking 

water in several zones. Arsenic concentrations in ground water exceeded the USEPA primary standard (finalized in 

2001) of 0.010 milligram per liter (mg/L) of arsenic in one zone.

Most of the ground water in the basin is not very susceptible to contamination because the depth to water in most areas 

is greater than 100 feet. Deposits in the inner valley of the Rio Grande, however, are more susceptible to contamination 

because the depth to water is generally less than 30 feet. There are four Superfund sites, three RCRA (Resource 

Conservation and Recovery Act of 1976) sites, and about 700 former and present leaking underground-storage-tank 

sites in the Middle Rio Grande Basin.
4

Ground-Water-Flow Modeling

Several ground-water-flow models of the Middle Rio Grande Basin have been developed. The most recent (2002) is a 

USGS model that incorporates new hydrogeologic data collected since 1995 (McAda and Barroll, 2002). The model 

encompasses the entire thickness of the Santa Fe Group in order to simulate probable flow paths in the lower part of 

the aquifer. Model simulations show that (1) prior to installation of the riverside drains along the Rio Grande, the river 

was losing flow, though currently (2002) the drains intercept much of this flow and divert it back into the river; (2) the 

Rio Grande and riverside drains are so closely related, especially during the nonirrigation season, that they function as 

one system; (3) the hydrologic connection between the Rio Grande and underlying Santa Fe Group aquifer system is 

variable and changes with the lithology of a particular river reach; (4) in much of the Santa Fe Group aquifer system 

throughout the basin, water removed from storage is partially replaced during the nonirrigation season; and (5) mountain-front recharge to the Santa Fe Group aquifer system is less than amounts estimated by previous models.

The McAda and Barroll (2002) ground-water-flow model of the Middle Rio Grande Basin does not make any projections of future conditions, though it could be modified to do so. However, it does provide water-resource managers a 

more accurate and powerful tool than previous models to evaluate the potential effects of management decisions.
5

This report summarizes the current (2002) understanding of water 

resources in the Middle Rio Grande Basin. The basin provides the water 

supply for the City of Albuquerque and other growing communities in the 

basin (with a combined population of about 690,000), as well as water for 

agricultural, industrial, and other uses. The goal of the Middle Rio Grande 

Basin Study is to provide the most complete scientific understanding of the 

hydrologic system in the region as a foundation for water-management 

policy. The goals of this report are to give the reader a better understanding 

of the major components of the hydrologic system and how the components interact, describe some of the scientific contributions of the Middle 

Rio Grande Basin Study, and describe how a ground-water-flow model is 

constructed and how it can be used to aid water-management decisions.

How much water do we have?

The answer to this question depends on our understanding of the 

natural hydrologic system as well as legal constraints on the management 

of water resources in the Middle Rio Grande Basin. Though scientists 

cannot definitively estimate how much available water remains in the 

aquifer system, Chapter 4, “The hydrologic system of the Middle Rio 

Grande Basin” (p. 41), describes the water resources in the basin and 

issues that affect the management of those resources.

How much water do we use?

Water use by municipalities can be quantified with some certainty; 

however, a large number of production wells in the Middle Rio Grande 

Basin are not metered, and irrigation use can only be estimated. The 

“Water use in the basin” section on page 60 describes what is known about 

water use in the basin.

Chapter 1: Common questions about water

resources in the Middle Rio Grande Basin

City of Albuquerque production 

well Leyendecker no. 1.
6

How long will our supplies last?

A definitive estimate of how long water supplies of suitable quality 

and quantity will last in the Middle Rio Grande Basin is not possible. The 

answer depends on future population growth rates and water demand, new 

technologies for producing or recharging water, newly available sources of 

water, and the environmental, economic, and social changes we are willing 

to accept in using ground and surface water. Currently, water is being withdrawn from the aquifer faster than it is being recharged or replaced; thus, 

ground-water levels are declining. Such ground-water use will eventually 

deplete the aquifer because there is a finite volume of water in the aquifer. 

As a result, Albuquerque is currently (2002) planning to use surface water 

to help create a sustainable water supply. Chapter 4, “The hydrologic 

system of the Middle Rio Grande Basin” (p. 41), discusses what is known 

about water supplies in the basin, and the “Effects of ground-water withdrawals” section (p. 85) describes the possible effects of declining water 

levels in the aquifer.

How effective are water conservation 

efforts in the area?

The City of Albuquerque reduced its water use by 23 percent 

between 1995 and 2000, with a stated goal of a total reduction of 

30 percent by 2005 (City of Albuquerque Public Works Department, 

2000). The Middle Rio Grande Conservancy District is currently considering ways to increase irrigation efficiency (Shah, 2001). By reducing 

water use, less ground water is pumped from the aquifer, and more remains 

available for future use. The “Water use in the basin” section on page 60 

describes what is known about water use in the basin.

How rapidly are ground-water levels 

declining?

Ground-water levels are declining in many parts of the Middle 

Rio Grande Basin; the water table has declined more than 160 feet since 

1945 in some areas. The “Ground-water-level declines” section on page 47 

describes what is known about predevelopment and current conditions.

Santa Fe Group sediments 

exposed near Bernalillo. Such 

deposits form some of the most 

productive zones of the aquifer.
7

Is municipal and(or) industrial 

pumping lowering ground-water 

levels outside major metropolitan 

areas?

Currently (2002), the largest ground-water-level declines in the 

Middle Rio Grande Basin are focused around municipal-supply wells. 

Eventually the effects of pumping will propagate outward from the wells 

and cause water-level declines in areas away from pumping centers. The 

“Ground-water-level declines” section beginning on page 47 shows 

ground-water-level maps of the basin during different years.

Have ground-water-level declines 

triggered land subsidence?

Some localized subsidence has occurred in the Albuquerque area, 

though this is probably related to the draining of swampy areas and not to 

ground-water pumping. The “Subsidence” section on page 86 and Box J

on page 88 describe this subsidence, discuss the potential for widespread 

subsidence due to aquifer depletion, and show how scientists are studying 

the issue.

How will water chemistry affect the 

use of ground water?

Several factors potentially can affect water quality (and thus the 

suitability of water for a particular use) in the Middle Rio Grande Basin: 

natural conditions, human-induced contamination, and pumping effects. 

Chapter 6 on page 91 discusses what is known about ground-water chemistry in the basin.

How much water in the basin is 

appropriated?

Under the terms of the Rio Grande Compact, water in the Rio 

Grande is fully appropriated between Colorado, New Mexico, Texas, and 

Mexico. Within the Middle Rio Grande Basin, water rights have not yet 

been adjudicated, though the New Mexico Office of the State Engineer 

considers the surface flows of the Rio Grande to be fully appropriated. The 

“Water appropriation” section on page 69 discusses the appropriation of 

water in the basin.

Rio Grande Conveyance Channel at San 

Marcial and USGS streamflow-gaging 

station. Completed in 1958, the channel 

has helped New Mexico meet its Rio 

Grande Compact obligations.
8

How much water can be pumped 

from the aquifer system using the 

present infrastructure?

This also is a difficult question to answer because much of the 

necessary information is unavailable. Wells have a limited life because of 

corrosion and mechanical deterioration; thus, any well will eventually need 

to be replaced. In addition, declining ground-water levels will necessitate 

the deepening of existing wells or construction of new, deeper wells. 

Water-level declines are dependent on ground-water withdrawals, which in 

turn are affected by population increases, conservation measures, and the 

use of additional sources of municipal water supply. The possible effects of 

declining water levels in the aquifer are discussed in the “Effects of 

ground-water withdrawals” section on page 85. 

How interrelated are the groundwater and surface-water systems?

As knowledge of the hydrology of the Middle Rio Grande Basin 

improves, so has the understanding of how the ground-water and surfacewater systems interact. The current understanding of this interaction and 

the techniques used in the Middle Rio Grande Basin Study are discussed in 

Chapter 5 on page 71, Box H on page 78, and the “What the ground-waterflow model tells us about the hydrologic system of the basin” section on 

page 110.

A USGS technician measures flow in 

the Jemez River below Jemez Dam. 

Such measurements are critical to 

understanding ground-water/surfacewater interaction.
9

Chapter 2: The Middle Rio Grande Basin

Physical characteristics

The Middle Rio Grande Basin covers approximately 3,060 square 

miles in central New Mexico, encompassing parts of Santa Fe, Sandoval, 

Bernalillo, Valencia, Socorro, Torrance, and Cibola Counties (fig. 2.1). In 

this report, “Middle Rio Grande Basin” refers to the geologic basin defined 

by the extent of deposits of Cenozoic age along the Rio Grande from about 

Cochiti Dam to about San Acacia. This basin lies almost entirely within 

the Rio Grande Valley and is equivalent to the Albuquerque Basin of 

Thorn, McAda, and Kernodle (1993) and Kernodle, McAda, and Thorn 

(1995). The extent of the Middle Rio Grande Basin has been defined many 

different ways in different reports; no standard or convention seems to 

apply.

The Middle Rio Grande Basin lies in an asymmetric, elongated 

valley along the Rio Grande. The basin encompasses the inner valley, or 

flood plain, of the Rio Grande and the surrounding terrain that slopes from 

surface-drainage divides toward the river. The eastern boundary of the 

basin is largely mountainous, with merging alluvial fans and stream 

terraces leading downslope to the Rio Grande. The basin surface west of 

the Rio Grande has only isolated mountains and volcanoes and generally 

slopes up to a rolling divide to the Rio Puerco (this surface is known as the 

Llano de Albuquerque). Both active and vegetated sand dunes and dune 

fields are found throughout the basin.

The Rio Grande inner valley is the area adjacent to the Rio Grande 

underlain by alluvium of Quaternary age of the most recent cut-and-fill 

episode of the river. In the basin, the inner valley ranges from approximately 0.5 to 5 miles wide and is incised into older Quaternary alluvium 

and Santa Fe Group sediments. The inner valley corresponds to the flood

plain of the pre-flood-control era (1971).

Elevation in the Middle Rio Grande Basin ranges from about 

4,650 feet above sea level on the Rio Grande at San Acacia to about 

8,000 feet on the flanks of the Manzano and Sandia Mountains. However, 

peaks in the adjacent Jemez, Sandia, and Manzano Mountains are greater 

than 10,000 feet above sea level, with the highest being Redondo Peak in 

the Jemez Mountains at 11,254 feet.

Climate

One of the definitions scientists use to define a desert is “a region 

with a mean annual precipitation of 10 inches or less, and so devoid of 

vegetation as to be incapable of supporting any considerable population” 

(Jackson, 1997). By using this definition, much of the Middle Rio Grande 

Basin may be classified as a desert.

Precipitation generally increases with elevation, and because the 

elevations of the basin and surrounding mountains span nearly 7,000 feet, 

Alluvial fans are the open-fan or coneshaped masses of sediment deposited 

by streams at canyon mouths along a 

mountain front. Terraces are the steplike benches that parallel a stream and 

represent different climatic and geologic 

episodes in the stream’s history. Sand 

dunes are mounds of loose windblown 

sediment ranging in height from inches 

to hundreds of feet. They are heavily 

influenced by climate, and their movement can be slowed or stopped by the 

growth of vegetation on their surfaces 

(Jackson, 1997).

Alluvium is a general term for sediment 

deposited by a stream or other running 

water. Typically, a late Cenozoic age is 

implied (Jackson, 1997).
10

Rio Puerco

Jemez

River

Rio Salado

GRANDE 

RIO 

GRANDE 

RIO 

Cochiti Lake

San

Ysidro

Cochiti

Santo Domingo

San Felipe

Bernalillo

Rio

Rancho

Albuquerque

Isleta

Los Lunas

Belen

Bernardo

San Acacia

McKINLEY

CIBOLA

VALENCIA

SOCORRO

TORRANCE

SANTA FE

BERNALILLO

SANDOVAL

EXPLANATION

Rio Grande inner valley Middle Rio Grande Basin

0 20 40 MILES

0 20 40 KILOMETERS

35 ̊30'

35 ̊45'

35 ̊15'

35 ̊

34 ̊45'

34 ̊30'

107 ̊15' 107 ̊ 106 ̊45' 106 ̊30' 106 ̊15' Sierra Nacimiento

Jemez

Mountains

Manzano Mountains

Manzanita

Mountains

Los Pinos

Mountains

Ladron

Peak

Sierra Lucero

Mesa

Lucero

Española Basin

San

Juan

Basin

Sandia Mountains

Figure 2.1.—Major physiographic features of the Middle Rio Grande Basin.

Era Period Epoch

Age estimates, in 

millions of 

years

Cenozoic Quaternary Holocene Present – 

0.010

Pleistocene 0.010 – 1.6

Tertiary Pliocene 1.6 – 5

Miocene 5 – 24

Oligocene 24 – 38

Eocene 38 – 55

Paleocene 55 – 66

Mesozoic Cretaceous 66 – 138

Jurassic 138 – 205

Triassic 205 – 240

Paleozoic Permian 240 – 290

Pennsylvanian 290 – 330

Mississippian 330 – 360

Devonian 360 – 410

Silurian 410 – 435

Ordovician 435 – 500

Cambrian 500 – 570

Scientists currently understand the Earth to 

be about 4.7 billion years old. To facilitate the 

study of rocks and their features, geologists 

have divided this geologic time into a hierarchical system of units characterized by 

distinct assemblages of rock types and 

fossils. The time prior to most of the fossil 

record is known as the Precambrian era, 

which encompasses the period from 4,700 to 

570 million years before the present (Ma). 

The remaining time until the present is 

divided into three eras: the Paleozoic 

(approximately 570 to approximately 

240 Ma), Mesozoic (approximately 240 to 

66 Ma), and Cenozoic (66 Ma to present) 

(Press and Siever, 1986; Hansen, 1991; 

Jackson, 1997).
11

climate in the basin ranges from arid to humid, though climate over most 

of the basin is semiarid (based on modified Thornwaite climate types by 

Tuan, Everard, and Widdison [1969]). The climate is characterized by 

sunshine and low humidity: Albuquerque receives 77 percent of the 

possible annual sunshine, and its average annual relative humidity at 

5:30 p.m. is 32 percent (Tuan, Everard, and Widdison, 1969).

The National Weather Service has seven weather stations in the 

Middle Rio Grande Basin with at least 10 years of record (table 2.1). The 

Sandia Crest station has also been included as representative of conditions 

in the mountains surrounding the basin. Locations of the weather stations 

are shown in figures 2.2 and 2.3.

Average annual temperatures at weather stations in the basin range 

from 54.0° F at the Corrales station to 56.5° F at the Belen station. At the 

Sandia Crest station, the average annual temperature is 37.6° F. The coldest 

month in the basin is January, with average temperatures ranging from 

33.5° F at the Cochiti Dam station to 35.1° F at the Albuquerque WSFO 

station. The warmest month is July, with average temperatures ranging 

from 74.4° F at the Corrales station to 78.5° F at the Belen station. January 

and July average monthly temperatures are 20.0 and 56.9°F, respectively, 

at the Sandia Crest station. Average monthly temperatures for the seven 

weather stations in the basin and Sandia Crest are shown in figure 2.2 

(National Weather Service, 2002).

Moisture in storms is derived mainly from the Gulf of Mexico 

(Tuan, Everard, and Widdison, 1969). July and August are typically the 

wettest months, though the rainy season may be considered to extend from 

July through October; 45 to 62 percent of annual precipitation falls during 

these 4 months (National Weather Service, 2002). Average annual precipitation ranges from 7.6 inches at Belen to about 23.0 inches at Sandia Crest. 

Average monthly precipitation is shown in figure 2.3. Precipitation in the 

Many different formal climate classification systems have been developed, 

each with its own terminology and 

basis of classification. However, the 

two most commonly used classification systems are Thornwaite climate 

types (based on a ratio of precipitation to evaporation) and Köppen 

climate types (based on temperature 

and precipitation). Various authors 

have modified these two classification 

systems to meet local, more specific 

conditions (Gates, 1972). 

Table 2.1.—National Weather Service weather stations in the Middle Rio Grande Basin and Sandia Crest station 

[National Weather Service (2002). WSFO, Weather Service Field Office; —, still in operation]

Station name Station 

number Latitude Longitude

Elevation 

(feet above 

sea level)

Dates in operation

Starting date Ending date

Albuquerque WSFO 290234 35° 03'N 106° 36'W 5,310 01/01/14 —

Belen 290846 34° 40'N 106° 46'W 4,800 11/01/41 05/31/76

Bernalillo 1 NNE, new 290903 34° 26'N 106° 49'W 5,045 02/01/24 08/31/82

Bernardo 290915 34° 25'N 106° 50'W 4,735 08/01/33 —

Cochiti Dam 291982 35° 38'N 106° 20'W 5,560 02/01/75 —

Corrales 292100 35° 14'N 106° 36'W 5,015 10/06/82 —

Los Lunas 3 SSW 295150 34° 46'N 106° 45'W 4,840 07/01/23 —

Sandia Crest 298015 35° 13'N 106° 27'W 10,680 02/16/53 04/30/79
12

Arroyo Chico

Rio Puerco

Rio Puerco

Jemez River

Arroyo de las

Calabacillas

Salado

Rio

Rio Salado

Jemez Canyon

Reservoir

Tijeras Arroyo

San

Jose 

Rio

Cochiti Lake

Arroyo

Tonque

River Fe

Santa

 Arroyo Abo

Creek

Galisteo

Creek

HellsCanyon Wash

RIO

GRANDE 

RIO 

GRANDE 

Las

tas er Hu

San

Ysidro

Cochiti

Santo

Domingo

San Felipe

Bernalillo

Rio

Rancho

Albuquerque

Isleta

Los Lunas

Belen

Bernardo

San Acacia

McKINLEY

CIBOLA

VALENCIA

SOCORRO

TORRANCE

SANTA FE

BERNALILLO

SANDOVAL

EXPLANATION

Middle Rio Grande Basin Weather stations

Average low temperatures

Average temperatures

Average high temperatures

0 20 40 MILES

0 20 40 KILOMETERS

Albuquerque, 1914–2000

Average annual temperature 56.5°F

0 20 40 60 80 100

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

0 20 40 60 80 100

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

0 20 40 60 80 100

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

0 20 40 60 80 100

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

0 20 40 60 80 100

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

0 20 40 60 80 100

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

0 20 40 60 80 100

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

TEMPERATURE, IN DEGREES

FAHRENHEIT

0 20 40 60 80 100

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

TEMPERATURE, IN DEGREES

FAHRENHEIT

Belen, 1941–76

Average annual temperature 56.5°F

Bernalillo, 1924–82

Average annual temperature 54.6°F

Bernardo, 1933–2000

Average annual temperature 55.7°F

Cochiti Dam, 1975–2000

Average annual temperature 54.2°F

Los Lunas, 1923–2000

Average annual temperature 55.2°F

Sandia Crest, 1953–79

Average annual temperature 37.6°F Corrales, 1982–2000

Average annual temperature 54°F

35°30'

35°15'

35°

34°45'

34°30'

107°15' 107° 106°45' 106°30' 106°15'

Figure 2.2.—Average monthly temperatures for selected National Weather Service stations in and near the Middle Rio 

Grande Basin. 
13

Arroyo Chico

Rio Puerco

Rio Puerco

Jemez River

Arroyo de las

Calabacillas

Salado

Rio

Rio Salado

Jemez Canyon

Reservoir

Tijeras Arroyo

San

Jose 

Rio

Cochiti Lake

Arroyo

Tonque

River Fe

Santa

 Arroyo Abo

Creek

Galisteo

Creek

HellsCanyon Wash

RIO

GRANDE 

RIO 

GRANDE 

Las

tas er Hu

San

Ysidro

Cochiti

Santo

Domingo

San Felipe

Bernalillo

Rio

Rancho

Albuquerque

Isleta

Los Lunas

Belen

Bernardo

San Acacia

McKINLEY

CIBOLA

VALENCIA

SOCORRO

TORRANCE

SANTA FE

BERNALILLO

SANDOVAL

EXPLANATION

Middle Rio Grande Basin Weather stations

0 20 40 MILES

0 20 40 KILOMETERS

Albuquerque, 1914–2000

Average annual precipitation

8.7 inches

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

PRECIPITATION, IN INCHES PRECIPITATION, IN INCHES

Belen, 1941–76

Average annual precipitation

7.6 inches

Bernalillo, 1924–82

Average annual precipitation 8.9 inches

Bernardo, 1933–2000

Average annual precipitation

7.8 inches

Cochiti Dam, 1975–2000

Average annual precipitation

12.7 inches

Los Lunas, 1923–2000

Average annual precipitation

9.2 inches

Sandia Crest, 1953–79

Average annual precipitation

22.9 inches

Corrales, 1982–2000 Average annual precipitation

10.8 inches

35°30'

35°15'

35°

34°45'

34°30'

107°15' 107° 106°45' 106°30' 106°15'

Figure 2.3.—Average monthly precipitation for selected National Weather Service stations in and near the Middle Rio 

Grande Basin.
14

basin comes from local thunderstorms due to orographic or convective 

uplift in the summer months and from frontal storms due to the interaction 

of large masses of air in the winter months (Bullard and Wells, 1992). 

Because thunderstorms can be localized and short lived, precipitation in the 

basin can be extremely variable from year to year and place to place.

Evaporation occurs from open water and moist soil; transpiration 

occurs from plants. Because open bodies of water generally compose a 

fairly small percentage of the area of continental interiors, hydrologists 

usually group the combined water loss from evaporation and transpiration 

into evapotranspiration. Many factors influence evapotranspiration rates, 

including temperature, windspeed, amount of solar radiation, and humidity. 

Annual potential evapotranspiration was estimated by Gabin and Lesperance (1977) to be 41.19 inches at Bernalillo, 47.58 inches at 

Albuquerque, 42.29 inches at Los Lunas, 45.25 inches at Belen, and 

39.97 inches at Bernardo. At all these sites, annual potential evapotranspiration is at least four times greater than annual precipitation.

As documented by tree ring and other data, drought has repeatedly 

occurred in the Southwestern United States at irregular intervals during the 

past several thousand years, though the complex climatic interactions 

responsible for triggering and sustaining drought remain poorly understood 

(National Drought Mitigation Center, 1995). The two most recent major 

droughts in the Southwest were during 1942–56 and 1976–77 (Thomas and 

others, 1963; Matthai, 1979). Though the effects of drought on surfacewater supplies are usually immediate and obvious, effects on ground-water 

supplies may not be. In addition to reducing recharge to ground water, 

drought often forces surface-water users to replace or augment their 

supplies by pumping from wells.

Periodic water-temperature fluctuations in the eastern equatorial 

Pacific Ocean, termed El Niño and La Niña, can influence episodes of 

drought in the Southwestern United States (Conlan and Service, 2000). 

El Niño conditions are characterized by warmer ocean temperatures and 

tend to cause an increase in moisture in the Southwest. La Niña conditions 

are characterized by cooler ocean temperatures and tend to cause drier 

conditions in the Southwest. Research into these phenomena has increased 

since the mid-1970’s; however, understanding remains incomplete, and 

patterns and effects cannot yet be predicted with much certainty. For additional information on the climate of the Middle Rio Grande Basin, the 

reader is referred to Tuan, Everard, and Widdison (1969), Gabin and 

Lesperance (1977), Scurlock (1998), Scurlock and Johnson (2001), and the 

National Weather Service (2002).

Major vegetation types

For the present-day Middle Rio Grande Basin and surrounding 

mountains, Scurlock (1998) defined eight main plant communities, listed in 

a progression from near the Rio Grande to the mountaintops: riparian, 

desert grassland, plains-mesa grassland, scrublands, juniper savanna, 

pinyon-juniper woodlands, ponderosa pine, and subalpine and mixed coniferous forest. Dick-Peddie (1993) further divided the scrubland in the basin 

into three separate plant communities: Great Basin desert scrub, plainsmesa sand scrub, and montane scrub. Martin (1986) used still another 

classification system.

The Rio Grande bosque at Paseo del Norte 

in northern Albuquerque. The tree in the left 

foreground is a Russian olive and the tallest 

trees on the opposite bank are cottonwoods.
15

The riparian woodland (or bosque) is highly prized for recreation 

and is protected as the Rio Grande State Park through much of the Albuquerque area. Today, the bosque consists of native species of cottonwood 

(Populus deltoids ssp. wislizeni) and willow (Salix sp.), as well as introduced exotic species, mainly Russian olive (Elaeaganus angustifolia) and 

tamarisk or salt cedar (Tamarix pentandra and Tamarix chinensis). 

Currently (2002) the bosque covers the flood plain of the river between the 

levees; when the Spanish arrived in the 16th century, however, the flood

plain supported scattered stands of predominantly cottonwood and willow 

(Bogan, 1998; Scurlock, 1998). The construction of flood-control projects 

since 1925 has stabilized the channel of the Rio Grande and eliminated the 

periodic flooding now considered necessary for cottonwood reproduction 

(Finch and others, 1995). Though reduced cottonwood reproduction is an 

issue, the largest factor in the change in composition of the bosque was the 

introduction of the exotic species prior to 1900 (Campbell and DickPeddie, 1964).

The bosque assumed its present character fairly recently, as can 

be seen in the photographs shown in figure 2.4. In the past 60 to 

70 years, the bosque has developed in an area that was formerly semibarren flood plain. A similar change can be seen in two oblique aerial 

photographs in a report by Ground-Water Science, Inc. (1995).

From a water-resources perspective, the bosque is of importance 

because it is composed largely of phreatophytes. Along the Rio Grande, 

the amount of riparian vegetation has increased (Ground-Water Science, 

Inc., 1995); therefore, it is probable that more water is required to maintain 

the dense vegetation of the bosque today than was required for the scattered stands of cottonwood and willow that existed in the past. GroundWater Science, Inc. (1995) estimated that evapotranspiration from riparian 

vegetation and evaporation from open water account for about two-thirds 

of surface-water consumptive use in the basin.

The remaining plant communities in the Middle Rio Grande Basin 

are of less interest from a hydrologic standpoint. Most have been altered 

by human activities such as grazing, fire suppression, and logging, as well 

as natural factors such as climatic variation (Scurlock, 1998). Detailed 

descriptions of these plant communities are in Dick-Peddie (1993) and 

Scurlock (1998).

A

Figure 2.4.—Photographs looking west across the Rio Grande toward the Albuquerque volcanoes. 

Photograph (A) was taken in the early 1930’s (courtesy of the Middle Rio Grande Conservancy District). Photograph (B) was 

taken in 1994 at the same location (courtesy of Gary Daves, City of Albuquerque Public Works Department).

B

Phreatophytes are plants that extend 

their roots to the water table. A phreatophyte acts as a pump by transporting 

ground water (in the Middle Rio Grande 

Basin, the source often is ultimately the 

river) upwards to be transpired from leaf 

surfaces. Tamarisk, willows, Russian 

olive, and cottonwood are all phreatophytes. In the past, phreatophyte-control 

projects were conducted along streams 

such as the Pecos River to enhance 

streamflow (Welder, 1988). The mixed 

success of these efforts, changing 

esthetic values, and threatened and (or) 

endangered-species issues have 

curtailed such efforts.
16

Farming in the Middle Rio Grande Basin is important for several 

reasons. Water use by irrigated agriculture in the basin is several times that 

of urban use, and because irrigated agriculture predates substantial urban 

growth in the basin, most senior water rights are held by irrigators. As part 

of its Middle Rio Grande Basin Water Assessment study, the Bureau of 

Reclamation developed crop-acreage estimates and cropping patterns for 

the basin, by county, from June 1992 aerial photography (Kinkel, 1995). 

These estimates were then compared to New Mexico Office of the State 

Engineer and New Mexico State University estimates. The Bureau of 

Reclamation estimates indicate that nine main crop types were being cultivated in the basin, including pasture. The most abundant crop type was 

alfalfa, composing 42 to 62 percent of the cultivated area in each county. 

The remaining crop types each covered less than 30 percent of the total 

crop area (Kinkel, 1995).

Another irrigated “crop” is turf grass in residential yards, parks, golf 

courses, and other urban land. In 1992, turf grasses in urban areas were the 

second most abundant crop (in terms of planted acreage) in Bernalillo 

County, after alfalfa. In Sandoval, Socorro, and Valencia Counties, 

turf-grass acreage composed a very minor percentage of total irrigated 

acreage (Kinkel, 1995). Nevertheless, Ground-Water Science, Inc. (1995) 

estimated that turf grasses in the Middle Rio Grande Basin transpired about 

12,000 acre-feet of water in 1990.

Human activities and water resources

More than 10,000 years of human settlement along the Rio Grande 

has been documented (Ware, 1984). By the 10th century, primitive irrigation systems had been developed in parts of New Mexico (Bullard and 

Wells, 1992), and by the early to mid-1300’s, most of the “major, historic” 

pueblos in the Rio Grande drainage had been founded (Scurlock, 1998). As 

the pueblos developed the water resources along the Rio Grande, populations began to abandon smaller villages and consolidate into the larger 

pueblos. The habitation of these pueblos was largely dependent on water, 

and they were often abandoned permanently or temporarily during drought 

(Scurlock, 1998).

Spanish settlement in New Mexico began in 1598 with a settlement 

at San Juan Pueblo and spread into the Middle Rio Grande Basin as far 

south as Isleta Pueblo by the 1620’s. Bernalillo was founded in 1700, Albuquerque in 1706, and Tomé (between Los Lunas and Belen) in 1739. The 

Spanish began development of the current irrigation system, patterned after 

the community irrigation ditches (or acequias) of the pueblos (Wozniak, 

1987). This acequia system was a successful means of assuring access to 

irrigation water and replenishing topsoil and nutrients depleted by farming. 

The Spanish continued to develop the irrigation system along the Rio 

Grande throughout the colonial period (Scurlock, 1998). Early settlers dug 

shallow wells in unconsolidated river alluvium for domestic use (Kelly, 

1982).

Most of New Mexico passed into the possession of the United States 

in 1848 with the Treaty of Guadalupe-Hidalgo. In the 1850’s, farms 

increased in number, size, and value in the Middle Rio Grande Basin as a 

result of the increasing number of Anglo farmers who introduced new 

crops, farming techniques, and equipment, including barbed wire and the 

steel plow. The arrival of the Santa Fe Railroad and other rail lines around 

Water-resource managers and scientists 

use the term acre-feet to describe a 

particular volume of water. One acrefoot is the amount of water it takes to 

cover 1 acre 1 foot deep in water. 

Though the term had its origins in 

describing irrigation diversions, it is 

used in referring to any large volume of 

water. One acre-foot is equivalent to 

43,560 cubic feet or about 

325,829 gallons.

Acequia is the Spanish word for 

irrigation ditch. It can also refer to a 

community-owned or maintained 

irrigation system, which is maintained by 

an acequia association.

In 1992, turf grasses in urban areas, such 

as this golf course, were the second most 

abundant crop (in terms of planted 

acreage) in Bernalillo County, after alfalfa.
17

1880 accelerated the influx of Anglo settlers. Albuquerque’s population 

was 1,307 in 1880 (Ground-Water Science, Inc., 1995). Territorial legislation was enacted to protect existing irrigation systems, farms, and irrigation rights; subsequent Federal legislation stimulated irrigation 

development in the region. Irrigated acreage probably peaked sometime in 

the early 1890’s, after which “droughts, sedimentation, aggradation of the 

main channel, salinization, seepage, and waterlogging” caused total 

acreage to decline (Wozniak, 1996). By 1889, the Rio Grande did not flow 

downstream from Albuquerque for 4 months of the year (Wozniak, 1996). 

Increased irrigation diversion of the Rio Grande upstream in the San Luis 

Valley of Colorado was responsible for at least some of these problems 

(Wozniak, 1996). During this period, most of the water for domestic use 

came from hand-dug wells (Scurlock, 1998).

The municipal water-supply system for Albuquerque started as a 

private utility with a few shallow wells around the time the city incorporated in 1885 (Daves, 1994; Ground-Water Science, Inc., 1995). Daves 

stated that the first municipal-supply well for Albuquerque was completed 

in 1875. By 1904, there were several wells more than 200 feet deep (the 

deepest well was 710 feet deep) and one 65-foot-diameter dug well (Lee, 

1907). The public sewage system began discharging untreated effluent into 

the Rio Grande in 1891–92; rudimentary treatment of the effluent began in 

1919 (Ground-Water Science, Inc., 1995).

Prior to the First World War, Albuquerque became a regional trade 

and railway center serving the largely agricultural economy in the Middle 

Rio Grande Basin. By 1910, the city had a population of 11,200 (GroundWater Science, Inc., 1995). Following the First World War, further development of the automobile and the opening of U.S. Route 66 in 1926 reinforced Albuquerque’s status as a regional trade and tourism center (Reeve, 

1961). Bernalillo, Los Lunas, and Belen also experienced growth around 

their railroad depots, though at a slower rate than Albuquerque (GroundWater Science, Inc., 1995).

The Albuquerque area began to grow significantly during the 

Second World War, and postwar growth led to a population increase in 

Albuquerque from about 35,000 to about 200,000 people between 1940 

and 1960 (Reeve, 1961). After an infrastructure redesign in 1948, an 

expanding network of municipal-supply wells supported the water needs 

of this growing population (Ground-Water Science, Inc., 1995), though 

little thought was given to monitoring or characterizing the ground-water 

resources of the basin. In about 1950, several Albuquerque municipalsupply wells were pumped dry, leading one of the major figures in the 

science of hydrogeology, C.V. Theis, to make the rather pointed remark, 

“What happened was that the city got a notice from its bank that its 

account was overdrawn and when it complained that no one could have 

foreseen this, only said in effect that it had no bookkeeping system” 

(Theis, 1953). These and other ground-water-supply problems led to the 

first efforts to understand the hydrogeology of the Middle Rio Grande 

Basin. Nevertheless, most people in the basin continued to believe that the 

aquifer beneath Albuquerque contained a volume of freshwater equivalent 

to one of the Great Lakes (Niemi and McGuckin, 1997).

Scientific studies completed in the early 1990’s (such as Hawley 

and Haase, 1992; Thorn, McAda, and Kernodle, 1993; and Kernodle, 

McAda, and Thorn, 1995) provided a much more comprehensive understanding of the ground-water system of the Middle Rio Grande Basin and 

showed conclusively that Albuquerque was withdrawing water from the 

aquifer faster than the water was being replenished (City of Albuquerque 

Name a great American city on a 

large body of water: 

Albuquerque.

Each year the Rio Grande Basin, an 

underground lake larger than Lake 

Superior, yields over 30 billion gallons to 

the City’s wells serving 109,000 residential and commercial Albuquerque 

customers. At the projected rate of 

growth, the City’s present water rights 

holdings will allow Albuquerque to tap 

this vast underground lake well into the 

twenty-first century.

—Paid advertisement, Albuquerque 

Living magazine, October 1984.

The Albuquerque skyline from the west.

(Courtesy of R.A. Durall, USGS.)
18

Public Works Department, 1997b). This led the City of Albuquerque to 

revise its water-use strategy and actively encourage water-use conservation 

and move toward the direct use of native Rio Grande water and San JuanChama Project water diverted into the Rio Grande upstream from the city 

(Brown and others, 1996; City of Albuquerque Public Works Department, 

1997b; Niemi and McGuckin, 1997). (The San Juan-Chama Project is 

discussed on page 67.) 

In 2000, the population of the Middle Rio Grande Basin was about 

690,000 or about 38 percent of the population of New Mexico. The steady 

population increase in New Mexico, Albuquerque, and the Middle Rio 

Grande Basin since 1900 is listed in table 2.2. Other than the growth of 

Albuquerque as a percentage of the population of New Mexico, the most 

interesting aspect of these data is the decrease in 2000 of Albuquerque’s 

population as a percentage of the population in the Middle Rio Grande 

Basin.

The population increase in the Middle Rio Grande Basin has led to 

the urbanization of irrigated agricultural land in the inner valley of the Rio 

Grande, as well as an increase in population in other communities in the 

basin including Rio Rancho, Los Lunas, Belen, Corrales, and Bernalillo. 

Currently (2002), residential development in response to economic growth 

in the Middle Rio Grande Basin is occurring primarily west and northwest 

of Albuquerque, in and east of the Los Lunas-Belen area, and outside the 

basin in the east mountain area (east of the Sandia, Manzanita, and 

Manzano Mountains). Secondary residential development is occurring on 

the north and south margins of Albuquerque, as well as on plots of vacant 

land within the Albuquerque city limits. A land-use and land-cover map of 

the Middle Rio Grande Basin in the early 1980’s is shown in figure 2.5.

Table 2.2.—Population in New Mexico, Albuquerque, and the Middle Rio Grande Basin, 1900–2000

[Data from Thorn, McAda, and Kernodle, 1993; Ground-Water Science, Inc., 1995; Famighetti, 1997; U.S. Census Bureau, 2001a, 2001b; 

--, no data]

Year

Population Percentage of population

New 

Mexico Albuquerque Middle Rio Grande Basin

Middle Rio 

Grande Basin/ 

New Mexico

Albuquerque/ 

Middle Rio 

Grande Basin

Albuquerque/

New Mexico

1900 195,310 6,238 -- -- -- 3.2

1910 327,301 11,200 -- -- -- 3.4

1920 360,350 15,160 -- -- -- 4.2

1930 423,317 26,570 -- -- -- 6.3

1940 531,818 35,400 -- -- -- 6.7

1950 681,187 96,800 -- -- -- 14

1960 951,023 201,200 -- -- -- 21

1970 1,017,055 244,500 314,900 31 78 24

1980 1,303,302 332,900 419,000 32 80 26

1990 1,515,069 384,600 563,600 37 68 25

2000 1,819,046 448,600 690,000 38 65 25
19

Arroyo

Chico

Rio Puerco Rio Puerco

Jemez River

Arroyo de las Calabacillas

Salado Rio

Rio Salado

Jemez Canyon

Reservoir

Tijeras Arroyo

San Jose 

Rio

Cochiti Lake Arroyo Tonque

River Fe

Santa

 Arroyo Abo

Creek

Galisteo

Creek

HellsCanyon Wash RIO

GRANDE RIO 

GRANDE Las

tas er Hu

San

Ysidro

San

Ysidro

Cochiti

Santo

Domingo

San Felipe

Bernalillo

Rio

Rancho

Albuquerque

Isleta

Los Lunas

Belen

San Acacia

Bernardo

McKINLEY

CIBOLA

VALENCIA

SOCORRO

TORRANCE

SANTA FE

BERNALILLO

SANDOVAL

McKINLEY

CIBOLA

VALENCIA

SOCORRO

TORRANCE

SANTA FE

BERNALILLO

SANDOVAL

EXPLANATION

Rangeland

Forest

Urban

Barren

Agricultural

Middle Rio Grande

 Basin boundary

Source U.S. Geological Survey (1983)

0 20 40 MILES

0 20 40 KILOMETERS

Sandia Mountains Manzano Mountains

Manzanita

Mountains

Sierra

Nacimiento

Jemez

Mountains Manzano Mountains

Manzanita

Mountains

Los Pinos Mountains

Ladron

Peak

Sierra Lucero

Mesa

Lucero

Española

Bas

i

n

San

Juan

Basin

Sandia Mountains

35

o

30'

35

o

15'

35

o

34

o

45'

34

o

30'

107

o

15' 107

o 106

o

45' 106

o

30' 106

o

15'

Figure 2.5.—Generalized land use and land cover in the Middle Rio Grande Basin in 

the early 1980’s. This is currently (2002) the most recent land-use and land-cover 

map of the entire basin.
20

The landscape changes that result from 

the growth of metropolitan areas are one 

subject of the USGS Land Cover Characterization Program. By using historical 

maps, aerial photography, and satellite 

imagery, scientists construct databases 

showing how urban land use has changed 

over several decades. These databases are 

then used to analyze how urbanization has 

affected the landscape as well as to model 

urban growth and land-use change to 

project future growth patterns and 

changes under different scenarios 

(U.S. Geological Survey, 1999).

The extent and characteristics of an urban 

area and its infrastructure are the result of 

differing social, economic, and environmental conditions. Understanding the 

factors that have contributed to shaping an 

urban area is essential for gaining an 

insight into the processes that will influence its growth and change in the future. 

Such an understanding can then be used 

to construct computer simulations 

(models) for projecting urban-landscape 

change in the future.

In the Albuquerque area, human-induced 

land changes were characterized by 

mapping the shape and extent of Albuquerque’s urban area as it evolved over 

time (table A.1 and figs. A.1 and A.2). 

Although Albuquerque has grown both on 

vacant land within developed areas (infill 

development) and on the fringes of developed areas (new development), the 

long-term trend was greater dispersed 

development, leading to an increase in the 

size of the urban area (urban expansion). 

Landscape change modeling

David J. Hester1 and Mark R. Feller1

A

1

U.S. Geological Survey, Denver, Colorado.

Table A.1.—Urban growth in Albuquerque, 1935–2050. Projections for 

2050 are based on SLEUTH model output

[--, not applicable]

Year Urban area

(acres)

Percent growth

Cumulative, 

since 1935

Since previous 

period

1935 4,372.2 -- --

1951 15,397.9 252 252

1973 49,746.1 1,038 223

1991 84,889.3 1,842 71

2050 124,608.5 2,750 47

50-YEAR

MODEL

PROJECTION

Conversion rate of nonurban to urban land,

annual percentage rate of change

EXPLANATION

Persons per acre of urban land

Acres of urban land per capita

0

2

4

6

8

10

12

14

0

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

1920 1940 1950 1960 1970 1980 1990 2000 2010 2020 2030 2040 2050 1930

PERSONS PER ACRE OF URBAN LAND,

CONVERSION RATE OF NONURBAN

TO URBAN LAND, IN ACRES PER YEAR

URBAN LAND PER CAPITA, IN ACRES

Figure A.1.—Changes in urban characteristics for Albuquerque, 

1935–2050. Projections for 2050 are based on University of New Mexico 

Bureau of Business and Economic Research population estimates.
21

B

C

A

Figure A.2.—Urban area in the vicinity of 

Albuquerque in (A) 1935, (B) 1991, and 

(C) 2050 projected using the SLEUTH model.

Assuming that redevelopment (the transition of an existing or prior land 

use into another land use category) did not contribute to the total urban 

area, the amount of urban land in the Albuquerque area per person (shown 

as acres of land per capita in fig. A.1) approximately doubled from 1940 to 

1990.

As part of the Middle Rio Grande Basin Study, the USGS modeled the 

Albuquerque area using the Slope, Land Use, Exclusions, Urban, Transportation, and Hillshade (SLEUTH) urban-growth model developed by the 

University of California-Santa Barbara (U.S. Geological Survey, U.S. 

Environmental Protection Agency, and University of California-Santa 

Barbara, 2001). The SLEUTH model is used to estimate the probability of 

an area becoming urbanized by using a database of contemporary landsurface characteristics (such as the current extent of urban lands, landsurface slopes likely to develop, lands excluded from development, and 

probable effects of the existing road network on future land-use patterns). 

For the Albuquerque area, simulations projected the urbanized area extent 

in 2050. This 50-year projection was chosen to correspond with the 

FOCUS 2050 Regional Plan of the Middle Rio Grande Council of Governments (Middle Rio Grande Council of Governments, 2000).

Because conditions in 1935 and 1991 are known (fig. A.2, A and B), model 

runs simulating the period 1935–91 were used to adjust model parameters 

in order to match the known conditions in 1991 (model calibration). Once a 

composite score indicated the “best” combination of variables, a projection 

between 1991 and 2050 was run. The resulting projection is shown in 

figure A.2, C. If the trend of dispersed development in the Albuquerque 

area continues until 2050, approximately 125,000 acres of the Middle Rio 

Grande Basin landscape will be urbanized, with a resulting population 

density of 11.8 persons per urban acre (fig. A.1).

The goal of landscape-change modeling is to provide accurate scientific 

information such as basic data (such as historical and contemporary 

landscape characteristics), projections (such as the 2050 simulated urban 

landscape that was forecast using SLEUTH), and perspectives (such as 

“land-surface characterization” analyses calculated from historical, 

contemporary, and future landscapes that can be used to analyze urbanization trends, rates, patterns, and densities) to help managers form sound 

policies for guiding sustainable growth. Because the Albuquerque area is 

surrounded by numerous boundaries with Federal and pueblo lands and 

because the availability of water may ultimately be limited, decisions on 

growth can only be improved by realistic projections of growth patterns 

and changes based on scientific methods.
22
23

The Santa Fe Group aquifer system, which supplies the groundwater resources for the Albuquerque metropolitan area and surrounding 

communities within the Middle Rio Grande Basin, is composed chiefly of 

sand and silt with lesser amounts of clay and gravel. Most of the sediment 

was transported into subsiding fault-bounded basins of the Rio Grande Rift 

by ancient streams and rivers that drained the surrounding regions. Additional deposition was a result of windblown sediment (eolian deposits), 

intermittent streams, and downslope creep from mountain uplifts. Because 

these geologic processes have been active in the Middle Rio Grande Basin 

for millions of years, the Santa Fe Group locally is thousands of feet thick. 

The varied processes and the available sediment combine to form a 

complex, three-dimensional framework of truncated and overlapping sedimentary units of contrasting hydrologic properties. (See Box B.)

The Rio Grande Rift

The geologic processes at work in this part of New Mexico have 

guided and controlled formation of the Santa Fe Group aquifer system. 

More than 25 million years ago, tectonic forces operating on the western 

North American continent began to pull apart the brittle upper crust, and 

the continent began to spread and extend toward the Pacific Ocean basin 

(Chapin and Cather, 1994; Pazzaglia and others, 1999). In New Mexico 

and Colorado, these forces created a more-or-less continuous north-south 

structural zone called the Rio Grande Rift (fig. 3.1). This rift formed in 

northern Mexico and southern New Mexico and slowly continued to split 

and extend toward the north as the Colorado Plateau block on the west 

separated from the North American continental interior block on the east. 

Since its inception, the floor of the rift has subsided, sporadically and 

unevenly, to local depths greater than 14,000 feet as the continental crust 

east and west of the rift continues to slowly pull apart (Grauch, Gillespie, 

and Keller, 1999).

The Rio Grande Rift is a zone of faults and sediment-filled basins 

extending along its length. Some faults appear to follow ancient lines of 

weakness in the brittle crust that are related to older geologic events, but 

many of the faults cut through older rock along new, crosscutting traces. 

These faults caused pieces of the brittle crust to pull apart and slide past 

each other; blocks on the inside of the rift zone generally dropped down 

under the influence of gravity relative to (uplifted) blocks on the outside 

edges of the rift. In this way, the rift has created a series of valleys along its 

length that have influenced the flow of streams and sediment deposition. 

Faulting, uplift, volcanic activity, subsidence, and deposition rates have 

varied through time in the rift. Nonetheless, the overall geologic processes 

have remained fairly constant. Geologic and geophysical data show that 

the rift consists of numerous discrete structural basins that mark the locations where faulting and subsidence rates and displacements have been 

greatest overall (see Box C). 

Chapter 3: Geology of the Santa Fe Group

aquifer system

An aquifer is defined as “a rock unit 

that will yield water in a usable quantity 

to a well or spring” (Heath, 1983). An 

aquifer system is two or more aquifers 

that are separated (at least locally) by 

impermeable rock units but function 

together as an aquifer with regional 

extent. The impermeable or lowpermeability rock units that bound 

aquifers are confining beds.

A rift is an elongated valley in the 

Earth’s crust that forms in response to 

the crust extending or spreading apart. 

The Rio Grande Rift forms one of the 

great rift valleys of the world, on a scale 

similar to the East African rift and the 

Lake Baikal rift in Russia.

Rock units may be classified and 

mapped on the basis of many different 

criteria including lithology, magnetic 

polarity, age, and depositional environment. The most common method is to 

classify rock strata of about the same 

age and similar physical characteristics 

into formations. Formations may be 

subdivided into members and beds or 

aggregated into groups. By convention, 

the formal name of the unit is a 

geographic feature near the type exposures (or outcrops) of the rock unit. 

Geologic maps typically portray the 

surface extent and structure of such 

stratigraphic units. However, young 

unconsolidated deposits are generally 

mapped and classified primarily by 

depositional environment and material 

properties.
24

The interplay of faulting and sedimentation within the Rio Grande Rift has 

controlled major aspects of aquifer geometry. Basin-fill sediment thickens substantially toward the center of the basin. 

Outcrop and drill-hole studies show that 

basin-fill sediments thicken abruptly 

across major faults, indicating that faults 

were active while sediment was accumulating (fig. B.1). Rising fault blocks were 

eroded, and the detritus was deposited on 

the sinking fault blocks in a process that 

recycled older sediment within the rift or 

stripped material off the rift-flank mountain ranges. The rising and falling fault 

blocks also shifted the internal stream 

drainage in the subbasins and caused 

various depositional environments (such 

as river channel, overbank flood plain, 

alluvial fan, and pediment) to migrate 

laterally over time (Cather and others, 

1994; Stone, 2001). In this dynamic 

setting, the types of sediment that accumulated across the rift basins were highly 

varied, and the location of their deposition 

changed as the basin filled. Erosion on the 

uplifted blocks created breaks in the sedimentary record that make it difficult to 

correlate sequences of strata from one 

location to another. 

The Middle Rio Grande Basin consists of 

three discrete subbasins distinctly separated by zones where the rocks underlying 

the basin-fill sediment (basement rocks) 

are high (fig. 3.2). Each subbasin has a 

unique structural and depositional history. 

Drainage was internal to each subbasin 

during the early history of the rift valley, 

as indicated by the type of sediment 

Structural, sedimentologic, and climate effects on the Middle 

Rio Grande Basin aquifer system

James C. Cole1 and Byron D. Stone2

1U.S. Geological Survey, Denver, 

Colorado.

2

U.S. Geological Survey, Storrs, 

Connecticut.

EXPLANATION

Fault; bar and ball

 on downthrown side

Production well,

 well-field name,

Monitoring well Line of section Don

1 98th

Street A A'

0 1 2 3 MILES

0 1 2 3 KILOMETERS

Modified from Allen and others (1998);

Stone and others (1998)

106 ̊45' 106 ̊40' 106 ̊35'

35 ̊10'

35 ̊05'

Land

surfaceINCREASING DEPTH

A 98th Street well

West Mesa no. 1 well

College no. 1 well

College no. 2 well

A'

A A'

SAN MATEO BLVD

4TH ST

COORS BLVD

Rio Grande

Inner

valley

Don

98th

Street

West

Mesa

College

CENTRAL AVE

COORS BLVD

Leavitt

1

2

3 4

1

2

1 2

1

2 3

Albuquerque

volcanic

field

Llano de

Albuquerque

Approximately

740 feet thick

Approximately

380 feet thick

? Atrisco beds

Atrisco beds

A

B

25

40

Map

area

Figure B.1.—Generalized section showing substantial thickening of the 

Atrisco silt- and clay-rich beds in the downthrown fault block east of the 

98th Street well location (A) and index map (B). All wells except the 

98th Street well are projected to the line of section, parallel to the northwesttrending fault trace.

B

 and well number
25

deposited; thus, no continuous hydrostratigraphic deposit in the deeper 

parts of the Santa Fe Group aquifer system extends across all three 

subbasins.

The youngest sediments that were deposited during roughly the last 5 

million years can be traced across the buried basement highs and the deep 

subbasin centers. These deposits differ from the older rift-fill deposits in 

ways that reflect significant changes in rift history and climate. First, these 

younger deposits are thinner (for a specific interval of time), indicating 

that the rates of subsidence began decreasing at least 5 million years ago. 

Second, the younger deposits are more tabular in form across all three 

subbasins and show less variation in thickness across faults, indicating that 

faulting was less active during deposition. Some subhorizontal younger 

sedimentary layers were deposited above erosion surfaces on top of 

inclined older deposits, consistent with a decline in the rate of tilting. 

Third, the younger deposits are only more than a few hundred feet thick 

along the central axis of the subbasins (Hawley, Haase, and Lozinsky, 

1995; Connell, Allen, and Hawley, 1998), showing that active faulting and 

subsidence occurred in a much narrower part of the rift than earlier in the 

rift's history. These younger deposits show that the supply of sediment was 

greater than subsidence; thus, stream deposition was able to fill the separate subbasins to form a connected, broad basin (Cather and others, 1994; 

Chapin and Cather, 1994; Pazzaglia and others, 1999).

The youngest sedimentary deposits also consist of coarser grained materials than most of the earlier rift-fill deposits. Coarse sand and pebble to 

cobble gravel are common in the younger 

deposits, indicating that streams transporting these materials had greater 

discharge and flowed at greater velocities. 

The change from fine- to coarse-grained 

sediment is evident on a regional scale 

and is consistent with regional and world 

evidence that rainfall and runoff increased 

substantially beginning about 5 million 

years ago (Krantz, 1991; Thompson, 

1991). These younger deposits locally are 

productive zones of the aquifer in the 

Middle Rio Grande Basin, but they 

compose only a small percentage of the 

rift-fill deposits and are not laterally 

extensive. These deposits are currently 

being eroded in the Rio Grande drainage.

Rift faults remain active today and 

continue to influence sedimentation. 

Outcrops along the western and northern 

basin margins show sequences of alluvial 

and windblown sediment that are thickest 

on top of the tilted, downdropped blocks 

of faults (Koning, Pederson, and Pazzaglia, 1998; Connell, Koning, and Cather, 

1999). The sediment accumulated next to 

the fault scarp and developed a calcareous 

soil as the surface stabilized. Subsequent 

faulting buried the calcareous soil beneath 

another layer of sand and silt, which then 

developed its own calcareous soil zone 

(Wright, 1946; Machette, 1978; Stone, 

2001). More than 10 buried soil zones are 

preserved in some locations (Wright, 

1946), which indicate repeated offsets 

across young rift faults (Personius, 

Machette, and Kelson, 1999).

Windblown silt

Calcareous soil

Figure B.2.—Oblique aerial photograph of outcrops in the upper Santa 

Fe Group sediment adjacent to the Zia fault in the northern Calabacillas 

subbasin. The prominent whitish zone is a buried calcareous soil that 

was buried by yellowish, windblown silt deposited following downdropping on the Zia fault. (Courtesy of J.C. Cole.)
26

Subsurface geologic information about an aquifer is 

obtained primarily from wells. Studies of sites 

where the aquifer crops out on the surface provide 

some geologic information, but such outcrops are 

often unsaturated and of limited extent. Consequently, geologic and hydrogeologic data used to 

characterize aquifers at depth are routinely obtained 

from petroleum exploration and water wells. Such 

subsurface data are typically obtained during the 

drilling and construction of wells and include (1) 

characteristics of rock cuttings removed by the drill 

bit and used to reconstruct the general sequence and 

composition of the rocks in the subsurface 

(lithology); (2) drillers’ notes of drilling conditions, 

including drilling rate; (3) measurements of the 

physical properties of the rock and fluids using 

borehole geophysical logging tools; (4) hydraulic 

conductivity as estimated from hydraulic tests; and 

(5) ground-water chemistry. Abundant geophysicallog data and lithologic descriptions have been 

obtained for wells in the Albuquerque-Rio Rancho 

metropolitan area and have been used to interpret 

hydrogeologic conditions of the Santa Fe Group 

aquifer system in the Middle Rio Grande Basin 

(Connell, Allen, and Hawley, 1998).

C

How well information is used to understand the 

hydrogeology of the basin

Sean D. Connell1 and David A. Sawyer2

Figure C.1.—Hypothetical responses of various borehole geophysical tools to alluvial deposits of contrasting 

texture and saturation and to volcanic rock units.

1

New Mexico Bureau of Geology and 

Mineral Resources, Albuquerque, New Mexico.

2

U.S. Geological Survey, Denver, Colorado.

Electrical

resistivity

(ohm-meters)

Electrical

conductivity

(millisiemens

per meter)

Lithology Natural

gamma

(American

Petroleum

Institute

units)

Borehole

caliper

(inches)

64-inch

resistivity

16-inch

resistivity

Well

casing

Water

table

Caving of

material

from

borehole

walls and 

fractures

Modified from Keyes (1989)

Sand

Gravel

Clay and silt

Basalt

Volcanic ash

Saturated zone

EXPLANATION

A USGS hydrologist using 

geophysical-logging equipment at 

the Del Sol Divider monitoring well. 
27

Modified from Allen and others (1998); Stone and others (1998)

EXPLANATION

Correlation line Fault, showing relative movement 

5,000

5,200

4,600

4,800

4,200

4,400

3,800

4,000

3,600

1,600

1,400

1,500

1,200

1,300

1,100

ELECTRICAL CONDUCTIVITY, IN MILLISIEMENS PER METER

ELEVATION ABOVE SEA LEVEL, IN METERS

ELEVATION ABOVE SEA LEVEL, IN FEET

Leavitt

no. 3

West Mesa

no. 4

Don

no. 2

98th St.

well

College

no. 1

400 0 400 400 0 400 0 400 0 0

The most common drilling method is mud rotary, which uses a thick drilling fluid to 

carry rock fragments to the surface after they are broken from the bottom of the 

hole by a spinning drill bit. Examination of these cuttings provides information 

about the mineralogy and general grain size of the deposit; however, fine-grained 

cuttings (clay, silt, and fine sand) often are suspended by the drilling fluid and are 

washed out of the sample, which tends to bias cutting descriptions toward the 

coarser fragments (medium- to coarse-grained sand and gravel). Borehole-geophysical logs measure the physical properties of the rock surrounding the well and provide essential qualitative and quantitative information about aquifers that cuttings 

cannot provide. Geophysical logs provide critical data on the fine-grained materials 

as well as information about features that affect ground-water movement. The most 

common geophysical logs in the Albuquerque area are of electromagnetic properties, natural gamma radioactivity, and borehole diameter (caliper).

Two types of geophysical logs that are measures of the response of fluid in the rock 

surrounding the borehole to an induced electromagnetic field are electrical (or resistivity) and induction logs. In freshwater aquifers, these logs are good indicators of 

the percentage of clay minerals in the deposit because moist clays conduct electricity much better than freshwater alone (Kwader, 1985). Thus, sand and gravel units 

are poor conductors of electric current because they contain few clays, and clay- or 

silt-rich units tend to be better conductors (fig. C.1). 

The most common radioactivity log measures natural gamma-ray production in the 

rock surrounding the borehole and is used 

to determine rock type. The log measures 

the natural radioactive decay of potassium, uranium, and thorium in feldspar, 

mica, and clay minerals. The amount of 

decay correlates with clay-mineral content because clays are generally rich in 

potassium, resulting in higher measurements (fig. C.1). In the Santa Fe Group, 

gamma-ray logs also respond to deposits 

of volcanic origin and ash beds that contain potassium, uranium, and thorium. 

Therefore, using only the gamma-ray log, 

these volcanic deposits can be misinterpreted as clay-rich beds; such mistakes 

can be avoided by using other geophysical 

logs or by evaluating the cuttings description. Another type of radioactivity log 

measures the response of the rock to a 

source of neutrons and is used to determine bulk density and porosity, 

Caliper logs show the shape and size of 

the borehole and delineate zones of loose 

and caving rock or sediment caused by 

weak cementation (such as unconsolidated gravel and sand) or breakage by 

faults (fig. C.1). Caliper logs are also used 

to correct and interpret other log data for 

variations in the distance between the 

borehole sensor and the surrounding rock.

Evaluation of geologic and hydrogeologic 

information for wells involves a systematic approach that uses all available lithologic, geophysical, and geochemical 

information for a given borehole or well 

field (Keyes, 1989). With multiple wells, 

distinctive geophysical features can be 

identified and correlated areally. An 

example in the Santa Fe Group aquifer 

system is a prominent clay-rich interval in 

western Albuquerque identified by a 

sharp change in electrical conductivity. 

The base of this unit was correlated for 

several miles between different well fields 

(fig. C.2) (Hawley and Haase, 1992; Allen 

and others, 1998). Such correlations aid in 

understanding the hydrogeology of the 

Santa Fe Group aquifer system (Connell, 

Allen, and Hawley, 1998).

Figure C.2.—Correlation of electrical-conductivity logs among 

Albuquerque well fields west of the Rio Grande. The dashed line indicates a 

rather abrupt boundary between overlying, fine-grained clayey sand and sand 

(high electrical conductivity) and underlying, medium-grained sand (lower 

electrical conductivity). Variations in the elevation of this boundary are interpreted to reflect tilted bedding and faults, especially between the 98th Street 

well and the College no. 1 well. See figure B.1A for a location map of the 

wells. The order of presentation is from well to well, not strictly south to north.
28

The Middle Rio Grande Basin consists of three discrete subbasins, 

separated by northwest-trending structural benches (fig. 3.2). Each 

subbasin contains more than 14,000 feet of rift-fill deposits in its deepest 

part, but structural benches and upthrown blocks separate these three 

subbasins where the sediment is as thin as 3,000 feet (Stone, 2001). 

Detailed geologic mapping and geophysical logs and cores obtained from 

petroleum-exploration wells show that the stratigraphic record for the 

lower and middle parts of each subbasin is distinct (Cole and others, 1999), 

indicating that the drainage system for each subbasin evolved differently in 

response to its unique structural history. Abundant fine-grained sediment 

and local lakebed deposits indicate that each subbasin drained internally 

during the early history of the Rio Grande Rift. Consequently, no major 

hydrostratigraphic unit extends across all three subbasins in the deeper 

parts of the aquifer system.

EXPLANATION

Rift basin

0 100 200 300 MILES

0 400 KILOMETERS 100 200 300

38°

37°

36°

35°

34°

33°

32°

31°

109° 108° 107° 106° 105° 104° 103° 102° 101° UTAH COLORADO KANSAS COLORADO

COLORADO

NEW MEXICO OKLAHOMA

NEW MEXICO

TEXAS

ARIZONA

NEW MEXICO

NEW MEXICO

TEXAS

UNITED STATES

MEXICO

Middle Rio 

Grande Basin

Rift

Grande

Rio

Elephant Butte Reservoir

Heron Reservoir El Vado Reservoir

Abiquiu Reservoir

Cochiti Lake

Elephant Butte

streamflowgaging station

Otowi streamflowgaging station

Elephant Butte Dam

Caballo Reservoir

Rio Grande

Rio Grande

Las Cruces

El Paso

Socorro

Albuquerque

Santa Fe

Santa Fe River

Figure 3.1.—Location of the Middle Rio Grande Basin and the Rio Grande Rift.

Lithology is the term used by Earth 

scientists to describe the physical and 

mineralogical characteristics of a rock 

(Jackson, 1997). Common lithologic 

names may denote a specific type of 

rock, for example, sandstone, basalt, or 

granite, or may denote the general 

mode of rock formation, for example, 

sedimentary, volcanic, or intrusive. 

Strata are layers or beds of sedimentary 

rock (Jackson, 1997).
29

Rift processes also have influenced the types of sediment transported into the Rio Grande Rift basins. The faulting and mountain uplift 

that have occurred along the rift have changed the topography and slope, 

and these changes have influenced the ability of streams to carry sediment 

toward the valleys. Rift-margin uplifts expose additional rock material to 

weathering and erosion and increase the supply of sediment to be transported by streams, wind, and gravity-driven processes. Changes in topography also have caused changes in local climate (especially precipitation) 

that affect weathering, streamflow, and sediment transport. The Rio 

Grande Rift has experienced widespread and diverse volcanic activity 

through time, and molten material has exploited weaknesses in the riftfaulted crust to rise from depth and erupt at the surface. Volcanic processes 

have provided new source areas for sediment, produced landforms that 

alter topography and drainage, and affected climate and vegetation patterns 

in the region of the Middle Rio Grande Basin.

The rift has altered river processes in the Middle Rio Grande Basin 

and has affected deposition (see Box B). Rivers in more geologically stable 

settings typically are in equilibrium and neither erode nor deposit much 

sediment but simply transport it through the basin. Faulting and subsidence 

in the Rio Grande Rift, however, have repeatedly produced sags and swales 

where the river has deposited sediment to maintain its gradient.

Geologic processes that shaped the 

aquifer system

The dynamic setting of the Rio Grande Rift has produced a complex 

geologic framework for ground water. The river and stream networks that 

deposited most of the sediment shifted across the landscape through time 

in response to tectonic uplift and subsidence and to climate change. The 

sediments deposited by running water typically are quite variable because 

of the very different depositional settings that form side by side (for 

example, main or axial channels, natural levees, and flood plains). Such 

sedimentary deposits commonly interfinger in complicated three-dimensional patterns, rather than form continuous tabular beds (fig. 3.3). In addition, faults that have been displaced after these sediments were buried have 

also offset the deposits (fig. B.1A). Chemical alteration, compaction, fracturing, and cementation over time have affected the hydrologic character 

of the sedimentary deposits in the Middle Rio Grande Basin to varying 

degrees.

The type of deposit and the distribution of sediment depend on the 

transport medium (water, wind, gravity, or ice), the energy of the transportation process, and the depositional environment. Depositional environments that have existed in the rift during deposition of the Santa Fe Group 

aquifer system are principally of five types: fluvial (sediment deposited by 

rivers and streams), alluvial-colluvial (sediment deposited on slopes and 

along mountain fronts), eolian (wind-transported sediment deposited in 

dunes), lacustrine (sediment deposited in lakes), and volcanic (molten rock 

erupted from vents in the form of lava flows or volcanic ash). Fluvial 

deposits are highly variable because the grain size and mixture of the sediment depend on the velocity and turbulence of the streamflow and on the 

amount of erosion and redeposition before burial and preservation. MainIndistinct subbasin boundary

Subbasin generally outlined

by –12-milligal line

of equal gravity anomaly

EXPLANATION

Rio Grande

Rio Puerco

0 30 MILES

0 30 KILOMETERSHubbell bench

Laguna

 bench

Ziana

anticline

Middle

Rio Grande Basin Santo Domingo

subbasin

Belen

subbasin

Calabacillas

subbasin

Modified from Grauch, Gillespie, and Keller (1999)

Figure 3.2.—Simplified structural features of 

the Middle Rio Grande Basin. Features are 

defined on the basis of gravity surveys, structural models of other authors, and geologic 

mapping. 

Faults mark parts of the Earth’s crust 

that have broken and where the two 

sides have slid past each other across 

the break (Jackson, 1997). This relative 

motion can be vertical, horizontal, or a 

combination. Not all faults are exposed 

at the land surface, either because 

younger deposits overlie the faults or 

because the break at depth did not 

propagate to the surface through the 

intervening rock. The gaping fault cracks 

depicted in popular movies are rare and 

are called fissures if they remain open 

(Jackson, 1997).
30

channel deposits tend to be coarser grained because the fine-grained sediment is carried away by the current, whereas overbank flood deposits on 

the margins of a river valley typically contain more silt and clay because of 

reduced current velocity. Alluvial-colluvial deposits that form near mountain fronts are composed of sediment ranging in size from boulders to sand 

and silt. In eolian deposits, the sediment grains typically are uniform in size 

and well rounded, and pore spaces are well connected. Lacustrine deposits 

consist of very fine grained sand, silt, and clay, and often, evaporitic salts. 

Volcanic rocks have highly variable hydraulic properties depending on the 

kind of deposit and the extent of alteration following deposition (such as 

fracturing). 

Ground water moves through the pore spaces between the grains and 

through fractures in the deposit. Unconsolidated deposits consisting primarily of medium- to coarse-grained sand or gravel have interconnected 

larger pore spaces that allow water to move freely in the deposit and, thus, 

make highly productive aquifers. Deposits containing a mixture of grain 

sizes (fine to coarse) have less pore space because finer grains fill the pore 

spaces between larger grains, thus reducing the interconnection between 

pore spaces. Deposits consisting of a high percentage of silt and clay have 

large proportions of pore spaces, but the pore spaces are smaller and interconnection is poor. Thus, water does not move freely in these deposits, and 

these deposits typically form confining units in an aquifer system. The 

interconnection of pore spaces in volcanic deposits is commonly due to 

fracturing after the rock has cooled.

Main-channel deposits tend to make more productive aquifers 

because of their coarse-grained size, whereas overbank deposits are likely 

to form confining units because of their fine-grained size. The poorly 

sorted range of grain sizes in alluvial-colluvial deposits typically make 

moderate to poor aquifers. Because of their uniform grain size, eolian 

deposits generally make very productive aquifers. Fine-grained lacustrine 

deposits tend to form confining units. 

Sandia Mountains

Rio Grande

Ziana horst

San Francisco fault

Sand Hill fault

WEST EAST

Calabacillas subbasin

EXPLANATION

Axial gravel Eolian sand and silt

Piedmont-slope deposits

Pre-Santa Fe Group units

Contact

Fault

Blanket gravel, sand

Medium-coarse sand

Silt and fine sand

Medium sand

Fine-medium sand

Figure 3.3.— East-west geologic section through the Calabacillas subbasin 

illustrating general relation of faults and sedimentary units.

Sedimentary particles are generally 

described according to their grain size. The 

classification system used is called the 

Modified Wentworth Scale (Ingram, 1989).

Largest 

diameter 

(inches)

Smallest 

diameter 

(inches)

Sizeclass 

name

Deposit 

name

161.3 10.1 Boulders Gravel

10.1 2.52 Cobbles Gravel

2.52 0.08 Pebbles Gravel

0.08 0.002 Sand Sand

0.002 0.0002 Silt Silt

0.0002 0.00001 Clay Clay
31

How the basin has changed over 

geologic time

The early history of the Rio Grande Rift and the Middle Rio Grande 

Basin is not well known because much of the geologic record is buried. 

However, several lines of evidence show that the basin has responded to 

significant changes in tectonic conditions, volcanic activity, and climatic 

conditions. Each of these changes has influenced the ground-water environment to varying degrees.

 Gravity data (see Box D) are most useful in defining the structural 

trends of the deeper and, therefore older, parts of the Middle Rio Grande 

Basin. Along the western margin of the central subbasin (Calabacillas) of 

the Middle Rio Grande Basin, the entire basin-fill sequence is only about 

1,400 feet thick, but several miles to the east rocks deposited over the same 

span of time are more than 14,000 feet thick (Tedford and Barghoorn, 

1999). The subbasins are bounded by steep gravity gradients (probably 

caused by buried faults) that trend toward the northwest and the north. 

These trends indicate that tectonic forces were oriented differently in the 

early stages of rift formation than they are today, when the most conspicuous faults trend toward the north.

Regional volcanic activity has accompanied faulting within the Rio 

Grande Rift, but the eruptions have varied considerably over space and 

time. Early volcanic eruptions occurred primarily south of the Middle Rio 

Grande Basin near Socorro and north of the basin near Santa Fe (fig. 3.1). 

These early volcanic rocks were eroded to form some of the first basin-fill 

sediments in the Socorro and Santa Fe areas. Volcanic deposits are generally missing in the central part of the Middle Rio Grande Basin, with the 

exception of thin ash beds that formed as a result of distant eruptions. 

Volcanic deposits are abundant in the northern part of the basin as a result 

of eruptions from volcanoes in the Jemez Mountains. Basalt flows are also 

common in several areas of the basin; most erupted during the last 4 

million years. With the exception of an area southwest of Albuquerque, 

most basalt flows are within the upper, unsaturated part of the Santa Fe 

Group and have little effect on ground-water resources.

Climate in the Southwestern United States has changed significantly during the time of sedimentation of the Rio Grande Rift (fig. 3.4). 

Variations in precipitation and aridity have affected vegetation and streamflow and thus the amount of erosion and sediment transported into and 

within the Middle Rio Grande Basin. Eolian deposits are common in the 

lower part of the Santa Fe Group in the northwestern part of the basin, 

indicating that a warm, arid climate existed until about 15 to 14 million 

years ago. The dominantly fluvial parts of the middle portions of the Santa 

Fe Group indicate a more temperate climate, but streamflows probably 

were not large because most deposits consist of fine-grained sand and silt. 

Beginning about 5 million years ago, rift-fill deposits across much of the 

basin became notably coarser grained, indicating that the climate became 

wetter, which led to more upland erosion, increased stream discharge, and 

the transport of coarse gravel into the central parts of the valley. This sedimentological change is consistent with independent climatic, isotopic, and 

paleobotanical evidence that rainfall and runoff increased significantly 

during the early Pliocene (about 5 million years ago) along with a general 

The Jemez Mountains. Volcanic activity 

in this area was the source of many of 

the volcanic deposits in the northern 

part of the Middle Rio Grande Basin.
32

cooling of the climate that preceded late Pliocene glaciations, which began 

as early as 2.8 to 2.7 million years ago (Thompson, 1991).

Sometime after 2.7 million years ago (late Pliocene), the first 

through-flowing Rio Grande in the Albuquerque area was formed, and it 

began to erode the rift-fill deposits laid down by smaller streams in closedbasin settings (Cole, 2001). This erosion indicates that the Rio Grande 

drainage system became connected southward through Socorro to lower 

elevations in other closed basins near Las Cruces and in northern Mexico 

(Gile, Hawley, and Grossman, 1981). This ancestral Rio Grande continued 

to intermittently erode into the rift-fill deposits in response to Pleistocene 

climatic fluctuations (Dethier, 1999) and in response to final connection to 

the Gulf of Mexico after about 700,000 years before present (Gile, Hawley, 

and Grossman, 1981).

DELTA 18

O (PER MILLION)

WARMING 

COOLING

1.5

2.5

3.5

4.5

5.5

0.5

0

25 20 15 10 5 Today

MILLION YEARS AGO

Sand dunes

Playa lakes

Sand-silt streams

Internal drainage

Sand-gravel rivers

External drainage

Oligocene Early Miocene Mid-Miocene Late Miocene Pliocene Pleistocene

Modified from Shackleton and others (1984); 

Krantz (1991); Pagani, Arthur, and

Freeman (1999)

Figure 3.4.—Variation of oxygen isotope composition of shells from bottom-dwelling micro-organisms 

in the Pacific and Atlantic Oceans during the last 25 million years. The oxygen isotope composition 

varies according to the temperature of seawater and reflects long-term climatic conditions (as indicated on the right side). Generally warm conditions existed until about 15 million years ago, roughly 

when the sedimentary record in the Rio Grande Rift indicates a change from sand dunes and playalake environments to braided stream systems. Significant cooling began about 5 million years ago, 

about when coarse sand and cobble-boulder gravel appeared prominently in the rift-fill deposits.

Typical gravels deposited by the throughflowing Rio Grande.
33

Three-dimensional form of the aquifer 

system today

The structure of the aquifer system within the Middle Rio Grande 

Basin today is complex. The major hydrostratigraphic units in the aquifer 

are tabular and wedge-shaped bodies that are truncated and displaced by 

numerous faults (fig. 3.3). Few of the major units are present continuously 

throughout all three subbasins, and most pinch out against the subsurface 

basement blocks that separate the subbasins. These major units are 

hundreds to thousands of feet thick, extend over tens of square miles, and 

primarily consist of unconsolidated and partially cemented deposits that 

interfinger in complex arrangements. The diverse rock types and intricate 

interbedding relations mean that the hydrologic characteristics of these 

units can be defined only in general terms.

Some of the greatest geologic complexity in the system is near the 

basin margins. Tectonic uplift of mountain ranges adjacent to the Rio 

Grande Rift has caused erosion and the formation of alluvial-fan deposits, 

chiefly next to the Sandia and Manzano Mountains on the east and Ladron 

Peak on the southwest. Persistent volcanic eruptions in the Jemez Mountains north of the basin produced thick deposits of volcanic rocks and 

transported volcaniclastic debris (fragments of volcanic rock) in that area. 

Most of the western margin of the rift basin has remained fairly stable 

through time. Deposits on the western margin are thin and are separated by 

breaks in deposition, representing times when the east-flowing streams 

neither eroded nor deposited sediment in the basin.

The hydrostratigraphic units of particular interest for ground-water 

resources in the Middle Rio Grande Basin are the coarse-grained sand and 

gravel facies that compose some of the most productive aquifer materials 

in the basin. These Pliocene (5 to 1.6 Ma) and younger deposits reflect 

deposition by streams and rivers during a period of significantly greater 

precipitation and increased streamflow in the last 5 million years as well 

as integration of the through-flowing Rio Grande drainage after about 

2.7 million years ago. These medium to coarse sand and pebble deposits 

form an irregular sheetlike zone that blankets the western and northern 

parts of the basin. The unit is locally several hundred feet thick below the 

water table, primarily in a broad band that follows the modern Rio Grande 

(Hawley, Haase, and Lozinsky, 1995).

A hydrostratigraphic unit is a body of 

rock or sediment distinguished and 

characterized by its hydrologic characteristics (Seaber, 1988).
34

Effect of faults on the aquifer system

Most faults in the Middle Rio Grande Basin trend in a north-south 

direction, although northeasterly trending faults are common in the 

northern (Santo Domingo) part of the basin. Faults have two principal 

effects on the aquifers and confining units, the first resulting from displacement and the second from the altered physical nature of the fault zone 

itself.

The lateral continuity of a hydrostratigraphic unit is broken where 

the displacement across a fault is greater than the thickness of the unit. For 

example, a highly permeable deposit might be faulted against low-permeability silt- and clay-rich deposits that restrict ground-water flow across the 

fault zone. Such a juxtaposition can lead to large changes in water-table 

elevation across the fault, as is observed in the Albuquerque area across the 

Isleta and West Sandia faults (Thorn, McAda, and Kernodle, 1993). Lesser 

displacements may not completely truncate a permeable unit but may 

reduce flow within the unit.

Fault displacement also affects the thickness of similar units in the 

adjoining fault blocks. Units of the same age tend to be thicker on the 

downthrown side of faults because faulting was more or less continuous 

with deposition (see fig. B.1). The downthrown block may have a thicker 

unit because more sediment is deposited on this block over time or because 

erosion removed material from the upthrown block. Faulting during deposition also can alter depositional facies along the fault scarp and change the 

hydrologic character of the deposits (see Box B; Cather and others, 1994).

Physical changes within the fault zone can alter the local hydrologic 

environment (Caine, Evans, and Forster, 1996). Faults can increase the 

number and extent of fractures in the rock medium and can disaggregate 

loosely consolidated deposits, resulting in enhanced permeability along the 

fault zone. In contrast, intense shearing along the core of the fault zone can 

grind rock fragments into fine-grained fault gouge (a soft, clayey material) 

that has lower permeability than the rock on either side of the fault zone. 

Thus, fault zones may become either conduits or barriers for horizontal 

ground-water movement at various places along their extents. 

In addition, increased permeability along a fault zone can enhance 

movement of ground water in contact with freshly broken rock. Ground 

water can have chemical reactions in fault zones as a result of enhanced 

movement, and mineral constituents may dissolve and (or) reprecipitate as 

cement. Carbonate and silica cements are common along some of the major 

fault zones in the Middle Rio Grande Basin (Mozley and Goodwin, 1995).

Permeability refers to the general ability 

of a rock unit to transmit fluid (Jackson, 

1997). It is a function of how well the 

pores in a rock unit are connected. 

Because different fluids such as petroleum or brines are found in rocks, the 

permeability can change depending on 

the fluid. For this reason, hydrologists 

use a water-dependent permeability 

called hydraulic conductivity, which is 

discussed on page 58. 

The East Paradise fault zone. Faults 

can affect ground-water movement 

by enhancing or retarding flow.
35

Contribution of geophysical data to 

understanding the aquifer system

Surface outcrops can provide only a general guide to the lithologic 

and hydrologic characteristics at depth; thus, various geophysical methods 

are used to gain information about subsurface conditions (see Box D). 

These methods rely on indirect measurements of rock properties. The most 

commonly used techniques are based on measurements of density, magnetization, natural radioactivity, or electrical conductivity. Geophysical data 

have been collected in the Middle Rio Grande Basin by equipment towed 

behind aircraft, lowered into deep boreholes, or transported across the land 

surface.

Density-based techniques, also called gravity methods, are 

conducted by measuring minor variations in the strength of the Earth’s 

gravitational force. Local variations in the gravity field primarily reflect 

variations in the density of rock, sediment, and pore fluids. In the Middle 

Rio Grande Basin, gravity methods have been especially useful in defining 

the buried margins of the subbasins and in estimating the thickness of lowdensity deposits of the aquifer system.

Magnetic methods measure minor differences in the Earth’s 

magnetic field strength from place to place. Local variations primarily 

reflect the concentration and type of minor magnetic minerals in different 

rock and soil materials but in some cases may also reflect an intrinsic 

magnetic field contained in the rock itself. Some of the most magnetic 

materials in the Middle Rio Grande region are the ancient granitic and 

metamorphic rocks that are exposed in the mountain uplifts around the 

margins of the basin. Most of these materials typically are barriers to 

ground-water movement. Buried young (Cenozoic age) volcanic rocks 

throughout the basin are also strongly magnetic. The magnetic data 

obtained from airborne surveys across much of the study area have been 

extremely useful in locating these rock units and in identifying faults that 

offset aquifer units (see Box D).

Earth materials contain minor amounts of naturally occurring radioactive elements, the most common of which are potassium, uranium, and 

thorium. Sophisticated versions of the Geiger counter can be towed behind 

an airplane or lowered down a borehole to measure variations in the 

concentrations of these elements. The borehole tool has been extremely 

useful in subsurface exploration of aquifer properties because it is sensitive 

to the potassium content of clay-rich layers and some volcanic materials 

(see Box C).

Measurements of electrical conductivity rely on sensing differences 

in the way Earth materials and pore fluids conduct electricity. The methods 

are varied, but the results can help define important properties of the 

ground-water system. In the Middle Rio Grande Basin Study, these 

methods have been most useful in identifying zones or layers rich in clay 

(good electrical conductor, poor aquifer properties) and zones rich in 

medium- to coarse-grained sand and gravel (poor electrical conductor, 

good aquifer properties).

Most people are familiar with the 

magnetic field of the Earth and its effect 

on a compass needle. Periodically, 

however, the Earth’s magnetic field 

reverses magnetic polarity, which would 

cause a compass needle to point the 

opposite direction. As some rocks are 

deposited (or heated above 870°F and 

cooled), some iron minerals align with 

the Earth’s magnetic field, thus 

preserving the magnetic polarity at the 

time of deposition or cooling. Because 

the reversals have not occurred at 

regular or uniform intervals, a paleomagnetic history can be used to date a 

sequence of rocks (Press and Siever, 

1986).

A converted Spanish transport plane used for 

airborne time-domain electromagnetic surveys 

in the Middle Rio Grande Basin. The wires 

wrapped around the plane compose the transmitting antenna.
36

Modified from Grauch, Gillespie, and Keller (1999)

Belen

subbasin

Albuquerque Albuquerque lbuquerque

Calabacillas

subbasin

Santo

Domingo

subbasin

0 50 MILES

0 50 KILOMETERS

107 ̊ 15' 106 ̊ 15'

-30

0

-15

15

30

45

Gravity-Anomaly Map

35 ̊

35 ̊ 30'

34 ̊ 30'

Middle

Rio Grande

Basin Boundary

MILLIGALS

Different rock units and the fluids contained in 

them can be characterized by their physical 

properties, such as density, magnetization, and 

electrical resistivity. Geophysicists use indirect 

methods to measure the differences in underground physical properties; these methods provide information about the subsurface without 

well information (though some well information is needed for the calibration of geophysical data). For example, measuring the 

variations in the Earth’s gravity or magnetic 

field at different places provides information 

about the density or magnetization of the subsurface deposits. Measuring the effects of an 

electric current transmitted through the ground 

gives clues to the electrical resistivity, a measure of how well or how poorly the subsurface 

deposits and their fluids conduct electricity.

In the Middle Rio Grande Basin, several different geophysical methods were used to 

determine specific aspects of the subsurface 

hydrogeology, three of which are listed in 

table D.1. The gravity geophysical method 

was used to estimate the total thickness of the 

Santa Fe Group deposits, which are less dense 

than the underlying and surrounding bedrock. 

The mapping provided a base for the geologic 

model of the Santa Fe Group aquifer system 

(fig. D.1). Aeromagnetic surveys can detect 

faults that offset water-bearing units in the 

Santa Fe Group and can be used to map the 

extent of buried igneous rocks, which have different hydraulic properties than the surrounding sedimentary deposits (fig. D.2). When 

correlated with lithologic and geophysical 

borehole logs, the airborne time-domain electromagnetic method can be used to determine 

changes in the electrical resistivity of the Santa 

Fe Group with depth that are related to variations in grain size and hydraulic properties.

How geophysical methods have been used to understand

the subsurface

V.J.S. Grauch,1 Brian D. Rodriguez,1 and Maryla Deszcz-Pan1

D

1U.S. Geological Survey, Denver, Colorado.

Figure D.1.—Gravity data for the entire Middle Rio Grande Basin and 

surrounding area. The Santa Fe Group has much lower density than the 

surrounding bedrock, producing low values (shown in blue and purple) on 

the gravity-anomaly map .
37

Buildings

Water

tank

Bridge Pipeline

Pipeline

Rio Grande

Aeromagnetic-Anomaly Map

0

–500

–900

500

1,000

1,350

NANOTESLAS

0 5 KILOMETERS

0 5 MILES

Modified from U.S. Geological Survey and 

Sander Geophysics, Ltd. (1998)

Table D.1.—Brief description of the geophysical methods used and the hydrogeologic features delineated by each

Geophysical

method

Geophysical

measurement

Associated physical 

property

Type of geophysical 

map and units

Hydrogeologic 

features delineated

Gravity Ground measurements 

of variations in the 

Earth’s gravity field

Bulk-rock density Gravity-anomaly map 

in milligals

Thickness of the Santa 

Fe Group

Aeromagnetic Airborne measurements of variations in 

the Earth’s magnetic 

field

Total rock magnetizationAeromagnetic anomaly 

map in nanoTeslas

Faults within the Santa 

Fe Group and buried 

igneous rocks

Time-domain

electromagnetic

Airborne monitoring of 

the time-varying 

effects of shutting off 

an electric current 

induced in the Earth

Electrical resistivity 

(inverse of electrical 

conductivity)

Electrical-resistivity 

maps for different 

depth slices in ohmmeters

Grain-size variations 

within the Santa Fe 

Group

Hydrogeologic Features

EXPLANATION 

Exposed igneous rocks

Igneous rocks estimated at 49-foot depth

Igneous rocks estimated at 490-foot depth

Interpreted fault trace

Rio Grande

0 5 KILOMETERS

0 5 MILES

Figure D.2.—Aeromagnetic-anomaly map of an area south of Albuquerque (A) and simplified map of important hydrogeologic features (B). Many geologic features and manmade structures can be seen on the anomaly map (A), which is 

displayed in color and shaded as though it were a relief map illuminated from the east. The most important hydrogeologic 

features expressed in the aeromagnetic map are faults and igneous rocks, depicted on the simplified map (B). Depths to 

the buried igneous rocks were estimated by analysis of the aeromagnetic data. Note the shallow, buried igneous rocks 

near the Rio Grande that probably affect ground-water flow.

A

B
38

In 1996, the USGS, in cooperation with the 

City of Albuquerque, drilled a 1,560-foot well 

into the Santa Fe Group aquifer system to 

obtain information about the conditions within 

the aquifer at depth and to establish a reference 

point that could be correlated with other wells. 

The well is located near the intersection of 

98th Street and Interstate Highway 40 immediately west of Albuquerque (see fig. B.1A for a 

location map). A continuous core collected 

during drilling provided samples of the undisturbed sediment that composes the aquifer. A 

number of studies were performed to characterize these continuous-core samples. Other 

information collected from this well (some of 

which is described here) allowed reinterpretation of previous work from other wells in the 

basin and consequently improved the accuracy 

of the geologic framework.

Geologic characterization of the Santa Fe 

Group aquifer system within the Middle Rio 

Grande Basin relies primarily on subsurface 

information collected from wells. As discussed in Box C, the information obtained 

from these wells is based chiefly on rock fragments recovered during drilling (cuttings), on 

geophysical logs that measure physical properties of the rock and fluids, and on hydrologic 

tests to determine aquifer properties. Because 

core samples are continuous pieces of aquifer 

material, they allow correlation between the 

geophysical-log responses and the grain-size 

and bedding characteristics as well as an 

improved interpretation of aquifer tests based 

on detailed knowledge of the variation in these 

hydrologic properties.

The types of sediments penetrated in the well 

and two geophysical logs from the borehole 

are shown in figure E.1 (the lowermost 60 feet 

of the borehole were not logged or described). 

Drilling penetrated an upper zone of about 

100 feet of gravel and coarse sand that was 

deposited by high-discharge stream networks 

flowing eastward into the valley during the Pliocene Epoch (Connell, Allen, and 

Hawley, 1998; Stone and others, 1998). This unit has large values of hydraulic conductivity and is an important ground-water source farther east where it is saturated 

beneath Albuquerque.

Beneath this coarse uppermost unit is a zone of about 700 feet of mostly silty fine 

sand, silt, and clay that were deposited by lower energy drainage systems of the 

ancestral Rio Puerco and Jemez River (Stone and others, 1998). The bottom part of 

this zone is conspicuously red and clay rich and is referred to as the Atrisco member 

of the Santa Fe Group (Connell, Allen, and Hawley, 1998). The Atrisco member 

appears to be laterally continuous between several wells in the central part of the 

basin and may restrict ground-water flow because of its low permeability.

The lowermost 700 feet of the 98th Street well is mostly fine- to medium-grained 

sand with discontinuous layers of pebble gravel, silty clay, coarse sand, and sandstone (fig. E.1). Like the silty sands above the Atrisco member, these sediments 

were also interpreted as deposits of east-flowing, low-energy streams.

The specific time of deposition of any of the sediments could not be established 

because no datable materials were found (for example, volcanic ash or pollen). 

Detailed measurements of magnetic polarity of the core indicated that most of the 

lower section was deposited during a period of normal magnetic polarity, although 

no unique correspondence to normal periods of the Earth’s magnetic polarity time 

scale could be detected (Hudson and others, 1998). On the basis of several possible 

correlations with the magnetic polarity time scale, most of the sediment below the 

uppermost coarse unit probably was deposited in a relatively short span of geologic 

time, possibly less than a few million years.

Geochemical analyses of core samples and ground water were conducted to determine the occurrence and concentrations of arsenic in Santa Fe Group sediments 

(Stanton and others, 1998a; 1998b). Core samples from selected depths were processed to isolate four geochemically different sediment fractions. Analyses of these 

fractions indicated that most of the arsenic was contained in the iron-oxide fraction 

of sediment that was probably deposited with clay minerals and silt-sized rock 

fragments. The most likely sources of these materials are the weathering of naturally occurring arsenic-rich volcanic rocks in the Jemez Mountains and Precambrian crystalline rocks in parts of the Sangre de Cristo Range (north of the Middle 

Rio Grande Basin in north-central New Mexico). Chemical treatment of some of 

the core sediment demonstrated that most of the arsenic in the deposits is not soluble in ground water of the Santa Fe Group aquifer system. No water sample collected from the 98th Street well contained more than 0.042 mg/L of total arsenic, 

though this isolated value is greater than the 2001 Federal drinking-water standard 

of 0.010 mg/L of arsenic (Stanton and others, 1998a). (See Chapter 6 for more 

information on water chemistry in the aquifer system.)

Knowledge gained from the 98th Street well core

Mark R. Stanton1 and James C. Cole1

E

1U.S. Geological Survey, Denver, Colorado.
39

Sand and gravel

Medium sand

Silty fine sand 

Clayey, sandy silt

Clay

Sandstone

EXPLANATION

Clay bed

Coarse-sand bed

Pebble-gravel bed

Conductivity 

0 100 200 300 400

MILLISIEMENS PER 

METER

150

Natural gamma

50 100

AMERICAN PETROLEUM

INSTITUTE UNITS

Sample

intervals

Depth,

in feet

200

400

600

800

1,000

1,200

1,400

0

1,500

Modified from Stone and others (1998)

Water table 378

Figure E.1.—Lithology and geophysical logs 

of the 98th Street well.

A USGS drilling rig collecting core 

at the 98th Street well.
40

Drill hole

Fault scarp

How the geologic model represents 

current interpretation of basin 

structure and stratigraphy

The combined geologic and geophysical studies in the Middle Rio 

Grande Basin over a 6-year period (1995–2001) have produced considerable new information about the geologic framework of the Santa Fe Group 

aquifer system. The three-dimensional geologic model that forms the basis 

of the new ground-water-flow model embodies the major elements of this 

refined understanding of the Rio Grande Rift and its basin-fill deposits 

(Cole and others, 1999; Cole, 2001).

Major structural elements of the basin are currently (2002) better 

known and located than elements used in previous ground-water-flow 

models. Interpretation of the regional gravity data (see Box D; Heywood, 

1992; Grauch, Gillespie, and Keller, 1999) has shown that the major subbasins are bounded at depth by northwest-trending faults, that the principal 

basin-bounding fault beneath Albuquerque is very near the Sandia Mountains uplift, and that the Belen subbasin is quite complex. These findings 

improve the preexisting structural framework model of Russell and Snelson 

(1994), on which the ground-water-flow model of Kernodle, McAda, and 

Thorn (1995) was based. The new aeromagnetic data provide detailed 

information about faults that offset aquifer units (see Box D) and allow for 

more accurate analysis of hydrologic relations among wells in adjacent 

fault blocks.

The stratigraphy of the basin-fill deposits that compose the aquifer 

system has always been difficult to define, largely because of the complex 

relation between rock units resulting from the interplay of faulting, climate, 

and deposition (see Box B). The current geologic model improves on 

previous concepts by recognizing that distinct stratigraphic assemblages 

were deposited over the same time period, but more or less independently, 

in the three subbasins (Santo Domingo, Calabacillas, and Belen) (fig. 3.2). 

This new geologic model includes numerous major faults that were identified and precisely located by the mapping and aeromagnetic surveys, and 

regional information about the thickness of rift-fill sediment based on 

calculations from the gravity data. In addition, the model accurately 

portrays laterally discontinuous and wedge-shaped units, particularly for 

the middle and deeper parts of subbasins where fault activity had the 

greatest effect on the composition and geometry of the aquifer system.

Perspective view of the southern part of a 

model of the Middle Rio Grande Basin 

showing the base of the Santa Fe Group 

aquifer system. The model was derived 

from gravity data and constrained by information for the deep drill holes shown as 

yellow circles. (Courtesy of V.J.S. Grauch, 

USGS.)
41

In discussions of the water resources of an area, the hydrologic 

system is commonly split into two components for convenience: surface 

water and ground water. However, in the Middle Rio Grande Basin, as in 

most other locales, the surface- and ground-water systems are intimately 

linked through a series of complex interactions. These interactions often 

make it difficult to recognize the boundary between the two systems. In 

this report, the surface- and ground-water systems are described separately, 

though one of the goals of the report is to show that they are both parts of 

the hydrologic system of the Middle Rio Grande Basin and that changes in 

one often affect the other.

As defined earlier, in this report “Middle Rio Grande Basin” refers 

to the geologic basin defined by the extent of deposits of Cenozoic age 

along the Rio Grande from about Cochiti Dam to about San Acacia. This 

definition includes nearly the entire ground-water basin; however, the 

extent of the surface-water basin is delimited topographically by drainage 

divides and is consequently somewhat larger than the ground-water basin.

Surface-water system

The most prominent hydrologic feature in the Middle Rio Grande 

Basin is the Rio Grande, which flows through the entire length of the 

basin, generally from north to south. The fifth longest river in the United 

States, its headwaters are in the mountains of southern Colorado. The Rio 

Grande is the largest river in New Mexico, with a drainage area of 

14,900 square miles where it enters the Middle Rio Grande Basin. It gains 

about 12,900 square miles of drainage area as it flows through the basin; 

much of that gain is from the Rio Puerco drainage basin.

Though flow in the Rio Grande is currently (2002) regulated by a 

series of dams and storage reservoirs, now, as historically, the greatest 

flows tend to occur in late spring as a result of snowmelt and for shorter 

periods during the summer in response to rainfall. Historically, the Rio 

Grande has flowed year-round through much of the basin, “except for 

those periods of severe, extended drought” (Scurlock, 1998).

Within the Middle Rio Grande Basin, tributary streams, wastewatertreatment plants, flood-diversion channels from urban areas, and a large 

number of arroyos and washes contribute flow to the Rio Grande. Among 

the major tributaries are the Santa Fe River, Jemez River, Rio Puerco, and 

Rio Salado. Of these four tributaries, only the Santa Fe River is perennial, 

and most of its flow is treated effluent from the City of Santa Fe wastewater-treatment plant. The cities of Bernalillo, Rio Rancho, Albuquerque, 

Los Lunas, and Belen discharge treated effluent directly into the Rio 

Grande. Two main flood-diversion channels, the North Floodway and 

South Diversion Channels, east of the Rio Grande intersect many smaller 

arroyos and divert the flow to the river at outlets north and south of Albuquerque. Among the major ephemeral arroyos that are tributary to the Rio 

Grande are Galisteo Creek, Arroyo Tonque, Las Huertas Creek, Arroyo de 

las Calabacillas, Tijeras Arroyo, Hells Canyon Wash, and Abo Arroyo 

(fig. 4.1).

Chapter 4: The hydrologic system of the Middle 

Rio Grande Basin

The Rio Grande is the only river I ever 

saw that needed irrigation. –attributed to 

Will Rogers

Ephemeral streams are those that flow 

occasionally, usually in direct response 

to precipitation. Perennial streams are 

those that flow year-round from either 

upstream flow or the contribution of 

ground water. 
42

Arroyo Chico

Rio Puerco

Rio Puerco

Jemez River

Arroyo de las

Calabacillas

Salado

Rio

Rio Salado

Jemez Canyon

Reservoir

Galisteo

Res

Tijeras Arroyo

San Jose 

Rio

Cochiti Lake

Arroyo

Tonque

River Fe

Santa

 Arroyo Abo

Creek

Galisteo

Creek

HellsCanyon Wash

RIO

GRANDE 

RIO 

GRANDE 

Las

tas er Hu

San

Ysidro

Cochiti

Santo

Domingo

San Felipe

Algodones

Bernalillo

Rio

Rancho

Albuquerque

Isleta

Los Lunas

Belen

Bernardo

San Acacia

McKINLEY

CIBOLA

VALENCIA

SOCORRO

TORRANCE

SANTA FE

BERNALILLO

SANDOVAL

EXPLANATION

Rio Grande inner valley Middle Rio Grande Basin

0 20 40 MILES

0 20 40 KILOMETERS

35 ̊30'

35 ̊15'

35 ̊

34 ̊45'

34 ̊30'

107 ̊15' 107 ̊ 106 ̊45' 106 ̊30' 106 ̊15'

Figure 4.1.—Major surface-water features of the Middle Rio Grande Basin.
43

Several different types of conveyance 

channels (fig. 4.2) make up the irrigation 

system in the Middle Rio Grande Basin. 

High-line canals run along the hills 

bordering the inner valley at relatively 

shallow grades. Low-line canals run 

along the valley floor. Laterals are 

somewhat smaller and usually have a 

heading in a canal. Acequias (or 

ditches) are the smallest channels. 

Wasteways and drains return unused or 

excess irrigation water to the river 

(Bullard and Wells, 1992).

Three major reservoirs are in the Middle Rio Grande Basin: Cochiti 

Lake, Jemez Canyon Reservoir, and Galisteo Reservoir. Cochiti Lake is 

located in Sandoval County on the Rio Grande at its confluence with the 

Santa Fe River and began filling in 1973. In 1981, the reservoir capacity 

was 596,400 acre-feet. Though originally authorized for flood and sediment control, the authorization was subsequently modified to establish a 

permanent pool of 50,000 acre-feet for wildlife and recreational purposes. 

In addition, because the construction of Cochiti Lake destroyed a Middle 

Rio Grande Conservancy District irrigation diversion structure, irrigation 

water is now diverted at the dam. Approximately 5,900 acre-feet of water 

is lost to evaporation annually from Cochiti Lake. The reservoir is operated and maintained by the U.S. Army Corps of Engineers (Bullard and 

Wells, 1992).

Jemez Canyon Reservoir is located in Sandoval County on the 

Jemez River approximately 2.5 miles upstream from its confluence with 

the Rio Grande. The dam was finished in 1953 and is authorized to be 

operated solely for flood and sediment control; thus, there is no provision 

for maintenance of a permanent pool, and lake level consequently fluctuates over a wide range. Jemez Canyon Reservoir has a capacity of 

102,700 acre-feet and is operated by the U.S. Army Corps of Engineers 

(Bullard and Wells, 1992).

A third reservoir, Galisteo Reservoir, is located in Santa Fe County 

on Galisteo Creek, approximately 12 miles upstream from its confluence 

with the Rio Grande. The reservoir was authorized for flood and sediment 

control, and the dam was finished in 1970. Though empty most of the 

time, the reservoir has a capacity of 88,900 acre-feet and also is operated 

by the U.S. Army Corps of Engineers (Bullard and Wells, 1992).

A number of small flood-retention dams in the AlbuquerqueRio Rancho area are operated by the Albuquerque Metropolitan Arroyo 

Flood Control Authority (AMAFCA) and the Southern Sandoval County 

Arroyo Flood Control Authority (SSCAFCA). These dams were 

constructed for the downstream reduction of peak flows and contain water 

for only short periods following precipitation.

The inner valley of the Rio Grande contains a complex network of 

irrigation canals, ditches, and drains that has evolved from the original 

acequia system. The Middle Rio Grande Conservancy District administers 

this irrigation system and diverts Rio Grande water at four points in the 

basin: Cochiti Dam, Angostura, Isleta, and San Acacia (which serves an 

irrigation area downstream from the basin). During irrigation season, 

water is diverted from the river and flows through the Rio Grande inner 

valley in a series of irrigation canals and smaller ditches for application to 

fields. This water recharges ground water, is lost to evaporation, is 

transpired by plants, or is intercepted by interior drains or wasteways and 

returned to the river. Figure 4.2 is a schematic showing the generalized 

inner valley irrigation network (Bullard and Wells, 1992; Kernodle, 

McAda, and Thorn, 1995; Anderholm, 1997).

The other main component of the inner-valley surface-water system 

is a network of riverside drains, which are deep canals that parallel the 

river immediately outside the levees. They are designed to intercept lateral 

ground-water flow from the river, thus preventing waterlogged conditions 

in the inner valley. The riverside drains then carry this intercepted groundwater flow back to the Rio Grande. Within the basin, riverside drains and 

levees are usually present on both banks of the river, except where bluffs 

adjoin the river.

Wasteway

Wasteway

Wasteway

Wasteway

Lateral canal

Lateral canal

Acequia

Acequia

Canal

Canal

Interior

drain

drain Interior

Riverside drain

drain Riverside

Diversion dam

Rio Grande

Modified from Bullard and Wells (1992)

Figure 4.2.—Schematic diagram of the inner 

valley irrigation network in the Middle Rio 

Grande Basin.
44

Surface-water quantity

Information collected from streamflow-gaging stations can be used 

to estimate how much water is flowing through the surface-water system of 

the Middle Rio Grande Basin. Currently (2002) 38 USGS streamflowgaging stations are being operated in or adjacent to the Middle Rio Grande 

Basin; 37 gaging stations have been operated in the past but have been 

discontinued (fig. 4.3). The sites with gaging stations include the Rio 

Grande and other streams tributary to the Rio Grande, irrigation canals and 

drains, arroyos and washes, and reservoirs. In addition to streamflow information, some of these gaging stations provide information about water 

chemistry and reservoir levels in the basin.

Table 4.1 shows surface-water inflows into and outflows from the 

Middle Rio Grande Basin for both the period of record for selected gaging 

stations or sites and for 1974–2000 (1974 is the first full water year in 

which flows in the Rio Grande were regulated by Cochiti Dam).

Streamflow in arroyos and washes is by definition ephemeral, and 

measuring ephemeral streamflow is problematic. For this and other 

reasons, most of the arroyos and washes tributary to the Rio Grande are not 

gaged; thus, the amount of water they contribute to the Rio Grande is an 

estimate. Streamflow in Galisteo Creek and Tijeras Arroyo is measured 

close enough to their confluence with the Rio Grande that their contribution to the flow of the Rio Grande is known. Streamflow in Abo Arroyo is 

also measured; however, the gaging station (Abo Arroyo near Blue 

Springs) is located where the arroyo enters the basin many miles upstream 

from the Rio Grande. This gaging station was installed to estimate recharge 

to ground water at the basin margin, and because many flows recorded at 

this station infiltrate or evaporate before they reach the Rio Grande, 

measurements are not a reliable indicator of Abo Arroyo’s contribution to 

Rio Grande flow, though it is included in table 4.1. The North Floodway 

and the South Diversion Channels in Albuquerque were designed to convey 

ephemeral flow to the Rio Grande, but the North Floodway now flows 

continuously at about 1 to 5 cubic feet per second in its lower reaches. The 

flow is the result of return flow from turf-grass irrigation and the City of 

Albuquerque’s practice of discharging municipal-well water to arroyos 

during the first few minutes of operation (Ground-Water Science, Inc., 

1995).

Treated sewage effluent contributes a volume of water to the Rio 

Grande. Because this water was originally withdrawn from the aquifer 

system rather than the river, it is counted as tributary inflow. The major 

municipalities in the basin have sewage-treatment plants: Bernalillo, Rio 

Rancho, Albuquerque, Los Lunas, and Belen. All discharge at least part of 

their treated effluent to the Rio Grande. Rio Rancho discharges a limited 

volume of its effluent into the Albuquerque system. Both Albuquerque and 

Rio Rancho use some of the treated effluent for turf-grass irrigation. Areas 

of the basin not served by a sewage system use septic tanks, cesspools, or 

open-pit toilets for waste disposal (Ground-Water Science, Inc., 1995).

Streamflow-gaging stations are the 

means by which hydrologists monitor 

the flow of water in streams and rivers. 

Gaging stations typically consist of a 

shelter that encloses a recorder to 

monitor water height (or stage). A correlation (known as a rating curve) can be 

made between stage and discharge by 

periodically measuring the streamflow 

rate (or discharge) of the stream and 

comparing it to the stage. An increasing 

number of recorders in gaging stations 

broadcast their stage data in real time 

or near real time by satellite or telephone. These data are used to automatically calculate discharge, and the 

discharge is then made available over 

the Internet. This streamflow information is useful not only for resource 

management and flood warning but 

also for recreational purposes such as 

fishing and boating. New Mexico 

streamflow information can be found on 

the Internet at http://nm.water.usgs.gov.

The North Floodway at Paseo del Norte in 

northern Albuquerque.
45

Water year describes the 12-month 

period from October 1 through 

September 30 of the following year. 

The water year is designated by the 

calendar year in which it ends. Thus, the 

12 months ending on September 30, 

2002, are water year 2002.

Cubic feet per second is the unit of 

measurement used to report discharge 

in the United States. Discharge is an 

instantaneous measurement of the 

volume of water that passes a given 

point in a set amount of time. One cubic 

foot of water is equivalent to 

7.48 gallons.

Rio Puerco

Jemez

River

Rio Salado

GRANDE 

RIO 

GRANDE 

RIO 

San

Ysidro

Cochiti

Santo Domingo

San Felipe

Bernalillo

Rio

Rancho

Albuquerque

Isleta

Los Lunas

Belen

Bernardo

San

Acacia

McKINLEY

CIBOLA

VALENCIA

SOCORRO

TORRANCE

SANTA FE

BERNALILLO

SANDOVAL

EXPLANATION

Middle Rio Grande Basin

Continuous-record streamflow-gaging station

Discontinued streamflow-gaging station

0 20 40 MILES

0 20 40 KILOMETERS

35°30'

35°15'

35°

34°45'

34°30'

107°15' 107° 106°45' 106°30' 106°15' Sierra Nacimiento

Jemez

Mountains

Manzano Mountains

Manzanita

Mountains

Los Pinos

Mountains

Ladron

Peak

Sierra Lucero

Mesa

Lucero

Española Basin

San

Juan

Basin

Sandia Mountains

Figure 4.3.—Current and discontinued streamflow-gaging stations in and 

adjacent to the Middle Rio Grande Basin.
46

Table 4.1.—Mean annual surface-water inflows into and outflows from the Middle Rio Grande Basin. Streamflow of the Santa Fe 

River above Cochiti Lake gaging station is not included in total inflow because it is included in streamflow for the Rio Grande below 

Cochiti Dam station. Streamflow for the Jemez River below Jemez Canyon Dam gaging station is not included in total inflow 

because it is downstream from the Jemez River near Jemez gage

[--, no data; period of record is in water years unless otherwise indicated]

Station name (station number) and period of record

Annual mean streamflow

Water years

1974–2000 Period of record

Cubic feet 

per second

Acre-feet 

per year

Cubic feet 

per second

Acre-feet

per year

Inflow to the Middle Rio Grande Basin

Rio Grande at Cochiti (08314500); 1924–70 -- -- 1,2 1,300 1,2 945,000

Rio Grande below Cochiti Dam (08317400); 1970–present 1,460 1,060,000 3 1,430 3 1,030,000

Sili main canal (at head) at Cochiti (08314000); 1954–present 47.6 34,400 35.7 25,800

Cochiti east side main canal at Cochiti (08313500); 1954–present 84.2 61,000 66.9 48,400

Galisteo Creek below Galisteo Dam (08317950); 1970–present 5.62 4,070 2 6.15 2 4,450

Jemez River near Jemez (08324000); 1936–41, 1949–50, 1951–52, 1953–present 86.0 62,200 77.8 56,300

Santa Fe River above Cochiti Lake (08317200); 1970–99 2 11.7 2 8,500 2 11.3 2 8,160

Jemez River below Jemez Canyon Dam (08329000); 1936–39, 1943–present 4 72.1 4 52,200 2 63.6 2 46,000

Abo Arroyo near Blue Springs (08331660); 1996–present 3 17.1 3 4,670 3 17.1 3 4,670

North Floodway Channel near Alameda (08329900); 1968–89, 1990–present 

[seasonal record 1968–89]

11.8 8,510 10.5 7,630

South Diversion Channel above Tijeras Arroyo near Albuquerque (08330775); 

1988–present

0.83 601 0.83 601

Tijeras Arroyo near Albuquerque (08330600); 1952–68, 1974–present 

[annual maximum only 1952–68; seasonal record 1974–98]

0.68 492 0.68 492

Rio San Jose at Correo (08351500); 1943–94 9.97 7,220 4 11.3 4 8,190

Rio Puerco near Bernardo (08353000); 1940–present 30.4 22,000 3 41.9 3 30,400

Rio Salado near San Acacia (08354000); 1947–84 5 8 5 5,900 6 14 6 10,400

Inflow from treated sewage effluent

Town of Bernalillo wastewater-treatment plant, 1985–2000 7 0.7 7 530 7 0.7 7 530

City of Rio Rancho wastewater-treatment plant, 1985–2000 7 2.5 7 1,780 7 2.5 7 1,780

City of Albuquerque wastewater-treatment plant, 1985–2000 7 80.4 7 58,200 7 80.4 7 58,200

Village of Los Lunas wastewater-treatment plant, 1985–2000 7 0.9 7 659 7 0.9 7 659

Town of Belen wastewater-treatment plant, 1985–2000 7 1.3 7 938 7 1.3 7 938

Total inflow into the Middle Rio Grande Basin

Total streamflow and sewage effluent measured 1,830 1,330,000 1,790 1,290,000

Outflow from the Middle Rio Grande Basin

Rio Grande Floodway at San Acacia (08354900); 1964–present 1,100 793,000 8 801 8 580,000

Rio Grande Conveyance Channel at San Acacia (08354800); 1958–present 230 167,000 8 345 8 250,000

Socorro Main Canal North at San Acacia (08354500); 1936–present 125 90,400 3,8 117 3,8 84,500

Total outflow from the Middle Rio Grande Basin

Total streamflow measured 1,450 1,050,000 1,260 914,000

1 U.S. Geological Survey (1971).

2 Not included in total inflow because of other downstream station or replacement.

3 Ortiz, Lange, and Beal (2001).

4

 Borland and Ong (1995).

5

 Thorn, McAda, and Kernodle (1993).

6 Denis, Beal, and Allen (1985).

7 Upper Rio Grande Water Operations Model (2002).

8 Period of record values are for water years 1964 through 2000.

Data not footnoted were retrieved directly from the USGS National Water Information System database.
47

Ground-water system

Most water-bearing units of the Middle Rio Grande Basin are 

unconsolidated deposits of the Santa Fe Group. Post-Santa Fe Group 

deposits (basin and valley fill) of Quaternary age formed during the last 

1.6 million years. These deposits are present on mountain slopes, in the 

incised valley of the Rio Grande, and along flood plains of tributaries to 

the Rio Grande. They are locally used as aquifers, although the deposits 

are generally saturated only in flood plains or the inner valley of the Rio 

Grande. Because the Santa Fe Group and basin and valley-fill deposits are 

hydraulically connected, they are commonly grouped together as the Santa 

Fe Group aquifer system, following the informal usage of Thorn, McAda, 

and Kernodle (1993). Though the aquifer is under confined conditions 

locally, it is considered to be an unconfined aquifer as a whole. (For 

ground-water-flow modeling, the upper part of the aquifer system is 

treated as unconfined and the lower part as confined.)

The geology of the Santa Fe Group aquifer system was described in 

detail in the previous chapter. To review, the thickness of the Santa Fe 

Group in the Middle Rio Grande Basin ranges from about 1,400 feet at the 

basin margins to approximately 14,000 feet in the center of the basin 

(Lozinsky, 1988; Hawley and Haase, 1992; Grauch, Gillespie, and Keller, 

1999). The Santa Fe Group is divided into three parts: upper (less than 

1,000 to 1,500 feet thick), middle (250 to 9,000 feet thick), and lower (less 

than 1,000 to 3,500 feet thick). In places, either the upper part or the upper 

and middle parts have eroded away. Because of the depositional history of 

the Santa Fe Group, much of the lower part may make a poor aquifer. For 

this and economic reasons, ground water is withdrawn mostly from the 

upper and middle parts; only about the upper 2,000 feet of the aquifer is 

used for ground-water withdrawal. The depth to water in the aquifer 

system varies widely, from less than 2 feet near the Rio Grande to as much 

as 1,180 feet in an area west of Albuquerque.

Ground-water-level declines

The main method by which ground-water managers and scientists 

track changes in the volume of water in an aquifer is comparing changes in 

ground-water levels in wells. These data are typically shown as groundwater-level maps or hydrographs. Box F describes how ground-water 

scientists use water levels to study an aquifer.

The earliest ground-water-level maps of the Middle Rio Grande 

Basin were of 1936 conditions (Theis, 1938). Theis’ detailed maps are 

limited to the inner valley of the Rio Grande between the Jemez River and 

a few miles north of San Marcial. No effects of ground-water pumping in 

the basin can be seen on these maps.

Bexfield and Anderholm (2000) constructed the most complete 

ground-water-level map of predevelopment conditions in the Middle Rio 

Grande Basin (fig. 4.4) using a number of sources. As expected for predevelopment conditions, no effects of ground-water production in the basin 

are evident. On the basis of shapes of the ground-water-level contours, the 

river reach between Corrales and Belen appears to be losing water from the 

river into the aquifer. This losing reach during predevelopment conditions 

was probably not due to ground-water production but may in fact indicate 

evapotranspiration from vegetation in the inner valley or, as geochemical 

data suggest, long-term water movement into the Santa Fe Group aquifer 

system. 

In an unconfined aquifer, the water level 

(water table) is free to rise and fall. The 

pressure is atmospheric at the water 

table. An aquifer bounded above and 

below by confining beds and completely 

filled with water under pressure is 

known as a confined aquifer (or an artesian aquifer) (Lohman and others, 1972; 

Heath, 1983; Jackson, 1997).

The ground-water level in a well 

completed in an unconfined aquifer 

rises to the level of the top of the saturated zone, or water table. In a well 

completed in a confined aquifer, the 

ground-water level in the well rises to an 

elevation higher than the top of the 

aquifer, but not necessarily to the land 

surface. Differences in the ground-water 

levels in multiple wells completed at 

different depths in a single location indicate the general direction of vertical flow 

within an aquifer (Heath, 1983). See 

Box F for a discussion of ground-waterlevel maps and flow.

The terms steady-state or predevelopment conditions refer to the hypothetical, unchanging state of the aquifer 

prior to ground-water production. It is 

the starting point that ground-water-flow 

models use to assess the effect of 

ground-water development. However, 

because ground-water-level measurements are seldom available for the early 

years of aquifer development and 

because natural climatic fluctuations 

affect water levels, predevelopment 

conditions are often speculative. 

Commonly, the earliest water-level 

measurements are assumed to represent predevelopment conditions.
48

A ground-water-level map is an essential tool 

to achieve a thorough understanding of a 

ground-water-flow system. This kind of map 

generally is used to indicate the elevation and 

shape of the water table. A carefully constructed map can be used to infer many distinct 

characteristics of a ground-water-flow system 

that are particularly important for the accurate 

construction of ground-water-flow models and 

the interpretation of hydrologic and geochemical data.

A ground-water-level map is constructed by 

measuring the depth to water in as many similarly constructed wells as possible. The part of 

an aquifer where all the rock openings and 

pores between sediment grains are completely filled with water is known as the saturated zone (fig. F.1). In an unconfined aquifer, such as the Santa Fe Group aquifer 

system, the upper surface of the saturated zone, the water table, is free to rise and 

fall. The water table is mapped using water-level measurements collected from 

wells that are open to the aquifer at or just below the water table. The measurements 

of depth to water obtained from these wells must be referenced to the same datum 

(commonly defined relative to sea level). For any particular well, a measuring point 

is defined as the elevation of the point from which the depth to water is always measured. After the depth to water in the well is measured, the value obtained is subtracted from the elevation of the measuring point to obtain the elevation of the water 

table above (or below) sea level (fig. F.1). When water-table elevations are plotted 

on a map of well locations, the values can be contoured to indicate the configuration 

of the water table (fig. F.2). Because the position of the water table varies in 

response to changes in the quantities of water entering and leaving the aquifer, a 

ground-water-level map should use only measurements from a time interval during 

which such changes are expected to be minimal.

Ground-water-level maps and how they are used to 

understand the aquifer

Laura M. Bexfield1

F

1U.S. Geological Survey, Albuquerque, 

New Mexico.

EXPLANATION

Location of well and elevation of water

 table above sea level, in feet

4,852

4850 Water-table contour—Shows elevation

 of water table. Interval 10 feet.

 Datum is sea level

Direction of ground-water flow

4,875 4,869

4,865

4,868

4,863

4,862

4,852

4870

4,859

4,856

4,853

4,852

4,858

4,847

4,848

4,842

4860

4850

Elevation of measuring

point = 4,950 feet

Water-table elevation = 4,875 feet

Water-table elevation = 4,870 feet

Elevation of measuring

point = 4,948 feet Distance between wells = 5,000 feet

Land surface

Water table

Depth to water

= 78 feet

Depth to

water

= 75 feet

UNSATURATED ZONE

SATURATED ZONE

Bottom of aquifer

Hydraulic gradient = Difference in water-table elevations

Distance between wells

5 feet

5,000 feet = = 0.001

Figure F.1.—Information needed to determine water-table elevations and to calculate hydraulic gradients.

Figure F.2.—Hypothetical well locations, water-table elevations, watertable contours, and approximate directions of ground-water flow.
49

One of the most common uses of a ground-water-level map is to infer the direction 

of ground-water flow in the aquifer. Water generally flows from areas of higher 

hydraulic head (higher water-table elevations) to areas of lower hydraulic head 

(lower water-table elevations) along the path of the steepest gradient. Lines drawn 

perpendicular to the water-table contours approximate the direction of groundwater flow (fig. F.2). Flow lines delimited in this manner are not exact because they 

assume that the aquifer is isotropic (that is, aquifer materials allow water to move 

with equal efficiency in all directions), which is often not the case, and because 

they do not reflect the vertical component of ground-water movement (Domenico 

and Schwartz, 1990). However, such flow lines generally are reasonably representative of ground-water-flow directions, particularly in the upper part of the aquifer. 

Changes in flow directions through time can be determined by comparing groundwater-level maps constructed using water-level measurements from different time 

periods. Flow directions may change as the result of sustained ground-water pumping, which can lower water levels both locally and regionally.

Areas where water recharges to and discharges from the aquifer can be inferred 

from the configuration of water-table contours. The water table slopes from areas 

of recharge to areas of discharge. Where water-table contours bend across a stream 

channel to form a “V” pointing downstream, the stream is losing water to (recharging) the aquifer and ground-water flow is away from the stream (fig. F.3). Conversely, where the contours bend to form a “V” pointing upstream, the aquifer is 

discharging water to the stream and ground-water flow is toward the stream. If 

there is no deflection of the water-table contours across a stream channel, there 

may be little or no interaction between the stream and the aquifer or the type of 

interaction may not be determined from the available data.

The spacing of water-table contours with a defined contour interval also provides 

important information about the hydraulic gradient of the aquifer, which is the 

difference in the elevation of the water table over a known horizontal distance 

(fig. F.1), and is a necessary component in determining how fast ground water 

moves through the aquifer. Differences in the hydraulic gradient (spacing in the 

water-table contours) across an area of interest generally indicate differences in the 

physical properties of the aquifer. For example, a flatter hydraulic gradient (greater 

spacing between contours) often indicates an area of larger aquifer thickness or 

greater hydraulic conductivity, which is a measure of the ability of aquifer materials to transmit water.

EXPLANATION

Water-table contour—Shows elevation

 of water table. Interval 10 feet.

 Datum is sea level

4850

Direction of ground-water flow

Losing stream Gaining stream

4850

4860

4870

4850

4860

4870

Figure F.3.—Examples of water-table 

contours and directions of ground-water 

flow in the vicinity of losing and gaining 

streams. Streamflow is toward bottom of the 

diagram.
50

Modified from Bexfield and Anderholm (2000)

Rio Puerco

Jemez

River

Rio Salado

GRANDE 

RIO 

GRANDE 

RIO Cochiti Lake

McKINLEY CIBOLA

VALENCIA

SOCORRO

TORRANCE

SANTA FE

BERNALILLO

SANDOVAL

EXPLANATION

Middle Rio Grande Basin Major fault located in the vicinity of

 a large hydraulic discontinuity

Rio Grande inner valley

Water-level contour—Interval, in feet,

is variable. Dashed where inferred.

Datum is sea level

Area of apparent hydraulic discontinuity

 not located near a known fault

0 20 40 MILES

0 20 40 KILOMETERS

35°

34°45'

34°30'

35°15'

35°30'

107°15' 107° 106°45' 106°30' 106°15'

5400

5500

5300

5600 5500

5500

5400

5300

5200

5100

5000

4850

4825

4875

4900

4800

4700

4725

4750

4775

4900 5200

4875

4825 4850

4900

5300

5500 5500

5400 5300

5600

5800

5700

5100

5100

4800

5500

5400

5300

53005500

5200

5100

5000

4875

5300

5400

5200

5200

5100

5400 5500

5600

5900

58005700

5200

5300

5100

5050

5000

4900

4925

4975

4975

4950

5000

5600

5700

5200

5500

5800

San Ysidro

Cochiti

Santo Domingo

San Felipe

Bernalillo

Albuquerque

Isleta

Los Lunas

Belen

Bernardo

San Acacia

Corrales Rio Rancho Sierra Nacimiento

Jemez

Mountains

Manzano Mountains

Manzanita

Mountains

Los Pinos

Mountains

Ladron

Peak

Sierra Lucero

Mesa

Lucero

Española Basin

San Juan Basin

Sandia Mountains

Figure 4.4.—Ground-water levels that represent predevelopment conditions in the Santa Fe Group aquifer system in the Middle Rio Grande Basin.

A pumping well lowers the ground-water 

level around the well in a funnel-like 

shape known as a cone of depression. 

In more permeable areas of an aquifer, 

the size of the cone of depression is 

smaller. Similarly, at larger pumping 

rates, the cone of depression is larger. 

As the diameter of the cone of depression around a pumped well increases, it 

may intersect other wells, lowering the 

water level in those wells. Because a 

pumped well locally depresses groundwater levels, ground-water-level 

measurements made in a recently 

pumped well show a lower water level 

than the undisturbed static water level 

outside the cone of depression. For this 

reason, ground-water-level measurements are best made in nonpumped 

observation or monitoring wells—

also called piezometers.
51

Thorn, McAda, and Kernodle (1993) combined ground-water-level 

maps of the Albuquerque area by Bjorklund and Maxwell (1961) and of 

Valencia County by Titus (1963) to construct a ground-water-level map for 

most of the Middle Rio Grande Basin that represented conditions in 1960–

61 (fig. 4.5). The effects of ground-water production by City of Albuquerque wells are shown by the presence of circular, closed water-level 

contours on the south side of Albuquerque and large deflections in the 

water-level contours in northeast Albuquerque. For this time period in 

most of the mapped area, the ground-water-level contours indicate water 

Modified from Bjorklund and Maxwell (1961); Titus (1963); Thorn, McAda, and Kernodle (1993)

Cochiti Lake

Sierra

Nacimiento

Jemez

Mountains Manzano Mountains

Manzanita

Mountains

Los Pinos Mountains

Ladron

Peak

Sierra Lucero

Mesa

Lucero

Española

Bas

i

n

San

Juan

Basin

Sandia Mountains

Arroyo

Chico

Rio Puerco Rio Puerco

Jemez River Arroyo de las Calabacillas

Salado Rio

Rio Salado

Jemez Canyon

Reservoir Tijeras Arroyo

San Jose Rio

Cochiti Lake Arroyo Tonque

River Fe

Santa

 Arroyo Abo

Creek

Galisteo

Creek

HellsCanyon Wash RIO

GRANDE RIO 

GRANDE Las

tas er Hu

San

Ysidro

Cochiti

Santo

Domingo

San Felipe

Bernalillo

Rio

Rancho

Albuquerque

Isleta

Los Lunas

Belen

Bernardo

San Acacia

McKINLEY

CIBOLA

VALENCIA

SOCORRO

TORRANCE

SANTA FE

BERNALILLO

SANDOVAL

EXPLANATION

Middle Rio Grande Basin

Rio Grande inner valley

Water-level contour—Interval, in feet,

is variable. Dashed where inferred.

Datum is sea level

0 20 40 MILES

0 20 40 KILOMETERS

35

°30'

35

°15'

35

°

34

°45'

34

°30'

107

°15' 107

° 106

°45' 106°30' 106°15'

5100 5200 5300 5000

5100

5000

5200

4900

5300 5200 5100

5300

5400

5600

5500

5000 4900

4800

4760

Figure 4.5.—Ground-water levels that represent 1960–61 conditions in 

the Santa Fe Group aquifer system in the Middle Rio Grande Basin.
52

movement from the river into the aquifer. Titus (1961) published a groundwater-level map of 1958–61 conditions using much of the same data but 

included areas outside and adjacent to the Middle Rio Grande Basin.

Several ground-water-level maps have been constructed showing 

conditions in the Albuquerque area in the late 1980’s (Summers, 1992) and 

early 1990’s (Thorn, McAda, and Kernodle, 1993). The ground-water-level 

map of the entire Middle Rio Grande Basin showing the most recent conditions was constructed by Tiedeman, Kernodle, and McAda (1998) and 

represents winter 1994–95 conditions (fig. 4.6). Well-defined cones of 

depression in the Albuquerque and Rio Rancho areas and marked distortion 

of water-level contours in the Albuquerque area are visible on this map.

Modified from Kernodle (1998); Tiedeman, Kernodle, and McAda (1998) Sierra Nacimiento

Jemez

Mountains

Manzano Mountains

Manzanita

Mountains

Los Pinos

Mountains

Ladron

Peak

Sierra Lucero

Mesa

Lucero

Española Basin

San

Juan

Basin

Sandia Mountains

McKINLEY

CIBOLA

VALENCIA

SOCORRO

TORRANCE

SANTA FE

BERNALILLO

SANDOVAL

EXPLANATION

Middle Rio Grande Basin

Rio Grande inner valley

Water-level contour—Interval, in feet,

is variable. Dashed where inferred.

Datum is sea level

Arroyo Chico

Rio Puerco

Rio Puerco

Jemez River

Arroyo de las

Calabacillas

Salado

Rio

Rio Salado

Jemez Canyon

Reservoir

Tijeras Arroyo

San Jose 

Rio

Cochiti Lake

Arroyo

Tonque

River Fe

Santa

 Arroyo Abo

Creek

Galisteo

Creek

HellsCanyon Wash

RIO

GRANDE 

RIO 

GRANDE 

Las

tas er Hu

0 20 40 MILES

0 20 40 KILOMETERS

35°30'

35°15'

35°

34°45'

34°30'

107°15' 107° 106°45' 106°30' 106 ̊15'

4,800

4,850

4,850

4,900

4,900

4,900

4,900

4,850

 

5,350

5,350

5,000

5,100

5,100

5,000

5,100

5,300

5,200

5,300

5,500

5,500

5,500

5,400

5,400

5,600

5,100

San

Ysidro

Cochiti

Santo

Domingo

San Felipe

Bernalillo

Rio

Rancho

Albuquerque

Isleta

Los Lunas

Belen

Bernardo

San Acacia

Figure 4.6.—Ground-water levels that represent winter 1994–95 conditions 

in the Santa Fe Group aquifer system in the Middle Rio Grande Basin.

A USGS hydrologist collecting groundwater levels at the Sierra Vista monitoring 

well. Frequent and consistent measurements of ground-water levels are crucial 

for understanding the aquifer system and 

tracking water-level declines.
53

Currently (2002), ground-water levels in the basin are monitored 

through two main programs conducted by the USGS: one in cooperation 

with the New Mexico Office of the State Engineer (NMOSE) and the other 

in cooperation with the City of Albuquerque. The NMOSE program is part 

of a monitoring network of selected wells in 34 areas in New Mexico and 

adjoining States that are measured periodically (usually every 5 years) or 

are equipped with continuous water-level recorders. The Middle Rio 

Grande monitoring area of this program extends from about Jemez Canyon 

Reservoir to about 35 miles south of Socorro and included 123 wells in 

1995 (Wilkins and Garcia, 1995).

Arroyo Chico

Rio Puerco

Rio Puerco

Jemez River

Arroyo de las

Calabacillas

Salado

Rio

Rio Salado

Jemez Canyon

Reservoir

Tijeras Arroyo

San Jose 

Rio

Cochiti Lake

Arroyo

Tonque

River Fe

Santa

 Arroyo

Abo

Creek

Galisteo

Creek

HellsCanyon Wash

RIO

GRANDE 

RIO 

GRANDE 

Las

tas er Hu

San

Ysidro Cochiti

Santo Domingo

San Felipe

Bernalillo

Rio

Rancho

Albuquerque

Isleta

Los Lunas

Belen

Bernardo

San Acacia

McKINLEY

CIBOLA

VALENCIA

SOCORRO

TORRANCE

SANTA FE

BERNALILLO

SANDOVAL

EXPLANATION

Middle Rio Grande Basin

Rio Grande inner valley

Well with hydrograph

shown in figure 4.8

0 20 40 MILES

0 20 40 KILOMETERS

35°30'

35°15'

35°

34°45'

34°30'

107°15' 107° 106°45' 106°30' 106°15'

Dome Road

Tierra

Mirage

Pueblo

of Sandia

Nor

Este

Intel Monitoring Wells

Paseo del Norte

La Luz del Sol City 2 Del Sol

Divider

Four

Hills

West Mesa

Nest 1A Rio Puerco

Trading Post

Rio Bravo Nest 1

Grasslands

Sevilleta National

 Wildlife Refuge

RWP002

Tome

Figure 4.7.—Location of selected wells in the Middle Rio Grande Basin. 

Hydrographs for these wells are shown in figure 4.8.

Electronic equipment used to automatically 

record ground-water levels. The white cylinder 

being held is a pressure transducer that is 

placed below the water surface in a well. As 

water levels fluctuate, the transducer detects 

changes in pressure and transmits the data to 

the electronic recorder.
54

The City of Albuquerque program encompasses the Albuquerque 

Basin (or Middle Rio Grande Basin as defined in this report) and includes 

255 wells. Ground-water levels in these wells are measured by the USGS 

and other agencies, and the measurement interval for wells in the network 

varies from continuous (collected by water-level recorder) to multiyear 

(Rankin, 2000).

Because of the limitations of ground-water levels measured in or 

near production wells, the USGS in cooperation with the City of Albuquerque, NMOSE, and Bernalillo County began a program in 1996 to 

install a number of specialized monitoring wells in the Middle Rio Grande 

Basin. Most of these wells are groups, or nests, of several wells completed 

at different depths in the aquifer. The locations for these wells were chosen 

to be at least 1 mile away from high-capacity production wells, and the 

goal was to monitor changes in the static water level of the aquifer over an 

extended period of time. (Because of the production-well density in much 

of the basin, however, the placement of the monitoring wells can only minimize the short-term fluctuations caused by pumped wells.) Currently 

(2002), 59 such monitoring wells have been installed at 23 sites. Continuous water-level recorders have been installed on nearly all these wells, and 

all have been incorporated into the City of Albuquerque ground-water-level 

monitoring program.

Locations of selected well nests and single wells in the Middle Rio 

Grande Basin are shown in figure 4.7. Hydrographs associated with these 

wells are shown in figure 4.8. Ground-water levels in wells located away 

from pumping centers generally do not show a continually declining trend 

over time, though some variation is present. However, wells located in 

areas near pumping centers have had a general decline in water levels. 

(Because of the high variability of aquifer conditions, not all wells show 

the same trends.)

Seasonal water-level fluctuations can be clearly seen in the hydrographs for three sites: Nor Este, Del Sol Divider, and Rio Bravo nest 1. 

These water-level fluctuations reflect increased municipal pumping from 

nearby wells during the summer months, when demand is greatest, and 

water-level recovery during the winter months, when demand is least. 

Wells completed at different depths at the same site do not always respond 

in the same manner, which indicates that the aquifer is not of uniform 

composition and that vertical water movement may be somewhat restricted.

Hydrographs from the eight sites with multiple wells can be used to 

determine the vertical direction of ground-water flow because water generally flows from areas of high hydraulic head (lesser depth to water) to areas 

of low hydraulic head (greater depth to water). Thus, at five sites (such as 

Paseo del Norte nest 1) flow appears to be downward; at three sites (such as 

West Mesa nest 1A) flow generally appears to be upward.

A graph showing water levels over time 

at a single site is known as a 

hydrograph. Hydrographs can be 

constructed for either ground- or 

surface-water levels, and they are a 

common way to visualize water-level 

changes over time. See figure 4.8 for 

examples of hydrographs.

The USGS monitoring well at Sister Cities 

Park.
55

Deep (1,305 feet)

Medium (1,025 feet)

Shallow (535 feet)

Dome Road

592.0

592.5

593.0

593.5

594.0

594.5

Tierra Mirage

400

410

420

430

440

450

460

470

480

490

Pueblo of Sandia

470

472

474

476

478

480

482

484

486

488

490

DEPTH TO WATER, IN FEET BELOW LAND SURFACE

1998 1999 2000 2001

1998 1999 2000 2001

1982 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 2001

210

215

220

225

230

235

240

245

250

255

260 1995 1996 1997 1998 1999 2000 2001

Intel monitoring wells A1, A3, A4

Paseo del Norte nest 1

10

20

30

40

50

60

DEPTH TO WATER, IN FEET BELOW LAND SURFACE

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

Nor Este

520

525

530

535

540

545

550

555

560

565

570 1997 1998 1999 2000 2001 0

Deep (1,200 feet)

Medium (710 feet)

Shallow (275 feet)

Deep (1,524 feet)

Medium (1,193 feet)

Shallow (608 feet)

A4 (660 feet)

A3 (440 feet)

A1 (250 feet)

Figure 4.8.—Water levels in selected wells in the Middle Rio Grande Basin. Water 

levels for separate wells in a single well nest are differentiated by total well depth.
56

0

50

100

150

200

250

320

330

340

350

360

3700

10

20

30

40

50

60

70

DEPTH TO WATER, IN FEET BELOW LAND SURFACE

City 2

Del Sol Divider

La Luz del Sol

1996 1997 1998 1999 2000 2001

1978 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 2001

1956 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 2001

Deep (1,567 feet)

Medium (842 feet)

Shallow (420 feet)

8.0

8.5

9.0

9.5

10.0

10.5

11.0

11.5

12.0

875

880

885

890

895

9000

10

20

30

40

50

60

70

DEPTH TO WATER, IN FEET BELOW LAND SURFACE

1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996

Four Hills

Rio Bravo nest 1

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

West Mesa nest 1A

Deep (1,175 feet)

Shallow (1,049 feet)

Deep (148.5 feet)

Medium (103.8 feet)

Shallow (38.4 feet)

Figure 4.8.—Water levels in selected wells in the Middle Rio Grande Basin. Water 

levels for separate wells in a single well nest are differentiated by total well 

depth—Continued.
57

130

135

140

145

150

155

160

165

170

175

180

DEPTH TO WATER, IN FEET BELOW LAND SURFACE

244

245

246

247

248

249

250

251

252

253

254

0

20

40

60

80

100

120

Grasslands

1960 1965 1970 1975 1980 1985 1990 1995 2000

1960 1965 1970 1975 1980 1985 1990 1995 2000

1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

Rio Puerco Trading Post

RWP002

124

126

128

130

132

134

136

138

140

142

DEPTH TO WATER, IN FEET BELOW 

LAND SURFACE 191

192

193

194

195

196

197

Sevilleta National Wildlife Refuge—Headquarters

1998 2000 1999 2001

1975 1980 1985 1990 1995 2000

Tomé

Deep (1,200 feet)

Medium (710 feet)

Shallow (275 feet)

Figure 4.8.—Water levels in selected wells in the Middle Rio Grande Basin. Water 

levels for separate wells in a single well nest are differentiated by total well 

depth—Continued.
58

Aquifer productivity

The aquifer definition stated previously on page 23 is quite subjective—there is no absolute standard that defines whether a rock unit is 

usable as an aquifer. Other than the presence of potable water, the most 

important characteristics that contribute to the productivity of an aquifer 

are hydraulic conductivity and saturated thickness. 

As mentioned in the previous chapter, sediments in each of the three 

parts of the Santa Fe Group were deposited in a range of different depositional environments that influence the hydraulic conductivity of the aquifer. 

For convenience, the Santa Fe Group is subdivided into units with similar 

characteristics and depositional history—these units are known as lithofacies. Because of their similarities, rock units within a lithofacies tend to 

have similar values of hydraulic conductivity. Thus, maps of lithofacies can 

be converted to maps showing the distribution of hydraulic conductivity in 

an aquifer or hydrostratigraphic units, as discussed in Chapter 3. Such 

maps are a necessary step in the creation of a ground-water-flow model.

Because actual measurements of hydraulic conductivity are scarce, 

any map of the hydraulic conductivity of an aquifer is an approximation at 

best. Zones of estimated values of horizontal hydraulic conductivity (in the 

east-west direction) in the upper part of the saturated zone of the aquifer (as 

used in the ground-water-flow model of McAda and Barroll [2002]), are 

shown in figure 4.9. This map shows that the aquifer beneath eastern Albuquerque has some of the highest hydraulic conductivity in the basin. 

Because Albuquerque’s post-Second World War growth was largely in this 

area, most of the new municipal-supply wells drilled to support the growth 

were completed in an area of high hydraulic conductivity, which led to the 

popular belief that the entire Middle Rio Grande Basin was underlain by a 

very productive aquifer and that the aquifer contained a volume of water 

equivalent to one of the Great Lakes (Albuquerque Living, 1984; Thorn, 

McAda, and Kernodle, 1993; Niemi and McGuckin, 1997).

Because of the large values of hydraulic conductivity, the City of 

Albuquerque has been able to complete wells that yielded large quantities 

of water. This is in stark contrast to other areas of New Mexico that have 

less productive aquifers. For instance, some wells in the Buckman well 

field in Santa Fe are completed in a portion of the Santa Fe Group aquifer 

system with hydraulic conductivity values approximately 100 times less 

than those in Albuquerque (Black and Veatch, 1978; Thorn, McAda, and 

Kernodle, 1993).

Perhaps the most important parameter 

that ground-water scientists use to 

characterize an aquifer is its hydraulic 

conductivity, which is a measure of how 

quickly water can move through a rock 

unit. In English units, hydraulic conductivity is commonly defined as the volume 

of water (in cubic feet) that will move in a 

unit of time (1 day) under a unit of 

hydraulic gradient (1 foot per foot) 

through a unit of area (1 square foot), 

but is simplified to units of velocity 

(distance divided by time or feet per 

day). This report uses feet per day to 

report hydraulic conductivity. The larger 

the value of hydraulic conductivity, the 

more water an aquifer is able to yield to 

wells and springs. Sand and gravel typically have values in the range of 1 to 

10,000 feet per day, whereas silt and 

clay can have values ranging from 

0.0000001 to 1 foot per day. In general, 

the coarser and more uniform the 

aquifer material, the higher the hydraulic 

conductivity (Heath, 1983).

Measurements of hydraulic conductivity 

can be made in several ways, the most 

common methods being aquifer tests, 

laboratory measurements of drill cores, 

and air permeameter measurements of 

the rock units where they crop out on 

the surface. All these methods have 

their limitations, and because they are 

expensive, usually only a limited 

number of hydraulic-conductivity values 

are obtained for a given rock unit. Typically, the estimated values of hydraulic 

conductivity for a rock unit are applied 

to large areas of the unit in the subsurface.
59

McKINLEY

CIBOLA

VALENCIA

SOCORRO

TORRANCE

SANTA FE

BERNALILLO

SANDOVAL

EXPLANATION

Middle Rio Grande Basin

Horizontal flow barrier

45

30

15

8

5.3

2

1.5

1

0.5

0.05

Hydraulic conductivity along rows, in feet per day

0 20 40 MILES

0 20 40 KILOMETERS

35°30'

35°15'

35°

34°45'

34°30'

107°15' 107° 106°45' 106°30' 106°15' Sierra Nacimiento

Jemez

Mountains

Manzano Mountains

Manzanita

Mountains

Los Pinos

Mountains

Ladron

Peak

Sierra Lucero

Mesa

Lucero

Española Basin

San Juan Basin

Sandia Mountains

Modified from McAda and Barroll (2002)

Figure 4.9.—Distribution of east-west horizontal hydraulic conductivity in the upper part of the Santa Fe Group aquifer system in the 

ground-water-flow model of McAda and Barroll (2002). View is of 

layer 1 (30 to 50 feet below the predevelopment water table).

Hydraulic conductivity in a rock unit 

usually differs in the horizontal and 

vertical directions, a property referred to 

as anisotropy. Sedimentary deposits, 

such as in the Middle Rio Grande 

Basin, are usually deposited in a series 

of beds with varying grain sizes. This 

bedding is responsible for lower 

hydraulic-conductivity values (by as 

much as several orders of magnitude) 

in the vertical direction. Generally, rock 

units with smaller values of hydraulic 

conductivity control vertical hydraulic 

conductivity; rock units with larger 

values of hydraulic conductivity control 

horizontal hydraulic conductivity 

(Ingebritsen and Sanford, 1998). The 

difference between vertical and horizontal hydraulic conductivity also 

varies with the scale on which it is 

examined: the greater the thickness or 

areal extent of the rock unit, the greater 

the difference tends to be (Freeze and 

Cherry, 1979).
60

Ground-water quantity

One of the most common questions about the Santa Fe Group 

aquifer system in the Middle Rio Grande Basin is “How much water is 

left?” This question is difficult to answer or, perhaps, the answer is of little 

use. It is comparatively easy to make assumptions about the porosity and 

saturated thickness of the Santa Fe Group aquifer system and thus estimate 

a volume of water. However, the composition of the aquifer remains an 

educated guess in much of the basin, and little is known about the water 

quality in much of the aquifer. In addition, silty units with large amounts of 

clay and low values of hydraulic conductivity will not conduct usable quantities of water to wells, so the water contained in these deposits is virtually 

unobtainable. Thus, any estimate of the volume of water remaining in the 

aquifer would include large volumes that are unusable or unobtainable, and 

a large uncertainty would be associated with the estimate.

Water use in the basin

At the current time (2002), the main direct consumptive use of 

surface water in the Middle Rio Grande Basin is irrigation in the inner 

valley of the Rio Grande. Water is also consumed by reservoir evaporation, 

recharge to ground water, and evapotranspiration by riparian vegetation. 

Other nonconsumptive uses include recreation, esthetics, and ceremonial 

use by Native Americans. 

Ground water from the Santa Fe Group aquifer system is currently 

(2002) the sole source of water for municipal supply and domestic, 

commercial, and industrial use in the Middle Rio Grande Basin. The 

municipalities of Bernalillo, Rio Rancho, Albuquerque, Bosque Farms, Los 

Lunas, and Belen have water-supply wells and distribution systems. A 

number of smaller communities such as Algodones and Cochiti Lake have 

formed Mutual Domestic Water Consumers Associations (MDWCA) to 

provide a public supply of water. Several private utilities such as Sandia 

Peak Utility Company or New Mexico Utilities Incorporated serve single 

or multiple subdivisions or parts of municipalities. Most of the pueblos in 

the Middle Rio Grande Basin have public-supply wells that serve at least 

part of the pueblo. Kirtland Air Force Base in southeast Albuquerque uses 

its own supply wells. A large number of domestic-supply wells in the basin 

furnish water for single households. In addition, small production wells 

scattered throughout the basin supply water for livestock. Finally, a number 

of commercial firms have their own wells to provide ground water for 

industrial use, the largest being Intel Corporation in Rio Rancho.

Every 5 years the NMOSE compiles and publishes water-use estimates for New Mexico, aggregated by counties and river basins. A 

summary of water use from 1995 estimates in the seven counties that make 

up the Middle Rio Grande Basin is listed in table 4.2 (Wilson and Lucero, 

1997). Neither county boundaries nor river-basin boundaries correspond to 

the boundaries of the Middle Rio Grande Basin, so estimates based on 

entire counties overestimate water use. However, the estimates are useful 

for a rough comparison of the source and use of water in each county. The 

relative ground- and surface-water use by category for the counties in the 

Middle Rio Grande Basin is shown in graph form in figure 4.10.

Porosity is the ratio of openings (or 

voids) to the total volume of a rock, 

such as between sedimentary grains or 

within fractures, and is usually 

expressed as a percentage. Such openings may not be connected; thus, a rock 

with significant porosity may have a low 

value of hydraulic conductivity. In 

general, the more uniform the rock 

material, the greater the porosity. Additionally, fine-grained materials tend to 

be better sorted than coarser materials. 

Thus, sands typically have porosity 

values in the range of 25 to 50 percent, 

whereas clays typically vary between 

40 and 70 percent. As shown on 

page 58, this relation between fine- and 

coarse-grained materials is opposite of 

that seen in typical values of hydraulic 

conductivity (Freeze and Cherry, 1979; 

Heath, 1983).

Saturated thickness is the thickness of 

the aquifer saturated with water. In an 

unconfined aquifer, the saturated thickness varies with the position of the 

water table.
61

Table 4.2.—Water withdrawal estimates during 1995 for counties in the Middle Rio Grande Basin

[Wilson and Lucero, 1997] 

County Category

Surface-water 

withdrawal

(acre-feet)

Ground-water 

withdrawal

(acre-feet)

Total

withdrawal

(acre-feet)

Bernalillo Public water supply 0.00 135,467.80 135,467.80

Domestic 0.00 2,162.33 2,162.33

Irrigated agriculture and livestock 65,261.43 4,661.87 69,923.30

Commercial, industrial, mining, and power generation 0.00 5,107.96 5,107.96

Reservoir evaporation 0.00 0.00 0.00

 County totals: 65,261.43 147,399.96 212,661.39

Cibola Public water supply 0.00 2,840.01 2,840.01

Domestic 0.00 968.76 968.76

Irrigated agriculture and livestock 3,131.31 2,534.07 5,665.38

Commercial, industrial, mining, and power generation 0.00 407.42 407.42

Reservoir evaporation 1,080.00 0.00 1,080.00

 County totals: 4,211.31 6,750.26 11,961.57

Sandoval Public water supply 125.95 15,201.07 15,327.02

Domestic 0.00 2,529.00 2,529.00

Irrigated agriculture and livestock 54,629.41 1,166.95 55,796.36

Commercial, industrial, mining, and power generation 10.00 1,987.60 1,997.60

Reservoir evaporation 15,033.00 0.00 15,033.00

 County totals: 69,798.36 20,884.62 90,682.98

Santa Fe Public water supply 5,365.55 10,039.81 15,405.36

Domestic 0.00 2,341.46 2,341.46

Irrigated agriculture and livestock 18,971.28 13,766.43 32,737.71

Commercial, industrial, mining, and power generation 19.54 544.09 563.63

Reservoir evaporation 143.00 0.00 143.00

 County totals: 24,499.37 26,691.79 51,191.16

Socorro Public water supply 0.00 2,183.55 2,183.55

Domestic 0.00 323.23 323.23

Irrigated agriculture and livestock 122,610.61 38,596.13 161,206.74

Commercial, industrial, mining, and power generation 0.00 1,079.76 1,079.76

Reservoir evaporation 7,570.00 0.00 7,570.00

 County totals: 130,180.61 42,182.67 172,363.28

Torrance Public water supply 0.00 982.72 982.72

Domestic 0.00 745.39 745.39

Irrigated agriculture and livestock 29.82 45,449.74 45,479.56

Commercial, industrial, mining, and power generation 0.00 104.66 104.66

Reservoir evaporation 0.00 0.00 0.00

 County totals: 29.82 47,282.51 47,312.33

Valencia Public water supply 0.00 4,917.37 4,917.37

Domestic 0.00 3,302.98 3,302.98

Irrigated agriculture and livestock 182,737.03 9,361.22 192,098.25

Commercial, industrial, mining, and power generation 0.00 1,116.73 1,116.73

Reservoir evaporation 0.00 0.00 0.00

 County totals: 182,737.03 18,698.30 201,435.33

Totals Public water supply 5,491.50 171,632.33 177,123.83

Domestic 0.00 12,373.15 12,373.15

Irrigated agriculture and livestock 447,370.89 115,536.41 562,907.30

Commercial, industrial, mining, and power generation 29.54 10,348.22 10,377.76

Reservoir evaporation 23,826.00 0.00 23,826.00

 Total for all counties: 476,717.93 309,890.11 786,608.04
62

Surface-water withdrawals by category

Agricultural and 

livestock

94%

Reservoir

evaporation

5%

Commercial and 

industrial

<1%

Public water

supply

1%

Ground-water withdrawals by category

Domestic

4%

Agricultural and 

livestock

37%

Public water 

supply

56%

Commercial and industrial 

3%

Data from Wilson and Lucero (1997)

Public water supply

EXPLANATION

Domestic

Agricultural and livestock

Commercial and industrial

Reservoir evaporation

Figure 4.10.—Water withdrawal estimates by category for surface and 

ground water during 1995 for counties in the Middle Rio Grande Basin. 

See table 4.2 for the data by county.
63

One of the most important data gaps in our understanding of the 

water resources in the Middle Rio Grande Basin is an exact accounting of 

ground-water withdrawals. The NMOSE requires a permit for the 

construction of all water wells and, in many cases, each well must be 

metered and the volume of water produced must be reported. However, 

production data that are reported are often incomplete or production totals 

are combined for a number of wells. Consequently, the locations and 

amounts of much of the ground-water withdrawal in the basin are poorly 

constrained estimates.

The NMOSE permits as much as 3 acre-feet per year to be withdrawn from single household domestic or stock wells, though pumpage 

does not have to be reported for either these wells or wells on pueblo lands. 

Consequently, no production information is available for a large number of 

wells in the basin. In addition, only about 60 to 70 percent of permits 

issued for these types of wells result in a completed well (Larry Webb, 

City of Rio Rancho, oral commun., 2000). Thus, the number of domesticsupply and stock wells and the amount of ground water pumped from them 

in the Middle Rio Grande Basin are unknown. 

Wilson and Lucero (1997) estimated the volume of water pumped 

from domestic-supply wells by county (table 4.2) by multiplying the population not served by municipal or private water systems in an area by an 

average per capita use of 85 gallons per day (0.095 acre-foot per day). In 

addition, communities such as Bosque Farms encourage the construction 

of domestic-supply wells by stipulating that municipally supplied water 

cannot be used for outside watering. The large number of unmetered 

domestic-supply wells in communities served by municipal water probably 

leads to underestimation of per capita water use in those communities. 

Wilson and Lucero (1997) used a similar process for estimating groundwater pumping for livestock uses, though in table 4.2, it is grouped with 

irrigated agriculture.

Water budgets

A water budget is essentially an accounting of water and its movement in a hydrologic system. It can be as simple as a few numbers representing water added to and subtracted from the system or as complex as a 

numerical simulation of the hydrologic system. This system can range in 

scale from global to site specific and may include only ground water, only 

surface water, or both. A water budget is a useful tool for helping waterresource scientists and managers conceptualize the hydrologic system. 

Because some of the inflows and outflows from the system cannot be 

measured directly, however, they must be estimated. Thus, the resulting 

water budget is only an approximation of the physical system, and the 

measured inflow and outflow totals may not balance exactly. 

Several water budgets have been developed for the Middle Rio 

Grande Basin with varying ranges of complexity and with different areas 

of emphasis. Water budgets by Thorn, McAda, and Kernodle (1993), 

Gould (1995), and the Action Committee of the Middle Rio Grande Water 

Assembly (1999) are quite comprehensive because they address the 

surface- and ground-water components of the hydrologic system. The 

essential values for inflows, outflows, and indirect parameters of the 

hydrologic system are the same for these three budgets, though the latter 

The USGS streamflow-gaging station on 

the Rio Grande at San Felipe. Such gaging 

stations provide critical streamflow data for 

water budgets and water management. 
64

Modified from the Action Committee of the Middle Rio Grande Water Assembly (1999)

Pumping from aquifer (all wells)

170 Septic tank return flow

10

Consumption (evaporation)

90

Mining deficit

70

Riparian

evapotranspiration

135

(range 75–195)

Springs

and

seeps

220

Evaporation from Elephant Butte Reservoir

140

(range 41–228)

Albuquerque

stormwater

inflow

5

Mountain-front and

tributary recharge

110

Ground-water

underflow into the basin

40

San Juan-Chama Project inflow

55

Tributary inflow (gaged)

95

Municipal

wastewater

70

To downstream users

(range 300–1,435)

Rio Grande

inflow

1,100

Open-water evaporation

above San Acacia

60

(range 30–90)

Irrigated agriculture

and valley-floor turf

(above San Acacia)

100

(range 70–130)

Otowi 

streamflowgaging

station

1,150

(range

300 - 2,200)

San 

Acacia

streamflowgaging

station

Elephant

Butte

Dam

Various

water

users

Riparian evapotranspiration,

irrigated agriculture, and

open-water evaporation

(below San Acacia)

100

(range 80–180)

Recharge

to aquifer

(above

San Acacia)

295

All numbers are in acre-feet. Values are annual average (rounded).

Natural variability is large for most values. Some, but not all,

variabilities are shown.

70

Deep

aquifer

Shallow

aquifer

Water delivery calculated from this water-budget analysis: 850

Average water deliveries from Rio Grande Compact records (1972–97): 729

Average water deliveries mandated by the Rio Grande Compact: 786

Average Elephant Butte effective supply (delivery plus change in storage): 799

two reports used a slightly different areal extent of the Middle Rio Grande 

Basin. A report by S.S. Papadopulos and Associates, Inc. (2000) attributes 

differences among the budgets to differing timeframes and to whether the 

ground- or surface-water system was emphasized. A new comprehensive 

water budget was not done as part of the USGS Middle Rio Grande Basin 

Study because of the relative agreement among these water budgets. The 

water budget for the Rio Grande between the Otowi streamflow-gaging 

station and Elephant Butte Dam (fig 3.1), as developed by the Action 

Committee of the Middle Rio Grande Water Assembly (1999), is shown in 

figure 4.11.

Figure 4.11.—Middle Rio Grande water budget for the reach from the Otowi stream-gaging station to Elephant Butte 

Dam as prepared by the Action Committee of the Middle Rio Grande Water Assembly (1999). Annual values are 

averages for 1972–97.
65

The ground-water-flow model of McAda and Barroll ( 2002) 

produced the latest ground-water-specific water budget of the Middle Rio 

Grande Basin. Previous versions of ground-water-specific water budgets 

were presented by Kernodle and Scott (1986); Kernodle, Miller, and Scott 

(1987); and Kernodle, McAda, and Thorn (1995). 

Major legal and institutional controls 

on water in the basin

New Mexico water law forms the basis for water-resource management in the Middle Rio Grande Basin. Based on Spanish water law (as 

developed in the generally arid climate of Spain), its main feature is the 

ownership of unappropriated surface and ground water by the public (to be 

administered by the State). Also called the doctrine of prior appropriation, 

the first person to put the water to beneficial use has the appropriation right 

to that water before the users of subsequent claims, sometimes summarized as “first in time, first in right.” Water rights are permitted by the State 

on the basis of “beneficial use,” including irrigation, livestock, municipal, 

domestic, and industrial uses. Rights are issued for “consumptive” use, 

though they sometimes take into account water returned to the stream for 

use by others. Rights are also issued by date of their permit application, 

with older (or senior) rights receiving priority. For rights claimed prior to 

enactment of the New Mexico Water Code in 1907 (or the declaration of a 

ground-water basin), the priority date is when the water was first put to 

beneficial use; these rights are called “vested.” Water users with pre-1907 

rights are not required to have a water-use permit unless changes are made 

in use or withdrawal. Water-use permits issued later cannot impair older 

rights; thus, during times of low flow, there may be no water remaining for 

the more junior users after holders of the oldest rights receive their water. 

Water rights cannot be detrimental to the public welfare and cannot be 

wasteful of water. If a water right is not put to beneficial use for 4 years 

(with some exceptions), after notice and an additional year, it expires and 

reverts to the public, though water rights may be transferred as long as 

other claims are not affected. Nearly all uses are considered beneficial, 

regardless of the economic value produced by the use (with the exception 

of willful waste). Currently (2002), New Mexico law does not recognize 

water remaining in a stream for the preservation of plants and animals as a 

beneficial use (Harris, 1984; Niemi and McGuckin, 1997).

In 1927 and 1931, the New Mexico Legislature included ground 

water in certain State Engineer-demarcated “declared basins” to be under 

prior appropriation regulations as well, thus subjecting it to similar laws 

as surface water. In 1956, the NMOSE declared the Rio Grande Underground Water Basin, thus formally bringing the development of ground 

water in the basin under the jurisdiction of the State. An important change 

in the laws affecting ground water was made in the 1999 New Mexico 

legislative session when the Ground Water Storage and Recovery Act was 

passed to allow local governments to store surface water underground by 

artificial recharge and to later withdraw that water for beneficial use.

The sovereignty of the pueblos in New Mexico differs from that of 

other Indian tribes in the United States, largely because the Spanish and 

Mexican governments recognized their sovereignty prior to New Mexico’s 

The Middle Rio Grande Conservancy District 

diversion dam on the Rio Grande at Isleta 

Pueblo. This structure diverts water from the 

Rio Grande for irrigation between Isleta and 

San Acacia.
66

incorporation into the United States. Pueblo water rights are not subject to 

New Mexico water law, and some obviously predate 1907. Because of 

these and other issues, the extent of pueblo water rights is currently (2002) 

unknown, though the collective recognized rights of the pueblos are 

18,579 acre-feet of consumptive use (Niemi and McGuckin, 1997). (For 

the purpose of comparison, tables 4.1 and 4.2, in addition to figure 4.11, 

may be used to gain an idea of the significance of the water volumes 

discussed in this section.) 

In 1925, after lobbying by the local community, the Middle Rio 

Grande Conservancy District (MRGCD) was formed as a political subdivision of the State in response to the reduction of productive farmland 

(mainly due to waterlogging) and an increase in flooding in the Middle Rio 

Grande Basin. The MRGCD, in cooperation with the Bureau of Reclamation and U.S. Army Corps of Engineers, has constructed flood and irrigation structures along the river and is responsible for delivering Rio Grande 

water to irrigators in the area between Cochiti Dam and San Marcial, about 

43 miles downstream from San Acacia. The MRGCD delivers most of the 

surface water for consumptive use in the Middle Rio Grande Basin by 

delivering irrigation water to Cochiti, Santo Domingo, San Felipe, Santa 

Ana, Sandia, and Isleta Pueblos as well as many other irrigators with vested 

or senior water rights. The MRGCD claims water rights to irrigate 

123,267 acres with 2.1 acre-feet of water per year, for a total consumptive 

use of 258,861 acre-feet per year (Bullard and Wells, 1992; Niemi and 

McGuckin, 1997).

Though many communities, subdivisions, and individuals withdraw 

water from the Santa Fe Group aquifer system, the largest user of ground 

water in the Middle Rio Grande Basin is the City of Albuquerque. Consequently, its water-management strategy is of the most importance. Since 

the 1960’s, Albuquerque’s water plan has consisted of meeting water 

demand solely by pumping ground water. The scientific understanding of 

the hydrogeology of the Middle Rio Grande Basin in the 1960’s suggested 

that seepage from the Rio Grande replenished the water in the aquifer withdrawn by pumping. To this end, Albuquerque began acquiring and retiring 

surface-water rights to offset the perceived depletion of the river caused by 

ground-water withdrawals. A substantial portion of this water was obtained 

with the purchase of 42,700 acre-feet annually of San Juan-Chama Project 

water. The revised understanding of the hydrogeology of the basin, 

including the connection between the Rio Grande and Santa Fe Group 

aquifer system, spurred Albuquerque to revise its water-use strategy: in 

addition to the direct use of the San Juan-Chama Project water, this revised 

plan calls for significant conservation and water reuse/recycling (City of 

Albuquerque Public Works Department, 1997b).

Rio Grande Compact

Perhaps the most important single document governing flow in the 

Rio Grande is the Rio Grande Compact—an agreement between Colorado, 

New Mexico, Texas, and Mexico that attempts to allocate the water in the 

Rio Grande upstream from Fort Quitman, Texas, in a fair and impartial 

manner. Though Congress gave permission to negotiate the Compact in 

1923, the three States and Congress did not approve it until 1939. The 

Kellner jetties in the bosque near Paseo del 

Norte. More than 100,000 Kellner jetties 

have been installed upstream from 

Elephant Butte Reservoir for bank stabilization (Bullard and Wells, 1992).
67

Compact is overseen by a board of commissioners with representatives 

from the three States and is chaired by a nonvoting Federal representative 

appointed by the President. The main feature of the Compact is explicit 

water-delivery requirements by the upstream State to the downstream State 

and Mexico. Since the Compact went into effect in 1939, there have been a 

number of years in which Colorado and New Mexico have been unable to 

meet their downstream obligations and have consequently been in debt 

(Bullard and Wells, 1992).

San Juan-Chama Transmountain Diversion Project

Though the San Juan-Chama Transmountain Diversion Project is 

outside the Middle Rio Grande Basin, it contributes to the amount of water 

that flows through the basin (fig. 4.12). In 1971, the San Juan-Chama 

Project was completed to move water from the Colorado River Basin over 

the Continental Divide into the Rio Grande Basin. On the Rio Blanco in 

Colorado, the Blanco Diversion Dam and the Blanco Tunnel convey water 

to the Oso Tunnel. On the Little Navajo River, the Little Oso Diversion 

Dam diverts water into the Oso Tunnel. On the Navajo River, the Oso 

Diversion Dam diverts water into the Azotea Tunnel, where it is joined 

with water from the Oso Tunnel. The Azotea Tunnel then moves the water 

into the Rio Chama Basin in New Mexico. Once in the Rio Chama Basin, 

San Juan-Chama Project water is stored in Heron and El Vado Reservoirs 

(Bureau of Reclamation, 2001d). The San Juan-Chama Project is authorized to divert a maximum of 270,000 acre-feet in any year, limited to a 

total of 1.35 million acre-feet in any 10-year period. The governmental 

agencies that have contracted with the U.S. Department of the Interior for 

San Juan-Chama Project water include the U.S. Department of Energy, 

Albuquerque, MRGCD, Santa Fe Metropolitan Water Board, Española, 

Taos, Twining, Pojoaque Valley Irrigation District, Los Lunas, and Bernalillo. The Bureau of Reclamation controls the remainder of the water, some 

of which is used to offset evaporation losses from the permanent pool at 

Cochiti Lake. Though San Juan-Chama Project water is generally not 

subject to regulation under the Rio Grande Compact, its release is 

controlled by the Compact under certain conditions (Bullard and Wells, 

1992).

Endangered species

The declaration by the U.S. Fish and Wildlife Service of the Rio 

Grande silvery minnow (Hybognathus amarus) as an endangered species 

in 1994 and the southwestern willow flycatcher (Empidonax traillii 

extemus) as endangered in 1995 have introduced new constraints on the 

management of water resources in the Middle Rio Grande Basin. For the 

Rio Grande silvery minnow, critical habitat has been proposed for the river 

reach immediately downstream from Cochiti Dam to near San Marcial, 

about 43 miles downstream from San Acacia, though 95 percent of the 

Rio Grande silvery minnow. (Courtesy of 

U.S. Fish and Wildlife Service.)
68

Modified from City of Albuquerque Public Works Department (1997a)

107 ̊ 106 ̊

37 ̊

36 ̊

35 ̊

CONTINENTAL

DIVIDE

Albuquerque

Española

Chama

COLORADO

NEW MEXICO

El Vado Reservoir

Heron Reservoir

Cochiti Lake

Abiquiu Reservoir

San

Juan River

GRANDE

RIO

GRANDE

RIO

Chama

Rio

Blanco

Rio

Navajo River

0 10 20 30 MILES

0 10 20 30 KILOMETERS

Azotea Tunnel

Oso Tunnel

Blanco Diversion Dam Blanco Tunnel

Little Oso Diversion Dam

Oso Diversion Dam

Figure 4.12.—Diversion dams and tunnels of the San Juan-Chama 

Transmountain Diversion Project.

Southwestern willow flycatcher. (Courtesy 

of Suzanne Langridge, USGS.)
69

extant population is concentrated downstream from the San Acacia diversion dam (Soussan, 2000). Among the actions proposed for its preservation 

and recovery are maintenance of minimum streamflows through certain 

reaches of the river and operation of reservoirs on the Rio Grande to more 

closely mimic natural streamflow conditions (U.S. Fish and Wildlife 

Service, 1999). 

The population of the southwestern willow flycatcher has declined 

primarily because of the loss of native riparian vegetation, though in 

Southwestern States other than New Mexico, the flycatchers have been 

found to nest in areas composed primarily of tamarisk. Parasitism by the 

brown-headed cowbird (Molothrus ater) and predation have also contributed to the population decline (U.S. Fish and Wildlife Service, 2001a). The 

U.S. Fish and Wildlife Service released a draft recovery plan in June 2001 

(U.S. Fish and Wildlife Service, 2001b). The recovery plan prioritizes 

38 implementation tasks including water acquisition, research, water-use 

efficiency gains, and additional regulations.

Water appropriation

Even though water rights in the Middle Rio Grande Basin are 

divided into senior and junior classes, they have not been adjudicated. 

Surface flows of the Rio Grande are considered fully appropriated by the 

NMOSE, and an equivalent surface-water right must be obtained to offset 

any ground-water withdrawals that deplete the river. Because the Rio 

Grande is fully appropriated and additional supply cannot be created for 

new uses, competing water demands in the Middle Rio Grande Basin 

exceed the available supply.

Water-rights adjudication is the process 

that “determines the extent and ownership of each water right in a specific 

geographical area, usually a riverdrainage or ground-water basin” (New 

Mexico Office of the State Engineer, 

2001b). There are two phases to the 

adjudication process in New Mexico: a 

technical phase in which a hydrographic 

survey maps and reports water rights in 

the adjudication area, and a legal 

phase in which the court system determines the amount, priority, and use of 

water to which each right holder is entitled. Because adjudication is complicated, the process can take many 

years; for example, the Upper Pecos 

stream system adjudication was begun 

in 1956 and has yet to be completed 

(New Mexico Office of the State Engineer, 2001a). Currently (2002), only 3 

of the 33 declared ground-water basins 

in New Mexico have been adjudicated 

(New Mexico Office of the State Engineer, 2001a).
70
71

One of the methods scientists use to conceptualize how an aquifer 

functions is to follow a hypothetical particle of water as it enters, moves 

through, and finally leaves the aquifer. In the Santa Fe Group aquifer 

system, such a flow path can be complicated because water enters the 

aquifer in several different settings, moves through the aquifer along a 

variety of paths, and then leaves the aquifer in several different ways. A 

wide variety of methods have been used to differentiate how water 

recharges, moves through, and finally discharges from the aquifer. This is 

critical to understanding how the aquifer operates and, ultimately, how 

much ground-water withdrawal an aquifer can support.

Recharge and underflow—How 

ground water enters the aquifer 

system

There are many processes and settings by which water enters a 

basin-fill aquifer, such as that in the Middle Rio Grande Basin, and they 

can be classified in a number of ways. In this report, recharge is discussed 

by the setting in which it occurs. There are four main settings in which 

water enters the Santa Fe Group aquifer system: mountain fronts and tributaries to the Rio Grande, the inner valley of the Rio Grande, the Rio 

Grande itself, and subsurface basin margins. Water entering the aquifer in 

the first three settings is usually termed recharge, whereas water that enters 

the basin in the subsurface is usually termed underflow.

Mountain-front recharge

Some of the surface water that enters the basin originates as springs 

or precipitation in uplifted areas adjacent to the basin. Some of this water 

is recharged at the basin margin (mountain-front recharge), some is 

recharged to ground water through the bottoms of tributaries and arroyos 

(tributary recharge), some is lost to evaporation and transpiration, and 

some reaches the Rio Grande as surface water. Mountain-front and tributary recharge are often grouped together because determining an exact 

division between the two can be difficult. In addition, ground-water underflow from mountains surrounding the basin is very difficult to quantify and 

is usually included as a component of mountain-front recharge.

Chapter 5: How water moves through the 

aquifer system

Generally speaking, infiltration refers to 

water that moves into the soil, though it 

may never reach the saturated zone 

because of evaporation or transpiration. 

Recharge refers to water that ultimately 

enters the saturated zone and thus 

contributes water to the aquifer.
72

Traditionally, the quantity of mountain-front recharge has been difficult to measure and has often been calculated indirectly through waterbudget or modeling methods. The ground-water-flow models of Kernodle 

and Scott (1986), Kernodle, Miller, and Scott (1987), and Kernodle, 

McAda, and Thorn (1995) relied on unpublished estimates of mountainfront recharge made using a water-yield regression method. These estimates for mountain-front recharge along the east side of the Middle Rio 

Grande Basin were approximately 72,000 acre-feet per year. The mountain-front areas in the southwestern part of the basin (Ladron Peak, Mesa 

Lucero, and the Sierra Lucero) were estimated to contribute about 

7,600 acre-feet per year. A ground-water-flow model by Tiedeman, Kernodle, and McAda (1998) estimated 58,000 acre-feet per year of mountainfront recharge along the east side of the basin. Sanford and others (2001) 

estimated 3,000 acre-feet per year of mountain-front recharge along the 

east side of the basin.

Prior to the model of McAda and Barroll (2002), mountain-front 

recharge estimates were poorly constrained in ground-water-flow models 

of the Middle Rio Grande Basin. Consequently, several studies have been 

done to improve understanding of the process. Anderholm (2000) estimated mountain-front recharge along the east side of the Middle Rio 

Grande Basin using the chloride-balance method and water-yield regression equations developed by other authors. (The water-yield regression 

method calculates only recharge from streams and not underflow from 

aquifers in the mountains.) Anderholm’s recharge estimates ranged from 

about 11,000 acre-feet per year for the chloride-balance method to 

38,000 acre-feet per year for the larger of the two water-yield regression 

estimates. The ground-water-flow model of McAda and Barroll (2002) 

uses the chloride-balance mountain-front-recharge values determined by 

Anderholm (2000). The McAda and Barroll model uses a total value of 

mountain-front recharge for the entire Middle Rio Grande Basin of 

12,000 acre-feet per year.

Another approach to determining mountain-front recharge is to 

make point measurements of infiltration rates at a number of selected 

points along the mountain front and apply these rates to similar settings. 

Though the point measurements may be very precise, a limitation of the 

approach is that the total surface area undergoing recharge must be estimated in order to calculate recharge volumes. As part of the Middle Rio 

Grande Basin Study, several different methods were used to determine 

recharge rates at different points along the margins of the basin 

(see Box G).

The water-yield regression method for 

estimating recharge derives an equation relating precipitation, drainage 

area, and measured streamflow in 

drainages with streamflow gages in 

order to characterize the volume of 

streamflow flowing past the mountain 

front in drainages without streamflow 

gages. It is assumed that all this water 

infiltrates into the aquifer and that evaporation and transpiration are small 

enough to be ignored (Anderholm, 

2000).

The chloride-balance method for estimating recharge uses the concentration 

of chloride in ground water near the 

mountain front compared with the chloride concentration in rainfall. By 

assuming that rainfall is the only source 

of chloride in the ground water (among 

other assumptions), an estimate of 

recharge is calculated. Variations of this 

technique have been applied to arid 

areas throughout the world (Anderholm, 

2000).
73

Using surface- and ground-water temperature, Niswonger and 

Constantz (2001) examined streamflow loss in Bear Canyon at the mountain front to estimate recharge (see Box G). Preliminary results from their 

study indicate that streamflow rarely reaches a distance of 1.2 miles 

beyond the mountain front. When completed, results from this study could 

be used to estimate mountain-front recharge along the Sandia and 

Manzano Mountains.

Ground-water geochemistry and age dating clearly indicate the 

presence of water in the Santa Fe Group aquifer system that originated as 

mountain-front recharge (Plummer and others, 2001) (see Chapter 6). 

Analysis of carbon-14 data in conjunction with the ground-water-flow 

model by Sanford and others (2001) suggests that mountain-front recharge 

is substantially less than estimates from earlier models and the chloridebalance method. Final analysis of these data is ongoing; however, the 

results may be useful for further refinement of mountain-front-recharge 

values.

A common misconception in the Middle Rio Grande Basin is that 

concrete-lined drainage channels in urban areas prevent the recharge of 

stormwater to the aquifer. In fact, away from the mountain front, little or 

no recharge occurs beneath unlined arroyos because the depth to ground 

water is usually several hundred feet. In a study of an unlined part of Grant 

Line Arroyo (in northeast Albuquerque) between 1989 and 1992, Thomas 

(1995) measured soil temperature and other properties at six depths 

beneath the arroyo. Data from September 1989 were typical of the data 

collected: flow in the arroyo following a precipitation event infiltrated to a 

depth between 3.5 and 5 feet, but no deeper. The depth to water beneath 

the study site was approximately 600 feet.

Tributary recharge

Some of the perennial tributaries that flow into the Middle Rio 

Grande Basin infiltrate completely within a short distance of the basin 

boundary (except during periods of precipitation runoff), such as Tijeras 

and Abo Arroyos and the Santa Fe River. Other perennial streams, such as 

the Jemez River and Rio Puerco, flow into the Rio Grande all or most of 

the year. Many arroyos with headwaters in the basin are ephemeral along 

their entire lengths, such as Arroyo de las Calabacillas. Many of the same 

techniques used for the determination of recharge from mountain-front 

streams can be applied to tributary recharge. Streams that have been 

studied in detail to determine recharge rates are Tijeras Arroyo (Thomas, 

1995; Constantz and Thomas, 1996), the Santa Fe River (Thomas, Stewart, 

and Constantz, 2000), Abo Arroyo (Nimmo, Lewis, and Winfield, 2001; 

Stewart and Constantz, 2001), and Bear Canyon (Niswonger and 

Constantz, 2001) (see Box G).

The amount of tributary recharge has been difficult to measure in 

the Middle Rio Grande Basin because many of the streams are ephemeral 

through at least part of their reach and because there are huge uncertainties 

regarding the amount of evaporation and transpiration; hence, this recharge 

has been calculated indirectly through water-budget or modeling methods. 

The ground-water-flow model of Kernodle, McAda, and Thorn (1995) 

estimated annual recharge to be 12,000 acre-feet from the Jemez River and 

Two photographs of Tijeras Arroyo at the Four 

Hills bridge in southeast Albuquerque. The 

upstream view from the bridge shows flowing 

water; the downstream view from the bridge 

taken at the same time shows a dry channel. 
74

One of the most difficult components to 

quantify in the hydrologic budget of a 

basin is the amount of recharge to ground 

water at mountain fronts along the basin 

margins. In the Middle Rio Grande Basin, 

the first estimates made of mountain-front 

recharge either were derived from water 

budgets or ground-water-flow models or 

were calculated as a percentage of the 

ratio of precipitation to drainage area. 

Consequently, recharge estimates were 

regarded as highly uncertain. In response 

to this uncertainty, several projects of the 

Middle Rio Grande Basin Study investigated methods of directly measuring the 

amount of mountain-front recharge in the 

basin.

Research on mountain-front recharge for 

the Middle Rio Grande Basin Study 

occurred at two main sites: Bear Canyon 

and Abo Arroyo. Bear Canyon, east of 

Albuquerque on the west side of the 

Sandia Mountains, is typical of approximately 100 small ephemeral streams 

along the front of the Sandia and 

Manzano Mountains on the eastern 

margin of the basin. (Bear Canyon is also 

known as Bear Arroyo or Bear Canyon 

Arroyo in its lower reaches.) Abo Arroyo, 

entering the basin between the Manzano 

and Los Pinos Mountains, is the largest 

stream in the southeastern part of the 

basin. Multiple methods were used at 

these two sites to allow for comparison of 

the recharge estimates independently 

derived from the different methods.

How mountain-front recharge is studied

James R. Bartolino1 and Jim Constantz2

G

1U.S. Geological Survey, Albuquerque, New Mexico.

2

U.S. Geological Survey, Menlo Park, California.

Arroyo Chico

Rio Puerco

Rio Puerco

Jemez River

Arroyo de las

Calabacillas

Salado

Rio

Rio Salado

Jemez Canyon

Reservoir

Tijeras Arroyo

San Jose 

Rio

Cochiti Lake

Arroyo

Tonque

River Fe

Santa

 Arroyo Abo

Creek

Galisteo

Creek

HellsCanyon Wash

RIO

GRANDE 

RIO 

GRANDE 

Las

tas er Hu

San

Ysidro Cochiti

Santo Domingo

San Felipe

Bernalillo

Rio Rancho

Albuquerque

Isleta

Los Lunas

Belen

Bernardo

San Acacia

McKINLEY

CIBOLA

VALENCIA

SOCORRO

TORRANCE

SANTA FE

BERNALILLO

SANDOVAL

EXPLANATION

Middle Rio Grande Basin

0 20 40 MILES

0 20 40 KILOMETERS Sierra Nacimiento

Jemez

Mountains

Manzano Mountains

Manzanita

Mountains

Los Pinos

Mountains

Ladron

Peak

Sierra Lucero

Mesa

Lucero

Española Basin

San Juan Basin

Sandia Mountains

35°30'

35°15'

35°

34°45'

34°30'

107°15' 107° 106°45' 106°30' 106°15'

Bear Canyon

Tijeras Arroyo

Santa Fe River

Abo Arroyo

Paseo del

 Norte site

Bernalillo

site

Corrales

site

Rio Bravo

 station

Figure G.1.—Locations of study sites for mountain-front recharge 

and water temperature in the Middle Rio Grande Basin.
75

FLOW

TIME

TIME

TEMPERATURE

STREAMFLOW 0

Piezometer

Water table

Water table

3 FEET

NO FLOW

TIME

TEMPERATURE

TIME

STREAMFLOW 0

Stream gage

Piezometer

Stream gage

3 FEET

Temperature has been used to quantify the amount and direction of water 

moving between the surface- and ground-water regimes in the Middle Rio 

Grande Basin along perennial reaches of the Santa Fe River, Tijeras 

Arroyo, and the Rio Grande (fig. G.1 and Box H). However, the use of 

water temperature as a tracer was expanded into the realm of ephemeral 

streams at Bear Canyon and Abo Arroyo. Using vertical-temperature 

measurements below the streambed and surface-temperature measurements 

of the streambed, the downward movement of water and the downstream 

extent of flow in the arroyos were determined (fig. G.2). (See Niswonger 

and Constantz, 2001; Stewart and Constantz, 2001.)

Another technique applied in the Middle Rio Grande Basin was the SteadyState Centrifuge (SSC) method. The method used core samples to determine recharge rates. After a core was collected, it was split into smaller 

samples and the water content of each was measured. These smaller 

samples were then placed in a large centrifuge and spun to simulate gravity 

drainage of water through the sample (though at a much faster rate). By 

applying different amounts of water to the core sample as it was spun in the 

centrifuge, the hydraulic conductivity was measured. The initial water 

content and hydraulic conductivity were then used to calculate a recharge 

rate. Recharge-rate estimates were made for several reaches of Abo Arroyo 

and the upland areas adjacent to the arroyo. (See Nimmo, 1997; Lewis and 

Nimmo, 1998; Lewis, Nimmo, and Stonestrom, 1999; Nimmo, Lewis, and 

Winfield, 2001.) 

Two geochemical methods were used to estimate recharge rates from cores 

collected at Bear Canyon and Abo Arroyo. The first method extracted all 

the water from a core sample (cores from upland areas and dry streambeds 

may yield only miniscule amounts of moisture). Tritium-dating techniques 

were then applied to these water samples to determine when the water 

entered the ground (see Box I). By using the amounts and ages of water at 

different depths, a recharge rate was calculated. The second method calculated recharge rates using chloride and bromide concentrations extracted 

from core samples from different depths, in combination with the water 

content of the sample to calculate recharge rates. (See Stonestrom, Akstin, 

and Michel, 1997; Stonestrom and Akstin, 1998.)

Other indirect methods of quantifying mountain-front recharge have been 

used in the Middle Rio Grande Basin Study. In addition to the groundwater-flow model described in Chapter 7, other geochemical methods have 

been used and are described in Boxes I, K, and N. The application of 

multiple techniques for calculating recharge in the Middle Rio Grande 

Basin has allowed comparison of new techniques that can be applied in 

other desert areas of the world.

Figure G.2.—Temperature compared to 

time at two depths in an ephemeral 

streambed during periods of no flow and 

flow. The top diagram shows a dry 

streambed with a streamflow-gaging station 

(right) recording no flow over approximately 

3 days. On the left, the temperature over the 

same period of time is shown at the 

streambed surface (top) and at the water 

table (bottom). Note that the streambedsurface temperature shows the daily fluctuation in air temperature and that the watertable temperature remains relatively 

constant in the absence of any recharge. 

The bottom diagram shows the same site 

during flow. Note that the surface temperature starts with the same daily variation as 

the top diagram, but with the onset of flow 

(shown by the hypothetical graph of streamflow on the right), the temperature fluctuation is significantly damped. The 

temperature graph for the water table shows 

a spike in temperature after the onset of 

flow, indicating that water is reaching the 

saturated zone as recharge. Gaging 

stations are seldom installed on ephemeral 

streams because of expense, uncertainty 

associated with ephemeral flows, and the 

destructive nature of many of the flow 

events.
76

8,000 acre-feet from the Rio Puerco. The ground-water-flow model of 

Tiedeman, Kernodle, and McAda (1998) estimated 11,000 and 4,000 acrefeet of recharge for the Jemez River and Rio Puerco, respectively. Sanford 

and others (2001) estimated 30 acre-feet per year of recharge from the 

Jemez River and 2,000 acre-feet from the Rio Puerco. 

The ground-water-flow model of McAda and Barroll (2002) uses an 

estimate of 9,000 acre-feet per year of tributary recharge for 1900–99 

(which includes 2,000 acre-feet per year from the Rio Puerco). For the 

Jemez River and Reservoir, they estimated 15,000 and 16,000 acre-feet of 

recharge for predevelopment and 1999 conditions, respectively. The 

substantial difference between the estimates of different models is largely 

due to different approaches to model design and calibration.

Analyses of sediment cores from six locations along Abo Arroyo by 

Nimmo, Lewis, and Winfield (2001) found that recharge varied among 

three reaches defined on the basis of geology. They estimated total recharge 

for the Abo Arroyo drainage between the mountain front of the Manzano 

Mountains and the Rio Grande to be approximately 1,300 acre-feet per 

year, a number that closely agrees with an estimate of 1,280 acre-feet by 

Anderholm (2000) using the chloride-balance method.

As with mountain-front recharge, the use of ground-water chemistry 

and age-dating data has allowed the identification of water in the Santa Fe 

Group aquifer system that originated as tributary recharge (Plummer and 

others, 2001) (see Chapter 6). Currently (2002), these data are still being 

analyzed; however, it is probable that the results will further refine estimates of the sources and amounts of tributary recharge.

Rio Grande and inner-valley recharge

The main sources of recharge to ground water in the inner valley of 

the Rio Grande are infiltration from the Rio Grande, irrigation canals, 

segments of interior drains that are now above the water table, and applied 

irrigation water. Other sources of recharge in the inner valley are infiltration of septic-tank effluent and precipitation (Kernodle, McAda, and 

Thorn, 1995; Anderholm, 1997).

The direction and amount of water flowing between the Rio Grande 

and the Santa Fe Group aquifer system is one of the most important hydrologic issues in the Middle Rio Grande Basin. Not only do the volume and 

direction of flow between surface and ground water affect the amount of 

water in the river, they affect the volume of ground water available in the 

aquifer. In the Albuquerque area, ground-water pumping has lowered 

ground-water levels so that the river loses more flow to ground water than 

it did during predevelopment conditions. However, in the river reaches 

upstream and downstream from Albuquerque, ground-water flow is to the 

river and, thus, the river gains flow from ground-water discharge. This 

latter case is discussed later on page 81. Ground-water recharge from reservoirs in the Middle Rio Grande Basin is usually included as a component of 

river recharge.

During the irrigation season, irrigation water within the inner valley 

of the Middle Rio Grande Basin is diverted from the Rio Grande at three 

points: Cochiti Dam, Angostura, and Isleta (fig. 4.1). Diverted water then 

flows through the inner valley in a series of irrigation canals and smaller 

The interaction between a stream and 

an aquifer can usually be described by 

whether the stream gains water from or 

loses water to the aquifer. A gaining 

stream receives or gains flow from 

ground water. A losing stream is one 

that loses or contributes flow to ground 

water. 

A typical core sample collected for the 

Middle Rio Grande Basin Study.
77

ditches for application to fields. This water recharges ground water, is lost 

to evaporation or evapotranspiration by plants, or is intercepted by interior 

drains and returned to the river. The other main component of the innervalley surface-water network is a system of riverside drains, which are 

deep canals that parallel the river immediately outside the levees. The 

drains are designed to intercept lateral ground-water flow from the river, 

thus preventing waterlogged conditions in the inner valley. Within the 

Middle Rio Grande Basin, riverside drains and levees are present on the 

east bank, and typically both banks, of the river (Kernodle, McAda, and 

Thorn, 1995; Anderholm, 1997).

Because the irrigation system and Rio Grande are linked through a 

complex series of irrigation structures, studying the processes of one 

component without considering the others is difficult. Thus, certain aspects 

of Rio Grande and inner-valley recharge often are combined for investigation. For 1994, the ground-water-flow model of Kernodle, McAda, and 

Thorn (1995) estimated river, canal, and reservoir leakage to ground water 

to be about 247,000 acre-feet; irrigation seepage to ground water to be 

about 28,300 acre-feet; and septic-tank effluent flow to ground water to be 

about 8,220 acre-feet. Similarly, the ground-water-flow model of 

McAda and Barroll (2002) estimated river and reservoir leakage to ground 

water to be 63,000 and 317,000 acre-feet per year for predevelopment and 

1999 conditions, respectively. For 1999, irrigation seepage to ground water 

was estimated to be 35,000 acre-feet in 1999, canal seepage to be 

90,000 acre-feet, and septic-tank effluent flow to ground water to be about 

4,000 acre-feet. A portion of the reservoir seepage is from under Cochiti 

Dam (Blanchard, 1993). The Bureau of Reclamation estimated this underflow to be 35,500 acre-feet per year (Thorn, McAda, and Kernodle, 1993).

Various methods have been used to study water movement in the 

inner valley and between the river and aquifer. These studies include direct 

measurement of flow (such as Bartolino and Niswonger, 1999) and indirect determinations using water-level relations, water budgets, or groundwater-flow models (such as Peter, 1987; and Kernodle, McAda, and Thorn, 

1995). Some of these studies are described in Box H. As with mountainfront recharge, some of these studies are point measurements of water 

movement between the river and aquifer. Though useful for confirming 

recharge rates, some uncertainty can be introduced when extrapolating 

these rates over extended reaches of the river.

Water-chemistry studies using environmental tracers, the presence 

of anthropogenic chemicals, and naturally occurring constituents have 

expanded understanding of water movement between the river and aquifer 

(such as Anderholm, 1997; and Plummer and others, 2001). Water chemistry of the Santa Fe Group aquifer system is discussed in more detail in 

Chapter 6.

Subsurface recharge or underflow

The volume of ground water flowing into a basin from adjacent 

basins is very hard to determine. Often, the volume is determined indirectly from a ground-water-flow model or water budget. Underflow enters 

the Middle Rio Grande Basin from two adjacent basins: the San Juan 

Basin to the northwest and the Española Basin to the northeast 

The headgate of an acequia (or ditch) near 

Paseo del Norte in northern Albuquerque.
78

Arroyo Chico

Rio Puerco

Rio Puerco

Jemez River

Arroyo de las

Calabacillas

Salado

Rio

Rio Salado

Jemez Canyon

Reservoir

Tijeras Arroyo

San Jose 

Rio

Cochiti Lake

Arroyo

Tonque

River Fe

Santa

 Arroyo Abo

Creek

Galisteo

Creek

HellsCanyon Wash

RIO

GRANDE 

RIO 

GRANDE 

Las

tas er Hu

McKINLEY

CIBOLA

VALENCIA

SOCORRO

TORRANCE

SANTA FE

BERNALILLO

SANDOVAL

San

Ysidro Cochiti

Santo Domingo

San Felipe

Bernalillo

Rio Rancho

Albuquerque

Isleta

Los Lunas

Belen

Bernardo

San Acacia

EXPLANATION

Middle Rio Grande Basin Sierra Nacimiento

Jemez

Mountains

Manzano Mountains

Manzanita

Mountains

Los Pinos

Mountains

Ladron

Peak

Sierra Lucero

Mesa

Lucero

Española Basin

San Juan Basin

Sandia Mountains

0 20 40 MILES

0 20 40 KILOMETERS

35°30'

35°15'

35°

34°45'

34°30'

107°15' 107° 106°45' 106°30' 106°15'

Rio Bravo

 station

Alameda

station

Paseo del

 Norte site

Bernalillo

site

Corrales

site

One of the most important questions 

being asked about the hydrology of the 

Middle Rio Grande Basin is how well the 

Rio Grande is hydrologically connected 

to the Santa Fe Group aquifer system. 

Until 1999, the New Mexico Office of the 

State Engineer (NMOSE) used a 

simplistic, theoretical formula derived by 

Glover and Balmer (1954) to calculate the 

volume of water that seeped from the Rio 

Grande into the aquifer in response to 

pumping large volumes of ground water 

(also known as stream or river depletion). 

The ground-water-flow model of the 

Albuquerque Basin by Kernodle, McAda, 

and Thorn (1995) and subsequent revisions by Kernodle (1997, 1998) showed 

that seepage from the Rio Grande into the 

aquifer in response to this pumping is 

much less than the Glover-Balmer equation estimates. In 1999, the NMOSE 

adopted a modified version of the Albuquerque Basin ground-water-flow model 

by Tiedeman, Kernodle, and McAda 

(1998) as the means by which river depletion in response to ground-water pumping 

would be calculated (Barroll, 2001). 

However, the values the ground-waterflow model provides for river depletion 

are derived indirectly and are estimates of 

the volume of streamflow lost to groundwater infiltration.

Several techniques have been used to 

directly measure streamflow loss from the 

Rio Grande. Gould (1994) installed 

permeameters in the active river channel. 

These permeameters were shallow wells 

completed into the top several feet of 

riverbed sand with a bladder of water 

attached to the top. By measuring how 

fast the water drained from the bladder 

How ground-water/surface-water interaction of the Rio 

Grande has been studied

James R. Bartolino1 

1

U.S. Geological Survey, Albuquerque, 

New Mexico.

H

Figure H.1.—Locations of study sites on the Rio Grande for water 

temperature and flood pulses.
79

The volume of water seeping from ground 

water or leaking into the aquifer along river 

reaches can be estimated by comparing 

careful measurements of Rio Grande flow 

and flow in riverside drains at different sites. 

Between December 1996 and February 

1998, during the months of December, 

January, and February, weekly streamflow 

measurements were made at two sites: the 

Rio Grande near Alameda gaging station 

(08329928) and, 16 hours later, the Rio 

Grande at Rio Bravo Bridge gaging station 

(08330150). (The measurements were made 

16 hours apart because that is the approximate traveltime of river water between the 

two stations.) At the Alameda station, there 

is one riverside drain on the east side of the 

river, whereas at the Rio Bravo Bridge 

station, there are drains on both sides of the 

river. For each measurement period, the 

release of water from Cochiti and Jemez 

Canyon Dams was held steady for 

2 days prior to the first measurement and 

during subsequent measurements. Measurements were made in the winter months when 

water was not diverted into the irrigation 

system and flow tended to remain fairly 

constant. In addition, evapotranspiration is at 

a minimum during the winter months. 

Because of uncertainty associated with flow 

measurement in the Rio Grande, three river 

measurements were made and the values 

were averaged (J.E. Veenhuis, U.S. Geological Survey, written commun., 2002).

Bartolino and Sterling (2000) used a qualitative approach to investigating the connection 

between the Rio Grande and the aquifer 

using ground-based electromagnetic 

geophysical surveys along the Rio Grande. 

The electrical properties of the Rio Grande 

flood plain through the Albuquerque area 

were mapped during this study. With these 

data, reaches of the Rio Grande were delineated that were underlain by fine-grained 

deposits that tend to restrict water seepage 

between the river and aquifer. This information was then used in the construction of the 

revised ground-water-flow model of the 

Middle Rio Grande Basin (McAda and 

Barroll, 2002).

into the riverbed, calculations were made of how fast water was seeping 

from the river into the aquifer.

Two studies have used “flood pulses,” in which water-level changes in the 

riverside drains and shallow wells close to the Rio Grande were monitored 

as they responded to large pulses of water released from Cochiti Lake and 

Jemez Canyon Reservoir (figs. H.1 and 4.1) (Pruitt and Bowser, 1994; 

Roark, 1998). Water seepage from the river into the aquifer is fairly 

constant, and it is difficult to measure the influence of the river on the 

aquifer under these constant conditions. By releasing a “controlled flood” 

and raising the water level (or stage) in the river, a pulse of water is sent into 

the aquifer that can be detected in the riverside drains and wells near the 

river. The water-level data are then used with information on the geology of 

the area surrounding the river to construct simple ground-water-flow 

models to interpret the results.

Bartolino and Niswonger (1999) and Bartolino and Stewart (2001) 

measured the temperature of ground water in shallow wells close to the 

river at four sites to determine the direction and rate of flow between the 

river and aquifer system (fig. H.1). Ground water beyond the influence of 

surface water has a relatively constant temperature, whereas surface-water 

temperature fluctuates on daily and seasonal cycles. During the winter 

months, water in the Rio Grande tends to be colder than ground water, and 

in the summer months, Rio Grande water tends to be warmer than ground 

water (fig. H.2). By measuring relatively shallow ground-water temperatures at different depths next to, and distances from, the river, it is possible 

to use the unique temperature pattern, or “signature,” of the changing 

surface-water temperatures and the resulting effects on ground-water 

temperatures to determine the direction and rate of water flow between the 

river and aquifer. Results were interpreted using a heat-transport model.

0

5

10

15

20

25

30

TEMPERATURE, IN DEGREES CELSIUS

Rio Grande

P08—15-foot depth

P07—15-foot depth

P06—13-foot depth

1999

MAR APR MAY JUNE JULY AUG SEPT OCT JAN NOV DEC

2000

FEB MAR APR MAY JUNE JULY

Figure H.2.—Thermographs from Paseo del Norte section showing 

Rio Grande temperature and ground-water temperatures measured in 

wells P06, P07, and P08. P06 is on the east bank of the Rio Grande, P07 

is 900 feet east, and P08 is 1,845 feet from the river and adjacent to the 

Albuquerque Riverside Drain. A delayed response and damping of watertemperature fluctuation can be seen with increasing distance from the 

river as water moves from the Rio Grande to the drain. These characteristics can be used to determine the direction and rate of water flow between 

the river and aquifer.
80

(Thorn, McAda, and Kernodle, 1993). A model of the San Juan Basin by 

Frenzel and Lyford (1982) estimated that approximately 1,200 acre-feet per 

year of ground water moved from the San Juan Basin into the Middle Rio 

Grande Basin as underflow. A model of the Tesuque aquifer system near 

Santa Fe by McAda and Wasiolek (1988) estimated that 12,600 acre-feet 

per year of ground water moved from the Española Basin into the Middle 

Rio Grande Basin. During calibration of their ground-water-flow model of 

the Middle Rio Grande Basin, McAda and Barroll (2002) determined 

underflow from adjacent basins to be 31,000 acre-feet per year, including 

the San Juan and Española Basins, as well as underflow from beneath the 

Jemez Mountains and the area around the Santa Fe River and Galisteo 

Creek. Geochemical methods using both standard water-chemistry and 

ground-water-age data also suggest the occurrence of underflow along the 

western and northern margins of the Middle Rio Grande Basin (Plummer 

and others, 2001).

Flow paths—How ground water 

moves through the aquifer system

Ground water travels from the area where it was recharged, through 

the aquifer, and to the point at which it discharges from the aquifer. The 

path followed by a “parcel” of water as it moves through the aquifer is 

known as a flow path or flow line. The discharge point can be either the 

natural end of the flow path, such as a spring or seep, or a well that intersects the flow path at some intermediate point. As discussed in Box F, 

water flows from areas of high hydraulic head to areas of low hydraulic 

head. Generally, scientists and engineers use ground-water-level maps to 

determine the direction of horizontal ground-water flow. By comparing 

water levels in piezometer nests, the direction of vertical ground-water 

movement can be determined. Ground-water-flow models use these head 

relations to determine overall directions and rates of ground-water movement.

Another method that is useful in determining ground-water movement and flow paths is ground-water age dating. By measuring the concentrations of certain substances and naturally occurring isotope ratios in 

ground water, calculations can be made to determine about when a parcel 

of water entered the aquifer. This method allows estimation of the rate at 

which water is moving through the aquifer. When combined with a groundwater-flow model, age-dating information can help to define the flow paths 

and the amount and rate of recharge.

In the Middle Rio Grande Basin, interpretation of water-level data 

and ground-water-flow modeling led to the conclusion that prior to extensive ground-water development, ground water generally was recharged at 

the basin margins (or entered the basin as underflow) and moved toward 

the inner valley where it was discharged into surface water or evapotranspired (fig. 4.4 and Box F). With population growth and increased groundwater withdrawals in the Albuquerque area, City of Albuquerque production wells interrupted predevelopment flow paths. As ground-water levels 

declined, some flow paths reversed direction and water entered the aquifer 

from the river and moved toward the pumped wells. Predevelopment flow 

paths remain in most areas outside the population centers of the basin.

A piezometer nest consists of multiple 

wells screened at different depths in the 

aquifer at a single location. A piezometer nest may have all the wells in a 

single borehole or may have separate 

boreholes close together.

Isotopes are different forms of the same 

chemical element with the same 

number of protons but different 

numbers of neutrons. The different 

isotopes of an element typically have 

slightly different chemical and physical 

properties that cause changes in their 

relative abundance as the result of 

different environmental processes. 

Isotopes can be naturally occurring, 

manmade, or sometimes both.
81

Recent water-chemistry studies by Plummer and others (2001) and 

Bexfield and Anderholm (2002) suggest that, except close to the basin 

margins, the predominant ground-water-flow direction in the basin has 

historically been north to south. Because water-chemistry patterns develop 

over long periods of time (as much as tens of thousands of years), these 

flow directions likely represent predevelopment conditions and not current 

conditions. Water chemistry of the Santa Fe Group aquifer system is 

discussed in more detail in the next chapter.

Discharge—How ground water 

leaves the aquifer system

Ground water leaves the Santa Fe Group aquifer system several 

ways: through pumpage from wells, seepage into the Rio Grande and 

riverside drains, springs, evapotranspiration, and outflow to the Socorro 

Basin (Kernodle, McAda, and Thorn, 1995; Anderholm, 1997).

Pumpage

As discussed on page 63, the volume and location of ground-water 

withdrawals from wells in the Middle Rio Grande Basin are poorly 

constrained estimates. Table 4.2 shows water-use estimates by county, 

though the data are for whole counties (not only the portion that lies in the 

Middle Rio Grande Basin). The area between Bernalillo and Belen is the 

most densely populated area of the basin; consequently, most of the 

ground-water pumpage occurs in this area. The ground-water-flow model 

of McAda and Barroll (2002) used a value of 150,000 acre-feet per year of 

ground-water withdrawal.

Seepage to drains and the Rio Grande and springs

Most of the seep or spring discharge from the Santa Fe Group 

aquifer system is into the drains of the inner valley or the Rio Grande. 

Because this discharge tends to be diffuse and below the water surface of 

the drains or river, it is difficult to measure and quantify directly. The 

ground-water-flow model of Kernodle, McAda, and Thorn (1995) estimated the flow volumes for 1994 to be 44,400 acre-feet of discharge into 

rivers, canals, and reservoirs and 219,000 acre-feet of discharge into 

drains. For 1999, the ground-water-flow model of McAda and Barroll 

(2002) estimated that 208,000 acre-feet per year of ground water 

discharged to riverside drains and 134,000 acre-feet per year of ground 

water discharged into interior drains. Box H describes other methods that 

have been used to quantify flow between the river and the aquifer.

The Bernalillo Riverside Drain at Bernalillo. 

Such drains form part of a complex irrigation 

network that is intimately linked with the Rio 

Grande and Santa Fe Group aquifer system.
82

1940

800

200

400

600

0

TRITIUM IN PRECIPITATION, DECAYED TO 1997, 

IN TRITIUM UNITS

1960 1980 2000

600

400

200

0

CFC AND SF6 CONCENTRATIONS IN AIR, IN 

PARTS PER TRILLION

Tritium

CFC-113

CFC-11

CFC-12

SF6 (x100)

Environmental tracers are natural and 

anthropogenic (manmade) chemical and 

isotopic substances that can be measured 

in ground water and used to understand 

hydrologic properties of aquifers (Alley, 

1993; Cook and Herczeg, 1999). These 

substances occur in the atmosphere or soil 

and are incorporated into precipitation 

and into water that infiltrates through the 

soil to recharge the aquifer. Different 

types of environmental tracers can 

provide different types of information 

about an aquifer. For example, the 

concentrations of environmental tracers in 

ground water can be used to identify 

water sources, trace directions of groundwater flow, measure the time that has 

elapsed since recharge (ground-water 

age), and interpret environmental conditions that occurred during recharge. The 

most useful environmental tracers in 

hydrologic studies (fig. I.1) do not react 

chemically in the aquifer after recharge, 

have concentrations that vary according to 

source and(or) age of the water, and can 

be measured analytically with sufficient 

accuracy to allow detection in the aquifer. 

Environmental tracers take several forms. 

Some are anthropogenic gases like chlorofluorocarbons (CFC’s, Freon 

compounds). CFC’s, first manufactured in 

the 1930’s for use in refrigeration, air 

conditioners, and many other uses, were 

released into the atmosphere over time. 

Very small quantities have dissolved naturally in water and, because of extremely 

low analytical detection limits, are detectable in ground water recharged since the 

1940’s. Because CFC’s allow scientists to find water that recharged 

recently, they improve the capability in the Middle Rio Grande Basin to 

trace seepage from the Rio Grande and recent recharge from arroyos and 

mountains and to detect leakage from landfills, industrial wastes, and septic 

tanks.

Some environmental tracers differ naturally in their isotopic composition, 

such as isotopes of hydrogen and oxygen in the water molecules themselves or isotopes of sulfur or carbon dissolved in ground water. Isotopes of 

a particular element have the same number of protons in the atomic nucleus 

but different numbers of neutrons. Thus, isotopes have the same atomic 

number but different atomic weights—a difference that permits precise 

Environmental tracers and how they are used to understand 

the aquifer

L. Niel Plummer1 

I

1

U.S. Geological Survey, Reston, Virginia.

Figure I.1.—Concentrations of tritium (3H) in precipitation, chlorofluorocarbons (CFC-11, CFC-12, and CFC-113) in air, and sulfur hexafluoride (SF6) 

in air over North America, 1940–97. The tritium concentrations in precipitation were decayed to 1997 for comparison with tritium concentrations 

(expressed as tritium units [TU]) measured in ground water as part of this 

study. A sample of water containing 1 TU has one tritium atom in 1018

hydrogen atoms—that is, 1:1,000,000,000,000,000,000. CFC and SF6 

concentrations in air are expressed as parts per trillion by volume (pptv). 

One pptv is one unit volume of the gas in 1012 volumes of air—that is, 

1:1,000,000,000,000 by volume.
83

analysis of their relative abundance. On Earth, most of the element 

hydrogen is in the form of 1H (or hydrogen-1), called hydrogen; only 

0.015 percent of all natural hydrogen on Earth occurs as the isotope 2

H, 

called deuterium; and less than 10–14 percent occurs in the form of 3

H, 

called tritium (Coplen, 1993), yet stable isotopes of hydrogen (and oxygen) 

are important environmental tracers in hydrology because their local abundance varies significantly with environmental factors such as temperature 

and altitude of precipitation, source of moisture, amount of rainfall, and 

extent of evaporation.

Stable isotopes of hydrogen and oxygen are particularly useful in the 

Middle Rio Grande Basin because water has recharged the aquifer at 

different altitudes and under different climatic conditions. For example, 

winter precipitation has less deuterium than summer precipitation in the 

basin. Also, ground water originating as seepage from the Rio Grande 

contains water from high-altitude snowmelt in southern Colorado and 

northern New Mexico and has less deuterium than precipitation falling in 

the relatively lower Albuquerque area or even in the Sandia Mountains east 

of Albuquerque. In addition, precipitation that fell 20,000 years ago during 

the last glacial period was colder than today and had less deuterium than 

today’s precipitation (Drever, 1988; Wright, 1989). Therefore, the isotopic 

composition of hydrogen (and oxygen) has large variation in ground water 

of the Middle Rio Grande Basin. In combination with other environmental 

tracers and dissolved substances in ground water, these tracers have been 

used successfully to recognize sources of recharge and trace flow 

throughout the basin (see Box K).

Finally, some environmental tracers are radioactive—that is, they are 

unstable isotopes that radioactively decay naturally into more stable 

isotopes. For example, tritium, the radioactive isotope of hydrogen, is part 

of the water molecule along with hydrogen and deuterium. Tritium, 

produced mostly from above-ground testing of nuclear weapons in the mid1960’s, but also occurring naturally, continues to be in rainfall but undergoes radioactive decay at a known rate (half-life). Every 12.4 years, half of 

the tritium in a given amount of water decays to an isotope of helium. By 

measuring the amounts of tritium and helium isotopes, the approximate 

length of time since a parcel of water fell as precipitation can be determined.

In the Middle Rio Grande Basin, CFC’s and tritium and helium isotopes 

were used to date ground water and to locate areas where recharge has 

occurred within the past 50 years, such as in the inner valley of the Rio 

Grande and along some arroyos and mountain-front areas. The resulting 

ground-water ages also provide calibration data for ground-water-flow 

models. Other environmental tracers that have been used in the Middle Rio 

Grande Basin include (1) carbon-14 (14C, a radioactive isotope with a halflife of 5,730 years), which has been used to date ground water recharged 

during the past 30,000 years (see Box N), (2) sulfur-34 (34S, a stable 

isotope of sulfur), which has been used to trace water from the Rio Grande 

near Albuquerque, and (3) sulfur hexafluoride (SF6, a trace atmospheric 

gas that also occurs naturally in granites and other rocks), which has been 

used to trace recharge from the Sandia Mountains.

A USGS hydrologist collecting a water 

sample for chlorofluorocarbon analysis. 

To prevent contamination of the sample, 

water is collected without atmospheric 

contact and flame sealed in a glass 

ampoule.
84

Few springs in the Middle Rio Grande Basin discharge ground water 

onto the land surface from the Santa Fe Group aquifer system, and all that 

do so have low flow rates. Most are scattered along fault scarps west of the 

Sandia, Manzanita, and Manzano Mountains, though at least one is on the 

flanks of the Jemez Mountains (White and Kues, 1992). 

Evapotranspiration

The amount of ground water lost to evapotranspiration is one of the 

most important yet unknown quantities in studies of the Middle Rio Grande 

Basin. Because it is very difficult to measure evapotranspiration in a natural 

setting, most estimates are based on broad assumptions or are indirect 

values derived from water budgets or models. Most evapotranspiration in 

the basin occurs in the inner valley of the Rio Grande from riparian vegetation such as cottonwood, tamarisk, and Russian olive (see Chapter 2). Estimates by the Bureau of Reclamation in 1989 suggest that the transpiration 

rate from riparian vegetation along the river is about 3 feet per year; when 

multiplied by the 37,300 acres of riparian vegetation along the Jemez 

River and Rio Grande this yields about 112,000 acre-feet of water a year 

lost to transpiration in the Middle Rio Grande Basin (Thorn, McAda, and 

Kernodle, 1993). The ground-water-flow model of McAda and Barroll 

(2002) estimated that evapotranspiration was 130,000 acre-feet per year for 

predevelopment conditions and 84,000 acre-feet per year for 1999 for the 

inner Rio Grande Valley and Jemez River. The values decrease because of 

lowering of the water table and reduction in the area covered by riparian 

vegetation. The Middle Rio Grande water budget of the Action Committee 

of the Middle Rio Grande Water Assembly (1999) estimated that between 

75,000 and 195,000 acre-feet of water is lost annually to evapotranspiration 

by the bosque in the river reach between Otowi (north of the basin) and 

San Acacia (fig. 4.11).

A new generation of tools to quantify evapotranspiration is being 

used in the Middle Rio Grande Basin, led by the Bureau of Reclamation. 

The centerpiece of these efforts is the Agricultural Water Resources Decision Support System (AWARDS) whose purpose is “to improve the efficiency of water management and irrigation scheduling by providing 

guidance on when and where to deliver water, and how much to apply” 

(Bureau of Reclamation, 2001a). Part of the AWARDS system is the ET 

Toolbox, which uses a network of weather stations to “accumulate highresolution daily rainfall and water-use estimates within specified river 

reaches” (Bureau of Reclamation, 2001b). These estimates are available on 

the Internet for agricultural and water-management uses (the reader is 

referred to the “References Cited” on page 122 for the Web site addresses). 

Work is also underway to integrate Light Detection And Ranging (LiDAR) 

technology, radar, and other atmospheric-measurement tools with standard 

weather data and plant-physiology measurements of individual trees to 

improve evapotranspiration measurements (Bureau of Reclamation, 

2001c).

Water naturally flowing from the subsurface onto the land surface or into a 

body of water is a spring (Meinzer, 

1923; Jackson, 1997). A seep is similar 

but typically has too little flow to be 

considered a spring (Jackson, 1997). 

The term seepage area is sometimes 

used to indicate a broader area of more 

diffuse discharge (Todd, 1980). All typically occur where the water table intersects the land surface or a body of 

water.
85

Underflow

Ground-water flow out of the Middle Rio Grande Basin appears to 

be limited to flow from the southern basin margin into the Socorro Basin. 

There has been a wide range of estimates for the volume of this flow, the 

highest being Kernodle and Scott’s (1986) estimate of 15,000 acre-feet per 

year. The models of Kernodle, McAda, and Thorn (1995) and McAda and 

Barroll (2002) did not use a separate value for underflow out of the basin 

because the value was very small and was indistinguishable from evapotranspiration in the southern part of the model. 

Effects of ground-water withdrawals

Unlike other means of discharge from the aquifer system, pumpage 

is not a natural process. If water is pumped from the aquifer system faster 

than it can be recharged or replaced, water is removed from storage and 

ground-water levels decline. Because the supply of water in an aquifer is 

limited, such pumping rates are not sustainable and will eventually deplete 

the resource and cause a number of adverse effects on the long-term use of 

the aquifer.

Deterioration of water quality

Few analyses have been made of the water chemistry in deeper parts 

of the Santa Fe Group aquifer system—that is, depths below current 

production zones (approximately 1,500–2,000 feet below land surface). 

Though some of the monitoring wells described on page 54 are completed 

below the production zone, chemical analyses of ground water from these 

wells do not all indicate similar trends in water chemistry with depth or 

show a clear temporal trend (Bexfield and Anderholm, 2002). Undesirable 

chemical constituents in water tend to increase with depth or distance 

along a flow path in many parts of the world (Freeze and Cherry, 1979). 

Any such increase in undesirable constituents in deeper zones of the Santa 

Fe Group aquifer system may be exacerbated by the presence of evaporites 

in parts of the middle and lower Santa Fe Group (Hawley and Haase, 

1992).

Bexfield and Anderholm (2002) conducted the only systematic 

analysis of long-term trends in ground-water chemistry in the Middle Rio 

Grande Basin. Using data for City of Albuquerque production wells 

collected over a 10-year period, they determined that water quality 

appears to be degrading over time in some locations but not in others. 

Moreover, different water-chemistry constituents showed different trends. 

Bexfield and Anderholm also determined that correlations between water 

chemistry and monthly pumpage volume were common but not consistent 

between different wells. They concluded that water in and near the production zone typically became poorer in quality with depth, although shallow 

water that has been affected by evapotranspiration or contamination can be 

of poorer quality than water at greater depths.

Aquifer storage refers to the ground 

water held in an aquifer, much as 

surface water is held in a reservoir. 

However, not all the water in storage in 

an aquifer is available for withdrawal. 

After water drains from an (unconfined) 

aquifer by the force of gravity, a thin film 

of water will remain on the rock openings in the aquifer due to capillary 

forces. Generally, the larger the openings in the rock, the less the volume of 

water retained. Fine-grained aquifer 

materials such as clay tend to retain a 

much higher percentage of water after 

the unconfined aquifer is drained by the 

force of gravity (Heath, 1983).
86

 In some areas of the United States, withdrawal of good-quality 

water from the upper parts of an aquifer has allowed underlying saline 

water to move upward and degrade water chemistry (Alley, Reilly, and 

Franke, 1999). Because so little is known about water chemistry in the 

lower parts of the aquifer, the potential for a similar occurrence in the 

Middle Rio Grande Basin cannot be evaluated.

Water-well problems

Declining ground-water levels have two main effects on water wells. 

First, as the depth to water increases, the water must be lifted higher to 

reach the land surface. As the lift distance increases, so does the energy 

required to drive the pump. Thus, power costs increase as ground-water 

levels decline. Depending on the use of the water and energy costs, it may 

no longer be economically feasible to use water for a given purpose. 

Second, ground-water levels may decline below the bottom of existing 

wells, necessitating the expense of deepening the well or drilling a deeper 

replacement well.

Another effect related to ground-water production was described by 

Haneberg and others (1998) from physical measurements made on core 

samples from the 98th Street well. The measurements show that greater 

decline of water levels in the aquifer may reduce the hydraulic conductivity 

of the aquifer, resulting in larger water-level drawdowns and increased 

pumping costs.

Subsidence

Nearly every State in the Southwest has areas with land subsidence 

related to the withdrawal of ground water. For example, in the Mimbres 

Basin near Deming, New Mexico, widespread land subsidence has 

occurred with water-level declines of 115 feet and less (Contaldo and 

Mueller, 1991; Haneberg and Friesen, 1995). Though several different 

processes can be responsible for such land subsidence, compaction of 

aquifer materials is of most concern in the Middle Rio Grande Basin. 

Currently (2002), maximum water-level declines in the Middle Rio Grande 

Basin are more than 160 feet in some locations (figs. 4.4–4.6).

In the Middle Rio Grande Basin, as much as 330 feet of sediment 

has been eroded from the center of the basin. The additional weight created 

by the 330 feet of sediments originally in place compacted the aquifer sediments beyond levels expected from the current thickness of the deposit. 

This overconsolidation in the past allows a greater water-level decline to 

occur today before the onset of aquifer compaction and land subsidence. 

Using information from five wells in the Albuquerque area, Haneberg 

(1995) calculated that “there is a considerable potential for widespread 

land subsidence if drawdown approaches the 260- to 390-foot range.” 

However, these calculations involved the estimation of several parameters, 

and Haneberg (1995) noted that they were “imprecise and highly speculative.”

Localized subsidence has been noted in the 

Albuquerque area.
87

Three methods are currently being used to monitor for the onset of 

land subsidence in the Middle Rio Grande Basin: repeated surveys of 

elevation for a network of benchmarks, an extensometer, and Interferometric Synthetic Aperture Radar (InSAR) analysis (see Box J). Currently 

(2002), the surveys of the benchmark network and the extensometer have 

not detected land subsidence greater than 0.5 inch, though both methods 

monitor limited areas of the basin. However, an InSAR analysis of part of 

the Middle Rio Grande Basin for five periods between July 1993 and 

September 1999 detected land subsidence and recovery in several areas in 

Albuquerque and Rio Rancho (fig. J.2). Maximum subsidence was 

2 inches and maximum uplift was 0.5 inch caused by both elastic and 

inelastic deformation (C.E. Heywood, U.S. Geological Survey, written 

commun., 2002).

A second type of land subsidence from ground-water withdrawals, 

the dewatering of organic soils, is occurring in the Middle Rio Grande 

Basin. Kernodle, McAda, and Thorn (1995) described land subsidence of 

as much as 2 feet in the center of broad depressions in the Rio Grande 

inner valley in the Albuquerque area. These areas of subsidence were 

correlated with “swampy or transitional wetlands mapped from 1935 aerial 

photography” and were attributed to the “lowering of the water table and 

dehydration of shallow beds of clay- and organic-rich material.” This land 

subsidence is permanent and irreversible; however, only limited areas of 

the basin in the inner valley are susceptible to this type of compaction. In 

addition, some areas of the basin contain hydrocompactive or collapsible 

soils (Connell, Love, and Harrison, 2001). Though not related to groundwater withdrawals, the collapse of these soils has caused damage to roads, 

utilities, and buildings in the basin and throughout the State and may be 

mistaken for subsidence.

Hydrocompactive or collapsible soils

are loose, dry, low-density deposits with 

high porosity. When wetted, such as by 

irrigation, they disaggregate and 

compact, with the individual grains 

collapsing to a more compact arrangement much in the same way that a 

house of cards collapses. In the Middle 

Rio Grande Basin, typical geologic 

settings for these deposits are young, 

alluvial-fan, alluvial-slope, or valley-fill 

environments that have not been saturated since deposition (Dennen and 

Moore, 1986; Connell, Love, and 

Harrison, 2001).
88

and is especially prevalent over aquifer systems containing large deposits 

of fine-grained sediment and significant long-term water-level declines. 

Excessive pumping of ground water in the Santa Clara Valley of California, 

for example, caused more than 14 feet of land subsidence in downtown San 

Jose. Despite a reduction of pumping and subsequent rebound in groundwater levels, this subsidence was permanent. Land subsidence from 

ground-water withdrawal is also known to have occurred in Deming, New 

Mexico, Las Vegas, Nevada, the Tucson-Phoenix areas, and elsewhere in 

south-central Arizona. Subsidence in various areas of the Nation is likely 

responsible for annual losses of hundreds of millions of dollars as a result 

of structural damage and flooding of lowered land surfaces (Galloway, 

Jones, and Ingebritsen, 1999).

In the Middle Rio Grande Basin, three methods are being used to check for 

the onset of land subsidence related to ground-water withdrawals. In the 

Albuquerque area, a high-precision survey network consisting of 44 benchmarks was established in 1993, using both existing survey markers and new 

markers installed for the study. By periodically resurveying this network of 

benchmarks, changes in their elevations can be detected. Repeat survey 

techniques originated in the 19th century; however, advances in survey 

instrumentation have improved measurement efficiency and accuracy. The 

Global Positioning System (GPS), which uses timed microwave signals 

from satellites to determine location and elevation, can be used to survey a 

network of benchmarks with accuracies typically on the order of 0.4 to 

0.8 inch. The Albuquerque subsidence network was surveyed with GPS in 

1993 and 1994 but GPS did not detect land subsidence greater than 

0.5 inch (C.E. Heywood, U.S. Geological Survey, written commun., 1995).

In 1994, the Montaño borehole extensometer was installed to a depth of 

1,035 feet in northern Albuquerque about 0.6 mile east of the Rio Grande. 

A borehole extensometer is a vertical strain gage that detects compression 

and expansion of an aquifer system (fig. J.1). A borehole extensometer is 

constructed by drilling a straight, vertical hole to a depth below the zone of 

the aquifer system to be measured. The hole is cased with steel pipe 

containing slip-joints, which allow the casing to deform vertically with the 

surrounding aquifer system. A smaller diameter pipe is suspended inside 

this well casing and allowed to rest lightly on the bottom of the well. 

Because the length of the extensometer pipe does not change, it moves 

upward relative to the land surface as the aquifer system compresses. The 

displacement of the top of the extensometer pipe with respect to a surface 

datum (benchmark) is accurately measured with an electronic strain gage 

and analog recorder. Currently (2002), the extensometer has not detected 

land subsidence greater than 0.5 inch (Heywood, 1998; Galloway, Jones, 

and Ingebritsen, 1999).

Galloway, Jones, and Ingebritsen (1999) 

defined land subsidence as “a gradual 

settling or sudden sinking of the Earth’s 

surface owing to subsurface movement of 

earth materials.” Though they noted that 

several different Earth processes can 

cause subsidence, more than 80 percent of 

the subsidence in the United States is 

related to the withdrawal of ground water. 

They also defined three main mechanisms 

by which ground-water withdrawals cause 

land subsidence: compaction of aquifer 

systems, dewatering of organic soils, and 

collapse of subsurface cavities. Of these 

three mechanisms, only the first two are 

of potential concern in the Middle Rio 

Grande Basin.

Because water supplies in the Southwest 

are primarily from ground water, most 

Southwestern States have areas that have 

experienced or are experiencing subsidence caused by ground-water withdrawal. 

When ground water is pumped, the 

removal of water reduces the pore-fluid 

pressure, which in turn transfers more 

stress to the rock matrix of the aquifer 

system (intergranular or effective stress). 

As long as ground-water levels remain 

above a certain elevation (which depends 

on the geologic and water-level history of 

the aquifer system), pore-fluid pressure is 

maintained and the effective stress 

remains above a critical level. Water-level 

fluctuations above this critical stress 

threshold cause elastic, or reversible, 

deformation of the aquifer system. If 

ground-water levels fall below this elevation, however, the aquifer-system matrix 

may compact to a more stable arrangement, resulting in a more substantial volumetric reduction that is inelastic, or 

irreversible. Subsidence is the surficial 

manifestation of this inelastic compaction 

Land subsidence and how it is being studied in the basin

Charles E. Heywood,1 James R. Bartolino,1 and Devin L. Galloway2

J

1

U.S. Geological Survey, Albuquerque, New Mexico.

2

U.S. Geological Survey, Sacramento, California.
89

Both the GPS network and the extensometer monitor land subsidence at 

discrete locations in the Middle Rio Grande Basin. Interferometric 

Synthetic Aperture Radar (InSAR), a fairly recent development in the 

Earth sciences, complements these techniques by mapping the spatial 

distribution of land-surface elevation changes. In standard Synthetic Aperture Radar (SAR) mapping, which has been used for mapping topographic 

features on the Earth and other planets, the distance to the land surface 

from the radar antennae on a satellite or aircraft is determined from the 

round-trip traveltime of the radar waves. The InSAR process compares two 

SAR images of the same area made at different times and generates an 

image of the land-surface displacements (an interferogram) that have 

occurred between the two SAR scenes. With InSAR it is possible to detect 

land-surface changes of 0.2 to 0.4 inch over an image pixel (about 17,000 

to 69,000 square feet) from satellite imagery (Galloway, Jones, and 

Ingebritsen, 1999).

InSAR analysis of part of the Middle Rio Grande Basin for five periods 

between July 1993 and September 1999 detected land subsidence and 

uplift in several areas in Albuquerque and Rio Rancho (C.E. Heywood, 

D.L. Galloway, and S.V. Stork, U.S. Geological Survey, written commun., 

2001). One interferogram (fig. J.2) shows a maximum of about 0.6 inch of 

land subsidence in several areas of Albuquerque and about 2 inches in an 

area near Rio Rancho well 16, which produced 250 to 290 acre-feet of 

water per month from September 1994 through September 1995. The 

subsequent interferogram shows land-surface uplift (or rebound) in these 

areas. The sequence of five interferograms, in conjunction with water-level 

data, shows elastic, and possibly inelastic, aquifer-system deformation in 

the Middle Rio Grande Basin.

Table-surface datum

Counterweighted lever arm

Pier

Counterweight

Strip-chart

recorder

Dial gage

Extensometer 

pipe

Well casing

Figure J.1.—Surface instrumentation of 

the Montaño extensometer. The top of the 

well casing is on the right; a counterweighted lever arm balances 80 percent of 

the weight of the extensometer pipe. A 

table suspended between piers anchored 

15–20 feet below land surface provides 

the surface datum; a strip-chart recorder 

rests on this table. Displacements 

between the extensometer pipe and the 

table-surface datum are measured with an 

electronic strain gage, the strip-chart 

recorder, and a dial gage.

Rio Rancho 16

0 5 10 15 20 25 KILOMETERS

0 5 10 15 20 25 MILES

RIO

GRANDE

34°55'

35°

35°05'

35°10'

35°15'

35°20'

106°55' 106°50' 106°45' 106°40' 106°35' 106°30' EXPLANATION

Change in

land-surface

elevation,

in millimeters

Change in

land-surface

elevation,

in inches

0

1.8

3.5

5.1

7.5

–68

–29

–10

–7

–4

–2

68

0

–2.7

–1.1

–0.39

–0.28

–0.16

–0.08

0.08

0.14

0.20

0.30

2.7

Municipal production wells—

Greater than 1,000 acre-feet

pumped January-August 1995

Municipal production wells—

Less than 1,000 acre-feet

pumped January-August 1995 Uplift Subsidence

Figure J.2.—Interferometric 

Synthetic Aperture Radar 

(InSAR) image of the Albuquerque area, July 2, 1993–

September 3, 1995. 

Maximum subsidence of 2 

inches is shown in the Rio 

Rancho area by purple and 

blue. The linear boundaries of 

subsidence features are 

parallel to and in the approximate locations of mapped 

faults in the area. In the Albuquerque area, maximum 

subsidence is about 0.4 to 0.6 

inch and is also shown by 

purple and blue. Municipal 

wells are shown as black dots 

sized according to January–

August 1995 production.
90
91

Water quality affects the daily lives of everyone and thus is one of 

the most important topics addressed in water-supply studies. Concerns 

about the quality and safety of the Nation’s water have led to the growth of 

a large industry devoted to filtering, treating, or bottling water for domestic 

use and human consumption. Not only is everyone aware of the effects of 

water quality on taste and plumbing fixtures, water-quality and watercontamination stories are now commonplace in the news media.

Because the Middle Rio Grande Basin Study was primarily 

concerned with understanding the physical aspects of the ground-water 

system, water-quality data for the study were collected for this purpose. 

However, ground- and surface-water sampling for the study has allowed 

the most complete and areally extensive view of water quality in the 

Middle Rio Grande Basin to date. The use of water quality for groundwater age dating and the definition of flow paths and traveltimes has made 

a large contribution to the understanding of the ground-water-flow system 

(see Boxes I and K). In addition, water-quality data for the Middle Rio 

Grande Basin Study adds to our knowledge of whether water in a particular area of the aquifer is suitable for a particular use (including human 

consumption) and whether human activities may be adversely affecting 

ground-water quality.

General quality of ground water and 

what it reveals about the groundwater system

In the same way that the geology of the Santa Fe Group aquifer 

system varies areally and with depth, so do the chemical properties of 

ground water in the aquifer. This variation is due to many factors including 

where water enters the aquifer, the distance it travels and the rock types it 

contacts within the aquifer, and human activity. Ground-water samples 

collected from 275 wells and analyzed by Plummer and others (2001) 

showed significant variation in many water-quality constituents and properties. Concentrations of some chemical constituents or properties in water 

varied over several factors of 10. This wide variation makes it difficult to 

generalize water quality in the basin as a whole.

A useful approach to characterizing ground-water quality in the 

Middle Rio Grande Basin is to divide the basin into zones of different 

water-quality (or hydrochemical) characteristics (Anderholm, 1988; 

Logan, 1990; Plummer and others, 2001). Plummer and others (2001) 

defined 13 hydrochemical zones by using analyses of ground-water 

samples from 275 different wells and springs (fig. 6.1), resulting in the 

most areally comprehensive water-quality study to date in the Middle Rio 

Chapter 6: Chemical characteristics of water in 

the aquifer system

A small truck-mounted soil-probing machine 

used in the Middle Rio Grande Basin to 

sample shallow ground water. The size and 

portability of this unit allow for the collection of 

more data with less disturbance.
92

Water acquires very small quantities of some solutes from dust and gases 

when it falls through the atmosphere as precipitation, but water typically 

acquires the majority of its solutes once it reaches the land surface. Solutes 

that were already present in the water increase in concentration because of 

the processes of evaporation and transpiration—processes that, for the most 

part, remove water while leaving the solutes behind. In some arid environments like New Mexico, plants can withdraw more than 90 percent of the 

precipitation that has infiltrated into the soil zone. As water infiltrates 

through the soil zone, it also tends to dissolve carbon dioxide (CO2) gas 

that exists in the soil in large quantities (relative to the atmosphere) because 

of biological activity. When CO2 dissolves in water in the soil zone, a weak 

acid is formed. This acid promotes the dissolution of minerals that are 

present in the soil and rocks, which releases solutes to the water and causes 

their concentrations to increase. Because of these processes, water in the 

soil zone can acquire the bulk of its chemistry before it reaches the water 

table.

In ground water, only seven solutes make up nearly 95 percent of all water 

solutes (Runnells, 1993; Herczeg and Edmunds, 1999). These solutes are 

calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), chloride (Cl), 

sulfate (SO4), and bicarbonate (HCO3). Although many sources and reactions influence the concentrations of these solutes, the predominant sources 

of these solutes to ground water in the Middle Rio Grande Basin (Anderholm, 1988) include (1) the dissolution of limestone (calcite, CaCO3) and 

dolomite (CaMg(CO3)2) for Ca, Mg, and HCO3; (2) the dissolution of 

gypsum (CaSO4·2H2O) and anhydrite (CaSO4) for Ca and SO4; (3) the 

dissolution of halite (NaCl) for Na and Cl; and (4) ion exchange reactions 

on the surfaces of some clay minerals whereby sodium is released to the 

water in exchange for calcium or magnesium. Sodium also is derived from 

the dissolution of silicate minerals, such as plagioclase feldspars, which 

make up some of the sand and gravel that fill the Middle Rio Grande Basin. 

Potassium is derived from the dissolution of some silicate minerals in 

granitic rocks and from reactions with some clay minerals. Few reactions 

remove these seven solutes from ground water. However, some minerals, 

such as calcite CaCO3, can precipitate from solution to form a solid phase.

In addition to the seven predominant solutes in water, some other solutes 

known as trace elements typically exist in very small quantities, as do 

particular isotopes of dissolved constituents (see Box I). Processes that 

affect the concentrations of trace elements and isotopes are not always well 

understood. However, combined with data on the predominant 

water-chemistry, trace-element and isotopic data for ground water can 

provide a powerful tool for tracking ground-water flow.

How ground-water chemistry helps us understand the aquifer

L. Niel Plummer,1 Laura M. Bexfield,2 and Scott K. Anderholm2

K

1

U.S. Geological Survey, Reston, 

Virginia.

2U.S. Geological Survey, Albuquerque, 

New Mexico.

Although water is commonly thought of 

as simply H2O, literally thousands of 

other substances are dissolved in water in 

the environment. Most of these 

substances occur naturally, and many are 

present in water in only small quantities. 

The term “water chemistry” (or water 

quality) refers to the quantities of these 

various substances (commonly called 

solutes) that are present in a particular 

water sample, making up its chemical 

composition. In the Santa Fe Group 

aquifer system of the Middle Rio Grande 

Basin, patterns in the water chemistry of 

ground water have helped refine important concepts about the ground-waterflow system, including sources of water, 

directions of flow, and traveltimes. The 

water chemistry of a ground-water sample 

can be thought of as a chemical signature 

that reflects the sum total of all physical 

processes and chemical reactions that 

affected the water from the time it began 

as dilute rainfall, infiltrated the soil above 

the water table, passed into the aquifer 

(ground-water recharge), and traveled, 

sometimes over great distances and depth, 

to the point of sample collection or 

discharge from the aquifer. 
93

In a very broad sense, the mineralogy of aquifers can be divided into two 

groups—those aquifers that contain relatively reactive minerals and those 

with mostly unreactive minerals. In aquifers composed of reactive rocks 

and minerals like limestone, dolomite, gypsum, halite, and organic matter, 

solute concentrations (and isotopic compositions) can change significantly 

with distance along a ground-water flow path, reflecting extensive chemical reaction. In aquifers composed of mostly unreactive material, like 

sand and gravel from the chemical and mechanical breakdown of silicate 

rocks and minerals, solute concentrations change only slightly with 

distance down a flow path. In these relatively unreactive aquifers, such as 

the Santa Fe Group aquifer system, water tends to acquire its predominant 

chemical composition during the process of recharge and retains that 

composition as it flows through the aquifer.

Much of the ground water in the Middle Rio Grande Basin has acquired its 

chemical (and isotopic) composition during recharge, either as infiltration 

of precipitation on the basin margin, as seepage from rivers and arroyos, or 

as ground-water underflow from adjacent aquifer systems that border the 

basin. Water chemistry differs depending on the source of water, the degree 

to which it has been evaporated, the types of rock and mineral it has 

encountered, and the time it has been in contact with reactive minerals. 

Therefore, water in the Middle Rio Grande Basin commonly differs in the 

concentration of any particular solute and the concentration of that solute 

relative to other solutes. These distinct differences allow for the delineation 

of areas of the aquifer that have similar chemical “signatures.” The spatial 

extents and configurations of these areas can provide important information about the ground-water-flow system. For example, the chemistry of an 

area with a particular signature can be compared with the chemistry that 

might be expected from water moving through a source area with a known 

rock type or seeping through a river with known surface-water chemistry. 

The likely source of the ground water can be determined from such 

comparisons. Boundaries between areas of dissimilar chemical signatures 

can represent general boundaries between waters from the different 

sources. The shapes of the areas can also broadly define the directions of 

ground-water flow. Also, the vertical extent of ground water in the aquifer 

having a particular chemical signature can indicate how well water is 

mixing vertically through the aquifer. If this vertical extent is known, the 

approximate volumes of ground water with different signatures can be 

calculated and used to estimate the relative amounts of recharge from 

different sources. 

Interpretations of water-chemistry data are most reliably made within a 

conceptual framework of the ground-water system that has been derived 

from several additional types of hydrologic and geologic data, such as 

water levels, that indicate general directions of ground-water flow (see 

Box F). In combination with the multitude of hydrologic and geologic data 

obtained as part of the USGS Middle Rio Grande Basin Study, water-chemistry data have improved the understanding of the aquifer through recognition of ground-water sources, delineation of flow paths, and determination 

of ground-water traveltimes calculated using isotopic data (see Box I).

Ground-water sampling at the 98th Street 

well. Because monitoring wells typically do 

not contain pumps, a portable sampling 

pump must be lowered into the well.
94

Grande Basin. Because their sampling relied primarily on existing production wells, results are not applicable to deeper areas of the aquifer beneath 

the production zone. Boundaries between the water-quality zones may not 

be vertical as implied by a two-dimensional map (fig. 6.1). The reader is 

referred to Plummer and others (2001) for a complete description, but 

general characteristics of the regions shown in figure 6.1 are summarized in 

table 6.1.

Not only can hydrochemical zones be used to characterize groundwater quality in different parts of the Middle Rio Grande Basin, they can 

also be used to delineate probable sources of recharge and their relative 

contributions, determine ground-water flow paths within the aquifer 

system, and provide an estimate of the sustainability of current groundwater pumping. Probable recharge sources for each of the hydrochemical 

zones defined by Plummer and others (2001) are listed in table 6.1. 

(Zone 13 is thought to represent a convergence of flow from multiple zones 

in the basin and does not represent a single recharge source.) For example, 

zone 4 contains the oldest ground water in the basin (based on carbon-14 

age; see Box N), and the strongly negative values of deuterium (see Box I) 

suggest that this water originated as precipitation at a higher elevation. 

These data, in combination with other water-quality information, led to the 

interpretation that zone 3 represents “recharge from the Jemez Mountains 

north of the basin, primarily during the last glacial period” (Plummer and 

others, 2001).

Because these hydrochemical zones were defined on the basis of a 

limited number of samples, the characteristics listed in table 6.1 are only 

generalizations. A well within one of the zones may contain water with 

substantially different chemical characteristics from those represented by 

the median, or typical, values for the zone.

Naturally occurring substances that 

limit the use of ground water

Current (2002) U.S. Environmental Protection Agency (USEPA) 

and State of New Mexico drinking-water standards and the significance of 

selected constituents are shown in table 6.2, along with the significance of 

each constituent for human health and (or) the esthetic properties of water. 

This listing is limited to constituents or properties listed in the preceding 

discussion of the ground-water-quality regions defined by Plummer and 

others (2001).

USEPA drinking-water standards are of two types: primary and 

secondary. Primary standards are the “maximum permissible level of a 

contaminant in water which is delivered to any user of a public water 

system” (U.S. Environmental Protection Agency, 2002). The standards are 

enforceble, in contrast to secondary standards, which are nonenforceble. 

Constituents covered by secondary standards may cause cosmetic or 

esthetic effects. The presence in drinking water of chemical constituents 

regulated by drinking-water standards does not necessarily pose a health 

risk. Many constituents that are essential for good health at low concentrations may pose a health risk at higher concentrations.

The concentration of dissolved oxygen

is a general indicator of how recently 

ground water entered the aquifer. In 

general, recently recharged water has a 

dissolved-oxygen concentration similar 

to surface water (which has relatively 

large values in comparison to most 

ground water), and concentration tends 

to decrease as ground water moves 

away from the point of recharge. The 

presence of organic material in the 

aquifer can cause more rapid oxygen 

depletion. However, in the Santa Fe 

Group aquifer system, some recently 

recharged river water has small values 

of dissolved oxygen because of organic 

material within inner-valley sediments, 

and some very old (greater than 

10,000 years) ground water has relatively large values of dissolved oxygen. 

(See Hem [1985] for a general discussion of dissolved oxygen in ground 

water.)

Specific conductance is an indicator of 

how mineralized a sample of water is. It 

is measured in microsiemens per centimeter (μS/cm) at a specified temperature, usually 25 degrees Celsius. Pure 

water is a poor conductor of electricity, 

but minerals dissolve in water, and the 

resulting ions conduct electricity. In 

general, the larger the value of specific 

conductance the greater the concentration of dissolved solids in the water 

sample and the poorer the water 

quality. The specific conductance of 

seawater is about 50,000 μS/cm, 

whereas the specific conductance of 

distilled water is approximately 1 μS/cm 

(Heath, 1983; Hem, 1985).
95

Jemez River

Rio Salado

Jemez Canyon

Reservoir

Tijeras Arroyo

San

Jose 

Rio

Cochiti Lake

 Arroyo Abo

RIO

GRANDE 

RIO 

GRANDE 

San

Ysidro

Cochiti

Santo

Domingo

San Felipe

Bernalillo

Rio

Rancho

Albuquerque

Isleta

Los Lunas

Belen

Bernardo

San Acacia

McKINLEY

CIBOLA

VALENCIA

SOCORRO

TORRANCE

SANTA FE

BERNALILLO

SANDOVAL

EXPLANATION

Middle Rio Grande Basin

Northern mountain-front recharge

Northern intrabasin recharge

Ground-water inflow along the

northern basin margin

Ground-water inflow from the

western basin margin

Ground water affected by recharge

from the Rio Puerco

Southwestern mountain-front

recharge

Ground water affected by recharge

from Abo Arroyo

Eastern mountain-front recharge

Ground-water inflow from the

Tijeras fault zone

Ground water affected by recharge

from Tijeras Arroyo

Ground-water inflow from the

northeast basin margin

Ground-water recharge from

the Rio Grande

Ground-water discharge

1

2

3

4

5

6

7

8

9

10

11

12

13

HYDROCHEMICAL ZONES

0 20 40 MILES

0 20 40 KILOMETERS

35°30'

35°15'

35°

34°45'

34°30'

107°15' 107° 106°45' 106°30' 106°15'

1

2

3

4

4

4

5

6

7

8

8

8

9

10

11

12

13

Figure 6.1.—Hydrochemical regions of the Middle Rio Grande Basin as defined by Plummer and others (2001).
96

Table 6.1.—Median values of selected parameters of the 13 hydrochemical zones delineated for the Santa Fe Group aquifer 

system of the Middle Rio Grande Basin

[Plummer and others (2001); years BP, years before present; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter] 

Hydrochemical zone and recharge source

12345 6 7

Northern 

mountainfront 

recharge

Northern 

intrabasin 

recharge

Groundwater inflow 

along the 

northern 

basin 

margin

Groundwater inflow 

from the 

western 

basin 

margin

Ground 

water 

affected by 

recharge 

from the Rio 

Puerco

Southwestern 

mountain-front 

recharge

Ground 

water 

affected by 

recharge 

from Abo 

Arroyo

Number of samples 16 10 44 10 12 2 5

Deuterium (parts per thousand) 1 –79 –63 –97 –64 –63 –64 –64

Carbon-14 age (years BP) 8,800 8,800 19,500 20,400 8,100 7,700 9,400

Specific conductance (μS/cm) 380 390 590 3,300 2,400 590 920

pH (standard units) 7.5 7.8 8.3 7.6 7.5 8.0 7.4

Dissolved oxygen (mg/L) 5.1 6.8 3.1 4.9 3.0 3.7 5.6

Chloride (mg/L) 9.5 6.2 12 2 530 180 26 24

Sulfate (mg/L) 25 35 95 2 670 2 980 80 2 310

Bicarbonate (mg/L) 150 140 170 250 180 230 170

Nitrate (mg/L) 0.6 5.2 1.3 1.1 1.5 0.6 1.4

Calcium (mg/L) 39 29 10 130 170 39 91

Sodium (mg/L) 26 47 100 450 280 44 49

Potassium (mg/L) 5.4 6.2 4.1 14 12 3.2 3.4

Silica (mg/L) 47 28 28 21 26 14 22

Arsenic (mg/L) 0.0051 0.0096 3 0.021 0.0018 0.0011 0.0011 0.0026

Hydrochemical zone and recharge source

8 9 10 11 12 13

Eastern 

mountainfront 

recharge

Groundwater inflow 

from the 

Tijeras fault 

zone

Ground 

water 

affected by 

recharge 

from Tijeras 

Arroyo

Groundwater inflow 

from the 

northeast 

basin 

margin

Groundwater 

recharge 

from the

Rio Grande

Ground-water 

discharge

Average for 

all zones

Number of samples 47 8 6 7 105 3 275

Deuterium (parts per thousand) 1 –81 –74 –75 –69 –95 –91 –90

Carbon-14 age (BP) 5,200 16,200 3,200 10,000 4,600 17,900 8,100

Specific conductance (μS/cm) 380 1,300 620 1,300 430 2,500 470

pH (standard units) 7.5 7.1 7.4 7.6 7.7 7.7 7.7

Dissolved oxygen (mg/L) 5.5 4.1 6.7 6.6 0.1 0.1 1.9

Chloride (mg/L) 7.7 87 29 22 16 2 680 16

Sulfate (mg/L) 34 150 110 2 400 63 2 290 67

Bicarbonate (mg/L) 170 290 220 170 160 160 160

Nitrate (mg/L) 0.4 1.0 3.3 1.9 0.1 0.4 0.5

Calcium (mg/L) 48 130 80 100 42 93 41

Sodium (mg/L) 22 87 29 87 29 210 44

Potassium (mg/L) 2.0 4.6 3.5 4.4 6.7 11 5.3

Silica (mg/L) 26 23 23 31 53 29 33

Arsenic (mg/L) 0.0017 0.002 0.001 0.0022 0.0055 0.008 0.005

1Deuterium values can be negative because they are expressed as parts per thousand differences relative to an ocean-water standard. 2

These values exceed the U.S. Environmental Protection Agency secondary water-quality standards in table 6.2.

3This value exceeds the U.S. Environmental Protection Agency primary water-quality standard for arsenic in table 6.2.
97

Table 6.2.—Current drinking-water standards and significance of constituents commonly found in ground water in the Middle 

Rio Grande Basin

[USEPA, U.S. Environmental Protection Agency; mg/L, milligrams per liter; --, no standard exists or no effects known]

Constituent

USEPA drinking-water 

standard maximum 

contaminant level 

(mg/L)1

State of New 

Mexico 

drinking-water 

standard 

maximum 

contaminant 

level 

(mg/L) 2

Significance

Primary 

standard

Secondary 

standard

Arsenic 0.01 -- 0.05 Skin damage; circulatory system problems; increased cancer risk.

1

Boron -- -- -- --

Calcium -- -- -- In large amounts, increases corrosiveness of water. In combination 

with sodium, gives water a salty taste.3

Chloride -- 250 -- In large amounts, increases corrosiveness of water. In combination 

with sodium, gives water a salty taste.3

Fluoride 4 2 4 Bone disease (pain and tenderness of the bones); children may get 

mottled teeth.

1

Manganese -- 0.05 -- Dark brown-black stains; bitter, metallic taste.3,4

Nitrate (measured 

as nitrogen)

10 10 10 Methemoglobinemia (“Blue baby syndrome”).1

pH

(in standard 

units)

-- 6.5–8.5 -- Values less than 4 indicate corrosive water that tends to dissolve metals 

and other substances that it contacts. Values greater than 8.5 indicate 

alkaline water that, on heating, tends to form scale in pipes and 

boilers.3

Potassium -- -- -- In combination with sodium can cause foaming, corrosion, and scale 

formation in boilers.5

Silica -- -- -- In combination with calcium and magnesium forms scale in pipes and 

boilers.5

Sodium -- -- -- See chloride, potassium; in large concentrations, may affect people 

with cardiac difficulties, hypertension, and certain other medical 

conditions. In combination with calcium and magnesium may be 

detrimental to certain irrigated crops.3

Sulfate -- 250 -- Medicinal taste; laxative effect. In combination with calcium forms 

scale in pipes and boilers.3,4

1

 U.S. Environmental Protection Agency (2002).

2 New Mexico Environment Department (1996).

3 Heath (1983).

4 National Water Quality Association (2002a, b).

5 Todd (1980).
98

An examination of the median values of selected water-quality 

parameters by the hydrochemical zones in table 6.1 shows that three 

constituents exceeded at least one of the three standards listed in table 6.2 

(USEPA primary or secondary standard or New Mexico standard). The 

median arsenic concentration of 0.021 mg/L in zone 3 exceeded the 

USEPA primary standard of 0.010 mg/L. The median concentrations of 

chloride in zones 4 and 13, 530 and 680 mg/L, respectively, exceeded the 

USEPA secondary standard of 250 mg/L. Concentrations of sulfate in zone 

4 (670 mg/L), zone 5 (980 mg/L), zone 7 (310 mg/L), zone 11 (400 mg/L), 

and zone 13 (290 mg/L) exceeded the USEPA secondary standard of 

250 mg/L.

The results reported in Plummer and others (2001) were a summary 

of a comprehensive suite of chemical analyses, not all of which were 

reported in the paper. In addition, the median concentration of manganese 

was 0.05 mg/L in zone 4, which is equivalent to the USEPA secondary 

standard (L.M. Bexfield, U.S. Geological Survey, written commun., 2001). 

An additional two points should be made about the chemical analyses of ground water and the applicability of Federal and State standards. 

First, water samples analyzed by Plummer and others (2001) were 

untreated samples obtained directly from wells. Because such water is not 

being delivered directly to the consumers of a municipal supply, the standards do not strictly apply. However, the comparison is provided to give an 

indication of untreated source water. Second, even though the median 

values presented in table 6.1 may not exceed a water-quality standard, individual samples from the zone may. Conversely, even though the median 

values in table 6.1 may exceed a water-quality standard, individual samples 

from the zone may not.

The naturally occurring water-quality constituent of most concern in 

ground water of the Middle Rio Grande Basin has been arsenic. In 1991, 

seven City of Albuquerque well fields had at least one well producing 

water with more than 0.030 mg/L of arsenic (CH2M Hill, 1991). Generally, 

by blending water from different wells in each well field, water of an 

acceptable concentration was delivered and the water supply was not 

affected; however, arsenic concentrations in the Don well field (fig. B.1A) 

were too large for such dilution, causing the entire field to be taken out of 

production (CH2M Hill, 1991). Concerns also have been raised about 

arsenic concentrations in the discharge of treated wastewater to the Rio 

Grande. Because essentially all of this wastewater originates as ground 

water and because the wastewater-treatment process does not remove 

arsenic, water with arsenic concentrations larger than the naturally occurring concentrations in the river could be conveyed to the Rio Grande. A 

study by Wilcox (1997) found that mean dissolved-arsenic concentrations 

in Rio Grande water generally increased downstream from 0.002 mg/L at 

San Felipe Pueblo to 0.004 mg/L at Los Lunas. Mean dissolved-arsenic 

concentrations in treated wastewater from the Bernalillo, Rio Rancho, and 

Albuquerque wastewater-treatment plants ranged from 0.008 mg/L to 

0.016 mg/L. Mean dissolved-arsenic concentration in the Jemez River 

below Jemez Reservoir was 0.018 mg/L.

In October 2001, the USEPA issued a final arsenic primary standard 

of 0.010 mg/L for drinking water and extended compliance beyond 

community water systems to all systems that serve at least 25 of the same 

people more than 6 months per year (U.S. Environmental Protection 

Agency, 2001a). Annual compliance costs for New Mexico are estimated at 

$49–$60 million to meet the primary standard of 0.010 mg/L of arsenic 

(Bitner, Thomson, and Chwirka, 2001).

Concentrations of chemical constituents 

in water are typically reported as milligrams per liter (mg/L) or micrograms 

per liter (μg/L), which are essentially 

equal to parts per million and parts per 

billion, respectively. An example of 

1 part per million is 1 ounce of a 

substance dissolved in 7,500 gallons of 

water (Heath, 1983). “Four drops of ink 

in a 55-gallon barrel of water would 

produce an “ink concentration” of 1 part 

per million” (Kimball, 2002). Similarly, 

1 part per billion is 1 ounce of a 

substance dissolved in 7.5 million 

gallons of water, or one drop of ink in 

one of the largest tanker trucks used to 

haul gasoline (Kimball, 2002).
99

Contaminants of human origin and 

ground water

Human contamination of ground water in the Middle Rio Grande 

Basin, though severe in some localities, is not widespread and does not 

affect a large quantity of water in the aquifer. Most of the ground water in 

the basin has a “low susceptibility to contamination because the depth to 

water is greater than 100 feet and there is virtually no natural mechanism 

for [direct] recharge to the ground-water system” (Anderholm, 1987). An 

exception is the basin- and valley-fill deposits of the inner valley of the Rio 

Grande, which have a “relatively high susceptibility to contamination 

because the depth to water is generally less than 30 feet and there are many 

types of recharge to the ground-water system” (Anderholm, 1987). Among 

the facilities or activities that are potential sources of ground-water 

contamination in the Middle Rio Grande Basin are military and industrial 

operations, leaking underground-storage tanks, landfills, agricultural activities, and domestic septic systems.

The USEPA currently (2002) lists five Superfund sites in the 

Middle Rio Grande Basin (U.S. Environmental Protection Agency, 

2001b). One of these sites was removed from the priority list after contaminated soil was removed from the site, and another was removed from the 

priority list after site investigation. The remaining three sites have ground 

water contaminated with organic chemicals and are currently undergoing 

remediation.

The New Mexico Environment Department (NMED) currently 

(2002) lists about 700 former and present leaking underground-storagetank sites in the Middle Rio Grande Basin (New Mexico Environment 

Department, 2001), though not all these leaks resulted in ground-water 

contamination. Most of these tanks stored some form of fuel.

Currently (2002), three RCRA (Resource Conservation and 

Recovery Act of 1976) sites are in the Middle Rio Grande Basin (U.S. 

Environmental Protection Agency, 1999). Two of these sites, Kirtland Air 

Force Base and Sandia National Laboratories, are composed of a number 

of individual sites on large installations. These individual sites represent 

activities such as landfilling, fire training, and explosives testing. Potential 

ground-water contaminants are organic chemicals, radioactive elements, 

and metals. The third RCRA site has ground water contaminated with 

organic chemicals from electronics manufacturing. All three sites are 

undergoing remediation.

A study by Anderholm (1997), intended to examine the effects of 

land use on water quality at the water table, sampled and analyzed ground 

water from 24 monitoring wells having total depths within 20 feet of the 

water table in the basin- and valley-fill deposits in the Albuquerque area. 

This study found that “human activities have affected shallow groundwater quality.” Organic chemicals (pesticides, solvents, metal degreasers, 

and a gasoline additive) were detected in water from 11 of the 24 wells 

sampled, though no concentrations were equal to or greater than applicable 

drinking-water standards (not all chemicals had standards) (Levings and 

others, 1998). Other water-quality constituents indicated that “infiltration 

from septic-system effluent . . . has affected the shallow ground-water 

composition” in parts of the inner valley in the Albuquerque area 

(Anderholm, 1997). A later study by Bexfield and Anderholm (1997) 

Basalt flows exposed in Boca Negra Canyon. 

Arsenic in ground water is commonly associated 

with volcanic rocks in the subsurface.
100

examined the chemical quality of ground water being used for domestic 

supply in an area susceptible to contamination. Water from 14 domestic 

supply wells was sampled and analyzed. These wells had total depths 

ranging from 45 to 350 feet below the water table, which included wells 

completed in basin- and valley-fill as well as Santa Fe Group deposits. 

Bexfield and Anderholm (1997) concluded, “no strong evidence was found 

of effects on ground-water chemistry from human activities.” 

Kues and Garcia (1995) sampled 81 water-supply wells in four unincorporated areas of Bernalillo County during 1990–93. Three of these areas 

were in the Middle Rio Grande Basin and included 61 wells of varying 

depth: the inner valley of the Rio Grande both north and south of Albuquerque and an area northeast of Albuquerque. Pesticide concentrations 

were greater than detection limits in three wells in the inner valley. Concentrations of detergent additives (indicating the presence of domestic sewage) 

were greater than detection limits in four wells: three in the inner valley 

and one in the northeast area.

All municipal and community water systems are required to periodically test their water to ensure that it meets applicable drinking-water standards and to report the results to water users. In Albuquerque, groundwater samples from each well in the distribution system are analyzed on a 

regular basis to ensure compliance with drinking-water standards (City of 

Albuquerque, 2000). The results from this compliance monitoring are periodically mailed to water-utility customers. The City of Albuquerque has 

voluntarily collected and analyzed additional ground-water samples from 

its production wells to better characterize the ground-water resource. These 

data, which were not collected for compliance purposes, are summarized 

by Bexfield, Lindberg, and Anderholm (1999).

One of the typical steps in producing a 

ground-water-flow model is model calibration. Inevitably, some of the values 

used in creating the model are estimated. Calibration is the process of 

changing these model-input values to 

reduce model error by varying the estimated values over a range of probable 

values until there is an acceptable 

match between simulated and observed 

data (Leake, 1997; Spitz and Moreno, 

1996).
101

Throughout the course of the Middle Rio Grande Basin Study, a 

revised ground-water-flow model of the basin has been viewed as the 

culmination of the study. The revised model incorporates new information 

gathered since 1995 into a “state-of-the-art” understanding of the hydrogeology of the basin.

Ground-water-flow model of the basin

Since Reeder, Bjorklund, and Dinwiddie (1967) constructed the 

first ground-water model of an area in the Middle Rio Grande Basin, there 

have been a large number of models with different goals (see Box L) 

covering all or parts of the basin. Most of these models cover fairly small 

areas and have been used in conjunction with site investigations for 

hazardous-waste cleanup.

In 1995, Kernodle, McAda, and Thorn published the results of a 

ground-water-flow model covering the entire Middle Rio Grande Basin. 

This model used new interpretations of the hydrogeology of the basin to 

project future effects of ground-water withdrawals on the Santa Fe Group 

aquifer system, with an emphasis on the Albuquerque area. Though the 

results from this model greatly expanded the understanding of the hydrogeology of the Middle Rio Grande Basin, it also raised questions about 

certain components of the system that were poorly understood. Kernodle 

(1997, 1998) updated this model with revisions and corrections.

Tiedeman, Kernodle, and McAda (1998) modified the groundwater-flow model of Kernodle, McAda, and Thorn (1995) to test several 

hypotheses regarding the hydrogeology of the basin. Though the 

Tiedeman, Kernodle, and McAda (1998) model used fewer cells and 

layers, in many respects it was a more complex representation of the 

hydrogeology of the basin. This model was done with the aid of a newer 

version of the modeling software that used statistical methods to aid in 

model calibration (Hill, 1992). In 1999, the NMOSE adopted a modified 

version of this model to help administer ground-water resources in the 

basin (Barroll, 2001).

McAda and Barroll (2002) constructed a new ground-water-flow 

model of the Middle Rio Grande Basin to incorporate the large volume of 

new hydrogeologic data collected since 1995. This new model consists of 

nine layers that get increasingly thicker with depth (about 20 to 1,000 feet 

thick for the upper seven layers and variable thickness for two deeper 

layers) (fig. 7.1). Each layer is divided into a grid of cells containing 

156 rows and 80 columns, and each cell is 3,281 feet (1 kilometer) on a 

side (fig 7.2). Thus, the model contains 112,320 cells, 50,449 of which are 

active. The model encompasses the entire thickness of the Santa Fe Group 

in order to reproduce probable flow paths in the lower portions of the 

Chapter 7: Computer simulations of the 

aquifer system

The scale of a ground-water-flow model 

has important effects on how the 

aquifer system is simulated, as well as 

the modeling results. An example of 

such scale-dependent issues is the 

representation of faults. Though a large 

number of faults have been mapped in 

the Middle Rio Grande Basin, only 

those that affect the basinwide flow 

system are represented in the McAda 

and Barroll (2002) model. However, in a 

ground-water-flow model designed to 

examine the effects of a leaking underground-storage tank, smaller faults 

might have an important effect on local 

ground-water movement and, thus, 

need to be represented in the model.
102

Fault CONFINING UNIT

CONFINING UNIT

UNCONFINED

AQUIFER

CONFINED

AQUIFER

During the past several decades, computer 

models for simulating ground-water and 

surface-water systems have played an 

increasing role in the evaluation of 

ground-water development and management alternatives. The use of these 

models has provided an opportunity for 

water managers to quantitatively understand how ground water moves and to 

estimate the effects of human use of the 

water. 

In the most general terms, a model is a 

simplified representation of the appearance or operation of a real object or 

system. Ground-water-flow models 

attempt to reproduce, or simulate, the 

operation of a real ground-water system 

with a mathematical counterpart (a mathematical model). Mathematical models 

may use different methods to simulate 

ground-water-flow systems (Konikow and 

Reilly, 1999). One such method is called 

the finite-difference method (for example, 

McDonald and Harbaugh, 1988), which is 

the method used to simulate the groundwater system in the Middle Rio Grande 

Basin. 

In a finite-difference model, a groundwater system, such as the example in 

figure L.1, is represented by a set of rectangular cells (fig. L.2). The Darcy equation is used to calculate the flow of water 

between cells (fig. L.3). The interaction of 

the ground-water system with streams, 

recharge, and other boundaries of the 

ground-water system are also represented 

by equations. The computer model is the 

collection of all the equations that represent ground-water flow between the cells 

and across the boundaries. All the equations are solved simultaneously to 

account for all flow of water through the 

entire system and for each cell. Thus, the model simply calculates the 

volume of water flowing both horizontally and vertically between the cells 

and any changes in the volume of water stored in each cell. If the cells and 

boundaries represent the actual ground-water system reasonably, then the 

model is a mathematical description of the water levels and flows in the 

system.

The underlying philosophy of the simulation approach is that an understanding of the basic laws of physics and an accurate description of the 

specific system under study will enable an accurate, quantitative understanding of the relations between ground-water flow-system stress (for 

example, pumpage) and response (for example, water-level decline). This 

understanding enables forecasts (projections) to be made for any defined 

set of conditions. Precise forecasts of future behavior of the ground-water 

system will rarely be possible because of the uncertainties in knowledge of 

the ground-water system associated with sparse or inaccurate data, errors in 

the scientists' understanding of the system, and poor definition of future 

Ground-water-flow models and how they are used to study 

the basin

Thomas E. Reilly1 and Douglas P. McAda2

1U.S. Geological Survey, Reston, 

Virginia.

2U.S. Geological Survey, 

Albuquerque, New Mexico.

L

Figure L.1.—Block diagram of a part of a hypothetical basin-fill groundwater system. The blue arrows show the direction of ground-water flow. 

Among the features shown are an unconfined aquifer overlying a confining 

unit and confined aquifer, a gaining stream, infiltration from irrigated 

agriculture, and mountain-front recharge. 
103

Fault

Q=C(∆h)

stresses. Although forecasts of future system behavior based on models are 

imprecise (even when developed competently and objectively), they represent the best available decision-making information at the time. 

Models that accurately represent the ground-water system being evaluated 

are expected to produce more accurate forecasts than models that fail to 

represent important aspects of the system. The determination of which 

aspects of an actual ground-water system should be incorporated into a 

computer simulation depends, in part, on the objectives of the study for 

which the model is being developed. The objectives of a study in which a 

computer simulation is used as an analysis tool influence the size of the 

modeled area, the depth of concern, the size and shape of the model cells or 

elements, and the methods used to represent the boundary conditions of the 

system.

The model created for the ground-water system in the Middle Rio Grande 

Basin can be used to estimate the consequences of changes in water use on 

the ground-water system and the water-budget components, such as the 

exchange of flow between the ground-water system and the Rio Grande. In 

addition, the model, by virtue of its attempt to mathematically reproduce all 

the important aspects of the ground-water-flow system, can indicate which 

components of the system are best known, which are poorly known, and 

which components are more important than others. This information can 

then be used to efficiently gather the information that will most improve 

further understanding of the Middle Rio Grande Basin ground-water 

system.

Figure L.2.—Block diagram of part of a hypothetical basin-fill ground-water 

system with some model cells shown superimposed. The model cells cover 

the entire ground-water system being simulated.

Figure L.3.—Subset of the 

model cells that represent 

an aquifer, indicating that 

flow is calculated between 

adjacent cells. A form of 

the Darcy equation, which 

is used to calculate flow 

between each cell, is 

shown. In the equation, ∆h 

is the head difference 

between the cell and adjacent cells, Q is flow, and C 

is the hydraulic conductance between the centers 

of the cells. The hydraulic 

conductance (C) is a 

model parameter that 

attempts to represent the 

water-transmitting properties of the aquifer between 

cells.
104

aquifer. In addition, the orientation of this model grid is north-south 

(parallel to the dominant trend of faults and the Rio Grande in the main part 

of the basin) to better align the principal directions of hydraulic conductivity in the basin. (Previous model versions aligned the model grid along 

the axis of the basin because of an incomplete understanding of the 

geologic framework; this also increased computational efficiency.)

The time simulated by a ground-water-flow model is divided into a 

series of stress periods. The McAda and Barroll (2002) model uses 5-year 

stress periods for 1900–74, 1-year stress periods for 1975–89, and irrigation/nonirrigation season stress periods for 1990–2000. Thus, the model 

uses a total of 52 stress periods for the entire simulation period.

The continued evolution of computers 

from the early days of ground-water 

modeling has allowed scientists and 

engineers to create increasingly more 

complex and realistic simulations of the 

ground-water-flow system, as well as 

allowed for easier calibration and 

improvement of methods for displaying 

results.

WEST

Approximate

elevation

Predevelopment water table

Land surface

Rio Grande

Layer 1

Layer 2

Layer 3

Layer 4

Layer 5

30–50 feet thick

50–80 feet thick

Layer 6

Layer 7

380–630 feet thick

210–350 feet thick

600 feet thick

1,000 feet thick

6,000 feet

Layer 9

Layer 8

800–7,800 feet thick

400–3,900 feet thick

Model base

Sea level

2,000 feet

–6,000 feet

–2,000 feet

Modified from McAda and Barroll (2002) Not to scale--approximate elevation shown.

Generalized section along model row 80.

Thicknesses shown are for the entire model.

100–160 feet thick

EAST

Figure 7.1.—Generalized configuration of ground-water-flow model layers 

used by McAda and Barroll (2002) along model row 80.
105

McKINLEY

CIBOLA

VALENCIA

SOCORRO

TORRANCE

SANTA FE

BERNALILLO

SANDOVAL

EXPLANATION

River cell

Active model cell

Middle Rio Grande Basin

Tributary- and subsurface-recharge cell

River and riverside-drain cell

Tributary-recharge cell

Mountain-front-recharge cell

Subsurface-recharge cell

0 20 40 MILES

0 20 40 KILOMETERS

35°30'

35°15'

35°

34°45'

34°30'

107°15' 107° 106°45' 106°30' 106°15'

1 20 40 60 80

1

20

40

60

80

100

120

140

156

Sierra

Nacimiento

Jemez

Mountains

Manzano Mountains

Manzanita

Mountains

Los Pinos

Mountains

Ladron

Peak

Sierra Lucero

Mesa

Lucero

Española Basin

San Juan Basin

Sandia Mountains

Modified from McAda and Barroll (2002)

Figure 7.2.—Active cells in the ground-water-flow model grid 

(layer 1) of McAda and Barroll (2002). Different types of recharge 

and drain cells are shown.

The Rio Salado and Ladron Peak from Interstate 

25. In the ground-water-flow model of McAda 

and Barroll (2002) the course of the Rio Salado 

is simulated as tributary-recharge cells.
106

Information used in the groundwater-flow model

A vast quantity of information goes into the construction of a 

ground-water-flow model. First, the basic characteristics need to be established, such as the model boundaries, the orientation of model axes, the 

model cell size, and the number of layers. These decisions are based on the 

geologic framework, the amount of data available, and the ultimate purpose 

of the model (such as projection of water-level changes, water-rights 

administration, or well-field management). Next, the geologic framework 

needs to be translated into the ground-water-flow model by assigning 

hydrologic properties to the different lithologies represented by the model 

(see Box M). Finally, the characteristics of the hydrologic system need to 

be added by designating saturated model cells and flow rates into and out 

of the model.

Because it is impossible to know every piece of information needed 

for a ground-water-flow model, some of the values used are estimates or 

“educated guesses.” By using other bits of indirect information such as 

geophysics or water chemistry, additional information can be gained about 

the aquifer or flow system that can be used to refine some of the estimates 

used in the model (see Box N).

The hydrogeology in the McAda and Barroll (2002) model is primarily based on the geologic framework developed as part of the Middle Rio 

Grande Basin Study and described in Chapter 3. However, information on 

some specific areas of the basin is based on the work of others, such as that 

of Hawley and Haase (1992). 

Because ground-water levels in wells are some of the most important data used in calibrating ground-water-flow models, the expanded 

ground-water-level network and new monitoring wells have contributed a 

large amount of new information unavailable to previous modelers. Though 

long-term data are lacking for these newly installed monitoring wells, they 

do provide information on vertical hydraulic gradients within the aquifer as 

well as ground-water levels in areas that previously lacked wells.

The most important features or processes simulated in the McAda 

and Barroll (2002) model are:

• Mountain-front recharge: The findings of the various studies of 

mountain-front recharge described in this report have constrained 

previous estimates.

• Tributary recharge: Tributary recharge is simulated from streams and 

arroyos tributary to the Rio Grande.

• Subsurface recharge or underflow: Ground-water inflow from adjacent basins is simulated.

• Pumpage: Domestic-well pumpage is estimated on the basis of population. NMOSE-permitted wells use data through 2000 based on 

reported values. Actual monthly pumping figures for several water 

utilities and some industrial wells are used in the model; where only 

annual values are available, seasonal pumping volumes are estimated.

An unlined canal near Paseo del Norte in 

northern Albuquerque. Such canals are now 

represented in the ground-water-flow model 

with variable leakage rates. 
107

• River leakage: River leakage is simulated from the Rio Grande and 

Jemez River. Previous models simulated river leakage from only the 

Rio Grande. 

• Drain leakage: Though earlier models simulated riverside and interior 

drains, they could only gain water. The model now allows riverside 

drains to gain or lose water, though interior drains can still only gain 

water.

• Canal leakage: Earlier models assumed that canals were in direct 

connection with the water table, and leakage varied with changes in 

the elevation of the water table. The canals and water table are no 

longer connected, and the leakage rates change over time in the 

model.

• Discharge from septic fields: Ground-water recharge from septic 

fields is simulated.

• Seepage to ground water from irrigation: Irrigation seepage is simulated in the uppermost active model layer along the Rio Grande and 

Jemez River. Previous models simulated irrigation seepage along 

only the Rio Grande.

• Evapotranspiration: Evapotranspiration is simulated along the Rio 

Grande and Jemez River. Previous models simulated evapotranspiration along only the Rio Grande.

• Anisotropy: Hydraulic conductivity is simulated by different values in 

three directions. The ratio of north-south to east-west hydraulic 

conductivity changes, though the ratio of east-west to vertical 

hydraulic conductivity is fixed at 150:1.

• Specific storage and specific yield: These hydraulic parameters are 

simulated as uniform throughout the model.

• Reservoir leakage: Reservoir leakage is now simulated from Cochiti 

Lake and Jemez Canyon Reservoirs, whereas previous models simulated leakage from only Cochiti. In addition, stage changes are now 

simulated in both reservoirs.

The upstream end of Cochiti Lake. The groundwater-flow model simulates leakage from the 

reservoir.
108

Ground-water-flow models are mathematical representations of real 

ground-water-flow systems, as described in Box L. With the finite-difference method used to model the Middle Rio Grande Basin, the system is 

represented by a set of rectangular cells (fig. M.1). Mathematical equations 

are used to calculate the flow of ground water between adjacent cells and 

between cells and the hydrologic boundaries of the system (for example, 

lateral boundaries of recharge and discharge, and boundaries between 

ground water and the surface flow of rivers and streams). 

The hydraulic characteristics used in the ground-water-flow model depend 

on the kinds of rock present and their hydraulic properties (see the “Aquifer 

productivity” section on page 58). The ground-water system of the Middle 

Rio Grande Basin consists primarily of various sedimentary deposits that 

vary widely in their hydraulic properties (see Box C). Direct or indirect 

measurements of these characteristics are obtained by tests conducted in 

wells or outcrops, but such test data are available for only limited parts of 

the whole ground-water system. One of the challenges in building a credible ground-water-flow model, then, is to understand what kind of rock was 

tested at various locations, to relate those test data to similar rock elsewhere, and to understand the geologic framework well enough to predict 

what kinds of rock probably lie in areas that have no wells. This then is the 

purpose of a geologic model: to define the three-dimensional distribution 

of rock units of broadly similar hydraulic characteristics. These make up 

the starting values for the mathematical calculations of the ground-waterflow model.

The first things to be established for the mathematical flow model are the 

size of the cells, the number of layers in the model, and the orientation of 

the layers of cells in relation to geologic features. Hydraulic characteristics 

must be uniform within each model cell, so the cells need to be small 

enough to represent the real-world variation in geologic materials 

(fig. M.2). However, the cells cannot be so small that the model requires 

too many calculations for a computer to handle efficiently. Therefore, the 

dimensions of individual cells generally reflect a balance between the variation in geologic materials, the objectives for which the model is to be 

used, and the computation time. Because the geometric dimensions of each 

model cell encompass large volumes of rock, the resulting model values for 

hydraulic characteristics are averages. Similarly, the number of vertical 

How the geologic framework is translated into a groundwater-flow model

Douglas P. McAda1 and James C. Cole2

M

1U.S. Geological Survey, Albuquerque, New Mexico.

2U.S. Geological Survey, Denver, Colorado.

Modified from McDonald and Harbaugh (1988)

EXPLANATION

Active model cell

Inactive model cell

Aquifer boundary

Model impermeable boundary

CROSS-SECTIONAL VIEW

MAP VIEW

Layer 1

Layer 2

Layer 3

Layer 4

Figure M.1.—Schematic representation of 

an aquifer in a finite-difference groundwater-flow model. 
109

The three-dimensional geologic framework 

of the Middle Rio Grande Basin is based on 

rock units in outcrops, wells, and extrapolations between the two. The interpretation is 

based on a conceptual understanding of the 

history of faulting and deposition in the rift 

basin (see Box C). Where the geologic 

framework shows that the depositional environment for the rift-fill sediments was 

similar over a broad area, the ground-waterflow model consists of side-by-side cells that 

have similar hydraulic properties. Where the 

geologic framework shows that the depositional environment was constant for a long 

period of time, the flow model consists of 

stacked cells that have similar hydraulic 

properties. Where the geologic framework 

shows that faulting was active during deposition of a particular kind of sediment, the flow 

model consists of a thicker stack of cells on 

the downthrown side of the fault than on the 

upthrown side.

During the process of model calibration, 

comparison of modeled results with historical data and adjustment of model-input 

values may continue through several cycles 

until the disparities are minimized. If the 

disparities remain large in some areas that 

can be resolved only by changing the kinds 

of geologic “sponges,” then the geologic 

framework is reviewed and revised accordingly.

Modified from McDonald and Harbaugh (1988)

Layer 1

Layer 2

Layer 3

Aquifer cross section

Aquifer cross section with model grid superimposed

Sand and gravel

Silt

Fine sand

Cells are rectangular.

This cell contains

material from three

stratigraphic units

Figure M.2.—Schematic representation of ground-water flow-model 

cells related to sedimentary deposits.

layers in the model should be enough to represent known layering in the 

geologic environment, but not so many that computations are unacceptably long for the intended use of the model. The orientation of the flowmodel axes is generally selected so that one direction is parallel to the 

dominant direction of greatest hydraulic conductivity. The ground-waterflow model of the Middle Rio Grande Basin is described in Chapter 7. 

The geologic environment for ground water in the Middle Rio Grande 

Basin can be visualized as a bathtub filled with rectangular sponges. The 

bottom of the bathtub is defined by rocks that are older than the Santa Fe 

Group (see Box C) and transmit much less water than the Santa Fe Group 

itself. In the flow model, the top of these older rocks represents the base 

of the model and is defined as a barrier to flow (fig. M.1; “inactive 

cells”). However, small amounts of water enter the basin through these 

rocks, at the sides of the bathtub, in the form of subsurface recharge or 

underflow (see the “Subsurface recharge or underflow” section on 

page 77). The hypothetical sponges, which have the dimensions of the 

model cells, can be thought of as representing individual volumes of 

Santa Fe Group deposits with differing hydraulic properties. For 

example, cells in the flow model that contain mostly coarse sand and 

gravel might correspond to a sponge with large, open pores that allow 

water to move freely. Model cells that contain mostly silt and clay might 

correspond to a sponge with small pores that restrict the flow of water.
110

What the ground-water-flow model 

tells us about the hydrologic system 

of the basin

A ground-water-flow model is a powerful tool for analyzing an 

aquifer system. Among the most important findings of McAda and Barroll 

(2002) are:

• Prior to installation of the riverside drains along the Rio Grande, the 

river was losing flow. This water probably was being evapotranspired 

and (or) was recharging the Santa Fe Group aquifer system. Currently 

(2002), the drains intercept much of this flow and divert it back into 

the river.

• The Rio Grande and riverside drains are so closely related, especially 

during the nonirrigation season, that they function as one system.

• The hydrologic connection between the Rio Grande and underlying 

Santa Fe Group aquifer system is variable and changes with the 

lithology of a particular river reach.

• In much of the Santa Fe Group aquifer system throughout the basin, 

water removed from storage is partially replaced during the 

nonirrigation season.

• Mountain-front recharge to the Santa Fe Group aquifer system is less 

than amounts estimated by previous models. This is partly due to the 

findings of the various studies of mountain-front recharge described 

in this report.

Table 7.1 shows the annual water budgets simulated by the groundwater-flow model of McAda and Barroll (2002) for predevelopment 

steady-state conditions and for 1999 (the two seasonal stress periods 

ending in March 1999 and October 1999). 

The mouth of Embudito Canyon in the 

Sandia Mountains. The Middle Rio Grande 

Basin Study has found ground-water 

recharge in such settings to be less than 

previously thought.
111

Table 7.1.—Simulated annual water budget for the ground-water-flow model of McAda and Barroll (2002). All 

values are in acre-feet per year

[--, 0 or not applicable]

Mechanism

Steady-state conditions 1999 conditions

Inflow 

(to 

aquifer)

Outflow 

(from 

aquifer)

Inflow 

(to 

aquifer)

Outflow 

(from 

aquifer)

Mountain-front recharge 12,000 -- 12,000 --

Recharge from intermittent tributaries 9,000 -- 9,000 --

Underflow from adjacent basins 31,000 -- 31,000 --

Canal seepage -- -- 90,000 --

On-farm irrigation seepage -- -- 35,000 --

Rio Grande main stem and Cochiti Lake 63,000 -- 317,000 --

Rio Grande riverside drains -- -- -- –208,000

Rio Grande interior drains -- -- -- –134,000

Jemez River and Reservoir -- -- 16,000 --

Ground-water withdrawals 15,000 -- -- –150,000

Septic-field return flow -- -- 4,000 --

Riparian and wetland evapotranspiration -- –130,000 -- –84,000

Aquifer storage -- -- 110,000 –49,000

 Totals: 130,000 –130,000 624,000 –625,000
112

precipitation that recharges ground water. Once underground and sheltered 

from cosmic rays, no more carbon-14 is formed and the existing carbon-14 

decays at a known, constant rate. Thus, the ratio of carbon-14 to carbon-12 in 

a ground-water sample from a well or spring reflects how long the water has 

been in the aquifer system. The length of time calculated from this ratio is 

referred to as the carbon-14 age, and the carbon-14 technique is used for 

dating water that has been in the ground-water system between about 1,000 

and 50,000 years.

The ground-water-flow model of the Middle Rio Grande Basin is described 

in Chapter 7 and Boxes L and M. Typically, water levels measured in a 

number of wells at different locations and times and the rates of ground-water 

discharges measured along streams are used to calibrate (check and adjust) 

ground-water models. These observations are crucial but are limited in calibrating large, complex ground-water-flow models with a large number of 

parameters. Models that rely predominantly on water levels as observations 

usually have a high degree of uncertainty associated with their predictions. 

Previous models constructed of the Middle Rio Grande Basin (Kernodle, 

McAda, and Thorn, 1995; Tiedeman, Kernodle, and McAda, 1998) have 

relied predominantly on water levels for their calibration because groundwater movement between the Rio Grande and aquifer has been difficult to 

measure accurately.

Ground-water models can be used to simulate not only water levels but also 

the rate of speed at which water is moving through the ground at any particular location. This type of information is very useful in the estimation of the 

movement of a contaminant or any other dissolved substance. Computer 

codes have been developed, such as Pollock (1994), that work with groundwater-flow models to estimate flow paths followed by parcels of ground 

water and their associated traveltimes. This type of simulation is being used 

in the Middle Rio Grande Basin to estimate the time of travel of water from 

recharge areas to wells where samples have been collected and analyzed for 

carbon-14 (fig. N.1). If the model is a good representation of the system, the 

carbon-14 ages should agree closely with the traveltimes estimated by the 

model. If the values do not agree, the model can be further calibrated until a 

best fit can be made with all the observations. Computer codes that can make 

optimum fits between observations and model parameters, such as Poeter and 

Hill (1998), can be used in this situation. Because carbon-14 ages provide 

information directly related to the flux of ground water through the basin, 

they make inherently better observations than water levels for estimating the 

long-term (greater than 1,000 years) rates of natural recharge to the basin. 

Both long-term and current rates of recharge are important for waterresources planning because they contribute to an understanding of the 

potential long-term ground-water yield of the basin. 

Carbon-14 (14C) is a natural, radioactive 

isotope of carbon that can be used to estimate the length of time that a sample of 

water collected from a well has been in 

the ground-water system (Kalin, 1999). 

Carbon-14 is continuously being created 

in the atmosphere as nitrogen is 

bombarded by cosmic rays from outer 

space. Over time, the carbon-14 (14C) 

radioactively decays to carbon-12 (12C) at 

a known rate. An approximate balance is 

reached between the production and 

decay of carbon-14, resulting in a relatively stable concentration in the atmosphere. Carbon-12 and carbon-14 are both 

equally incorporated into carbon dioxide 

gas in the atmosphere and in bicarbonate 

(HCO3) ions dissolved in rainwater. The 

constant concentration of carbon-14 in the 

atmosphere leads to an equilibrium 

concentration of bicarbonate dissolved in 

How carbon-14 data were used to improve the ground-waterflow model

Ward E. Sanford1

N

1

U.S. Geological Survey, Reston, Virginia.
113

0 5 10 MILES

0 5 10 KILOMETERS

Jemez River

Rio Puerco

Jemez

Canyon

Reservoir

Cochiti Lake

RIO

GRANDE 

Boundary of the Middle

Rio Grande Basin

Edge of the

model grid

A

A'

Predicted

ground-water

flow path

55,000

years

Well

44,000

EXPLANATION

Predicted traveltime, in years,

for the predicted flow path

Carbon-14 age

35°30'

35°15'

35°

107° 106°45' 106°30' 106°15'

4,000

years

15,000

years

55,000

years

Land surface

South North

Vertical exaggeration = 50X

A A’ Rio Grande Jemez River

26,000

7,000

44,000

Figure N.1.—Traveltimes and ground-water flow paths predicted by a preliminary 

version of the current revision of the ground-water-flow model of the Middle Rio 

Grande Basin (Sanford, 1999). Three flow paths are shown that extend from 

recharge areas to observation wells from which samples were analyzed for 

carbon-14. The illustration is simplified in that no vertical mixing is shown.
114

What the ground-water-flow model 

tells us about future conditions

Ground-water-flow models are commonly constructed to make 

projections of future conditions based on varying management scenarios. 

Though these model projections are based on incomplete data and estimates of future conditions, they are often the best tool available for 

management decisions (Alley, Reilly, and Franke, 1999). The model of 

Kernodle, McAda, and Thorn (1995) included projections for conditions 

up to 2020, but this model was modified by CH2M Hill to make projections 

up to 2060 (City of Albuquerque Public Works Department, 1995). As 

mentioned in Chapter 2, these forecasts were instrumental in the City of 

Albuquerque revising its water-use strategy.

The McAda and Barroll (2002) ground-water-flow model of the 

Middle Rio Grande Basin does not make any projections of future conditions, though it could be modified to do so. It does provide water-resource 

managers a more accurate and powerful tool to evaluate the potential 

effects of management decisions.

Steady-state conditions in a groundwater-flow model refer to flow conditions that do not change over time. The 

natural hydrologic conditions prior to 

ground-water development and largescale alteration of the surface-water 

system are usually assumed to be 

steady state (Spitz and Moreno, 1996). 
115

Instead of providing final, definitive answers, the study of the water 

resources of an area tends to lead to more questions about the system. This 

may be because new data conflict with the current understanding of the 

system or because changes in the management and use of water raise new 

questions. Though many of the elements listed in the plan of study by 

McAda (1996) have been addressed by the Middle Rio Grande Basin 

Study, we still do not have all the information that lawmakers and 

managers will ultimately need to best manage the water resources in the 

basin. Therefore, it is important to continue studying the Middle Rio 

Grande Basin to deal with the issues of today and be prepared for those of 

tomorrow. Among the questions that could be better defined:

How much water is pumped where 

and by whom?

Until the locations and pumping characteristics of the major supply 

wells in the Middle Rio Grande Basin are known with more certainty, estimates of these important parameters will introduce error into simulations 

and estimations of ground-water behavior. However, it may be impossible 

to know exactly the locations of all domestic-supply wells in the basin and 

the volumes of water pumped from each. 

What are the availability and quality 

of water in deeper parts of the 

aquifer?

On the basis of limited data and similar conditions in other aquifers, 

ground water in the deeper parts of the aquifer is assumed to be of limited 

quantity and poor quality. Until more is known, however, the suitability of 

this water for a given use remains speculative. Few deep wells have been 

drilled in the basin because deep wells are expensive and because shallower wells have provided adequate supply. The expense to drill deeper 

may be justified in the future if deeper supplies are needed.

Chapter 8: Important questions that remain about

water resources of the Middle Rio Grande Basin

Upper Santa Fe Group (Ceja Member of 

the Arroyo Ojito Formation) sediments 

exposed on the northern side of the Los 

Lunas volcano. Much of the Santa Fe 

Group aquifer system in the Middle Rio 

Grande Basin is composed of such 

deposits. (Courtesy of J.C. Cole.)
116

How much water does vegetation in 

the bosque use?

As discussed in Chapter 5, estimates of evapotranspiration in the 

Middle Rio Grande Basin vary because it is a difficult parameter to 

measure directly. Because maintenance of the bosque has become a priority 

for esthetic and wildlife purposes, the measurement of actual evapotranspiration is of critical importance. With the availability of new techniques for 

quantifying evapotranspiration, several groups including Dahm and others 

(2000) and the Bureau of Reclamation (2001a, b, c) have begun to work to 

refine previous estimates of evapotranspiration.

How is the aquifer responding to 

pumping over the long term?

To characterize the long-term response of the aquifer to groundwater pumping, ground-water levels in the monitoring network must 

continue to be measured. Such long-term monitoring is perhaps the most 

important information that can be collected for long-term aquifer-system 

and water-resource management.

Another aspect of aquifer response to ground-water pumping is 

subsidence. By using new and traditional tools, such as interferometric 

synthetic aperture radar (InSAR) and repeat surveys, respectively, the onset 

of subsidence can be detected early.

Is septic-system effluent

contaminating ground water?

The possibility of effects from septic-system effluent on the quality 

of water from domestic-supply wells in rapidly developing rural areas will 

continue to raise questions. The continuing development of new methods 

may improve the unambiguous detection of septic-system effluent in 

ground water.

How will the more stringent arsenic 

standard affect water supplies?

The reduction in the drinking-water standard for arsenic presents 

new challenges for water-resource managers. To reduce treatment costs, 

wells pumping water with large concentrations of arsenic may need to be 

taken out of production or the water blended with water of an acceptable 

concentration. As more is learned about naturally occurring arsenic in 

ground water, the completion of production wells might be possible in 

areas or at specific depths of the aquifer with acceptable concentrations of 

arsenic.

Tamarisk (in the foreground) and cottonwood 

(in the background) along the Albuquerque 

Drain near Paseo del Norte. Such plants in 

the bosque account for much of the water 

consumption in the Middle Rio Grande Basin.
117

Are pharmaceuticals present in 

ground or surface water?

Recently, pharmaceutically active compounds have been detected at 

very small (parts per billion) concentrations in treated wastewater either 

discharged to surface water or recharged to ground water. Though the 

effects of these very small concentrations on humans are unknown, 

concentrations as small as parts per trillion have been found to adversely 

affect fish (Sedlak, Gray, and Pinkston, 2000). In 1999 and 2000, USGS 

researchers sampled 139 streams in 30 States for 95 pharmaceuticals, 

hormones, and other organic wastewater contaminants (Kolpin and others, 

2002). These compounds were detected in 80 percent of the streams 

sampled, and of the 95 compounds, 82 were detected in surface water. In 

2000, the New Mexico Environment Department and Department of 

Health began analyzing ground- and surface-water samples for 28 drug 

residues from 24 sites throughout the State and found five different 

compounds at eight sites (McQuillan and others, 2000). Given concern 

about the silvery minnow and other fish species in the Rio Grande, as well 

as the planned direct use of surface water for municipal supplies, this topic 

will likely be investigated in more detail in the Middle Rio Grande Basin 

in the near future. 

USGS personnel sampling shallow ground 

water for chemical analysis on the Rio Grande 

upstream from Corrales. (Courtesy of F.E. 

Gebhardt, USGS.)
118
119

The most prominent hydrologic feature in the largely semiarid 

Middle Rio Grande Basin is the Rio Grande, whereas the sole source of 

water for municipal, domestic, and commercial supply is currently (2002) 

the Santa Fe Group aquifer system. The water resources of the Middle Rio 

Grande Basin are a combination of these surface- and ground-water 

systems, which are intimately linked through a series of complex interactions. These interactions often make recognizing the boundary between the 

two systems difficult, and changes in one system often affect the other. The 

most important points in our present understanding of the water resources 

of the Middle Rio Grande Basin are:

• When ground water is pumped from an aquifer system faster than it is 

recharged, ground-water levels decline, a condition known as groundwater mining. Ground-water levels have declined with the economic 

development of the Middle Rio Grande Basin. The effects of groundwater pumping are evident when comparing historical (1960–61) and 

the most recent (1994–95) ground-water-level maps; water-level 

declines are more than 160 feet in an area beneath east Albuquerque. 

• Previous studies found the Rio Grande to be very well connected 

hydraulically to the Santa Fe Group aquifer system, and years of 

water-management policy were based on this understanding. Recent 

studies of the interaction between the river and aquifer (including 

ground-water-flow models) indicate that the hydraulic connection is 

less than previously thought. 

• As Albuquerque grew, most of the new municipal-supply wells were 

completed in high-quality parts of the Santa Fe Group aquifer system. 

The quantity and quality of the water led to the popular belief that the 

entire Middle Rio Grande Basin was underlain by a high-quality 

aquifer; it is now known that such areas of high-quality aquifer are 

relatively limited and that much less water is available for pumping 

than previously thought.

• Geophysical studies of the Middle Rio Grande Basin in conjunction 

with computer modeling of the Santa Fe Group aquifer system indicate that faults are more numerous than previously thought and that 

they can affect ground-water movement, particularly when they 

juxtapose aquifer materials of substantially different hydraulic properties.

• Previous estimates of mountain-front recharge were based on indirect 

calculations from water budgets and computer modeling of the Santa 

Fe Group aquifer system. New studies using direct measurements and 

ground-water age dating have shown that mountain-front recharge is 

substantially less than previously believed.

Chapter 9: Key points regarding water resources 

of the Middle Rio Grande Basin

A USGS hydrologist collecting geophysical data. 

Geophysical studies such as this one have 

contributed to understanding the Santa Fe 

Group aquifer system.
120

• The bosque assumed its present character in about the past 60 to 

70 years, developing in an area that was formerly semibarren flood 

plain with scattered stands predominantly of cottonwood and willow. 

The present character was caused by the spread of exotic plant species 

and the construction of bank-stabilization and flood-control structures, including dams and levees. Though estimates vary, a substantial 

amount of ground and surface water is consumed by evapotranspiration from the bosque.

By increasing the understanding of the water resources of the 

Middle Rio Grande Basin, water-resource managers and planners will have 

additional tools to make sound, scientifically based decisions on the future 

of water in the basin.
121

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AMAFCA: Albuquerque Metropolitan Arroyo Flood Control Authority

API: American Petroleum Institute

As: arsenic

AWARDS: Agricultural Water Resources Decision Support System

BP: before present

°C: degree Celsius

Ca: calcium

CaCO3: calcite

CaMg(CO3)2: dolomite

CaSO4: anhydrite

CaSO4·2H2O: gypsum

CERCLA: Comprehensive Environmental Response Compensation and Liability Act of 1980 (“Superfund”)

CFC: chlorofluorocarbon (Freon compounds)

Cl: chloride

cm: centimeter

CO2: carbon dioxide

ET: evapotranspiration

°F: degree Fahrenheit

GPS: Global Positioning System

1H: hydrogen

2H: deuterium

3H: tritium

HCO3: bicarbonate

H2O: water

InSAR: Interferometric Synthetic Aperture Radar

K: potassium

LiDAR: Light Detection and Ranging

Ma: mega-annum (million years before present)

MCL: maximum contaminant level

MDWCA: Mutual Domestic Water Consumers Association

Mg: magnesium

mg/L: milligrams per liter, approximately equal to parts per million

mGal: milligal

mmho: millimho, equivalent to millisiemen

MRGCD: Middle Rio Grande Conservancy District

MRGCOG: Middle Rio Grande Council of Governments

mS: millisiemens, equivalent to millimhos

μg/L: micrograms per liter, approximately equal to parts per billion

μS/cm: microsiemens per centimeter

N: nitrogen

Na: sodium

NaCl: halite (sodium chloride or table salt)

NMBGMR: New Mexico Bureau of Geology and Mineral Resources, formerly NMBMMR

NMBMMR: New Mexico Bureau of Mines and Mineral Resources, now NMBGMR

NMED: New Mexico Environment Department

NMOSE: New Mexico Office of the State Engineer

Abbreviations and Chemical Notation
132

NO3: nitrate

nT: nanoTesla

ohm-m: ohm-meter

ppt: parts per thousand

pptv: parts per trillion volume

RCRA: Resource Conservation and Recovery Act of 1976

S: siemen

S: sulfur

SAR: synthetic aperture radar

SF6: sulfur hexafluoride

SI: International System of Units (metric system)

SiO2: silica (silicon dioxide or quartz)

SLEUTH: Slope, Land Use, Exclusions, Urban, Transportation, and Hillshade

SO4: sulfate

SSC: steady-state centrifuge

SSCAFCA: Southern Sandoval County Arroyo Flood Control Authority

TDEM: time-domain electromagnetic

TU: tritium units

URGWOM: Upper Rio Grande Water Operations Model

USACE: U.S. Army Corps of Engineers

USEPA: U.S. Environmental Protection Agency

USFWS: U.S. Fish and Wildlife Service

USGS: U.S. Geological Survey

VOC: volatile organic compound

WSFO: Weather Service Field Office

Prefixes for Abbreviations for Multiples and Submultiples

T: tera (1012)

M: mega (106)

k: kilo (104)

c: centi (10–2)

m: milli (10–3)

μ: micro (10–6)

n: nano (10–9)

p: pico (10–12)