U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2019–5122

Prepared in cooperation with the Ute Mountain Ute Tribe

Hydrogeologic Characterization, Groundwater Chemistry, and 

Vulnerability Assessment, Ute Mountain Ute Reservation, 

Colorado and Utah
Cover. Top right: Windmill on the Ute Mountain Ute Reservation. Photograph by Jeannette H. Oden, USGS.

Top left: Mesas in the eastern portion of the Ute Mountain Ute Reservation. Photograph by Jeannette H. Oden, USGS. 

Bottom left: Chimney Rock, showing the intertonguing and gradational relations between the Mancos Shale and the 

lower part of the Point Lookout Sandstone. Photograph by Jeannette H. Oden, USGS.

Bottom right: Spring on the Ute Mountains. Photograph by Nancy J. Bauch, USGS.
Hydrogeologic Characterization, 

Groundwater Chemistry, and Vulnerability 

Assessment, Ute Mountain Ute 

Reservation, Colorado and Utah

By Nancy J. Bauch and L. Rick Arnold

Prepared in cooperation with the Ute Mountain Ute Tribe

Scientific Investigations Report 2019–5122

U.S. Department of the Interior

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

DAVID BERNHARDT, Secretary

U.S. Geological Survey

James F. Reilly II, Director

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

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

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Suggested citation:

Bauch, N.J., and Arnold, L.R., 2020, Hydrogeologic characterization, groundwater chemistry, and vulnerability 

assessment, Ute Mountain Ute Reservation, Colorado and Utah: U.S. Geological Survey Scientific Investigations 

Report 2019–5122, 76 p., https://doi.org/10.3133/sir20195122.

Associated data for this publication:

Bauch, N.J., 2020, Geospatial datasets for estimating depth to the top of the Dakota Sandstone, Ute Mountain Ute 

Reservation, Colorado, 2017: U.S. Geological Survey data release, https://doi.org/10.5066/P9S4MOB6.

ISSN 2328-0328 (online)
iii

Acknowledgments

The authors thank Colin Larrick and Scott Clow of the Ute Mountain Ute Environmental Program 

for their assistance on this assessment of the groundwater resources of the Ute Mountain Ute 

Reservation.

The authors thank several U.S. Geological Survey staff for assistance with the report. Helpful 

discussions with Pete McMahon enhanced the understanding and interpretation of environmental tracers in groundwater. Tara Gross developed the maps published in this report, and Will 

McDermott assisted in the preparation of maps and figures. The report was improved by review 

comments from Pete McMahon, Suzanne Paschke, Kimberly Beisner, Katie Walton-Day, Alisa 

Mast, and Jeannette Oden.
iv

Contents

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

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

Introduction.....................................................................................................................................................2

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

Description of Study Area ...................................................................................................................2

Physiography................................................................................................................................2

Geology..........................................................................................................................................4

Jurassic System .................................................................................................................5

Cretaceous System ............................................................................................................5

Late Cretaceous and Tertiary Systems ...........................................................................7

Quaternary System.............................................................................................................7

Climate...........................................................................................................................................7

Surface-Water Hydrology ..........................................................................................................8

Groundwater Hydrology .............................................................................................................9

Land Cover and Land and Water Use.......................................................................................9

Methods of Hydrogeologic Characterization..........................................................................................10

Surficial Deposits................................................................................................................................10

Dakota Sandstone...............................................................................................................................10

Methods for Compilation and Analysis of Groundwater-Chemistry Data..........................................14

Data Sources.......................................................................................................................................14

Types of Groundwater-Chemistry Data...........................................................................................18

Data-Quality Assurance.....................................................................................................................19

Data Aggregation and Summarization ............................................................................................20

Water-Quality Standards...................................................................................................................20

Hydrogeologic Characterization of Surficial Deposits and Dakota Sandstone ................................25

Groundwater Chemistry..............................................................................................................................25

Physical Properties.............................................................................................................................29

Total Dissolved Solids and Major Ions ............................................................................................35

Total Dissolved Solids ...............................................................................................................35

Water Type..................................................................................................................................35

Major Ions and Fluoride............................................................................................................40

Nutrients...............................................................................................................................................41

Trace Elements and Uranium............................................................................................................41

Pesticides and Volatile Organic Compounds .................................................................................48

Coliform Bacteria................................................................................................................................48

Environmental Tracers .......................................................................................................................48

Vulnerability Assessment...........................................................................................................................54

Information Needs.......................................................................................................................................59

Summary........................................................................................................................................................59

References Cited..........................................................................................................................................61

Appendix 1. Hydrogeologic Characterization......................................................................................67

Appendix 2. Supplemental Information for Data-Quality Assurance ..............................................74
v

Figures

1. Map showing the location and extent of the Ute Mountain Ute Reservation in 

Colorado, New Mexico, and Utah..............................................................................................3

2. Map showing the altitude of the Ute Mountain Ute Reservation in Colorado ...................4

3. Map showing geology of the Ute Mountain Ute Reservation in Colorado .........................5

4. Map showing land cover and land use on the Ute Mountain Ute Reservation in

Colorado .........................................................................................................................................8

5. Map showing location of Ute Mountain Ute Tribe wells and springs where

water-level and (or) groundwater-chemistry data were collected on the Ute

Mountain Ute Reservation in Colorado...................................................................................11

6. Map showing location of U.S. Geological Survey and Colorado Oil and Gas

Conservation Commission springs and wells with historical water-level

and (or) gr oundwater-chemistry data on the Ute Mountain Ute Reservation in

Colorado .......................................................................................................................................13

7. Map showing generalized depth to the top of the Dakota Sandstone in feet below

land surface on the Ute Mountain Ute Reservation in Colorado........................................26

8. Boxplots showing distribution of specific conductance in water samples collected

by the Ute Mountain Ute Tribe in 1998–2002 and 2011–17 for springs and wells on

the Ute Mountain Ute Reservation in Colorado and Utah....................................................31

9. Boxplots showing distribution of total dissolved solids in water samples collected

by the Ute Mountain Ute Tribe in 1996–2017 for springs and wells on the Ute

Mountain Ute Reservation in Colorado and Utah..................................................................36

10. Piper diagram showing water type for samples collected by the Ute Mountain Ute

Tribe in 1996–2017 for springs and wells on the Ute Mountain Ute Reservation in

Colorado and Utah......................................................................................................................39

11. Boxplots showing distribution of fluoride in water samples collected by the Ute

Mountain Ute Tribe in 2002 and 2011–17 for springs and wells on the Ute Mountain

Ute Reservation compared to the Colorado Department of Public Health and

Environment water-quality standard for agricultural use of groundwater.......................40

12. Scatter plots showing distribution of unfiltered ammonia and unfiltered nitrate

plus nitrite in water samples collected by the Ute Mountain Ute Tribe in 2000–17 for

springs and wells on the Ute Mountain Ute Reservation in Colorado and Utah..............42

13. Graph showing the hydrogen (δ2H) and oxygen (δ18O) isotopic composition of

water samples collected by the Ute Mountain Ute Tribe in 2017 for one spring and

five wells on the Ute Mountain Ute Reservation in Colorado, plotted in relation to

the Global Meteoric Water Line...............................................................................................52

14. Graph showing tritium concentrations in relation to carbon-14 concentrations in

water samples collected by the Ute Mountain Ute Tribe in 2017 for one spring and

five wells on the Ute Mountain Ute Reservation in Colorado, with concentrations of

methane and nitrate plus nitrite ...............................................................................................53

15. Graph showing precipitation departure from average for meteorological station

051886 at Cortez, Colorado, 1930–2016....................................................................................58
vi

Tables

1. Generalized stratigraphic section of the geologic formations of the Ute Mountain

Ute Reservation in Colorado .......................................................................................................6

2. Ute Mountain Ute Tribe water-level data for unconsolidated surficial deposits, Ute

Mountain Ute Reservation in Colorado...................................................................................12

3. Sources of groundwater-chemistry data, number of sampling sites, period of

groundwater-chemistry record, and type of groundwater-chemistry data reported

by various organizations for springs and wells on the Ute Mountain Ute

Reservation in Colorado and Utah ...........................................................................................14

4. Description of springs and wells with groundwater-chemistry data on the Ute

Mountain Ute Reservation in Colorado and Utah, with sample year, number of

environmental sample days and samples, and type of groundwater-chemistry data....15

5. Aggregation of constituent names and data retrieved from the Water Quality Portal...21

6. Ute Mountain Ute Tribe water-quality standards for surface waters of the

Ute Mountain Ute Reservation and Colorado Department of Public Health and

Environment basic standards for agricultural use of groundwater...................................23

7. Estimation of lithology for springs and wells located on the Ute Mountain Ute

Reservation in Colorado and Utah and information on select monitoring wells in

Colorado .......................................................................................................................................27

8. Statistical summary for physical-property measurements collected by the Ute

Mountain Ute Tribe for springs and wells on the Ute Mountain Ute Reservation in 

Colorado and Utah, 1996–2017..................................................................................................31

9. Summary of physical-property measurements and concentrations of

groundwater-chemistry constituents in water samples collected by the Ute

Mountain Ute Tribe (UMUT) for springs and wells on the Ute Mountain Ute

Reservation in Colorado that exceed water-quality standards established by the

UMUT and the Colorado Department of Public Health and Environment. ........................32

10. Statistical summary for total dissolved solids and major ions in water samples

collected by the Ute Mountain Ute Tribe for springs and wells on the Ute

Mountain Ute Reservation in Colorado and Utah, 1996–2017 .............................................37

11. Select total dissolved solids data for the 1950s, 1970s, and some years from 1996 to

2017 for Ute Mountain Ute Tribe, U.S. Geological Survey, and Colorado Oil and Gas 

Conservation Commission wells on the Ute Mountain Ute Reservation in Colorado, 

sorted by likely lithology ............................................................................................................38

12. Statistical summary for nutrients in water samples collected by the Ute Mountain

Ute Tribe for springs and wells on the Ute Mountain Ute Reservation in Colorado

and Utah, 2000–17.......................................................................................................................43

13. Statistical summary for total recoverable and dissolved trace elements and total

recoverable and dissolved uranium in water samples collected by the Ute

Mountain Ute Tribe for springs and wells on the Ute Mountain Ute

Reservation in Colorado and Utah, 1996–2017.......................................................................44

14. Summary of sample collection and analysis by the Ute Mountain Ute Tribe for

pesticides and volatile organic compounds in wells on the Ute Mountain Ute

Reservation in Colorado, 2000–13 ............................................................................................49

15. Summary of data for total coliform and Escherichia coli bacteria for water samples

collected by the Ute Mountain Ute Tribe for springs and wells on the Ute

Mountain Ute Reservation in Colorado and Utah, 2001–16 .................................................50
vii

16. Summary of data for stable isotopes of hydrogen and oxygen of water and nitrogen

and oxygen of nitrate for water samples collected by the Ute Mountain Ute Tribe in

2017 for one spring and five wells on the Ute Mountain Ute Reservation in Colorado...52

17. Summary of tritium and carbon-14 data for water samples collected by the Ute

Mountain Ute Tribe in 2017 for one spring and five wells on the Ute Mountain Ute

Reservation in Colorado ............................................................................................................53

18. Summary of chlorofluorocarbon and apparent age for water samples collected 

by the Ute Mountain Ute Tribe in 2017 for one spring and four wells on the

Ute Mountain Ute Reservation in Colorado............................................................................55

19. Summary of dissolved gas data for water samples collected by the Ute Mountain

Ute Tribe in 2017 for one spring and four wells on the Ute Mountain Ute Reservation

in Colorado, with estimated recharge dates and concentrations of total

recoverable ammonia and sulfate ...........................................................................................55

20. Summary of noble gas data for water samples collected by the Ute Mountain Ute

Tribe in 2017 for one spring and four wells on the Ute Mountain Ute Reservation in

Colorado .......................................................................................................................................56

21. Land use and natural risk in groundwater vulnerability for the Ute Mountain Ute

Reservation..................................................................................................................................57
viii

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 0.004047 square kilometer (km2)

square mile (mi2) 2.590 square kilometer (km2) 

Flow rate

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

International System of Units to U.S. customary units

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

micrometer (μm) 0.00003937 inch (in.)

Volume

liter (L) 0.2642 gallon (gal)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 × °C) + 32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C = (°F – 32) / 1.8.

Datum

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

(NAVD88) or the National Geodetic Vertical Datum of 1929 (NGVD29).

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD27) 

or the North American Datum of 1983 (NAD83).

Altitude and elevation, as used in this report, refers to distance above the vertical datum.

Supplemental Information

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25 °C).

Concentrations of chemical constituents in water are given in either milligrams per liter (mg/L) 

or micrograms per liter (μg/L).

Concentrations of total coliform and Escherichia coli (E. coli) in water are reported as colonyforming units per 100 milliliters (cfu/100 mL).
ix

One milliequivalent per liter (meq/L) is equal to one thousand milligram-equivalents per one 

thousand milliliters (meq/mL). Chemical analyses of solutes in a sample are expressed in unit 

concentrations that are chemically equivalent in terms of atomic or molecular weight and 

electrical charge.

Results for measurements of stable isotopes of an element (with symbol E) in water, solids, 

and dissolved constituents commonly are expressed as the relative difference in the ratio of 

the number of the less abundant isotope (iE) to the number of the more abundant isotope of a 

sample with respect to a measurement standard.

Abbreviations

δ2H hydrogen-2/hydrogen-1 isotopic ratio 

δ15N nitrogen-15/nitrogen-14 isotopic ratio

δ18O oxygen-18/oxygen-16 isotopic ratio

bls below land surface

CDPHE Colorado Department of Public Health and Environment

CFC chlorofluorocarbon

COGCC Colorado Oil and Gas Conservation Commission

DEHP di(2-ethylhexyl) phthalate 

DEM digital elevation model

DO dissolved oxygen

DOE U.S. Department of Energy

EPA U.S. Environmental Protection Agency

GMWL Global Meteoric Water Line

MVNP Mesa Verde National Park

NURE National Uranium Resource Evaluation

NWIS National Water Information System

per mil parts per thousand

pmc percent modern carbon

redox reduction-oxidation

RPD relative percent difference

TDS total dissolved solids

TU tritium unit

UMUR Ute Mountain Ute Reservation

UMUT Ute Mountain Ute Tribe

USGS U.S. Geological Survey

VOC volatile organic compound

Hydrogeologic Characterization, Groundwater Chemistry, 

and Vulnerability Assessment, Ute Mountain Ute 

Reservation, Colorado and Utah

By Nancy J. Bauch and L. Rick Arnold

Abstract

The U.S. Geological Survey, in cooperation with the 

Ute Mountain Ute Tribe (UMUT), initiated a study in 2016 

to increase understanding of the hydrogeology and chemistry 

of groundwater within select areas of the Ute Mountain Ute 

Reservation (UMUR) in Colorado and Utah, identify vulnerabilities to the system and other natural resources, and outline 

information needs to aid in the understanding and protection 

of groundwater resources. The results presented for this study 

can be used to support the UMUT’s goal of protecting their 

vital groundwater resources on the UMUR. 

Hydrogeologic conditions were characterized for the 

surficial aquifer contained in Quaternary-age unconsolidated 

surficial deposits and the Dakota aquifer contained in the 

Cretaceous-age Dakota Sandstone. In the surficial aquifer, 

median depth to water ranges from about 5.4 to 17.2 feet 

below land surface in the Farm and Ranch Enterprise area 

and 11 to 34 feet below land surface in the Towaoc area, and 

the water table slopes generally southwest or south. A map 

of depth to the top of the Dakota Sandstone was constructed 

from existing well data. Depths range from zero in outcrop 

areas to more than 3,000 feet below land surface on mesas in 

the southeastern part of the UMUR.

Groundwater-chemistry data were collected by the UMUT 

from 13 springs and 31 wells from 1996 through 2017. Specific 

conductance was much lower for samples from springs than 

from wells; median values were 512 and 6,024 microsiemens 

per centimeter at 25 degrees Celsius, respectively. Spring 

samples were well oxygenated. A few well samples were anoxic 

(dissolved oxygen concentrations less than 0.5 milligrams per 

liter [mg/L]), indicating reducing conditions in the aquifer. 

About 75 percent of spring samples had fresh water (total dissolved solids concentrations less than 1,000 mg/L), and about 

85 percent of well samples had brackish or highly saline water 

(total dissolved solids concentrations greater than 1,000 mg/L). 

Water type for springs on the Ute Mountains was calcium bicarbonate. Lower-altitude springs had a calcium-sulfate water type. 

Most well samples had sodium as the dominant cation, and sulfate, bicarbonate, and chloride as the dominant anions. Fluoride 

concentrations in about 45 percent of well samples were greater 

than an agricultural-use standard of 2 mg/L. 

Nitrate plus nitrite concentrations in most spring and well 

samples were less than about 1.6 mg/L per liter. Concentrations in samples from wells in the irrigated agricultural area 

were elevated; the maximum concentration was 78.5 mg/L. 

About one-half of the trace-element samples had concentrations that were less than laboratory reporting limits. Only 

aluminum, arsenic, and selenium in spring samples, and boron 

and selenium in well samples, were detected at concentrations 

greater than surface-water standards or water-quality standards 

for agricultural use of groundwater.

Only three organic compounds, the pesticides alachlor and 

atrazine and the volatile organic compound di(2-ethylhexyl) 

phthalate, were detected in well samples. The Escherichia coli

bacteria was detected in 47 and 23 percent of samples from 

wells and springs, respectively. The E. coli detections included 

samples from three culturally significant springs, which did not 

meet the UMUT cultural-use standard of total absence of E. coli.

Tritium and carbon-14 were the primary environmental 

tracers used for interpreting groundwater ages for Lopez 2 

Spring and five wells (AP–1, 5000 Block, Cottonwood Spring, 

Goodknight, and SE Toe). Water from the AP–1 well contained a mixture of pre- and post-1950s recharge. Tritium and 

carbon-14 recharge ages for Lopez 2 Spring (post-1950s in 

age), Goodknight and SE Toe wells (pre-1950s in age), and 

Cottonwood Spring well (primarily pre-1950s in age) are supported by helium-4 data. The helium-4 data for the 5000 Block 

well are inconsistent with the tritium and carbon-14 age of 

pre-1950s recharge because of interference caused by high 

methane concentrations in the water. 

Springs and surficial deposits are more vulnerable to 

contamination from anthropogenic chemicals than deeper 

bedrock wells. Bedrock aquifers are vulnerable in areas 

where the geologic formations containing the aquifers are 

exposed at the land surface. Groundwater in deep bedrock 

aquifers is likely thousands of years old and is not currently 

affected by present-day land uses. Both shallow and deep 

groundwater are vulnerable to naturally occurring salts 

and minerals, such as of total dissolved solids, major ions, 

nitrate, and trace elements. 
2 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

Effects of a changing climate on water resources and 

other ecological characteristics of the UMUR could include 

changes in evapotranspiration, a decrease in snowpack, 

decreased aquifer recharge and flow of springs, a decrease in 

soil moisture, and increased occurrence of wildfires and forest 

mortality. Of particular interest for the UMUT are possible 

effects of a changing climate on medicinal and culturally 

important plants and springs. 

Several information needs were identified during this 

study that would aid in the understanding and protection of 

groundwater resources on the UMUR. These include wellcompletion information for bedrock wells, the collection of 

environmental tracer data at additional wells, the addition of 

methane and hydrocarbon analysis to well sampling plans, and 

the resampling of springs and wells that were last sampled in 

2002 or earlier. 

Introduction

In the semiarid Colorado Plateau region of Colorado, 

New Mexico, and Utah, water sustains the cultural, spiritual, 

and economic health of the Ute Mountain Ute Tribe (UMUT) 

and the Ute Mountain Ute Reservation (UMUR) (fig. 1). The 

UMUT has recognized that, whereas current and future land 

use and business activities on the UMUR are necessary for 

long-term viability, there could be potential effects of these 

activities on groundwater resources. With limited availability of surface water and the possibility of drought conditions 

in future years, protection of groundwater resources on the 

UMUR is vital for the UMUT. 

In 2004, a Groundwater Protection Plan was developed 

by and for the UMUT (UMUT, 2004) that focused on the vulnerability of aquifers to potential toxic or hazardous chemicals 

from land-use activities, particularly to pesticide use and management on the UMUR. Previous studies of the water quality 

of the groundwater system on the UMUR concentrated on 

New Mexico and specific areas in Colorado and Utah (Irwin, 

1966; Geldon, 1985; Naftz and others, 2011; UMUT, 2014).

In 2016, the U.S. Geological Survey (USGS), in cooperation with the UMUT, initiated a study to compile and 

analyze existing hydrogeologic and groundwater-chemistry 

information for the UMUR. In addition, in 2017, the USGS 

assisted the UMUT in developing and implementing a 

plan to collect water samples from selected springs and 

wells for analysis of environmental tracers as indicators of 

groundwater age and sources of recharge. This study was 

initiated to increase understanding of the hydrogeology and 

chemistry of groundwater within select areas of the UMUR 

in Colorado and Utah, identify vulnerabilities to the system 

and other natural resources, and outline information needs 

to aid in the understanding and protection of groundwater 

resources. The results presented for this study can be 

used to support the UMUT’s goal of protecting their vital 

groundwater resources on the UMUR.

Purpose and Scope

The purposes of this report are to describe the hydrogeologic characterization, groundwater chemistry, and vulnerability 

assessment of select areas of the UMUR. The report is focused 

on the Colorado and Utah portions of the UMUR, excluding 

the White Mesa area in Utah, and includes (1) characterization 

of hydrogeologic conditions in selected aquifers by determining water-table depth and the direction and gradient of the 

water-table slope for the surficial aquifer contained in unconsolidated surficial deposits and mapping the depth to the top of 

the Dakota Sandstone; (2) compilation and analysis of available 

groundwater-chemistry data for springs and wells as a baseline for future activities, focusing primarily on groundwaterchemistry data collected by the UMUT from 1996 through 

2017; (3) interpretation of environmental tracer data collected 

by the UMUT in 2017; (4) assessments of the vulnerability of 

groundwater to contamination from anthropogenic and natural 

sources and the vulnerability of water resources and other ecological characteristics of the UMUR to changes in climate; and 

(5) identification of information needs to advance the protection 

and understanding of groundwater resources. 

Description of Study Area

The UMUR encompasses about 597,000 acres (933 square 

miles) of trust land in Colorado, New Mexico, and Utah in the 

Four Corners region of the Colorado Plateau (fig. 1). Most of 

the UMUR is in southwestern Colorado. A small contiguous 

portion is in northwestern New Mexico. Reservation land in 

southeastern Utah includes the White Mesa community and 

individual or adjacent parcels of trust land. The UMUT also 

owns seven off-reservation ranches in Colorado and Utah 

encompassing about 34,000 acres (UMUT, 2004). The study 

area for this report consists of reservation lands in Colorado and 

Utah except for the White Mesa area of Utah. The New Mexico 

portion of the UMUR is not included in the study area. Water 

quality of the White Mesa area was previously characterized 

in Naftz and others (2011), and groundwater resources of the 

UMUR in New Mexico were previously characterized by the 

UMUT (UMUT, 2014).

Enrolled Tribal membership is 2,134 (Colorado 

Commission of Indian Affairs, 2018). Most Tribal members 

reside in two communities on the UMUR. The community 

of Towaoc, in Montezuma County, Colorado, is home of the 

UMUT Tribal government, and the small community of White 

Mesa is in San Juan County, Utah (fig. 1).

Physiography

The UMUR lies within the Four Corners platform of 

the Colorado Plateau (Pratt and others, 1976; UMUT, 2005). 

Reservation land ranges in altitude from 4,590 feet (ft) near 

the Four Corners (junction of the States of Arizona, Colorado 

New Mexico, and Utah) to 9,977 ft on Ute Peak in the Ute 
Introduction 3

\\IGSKAHCMVSFS002\Jeff\den19-0055-bauch\den19-0055_report_figures\den19-0055_fig01.ai

MESA VERDE

NATIONAL PARK

Marble Wash

White Mesa

UTAH

ARIZONA

COLORADO

NEW MEXICO

ARIZONA

NEW MEXICO

UTAH

COLORADO

SAN JUAN COUNTY

MONTEZUMA COUNTY

SAN JUAN COUNTY

APACHE COUNTY

DOLORES COUNTY

LA PLATA

COUNTY

Towaoc

Cortez

Blanding

Dolores

River

Mancos

Ri ver

McElmo

Creek

McPhee

Reservoir

028468

055531

051886

S13

Four

Corners

San Juan River

Mariano Wash

Towaoc

Highline

Canal Navajo Wash

109°30'

37°30'

37°

109° 108°30'

EXPLANATION

S13

Ute Mountain Ute Reservation

Spring with identifier

Climate station with identifier 028468

Map

area

COLORADO

PLATEAU

UTAH

ARIZONA

COLORADO

NEW MEXICO

UNITED

STATES

MEXICO

Base from U.S. Geological Survey digital data, 2019, 1:1,000,000

Elevation Derivatives for National Applications (EDNA) 

Geographic Coordinate System 

North American Datum of 1983

262

162

145

184

170

95

191

160

64

160

160

160

491

491

491

0 5 10 15 20 KILOMETERS

0 5 10 15 20 MILES

Figure 1. Location and extent of the Ute Mountain Ute Reservation in Colorado, New Mexico, and Utah.
4 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

Mountains (fig. 2). The northeastern part of the reservation 

abuts Mesa Verde National Park (MVNP). The landscape of 

the Colorado portion of the UMUR is dominated by the Ute 

Mountains in the northwest and tableland mesas in the eastern 

portion of the UMUR, similar to those in MVNP (fig. 2). 

South of the Ute Mountains, a rolling and irregular plain 

slopes south to the Mancos River (fig. 2). Gullies on the plain 

cut into the Cretaceous-age Mancos Shale and Quaternary-age 

unconsolidated surficial deposits (fig. 3). In the eastern portion 

of the reservation, Mesa Verde and other mesas rise about 

1,000 ft above Montezuma Valley and are dissected by deeply 

cut canyons of the Mancos River and smaller tributaries. 

Geology

Most of the UMUR in Colorado is underlain by south 

and southeast dipping sedimentary rocks of Mesozoic age 

(Pratt and others, 1976; UMUT, 2005). Surface exposures 

of bedrock primarily are Cretaceous-age sandstones, shales, 

and mudstones (fig. 3, table 1). Surface exposures of the 

oldest sedimentary rock are Late Jurassic-age, possibly Late 

Triassic-age, rocks along part of the northern boundary of the 

reservation in McElmo Canyon, defined by McElmo Creek. 

The youngest sedimentary rocks are Late Cretaceous-age 

rocks caping the mesas in the eastern portion of the UMUR 

(Pratt and others, 1976). The most prominent nonsedimentary 

rocks are the Late Cretaceous- and Tertiary-age igneous rocks 

that form the Ute Mountains (Irwin, 1966). Unconsolidated 

surficial deposits include Quaternary-age pediment gravels, 

landslide deposits, and eolian materials found in areas surrounding the Ute Mountains, and alluvium associated with 

major tributaries. In-depth discussion of the geology of the 

UMUR is in Ekren and Houser (1965), Irwin (1966), and Pratt 

and others (1976).

All geologic units shown within the geologic map of the 

UMUR in Colorado (fig. 3) are included in the generalized 

stratigraphic section table (table 1) but may not be discussed 

herein. In this report, discussion of the geology of the UMUR 

in Colorado is focused primarily on the units of hydrogeologic 

and groundwater-chemistry importance. 

160

160

160

491

491

162

Ute Peak

Cortez

Four Corners

UTAH

San Juan River

Montezuma Valley

Ute

Mountains

Tanner Mesa

Base from U.S. Geological Survey National Elevation

Dataset 30-meter digital elevation model 

North American Datum of 1983 (NAD83), 1:400,000

37°15'

37°

109° 108°45' 108°30' 108°15'

COLORADO

NEW MEXICO

COLORADO

Towaoc

MESA VERDE

NATIONAL PARK

McElmo Creek

Mancos River

Navajo Wash

9,977 feet

4,590 feet

EXPLANATION

Altitude—in feet above North American

 Vertical Datum of 1988 (NAVD88)

Four Corners Map area

0 2 4 6 8 10 KILOMETERS COLORADO

0 2 4 6 8 10 MILES

UTE MOUNTAIN UTE RESERVATION

Figure 2. Altitude of the Ute Mountain Ute Reservation in Colorado.
Introduction 5

Jurassic System 

Sedimentary rocks of Jurassic-age crop out in a few areas 

of the UMUR, most prominently in the McElmo Canyon area. 

The Navajo Sandstone, the oldest Jurassic-age rocks on the 

UMUR, is mapped as “JTRn” on figure 3. Other Jurassic-age 

rocks along McElmo Creek are mapped together on figure 3, 

including the Entrada Sandstone, Summerville Formation, 

and Morrison Formation as “Jmse,” or with the Junction 

Creek Sandstone as “Jmjse.” Depositional environments were 

marine, lacustrine, or eolian (Entrada Sandstone), marine and 

marginal marine (Summerville Formation), shallow marine 

and eolian (Junction Creek Sandstone), and streams and 

floodplains (Morrison Formation) (Ekren and Houser, 1965; 

Pratt and others, 1976; Naftz and others, 2011). The Morrison 

Formation (“Jm”) also outcrops in a few areas in or near the 

Ute Mountains and the west and southwest boundaries of the 

UMUR (fig. 3). 

Cretaceous System

Cretaceous-age sedimentary rocks that crop out on the 

UMUR are, in ascending order, the Burro Canyon Formation, 

Dakota Sandstone, Mancos Shale; and the Point Lookout 

Sandstone, Menefee Formation, and Cliff House Sandstone 

of the Mesaverde Group (table 1). For most of the UMUR, 

the boundary between the Jurassic and Cretaceous Systems 

cannot be precisely located because of intertonguing, lithologic gradation, and lack of fossils (Irwin, 1966; Pratt and 

others, 1976). \\IGSKAHCMVSFS002\Jeff\den19-0055-bauch\den19-0055_report_figures\den19-0055_fig03.ai

0 2 4 6 8 10 KILOMETERS

0 2 4 6 8 10 MILES

Km Kch

Km

Kdb

Km

Kmj

TKi

Qe

Kmp

Kmp

Kmp

Kmp

Kch

Kdb

Kch

Kch

Ql

Qa

Kmj

Kdb

Qe

Kch

Kdb

Km

Jm

Kch

Qe

Ql

Qgo

Qa

TKi

Qe

TKi

TKi

Jm Km

Km

Kdb

Kdb

TKi

Kch

Kch

Tmi

Jm

Tmi

Jm

Kch

Kmj

Jmjse

Jm

Jmse

Kdb

Kch

Km

Jmse

Qa

Kch

Qg

Kdb

Kdb

Kdb

Qa

Kch

Kch

Kmp

Kmp

Km

JTRn

Kch

Kch

Qe

Kch

Kdb

Kch

Kmj Tmi

Kmp

Kdb Kdb

Kdb

Qe

Qe

Kdb

Kdb

Qa

Qgo

Kmp

Base from U.S. Geological Survey National Elevation

Dataset 30-meter digital elevation model 

North American Datum of 1983 (NAD83), 1:400,000

Cottonwood

Wash 

Unnamed

tributary 

Marble Wash

Coyote Wash

Mariano Wash

37°15'

37°

109° 108°45' 108°30' 108°15'

UTAH

COLORADO

NEW MEXICO

COLORADO

Towaoc

MESA VERDE NATIONAL PARK

Cortez

McElmo Creek

Mancos

. River Navajo Wash

San Juan River

Colorado geology by G.N. Green, 1992

EXPLANATION

Qa Quaternary modern alluvium

Qe Quaternary eolian deposits

Ql Quaternary landslide deposits

Qgo Quaternary older pediment gravels

Qg

Tmi Tertiary igneous intrusive rocks

TKi Tertiary igneous Laramide intrusive rocks

Kch Cretaceous Cliff House Sandstone

Kmp Cretaceous Menefee Formation and Point

 Lookout Sandstone

Km Cretaceous Mancos Shale

Kmj Cretaceous Juana Lopez Member of the

 Mancos Shale

Kdb Cretaceous Dakota Sandstone and Burro

 Canyon Formation

Jm Jurassic Morrison Formation

Jmjse Jurassic Morrison Formation, Junction

 Creek Sandstone, Summerville

 Formation, and Entrada Sandstone

Jmse Jurassic Morrison Formation, Summerville

 Formation, and Entrada Sandstone

JTRn Jurassic Glen Canyon Group (Navajo

 Sandstone)

UTE MOUNTAIN UTE RESERVATION

Quaternary gravels

Four Corners Map area

COLORADO

Figure 3. Generalized geology of the Ute Mountain Ute Reservation in Colorado. Because of scale, detail on the map has been 

simplified from formations shown on the geologic source map (modified from Green, 1992).
6 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

Table 1. Generalized stratigraphic section of the geologic formations of the Ute Mountain Ute Reservation in Colorado. 

[Modified from Pratt and others (1976) and Irwin (1966). Although mentioned in this report, the Pennsylvanian-age Paradox Formation is not included in 

table 1 because there are no surface exposures in the study area. na, not applicable; ?, maybe]

System Series Group Formation Member Symbol 

on map

Physical

character

Quaternary

Holocene Modern alluvium na Qa Gravel, sand, silt, clay

Pleistocene

Eolian deposits na Qe Dune sand, silt, loess

Landslide deposits na Ql Soil, fine materials, cobbles, boulders, and rock slabs

Older pediment 

gravels na Qgo Predominately pebbles, cobbles, and boulders ofigneous origin

Tertiary 

and

Tertiary or 

Cretaceous

Igneous rocks na Tmi Small plugs and dikes of intrusive igneous rocks

Igneous rocks na TKi

Lacoliths, sills, dikes, and stocks intruded into

sedimentary rocks forming the Ute Mountains. For this 

report, TKi includes talus deposits and related block 

rubble on the slopes of the Ute Mountains.

Cretaceous

Upper

Cretaceous

Mesaverde 

Group

Cliff House

Sandstone na Kch Yellowish-orange, massive cliff-forming fine-grained sandstone and some shaly sandstone beds

Menefee

Formation na Kmp

Gray to grayish-orange, fine- to medium-grained 

crossbedded sandstone and gray to black carbonaceous 

shale and coal beds

Point Lookout 

Sandstone na Kmp

Yellowish-orange to white, massive cliff-forming

fine-grained sandstone. Lower parts contain interbedded 

thin sandstone and sandy mudstone.

Mancos

Shale

na Km

Gray to dark-gray/black gypsiferous shaly mudstone 

with thin beds of grayish-brown sandy limestone and 

limestone concretions

Juana 

Lopez 

Member

Kmj

Lower member of Mancos Shale. Yellowish-brown 

sandy fossiliferous limestone and gray to brown shale. 

Approximately 475 to 525 feet above the

Mancos Shale base

Dakota

Sandstone na Kdb

Light-gray to yellowish-gray, fine- to medium-grained 

sandstone interbedded with carbonaceous shale and 

some thin coal beds

Lower

Cretaceous

Burro Canyon

Formation na Kdb

Light-gray to white sandstone and conglomeratic 

sandstone interbedded with grayish-green and some 

grayish-red mudstone

Jurassic Upper 

Jurassic

Morrison

Formation na

Jm, 

Jmjse, 

Jmse

Bentontic mudstone with siltstone and siliceous

sandstone lenses. Interbedded light-tan to light-gray, 

fine- to medium-grained sandstone and thin red or

green siltstone and mudstone in the

middle and lower members

 Junction Creek 

Sandstone na Jmjse Pale-red to light-brownish-gray, fine- tomedium-grained sandstone

Summerville

Formation na Jmjse, 

Jmse

Reddish-brown silty fine-grained sandstone and pale-red 

to moderate-brown siltstone or mudstone

Entrada

Sandstone na Jmjse, 

Jmse

Upper unit: Grayish-orange-pink to reddish-orange

fine-grained sandstone, cliff forming 

Lower unit: Pale-reddish-brown to grayish-red very 

fine-grained silty sandstone and siltstone

Triassic(?) 

and

Jurassic

Glen

Canyon 

Group

Navajo

Sandstone na JTRn Grayish-orange-pink to reddish-orange fine-grained crossbedded sandstone
Introduction 7

The Burro Canyon Formation consists of mudstone interbedded with lenses of conglomerate and conglomeratic sandstone (Pratt and others, 1976); it is grouped with the Dakota 

Sandstone on figure 3 as “Kdb.” The Dakota Sandstone overlies the Burro Canyon Formation or the Morrison Formation if 

the Burro Canyon Formation is not present or cannot be distinguished. The Dakota Sandstone consists of quarzitic sandstone 

and conglomeratic sandstone with thin lenticular beds of shale, 

claystone, carbonaceous sandstone, and impure coal (Haynes 

and others, 1972). Sediments of the Dakota Sandstone likely 

were deposited in fluvial, lagoon, and beach environments 

(Ekren and Houser, 1965). Outcrops of Dakota Sandstone 

are near McElmo Creek, along the western boundary of the 

UMUR, and near the Four Corners area (fig. 3). Except for 

outcrops, the Dakota Sandstone is in the subsurface throughout the UMUR. The formation generally ranges from 100 

to160 ft thick with an average thickness of about 135 ft (Irwin, 

1966). However, the total thickness of the Dakota Sandstone 

combined with the underlying Burro Canyon Formation 

(where present) generally is 200–243 ft (Irwin, 1966). In the 

eastern half of the UMUR, the Dakota Sandstone lies beneath 

several thousand feet of younger Cretaceous-age sedimentary 

rocks. Hydraulic conductivity values specific for the Burro 

Canyon Formation and Dakota Sandstone on the UMUR could 

not be discerned. Geldon (1985) reported a maximum hydraulic conductivity of 0.0077 ft per day for the Burro Canyon 

Formation and Dakota Sandstone in northwestern Colorado 

and eastern Utah. 

Conformably overlying the Dakota Sandstone is the 

Mancos Shale (“Km” on fig. 3), which was deposited in an 

inland sea and primarily is marine shale. The Mancos Shale 

occurs at the land surface across much of the UMUR, especially in the western half where it forms rolling plains and low 

ridges. Along the mesas in the east, the Mancos Shale forms 

steep slopes beneath overlying weather-resistant sandstones. 

The Mancos Shale is composed primarily of gypsiferous mudstone, and there are thin sandy limestone lenses and limestone 

concretions throughout the formation (Ekren and Houser, 1965; 

Irwin, 1966). The Juana Lopez Member (“Kmj” on fig. 3) of the 

Mancos Shale is exposed as a prominent ridge south of the Ute 

Mountains (Ekren and Houser, 1965; Irwin, 1966). A maximum 

hydraulic conductivity of 0.028 ft per day was reported by 

Geldon (1985) for the Mancos Shale in northwestern Colorado.

The youngest sedimentary rocks exposed on the UMUR 

are the three units of the Mesaverde Group; in ascending order, 

they are the Point Lookout Sandstone and Menefee Formation 

(“Kmp” on fig. 3), and Cliff House Sandstone (“Kch” on fig. 3). 

These outcrops are in the eastern half of the UMUR around the 

rim of the mesa containing the MVNP and in the canyons dissecting it and other mesas in the east (fig. 3). The upper part of 

the Point Lookout Sandstone forms the most prominent cliffs on 

the eastern side of the UMUR (Irwin, 1966). 

Late Cretaceous and Tertiary Systems

Northwest of Towaoc, intrusive igneous rocks (“TKi” on 

fig. 3) form the Ute Mountains (fig. 3; Pratt and others, 1976). 

The Ute Mountains, also known as Sleeping Ute Mountains 

because of their profile, are Late Cretaceous- to middle 

Tertiary-age laccoliths, sills, dikes, and cylinders of igneous 

rock intruded into and between layers of older Cretaceous 

sedimentary rocks. Talus deposits and related block rubble 

of Quaternary age that are common on the slopes of the Ute 

Mountains are mapped on figure 3 with the Late Cretaceousto middle Tertiary-age igneous intrusive rocks “TKi.” Igneous 

pebbles, cobbles, and boulders that comprise the talus deposits 

occur below their source rocks (Pratt and others, 1976). Small 

plugs and dikes of Tertiary-age igneous rock (“Tmi” on fig. 3) 

crop out in sedimentary rocks in Mancos Canyon, defined by 

Mancos River (fig. 3; Pratt and others, 1976).

Quaternary System

Quaternary-age unconsolidated surficial deposits on the 

UMUR are composed of pediment gravels, landslide deposits, eolian materials, and modern alluvium (fig. 3; Haynes 

and others, 1972; Condon, 1991). On the land surface, these 

deposits are much more extensive than those shown on the 

geology map because of the map scale. The pediment gravels, 

mapped as “Qgo” on figure 3, are predominately pebbles, 

cobbles, and boulders of igneous origin (Irwin, 1966). The 

pediment gravels occur as discontinuous erosion surfaces 

that extend radially away from the Ute Mountains (Ekren 

and Houser, 1965). Landslide deposits (“Ql” on fig. 3) on the 

UMUR are formed when soil, other fine materials, cobbles, 

boulders, and rock move downward because of the combined effects of gravity and precipitation (Ekren and Houser, 

1965). The predominant exposure of landslide deposits is on 

the north-facing slopes of the Ute Mountains (fig. 3). Eolian 

materials (“Qe” on fig. 3) are composed of very fine-grained 

sand, silt, and windblown clay. The materials cover mesa surfaces and pediment deposits and range in thickness from very 

shallow near the mesa edges to 10–15 ft deep on pediments 

(Natural Resources Conservation Service, 2008). Eolian 

materials are primarily exposed in the Farm and Ranch Enterprise area southwest of the Ute Mountains (fig. 4). Eolian 

materials form an excellent porous soil capable of retaining 

water for long periods of time (Ekren and Houser, 1965). 

Modern alluvium (“Qa” on fig. 3, except for the Mancos 

River alluvium that is not displayed) occurs along the Mancos 

River, in the Towaoc area, and in a few areas south of the Ute 

Mountains. Alluvium near Towaoc is composed of silt, clay, 

sand, and gravel derived from nearby Cretaceous-age shale 

and sandstone and igneous pebbles and cobbles derived from 

the Ute Mountains intrusive rocks (Irwin, 1966). Geldon 

(1985) reported a hydraulic conductivity of 50 ft per day for a 

well completed in pediment alluvium on the reservation. 

Climate

Climate on the reservation is semiarid, with a wide 

range in temperature and precipitation depending on altitude. Average annual temperatures at three climate stations 
8 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

near the UMUR (fig. 1) for 1963–2017 were warmest 

(55.9 degrees Fahrenheit [°F]) near Four Corners and 

49.2 °F at Cortez and MVNP (Western Regional Climate 

Center, 2018b). During summer, temperatures can fluctuate from daytime highs around 90 °F to nighttime lows 

around 55 °F (Western Regional Climate Center, 2018a). The 

mean monthly coldest temperatures occur in January and 

range from 13.2 °F to 20.0 °F at the three stations (Western 

Regional Climate Center, 2018a). Average annual precipitation for 1963–2017 was 8.1 inches per year near Four 

Corners and increased with altitude to 12.5 inches per year at 

Cortez and 18.1 inches per year at MVNP (Western Regional 

Climate Center, 2018b). Summer thunderstorms can produce several inches of rain in a few hours or less, and winter 

storms can drop 1 foot or more of snow at higher altitudes 

during a single storm event. With hot temperatures during the 

summer, evapotranspiration rates can exceed precipitation 

such that only a small fraction of the precipitation infiltrates 

to the subsurface as groundwater recharge (Irwin, 1966). 

Surface-Water Hydrology

Surface-water drainage on the UMUR is characterized by 

ephemeral stream channels draining toward the Mancos and 

San Juan Rivers. The ephemeral Navajo Wash and its tributaries 

drain the area east of the Ute Mountains near Towaoc southward toward the Mancos River. The Mancos River, a perennial 

stream with headwaters in the mountains northeast of MVNP, 

flows southwest across the northeast portion of the reservation toward its confluence with the San Juan River in the Four 

Corners area (fig. 1). A small segment of the San Juan River 

crosses the southwest corner of the UMUR. The western portion 

of the UMUR in Colorado is drained by the ephemeral Mariano 

and Marble Washes and their tributaries (fig. 1), whose waters 

\\IGSKAHCMVSFS002\Jeff\den19-0055-bauch\den19-0055_report_figures\den19-0055_fig04.ai

160

160

160

491

491

162

Base from U. S. Department of Agriculture digital data, 1:400,000

National Land Cover Dataset 

North American Datum of 1983 (NAD83)

MESA VERDE

NATIONAL PARK

Navajo Wash

Mancos

. River

Unnamed

Tributary 

Cortez

Towaoc

McElmo Creek

UTAH

COLORADO

San Juan River

Wash 

Cottonwood

Marble Wash

Mariano

Wash

Coyote

Wash

COLORADO

NEW MEXICO

UTE MOUNTAIN UTE RESERVATION

Four Corners

109° 108°45' 108°30' 108°15'

37°15'

37°

EXPLANATION

Open water

Perennial ice/snow

Developed, open space

Developed, low intensity

Developed, medium intensity

Developed, high intensity

Barren land (rock/sand/clay)

Deciduous forest

Evergreen forest

Mixed forest

Shrub/scrub

Grassland/herbaceous

Pasture/hay

Cultivated crops

Emergent herbaceous wetlands

Woody wetlands

Farm and Ranch Enterprise

National Land Cover Dataset Classifications

Four Corners Map area

COLORADO

0 2 4 6 8 10 KILOMETERS

0 2 4 6 8 10 MILES

Figure 4. Land cover and land use on the Ute Mountain Ute Reservation in Colorado. 
Introduction 9

flow into the San Juan River in Utah. Small tributaries on the 

northern flanks of the Ute Mountains drain into McElmo Creek, 

beyond the northwestern boundary of the reservation. 

Groundwater Hydrology

Groundwater occurs in confined aquifers contained in 

sandstone geologic formations and in the surficial aquifer 

contained in unconsolidated surficial deposits on the UMUR 

(UMUT, 2005). Bedrock aquifers beneath the UMUR in 

Colorado include the Dakota aquifer contained in the Dakota 

Sandstone, which is the main water-bearing unit beneath 

the UMUR, and aquifers contained in the sandstone units of 

the Mesaverde Group (primarily the Cliff House Sandstone 

and the upper part of the Point Lookout Sandstone). Small 

quantities of groundwater are present in the surficial aquifer 

contained in unconsolidated surficial deposits such as nearsurface alluvium, colluvium, talus, rubble, and pediment 

deposits (Irwin, 1966; Geldon, 1985; UMUT, 2004).

Sources of recharge to groundwater include rain or snow, 

irrigation water applied to agricultural areas or landscaping, 

and seepage of surface water downstream from springs or to 

the alluvium of streams or washes (Irwin, 1966; Geldon, 1985). 

Recharge occurs when water percolates downward through the 

unsaturated zone to the water table where it becomes part of 

the regional groundwater flow system or is trapped by impervious material and is perched above the regional flow system 

(Whitfield and others, 1983). Part of the precipitation that 

moves into the unsaturated zone is evaporated from soils and 

subsurface material or is transpired by plants. 

Groundwater movement in saturated deposits is largely 

controlled by the hydraulic conductivity of the aquifer 

material. Shale, mudstone, and siltstone generally have low 

hydraulic conductivities and transmit little water, whereas 

sandstones, conglomerate, and gravel have a wide range of 

conductivities and generally transmit more water than the less 

permeable rocks (Whitfield and others, 1983). Local movement of groundwater generally is downward, but groundwater 

may move laterally to discharge into springs when impervious 

or low-permeability material is encountered or into streams. 

Flow in the alluvium typically is lateral towards canyons and 

tributaries of the Mancos and San Juan Rivers. Regionally, 

groundwater recharged in structurally and topographically 

high areas, such as the Ute Mountains, moves downdip into 

structurally low areas toward discharge areas (Irwin, 1966). 

Regional flow direction for the aquifers contained in sandstone formations is toward the San Juan River (Whitfield and 

others, 1983). 

Outflow of groundwater can occur as evapotranspiration 

by plants in areas of a shallow water table, discharge to springs 

and streams, and withdrawal from wells, either through pumping for domestic and livestock supply or naturally because 

of flowing artesian conditions. Groundwater discharged in 

springs occurs along canyon walls or lithologic contacts, 

where generally impervious material impedes the downward 

movement of water through more permeable material, or in 

the Ute Mountains, where groundwater emerges as springs 

at the contact between the intrusive fractured intrusive rocks 

and underlying low-permeability rocks. Many springs are 

recharged by snowmelt flow in spring and early summer and 

are dry by late summer. Discharge of groundwater to perennial streams, such as the Mancos and San Juan Rivers, is a 

dominant component of streamflow in late summer, fall, and 

winter when direct runoff from thunderstorms or snowmelt is 

absent. Some wells that have been drilled on the UMUR are 

flowing artesian wells and discharge groundwater above the 

land surface. 

Land Cover and Land and Water Use

Most of the reservation is covered by shrubs/scrubs, 

grassland, and forests (fig. 4). Sagebrush, cacti, and grasses 

occur on low-altitude areas, and cottonwood trees may be 

present in washes and along creeks. Forests of mixed conifers 

and aspen occur on the Ute Mountains and higher-altitude 

mesas. Land on the UMUR is primarily used for Tribal government facilities, housing for Tribal members, a Tribal park, 

the Farm and Ranch Enterprise, livestock grazing, oil and gas 

development, tourism facilities, and other commercial activities (UMUT, 2005). The Farm and Ranch Enterprise (fig. 4) is 

an irrigated agricultural project where corn, alfalfa, and wheat 

are grown. 

Surface water is imported into the UMUR from the 

Dolores Project facilities (Bureau of Reclamation, 2019). 

Water is conveyed from McPhee Reservoir through a pipeline 

and the Towaoc Highline Canal (fig. 1) and used for municipal supply and for UMUT enterprises around Towaoc. The 

Dolores Project also supplies irrigation water for the Farm and 

Ranch Enterprise (UMUT, 2004). 

Water pumped from the Dakota aquifer is used primarily for livestock (UMUT, 2005) but also is tapped for the 

three domestic wells on the UMUR, two private wells near 

McElmo Canyon on the northern boundary, and a well at the 

Farm and Ranch Enterprise headquarters. Use of groundwater 

from aquifers in the Cliff House Sandstone and Point Lookout 

Sandstone is limited. In the eastern and southeastern part of 

the UMUR, the Mancos River and its tributaries have cut steep 

and narrow canyons into the landscape, and the Cliff House 

Sandstone and Point Lookout Sandstone are drained by seeps 

and springs on the canyon walls. Groundwater is not a source 

of irrigation water for the UMUR because of the limited quantity of groundwater (UMUT, 2004).

Springs on the UMUR can be important sources of water 

for wildlife and vegetation. On steep hillsides or canyons 

with mostly barren ground or rock, the location of springs can 

easily be identified by the presence of greenery. Springs on the 

Ute Mountains (fig. 2) and the Whiskers Draw Spring in Utah 

(S13 on fig. 1) are spiritually and culturally significant for the 

UMUT (UMUT, 2004).
10 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

Methods of Hydrogeologic 

Characterization

This section describes methods used to characterize 

hydrogeologic conditions for the surficial aquifer contained 

in unconsolidated surficial deposits and the Dakota aquifer 

contained in the Dakota Sandstone within the UMUR in 

Colorado. Depth to water below land surface and the direction and gradient of the water-table slope was determined for 

the surficial aquifer, and the depth to the top of the Dakota 

Sandstone below land surface was mapped. Hydrogeologic 

characterization was focused on these two units because 

of their current or potential use as water supplies and their 

potential vulnerability to land-use activities. 

Surficial Deposits

Because of limited availability of water-level data, characterization of the water-table altitude for the entire UMUR 

was not possible; instead, the study focused on the Farm and 

Ranch Enterprise area and an area near Towaoc where some 

water-level data were available for the surficial aquifer. Waterlevel data from monitoring wells associated with the Farm 

and Ranch Enterprise (fig. 5) were compiled from records 

provided by the UMUT (table 2, table 1.1 in app. 1). Historical 

water-level data for shallow wells near Towaoc (fig. 6) were 

compiled from records in the USGS National Water Information System (NWIS; USGS, 2016b), Irwin (1966), and Geldon 

(1985) (table 1.1 in app. 1).

To estimate direction and gradient of the water-table 

slope, an effort was made to create lines of equal water-table 

altitude (water-table contours) for the Farm and Ranch Enterprise and Towaoc areas with consideration of topography, 

surface geology, and drainage features. Because of the limited 

data available, a map of the water-table contours is not 

included in this report, but calculations of the slope direction 

and gradient were performed using the available data. The 

method entailed obtaining a land-surface altitude above the 

North American Vertical Datum of 1988 (NAVD88) for each 

well from USGS digital elevation models (DEMs) (USGS, 

2019). Next, water-level altitudes at each well were determined by subtracting the measured water-level depth below 

land surface from land-surface altitude. In cases where more 

than one water-level measurement was available for a well, 

the median water level was used. The water-table surface 

was partially contoured manually and reviewed to verify 

that the water-level altitudes accurately represented the data, 

progressed in a logical spatial order, and did not exceed landsurface altitudes. Finally, direction of slope and slope gradient (altitude of water table over distance on the ground) were 

estimated from the data. Because water-level data represent 

various measurement dates under different hydrologic conditions, these results should be considered representative of 

generalized water-table conditions rather than precise conditions for a specific time or place. 

Dakota Sandstone

A map of the depth to the top of the Dakota Sandstone 

in feet below land-surface datum in Colorado was developed 

using well location and lithologic data compiled from Irwin 

(1966), the Colorado Oil and Gas Conservation Commission 

(COGCC, 2016), and New Mexico Oil Conservation Division (2012) (compiled data in table 1.2 in app. 1). Lithologic 

data for wells in New Mexico were included in the dataset 

to improve interpolation across areas lacking data within 

Colorado. At each well, the structural altitude at the top of the 

Dakota Sandstone in feet above NAVD88 was first computed 

as the difference between the land-surface altitude, determined 

from the DEM dataset (USGS, 2019) in feet above NAVD88, 

and the depth to the top of the Dakota Sandstone in feet below 

land surface based on lithologic data in well construction 

records. Wells were removed from the dataset in cases where 

land-surface altitude reported by construction records differed from that of the DEM by more than 50 ft, and the well 

location could not be confirmed from other sources. Similarly, 

wells indicating anomalous altitude values for the top of the 

Dakota Sandstone were removed from the dataset if the values 

could not be substantiated. Otherwise, conflicting values 

were retained in the dataset to indicate the variability inherent 

within the data. 

Using outcrop and subcrop areas and structural features digitized from surface geologic maps (Condon, 1991; 

Haynes and others, 1972), structural-altitude contours of 

the top of the Dakota Sandstone were drawn by hand to 

improve interpolation in areas of sparse data. Contours were 

drawn using an interval of 100 ft and were estimated to have 

an accuracy of about 50-60 ft where the data provide good 

structural control. In areas where structural data were unavailable, structural contours representing the base of the Dakota 

Sandstone were used to infer structural contours for the top of 

the Dakota, and the accuracy of these contours is unknown. 

The depth to the top of the Dakota Sandstone in feet 

below land surface was determined by using a geographic 

information system to generate a raster grid of values 

from the structural-altitude contours and subtracting the 

raster-based structural altitude from the DEM land surface. 

The resulting raster-based depth to the top of the Dakota 

Sandstone was then contoured in a geographic information 

system using an interval of 100 ft for the western portion of 

the UMUR and 500 ft for the eastern portion of the UMUR 

because of the tightness of the 100 ft contours. In areas 

where the structural altitude of the Dakota Sandstone is well 

defined, the accuracy of the contours is considered to be 

50–60 ft for 100-ft contours and about 250–300 ft for 500-ft 

contours. All geospatial datasets generated during this process are available in Bauch (2020).
Methods of Hydrogeologic Characterization 11

\\IGSKAHCMVSFS002\Jeff\den19-0055-bauch\den19-0055_report_figures\den19-0055_fig05.ai

160

160

160

491

491

162

S9

W20

AP-16 AP-15

AP-11

AP-10

AP-1

W3

W2

W1

S8

S7

S6 S5

S4

S3

S2

S1

W23

W22

W21

W19

W18 W17 W16

W15

W13 W14

W11

W7

W10

W9

W8

W6

W5

W4

AP-5

AP-24

S12

S10

S11

AP-14

W12

AP-2

AP-3

AP-4

AP-17

AP-22

Base from U. S. Department of Agriculture digital data, 1:400,000

National Land Cover Dataset 

North American Datum of 1983 (NAD83)

MESA VERDE

NATIONAL PARK

Navajo Wash

Mancos River

Cortez

Towaoc

McElmo Creek

UTAH

COLORADO

San Juan River

Marble Wash

Mariano

Wash

Coyote

Wash

COLORADO

NEW MEXICO

Four Corners MONTEZUMA

COUNTY

LA PLATA

COUNTY

37°15'

37°

109° 108°45' 108°30' 108°15'

Four Corners Map area

COLORADO 0 2 4 6 8 10 KILOMETERS

0 2 4 6 8 10 MILES

EXPLANATION

Ute Mountain Ute Reservation

Farm and Ranch Enterprise

S9 Spring and identifier

Well with groundwater-chemistry

 and water-level data and

 identifier

Well with water-level data and

 identifier

Well with groundwater-chemistry

 data and identifier

W21

AP–16

AP–17

Figure 5. Location of Ute Mountain Ute Tribe wells and springs where water-level and (or) groundwater-chemistry data were 

collected on the Ute Mountain Ute Reservation in Colorado. 
12 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

Table 2. Ute Mountain Ute Tribe water-level data for 

unconsolidated surficial deposits, Ute Mountain Ute 

Reservation in Colorado.—Continued

[Median water level is in bold. ID, identification; fig., figure; ft bls, 

feet below land surface]

Site ID

(see fig. 5) Date Water level(ft bls)

AP−1 08/15/2008 10.7

AP−1 03/31/2009 10.1

AP−1 03/01/2010 12.1

AP−1 11/29/2010 10.0

AP−1 06/08/2011 10.7

AP−1 01/04/2012 11.0

AP−1 07/27/2012 12.1

AP−1 04/10/2013 13.6

AP−1 08/14/2013 14.4

AP−1 04/10/2014 24.9

AP−1 08/03/2014 15.6

AP−1 Median 12.1

AP–2 08/15/2008 12.2

AP–2 11/29/2010 9.9

AP–2 Median 11.1

AP–3 08/15/2008 9.8

AP–3 03/31/2009 0.9

AP–3 03/01/2010 13.2

AP–3 11/29/2010 9.7

AP–3 Median 9.8

AP–4 03/31/2009 13.9

AP–4 11/29/2010 11.5

AP–4 06/08/2011 13.2

AP–4 01/04/2012 12.9

AP–4 07/27/2012 12.5

AP–4 Median 12.9

AP–5 08/11/2008 7.9

AP–5 03/31/2009 6.2

AP–5 03/03/2010 5.8

AP–5 11/29/2010 5.7

AP–5 06/08/2011 3.9

AP–5 01/04/2012 5.3

AP–5 07/27/2012 5.0

AP–5 04/10/2013 6.6

AP–5 08/03/2014 6.0

AP–5 Median 5.8

AP−10 08/15/2008 11.4

AP−10 04/07/2009 17.2

AP−10 03/03/2010 18.1

AP−10 11/22/2010 16.5

AP−10 06/15/2011 16.9

AP−10 01/04/2012 16.1

AP−10 07/27/2012 17.7

AP−10 04/10/2013 19.3

AP−10 08/14/2013 16.5

AP−10 04/10/2014 19.2

AP−10 08/03/2014 19.7

Table 2. Ute Mountain Ute Tribe water-level data for 

unconsolidated surficial deposits, Ute Mountain Ute 

Reservation in Colorado.—Continued

[Median water level is in bold. ID, identification; fig., figure; ft bls, 

feet below land surface]

Site ID

(see fig. 5) Date Water level(ft bls)

AP−10 Median 17.2

AP−14 05/02/2008 5.8

AP−14 04/07/2009 5.4

AP−14 02/22/2010 3.3

AP−14 11/22/2010 4.0

AP−14 06/08/2011 3.3

AP−14 01/03/2012 5.0

AP−14 07/27/2012 4.0

AP−14 04/10/2013 6.0

AP−14 08/14/2013 9.5

AP−14 04/10/2014 12.1

AP−14 08/03/2014 7.3

AP−14 Median 5.4

AP−15 02/22/2010 5.6

AP−15 11/22/2010 7.8

AP−15 06/08/2011 6.4

AP−15 01/03/2012 7.4

AP−15 07/27/2012 5.0

AP−15 04/10/2013 5.4

AP−15 08/14/2013 10.6

AP−15 04/10/2014 6.6

AP−15 08/03/2014 5.0

AP−15 Median 6.4

AP−16 05/02/2008 8.3

AP−16 04/07/2009 8.9

AP−16 02/22/2010 6.8

AP−16 11/22/2010 8.4

AP−16 06/08/2011 8.6

AP−16 01/03/2012 9.7

AP−16 07/27/2012 9.1

AP−16 04/10/2013 9.7

AP−16 08/14/2013 5.9

AP−16 04/10/2014 10.4

AP−16 08/03/2014 9.7

AP−16 Median 8.9

AP−17 05/02/2008 16.2

AP−17 04/07/2009 16.2

AP−17 02/22/2010 14.4

AP−17 11/22/2010 14.2

AP−17 06/08/2011 16.8

AP−17 01/03/2012 15.1

AP−17 04/10/2013 16.0

AP−17 Median 16.0

AP–22 03/01/2010 6.1

AP–24 01/04/2012 9.2

AP–24 07/27/2012 6.8

AP–24 08/03/2014 4.8

AP–24 Median 6.8
Methods of Hydrogeologic Characterization 13

\\IGSKAHCMVSFS002\Jeff\den19-0055-bauch\den19-0055_report_figures\den19-0055_fig06.ai

160

160

160

491

491

162

A

B

Base from U. S. Department of Agriculture digital data, 1:400,000

National Land Cover Dataset 

North American Datum of 1983 (NAD83)

MESA VERDE

NATIONAL PARK

Mancos River

Cortez

Towaoc

McElmo Creek

UTAH

COLORADO

San Juan River

Marble Wash

Coyote

Wash

COLORADO

NEW MEXICO

Four Corners MONTEZUMA

COUNTY

LA PLATA

COUNTY

Mariano Wash

Navajo Wash

CW3

CW2 CW1

NW9

NW8

NW7

NW6 NW5 NW3 NW4

NW2

NW1

NUW5 NS4

NUW4

NUW3

NUW1

NUS3

NUS2

NUS1

NW27

NW26 NW25

NW13

NW12

37°15'

37°

109° 108°45' 108°30' 108°15'

Four Corners Map area

COLORADO 0 2 4 6 8 10 KILOMETERS

0 2 4 6 8 10 MILES

EXPLANATION

Ute Mountain Ute Reservation

NS8

NUW2

CW1 Colorado Oil and Gas Conservation Commission well and

 identifier

Ute Mountain Ute Tribe spring or well—See figure 5

U.S. Geological Survey National Water Information System

 or National Uranium Resource Evaluation well and

 identifier

U.S. Geological Survey National Water Information System

 or National Uranium Resource Evaluation spring and

 identifier

NS7

NS6 NS5

NS3

NS2

NS1

NUW2

NUS5

NUS4

NW32

NW30

NW29

NW28

NW23 NW24

NW22

NW21

NW20

NW19

NW17

NW15 NW16

NW11

NW10

NW18

NW14

NW31

Navajo Wash

108°44' 108°42'

37°12'

37°10'

B

Towaoc

160

491

0 0.5 1 KILOMETER

0 0.5 1 MILE

A

NS8

NS18

NUS8

NS17

NS16 NS15

NS14 NS13

NUS6

NS11

NS9

NS10

NS12 NUS7

108°49' 108°48' 108°47' 108°46' 108°45'

37°17'

37°16'

37°14'

37°13'

37°15'

108°44' 108°43'

0 1 2 KILOMETERS

0 1 2 MILES

Figure 6. Location of U.S. Geological Survey (USGS) and Colorado Oil and Gas Conservation Commission (COGCC) springs 

and wells with historical water-level and (or) groundwater-chemistry data on the Ute Mountain Ute Reservation in Colorado. 

Site labels beginning with “NU” are from USGS National Uranium Resource Evaluation (USGS, 2014); all other site labels 

beginning with “N” are from USGS National Water Information System (USGS, 2016b), Irwin (1966), and Geldon (1985). Site 

labels beginning with “CW” are from COGCC (COGCC, 2018).
14 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

Methods for Compilation and Analysis 

of Groundwater-Chemistry Data

This report utilized multiple types of groundwaterchemistry data from multiple sources (table 3). Select chemistry data were compiled, quality assured, aggregated, and 

summarized as described in the following sections. Comparisons with water-quality standards were used to assess suitability of water for various designated uses. Data collection 

and laboratory analytical methods for environmental tracer 

data for select springs and wells collected by the UMUT in 

2017 also are described. 

Data Sources

The primary groundwater-chemistry data used for this 

study were collected by the UMUT from 1996 through 2017. 

Groundwater-chemistry data for 44 sites, 13 springs and 31 

wells, were retrieved in an electronic format from the Water 

Quality Portal (https://www.waterqualitydata.us/) (National 

Water Quality Monitoring Council, 2017) on September 9, 

2017 (fig. 5, table 4). All UMUT sites are in Colorado except 

for the Whiskers Draw Spring in Utah (S13), which is shown 

on figure 1. The number of sample days and the number of 

samples collected at each site varied (table 4). 

The groundwater-chemistry data collected by the 

UMUT are supplemented by older data from the USGS and 

the COGCC (fig. 6, table 4). The supplemental data were 

obtained in an electronic format from three databases: the 

USGS NWIS (USGS, 2016b); National Uranium Resource 

Evaluation (NURE), hosted by the USGS (USGS, 2014); 

and COGCC GIS Online (COGCC, 2018). Groundwaterchemistry data for 45 USGS sites, 18 springs and 27 wells, 

retrieved from NWIS were collected in the 1950s, 1960, 

1979, 1982, 1987, and 2003 (tables 3 and 4). These data 

are described further in Irwin (1966), Geldon (1985), and 

Wright (2006) (tables 3 and 4). Data for 13 NURE sites, 

8 springs and 5 wells, on the UMUR were collected during 

1976–78 (tables 3 and 4). Groundwater-chemistry data from 

the COGCC were collected from three wells during 1971 and 

1976 by oil and gas companies at selected COGCC facilities 

(tables 3 and 4). Detailed analysis of the NWIS, NURE, and 

COGCC data are not included in this report. 

Table 3. Sources of groundwater-chemistry data, number of sampling sites, period of groundwater-chemistry record, and type of 

groundwater-chemistry data reported by various organizations for springs and wells on the Ute Mountain Ute Reservation in Colorado 

and Utah.

[UMUT, Ute Mountain Ute Tribe; WQP, Water Quality Portal; PP, physical properties; TDS, total dissolved solids; MI, major ions; N, nutrients; TE, trace elements; U, uranium; P, pesticides; VOC, volatile organic compound; CB, coliform bacteria; ET, environmental tracers; U-I, uranium isotopes; RN, radiochemicals; USGS, U.S. Geological Survey; NWIS, National Water Information System; NURE, National Uranium Resource Evaluation; COGCC, Colorado Oil and 

Gas Conservation Commission; DS, dissolved solids]

Reporting 

organization Source

Number of 

sampling 

sites

(springs/

wells)

Period of

groundwater-chemistry

record

Type of

groundwater-chemistry

data1

Availability 

of analytical 

methods

Type of 

qualityassurance 

data

UMUT WQP2 13/31 1996–2007, 2009−17 PP, TDS, MI, N, TE, U, P, VOC, 

CB, ET, U-I, RN, oil and gas Yes

Field 

blanks and 

replicates

USGS NWIS3 18/27 41950–60, 1979, 1982, 1987, 2003 PP, TDS, MI, N, TE, CB No None

USGS NURE5 8/5 1976–78 PP, MI, TE Yes None

COGCC COGCC6 70/3 1971, 1976 PP, DS, MI No None

1

Not all available data listed were analyzed for the study.

2

National Water Quality Monitoring Council, 2017.

3

USGS, 2016b.

4

No data for 1952 and 1955.

5

USGS, 2014.

6

COGCC, 2018.

7

COGCC wells are environmental sampling sites. The COGCC map of environmental sampling sites shows four wells located within the boundaries of the 

Ute Mountain Ute Reservation in Colorado. One well, sample site ID 701784, is excluded from the report because there is conflicting information on the location of the well.
Methods for Compilation and Analysis of Groundwater-Chemistry Data 15

Table 4. Description of springs and wells with groundwater-chemistry data on the Ute Mountain Ute Reservation in Colorado and 

Utah, with sample year, number of environmental sample days and samples, and type of groundwater-chemistry data.—Continued

[See table 3 for water-quality data source. Sites sampled for the 2017 environmental tracer study are in bold. ID, identification; figs., figures; LatitudeDD, latitude in decimal degrees; LongitudeDD, longitude in decimal degrees; ft abv lsd, feet above land surface datum; No., number; env., environmental; UTEMTN, 

Ute Mountain Ute Tribe; PP, physical properties; CB, coliform bacteria; TDS, total dissolved solids; MI, major ions; N, nutrients; TE, trace elements; U-I, 

uranium isotopes; R, replicate quality assurance; U, uranium; ET, environmental tracers; RN, radiochemicals; VOC, volatile organic compound; P, pesticides; 

USGS, U.S. Geological Survey; NWIS, National Water Information System; na, not applicable; NURE, National Uranium Resource Evaluation]

Site ID

(see figs. 

5, 6)

Unique site identifier1 Site name used

in report

Latitude

DD2

Longitude

DD2

Altitude

(ft abv lsd)3

Sample

year

No. of env. 

sample 

days

No. of env. 

samples

Type of groundwaterchemistry data4

Ute Mountain Ute Tribe—Springs

S1 UTEMTN-Bancroft Spring Bancroft Spring 37.239 −108.765 56,836 2012 1 5 PP, CB

S2 UTEMTN-Cottonwood Wash Spring Cottonwood Wash 

Spring 37.256 −108.783 57,626 2015 1 1 PP, TDS, MI, N, TE, CB, U-I

S3 UTEMTN-EAST_TOE_Spring East Toe Spring 37.160 −108.821 5,758 1998–2000 4 4 PP, TDS, MI, TE

S4 UTEMTN-Elk Meadows Spring Elk Meadows 

Spring 37.271 −108.781 58,149 2012, 2015 2 4 PP, TDS, MI, N, TE, CB, U-I

S5 UTEMTN-Hanna 1 Hanna Spring6 37.282 −108.761 57,535 2010–15 9 11 PP, TDS, MI, N, TE, 

CB, U-I, R

S6 UTEMTN-Last Lake Spring Last Lake Spring 37.284 −108.793 57,512 2015 1 1 PP, TDS, MI, N, TE, 

CB, U-I

S7 UTEMTN-Lopez 1 Lopez 1 Spring6 37.249 −108.799 57,851 2010, 2011 4 6 PP, MI, TE, CB, U-I, R

S8 UTEMTN-Lopez 2 Lopez 2 Spring6 37.248 −108.799 57,812 2011–13, 2017 5 7 PP, N, U, CB, ET, R

S9 UTEMTN-NAVAJO Spring Navajo Spring 37.164 −108.712 5,461 2001, 2016 3 3 PP, TDS, MI, N, TE, 

U, CB

S10 UTEMTN-Ute Spring Ute Spring6 37.305 −108.781 56,812 2014, 2015 2 3 PP, TDS, MI, N, TE, 

CB, U-I, R

S11 UTEMTN-W-TOE-SPG, -WEST_

TOE_Spring West Toe Spring 37.162 −108.824 5,773 1998, 1999 3 3 PP, TDS, MI, TE

S12 Whisky Road Spring Whisky Road 

Spring 37.271 −108.742 56,817 2014, 2015 3 3 PP, TDS, MI, N, TE, CB, U-I

S13 UTEMTN-Whiskers Draw Whiskers Draw 

Spring6,7 37.616 −109.636 55,483 2013 2 2 PP, TDS, MI, N, TE, CB, RN, U-I

Ute Mountain Ute Tribe—Wells

W1 UTEMTN-4000B_SOLARWELL 4000B well 837.219 8−108.971 5,333 2016 1 1 PP, TDS, MI, N, TE, 

U, CB

W2 UTEMTN-4C-WELL 4C well 837.000 8−109.034 4,641 2002–04, 2006, 

2007 7 7 PP, TDS, MI, N, TE, CB, VOC

W3 UTEMTN-5000 Block Old Windmill

5000 Block

well 37.161 −108.836 95,659 2017 1 1 PP, MI, N, TE, U, ET

AP−1 UTEMTN-AP−1 AP−1 837.190 8−108.951 5,221

2001, 2003, 

2004, 2009, 

2011, 2013, 

2014, 2017

8 8

PP, TDS, MI, N, TE, 

U, CB, P, VOC, ET, 

U-I

AP–5 UTEMTN-AP–5 AP–5 837.171 8−108.994 5,017 1997, 1998, 

2000–02, 2014 9 9 PP, TDS, MI, N, TE, P

AP−10 UTEMTN-AP−10 AP−10 837.186 8−108.933 5,305 2001 1 1 PP, MI, TE, P

AP−11 UTEMTN-AP−11 AP−11 837.178 8−108.943 5,221 102004 0 0 P

AP−14 UTEMTN-AP−14 AP−14 837.159 8−108.923 5,237

1997–2001, 

102003, 2004, 

2005, 102007, 

2011, 2014

14 14 PP, TDS, MI, N, TE, 

P, VOC

AP−15 UTEMTN-AP−15 AP−15 837.150 8−108.958 5,041 102011, 2012 1 1 PP, TDS, MI, N, TE, 

CB, P, VOC

AP−16 UTEMTN-AP−16 AP−16 837.152 8−108.934 5,150 2001, 2003–05, 

2007 6 6 PP, MI, TE, P, VOC

AP–24 UTEMTN-AP–24 AP–24 837.196 8−108.964 5,202 2001, 2014 2 3 PP, MI, N, TE, P

W4 UTEMTN-AW HWY 141 11AW Hwy 141 37.099 −109.008 4,986 1996, 2000, 2002 3 3 PP, TDS, MI, N, TE, CB

W5 UTEMTN-AW HWY 160/141 11AW Hwy 160/141 37.032 −108.970 4,913 1996, 2000, 2002 3 3 PP, TDS, MI, N, TE, CB
16 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

Table 4. Description of springs and wells with groundwater-chemistry data on the Ute Mountain Ute Reservation in Colorado and 

Utah, with sample year, number of environmental sample days and samples, and type of groundwater-chemistry data.—Continued

[See table 3 for water-quality data source. Sites sampled for the 2017 environmental tracer study are in bold. ID, identification; figs., figures; LatitudeDD, latitude in decimal degrees; LongitudeDD, longitude in decimal degrees; ft abv lsd, feet above land surface datum; No., number; env., environmental; UTEMTN, 

Ute Mountain Ute Tribe; PP, physical properties; CB, coliform bacteria; TDS, total dissolved solids; MI, major ions; N, nutrients; TE, trace elements; U-I, 

uranium isotopes; R, replicate quality assurance; U, uranium; ET, environmental tracers; RN, radiochemicals; VOC, volatile organic compound; P, pesticides; 

USGS, U.S. Geological Survey; NWIS, National Water Information System; na, not applicable; NURE, National Uranium Resource Evaluation]

Site ID

(see figs. 

5, 6)

Unique site identifier1 Site name used

in report

Latitude

DD2

Longitude

DD2

Altitude

(ft abv lsd)3

Sample

year

No. of env. 

sample 

days

No. of env. 

samples

Type of groundwaterchemistry data4

W6 UTEMTN- Chimney_Rock_Windmill Chimney Rock well 1237.106 12−108.710 55,423 2016 1 1 PP, TDS, MI, N, TE, U

W7 UTEMTN-Corral Well Horse Canyon HC Corral well 1237.183 12−108.356 56,065 2012 1 1 PP, TDS, MI, N, TE

W8 UTEMTN- Cottonwood Spring Cottonwood 

Spring well11 37.171 −108.727 95,561 2014, 2017 2 2 PP, TDS, MI, N, TE, U, CB, ET, U-I

W9 UTEMTN-FW-W FW-W11 37.128 −109.022 54,895 2013 1 1 PP, TDS, MI, N, TE, CB

W10 UTEMTN- Goodknight Well Goodknight well 37.052 −108.792 55,187 2017 1 1 PP, MI, N, TE, U, ET

W11 UTEMTN-KNIGHT WELL Knight well 37.052 −108.789 5,100 2000, 2001, 2013 4 4 PP, TDS, MI, N, TE, CB

W12 UTEMTN-LAGOON 1 WELL 1 Lagoon 1 well 1 837.184 8−108.718 5,598 2010 2 2 PP, TDS, MI, N, TE

W13 UTEMTN-LAGOON 1 WELL 3 Lagoon 1 well 3 837.186 8−108.717 55,601 2003, 2004, 2010 5 5 PP, TDS, MI, N, TE, 

CB, P, VOC, R

W14 UTEMTN- LAGOON 2 WELL 2 Lagoon 2 well 2 837.189 8−108.701 5,560 2002 1 1 PP, CB

W15 UTEMTN-Lewis Well Lewis well 1237.154 12−108.312 56,805 2012 1 1 PP, TDS, MI, N, TE

W16 UTEMTN-LF_WELL1 LF well 1 837.182 8−108.719 5,596 2009 1 1 TE, R

W17 UTEMTN-LF_WELL3 LF well 3 837.178 8−108.718 5,576 2009 1 1 TE

W18 UTEMTN- Mariano-FW Mariano-FW11 37.168 −108.885 55,453 2013 1 1 PP, TDS, MI, N, TE, CB

W19 UTEMTN- MR-FW MR-FW11 37.031 −108.753 35,105 2011 1 1 PP, TDS, MI, TE

W20 UTEMTN-SE Toe Old Solar SE Toe well 37.188 −108.743 55,862 2017 1 1 PP, MI, N, TE, U, ET

W21 UTEMTN-TF-CORRAL-WELL TF-Corral well 37.020 −108.759 5,020 2002 1 1 P

W22 UTEMTN-Toe Windmill Toe well 1237.168 12−108.826 55,842 2016 1 1 PP, TDS, MI, N, TE, U, 

CB, RN, U-I, R

W23 WING-WELL, WING WELL Wing well 37.160 −108.981 4,986 2000, 2001, 

2003, 2012 4 4 PP, TDS, MI, N, TE, CB, P, VOC, oil and gas

USGS NWIS—Springs

NS1 370905108432101 na 37.151 −108.723 5,390 1982 1 1 PP

NS2 370945108423401 S–15 Spring 37.162 −108.710 135,400 1951 1 1 PP, TDS, MI, N

NS3 370950108424201 Spring 16 37.164 −108.712 5,470 1951, 1982 2 2 PP, TDS, MI, N

NS4 371056108520501 na 37.182 −108.869 135,723 1956 1 1 PP, TDS, MI

NS5 371107108433201 na 37.185 −108.726 135,700 1960 1 1 PP, TDS, MI, N, TE

NS6 371107108433801 na 37.185 −108.728 5,670 1950, 1982 3 3 PP, TDS, MI, N, TE

NS7 371113108433301 na 37.187 −108.726 5,680 1960 2 2 PP, TDS, MI, N, TE

NS8 371340108442501 na 37.228 −108.741 6,365 1982 3 3 PP, TDS, MI, N, TE, CB

NS9 371345108472301 na 37.229 −108.790 7,860 1982 3 3 PP, TDS, MI, N, TE

NS10 371357108473701 na 37.232 −108.794 7,960 1982 2 2 PP, TDS, MI, N, TE

NS11 371416108455201 Spring 9 37.238 −108.765 136,850 1951 1 2 PP, TDS, MI, N

NS12 371428108483001 na 37.241 −108.809 8,120 1982 1 1 PP, TDS, MI, N, TE

NS13 371454108475201 Spring 5,

S–3 Spring 37.248 −108.798 7,800 1982 3 3 PP, TDS, MI, N, TE, CB

NS14 371508108465901 na 37.252 −108.784 7,400 1982 3 3 PP, TDS, MI, N, TE

NS15 371538108483201 na 37.261 −108.810 8,560 1982 1 1 PP, TDS, MI, N, TE

NS16 371601108472501 na 37.267 −108.791 8,080 1982 3 3 PP, TDS, MI, N, TE, CB

NS17 371610108472201 na 37.269 −108.790 8,160 1982 2 2 PP, TDS, MI, N, TE

NS18 371634108455701 Elbow Spring 37.276 −108.766 7,871 2003 1 1 PP, TDS, MI, N, TE
Methods for Compilation and Analysis of Groundwater-Chemistry Data 17

Table 4. Description of springs and wells with groundwater-chemistry data on the Ute Mountain Ute Reservation in Colorado and 

Utah, with sample year, number of environmental sample days and samples, and type of groundwater-chemistry data.—Continued

[See table 3 for water-quality data source. Sites sampled for the 2017 environmental tracer study are in bold. ID, identification; figs., figures; LatitudeDD, latitude in decimal degrees; LongitudeDD, longitude in decimal degrees; ft abv lsd, feet above land surface datum; No., number; env., environmental; UTEMTN, 

Ute Mountain Ute Tribe; PP, physical properties; CB, coliform bacteria; TDS, total dissolved solids; MI, major ions; N, nutrients; TE, trace elements; U-I, 

uranium isotopes; R, replicate quality assurance; U, uranium; ET, environmental tracers; RN, radiochemicals; VOC, volatile organic compound; P, pesticides; 

USGS, U.S. Geological Survey; NWIS, National Water Information System; na, not applicable; NURE, National Uranium Resource Evaluation]

Site ID

(see figs. 

5, 6)

Unique site identifier1 Site name used

in report

Latitude

DD2

Longitude

DD2

Altitude

(ft abv lsd)3

Sample

year

No. of env. 

sample 

days

No. of env. 

samples

Type of groundwaterchemistry data4

USGS NWIS—Wells

NW1 370410108583701 na 37.071 −108.978 4,900 1959 1 1 PP, TDS, MI

NW2 370518108540601 na 37.092 −108.896 5,220 1956 1 1 PP, TDS, MI

NW3 370554109002701 na 37.098 −109.008 4,965 1956, 1959, 

1979, 1987 4 4 PP

NW4 370557109003201 B−11 37.099 −109.010 134,989 1959 1 1 PP, TDS, MI

NW5 370612108424001 na 37.106 −108.710 5,400 1959, 1987 2 2 PP, TDS, MI

NW6 370617108504201 na 37.104 −108.843 5,290 1956, 1987 2 2 PP, TDS, MI

NW7 370717108532501 na 37.126 −108.891 5,330 1956 1 1 PP, TDS, MI

NW8 370806108485801 na 37.135 −108.815 5,483 1956 1 1 PP, TDS, MI

NW9 370913108563901 na 37.154 −108.944 5,110 1956, 1987 2 2 PP, TDS, MI

NW10 371000108451001 na 37.167 −108.753 135,680 1956 1 1 PP, TDS, MI

NW11 371003108451301 na 37.167 −108.754 5,690 1956 1 1 PP, TDS, MI

NW12 371006108530401 na 37.169 −108.882 4,440 1959 1 1 PP, TDS, MI

NW13 371007108575101 na 37.169 −108.963 5,078 1956, 1987 2 2 PP, TDS, MI

NW14 371015108433601 na 37.171 −108.727 5,556 1982, 1987 2 2 PP

NW15 371112108443401 na 37.188 −108.743 5,848 1958 2 2 PP, TDS, MI

NW16 371115108432001 na 37.187 −108.723 5,739 1957 1 1 PP, TDS, MI

NW17 371152108435401 na 37.198 −108.732 5,877 1957 1 1 PP, TDS, MI, N

NW18 371159108434801 na 37.200 −108.731 5,885 1954 1 1 PP, TDS, MI, N

NW19 371204108433801 na 37.201 −108.728 135,880 1953 1 1 PP, TDS, MI, N

NW20 371204108434301 na 37.201 −108.729 5,885 1954 1 1 PP, TDS, MI

NW21 371208108433601 na 37.202 −108.727 5,880 1953 2 2 PP, TDS, MI, N

NW22 371208108433801 na 37.202 −108.728 5,885 1954, 1982 3 3 PP, TDS, MI, N, TE

NW23 371217108435701 na 37.205 −108.733 5,922 1953 1 1 PP, MI

NW24 371218108433301 na 37.205 −108.726 5,917 1959 1 1 PP, MI

NW25 371248108402201 na 37.216 −108.674 5,880 1956 2 2 PP, TDS, MI

NW26 371307108581301 A–8 37.219 −108.971 5,320 1956 1 1 PP, TDS, MI

NW27 371443108544701 na 37.247 −108.916 5,755 1956 1 1 PP, TDS, MI

USGS NURE—Springs12,13

NUS1 C24367 na 37.093 −108.561 5,690 1977 1 1 PP, MI, TE

NUS2 C24392 na 37.064 −108.658 5,325 1977 1 1 PP, MI, TE

NUS3 C24434 na 37.158 −108.524 6,283 1977 1 1 PP, MI, TE

NUS4 C24450 na 37.169 −108.726 5,531 1977 1 1 PP, MI, TE

NUS5 C24451 na 37.164 −108.712 5,471 1977 1 1 PP, MI, TE

NUS6 C24456 na 37.238 −108.764 6,813 1977 1 1 PP, MI, TE

NUS7 C24458 na 37.241 −108.808 8,128 1977 1 1 PP, MI, TE

NUS8 C24531 na 37.264 −108.789 8,065 1977 1 1 PP, MI, TE

USGS NURE—Wells12,13

NUW1 C24003 na 37.068 −108.318 6,956 1976 1 1 PP, MI, TE

NUW2 C24448 na 37.145 −108.738 5,442 1977 1 1 PP, MI, TE

NUW3 C24858 na 37.219 −108.970 5,322 1977 1 1 PP, MI, TE
18 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

Table 4. Description of springs and wells with groundwater-chemistry data on the Ute Mountain Ute Reservation in Colorado and 

Utah, with sample year, number of environmental sample days and samples, and type of groundwater-chemistry data.—Continued

[See table 3 for water-quality data source. Sites sampled for the 2017 environmental tracer study are in bold. ID, identification; figs., figures; LatitudeDD, latitude in decimal degrees; LongitudeDD, longitude in decimal degrees; ft abv lsd, feet above land surface datum; No., number; env., environmental; UTEMTN, 

Ute Mountain Ute Tribe; PP, physical properties; CB, coliform bacteria; TDS, total dissolved solids; MI, major ions; N, nutrients; TE, trace elements; U-I, 

uranium isotopes; R, replicate quality assurance; U, uranium; ET, environmental tracers; RN, radiochemicals; VOC, volatile organic compound; P, pesticides; 

USGS, U.S. Geological Survey; NWIS, National Water Information System; na, not applicable; NURE, National Uranium Resource Evaluation]

Site ID

(see figs. 

5, 6)

Unique site identifier1 Site name used

in report

Latitude

DD2

Longitude

DD2

Altitude

(ft abv lsd)3

Sample

year

No. of env. 

sample 

days

No. of env. 

samples

Type of groundwaterchemistry data4

NUW4 C25005 na 37.099 −109.008 4,979 1978 1 1 PP, MI, TE

NUW5 C25010 na 37.179 −109.017 4,896 1978 1 1 PP, MI, TE

Colorado Oil and Gas Conservation Commission12,13

CW1 213879 213879 37.007 −108.308 6,889 1971 1 1 PP, TDS

CW2 213907 213907 37.017 −108.302 6,945 1976 1 1 PP, TDS

CW3 214329 214329 37.027 −108.283 7,015 1976 1 1 PP, TDS

1

The term “Unique site identifier” used here is titled differently in the source databases: “MonitoringLocationIdentifier" in the Water Quality Portal, 

“Site Number” in NWIS, “Prime_ID” in the NURE database, and “Sample Site ID” in the Colorado Oil and Gas Conservation Commission database.

2

Latitude, longitude datum is North American Datum of 1983, unless otherwise noted.

3

Altitude datum is National Geodetic Vertical Datum of 1929, unless otherwise noted.

4

Not all available data listed were analyzed for the study.

5

Altitude from Google Earth (https://www.google.com/earth/). Altitude datum is unknown.

6

Culturally significant spring (Larrick and Clow, 2011).

7

Spring, shown on figure 1, is in Utah. All other sites are in Colorado.

8

Latitude, longitude datum is North American Datum of 1927.

9

Altitude from Ute Mountain Ute Tribe. Altitude datum is unknown.

1

0Quality assurance (field blank) sample only.

1

1UMUT flowing artesian well.

12Latitude, longitude datum is unknown.

13Altitude datum is unknown.

Types of Groundwater-Chemistry Data

The groundwater-chemistry data used by this assessment include physical properties and concentrations of total 

dissolved solids (TDS), major ions, nutrients, trace elements, 

uranium, pesticides, volatile organic compounds (VOCs), 

and coliform bacteria (total coliform and Escherichia coli). 

Concentration data for groundwater-chemistry constituents 

are reported as filtered (through a 0.45-micrometer filter, 

described as “dissolved”) and unfiltered (described as “total”). 

Trace-element and some ammonia data are reported as “total 

recoverable,” which indicates possible incomplete digestion of 

particulate matter in the laboratory (Alpers and others, 2000). 

Most (47 of 57) TDS concentrations presented in this 

report were retrieved from the Water Quality Portal (National 

Water Quality Monitoring Council, 2017) as residue on 

evaporation at 180 degrees Celsius in milligrams per liter 

(mg/L, milligrams of a constituent per liter of water). For 

10 samples collected in 2016 and 2017, TDS concentrations 

were calculated as the sum of constituents, which is the sum of 

the major-ion concentrations retrieved from the Water Quality 

Portal for each sample. 

Samples for environmental tracers, used for assessing recharge, groundwater age, and geochemical conditions, were collected by the UMUT in collaboration with 

the USGS from one spring and five wells in May 2017 

(table 4) and analyzed by USGS laboratories. The environmental tracer samples were analyzed for stable isotope 

ratios (hydrogen and oxygen in water, nitrogen in nitrate, 

and carbon in dissolved inorganic carbon), tritium, chlorofluorocarbons (CFCs), dissolved gases (methane, carbon 

dioxide, nitrogen, oxygen, and argon), and noble gases 

(helium-4, neon, argon, krypton, and xenon). The nitrogenand carbon-isotope samples were filtered through disposable, 0.45-micrometer filters, and the rest of the samples 

were collected as unfiltered or raw water. Sample-collection 

procedures for stable isotopes of hydrogen, oxygen, and 

nitrogen are described by USGS (2017b) and for carbon 

isotopes by USGS (variously dated). Procedures for CFCs 

and dissolved gases are described by USGS (2017a). Noble 

gas samples were collected in sealable copper tubes using a 

back-pressure system to decrease the possibility of bubble 

formation and degassing of the sample water during collection (Plummer and others, 2012b). 
Methods for Compilation and Analysis of Groundwater-Chemistry Data 19

for 185 replicate pairs (environmental concentration and 

paired replicate concentration for a constituent of interest) 

for 16 samples at 7 sites collected by the UMUT from 2009 

through 2016 (table 4). Constituents included TDS, alkalinity, major ions, nutrients, trace elements, pesticides, VOCs, 

and coliform bacteria. Of the replicate pairs, 34 percent had 

both concentrations reported as less than laboratory reporting 

limits; these data were not included in replicate analysis. 

Variability in constituent detection was estimated by 

calculating the percentage of replicate pairs with inconsistent 

detections (a pair containing a detected concentration and a 

concentration less than the laboratory reporting limit) using 

equation 1 (Mueller and others, 2015). 

PID = [number of inconsistent detections/

(total number of replicate pairs–the number 

of replicate pairs with both concentrations

less than the reporting limit)] x 100, (1)

where

PID is the percentage of replicate pairs with 

inconsistent detections.

Of the replicate pairs, 14 percent had inconsistent detections. 

All data were retained for analysis.

Variability in constituent concentrations was estimated 

as either the standard deviation of the replicate-pair concentrations, used for concentrations less than (<) 1.0 mg/L or 

1.0 μg/L (eq. 2), or as the relative percent difference of the 

replicate-pair concentrations (RPDrep), used for concentrations greater than or equal to (≥) 1.0 mg/L or 1.0 μg/L (eq. 3; 

Mueller and others, 2015). 

SD = SQRT[∑((env sample–replicate sample)/2)/n], (2)

where

SD is the standard deviation, 

SQRT is the square root,

∑ is the “sum of,”

env sample is the concentration of the environmental 

sample, and

n is number of replicate pairs.

RPDrep = ABS[(env sample–replicate sample)/

((env sample + replicate sample)/2)] x 100, (3)

where

RPDrep is the relative percent difference of the 

replicate-pair concentrations, 

ABS is the absolute value, and

env sample is the concentration of the environmental 

sample.

The mean standard deviation of 17 replicate pairs with both 

concentrations <1.0 mg/L or 1.0 μg/L was 0.2 or less, and 

data were retained for analysis. Mean RPDrep values for the 

88 replicate pairs with both concentrations of 1.0 mg/L or 

1.0 μg/L or more ranged from 0 to 181 percent. Many of 

Samples for hydrogen-, oxygen-, and nitrogen-isotope 

determination were analyzed at the USGS Reston Stable Isotope Laboratory in Reston, Virginia, using methods described 

in Coplen and others (2012) and Révész and Coplen (2008a, 

2008b). Samples for the determination of carbon-14, the 

radioactive isotope of carbon, and the related isotopic ratio 

of carbon-13 to carbon-12 were analyzed at the National 

Ocean Sciences Accelerator Mass Spectrometry Facility 

in Woods Hole, Massachusetts, following methods specified by the Woods Hole Oceanographic Institution (2011). 

Samples were analyzed for tritium, the radioactive isotope of 

hydrogen, at the USGS Tritium Laboratory in Menlo Park, 

California, using methods described in Thatcher and others 

(1977) and Östlund and Werner (1962). Analysis of samples 

for CFCs and dissolved gases were conducted at the USGS 

Reston Groundwater Dating Laboratory in Reston, Va., following methods described in USGS (2017a), and samples for 

noble gas determination were analyzed at the USGS Noble 

Gas Laboratory in Lakewood, Colorado, following methods 

described in Hunt (2015). 

Data-Quality Assurance

Several quality-assurance procedures were applied to the 

compiled groundwater-chemistry dataset including (1) checks 

for duplicated results from the same data source, that is, 

identical measurements and analytical results for an environmental sample collected at the same site and date as another 

environmental sample; (2) examination of data for zero values, inconsistent results, and outliers; and (3) comparison of 

total to dissolved concentrations for the same constituent in a 

sample. Additionally, data for field blanks and field replicates 

were used to assess the variability and bias of groundwaterchemistry data that may have been introduced by sample 

collection, processing, shipping, and analysis. Finally, cationanion charge balance differences were calculated for samples 

with complete major-ion data to evaluate the accuracy of 

laboratory analysis. Specific information on quality-control 

procedures, analysis methods, and analytical or statistical 

results are presented in appendix 2. 

Potential contamination was evaluated using 19 fieldblank samples that were collected by the UMUT at 11 sites 

from 2001 through 2015 and included data for all chemical constituent groups except environmental tracers. About 

3 percent (11 of 392) of the field-blank results had concentrations greater than laboratory reporting limits (table 2.1 

in app. 2), indicating that the potential for contamination of 

environmental samples is low. The concentration of dissolved zinc (9 micrograms per liter [μg/L]) in a field blank 

collected at Lagoon 1 well 3 in 2010 was the same as the 

concentration in the environmental sample collected on the 

same day. The environmental result for dissolved zinc was 

excluded from analysis. 

Replicate samples were used to test for variability, 

which is the degree of random error in independent measurements of the same quantity. Replicate data were available 
20 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

the higher RPDrep values were for trace elements. For many 

trace-element replicate pairs, the environmental concentration was substantially lower than the concentration in 

the replicate. The environmental sample concentrations in 

replicate pairs with a RPDrep of 100 percent or more were 

excluded from analysis. 

The accuracy of major-ion results was estimated by 

calculating the cation-anion balance percent difference for 

samples with data for dissolved cations (calcium, magnesium, 

potassium, sodium) and dissolved anions (bicarbonate, carbonate, chloride, sulfate). The difference was calculated for 

34 samples collected by the UMUT using equation 4. 

Cation-anion balance percent difference = ABS

[(∑cations − ∑anions)/

(∑cations + ∑anions)] x 100, (4)

where

ABS is the absolute value, 

∑cations is the sum of the concentrations of dissolved 

cations (calcium, magnesium, potassium, 

sodium) in milliequivalents per liter, and 

∑anions is the sum of the concentrations of dissolved 

anions (bicarbonate, carbonate, chloride, 

sulfate) in milliequivalents per liter.

For cation or anion concentrations that were less than laboratory 

reporting limits, one-half of the reporting limit was used in 

equation 4. For this report, ion balances of 5 percent or less 

were deemed acceptable. Only three samples had chargebalance percent differences greater than (>) 10 percent, and nine 

samples had differences between 5 and 10 percent. As described 

in appendix 2, these charge-balance differences were deemed 

acceptable, and the major-ion data were retained for analysis. 

Data Aggregation and Summarization

Some chemical constituent data retrieved from the Water 

Quality Portal (National Water Quality Monitoring Council, 

2017) used different names for the same constituent; for 

example, “inorganic nitrogen” (nitrate and nitrite) and “nitrate 

+ nitrite” represent the same constituents. Data for constituents 

with multiple names were combined under one name (table 5). 

Methods used for laboratory analysis, also retrieved from the 

Water Quality Portal, were reviewed to determine or verify 

chemical forms of constituents; for example, nitrate plus 

nitrite as nitrogen rather than as nitrate. Review of methods 

for trace-element analysis confirmed that samples for total 

analysis were digested in the laboratory; the chemical form of 

“total” was changed to “total recoverable” as a result. Concentration data for trace element, pesticide, and VOC results that 

were originally reported as milligrams per liter were converted 

to micrograms per liter.

Summary statistics were calculated for each chemical 

constituent and fraction. Estimating the median statistic for 

groundwater-chemistry data was complicated by the presence of multiple laboratory reporting limits for many of 

the constituents. When groundwater-chemistry results were 

reported as less than laboratory reporting limits, estimates 

of the median (50th percentile) were calculated using (1) the 

Kaplan-Meier method when fewer than 50 percent of the 

data were less than laboratory reporting limits or (2) regression of ordered statistics methods when the less-than percentages were 50 to 80 percent (Helsel, 2005). The median was 

not calculated when more than 80 percent of the data were 

less-than values. Summary statistics, boxplots, a Piper diagram, and scatter plots are used in this assessment to depict 

the variability in select groundwater-chemistry properties 

and constituents. 

Water-Quality Standards

Groundwater-chemistry data collected by the UMUT 

for springs were compared to surface-water quality standards 

established by the UMUT (table 6) (Larrick and Clow, 2011). 

Standards are applicable to one or more designated uses for 

springs including Tribal cultural use, warm-water aquatic 

life, and agricultural use. Springs specifically designated for 

the cultural-use standard are Hanna, Lopez 1 and 2, Ute, and 

Whiskers Draw (Larrick and Clow, 2011). For a stream segment with more than one designated use, the most stringent 

criterion is considered the applicable water-quality standard 

(Larrick and Clow, 2011). Aquatic-life standards for some 

metals are based on hardness; hardness-based formulas are 

included in table 6. 

Groundwater-chemistry data for specific wells in 

Colorado were compared to basic standards for groundwater 

established by the Colorado Department of Public Health 

and Environment (CDPHE) (CDPHE, 2017) (table 6). The 

CDPHE basic standards for groundwater have been established to protect existing and potential beneficial uses of 

groundwater. For this assessment, groundwater standards 

for agricultural use are applied to wells that are or could 

potentially be used for livestock watering. Comparison of the 

livestock-water standards is applied to data from all wells 

except the AP, Lagoon, and LF wells, which were established 

for specific monitoring purposes. Comparison of data to 

water-quality standards is used in this report as a guideline 

for giving qualitative interpretations on the status of groundwater quality on the reservation; the standards are not used in 

this report for regulatory purposes. 
Methods for Compilation and Analysis of Groundwater-Chemistry Data 21

Table 5. Aggregation of constituent names and data retrieved from the Water Quality Portal (WQP).—Continued

[See National Water Quality Monitoring Council (2017) for the WQP. μS/cm, microsiemens per centimeter; —, no conversion; mg/L, milligrams per liter; 

CaCO3, calcium carbonate; Ca, calcium; Mg, magnesium; ROE, residue on evaporation at 180 degrees Celsius; SUM, sum of constituents; <, less than; N, 

nitrogen; P, phosphorus; μg/L, micrograms per liter]

Consituent name

as retrieved from WQP

Sample fraction

as retrieved from WQP

Number of 

samples

Concentration 

range

Conversion

Constituent name

and sample fraction 

used in report

Specific conductance (μS/cm)

Conductivity No fraction 35 3.9–10,520 — Specific conductance Specific conductance No fraction 49 178–9,080 —

Alkalinity (mg/L)

Alkalinity, total, as CaCO3 Dissolved 1 328 —

Alkalinity, as CaCO3

Alkalinity, total Dissolved 30 77–2,000 —

Alkalinity, total Total 36 73–1,335 —

Alkalinity, total, as CaCO3 No fraction 1 428 —

Alkalinity, total No fraction 1 290 —

Hardness (mg/L)

Hardness, as CaCO3 No fraction 1 3,200 —

Hardness, as CaCO3

Hardness, carbonate Dissolved 27 7.7–3,793 —

Hardness, Ca, Mg Dissolved 7 87–2,903 —

Hardness, Ca, Mg Total 2 98; 3,910 —

Hardness Dissolved 1 918 —

Total dissolved solids (mg/L)

Total dissolved solids (ROE) Dissolved 45 75–6,860 —

Total dissolved solids (ROE) Total 2 3,400; 20,000 — Total dissolved solids

Total dissolved solids (SUM) — 10 324–6,318 —

Major ions (mg/L)

Alkalinity, bicarbonate, as CaCO3 No fraction 2 302; 428 —

Bicarbonate, as CaCO3

Alkalinity, bicarbonate Dissolved 10 77–1,290 —

Alkalinity, bicarbonate No fraction 5 243–1,760 —

Bicarbonate Dissolved 43 85–1,959 —

Alkalinity, carbonate, as CaCO3 Dissolved 1 26 —

Carbonate, as CaCO3

Alkalinity, carbonate, as CaCO3 No fraction 1 <10 —

Alkalinity, carbonate Dissolved 10 <10–240 —

Alkalinity, carbonate No fraction 5 <10–280 —

Carbonate Dissolved 43 0–240 —

Nutrients (mg/L)

Ammonia Total 4 <0.05–0.08 —

Ammonia, unfiltered, 

as N

Ammonia Total recoverable 13 <0.024–1.85 —

Ammonia as N Total recoverable 3 <0.043 —

Ammonia Unfiltered 2 <0.05; 0.05 —

Inorganic nitrogen (nitrate and nitrite) Total 11 <0.011–52.3 —

Nitrate plus nitrite, 

unfiltered, as N

Nitrate + Nitrite Total 18 <0.01–45.8 —

Nitrate/Nitrite as N Total 3 <0.011–68 —

Nitrate Total 4 0.409–78.5

Sum

Nitrite Total 4 0.023–0.07
22 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

Table 5. Aggregation of constituent names and data retrieved from the Water Quality Portal (WQP).—Continued

[See National Water Quality Monitoring Council (2017) for the WQP. μS/cm, microsiemens per centimeter; —, no conversion; mg/L, milligrams per liter; 

CaCO3, calcium carbonate; Ca, calcium; Mg, magnesium; ROE, residue on evaporation at 180 degrees Celsius; SUM, sum of constituents; <, less than; N, 

nitrogen; P, phosphorus; μg/L, micrograms per liter]

Consituent name

as retrieved from WQP

Sample fraction

as retrieved from WQP

Number of 

samples

Concentration 

range

Conversion

Constituent name

and sample fraction 

used in report

Phosphorus Total 34 <0.011–0.43 — Total phosphorus, as P Phosphorus, Total Total 3 <0.011–0.053 —

Trace elements (μg/L)

Aluminum Total 4 250–10,300 — Aluminum, total

Aluminum Total recoverable 20 <1–817 — recoverable

Antimony Total 3 <100 — Antimony, total

Antimony Total recoverable 4 <0.4 — recoverable

Arsenic Total 37 <0.5–224 — Arsenic, total

Arsenic Total recoverable 20 <0.1–7.6 — recoverable

Barium Total 11 <10–99 — Barium, total

Barium Total recoverable 7 4.8–207 — recoverable

Boron Total 2 <100 Boron, total

Boron Total recoverable 1 <300 recoverable

Cadmium Total 8 <0.09–<50 — Cadmium, total

Cadmium Total recoverable 18 <0.01–<0.1 — recoverable

Chromium Total 3 <3.7–8.4 — Chromium, total

Chromium Total recoverable 14 <0.1–14 — recoverable

Copper Total 5 <5–20 — Copper, total

Copper Total recoverable 20 0.2–35.3 — recoverable

Iron Total 9 <50–6,310 — Iron, total

recoverable Iron Total recoverable 22 <24–1,480 —

Lead Total 15 <0.2–<100 — Lead, total

Lead Total recoverable 8 <0.03–1.4 — recoverable

Manganese Total 7 <5–484 — Manganese, total 

Manganese Total recoverable 8 4.9–538 — recoverable

Molybdenum Total 2 <50 — Molybdenum,

Molybdenum Total recoverable 16 <0.05–14.2 — total recoverable

Nickel Total 4 3–8.1 — Nickel, total

Nickel Total recoverable 13 1–13.4 — recoverable

Selenium Total 37 <0.5–231 — Selenium, total

Selenium Total recoverable 17 <0.3–212 — recoverable

Silver Total 1 <0.1 — Silver, total

Silver Total recoverable 7 <0.02–<0.1 — recoverable

Vanadium Total 2 <20 — Vanadium, total

Vanadium Total recoverable 17 <0.5–5 — recoverable

Zinc Total 11 <1–<200 — Zinc, total

Zinc Total recoverable 20 <0.4–486 — recoverable
Methods for Compilation and Analysis of Groundwater-Chemistry Data 23

Table 6. Ute Mountain Ute Tribe (UMUT) water-quality standards for surface waters of the Ute Mountain Ute Reservation and 

Colorado Department of Public Health and Environment (CDPHE) basic standards for agricultural use of groundwater.—Continued

[UMUT water-quality standards are from Larrick and Clow (2011). CDPHE basic standards for groundwater are from CDPHE (2017). °C, degrees Celsius; —, 

no standard; <, less than; mg/L, milligrams per liter; ≤, less than or equal to; dis, dissolved; NH3, unionized ammonia; N, nitrogen; μg/L, micrograms per liter, 

trec, total recoverable; cfu/100 mL, colony-forming units per 100 milliliters]

Contaminant

UMUT water-quality standards for surface waters by designated use1,2 CDPHE basic

standards for

agricultural use of 

groundwater3

Tribal

cultural use

Warm water aquatic life Agriculture,

irrigation, and (or)

Acute Chronic livestock watering

Physical properties

pH (standard units) 6.5–8.5 6.5–9.0 6.5–9.0 6.5–8.5

Termperature (°C) — <30 °C with maximum 3 °C increase <50 °C —

Dissolved oxygen (mg/L) — (4) — —

Total dissolved solids and major ions (mg/L)

Total dissolved solids ≤500 — — Livestock

consumption: ≤5,000

Based on

background value5

Fluoride — — — — 2 (dis)

Nutrients (mg/L)

Ammonia, NH3, as N 0.5 (dis)6 Formula (total)7 Formula (total)6,7 — —

Nitrite, as N 1.0 (acute)8 Formula (total)9 Formula (total)6,9 10 (acute)8 10 (dis)

Nitrate plus nitrate, as N 10 (chronic)8 — — 100 (chronic)6 100 (dis)

Trace elements and uranium (μg/L)

Aluminum 200 (trec) 750 (trec) 87, 750 (trec)10 — 5,000 (dis)

Antimony 5.6 (trec)6 — — — —

Arsenic 0.018 (trec)8 340 (trec) 150 (trec) 100 (trec)6 100 (dis)

Barium 1,000 (trec)8 — — — —

Beryllium — — — — 100 (dis)

Boron — — — 750 (dis) 750 (dis)

Cadmium 5 (trec)8 Formula (dis)11,12,13 Formula (dis)11,12,13 10 (trec)6 10 (dis)

Chromium 50 (trec)8 16 (dis) 11 (dis) 100 (trec)6 100 (dis)

Cobalt — — — — 50 (dis)

Copper 1,000 (trec)6 Formula (dis)12,13,14 Formula (dis)12,13,14 200 (trec)6 200 (dis)

Iron — — — — 5,000 (dis)

Lead 50 (trec)8 Formula (dis)12,13,15 Formula (dis)12,13,15 100 (trec)6 100 (dis)

Manganese — — — — 200 (dis)

Mercury 0.05 (total)8,16 1.4 (total)16 0.012 (total)16 10 (total)6,16 10 (dis)

Nickel 100 (trec)6 Formula (dis)12,13,17 Formula (dis)12,13,17 200 (trec)6 200 (dis)

Selenium 50 (trec)6 20 (trec) 5 (trec) 20 (trec)6 20 (dis)

Silver 100 (trec)8 Formula (dis)12,13,18 Formula (dis)12,13,18 — —

Vanadium — — — — 100 (dis)

Zinc 5,000 (trec)6 Formula (dis)12,13,19 Formula (dis)12,13,19 2,000 (trec)6 2,000 (dis)

Uranium 30 (trec) — — — —

Pesticides (μg/L)20

Alachlor 212 — — — —

Atrazine 213 — — — —
24 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

Table 6. Ute Mountain Ute Tribe (UMUT) water-quality standards for surface waters of the Ute Mountain Ute Reservation and 

Colorado Department of Public Health and Environment (CDPHE) basic standards for agricultural use of groundwater.—Continued

[UMUT water-quality standards are from Larrick and Clow (2011). CDPHE basic standards for groundwater are from CDPHE (2017). °C, degrees Celsius; —, 

no standard; <, less than; mg/L, milligrams per liter; ≤, less than or equal to; dis, dissolved; NH3, unionized ammonia; N, nitrogen; μg/L, micrograms per liter, 

trec, total recoverable; cfu/100 mL, colony-forming units per 100 milliliters]

Contaminant

UMUT water-quality standards for surface waters by designated use1,2 CDPHE basic

standards for

agricultural use of 

groundwater3

Tribal

cultural use

Warm water aquatic life Agriculture,

irrigation, and (or)

Acute Chronic livestock watering

Volatile organic compounds (μg/L)20

Di(2-ethylhexyl) phthalate22 211.2 — — — —

Bacteria (cfu/100 mL)

Escherichia coli 0 (absent) — — — —

1

For this report, surface-water standards are applied to spring data only. For a water body with multiple use designations, the most stringent criteria will be the 

goal of its water-quality standard.

2

For constituents that lack numeric water-quality criteria or for which numeric criteria are not protective or representative of clean water goals, the following 

narrative water-quality criteria apply. "All Reservation surface waters shall be free from substances, from any pollution source, that:

a) Settle to form objectionable deposits;

b) Float as debris, scum, oil, or other matter forming nuisances;

c) Produce objectionable color, odor, taste, or turbidity;

d) Cause injury to, or are toxic to, or produce adverse physiological responses in humans, animals, or plants; or

e) Produce undesirable or nuisance aquatic life." (Larrick and Clow, 2011, p. 10)

3

For the purposes of this report, the standard is applied to groundwater that is currently or could potentially be used for livestock watering. This excludes the 

AP, Lagoon, LF, and Wing wells, which were established for specific monitoring purposes.

4

Warm-water aquatic life standards. Early life stages: 5.0 mg/L, 1-day mean minimum; 6.0 mg/L, 7-day mean. Other life stages: 3.0 mg/L, 1-day mean minimum; 4.0 mg/L 7-day mean minimum, 5.5 mg/L, 30-day mean. Standards used for comparison purposes are the 1-day mean minimum for early and other life 

stages.

5

CDPHE standards for dissolved solids:

a) Background value 0–500 mg/L, standard 400 mg/L or 1.25 times background, whichever is least restrictive.

b) 501–10,000 mg/L, 1.25 times background.

c) 10,001 mg/L or greater, no limit.

6

30-day standard.

7

Ammonia (NH3). Acute criterion (1-hour): [0.411/(1+107.204–pH)]+[58.4/(1+10pH–7.204)]. Chronic criterion:

[0.0577/(1+107.688–pH)+(2.487/1+10pH−7.688)]*(1.45*100.028*MAX(25–T, 7)).

8

1-day standard.

9

Nitrite. Acute criterion: (1-hour): 0.20(2.00[Cl-]+0.73). Chronic criterion: 0.10(2.00[Cl-]+0.73). [Cl-] = chloride ion concentration in mg/L, upper Cl- limit =

22 mg/L.

10Chronic criterion is 87 μg/L, unless the pH is 7.0 or greater and the hardness is 50 mg/L as CaCO3 or greater.

11Cadmium. Acute criterion: e^(1.0166[ln(hardness)]−3.924)*(1.136672[ln(hardness)(0.041838)]). Chronic criterion: e^(0.7409[ln(hardness)]−4.719)*(1.1016

72–[ln(hardness)(0.041838)]).

12Hardness-dependent criteria are based on hardness expressed as mg/L CaCO3. For waters with a hardness value greater than 400 mg/L as CaCO3

, the criterion should be calculated using a hardness value of 400 mg/L, unless a water-effects ratio calculation is to be used.

13Not to be exceeded more than once every 3 years on average. The acute criteria has a 1-day averaging period. The chronic criteria has a 4-day averaging 

period.

14Copper. Acute criterion: e^(0.9422[ln(hardness)]–1.700)(0.960). Chronic criterion: e^(0.8545[ln(hardness)]−1.702)(0.960).

15Lead. Acute criterion: e^(1.273[ln(hardness)]–1.460)*(1.46203–[ln(hardness)(0.145712)]). Chronic criterion: e^(1.273[ln(hardness)]–4.705)*(1.46203–

[ln(hardness)(0.145712)]).

16Mercury criteria are μg/L of total mercury.

17Nickel. Acute criterion: e^(0.8460[ln(hardness)]+2.255)(0.998). Chronic criterion: e^(0.8460[ln(hardness)]+0.0584)(0.997).

18Silver. Acute criterion: e^(1.72[ln(hardness)]−6.52)(0.85). Chronic criterion: e^(1.72[ln(hardness)]−9.06)(0.85).

19Zinc. Acute criterion: e^(0.8473[ln(hardness)]+0.884)(0.978). Chronic criterion: e^(0.8473[ln(hardness)]+0.884)(0.986).

20Only includes constituents with a detected value; that is, a value greater than the detection level or reporting limits.

21Human health criteria (health advisory) 30-day average or chronic value. Criteria applies to water designated as drinking-water source.

22Listed as “Bis(2-ethylhexyl) phthalate” in Larrick and Clow, 2011.
Groundwater Chemistry 25

Hydrogeologic Characterization 

of Surficial Deposits and Dakota 

Sandstone

In the Farm and Ranch Enterprise area, the surficial 

deposits occur primarily on upland areas separated by the 

incised drainages of Marble, Coyote, and Mariano Washes, 

which create local areas of saturation that are largely disconnected by bedrock outcrops (fig. 4). The water table in the 

surficial aquifer contained in the surficial deposits in the Farm 

and Ranch Enterprise area ranged from 0.9 to 24.9 ft below 

land surface (bls), and median values were 5.4 to 17.2 ft bls 

(table 2). The water surface slopes to the southwest away from 

the Ute Mountains with a mean gradient of about 94 ft per 

mile. Because subsurface lithologic information was available 

for only one well in the Farm and Ranch Enterprise area, the 

thickness of surficial deposits in the upland areas could not be 

estimated. However, well depths reported by the UMUT for 

monitoring wells completed in the surficial aquifer on upland 

areas range from 6.4 to 26.6 ft bls (table 1.1 in app. 1). 

Near Towaoc, the surficial deposits occur primarily 

along the drainages and associated terraces of Cottonwood 

Wash, Navajo Wash, and an unnamed tributary of Navajo 

Wash (fig. 3). Again, local areas of saturation are disconnected 

by bedrock outcrops. The bedrock near Towaoc, however, 

generally crops out in upland areas (rather than along incised 

drainages) that separate lower-lying surficial deposits. Water 

levels measured in wells completed in the surficial aquifer 

near Towaoc indicate that the water table ranged from about 

11 to 34 ft bls (table 1.1 in app. 1), and the water table slopes 

generally southward with a mean gradient of about 143 ft per 

mile. Well records indicate surficial deposits near Towaoc are 

30–44 ft thick (Irwin, 1966). 

The Dakota aquifer contained in the Dakota Sandstone 

is the primary bedrock aquifer beneath the UMUR. Where the 

underlying Burro Canyon Formation is present, it is often difficult to distinguish from the Dakota Sandstone in the subsurface, 

and the two formations generally are considered a single hydrostratigraphic unit (Irwin, 1966). The structure of the Dakota 

Sandstone in the UMUR exhibits substantial folding because of 

past tectonic forces in the region. The predominant dip of the 

formation generally is to the south and east. However, this general trend is disrupted by uplift related to igneous activity in the 

vicinity of the Ute Mountains and by other structural features 

such as basins, domes, faults, synclines, and anticlines. 

The depth to the top of the Dakota Sandstone is affected 

by both the subsurface structure of the formation and the 

topography of the land surface. In the western part of the 

UMUR, where topography generally has low relief, the depth 

to the top of the formation in feet below land surface increases 

somewhat consistently to the east (fig. 7A), reflecting the 

eastward dip direction of the formation in the subsurface. 

Farther to the east, topographic relief is high with steep slopes 

and mesas dissected by canyons, and the depth to the top of 

the Dakota Sandstone primarily is affected by the topography 

of the land surface. Within the boundaries of the UMUR in 

Colorado, depths to the top of the Dakota Sandstone range 

from zero in outcrop areas to 1,000 ft bls in the western part of 

the UMUR (fig. 7A) and >3,000 ft bls on mesas in the southeastern part of the UMUR (fig. 7B). 

Groundwater Chemistry

The chemical quality of groundwater is determined by 

natural factors and processes as well as human activities. 

Primary natural factors and processes that affect groundwater 

chemistry include source, chemical composition, and amount 

of recharge water; lithologic and hydrologic properties of 

geologic materials (sediments, minerals, and rocks); chemical processes affecting geologic materials and groundwater; 

and the length of time groundwater is in contact with geologic 

materials. Human activities that change land cover and land 

use from natural grasslands to agriculture, urbanization, and 

oil and gas development also can affect groundwater quality. 

Nutrients and pesticides can be added to groundwater through 

agricultural practices, and VOCs can be added from chemical 

and gasoline spills and usage. Contaminants can be released to 

the environment and groundwater from leaking underground 

storage tanks and waste ponds, urban runoff, and commercial 

activities. Because most of the UMUR is undeveloped land, 

the chemical quality of groundwater is largely determined by 

natural factors and processes.

A thorough understanding of groundwater chemistry 

on the UMUR is limited because of incomplete knowledge 

of spring and well lithology and the lack of well information 

(well depth and screen location). Where possible, estimations 

of spring lithology are based on comparisons of groundwater 

chemistry data of springs assessed in this report to historical 

spring chemistry data and lithology (Irwin, 1966; Geldon, 

1985; USGS, 2016b) and on spring location (fig. 5, table 7). 

Lithology and well information were sourced from the UMUT 

(UMUT, 2004), Colorado Division of Water Resources (Colorado Department of Natural Resources, 2019), Irwin (1966), 

Geldon (1985), and USGS (2016b), and information on depth 

to the Dakota Sandstone provided in this report (table 7).

Springs on the UMUR likely originate from igneous 

debris and pediment gravels, weathered Mancos Shale, and 

alluvium (table 7). High-altitude springs on the Ute Mountains 

discharge from igneous debris at contacts with less permeable 

material. Irwin (1966) reports that talus and block rubble on 

mountain slopes are catchment areas for snowmelt, which discharges as springs at the base of slopes overlying less permeable material, such as Mancos Shale. Similarly, Geldon (1985) 

reports that block rubble overlies Mancos Shale and igneous rocks. Springs that likely originate from talus and block 

rubble include Cottonwood Wash, Elk Meadows, Hanna, 

Last Lake, Lopez 1 and 2, Ute, and Whisky Road (table 7). 

Bancroft Spring, which is in the same location as Spring 9 in 

Geldon (1985), likely originates from older pediment gravels 

(table 7). On the lower-altitude plains, the East and West Toe 
26 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

\\IGSKAHCMVSFS002\Jeff\den19-0055-bauch\den19-0055_report_figures\ den19-0055_fig07.ai

EXPLANATION

Ute Mountain Ute Reservation

Dakota Formation outcrop

Contour line of equal depth to the top of

 the Dakota Sandstone in feet below

 land surface—Map A has a contour

 interval of 100 feet. Map B has a

 contour interval of 500 feet. Vertical

 datum is North American Vertical

 Datum of 1988 (NAVD88)

900 

Map area

UTAH

ARIZONA

COLORADO

NEW MEXICO

UNITED

STATES

MEXICO

Base modified from U.S. Geological Survey, 1:400,000

Geographic coordinate system projection

North American Datum of 1983 (NAD83) 0 2 4 6 8 10 KILOMETERS

0 2 4 6 8 10 MILES

2,500

NEW MEXICO

1,000

MESA VERDE

NATIONAL PARK

2,000

2,000

1,500

2,500

3,000

2,500

2,500

3,000

2,500

3,000

3,000

COLORADO

Mancos

River

B

37°10'

37°

108°30'

108°40' 108°20'

37°20'

Towaoc

UTAH

COLORADO

Navajo

Wash

Ute

Mountains

Mancos 1,000

500

0

100

200

300

400

600

700

800

900

200

100

100

200

100

100

San Juan River

NEW MEXICO

COLORADO

A

108°50'

37°10'

109°

37°20'

37°

Figure 7. Generalized depth to the top of the Dakota Sandstone in feet below land surface on the Ute Mountain Ute Reservation in 

Colorado. The contour lines are lines of equal depth to the top of the Dakota Sandstone in feet below land surface. The map has been 

split because of a difference in contour intervals. Map A has a contour interval of 100 feet. Map B has a contour interval of 500 feet.
Hydrogeologic Characterization of Surficial Deposits and Dakota Sandstone 27

Table 7. Estimation of lithology for springs and wells located on the Ute Mountain Ute Reservation in Colorado and Utah and 

information on select monitoring wells in Colorado.—Continued

[Unless stated otherwise, all well and formation depths and screen intervals are assumed to be measured from the land surface. Colorado Division of Water 

Resources (CDWR) permits are from Colorado Department of Natural Resources (2019). fig., figure; ID, identification; na, not applicable; TDS, total dissolved 

solids; —, no information; ft, feet; bls, below land surface; UMUT, Ute Mountain Ute Tribe; btoc, below top of casing]

Site

(see fig. 5, site ID

in parentheses

is used on figure)

Lithology Monitoring-well

information

Springs

Bancroft Spring (S1) Older pediment deposits (Geldon, 1985; designated Spring 9) na

Cottonwood Wash Spring (S2) Talus and block rubble based on water chemistry and spring location na

East Toe Spring (S3) Likely younger pediment deposits and weathered Mancos Shale na

Elk Meadows Spring (S4) Talus and block rubble based on water chemistry and spring location na

Hanna Spring (S5) Talus and block rubble based on water chemistry and spring location na

Last Lake Spring (S6) Talus and block rubble based on water chemistry and spring location na

Lopez 1 Spring (S7) Talus and block rubble based on water chemistry and spring location. 

Block rubble overlying Juana Lopez Member of Mancos Shale 

(Geldon, 1985; designated Spring 5). Similar location as Juana 

Lopez Spring of Irwin (1966), designated S–3 Spring

na

Lopez 2 Spring (S8) Talus and block rubble based on water chemistry and spring location. 

Block rubble overlying Juana Lopez Member of Mancos Shale 

(Geldon, 1985; designated Spring 5). Similar location as Juana 

Lopez Spring of Irwin (1966), designated S–3 Spring

na

Navajo Spring (S9) Younger pediment deposits (Geldon, 1985, designated Spring 16), 

alluvium and Mancos Shale (Irwin, 1966; designated S–15 Spring), 

and weathered Mancos Shale

na

Ute Spring (S10) Talus and block rubble based on water chemistry and spring location na

West Toe Spring (S11) Likely younger pediment deposits and weathered Mancos Shale. na

Whisky Road Spring (S12) Talus and block rubble based on water chemistry and spring location na

Whiskers Draw Spring (S13)1 Likely discharges from alluvium and eolian deposits that overlie 

Jurassic-age rocks; based on location on geologic map of Utah (Utah 

Geological Survey, 2013)

na

Wells

4000B well (W1) Dakota Sandstone. Similar well location and mostly similar water 

chemistry (TDS, cations, anions, water type) as Irwin (1966) well 

A–8. Lithology of A–8 from U.S. Geological Survey, 2016b

na

4C well (W2) — na

5000 Block well (W3) — na

AP–1

Eolian deposits, weathered Mancos Shale 

Shallow (6.4–26.6 ft bls, UMUT) 

monitoring wells downgradient 

from irrigation center pivots 

on Farm and Ranch Enterprise 

Irrigation project; used to assess 

effects of agricultural operations 

and irrigation return flows on 

water quality 

AP–10

AP–11

AP–14

AP–15

AP–16

AP–24

AP–5 Possibly eolian deposits
28 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

Table 7. Estimation of lithology for springs and wells located on the Ute Mountain Ute Reservation in Colorado and Utah and 

information on select monitoring wells in Colorado.—Continued

[Unless stated otherwise, all well and formation depths and screen intervals are assumed to be measured from the land surface. Colorado Division of Water 

Resources (CDWR) permits are from Colorado Department of Natural Resources (2019). fig., figure; ID, identification; na, not applicable; TDS, total dissolved 

solids; —, no information; ft, feet; bls, below land surface; UMUT, Ute Mountain Ute Tribe; btoc, below top of casing]

Site

(see fig. 5, site ID

in parentheses

is used on figure)

Lithology Monitoring-well

information

AW Hwy 141 (W4) Likely Junction Creek Sandstone. Similar well location and water 

chemistry (TDS, cations, anions, water type) as Irwin (1966) well 

B–11. Lithology of B–11 from U.S. Geological Survey, 2016b

na

AW Hwy 160/141 (W5) — na

Chimney Rock well (W6) Dakota Sandstone, based on well depth (1,346 ft bls, UMUT) and well 

location in relation to depth to top of Dakota Sandstone

na

HC Corral well (W7) Mancos Shale. CDWR permit 77484–F, Well Construction and Test 

Report. Well depth 500 ft; Mesaverde Group 7–30 ft, Mancos Shale 

30–500 ft, water level 160 ft bls

na

Cottonwood Spring well (W8) — na

FW-W (W9) — na

Goodknight well (W10) Mancos Shale, based on well depth (approximately 240 ft bls, UMUT), 

well location in relation to depth to top of Dakota Sandstone, and 

geologic log for nearby well (CDWR permit 52885–FR, shale 

16–772 ft)

na

Knight well (W11) na na

Lagoon 1 well 1 (W12) Weathered Mancos Shale, Mancos Shale. CDWR permit MH–39051. 

Well depth 20 ft, screen 10–20 ft in sandy clay and dark shale 

Shallow monitoring well used to 

assess potential migration of 

constituents into Navajo Wash 

and groundwater. Well downgradient from wastewater Lagoon 1 

system

Lagoon 1 well 3 (W13) Weathered Mancos Shale. CDWR permit MH–39049. Well depth 28 ft, 

screen 18–28 ft in clay 

Shallow monitoring well used to 

assess potential migration of 

constituents into Navajo Wash 

and groundwater. Well downgradient from wastewater Lagoon 1 

system 

Lagoon 2 well 2 (W14) Weathered Mancos Shale, Mancos Shale. CDWR permit MH–39059. 

Well depth 30 ft, screen 20–30 ft in sandy clay and dark shale

Shallow monitoring well used 

to assess potential migration 

of constituents into Navajo 

Wash. Well downgradient from 

Lagoon 2 sewer system 

Lewis well (W15) — na

LF well 1 (W16) Weathered Mancos Shale, Mancos Shale. CDWR permit MH–39048. 

Well depth 20 ft, screen 10–20 ft in clay and dark shale

Shallow monitoring well used to 

assess potential migration of 

constituents from landfill into 

Navajo Wash

LF well 3 (W17) DWR permit MH–39057. Well depth 38 ft, screen 28–38 ft in clay and 

sandstone 

Shallow monitoring well used to 

assess potential migration of 

constituents from landfill into 

Navajo Wash 

Mariano-FW (W18) — na

MR-FW (W19) — na
Groundwater Chemistry 29

Table 7. Estimation of lithology for springs and wells located on the Ute Mountain Ute Reservation in Colorado and Utah and 

information on select monitoring wells in Colorado.—Continued

[Unless stated otherwise, all well and formation depths and screen intervals are assumed to be measured from the land surface. Colorado Division of Water 

Resources (CDWR) permits are from Colorado Department of Natural Resources (2019). fig., figure; ID, identification; na, not applicable; TDS, total dissolved 

solids; —, no information; ft, feet; bls, below land surface; UMUT, Ute Mountain Ute Tribe; btoc, below top of casing]

Site

(see fig. 5, site ID

in parentheses

is used on figure)

Lithology Monitoring-well

information

SE Toe well (W20) Mancos Shale/upper Dakota Sandstone, based on well depth (383 ft 

btoc, UMUT) and well location in relation to top of Dakota Sandstone

na

TF-Corral well (W21) — na

Toe well (W22) Likely Mancos Shale/upper Dakota Sandstone, based on well depth 

(128 ft, UMUT) and well location in relation to depth to top of 

Dakota Sandstone

na

Wing well (W23) Weathered Mancos Shale Monitoring well used to assess 

effects of agricultural operations 

and irrigation return flows on 

water quality and use attainment 

for livestock drinking

 1Spring is shown on figure 1.

Springs (S3 and S11) likely discharge from pediment gravels 

and weathered Mancos Shale, whereas the Navajo Spring (S9) 

likely discharges from pediment gravels, weathered Mancos 

Shale, and alluvium (fig. 5, table 7). As with higher-altitude 

springs, the two Toe Springs and the Navajo Spring are contact 

springs at which water percolating though permeable material 

discharges at the contact with less permeable shale. Based on 

the geologic map of Utah (Utah Geological Survey, 2013), 

Whiskers Draw Spring (S13 on fig. 1) likely discharges from 

alluvium and eolian deposits that overlie Jurassic-age rocks.

Shallow wells, those with well depths of less than or 

equal to 38 ft bls, have been installed for specific monitoring 

purposes and tap different materials depending on monitoring 

use. The AP and Wing (W23) wells, which were installed in the 

Farm and Ranch Enterprise area to assess effects of agricultural 

operations and irrigation return flows on groundwater chemistry, likely tap eolian deposits and (or) weathered Mancos Shale 

(table 7). Elevated values of specific conductance and concentrations of nitrate plus nitrite and selenium in most samples can 

be indicative of groundwater in weathered Mancos Shale (U.S. 

Department of Energy [DOE], 2011). The Lagoon wells (W12, 

W13, and W14) and LF wells (W16 and W17), installed near 

Towaoc (fig. 5) to monitor the effects of the wastewater lagoon 

systems and landfill on groundwater chemistry, are likely 

completed in weathered Mancos Shale (table 7). The source of 

water for these wells, however, could also include lagoon and 

landfill discharges in the underlying shale.

The lithology and source of groundwater at deeper wells 

were more difficult to determine. A lithologic log was only 

located for the HC Corral well (Colorado Department of 

Natural Resources, 2019, permit 77843-F); the log indicated 

Mancos Shale as the source of water (table 7). Lithology for 

two wells, 4000B and AW Hwy 141, was estimated based on 

two wells with a similar location and groundwater chemistry that are described in Irwin (1966) and well information 

provided for each site in NWIS (USGS, 2016b). The 4000B 

well likely taps the Dakota Sandstone, similar to A-8 well of 

Irwin (1966), and AW Hwy 141 well likely taps the Junction 

Creek Sandstone, similar to B-11 well of Irwin (1966) 

(table 7). For other wells (Chimney Rock, Goodknight, SE 

Toe, and Toe), the likely source of water was estimated based 

on the well depth, well location in relation to depth to the top 

of the Dakota Sandstone, and (or) lithology of a nearby well 

(table 7). The specific source of water for the remaining wells 

(4C, 5000 Block, AW Hwy 160/141, Cottonwood Spring, 

FW-W, Knight, Lewis, Mariano-FW, MR-FW, and TF-Corral) 

could not be determined because of the lack of information on 

well depth, well completion and screen interval, and lithology. 

Physical Properties

Physical properties reported herein include specific conductance, pH, water temperature, dissolved oxygen (DO), and 

hardness. Specific conductance is the ability of a substance to 

conduct an electrical current (Hem, 1985). In water, it is proportional to the concentration of major dissolved constituents 

(calcium, magnesium, potassium, sodium, bicarbonate, carbonate, chloride, and sulfate). In this report, specific conductance is 

reported as microsiemens per centimeter at 25 degrees Celsius 
30 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

(μS/cm @ 25 °C; henceforth “μS/cm”). The weathering of minerals in soil and bedrock is a primary source of major dissolved 

constituents in water. Igneous rocks and materials derived 

from igneous rocks have comparatively slow weathering rates. 

Sedimentary rocks, which underlie non-Ute Mountains areas 

of the UMUR, have faster weathering rates, which results in an 

increase in dissolved constituents and specific conductance in 

water compared to water sourced from igneous materials. 

Specific conductance in 13 springs sampled by the UMUT 

ranged from 178 to 1,647 μS/cm with a median of 512 μS/cm 

(table 8). Specific conductance values less than the median 

typically were measured in water samples from five of the eight 

springs on the Ute Mountains, including Hanna (S5), Last Lake 

(S6), Lopez 1 (S7), Lopez 2 (S8), and Ute (S10) (fig. 5). Almost 

all specific conductance values for Ute Mountain springs were 

less than those for lower-altitude springs (fig. 8). Specific 

conductance values >1,000 μS/cm typically were measured in 

the lower-altitude springs: East Toe (S3), Navajo (S9), and West 

Toe (S11) (fig. 5). Water for these springs likely is discharged 

from materials that include the marine Mancos Shale (table 7), 

where high specific conductance would be expected. 

Groundwater samples from 21 wells contained more dissolved materials than spring samples (fig. 8, table 8). Specific 

conductance values for wells sampled by the UMUT ranged 

from 646 to 10,520 μS/cm, and the median was 6,024 μS/cm 

(table 8). For shallow wells, values >4,000 μS/cm (fig. 8) were 

measured in samples from most AP wells. The interaction of 

infiltrating irrigation water with minerals in the subsurface 

has likely increased the amount of dissolved constituents in 

water that recharges the shallow aquifer system. Only samples 

from AP–5 and Lagoon 2 wells had values less than about 

1,500 μS/cm (fig. 8). The lower values for AP–5 indicate that 

the water in the well is different than the other AP wells. However, without specific information on lithology thickness and 

well-screen interval, the difference in specific conductance for 

the AP wells cannot be confidently explained. 

In deeper parts of the groundwater system, dissolved 

materials can increase because of natural reactions occurring 

between groundwater and rocks as water slowly (centuries 

to millennia) flows from shallow to deeper parts of the system. For example, some of the Junction Creek Sandstone 

was deposited in a marine environment and has minerals that 

may contribute to increased specific conductance. Specific 

conductance in deeper wells sampled by the UMUT ranged 

from 1,010 to 9,080 μS/cm, and the median was 3,670 μS/cm 

(fig. 8). Groundwater in the Mancos Shale can naturally contain 

large amounts of dissolved materials, for example, specific 

conductance ranged from 418 to 70,002 μS/cm in samples 

from shale beds in Colorado, New Mexico, and Utah (DOE, 

2011). Specific conductance in the Goodknight (fig. 8) and HC 

Corral wells, deep wells identified as likely tapping only the 

Mancos Shale (table 7), were 9,080 and 2,860 μS/cm, respectively. Wells that likely tap the Dakota Sandstone, the 4000B 

and Chimney Rock Windmill wells, had a specific conductance 

of 3,115 and 2,953 μS/cm, respectively (fig. 8). These measurements are well within the range of 347 to 12,100 μS/cm for 

groundwater in the Dakota Sandstone in the San Juan structural 

basin, which is mostly in New Mexico (Craigg and others, 

1989). Specific conductance values of 7,100 and 7,420 μS/cm 

for the AW Hwy 141 well were similar to the specific conductance of 7,240 μS/cm reported for well B-11 by Irwin (1966); 

both wells likely tap the Junction Creek Sandstone (table 7). 

A pH value represents the effective concentration (activity) of hydrogen ions in water and is measured as the negative 

logarithm of the hydrogen ion activity (Hem, 1985). The pH 

of a water sample is important because the health of aquatic 

life is susceptible to pH, and the solubility and biological 

availability of nutrients and trace elements and some chemical 

processes are pH dependent. The pH for spring samples 

ranged from 6.4 to 8.6 (table 8), and most of the pH values 

(33 of 35) were within the ranges established by the UMUT 

for cultural use of water, aquatic-life criteria, and agricultural 

uses of surface water (table 9). The pH values for well samples 

ranged from 6.8 to 9.0 (table 8). The CDPHE standard was 

exceeded for samples from four wells (table 9). 

Water temperature is an important property that controls 

biological and chemical reaction rates. Temperature often 

directly affects the life cycles of aquatic organisms and DO 

concentrations (Hem, 1985). Many spring samples had a 

lower water temperature than well samples, reflecting the high 

altitude of many springs on the Ute Mountains and recharge 

from snowmelt (table 8). There were no exceedances of waterquality standards for water temperature.

Dissolved oxygen is the measurement of the oxygen content in water. Reduction-oxidation (redox) processes, including DO, nitrate, iron, manganese, and sulfate reduction, affect 

groundwater chemistry in all groundwater systems (Hem, 

1985). Understanding redox processes can be a valuable tool 

in interpreting groundwater-chemistry data and assessing the 

susceptibility or vulnerability of an aquifer to land-use activities. Groundwater with DO concentrations ≥0.5 mg/L (oxic 

conditions) can be susceptible to nitrate contamination because 

nitrate is generally stable and persistent in the presence of 

oxygen (Dubrovsky and others, 2010). Groundwater with DO 

concentrations <0.5 mg/L (anoxic, reducing conditions) can 

be more susceptible to contamination from sulfate, iron, and 

manganese (Bauch and others, 2014). Concentrations of DO 

in spring and well samples ranged from <0.01 to 14.6 mg/L 

(table 8). Most samples were well oxygenated. However, samples from Elk Meadows, Navajo, or Whiskers Draw Springs 

did not meet a 1-day mean minimum standard of 5.0 mg/L 

DO for protection of early life stages of aquatic life or a 1-day 

mean minimum standard of 3.0 mg/L DO for other life stages 

(table 9). Samples from five wells (5000 Block, Goodknight, 

Lagoon 1 well 1, Lagoon 1 well 3, and MR-FW) were anoxic. 

Reducing conditions in groundwater for these wells could 

affect groundwater chemistry and the types and concentrations 

of dissolved and noble gases in the groundwater. 

Hardness generally is measured by the presence of the cations calcium and magnesium in water and is reported in terms 

of an equivalent concentration of calcium carbonate (Hem, 

1985). Hardness can affect the anthropogenic uses of water and 
Groundwater Chemistry 31

Figure 8. Boxplots showing distribution of specific 

conductance in water samples collected by the 

Ute Mountain Ute Tribe in 1998–2002 and 2011–17 

for springs and wells on the Ute Mountain Ute 

Reservation in Colorado and Utah.

Table 8. Statistical summary for physical-property measurements collected by the Ute Mountain Ute Tribe (UMUT) for springs and 

wells on the Ute Mountain Ute Reservation in Colorado and Utah, 1996–2017.

[The UMUT water-quality standards are from Larrick and Clow (2011). The Colorado Department of Public Health and Environment (CDPHE) basic standards 

for groundwater are from CDPHE (2017). No., number; Min, minimum; Max, maximum; fig., figure; ID, identification; μS/cm, microsiemens per centimeter 

at 25 degrees Celsius (°C); —, no standard; T, UMUT water-quality standard for Tribal cultural use of surface water; A-WWAL, UMUT acute water-quality 

standard for warm-water aquatic life; C-WWAL, UMUT chronic water-quality standard for warm-water aquatic life; AG, UMUT water-quality standard for 

agricultural, irrigation, and (or) livestock watering use of surface water; ne, no exceedance; mg/L, milligrams per liter; WWAL, UMUT water-quality standard 

for warm-water aquatic life; CaCO3, calcium carbonate; C-GW, CDPHE basic standard for agricultural use of groundwater; <, less than]

Physical

property

No. of 

sites

No. of 

samples

Measured value or

concentration

Site with minimum

concentration

(see fig. 5, site ID

in parentheses is

used on figure)

Site with maximum 

detected concentration

(see fig. 5, site ID

in parentheses is

used on figure)

Water-quality 

standard

exceeded

(see tables 6, 9) Min Median Max

Springs

Specific conductance

(μS/cm) 13 33 178 512 1,647 Hanna Spring (S5) Navajo Spring (S9) —

pH (standard units) 13 35 6.4 7.5 8.6 Hanna Spring (S5) Navajo Spring (S9) T, A-WWAL,

C-WWAL, AG

Water temperature (°C) 11 28 2.9 9.4 23.6 Last Lake Spring (S6)

Whisky Road Spring (S12)

Bancroft Spring (S1) ne

Dissolved oxygen (mg/L) 11 27 1.4 7.4 11.7 Whiskers Draw Spring (S13)1 Last Lake Spring (S6) WWAL

Hardness, CaCO3 (mg/L) 5 8 87 580 761 Hanna Spring (S5) Navajo Spring (S9) —

Wells

Specific conductance

(μS/cm) 21 45 646 6,024 10,520 AP–5 AP–10 —

pH (standard units) 24 49 6.8 7.7 9.0 Mariano-FW (W18) Lagoon 1 well 3 (W13) C-GW

Water temperature (°C) 21 40 14.3 17.4 29.1 AP–5 Mariano-FW (W18) ne

Dissolved oxygen (mg/L) 15 26 <0.01 4.0 14.6 Goodknight well (W10) Lagoon 2 well 2 (W14) —

Hardness, CaCO3 (mg/L) 15 29 7.7 428 3,910 Knight well (W11) Lagoon 1 well 1 (W12) —

1

Spring is shown on figure 1.

24 7 2 25 20

Specific conductance, in microsiemens per centimeter

2,500

Well,

shallow

Site type

Spring,

Ute

Mountains

Spring,

low

altitude

Whiskers

Draw

Spring,

Utah

Well,

deep

7,500

5,000

10,000

0

12,500

4000B and

Chimney Rock

wells

AP–5 well and

Lagoon 2

well 2

Goodknight

well

AW Hwy 141

well

EXPLANATION

90th Percentile

75th Percentile

50th Percentile

25th Percentile

10th Percentile

Data value

20 Number of samples
Table 9. Summary of physical-property measurements and concentrations of groundwater-chemistry constituents in water samples collected by th(UMUT) for springs and wells on the Ute Mountain Ute Reservation in Colorado that exceed water-quality standards established by the UMUT and the Public Health and Environment (CDPHE).—Continued [All samples were collected by the UMUT. Water-quality standards are shaded in gray. The measured value or constituent concentration for a sample was compared to the relevaUMUT water-quality standards are from Larrick and Clow (2011). The CDPHE basic standards for groundwater are from CDPHE (2017). fig., figure; ID, identification; E, excenot met; na, comparison of data value to standard not applicable, —, no standard; ne, no exceedance of standard; mg/L, milligrams per liter; ≤, less than or equal to; bv, based on solved; μg/L, micrograms per liter; trec, total recoverable; cfu/100 mL, colony-forming units per 100 milliliters of water] Site (see fig. 5, site ID in parentheses is used on figure) Site type Sample date Measured value or concentration UMUT water-quality standards for surface wate

by designated use1 

Tribal cultural use Warm water aquatic life Agri

irriga

livestoc

Acute Chronic pH pH 6.5–8.5 6.5–9.0 6.

Hanna Spring (S5)4 Spring 6/13/2011 6.4 E E E Navajo Spring (S9) Spring 11/7/2001 8.6 E — — AW Hwy 160/141 (W5) Well 3/1/2000 8.6 — — — Chimney Rock well (W6) Well 9/21/2016 8.7 — — — Cottonwood Spring well (W8) Well 7/28/2014 8.7 — — — Cottonwood Spring well (W8) Well 5/24/2017 8.6 — — — Knight well (W11) Well 6/7/2013 8.7 — — — Knight well (W11) Well 7/15/2013 8.6 — — — 

Dissolved oxygen (mg/L) Dissolved oxygen (mg/L) — (5) — 

Elk Meadows Spring (S4) Spring 5/26/2015 1.8 — E — Navajo Spring (S9) Spring 9/20/2016 1.8 — E — Whiskers Draw Spring (S13)4,6 Spring 3/5/2013 3.4 — E — Whiskers Draw Spring (S13)4,6 Spring 8/28/2013 1.4 — E — 

Total dissolved solids (mg/L) Total dissolved solids (mg/L) ≤ 500 — — 75

Cottonwood Wash Spring (S2) Spring 6/22/2015 505 E — — East Toe Spring (S3) Spring 12/22/1998 1,034 E — — East Toe Spring (S3) Spring 2/18/1999 1,040 E — — East Toe Spring (S3) Spring 5/21/1999 994 E — — East Toe Spring (S3) Spring 3/1/2000 986 E — — Navajo Spring (S9) Spring 7/25/2001 1,272 E — — West Toe Spring (S11) Spring 12/22/1998 1,034 E — — West Toe Spring (S11) Spring 2/18/1999 996 E — — West Toe Spring (S11) Spring 5/21/1999 950 E — — Whiskers Draw Spring (S13)4,6 Spring 3/5/2013 1,439 E — — Whiskers Draw Spring (S13)4,6 Spring 8/28/2013 570 E — — 
Table 9. Summary of physical-property measurements and concentrations of groundwater-chemistry constituents in water samples collected by th(UMUT) for springs and wells on the Ute Mountain Ute Reservation in Colorado that exceed water-quality standards established by the UMUT and the Public Health and Environment (CDPHE).—Continued[All samples were collected by the UMUT. Water-quality standards are shaded in gray. The measured value or constituent concentration for a sample was compared to the relevaUMUT water-quality standards are from Larrick and Clow (2011). The CDPHE basic standards for groundwater are from CDPHE (2017). fig., figure; ID, identification; E, excenot met; na, comparison of data value to standard not applicable, —, no standard; ne, no exceedance of standard; mg/L, milligrams per liter; ≤, less than or equal to; bv, based on solved; μg/L, micrograms per liter; trec, total recoverable; cfu/100 mL, colony-forming units per 100 milliliters of water]

Site

(see fig. 5, site ID

in parentheses is

used on figure)

Site

type

Sample

date

Measured value

or concentration

UMUT water-quality standards for surface wate

by designated use1

Tribal

cultural

use

Warm water

aquatic life

Agri

irriga

livestoc

Acute Chronic

Fluoride (mg/L)

Fluoride (mg/L) — — — 

5000 Block well (W3) Well 5/2/2017 2.3 (dis) — — — AW Hwy 141 (W4) Well 10/16/2002 7.91 (dis) — — — AW Hwy 160/141 (W5) Well 10/16/2002 6.6 (dis) — — — Chimney Rock well (W6) Well 9/21/2016 11.2 (dis) — — — FW-W (W9) Well 2/27/2013 3.7 (dis) — — — Goodknight well (W10) Well 5/10/2017 2.83 (dis) — — — Knight well (W11) Well 7/15/2013 7.22 (dis) — — — Mariano-FW (W18) Well 7/15/2013 7.59 (dis) — — — MR-FW (W19) Well 5/10/2011 6.2 (dis) — — — Toe well (W22) Well 9/20/2016 2.88 (dis) — — — 

Trace elements (μg/L)

Aluminum

Aluminum (μg/L) 200 (trec) 750 (trec) 750 (trec) 

Elk Meadows Spring (S4) Spring 5/26/2015 815 (trec) E E E Ute Spring (S10)4 Spring 6/16/2014 258 (trec) E ne ne Whiskers Draw Spring (S13)4,6 Spring 8/28/2013 817 (trec) E E E 

Arsenic

Arsenic (μg/L) 0.018 (trec, 1-day) 340 (trec) 150 (trec) 100 (tre

Cottonwood Wash Spring (S2) Spring 6/22/2015 0.6 (trec) E ne ne Hanna Spring (S5)4 Spring 6/16/2014 0.5 (trec) E ne ne Last Lake Spring (S6) Spring 5/26/2015 1.3 (trec) E ne ne Navajo Spring (S9) Spring 9/20/2016 1.2 (trec) E ne ne Whisky Road Spring (S12) Spring 5/26/2015 0.5 (trec) E ne ne Whiskers Draw Spring (S13)4,6 Spring 3/5/2013 5.3 (trec) E ne ne Whiskers Draw Spring (S13)4,6 Spring 8/28/2013 6.5 (trec) E ne ne 
Table 9. Summary of physical-property measurements and concentrations of groundwater-chemistry constituents in water samples collected by th(UMUT) for springs and wells on the Ute Mountain Ute Reservation in Colorado that exceed water-quality standards established by the UMUT and the Public Health and Environment (CDPHE).—Continued [All samples were collected by the UMUT. Water-quality standards are shaded in gray. The measured value or constituent concentration for a sample was compared to the relevaUMUT water-quality standards are from Larrick and Clow (2011). The CDPHE basic standards for groundwater are from CDPHE (2017). fig., figure; ID, identification; E, excenot met; na, comparison of data value to standard not applicable, —, no standard; ne, no exceedance of standard; mg/L, milligrams per liter; ≤, less than or equal to; bv, based on solved; μg/L, micrograms per liter; trec, total recoverable; cfu/100 mL, colony-forming units per 100 milliliters of water] Site (see fig. 5, site ID in parentheses is used on figure) Site type Sample date Measured value or concentration UMUT water-quality standards for surface wate

by designated use1 

Tribal cultural use Warm water aquatic life Agri

irriga

livestoc

Acute Chronic Boron Boron (μg/L) — — — 75

Mariano-FW (W18) Well 7/15/2013 766 (dis) na na na 

Selenium Selenium (μg/L) 50 (trec, 30-day) 20 (trec) 5 (trec) 20 (tre

Cottonwood Wash Spring (S2) Spring 6/22/2015 5.2 (trec) ne ne E East Toe Spring (S3) Spring 2/18/1999 9.9 (trec) ne ne E East Toe Spring (S3) Spring 5/21/1999 10.9 (trec) ne ne E East Toe Spring (S3) Spring 3/1/2000 30.8 (trec) ne E E Navajo Spring (S9) Spring 11/7/2001 7.4 (trec) ne ne E Navajo Spring (S9) Spring 9/20/2016 8.7 (trec) ne ne E West Toe Spring (S11) Spring 5/21/1999 8.4 (trec) ne ne E Goodknight well (W10) Well 5/10/2017 21.7 (dis) na na na 

Escherichia coli (cfu/100 mL

Escherichia coli (cfu/100 mL) 0 (absent) — — 

Hanna Spring (S5)4 Spring 6/16/2014 12.2 E — — Lopez 2 Spring (S8)4 Spring 6/24/2013 1 E — — Whiskers Draw Spring (S13)4,6 Spring 3/5/2013 1 E — — Whiskers Draw Spring (S13)4,6 Spring 8/28/2013 136.4 E — — 

1For this report, surface-water standards are applied to spring data only. The agricultural-use standards used for springs are for livestock watering. For a water body with multi

stringent criteria will be the goal of its water-quality standard. 2For the purposes of this report, the standards are applied to groundwater from springs that is currently or could potentially be used for livestock watering. 3For purposes of this report, the standards are applied to groundwater from wells that is currently or could potentially be used for livestock watering. This excludes the AP, Lawere established for specific monitoring purposes. 4Culturally significant spring. 5Warm-water aquatic-life standard: Early life stages: 5.0 mg/L, 1-day mean minimum. Other life stages: 3.0 mg/L, 1-day mean minimum. Standards are not specifically "acute

6Spring is shown on figure 1. 7Exceedance of the UMUT standard for dissolved solids is for livestock consumption.8Dissolved-solids standard based on background value. See table 6.
Groundwater Chemistry 35

the toxicity of metals to aquatic life (Hem, 1985; Newman, 

1995). Hem (1985) reports the following classification system 

for water hardness in milligrams per liter as calcium carbonate: soft, 0–60; moderately hard, 61–120; hard, 121–180; and 

very hard, >180. The movement of hard water through pipes 

can result in scaling, the precipitation of dissolved minerals 

on the inside surfaces of pipes. Median hardness values of 580 

and 428 mg/L (table 8) for UMUT spring and well samples, 

respectively, indicate very hard water in many samples. Geldon 

(1985) reported hard to very hard water in spring water sourced 

from alluvium, colluvium, block rubble, talus, and Mancos 

Shale, and Irwin (1966) reported soft to very hard water for 

well samples. 

Total Dissolved Solids and Major Ions

Naturally occurring dissolved minerals, or TDS, in 

groundwater originate when groundwater reacts with geologic 

materials in the subsurface. In an arid environment such as the 

UMUR, evapotranspiration of water from plants and evaporation from the water table also can concentrate dissolved solids 

in the subsurface. The TDS is a measure of inorganic salts 

(principally the major ions) and organic substances dissolved 

in water. The most common dissolved solids in water are the 

major ions—calcium, magnesium, potassium, sodium, chloride, fluoride, sulfate, bicarbonate, and carbonate. 

Knowledge of the amount of TDS in water resources on 

the UMUR is important for the cultural use of springs and, 

combined with knowledge of major-ion content, for agricultural 

use to prevent adverse effects on livestock health and soil productivity. Elevated concentrations of some major ions can affect 

livestock health, and too much salt can affect soil productivity. 

Water type, calculated from major-ion concentrations, provides 

information on the chemical quality of water and is used to differentiate the groundwater chemistry of springs and wells. 

Total Dissolved Solids

Concentrations of TDS in spring and well samples 

collected by the UMUT indicated fresh (<1,000 mg/L), 

brackish (1,000 to 10,000 mg/L), and highly saline water 

(>10,000 mg/L) according to the classification of Stanton and 

others (2017) (fig. 9). The UMUT spring samples had fresh 

and brackish water; TDS concentrations ranged from 75 to 

1,439 mg/L (fig. 9, table 10). Well samples had fresh, brackish, 

and highly saline water; TDS concentrations in wells ranged 

from 412 to 20,000 mg/L (fig. 9, table 10). All concentrations but one were 6,680 mg/L or less. Only the maximum 

concentration of 20,000 mg/L, for a sample from Lagoon 1 

well 1, was highly saline. Brackish groundwater is commonly 

detected throughout the Colorado Plateau region, particularly 

in water from the Mancos Shale (DOE, 2011).

About 72 percent of UMUT spring samples had TDS 

concentrations <1,000 mg/L (fig. 9), indicating fresh water. 

The low concentration of 75 mg/L was reported for Hanna 

Spring. On the Ute Mountains, recharge from rainfall and 

snowmelt is discharged as spring water from the base of talus 

deposits derived from igneous rocks (Irwin, 1966). Water 

discharged from lower-altitude springs south of the Ute 

Mountains (East Toe [S3], Navajo [S9], and West Toe [S11] 

Springs; fig.5) in areas underlain by Mancos Shale was more 

brackish than water discharged from the igneous materials on 

the Ute Mountains. Total dissolved solid concentrations for the 

lower-altitude springs were ≥950 mg/L. The increase in TDS 

in samples from the lower-altitude springs generally is related 

to an increase in the sulfate concentrations (described further 

in the “Water Type” section). Samples from five springs, four 

lower-altitude springs (Cottonwood Wash, East Toe, Navajo, 

and West Toe Springs) with water sourced from Mancos Shale 

and Whiskers Draw Spring, had TDS concentrations greater 

than the Tribal cultural use standard of 500 mg/L (table 9). 

However, of the five springs, only Whiskers Draw Spring is 

designated for cultural use. 

Overall, well water was more mineralized than spring 

water. About 85 percent of UMUT well samples had TDS 

concentrations >1,000 mg/L (fig. 9), indicating brackish or 

highly saline water. Freshwater samples were collected only 

from the AP–5 (412-530 mg/L) and Cottonwood Spring (773, 

860 mg/L) wells. The highest TDS concentrations, those 

greater than the 90th percentile concentrations shown in 

figure 9, were in samples from the shallow Lagoon 1 well 1 

(6,860 mg/L) and Lagoon 1 well 3 (20,000 mg/L) and the deep 

AW Hwy 141 (5,014 mg/L) and Goodknight (5,414 mg/L) 

wells. Water for the AW Hwy 141 and Goodknight wells likely 

was sourced from the Junction Creek Sandstone and the Mancos Shale, respectively (table 7). 

Historical TDS data for wells likely completed in the 

Mancos Shale, Dakota Sandstone, Junction Creek Sandstone, 

and the Pennsylvanian-age Paradox Formation were available for samples collected in the 1950s, 1970s, and some 

years from 1996 to 2017 (table 11) (Irwin, 1966; USGS, 

2016b; COGCC, 2018). Concentrations for samples from 

wells completed in the Mancos Shale, Dakota Sandstone, and 

Junction Creek Sandstone ranged from 920 to 6,000 mg/L 

(table 11). One COGCC sample from a well completed in the 

Paradox Formation was highly saline with a concentration of 

61,500 mg/L. The COGCC wells are in the southeastern portion of the UMUR (fig. 5), where the salt-rich Paradox Formation is at least 5,400 ft beneath the Dakota Formation.

Water Type

The type of water for the major-ion data collected by the 

UMUT is illustrated using a Piper diagram (see for example 

fig. 10; Hem, 1985). The diagram shows the relationship 

between the dominant cations (calcium, magnesium, sodium, 

potassium) and the dominant anions (bicarbonate, chloride, 

sulfate) in percent total milliequivalents per liter and is used to 

classify and compare water types based on ionic composition. 

The lower left triangle illustrates the water type for cations, 

and lower right triangle illustrates the water type for anions. 
36 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

Percentage values for the cations and anions are combined on 

the central graph to show the overall chemical quality of water 

and define the water type based on cation and anion composition. For sites with more than one sample of applicable data, 

median concentrations of the cations and anions are plotted on 

the diagram.

Complete major-ion data were available to calculate 

water types for nine UMUT springs. Calcium was the dominant cation for 89 percent of the spring samples, and bicarbonate or sulfate were the dominant anions (fig. 10). Springs 

on the Ute Mountains have a calcium-bicarbonate water type 

(fig. 10), whereas the lower-altitude East Toe and Navajo 

Springs south of the Ute Mountains have a calcium-sulfate 

water type. Whiskers Draw Spring in Utah has a mixedcalcium-magnesium-sulfate water type (fig. 10). The Geldon 

(1985) study of Cottonwood Wash in Colorado reported that 

springs with calcium-bicarbonate water type discharged from 

igneous block rubble and talus and old pediment. Springs 

with calcium-sulfate water type, such as Navajo Spring, discharged from the Mancos Shale, colluvium, young pediment 

alluvium, and channel alluvium. The Mancos Shale contains 

gypsum, which can be an important source of dissolved 

calcium and sulfate.

The dominant cations and anions in water samples from 

21 UMUT wells varied. Unlike the springs, sodium was the 

dominant cation in 71 percent of wells (fig. 10). This likely 

indicates dissolved calcium has exchanged for sodium on 

clays within the aquifer materials. Mixtures of cations were 

present for other well samples. The dominant anions, and 

their percentages of well samples, were sulfate (43 percent), 

bicarbonate (14 percent), and chloride (14 percent) (fig. 10). 

A mixture of anions was present in about 29 percent of 

well samples; mixtures included bicarbonate-chloride, 

bicarbonate-sulfate, chloride-bicarbonate, sulfate-chloride, and 

sulfate-chloride-bicarbonate. 

Numerous water types are present in the water samples 

from wells (fig. 10). Samples from four wells (AP–1, AP–14, 

AP–15, and Wing) in the Farm and Ranch Enterprise area, 

which likely tap eolian deposits and (or) weathered Mancos 

Shale, are a mixed-cation-sulfate water type (fig. 10). The HC 

Corral well sample also is a mixed-cation-sulfate water type 

with water sourced from the Mancos Shale (table 7). The sample for the AP–5 well, also in the Farm and Ranch Enterprise 

area, has a mixture of cations, similar to the other AP wells, but 

the dominant anion is bicarbonate. Water types for the remaining well samples are a continuum from sodium-bicarbonate to 

sodium-sulfate and sodium-chloride (fig. 10). The Goodknight, 

SE Toe, and Toe wells, which likely tap the Mancos Shale or 

Mancos Shale/Dakota Sandstone, have predominately a sodiumchloride water type (Goodknight, SE Toe wells) or sodiummixed-anion (bicarbonate-chloride) water type (Toe well). The 

4000B and Chimney Rocks wells, which likely tap the Dakota 

Sandstone, have sodium as the dominant anion and either 

sulfate (4000B well) or bicarbonate (Chimney Rock well) as the 

dominant anion. The sample for The AW Hwy 141 well water, 

likely sourced from the Junction Creek Sandstone (table 7), is a 

sodium-mixed-sulfate-chloride water type. 

The water types for UMUT wells, likely completed in the 

Mancos Shale or Dakota aquifer, can be compared to water 

types for other wells that tap the same formations in nearby 

areas. Samples from deep unweathered Mancos Shale in 

southeast Utah, northwest New Mexico, and western Colorado 

are a sodium-chloride water type and almost all anion content 

is chloride (DOE, 2011). Similarly, the only UMUT sample 

likely collected from the Mancos Shale, the Goodknight 

well, is a sodium-chloride water type. Samples from wells 

completed in the Dakota aquifer in northwest New Mexico 

are sodium-bicarbonate or sodium-sulfate water types (Dam, 

1995), which are mostly similar to the water types for the 

UMUT water samples from wells completed in the Dakota 

aquifer. The sodium-chloride water type has been noted in 

wells in southern Nebraska completed near the boundary 

between the Dakota Sandstone and overlying confining shales 

(Gosselin and others, 2001). 

Brackish Highly saline Fresh

Water quality

 Ute Mountain Ute Tribe

cultural-use standard Total dissolved solids, in milligrams per liter

Spring

18,000

22,000

20,000

8,000

6,000

4,000

2,000

0

18 19 20

Well,

shallow

Well,

deep

Site type

EXPLANATION

90th Percentile

75th Percentile

50th Percentile

25th Percentile

10th Percentile

Data value

20 Number of samples

Figure 9. Boxplots showing distribution of total 

dissolved solids in water samples collected by the 

Ute Mountain Ute Tribe in 1996–2017 for springs 

and wells on the Ute Mountain Ute Reservation in 

Colorado and Utah.
Table 10. Statistical summary for total dissolved solids and major ions in water samples collected by the Ute Mountain Ute Tribe (UMUT) for springs Mountain Ute Reservation in Colorado and Utah, 1996–2017.[A censored concentration is a concentration less than the laboratory reporting limit. The UMUT water-quality standards are from Larrick and Clow (2011). The Colorado DepaEnvironment (CDPHE) basic standards for groundwater are from CDPHE (2017). No., number; mg/L, milligrams per liter; Min, minimum; Max, maximum; fig., figure; ID, ideT, UMUT water-quality standard for Tribal cultural use of surface water; CaCO3, calcium carbonate; —, no standard; nc, not calculated; <, less than; nd, not detected; C-GW, CDcultural use of groundwater]

Constituent No. of sites No. of samples No. of censored samples Concentration (mg/L)

Site with minimum

concentration

(see fig. 5, site ID in

parentheses is used

on figure)

Site with maximu

concentra

(see fig. 5, sit

parentheses i

on figure

Min Median Max Max detected, if censored

Springs

Total dissolved solids 12 18 0 75 760 1,439 na Hanna Spring (S5) Whiskers Draw SpAlkalinity, as CaCO3 11 22 0 77 178 343 na Hanna Spring (S5) Whiskers Draw SpBicarbonate, as CaCO3 12 20 0 77 206 1,722 na Hanna Spring (S5) West Toe SprinCarbonate, as CaCO3 12 20 12 0 nc <20 nd Whiskers Draw Spring (S13)1 na Calcium 12 21 0 28.4 109 216 na Hanna Spring (S5) Navajo SprinChloride 11 19 8 <10 10.9 98.6 na Lopez 1 Spring (S7) Navajo SprinFluoride 10 15 11 <0.019 <0.2 0.384 na Whiskers Draw Spring (S13)1 Whiskers Draw SpMagnesium 12 21 0 3.72 19.4 118 na Last Lake Spring (S6) Whiskers Draw SpPotassium 11 17 14 <0.094 nc 3.75 na Lopez 1 Spring (S7) Whiskers Draw SpSilica 9 14 0 6.35 18 28.6 na Whiskers Draw Spring (S13)1 Whisky Road SpSodium 12 19 0 3.59 14.4 106 na Last Lake Spring (S6) Navajo SprinSulfate 12 22 1 <10 111 723 na Hanna Spring (S5) Whiskers Draw Sp

Wells

Total dissolved solids 23 39 0 412 4,284 20,000 na AP–5 Lagoon 1 well Alkalinity, as CaCO3 25 48 0 73 387 2,000 na AP–14 Toe well (WBicarbonate, as CaCO3 23 41 0 118 434 1,959 na AP–5 AP–14 Carbonate, as CaCO3 22 40 5 0 0 280 na (2) Chimney Rock wCalcium 22 37 0 1.48 37.3 508 na Mariano-FW (W18) AP–14 Chloride 20 39 1 <10 276 2,180 na AP–5 Goodknight weFluoride 20 23 1 <0.16 1.37 11.2 na AP–1 Chimney Rock wMagnesium 22 36 2 <0.019 10.2 580 na Knight (W11) Mariano-FW (W18) Lewis well (Potassium 21 39 7 <0.17 1.5 17.5 na AP–14 AW Hwy 160/1Silica 13 14 3 <2.98 11.6 38.6 na (3) AP–14 Sodium 21 39 0 19.4 864 1,920 na AP–5 Goodknight weSulfate 22 38 3 <1.56 1,173 4,200 na 5000 Block well (W3) Goodknight well (W10) Lewis well (

1Spring is shown on figure 1.2Wells AP–1, AP–14, AP–16, AP–24, AP–5, AW Hwy 141 (W4), AW Hwy 160/141 (W5), and Knight (W11).3Wells 5000 Block (W3), Goodknight (W10), and SE Toe (W20).
38 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

Table 11. Select total dissolved solids data for the 1950s, 1970s, and some years from 1996 to 2017 for Ute Mountain Ute Tribe 

(UMUT), U.S. Geological Survey (USGS), and Colorado Oil and Gas Conservation Commission (COGCC) wells on the Ute Mountain Ute 

Reservation in Colorado, sorted by likely lithology.

[Water Quality Portal (WQP) data are from National Water Quality Monitoring Council (2017). National Water Information System (NWIS) data are from 

USGS (2016b). COGCC data are from COGCC (2018). figs., figures; ID, identification; mg/L, milligrams per liter] 

Site

(see figs. 5, 6; site ID in

parentheses is used on figures)

Total dissolved solids

Data source Sample date Concentration

(mg/L)

Mancos Shale

Goodknight well (W10) WQP 5/10/2017 15,414

HC Corral well (W7) UMUT 10/2/2012 2,280

370617108504201 (NW6) Irwin (1966), NWIS 12/5/1956 6,000

371006108530401 (NW12) Irwin (1966), NWIS 6/24/1959 1,610

371159108434801 (NW18) Irwin (1966), NWIS 3/15/1954 946

Mancos Shale/upper Dakota Sandstone

SE Toe well (W20) WQP 5/2/2017 13,309

Toe welll (W23) WQP 9/20/2016 14,668

Dakota Sandstone

4000B well (W1) WQP 9/20/2016 12,597

Chimney Rock well (W6) WQP 9/21/2016 12,328

370410108583701 (NW1) Irwin (1966), NWIS 6/24/1959 1,020

370518108540601 (NW2) Irwin (1966), NWIS 12/5/1956 1,890

370612108424001 (NW5) Irwin (1966), NWIS 6/25/1959 1,760

370717108532501 (NW7) Irwin (1966), NWIS 12/5/1956 1,470

370806108485801 (NW8) Irwin (1966), NWIS 12/5/1956 2,420

370913108563901 (NW9) Irwin (1966), NWIS 12/6/1956 920

371248108402201 (NW25) Irwin (1966), NWIS 12/5/1956 1,320

371307108581301 (NW26) Irwin (1966), NWIS 12/7/1956 2,560

371443108544701 (NW27) Irwin (1966), NWIS 12/6/1956 5,860

Junction Creek Sandstone

AW Hwy 141 (W4) WQP 8/20/1996 4,612

AW Hwy 141 (W4) WQP 3/1/2000 5,014

370557109003201 (NW4) Irwin (1966), NWIS 6/24/1959 4,670

371152108435401 (NW17) Irwin (1966), NWIS 1/3/1957 1,410

Paradox Formation

213879 (CW1) COGCC 12/1/1971 2,460

213907 (CW2) COGCC 12/22/1976 5,000

214329 (CW3) COGCC 1/12/1976 61,500

1

Sum of constituents.
Groundwater Chemistry 39

\\IGSKAHCMVSFS002\Jeff\den19-0055-bauch\den19-0055_report_figures\den19-0055_fig10.ai

100

80

60

40

20

0

Calcium Chloride

PERCENT

Ca type Na or K type

Mg type

No

dominant

type

Magnesium

Sodium

plus Potassium

0

20

40

60

80

100 0

20

40

60

80

100

100

80

60

40

20

0

0

20

40

60

80

100

0

20

40

60

80

100

Bicarbonate

Sulfate

SO4 type

No

dominant

type

HCO3

 type Cl type

100

80

60

40

20

0

100

80

60

40

20

0

0

20

40

60

80

100

100

80

60

40

20

0

PERCENT

PERCENT

Sulfate plus

chloride

Calcium

plus

magnesium

Na-HCO3

Na-m-anion

Na-Cl,

Na-SO4,

Na-m-SO4-Cl

Ca-HCO3

m-cation-SO4

m-cation-HCO3

Na-SO4

Ca-SO4

m-Ca-Mg-SO4

EXPLANATION

Spring

Well

Ca Calcium

Site Type

Major Ions

Water Type

Ca-SO4 Calcium-sulfate

Mg

HCO3

Chloride

Bicarbonate

Magnesium

Sodium

Sulfate

Ca-HCO3 Calcium-bicarbonate

m-cation-HCO3 Mixed-cation-bicarbonate

m-cation-SO4 Mixed-cation-sulfate

Na-Cl Sodium-chloride

Na-m-anion Sodium-mixed-anion

Na-HCO Sodium-bicarbonate 3

Na-SO Sodium-sulfate 4

SO4

Na

K

Cl

Potassium

m-Ca-Mg-SO4 Mixed-calcium-magnesium-sulfate

Na-m-SO4-Cl Sodium-mixed-sulfate-chloride

Figure 10. Piper diagram showing water type for samples collected by the Ute Mountain Ute 

Tribe in 1996–2017 for springs and wells on the Ute Mountain Ute Reservation in Colorado and 

Utah. Areas circled in red represent water type. For example, Na-HCO3 is a sodium-bicarbonate 

water type. 
40 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

Major Ions and Fluoride

Summary statistics for major-ion and fluoride data collected 

by the UMUT from springs and wells are provided in table 10. In 

general, maximum concentrations of the major ions were less in 

springs than in wells (table 10). Alkalinity concentrations <100 

mg/L (for example, the minimum concentration of 77 mg/L measured in a sample from Hanna Spring [table 10]) indicate that 

some spring water is not well buffered and could be susceptible 

to input of acidic water. Some concentrations of bicarbonate in 

spring samples and bicarbonate, chloride, sodium, and sulfate in 

well samples were >1,000 mg/L (table 10).

The only major ion with an established water-quality 

standard is fluoride (table 6). The CDPHE agricultural-use 

standard for fluoride of 2 mg/L is for the protection of animal 

skeletal health (CDPHE, 2017). Consumption of water with 

elevated fluoride levels can adversely affect the teeth and 

bones of livestock because excess fluoride can cause mottled 

teeth and skeletal fluorosis, the calcification of joints.

Fluoride was much less common in UMUT spring samples 

than in well samples (fig. 11, table 10). The CDPHE 2 mg/L 

agricultural-use standard for dissolved fluoride in groundwater 

was exceeded in about 45 percent of well samples—one sample 

each from 10 deep wells (table 9). Concentrations greater 

than the standard ranged from 2.3 to 11.2 mg/L (table 9). The 

maximum concentration of 11.2 mg/L, measured in a sample 

from the Chimney Rock well with water likely sourced from the 

Dakota aquifer, is slightly higher than the maximum concentration of 10 mg/L reported for the San Juan structural basin, which 

is mostly in New Mexico (Craigg and others, 1989) and 8 mg/L 

for the Dakota aquifer in Kansas (Whittemore and others, 2014).

Most dissolved fluoride in groundwater comes from 

natural sources, including igneous rocks and the minerals 

fluorite, apatite, micas, and amphiboles (Hem, 1985). Most 

natural waters contain a small amount of fluoride, generally 

<1.0 mg/L (Hem, 1985). Concentrations increase because of 

dissolution of fluoride minerals. Fluoride solubility is limited 

in the presence of calcium (Edmunds and Smedley, 1996). 

For UMUT spring samples, the maximum fluoride concentration was 0.384 mg/L (table 10), and the dominant cation 

was calcium (fig. 10). These samples include spring water 

discharged from igneous rocks that can be a source of fluoride 

to groundwater. The UMUT well samples with high concentrations of fluoride all had sodium as the dominant cation and 

a limited amount of calcium, which allows for higher concentrations of fluoride. Concentrations increase in groundwater 

where sodium takes the place of calcium in cation exchange 

(Edmunds and Smedley, 1996). 

Although fluoride is the only major ion with an established water-quality standard reported herein, high concentrations of other major ions, such as magnesium and sulfate, 

can have health implications for livestock. Ayers and Westcot 

(1994) reported that most major ions that comprise dissolved 

solids are not very toxic, but magnesium is the exception. A 

high level of magnesium can cause scouring and diarrhea, 

and a suggested limit of magnesium in water for beef cattle 

is 40 mg/L (Ayers and Westcot, 1994). For the UMUT data, 

magnesium concentrations >40 mg/L were most commonly 

detected in samples from AP wells, but the maximum 

magnesium concentration of 580 mg/L in a sample from the 

Lewis well also exceeded the suggested limit (table 10). A 

combination of sulfate concentrations >2,000 mg/L in water 

and high levels of sulfate in feedstock can be associated 

with neurological disease in cattle (Parker, 2011). As with 

magnesium, sulfate concentrations in AP wells were commonly >2,000 mg/L, as was the maximum concentration of 

4,200 mg/L for the Lewis well (table 10). 

Figure 11. Boxplots showing distribution of fluoride in water samples collected 

by the Ute Mountain Ute Tribe in 2002 and 2011–17 for springs and wells on the Ute 

Mountain Ute Reservation compared to the Colorado Department of Public Health 

and Environment water-quality standard for agricultural use of groundwater.

15 22

Dissolved fluoride, in milligrams per liter

6

4

2

0

8

12

10

Colorado Department of

Health and Environment

agricultural-use standard

Well

Site type

Spring

EXPLANATION

90th Percentile

75th Percentile

50th Percentile

25th Percentile

10th Percentile

Data value

22 Number of samples

Value less than laboratory

 reporting limit

Median value less than 

 laboratory reporting limit
Groundwater Chemistry 41

Nutrients

Nutrients, essential food for plant and animal life, can 

occur naturally in water from the breakdown of organic 

matter, weathering and erosion of rocks and minerals, and 

atmospheric deposition of naturally occurring nitrogen 

(Dubrovsky and others, 2010). Nutrients also are contributed 

to the environment by human activities such as the application of fertilizers, runoff and erosion in agricultural and 

urban areas, animal waste, septic systems, effluent from the 

wastewater treatment process, atmospheric deposition of 

nitrogen from fossil fuel combustion, and volatilization of 

ammonia from fertilizer and manure (Dubrovsky and others, 

2010). Once in groundwater, the concentrations and types 

of nutrients present are affected by factors such as transport 

mechanisms, availability of oxygen, and geochemical processes. Elevated concentrations of nutrients in surface water 

and groundwater can have health and environmental effects 

(Dubrovsky and others, 2010). To better protect the health of 

organisms and the environment, water-quality standards for 

nutrients have been established by the UMUT and the State 

of Colorado (table 6). 

Nutrient data included in this assessment are un-ionized 

ammonia, nitrate plus nitrite, and total phosphorus from 

9 UMUT springs and 23 UMUT wells. Only one spring sample 

had an unfiltered ammonia concentration that was more than 

0.2 mg/L (fig, 12A, table 12), generally considered the natural 

background concentration in groundwater (Water Security 

Agency and Saskatchewan Ministry of Environment, 2012 or 

later). No concentrations were greater than the UMUT culturaluse standard of 0.5 mg/L for dissolved ammonia (table 6) or 

aquatic-life criteria for ammonia, which varies depending on 

the water pH and temperature. Unfiltered ammonia concentrations in about 73 percent (8 of 11) well samples were similar 

to or <0.2 mg/L (fig. 12A). Concentrations >1 mg/L (fig. 12A) 

were only detected in anoxic samples from the 5000 Block, 

Goodknight, and SE Toe wells. Ammonia is present in lowoxygen environments because of the degradation of naturally 

occurring organic matter. 

Concentrations of unfiltered nitrate plus nitrite were 

1.6 mg/L or less in all samples from springs and many samples 

from wells (fig. 12B). Elevated concentrations (9–78.5 mg/L) 

were only detected in samples from wells in the irrigated areas 

of the Farm and Ranch Enterprise, the shallow AP wells (AP–1, 

AP–14, AP–24), and the Wing well (fig. 12B). For these wells, 

it is likely that excess recharge from irrigation has moved 

naturally occurring nitrate in the soil or nitrate from fertilizers, 

or both, down to the water table. Nitrate can be released naturally at high concentrations from Mancos Shale (DOE, 2011). 

Elevated nitrate concentrations have been reported for soils 

derived from Mancos Shale that have not been irrigated (Mast 

and others, 2014). Previous studies have shown that the source 

of elevated nitrate concentrations in areas of western Colorado 

likely is geologic, probably from the oxidation of organic matter (Morrison and others, 2012; Mills and others, 2016). The 

small amount of nitrate plus nitrite for AP–5 (0.416 mg/L) is 

additional evidence, along with low specific conductance and 

fresh water (figs. 8 and 9 [TDS 412-530 mg/L]), that the source 

water or processes affecting the AP–5 water are different than 

those for other AP wells. 

Once nitrate is in groundwater, it can be removed naturally only by denitrification, a process that reduces nitrate 

to harmless nitrogen gas (Dubrovsky and others, 2010). 

The long amount of time required for water to travel from 

the water table to deeper parts of an aquifer system provides more time for nitrate to be converted to nitrogen gas 

by denitrification. The nitrate plus nitrite concentrations in 

12 of 13 samples from deep wells were 0.203 mg/L or less 

(fig. 12B), which might reflect denitrification along long 

groundwater flowpaths or older groundwater that recharged 

before development occurred. 

Total phosphorus concentrations in 37 spring and well 

samples were low, 0.43 mg/L or less (table 12). Phosphorus 

often adsorbs to the surface of sediment and organic particles, 

which reduces phosphorus concentrations in groundwater. 

Water-quality standards for phosphorus in springs and groundwater have not been established by the UMUT or the States of 

Colorado or Utah.

Trace Elements and Uranium

For this assessment, trace elements are metallic and 

nonmetallic elements that generally occur in small (<1 mg/L) 

concentrations (Hem, 1985). Many trace elements are 

essential nutrients required by biota in small amounts, but 

substantial concentrations of trace elements can be toxic to 

aquatic life and possibly to wildlife, livestock, and people 

(Ayotte and others, 2011). Some trace elements can bioaccumulate in biota and bioconcentrate in the food chain. 

Trace-element type and concentration in water are often 

directly related to natural sources such as soils, geology, 

geochemical conditions, and the presence of thermal springs. 

Groundwater in mineralized areas may contain naturally high 

background concentrations of metals from the oxidation and 

weathering of minerals in rocks and soils (Bauch and others, 

2014). Common anthropogenic sources of trace elements in 

water are the deposition of metals released to the atmosphere 

from industrial activities and combustion, industrial water 

releases, and urban runoff.

Trace-element data collected by the UMUT were available for 11 spring and 28 well samples for 1996 through 2017. 

Uranium data were available for two springs and eight wells 

(table 4). Summary statistics are provided in table 13 for total 

recoverable and dissolved forms of 21 trace elements and uranium. Of the analytical results, 50 percent (338 of 676) were 

less than laboratory reporting limits, including all results for 

antimony, beryllium, and mercury (table 13). 

Most detected concentrations of trace elements and 

all uranium concentrations in spring samples were <10 

μg/L (table 13). Concentrations >20 μg/L were detected for 

total recoverable aluminum, barium, iron, manganese, and 

selenium; and dissolved iron and manganese. Maximum 
42 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

concentrations of total recoverable aluminum and barium 

were in samples from Whiskers Draw Spring and West Toe 

Spring, respectively (table 13). Maximum concentrations of 

total recoverable iron and manganese were in samples from 

Navajo Spring (table 13). Concentrations of total recoverable aluminum, arsenic, and selenium were greater than one 

or more UMUT water-quality standards for surface water 

(table 9). In particular, exceedances of cultural-use standards 

for aluminum and arsenic were detected in samples from the 

culturally significant Hanna, Ute, and (or) Whiskers Draw 

Springs (table 9). 

Many trace elements were detected at higher concentrations in the UMUT samples from wells than from springs. In 

well samples, 13 trace elements in the total recoverable and 

(or) dissolved forms were detected at concentrations >20 μg/L 

compared to 5 trace elements for spring samples (table 13). For 

uranium, only a sample from AP–1 well had a dissolved concentration >20 μg/L. Concentrations ≥500 μg/L were detected 

for total recoverable aluminum and iron and dissolved barium, 

boron, and iron (table 13). Maximum concentrations of total 

recoverable arsenic and total and dissolved selenium were in 

samples from AP wells. Both of these trace elements are often 

present in materials derived from Mancos Shale (Morrison and 

others, 2012; Tuttle and others, 2014a). The downward flow of 

irrigation recharge near the AP wells likely has moved arsenic 

and selenium in weathered Mancos Shale from the subsurface 

into the shallow groundwater system (Gerla and others, 2011; 

Tuttle and others, 2014b; Mills and others, 2016). The CDPHE 

water-quality standards for agricultural use of water have been 

established for the dissolved form of many trace elements 

(table 6). The standards for dissolved boron and selenium were 

exceeded in a sample from the Mariano-FW and Goodknight 

wells, respectively (tables 9 and 13). 

Additional historical trace-element data for the UMUR 

were available from the USGS NWIS and NURE databases 

(tables 3 and 4). Ten springs with trace-element data from 

NWIS for 1982 were sampled as part of a Cottonwood Wash 

study (Geldon, 1985), and the 1 spring (Elbow Spring on east 

side of the Ute Mountains) with NWIS data for 2003 was 

sampled as part of a Yucca House National Monument study 

(Wright, 2006). About 43 percent of the detected trace-element 

concentrations for these 11 spring samples were <10 μg/L. 

Dissolved barium, iron, manganese, and strontium were 

the only trace elements in these spring samples detected at 

concentrations of 20 μg/L or more. The one well sample from 

NWIS, an alluvial well in Towaoc (NW22), had detections of 

dissolved barium, iron, manganese, and selenium. The NURE 

data included data for nine trace elements and uranium collected from eight springs and five wells (tables 3 and 4). Concentrations of dissolved chromium, cobalt, copper, lead, iron, 

manganese, nickel, titanium, zinc, and uranium were >20 μg/L 

in the spring and (or) well samples. 

\\IGSKAHCMVSFS002\Jeff\den19-0055-bauch\den19-0055_report_figures\den19-0055_fig12.ai

5000 Block

well

Spring Well,

shallow

Site type

Well,

deep

Spring Well

Site type

Unfiltered nitrate plus nitrite, in

milligrams per liter as nitrogen 10

0.01

0.1

1

100

B

0

0.5

1.0

1.5

2.0

A

Unfiltered ammonia, in milligrams per liter as nitrogen

AP–1

well

Wing well

Farm and Ranch

Enterprise wells

AP–5

well

13 13

12

SE Toe well

Goodknight well

11 11

EXPLANATION

Data value

Value less than laboratory

 reporting limit

22 Number of samples

Figure 12. Scatter plots showing distribution of A, unfiltered ammonia and B, unfiltered nitrate plus 

nitrite in water samples collected by the Ute Mountain Ute Tribe in 2000–17 for springs and wells on 

the Ute Mountain Ute Reservation in Colorado and Utah.
Table 12. Statistical summary for nutrients in water samples collected by the Ute Mountain Ute Tribe for springs and wells on the Ute Mountain Ute and Utah, 2000–17.[No., number; mg/L, milligrams per liter; Min, minimum; Max, maximum; fig., figure; ID, identification; N, nitrogen; <, less than;, ne, no exceedance; P, phosphorus, —, no stan

Constituent No. of sites No. of samples No. of censored samples Concentration (mg/L) Site with minimum concentration (see fig. 5, site ID in parentheses is used on figure) Site with max

detected conce

(see fig. 5, sit

parentheses i

on figure

Min Median Max

Springs

Ammonia, unfiltered, as N 8 11 7 <0.024 <0.05 0.287 (1) Ute Spring (

Nitrate plus nitrite, unfiltered, as N 9 13 3 <0.01 0.09 1.26 Cottonwood Wash Spring (S2)

Elk Meadows Spring (S4)

Last Lake Spri

Total phosphorus, as P 9 12 4 <0.018 0.071 0.146 Navajo Spring (S9) Elk Meadows Sp

Wells

Ammonia, unfiltered, as N 10 11 3 <0.043 0.108 1.85 AP–1 Cottonwood Spring well (W8) 5000 Block weNitrate plus nitrite, unfiltered, as N 20 25 8 <0.011 0.040 78.5 (2) AP–14 Total phosphorus, as P 19 25 8 <0.011 0.08 0.43 (3) AP–15 

1Cottonwood Wash (S2), Elk Meadows (S4), Hanna (S5), and Whisky Road (S12) Springs.2Chimney Rock (W6), Cottonwood Spring (W8), and Toe Windmill (W22) wells.3AP–1, Cottonwood Spring (W8), Goodknight (W10), and SE Toe (W20) wells.
Table 13. Statistical summary for total recoverable and dissolved trace elements and total recoverable and dissolved uranium in water samples colUte Tribe (UMUT) for springs and wells on the Ute Mountain Ute Reservation in Colorado and Utah, 1996–2017.—Continued [A censored concentration is a concentration less than the laboratory reporting limit. The UMUT water-quality standards are from Larrick and Clow (2011). The Colorado DepaEnvironment (CDPHE) basic standards for groundwater are from CDPHE (2017). μg/L, micrograms per liter; No., number; Min, minimum; Max, maximum; fig., figure; ID, idenot applicable; T, UMUT water-quality standard for Tribal cultural use of surface water; A-WWAL, UMUT acute water-quality standard for warm-water aquatic life; C-WWALstandard for warm-water aquatic life; ne, no exceedance; nc, not calculated; —, no standard; AG, UMUT water-quality standard for agricultural, irrigation, and (or) livestock waC-GW, CDPHE basic standard for agricultural use of groundwater] Constituent No. of sites No. of samples No. of censored samples Concentration (μg/L) Site with minimum concentration (see fig. 5, site ID in parentheses is used on figure) Site with maximum det

concentration (see fig. 5, site ID in parentheses is used on figure) 

Min Median Max 

Max detected, if censored Springs (total recoverable) Aluminum 8 12 3 <20 89 817 na Hanna (S5), Last Lake (S6), Navajo (S9) Springs Whiskers Draw Spring (S

Antimony 1 1 1 <0.4 <0.4 <0.4 na Navajo Spring (S9) na Arsenic 11 20 13 <0.2 nc <100 6.5 Elk Meadows (S4), Hanna (S5), Ute (S10) Springs Whiskers Draw Spring (SBarium 6 8 0 4.8 22.0 60.9 na Hanna Spring (S5) West Toe Spring (S11Beryllium 4 4 4 <0.08 nc <0.5 na Navajo Spring (S9) na Boron 2 2 2 <100 nc <100 na Hanna (S5), Lopez 1 (S7) Springs na Cadmium 8 12 12 <0.01 nc <0.1 na (2) na Chromium 5 5 5 <0.1 nc <1.1 na Whiskers Draw Spring (S13)1 na Cobalt 4 4 1 <0.1 0.2 0.8 na Hanna Spring (S5) Navajo Spring (S9) Copper 8 12 0 0.2 0.8 2.5 na Last Lake Spring (S6) Whiskers Draw Spring (SIron 9 14 2 <50 108 706 na Lopez 1 (S7), Whisky Road (S12) Springs Navajo Spring (S9) Lead 2 4 4 <0.03 nc <1 na Whiskers Draw Spring (S13)1 na Manganese 4 4 2 <5 186 538 na Hanna (S5), Lopez 1 (S7) Springs Navajo Spring (S9) Mercury, total 7 7 7 <0.02 nc <0.09 na (2) na Molybdenum 8 8 0 2 4.2 10.1 na Whiskers Draw Spring (S13)1 Last Lake Spring (S6Nickel 7 10 0 0.7 2.6 13.4 na Hanna Spring (S5) Navajo Spring (S9) Selenium 11 17 5 <0.3 nc <200 30.8 Hanna Spring (S5) East Toe Spring (S3) Silver 4 4 4 <0.02 nc <0.1 na Navajo Spring (S9) na Thallium 4 4 4 <0.04 nc <0.1 na Navajo Spring (S9) na Vanadium 9 14 3 <0.7 nc <20 3.3 Cottonwood Wash Spring (S2) Last Lake Spring (S6Zinc 10 15 10 <0.4 nc <50 18.3 Last Lake (S6), Ute (S10) Springs Hanna Spring (S5) Uranium 1 1 1 5.5 5.5 5.5 na Navajo Spring (S9) Navajo Spring (S9) 

Wells (total recoverable)

Aluminum 12 13 7 <1 <50 10,300 na Knight well (W11), Mariano-FW (W18) Lagoon 1 well 3 (W13
Table 13. Statistical summary for total recoverable and dissolved trace elements and total recoverable and dissolved uranium in water samples colUte Tribe (UMUT) for springs and wells on the Ute Mountain Ute Reservation in Colorado and Utah, 1996–2017.—Continued[A censored concentration is a concentration less than the laboratory reporting limit. The UMUT water-quality standards are from Larrick and Clow (2011). The Colorado DepaEnvironment (CDPHE) basic standards for groundwater are from CDPHE (2017). μg/L, micrograms per liter; No., number; Min, minimum; Max, maximum; fig., figure; ID, idenot applicable; T, UMUT water-quality standard for Tribal cultural use of surface water; A-WWAL, UMUT acute water-quality standard for warm-water aquatic life; C-WWALstandard for warm-water aquatic life; ne, no exceedance; nc, not calculated; —, no standard; AG, UMUT water-quality standard for agricultural, irrigation, and (or) livestock waC-GW, CDPHE basic standard for agricultural use of groundwater]

Constituent

No. 

of 

sites

No.

of 

samples

No. of 

censored 

samples

Concentration (μg/L) Site with minimum concentration

(see fig. 5, site ID in

parentheses is

used on figure)

Site with maximum det

concentration

(see fig. 5, site ID in

parentheses is

used on figure)

Min Median Max 

Max

detected, if 

censored

Antimony 6 6 6 <0.4 nc <100 na 4000B well (W1), Chimney Rock well (W6), Toe well (W22) na Arsenic 20 35 13 <0.1 7.6 224 na Knight well (W11), Mariano-FW (W18) AP–16 Barium 9 10 2 <6.8 32.9 207 na 4000B well (W1) Chimney Rock well (WBeryllium 3 3 3 <0.04 nc <0.04 na 4000B well (W1), Chimney Rock well (W6), Toe well (W22) na Boron 1 1 1 <300 <300 <300 na Cottonwood Spring well (W8) na Cadmium 11 14 13 <0.04 nc <50 0.09 4000B well (W1), Chimney Rock well (W6), Toe well (W22) Lagoon 1 well 1 (W12Chromium 10 12 7 <0.1 1.0 14 na Knight well (W11), Mariano-FW (W18) Lagoon 1 well 1 (W12Cobalt 3 3 0 0.1 0.1 0.2 na Chimney Rock well (W6), Toe well (W22) 4000B well (W1) Copper 11 13 4 <20 <20 35.3 na Cottonwood Spring well (W8)3 Toe well (W22) Iron 14 16 2 <24 564 6,310 na Lewis well (W15)3 4C well (W2) Lead 14 18 10 <0.08 nc <100 13.4 4000B well (W1) 4C well (W2) Manganese 9 10 0 0.19 19.1 484 na Lewis well (W15) 4C well (W2) Mercury, total 10 11 11 <0.05 nc <0.2 na 4C well (W2) na Molybdenum 10 10 7 <0.05 nc <50 14.2 Knight well (W11), Mariano-FW (W18) FW-W (W9) Nickel 5 6 0 1 2.8 8.1 na Toe well (W22) Lagoon 1 well 3 (W13Selenium 19 34 12 <0.4 9.6 231 na Knight well (W11), Mariano-FW (W18) AP–1 Silver 4 4 4 <0.02 nc <0.02 na 4000B well (W1), Chimney Rock well (W6), Toe well (W22) na Thallium 3 3 3 <0.04 nc <0.04 na 4000B well (W1), Chimney Rock well (W6), Toe well (W22) na Vanadium 5 5 4 <0.5 nc <2.5 0.5 Cottonwood Spring well (W8) AP–1 Zinc 14 15 8 <0.5 59.8 486 na Mariano-FW (W18) Chimney Rock well (WUranium 3 3 2 <0.02 <0.02 1.3 na Chimney Rock well (W6), Toe well (W22) 4000B well (W1) 

Springs (dissolved)

Aluminum 3 3 3 <1 nc <20 na Whiskers Draw Spring (S13)1 na Antimony 1 1 1 <0.07 <0.07 <0.07 na Navajo Spring (S9) na 
Table 13. Statistical summary for total recoverable and dissolved trace elements and total recoverable and dissolved uranium in water samples colUte Tribe (UMUT) for springs and wells on the Ute Mountain Ute Reservation in Colorado and Utah, 1996–2017.—Continued [A censored concentration is a concentration less than the laboratory reporting limit. The UMUT water-quality standards are from Larrick and Clow (2011). The Colorado DepaEnvironment (CDPHE) basic standards for groundwater are from CDPHE (2017). μg/L, micrograms per liter; No., number; Min, minimum; Max, maximum; fig., figure; ID, idenot applicable; T, UMUT water-quality standard for Tribal cultural use of surface water; A-WWAL, UMUT acute water-quality standard for warm-water aquatic life; C-WWALstandard for warm-water aquatic life; ne, no exceedance; nc, not calculated; —, no standard; AG, UMUT water-quality standard for agricultural, irrigation, and (or) livestock waC-GW, CDPHE basic standard for agricultural use of groundwater] Constituent No. of sites No. of samples No. of censored samples Concentration (μg/L) Site with minimum concentration (see fig. 5, site ID in parentheses is used on figure) Site with maximum det

concentration (see fig. 5, site ID in parentheses is used on figure) 

Min Median Max 

Max detected, if censored Arsenic 4 4 2 <0.08 nc <10 6.4 Lopez 2 Spring (S8) Whiskers Draw Spring (S

Barium 2 2 0 15.4 17.5 19.6 na Lopez 2 Spring (S8) Navajo Spring (S9) Beryllium 1 1 1 <0.02 <0.02 <0.02 na Navajo Spring (S9) na Boron 2 3 3 <24 nc <100 na Whiskers Draw Spring (S13)1 na Cadmium 2 2 2 <0.01 nc <0.04 na Navajo Spring (S9) na Chromium 1 1 0 4.3 4.3 4.3 na Navajo Spring (S9) Navajo Spring (S9) Cobalt 1 1 0 0.7 0.7 0.7 na Navajo Spring (S9) Navajo Spring (S9) Copper 1 1 0 2.5 2.5 2.5 na Navajo Spring (S9) Navajo Spring (S9) Iron 3 3 2 <4 nc 577 na Whiskers Draw Spring (S13)1 Navajo Spring (S9) Lead 2 2 2 <0.03 nc <0.04 na Whiskers Draw Spring (S13)1 na Manganese 3 3 0 1 208 521 na Lopez 2 Spring (S8) Navajo Spring (S9) Mercury 1 1 1 <0.09 <0.09 <0.09 na Navajo Spring (S9) na Molybdenum 2 2 0 1.8 2.2 2.5 na Whiskers Draw Spring (S13)1 Navajo Spring (S9) Nickel 1 1 0 9.4 9.4 9.4 na Navajo Spring (S9) Navajo Spring (S9) Selenium 4 4 1 <0.4 6.7 17.3 na Whiskers Draw Spring (S13)1 East Toe Spring (S3) Silver 1 1 1 <0.03 <0.03 <0.03 na Navajo Spring (S9) na Thallium 1 1 1 <0.01 <0.01 <0.01 na Navajo Spring (S9) na Vanadium 3 3 1 <0.2 1.8 3.2 na Lopez 2 Spring (S8) Whiskers Draw Spring (SZinc 2 2 0 4.1 7.8 11.5 na Navajo Spring (S9) Whiskers Draw Spring (SUranium 2 2 0 1.5 3.6 5.8 na Lopez 2 Spring (S8) Navajo Spring (S9) 

Wells (dissolved) Aluminum 11 12 10 <1 nc <201 167 Mariano-FW (W18) AP–1 

Antimony 5 5 5 <0.07 nc <50 na 4000B well (W1), Chimney Rock well (W6), Toe well (W22) na Arsenic 18 22 8 <0.4 6.1 110 na Cottonwood Spring well (W8) LF well 1 (W16), LF well 3 
Table 13. Statistical summary for total recoverable and dissolved trace elements and total recoverable and dissolved uranium in water samples colUte Tribe (UMUT) for springs and wells on the Ute Mountain Ute Reservation in Colorado and Utah, 1996–2017.—Continued[A censored concentration is a concentration less than the laboratory reporting limit. The UMUT water-quality standards are from Larrick and Clow (2011). The Colorado DepaEnvironment (CDPHE) basic standards for groundwater are from CDPHE (2017). μg/L, micrograms per liter; No., number; Min, minimum; Max, maximum; fig., figure; ID, idenot applicable; T, UMUT water-quality standard for Tribal cultural use of surface water; A-WWAL, UMUT acute water-quality standard for warm-water aquatic life; C-WWALstandard for warm-water aquatic life; ne, no exceedance; nc, not calculated; —, no standard; AG, UMUT water-quality standard for agricultural, irrigation, and (or) livestock waC-GW, CDPHE basic standard for agricultural use of groundwater]

Constituent

No. 

of 

sites

No.

of 

samples

No. of 

censored 

samples

Concentration (μg/L) Site with minimum concentration

(see fig. 5, site ID in

parentheses is

used on figure)

Site with maximum det

concentration

(see fig. 5, site ID in

parentheses is

used on figure)

Min Median Max 

Max

detected, if 

censored

Barium 12 11 1 <6.3 72.0 500 na 4000B well (W1) Goodknight well (W10Beryllium 5 5 5 <0.02 nc <4 na 4000B well (W1), Chimney Rock well (W6), Toe well (W22) na Boron 8 9 4 <426 <851 2,410 na Cottonwood Spring well (W8) AP–1 Cadmium 13 14 13 <0.01 nc 180 na 4000B well (W1), Chimney Rock well (W6), Toe well (W22) LF well 3 (W17) Chromium 8 7 4 <1 <10 48 na HC Corral well (W7) LF well 3 (W17) Cobalt 3 3 0 0.2 0.3 1.1 na Toe well (W22) 4000B well (W1) Copper 6 6 1 <5.7 <20 31.4 na HC Corral well (W7) Chimney Rock well (WIron 13 14 10 <3 nc 790 na 4000B well (W1) 4C well (W2) Lead 11 11 7 <0.04 <0.5 <70 67.8 4000B well (W1), Chimney Rock well (W6), Toe well (W22) AW Hwy 141 Manganese 10 11 3 <0.7 6.5 69 na AP–1 4C well (W2) Mercury 9 9 9 <0.09 nc <0.2 na 4000B well (W1), Chimney Rock well (W6), Toe well (W22) na Molybdenum 5 5 3 <0.02 <0.05 1.9 na Chimney Rock well (W6) AP–1 Nickel 4 4 0 0.7 2.2 6.6 na Toe well (W22) HC Corral well (W7) Selenium 17 21 10 <0.8 1.5 207 na Cottonwood Spring well (W8) AP–1 Silver 6 6 5 <0.03 nc <26 0.43 4000B well (W1), Chimney Rock well (W6), Toe well (W22) AW Hwy 141 (W4) Thallium 5 5 4 <0.01 nc <50 0.5 4000B well (W1), Chimney Rock well (W6), Toe well (W22) HC Corral well (W7) Vanadium 8 9 7 <0.04 <3.7 28.4 na Toe well (W22) Chimney Rock well (WZinc 8 8 0 8.4 12.4 178 na Mariano-FW (W18) Toe well (W22) Uranium 8 8 6 <0.008 nc 51.6 na Chimney Rock well (W6), Toe well (W22) AP–1 

1Spring is shown on figure 1.2Cottonwood Wash (S2), Elk Meadows (S4), Hanna (S5), Last Lake (S6), Ute (S10), and Whisky Road (S12) Springs.3Minimum detected cconcentration.4Standard applies to wells that are or could potentially be used for livestock watering. This excludes AP and LF wells, which were established for specific monitoring purpose5Standard is exceeded for Mariano-FW well (766 μg/L). Standard applies to sensitive crops. See Larrick and Clow (2011) and CDPHE (2017).6Standard is exceeded for Goodknight well (21.7 μg/L).
48 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

Pesticides and Volatile Organic Compounds

Pesticides and VOCs are organic chemicals that can be 

present in groundwater because of their release at or near 

the land surface. Pesticides are chemicals used to prevent 

or control unwanted plants, insects, fungi, and other pests. 

Volatile organic compounds are carbon-based compounds that 

can move between air and water and are used or produced in a 

variety of industrial, commercial, and domestic applications. 

The occurrence of pesticides and VOCs in groundwater is of 

concern because of potential human-health effects (Gilliom 

and others, 2006; Zogorski and others, 2006). Human-health 

benchmarks have been established for some but not all pesticides and VOCs (Toccalino and others, 2014). 

On the UMUR, 23 samples for pesticide analysis were 

collected from 10 wells from June 2000 through August 2013 

(table 14). Sample collection was most common from AP wells 

and other monitoring wells in the Farm and Ranch Enterprise 

area. A total of 499 analytical results were originally available 

for 74 pesticides. Only the pesticides alachlor and atrazine, 

selective herbicides used to control grasses and broadleaf 

weeds, were detected at concentrations greater than or equal to 

laboratory reporting limits. Alachlor and atrazine were detected 

once (0.3 and 0.2 μg/L, respectively) in samples from AP–16 

well, and atrazine was detected once (1.1 μg/L) in a sample 

from AP–24 well (table 14). The detections were less than the 

CDPHE groundwater standards for drinking water for alachlor 

and atrazine of 2 and 3 μg/L, respectively (CDPHE, 2017).

Ten samples for VOC analysis were collected from 

7 wells from June 2000 through August 2012 (table 14). 

Similar to the pesticide sampling, AP wells were most commonly sampled for VOCs. The analyses for the AP wells 

only included three VOCs—benzo[a]pyrene, di(2-ethylhexyl) 

adipate, and di(2-ethylhexyl) phthalate (DEHP). Only DEHP, 

a manufactured chemical commonly added to plastics to make 

them flexible (Agency for Toxic Substances and Disease 

Registry, 2002), was detected at concentrations greater than 

laboratory reporting limits in one sample each from AP–1 

(1.9 μg/L) and AP–14 (0.8 μg/L) (table 14). The only UMUT 

water-quality standard for DEHP is for cultural use of springs, 

which is not applicable to the AP wells (table 6). Both detected 

concentrations of DEHP were less than the U.S. Environmental Protection Agency (EPA) drinking water standard of 

6 μg/L (EPA, 2017). A broad suite of VOCs was analyzed in 

samples from the 4C well and Lagoon 1 well 3; VOCs were 

not detected (table 14).

Coliform Bacteria

Coliforms are bacteria present in the digestive tracts of 

warm-blooded animals and in soil and vegetation. The bacteria 

are not likely to cause illness themselves, but their presence in 

water indicates that disease-causing pathogens could also be 

in the water (Bauch and others, 2014). Total coliform consists 

of a large group of different types of bacteria. Fecal coliform 

are bacteria that are present in the intestines and feces of 

warm-blooded animals. Their presence in water indicates 

recent contamination by animal waste or sewage. The E. coli

bacterium is a subgroup of fecal coliform bacteria and is the 

only coliform group with a UMUT water-quality standard. 

The water-quality standard of total absence of E. coli in the 

water of culturally significant springs is to protect the health 

of Tribal members during ceremonial use of springs (table 6; 

Larrick and Clow, 2011). 

The UMUT collected water samples from springs and 

wells for bacterial analysis during most years since 2000 

(table 15). The number of sample-collection days varied 

among the springs and wells. For some sites, more than one 

sample was collected on a sample day. About 77 percent 

(44 of 57) of spring and well samples had detections of total 

coliform bacteria, and 30 percent (18 of 60) of samples had 

detections of E. coli. The E. coli detections were more common for well samples (8 of 17, 47 percent) than for spring 

samples (10 of 43, 23 percent). Concentrations of E. coli in 

the 10 spring samples ranged from 1 to 1,300 colony-forming 

units per 100 milliliters of water, which exceeded the UMUT 

cultural-use standard of total absence of E. coli in spring 

water. Exceedances included samples from culturally significant Hanna, Lopez 2, and Whiskers Draw Springs (tables 9 

and 15). 

Environmental Tracers

Lopez 2 Spring and five wells (AP–1, 5000 Block, Cottonwood Spring, Goodknight, and SE Toe wells) were sampled 

in May 2017 for environmental tracers in the spring and well 

water (table 4). Tracers included stable isotopes (hydrogen and 

oxygen of water, nitrogen and oxygen of nitrate, and carbon 

in dissolved organic carbon), tritium, CFCs, dissolved gases 

(methane, carbon dioxide, nitrogen and oxygen, argon), and 

noble gases (helium-4, neon, argon, krypton, xenon). Environmental tracers can provide information on recharge, geochemical conditions, the age of groundwater, and other aquifer processes or conditions. The term “groundwater age” is defined as 

the time required for a water molecule to travel from a point 

of recharge to a measurement point such as a spring or well 

(Shapiro and others, 2012). Therefore, an estimate of the time 

since a water molecule in a spring or well was recharged can 

be used as an estimate of groundwater age.

Stable isotope ratios of hydrogen and oxygen of water 

commonly are used in hydrologic studies to provide information on the source of groundwater and recharge, geochemical 

history of groundwater, and processes that affect water after 

it has entered an aquifer, such as water-rock interaction (Gat 

and Gonfiantini, 1981; Clark and Fritz, 1997; Coplen and 

others, 2000). Groundwater samples from Lopez 2 Spring and 

the five wells were analyzed for stable isotopes of hydrogen 

(hydrogen-2/hydrogen-1 ratio [δ2H]) and oxygen (oxygen-18/

oxygen-16 ratio [δ18O]) in water; the composition of isotopes 

is reported using delta (δ) notation, which indicates parts 

per thousand or per mil. Values of δ2H and δ18O of water for 
Groundwater Chemistry 49

Table 14. Summary of sample collection and analysis by the Ute Mountain Ute Tribe for pesticides and 

volatile organic compounds in wells on the Ute Mountain Ute Reservation in Colorado, 2000–13.

[fig., figure; ID, identification; μg/L, micrograms per liter; —, no detection]

Site

(see fig. 5, site ID in

parentheses is

used on figure)

Sample

date

Number of 

analytes

Detected

compound

Concentration 

of detected 

compound

(μg/L)

Pesticides

AP–1 9/18/2003 26 — —

AP–1 4/1/2004 32 — —

AP–1 5/27/2009 6 — —

AP–1 7/25/2011 42 — —

AP–1 8/29/2013 33 — —

AP–10 10/30/2001 35 — —

AP–14 6/13/2000 17 — —

AP–14 4/1/2004 25 — —

AP–14 5/11/2004 7 — —

AP–14 6/15/2005 1 — —

AP–14 7/25/2011 42 — —

AP–15 8/15/2012 42 — —

AP–16 10/30/2001 35 Alachlor 0.3

AP–16 9/19/2003 25 — —

AP–16 4/1/2004 7 — —

AP–16 6/15/2005 1 Atrazine 0.2

AP–16 4/3/2007 3 — —

AP–24 10/31/2001 35 Atrazine 1.1

AP–5 10/31/2001 35 — —

AP–5 8/5/2002 35 — —

Lagoon 1 well 3 (W13) 9/15/2010 1 — —

TF-Corral well (W21) 8/8/2002 7 — —

Wing well (W23) 3/9/2001 7 — —

Volatile organic compounds

4C well (W2) 1/24/2002 43 — —

AP–1 5/27/2009 2 Di(2-ethylhexyl) phthalate 1.9

AP–1 7/25/2011 3 — —

AP–14 6/13/2000 2 — —

AP–14 6/15/2005 3 — —

AP–14 7/25/2011 3 Di(2-ethylhexyl) phthalate 0.8

AP–15 8/15/2012 3 — —

AP–16 6/15/2005 3 — —

Lagoon 1 well 3 (W13) 9/15/2010 65 — —

Wing well (W23) 8/16/2012 4 — —
Table 15. Summary of data for total coliform and Escherichia coli bacteria for water samples collected by the Ute Mountain Ute Tribe (UMUT) for spMountain Ute Reservation in Colorado and Utah, 2001–16. [Culturally significant springs are in bold. The UMUT water-quality standards are from Larrick and Clow (2011). fig., figure; ID, identification; No., number; cfu/100 mL, colonliliters of water; tntc, too numerous to count; na, not applicable; nd, no detection; T, UMUT water-quality standard for Tribal cultural use of surface water; ne, no exceedance; —

Site (see fig. 5, site ID in parentheses is used on figure) Total coliform Escherichia coli Sample years No. of sample days/No. of sample days with detections1 No. of samples No. samples with detections Concentration range of detections (cfu/100 mL) Sample years No. of sample days/No. of sample days with detections1 No. of samples No. samples with detections 

Springs Bancroft Spring (S1) 2012 1/1 5 4 1–tntc 2012 1/1 5 3 

Cottonwood Wash Spring (S2) 2015 1/1 1 1 8.6 2015 1/0 1 0 Elk Meadows Spring (S4) 2012, 2015 2/2 4 2 1; 1,120 2012, 2015 2/1 4 1 Hanna Spring (S5) 2011–15 8/8 10 10 2–120 2010–15 9/1 11 1 Last Lake Spring (S6) 2015 1/0 1 0 nd 2015 1/0 1 0 Lopez Spring 1 (S7) 2011 2/2 4 3 7.3–11 2010, 2011 3/0 6 0 Lopez 2 Spring (S8) 2011–13 5/4 6 4 1–105 2011–13 5/1 6 1 Navajo Spring (S9) 2001, 2016 2/2 3 3 58.1–149 2001, 2016 2/1 3 1 Ute Spring (S10) 2014, 2015 2/2 2 2 1 2014, 2015 2/0 2 0 Whisky Road Spring (S12) 2014, 2015 2/2 2 2 22.8; 51.2 2014, 2015 2/1 2 1 Whiskers Draw Spring (S13)3 2013 2/2 2 2 31.5; 2,420 2013 2/2 2 2 

Wells 4000B well (W1) 2016 1/1 1 1 2,420 2016 1/1 1 1 

4C well (W2) 2002, 2004, 2006 3/2 4 3 tntc 2004, 2006 2/2 4 4 AP–1 2013 1/0 1 0 nd 2013 1/0 1 0 AP–15 2012 1/0 1 0 nd 2012 1/0 1 0 AW Hwy 141 (W4) 2002 1/0 1 0 nd 2002 1/0 1 0 AW Hwy 160/141 (W5) 2002 1/1 1 1 tntc 2002 1/1 1 1 Cottonwood Spring well (W8) 2014 1/0 1 0 nd 2014 1/0 1 0 FW-W (W9) 2013 1/0 1 0 nd 2013 1/0 1 0 Knight well (W11) 2013 1/1 1 1 2,420 2013 1/0 1 0 Lagoon 1 well 3 (W13) 2010 1/1 1 1 1 2010 1/0 1 0 Lagoon 2 well 2 (W14) 2002 1/1 1 1 1,300 2002 1/1 1 1 Mariano-FW (W18) 2013 1/1 1 1 90.5 2013 1/0 1 0 Toe well (W22) 2016 1/1 1 1 2,420 2016 1/1 1 1 Wing well (W23) 2012 1/1 1 1 tntc 2012 1/0 1 0 

1For some sites, more than one sample was collected on a sample day. 2Spring is not culturally significant. 3Spring is shown on figure 1.
Groundwater Chemistry 51

Lopez 2 Spring were −99.61 and −13.8 per mil, respectively 

(table 16). For the five wells, values of δ2H of water ranged 

from −86.25 to −108.11 per mil, and values δ18O of water 

ranged from −11.11 to −14.32 per mil (table 16).

The relationship between δ2H and δ18O of water can be 

used to evaluate sources of recharge to an aquifer and processes that have affected the recharge since it entered the 

aquifer. The relationship in precipitation measured worldwide 

is called the Global Meteoric Water Line (GMWL; Craig, 

1961). Locally, the δ2H and δ18O composition of groundwater 

can differ from the GMWL because of different local climatic 

conditions, geographic differences such as altitude, recharge 

processes, and evaporation compared to global averages (Gat 

and Gonfiantini, 1981). Comparison of the stable isotope 

values for the UMUR groundwater to the GMWL indicate 

that recharge to groundwater from Lopez 2 Spring and the 

five wells primarily was derived from precipitation (fig. 13). 

Isotopic data for four of the five wells plotted slightly below 

and parallel to the GMWL (fig. 13), indicating that the groundwater was not affected by evaporation at these locations. The 

composition of the groundwater sample from the AP–1 well 

was enriched (isotopically heavier) relative to the values of 

δ2H and δ18O of water for the other wells; accordingly, it plots 

farther from the GWML than the other wells. The AP–1 well 

is a shallow well (well depth 26.6 ft bls; table 1.1 in app. 1) in 

the Farm and Ranch Enterprise area of the UMUR. The Farm 

and Ranch Enterprise receives irrigation water from McPhee 

Reservoir through the Dolores Project, and enrichment of δ2H 

and δ18O of water in the AP–1 sample could result from evaporative processes, possibly evaporation of water from McPhee 

Reservoir and evaporation of soil water in the irrigated area. 

Subsequent applications of irrigation water could flush the 

enriched soil water down to the shallow water table at the 

AP–1 well, which typically was between 10.0 and 15.6 ft bls 

for most years between 2008 and 2017 (table 2). 

Stable isotope ratios of nitrogen (nitrogen-15/nitrogen-14 

ratio [δ15N]) and δ18O of nitrate can be used to differentiate 

sources of nitrate in groundwater. Only the water sample from 

the AP–1 well was measured for δ15N and δ18O of nitrate. Values were 6.43 and 2.87 per mil, respectively (table 16). These 

values are well outside the range of values expected for synthetic fertilizer but fall within the range for manure fertilizer 

and soil organic matter (Kendall, 1998). Nitrate plus nitrite 

concentrations as high as 68 mg/L in samples from the AP–1 

well (fig. 12B) could result from a combination of nitrate from 

manure-derived fertilizer and nitrate that occurs naturally in 

soils derived the Mancos Shale. 

Tritium, the radioactive isotope of hydrogen, can be used 

to identify groundwater that has been recharged since the early 

1950s (“young” groundwater), groundwater that recharged 

before the early 1950s (“old” groundwater), and groundwater 

that contains a mixture of young and old water (McMahon and 

others, 2013). Prior to the start of above-ground nuclear weapons testing (atomic bomb testing) in 1952, tritium concentrations in precipitation that recharged groundwater probably 

did not exceed 2–8 tritium units (TUs) (Plummer and others, 

1993). Atomic-bomb testing from 1952 to the mid-1960s 

released large amounts of tritium into the atmosphere where 

it became incorporated into the water molecules of precipitation and entered groundwater systems as recharge. Because 

groundwater naturally has very low concentrations of tritium, 

measurable amounts of tritium in a groundwater sample indicate some portion of recharge occurred since the early 1950s 

(McMahon and others, 2013). 

Unlike tritium, the radioactive isotope carbon-14 is suitable for dating groundwater that recharged around a thousand 

to tens of thousands of years ago because of its relatively long 

radioactive half-life of 5,730 years (Clark and Fritz, 1997). 

Carbon-14 is transported in groundwater as dissolved inorganic 

carbon or dissolved organic carbon (Clark and Fritz, 1997). 

To date groundwater using carbon-14, the carbon isotope is 

measured for dissolved inorganic carbon, and the result is typically expressed as percent modern or percent modern carbon 

(Plummer and others, 2012a). Carbon-14 values reported from 

laboratory analysis are typically normalized for carbon-13 fractionation and reported as percent modern. For this assessment, 

normalized carbon-14 values have been converted to nonnormalized values, reported as percent modern carbon, using 

techniques of Plummer and others (2012a). The nonnormalized 

values are the focus for data analysis. Percent modern carbon 

is the preferred measurement unit for groundwater age dating 

(Mook and van der Plicht, 1999; Plummer and others, 2012a).

Tritium and carbon-14 were the primary tracers used for 

interpreting groundwater ages for Lopez 2 Spring and the five 

wells (table 17). The samples were grouped into three groundwater-age classifications based on tritium and carbon-14 

concentrations (fig. 14, table 17). The area of post-1950s water 

on figure 14 is defined by tritium concentrations >1.8 TU and 

carbon-14 concentrations >90 percent modern carbon (pmc). 

Samples plotting in these ranges likely represent groundwater 

that recharged after the start of above-ground atomic bomb 

testing in the early 1950s. The area of pre-1950s water on 

figure 14 is defined by tritium concentrations <0.2 TU and 

carbon-14 concentrations <90 pmc. Samples plotting is these 

ranges likely represent groundwater that recharged prior to 

atomic bomb testing in the early 1950s. Those samples with 

the lowest carbon-14 concentrations could represent water 

that recharged thousands of years ago. The tritium boundary 

of 1.8 TU is the probable current (2018) minimum concentration of tritium remaining from the concentrated atomic 

bomb testing in the early 1960s, and the boundary of 0.2 TU 

is the probable current maximum concentration of prebomb 

tritium because of the radioactive decay of tritium (half-life 

of 12.32 years) (Michel, 1989; Lucas and Unterweger, 2000; 

Jurgens and others, 2012). The numbers used for the tritium 

boundaries vary depending on location. The predominance 

of test sites in the northern hemisphere and air mass circulation resulted in a latitudinal gradient of tritium concentrations 

in precipitation (Plummer and others, 2012a). The assumed 

carbon-14 boundary of 90 pmc for post-1950s recharge is 

between the values for water samples from Lopez 2 Spring 

(103 pmc) and the AP–1 well (81.4 pmc) (table 17). 
52 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

The sample from Lopez 2 Spring was the only sample 

classified as having all post-1950s water (recharge after 

the early 1950s) (fig. 14). Recharge for samples from the 

5000 Block, Goodknight, and SE Toe wells was pre-1950s 

water. Samples for these three wells had the lowest carbon-14 

concentrations (3.90 pmc or less) and were likely recharged 

thousands of years ago. The Cottonwood Spring well sample 

also was classified as pre-1950s water, but the higher carbon-14 concentration (18.6 pmc) indicates that recharge 

–110

–100

–90

–80

–70

–60

δ2H, in per mil (parts per thousand) 

δ18O, in per mil (parts per thousand) 

–18 –14 –12 –10 –8 –120

Global Meteoric Water Line –16

Goodknight well

5000 Block well

SE Toe well

AP–1 well

Lopez 2 Spring

Cottonwood Spring well

EXPLANATION

Figure 13. The hydrogen (δ2H) and oxygen (δ18O) isotopic 

composition of water samples collected by the Ute Mountain Ute 

Tribe in 2017 for one spring and five wells on the Ute Mountain Ute 

Reservation in Colorado, plotted in relation to the Global Meteoric 

Water Line as described by Craig (1961). 

Table 16. Summary of data for stable isotopes of hydrogen and oxygen of water and nitrogen and oxygen of 

nitrate for water samples collected by the Ute Mountain Ute Tribe in 2017 for one spring and five wells on the 

Ute Mountain Ute Reservation in Colorado.

[Samples were analyzed at the U.S. Geological Survey Reston Stable Isotope Laboratory in Reston, Virginia. fig., figure; ID, 

identification; δ2H, hydrogen-2/hydrogen-1 isotopic ratio; per mil, parts per thousand; δ18O, oxygen-18/oxygen-16 isotopic ratio; 

δ15N, nitrogen-15/nitrogen-14 isotopic ratio; —, no data]

Site

(see fig. 5, site ID in parentheses 

is used on figure)

Sample

date

Stables isotopes of

hydrogen and oxygen

of water

Stable isotopes of

nitrogen and oxygen

of nitrate in water

(per mil)

δ2H

(per mil)

δ18O

(per mil)

δ15N

(per mil)

δ18O

(per mil)

Lopez 2 Spring (S8) 5/23/2017 −99.61 −13.80 — —

AP–1 well 5/24/2017 −86.25 −11.11 6.43 2.87

5000 Block well (W3) 5/03/2017 −101.27 −13.52 — —

Cottonwood Spring well (W8) 5/24/2017 −107.23 −14.32 — —

Goodknight well (W10) 5/10/2017 −93.58 −12.62 — —

SE Toe well (W20) 5/02/2017 −108.11 −14.30 — —

probably was not as old as the other three wells. Undetected 

(that is, less than the laboratory reporting limit) concentrations of tritium for samples from 5000 Block, Goodknight, 

SE Toe, and Cottonwood Spring wells also indicate that the 

groundwater has not been affected by recharge since the 

early 1950s. The sample for the AP–1 well plots outside the 

pre- and post-1950s boxes in the “mixed” area of figure 14 

and contains a combination of groundwater that recharged 

before and after the early 1950s. Recharge to the AP–1 well 

was mostly post-1950s, which is consistent with a nitrate plus 

nitrite concentrations of 45-68 mg/L (fig. 12B) and δ15N and 

δ18O values of nitrate of 6.43 and 2.87 per mil, respectively 

(table 16): this indicates there might be anthropogenic sources 

of nitrate in the well sample. 

Chlorofluorocarbons are synthetic organic compounds 

that were developed in the early 1930s for refrigeration and 

have been used in a variety of industrial and refrigeration 

applications. The presence of CFCs can be used to estimate the 

apparent age of water that has recharged an aquifer since 1940 

and also can be used to estimate the date of recharge (Coplen 

and others, 2000). To determine apparent CFC ages, measured 

CFC concentrations in groundwater samples are converted to 

equivalent air concentrations using known solubility relationships and recharge temperature with corrections made for 

excess air when needed (USGS, 2016a). The resulting concentrations are compared with the atmospheric concentration 

curves of CFCs to determine the apparent CFCs ages. Factors 

affecting the determination of age based on CFCs include 

transport processes; chemical processes, such as degradation 

and sorption during transit or redox conditions; excess air 

in a sample; and estimated recharge altitude or temperature 

(USGS, 2016a). 
Groundwater Chemistry 53

Figure 14. Tritium concentrations in relation to carbon-14 

concentrations in water samples collected by the Ute 

Mountain Ute Tribe in 2017 for one spring and five wells 

on the Ute Mountain Ute Reservation in Colorado, with 

concentrations of methane and nitrate plus nitrite.

Table 17. Summary of tritium and carbon-14 data for water samples collected by the Ute Mountain Ute Tribe in 2017 for one spring 

and five wells on the Ute Mountain Ute Reservation in Colorado.

[The conversion of picocuries per liter (pCi/L) to tritium unit (TU), based on a half-life of 12.32 years (Lucas and Unterweger, 2000), is approximately 1 

pCi/L = 0.3135 TU. fig., figure; ID, identification; δ13C, carbon-13/carbon-12 isotopic ratio; DIC, dissolved inorganic carbon; per mil, parts per thousand; pmc, 

percent modern carbon]

Site

(see fig. 5, site ID in

parentheses is

used on figure)

Sample

date

Tritium

(pCi/L)1

Tritium

(TU)

δ13C-DIC

(per mil)2

Carbon-14-DIC

(nonnormalized)

(pmc)3

Carbon-14

(normalized)

(pmc)2

Tritium/cabon-14 

category

(see fig. 14)4

Lopez 2 Spring (S8) 5/23/2017 17.1 5.36 −11.97 103 100.15 Post-1950s

AP-1 well 5/24/2017 12.8 4.01 −12.78 81.4 79.37 Mixed

5000 Block well (W3) 5/03/2017 0.18 0.056 2.65 3.37 3.19 Pre-1950s

Cottonwood Spring well (W8) 5/24/2017 −0.38 −0.119 −12.36 18.6 18.13 Pre-1950s

Goodknight well (W10) 5/10/2017 −0.24 −0.075 −2.69 0.952 0.91 Pre-1950s

SE Toe well (W20) 5/02/2017 −0.11 −0.034 −0.55 3.90 3.71 Pre-1950s

1

Tritium result reported by the U.S. Geological Survey Tritium Laboratory in Menlo Park, California. Results for 5000 Block, Cottonwood Spring, 

Goodknight, and SE Toe wells are less than laboratory reporting limits, which range from 0.34 to 0.39 pCi/L.

2

Carbon-13 and carbon-14 results reported by the National Ocean Sciences Mass Spectrometry Facility in Woods Hole, Massachusetts. Although not specifically discussed in the report, the isotopic data for carbon-13 are included in the table for completeness of laboratory results.

3

Nonnormalized data: data have not been adjusted for isotopic fractionation.

4

Post-1950s: recharge after the early 1950s. Pre-1950s: recharge before the early 1950s.

Mixed

Pre-1950s water

Post-1950s water

Lopez 2 Spring

Goodknight well

5000 Block well

SE Toe well

Cottonwood Spring well

AP–1 well

6

8

0

4

10

2

0

1 2 3 4 5 6

Tritium, in tritium units

12

14

16

18

20

40

60

80

100

120

Carbon-14 in dissolved inorganic carbon, in percent modern carbon

EXPLANATION

Nitrate plus nitrite, as nitrogen,

 in milligrams per liter

Methane, in milligrams per liter

0.0 to 0.1

Greater than 25

Not measured

Less than 0.055

Greater than 50

Goodknight well Water sample and identifier
54 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

Chlorofluorocarbons were analyzed for groundwater 

samples collected from Lopez 2 Spring and the 5000 Block, 

Cottonwood Spring, Goodknight, and SE Toe wells (table 18). 

Elevated CFC concentrations in the Lopez 2 Spring sample and 

an apparent CFC age of late 1990s or younger are consistent 

with tritium and carbon-14 results that indicate post-1950s 

recharge. The CFC results for the Cottonwood Spring well 

sample indicate that recharge occurred in the mid-1950s (table 

18), which is inconsistent with an absence of tritium and an age 

classification of pre-1950s recharge from the tritium and carbon-14 data. The discrepancy in recharge age could be caused 

by contamination during CFC sampling, air getting into the 

well bore, or introduction of air if the water level is within the 

screened interval of the well. Unlike CFC samples, recharge 

ages for tritium and carbon-14 samples are not affected by 

air exposure. Laboratory results for CFC samples from the 

5000 Block, Goodknight, and SE Toe wells noted that all CFCs 

were degraded. Each sample was anoxic (DO concentrations 

<0.5 mg/L), and numerous studies have reported degradation of 

CFCs in anaerobic environments (Solomon and others, 1998; 

Sebol and others, 2007; Chambers and others, 2018). As with 

the Cottonwood Spring well sample, the presence of CFCs in 

the three wells, though degraded, are inconsistent with tritium 

and carbon-14 dating of pre-1950s recharge. Samples from the 

5000 Block, Goodknight, and SE Toe wells could also have 

been contaminated, or air could have been introduced during 

sampling. The CFC sample results for the Cottonwood Spring, 

5000 Block, Goodknight, and SE Toe wells are excluded from 

evaluation of recharge age. 

Samples of groundwater from Lopez 2 Spring and 

5000 Block, Cottonwood Spring, Goodknight, and SE Toe wells 

also were analyzed for dissolved and noble gases (tables 19 

and 20). Dissolved gas concentrations, as well as the ratios of 

dissolved gas concentrations, can be used to provide information on geochemical conditions, such as microbial degradation; 

calculate the recharge temperature of a groundwater sample; 

and determine excess air. Concentrations of noble gases also 

are useful for determining the age and source of groundwater 

and for determining recharge temperature and excess air (Hunt, 

2015). For this report, interpretation of dissolved gas and noble 

gas data is focused on the dissolved gases methane and oxygen 

and geochemical conditions, and the noble gas helium-4 and 

groundwater age. Data for other dissolved and noble gases, 

although not specifically discussed, are included in tables 19 

and 20 for completeness of laboratory results. 

Concentrations of methane gas were elevated (25.9 mg/L 

or more) in water samples from the 5000 Block, Goodknight, 

and SE Toe wells (table 19). Each sample was old (pre1950s recharge), anoxic (DO water and gas concentrations 

<0.5 mg/L), enriched with ammonia, and low in sulfate 

(excluding the SE Toe well) (table 19). These conditions are 

consistent with what could be expected for methanogenesis, 

the natural production of methane within aquifers by methanogenic bacteria in low-oxygen environments (McMahon 

and others, 2017). The cooccurrence of high methane and 

sulfate concentrations in the SE Toe well sample indicates 

possible mixing of methanogenic and sulfate-enriched waters 

(McMahon and others, 2017). 

Dates interpreted from helium-4 data for the Lopez 2 

Spring and the Cottonwood Spring, Goodknight, and SE Toe 

wells are consistent with the tritium- and carbon-14-based 

age classifications (fig. 14). A very low helium-4 concentration like that detected for the Lopez 2 Spring (table 20) occurs 

when water equilibrates with air, which indicates young water. 

Helium-4 concentrations, such as those for the Cottonwood 

Spring, Goodknight, and SE Toe wells (table 20), are greatest in older groundwater, increasing with residence time of 

water as helium-4 is produced from the decay of uranium and 

thorium in aquifer materials (Heaton, 1984; Solomon and 

others, 1998). For the 5000 Block well, the very high methane 

concentration (table 19) appears to have caused substantial 

stripping of helium-4 from the sample (table 20), possibly 

during sample collection. Gases that are in solution within 

an aquifer because of hydrostatic pressure can come out of 

solution as pressure is reduced when water is pumped to the 

surface. When samples with high levels of methane degas, the 

methane can strip relatively insoluble gases like helium-4 out 

of solution (Danabalan and others, 2017). 

Vulnerability Assessment

The protection of water resources on the UMUR has been 

an overriding goal of the UMUT. Data collection efforts have 

been designed to assess the current state of water resources, 

protect designated uses, assess water-quality trends, and identify potential sources of impairment to water quality and areas 

vulnerable to land-use activities. The UMUT Groundwater 

Protection Plan was developed to identify the vulnerability of 

aquifers to potential toxic or hazardous chemicals, particularly 

pesticides, from land-use activities, and to organize a protection strategy for the aquifers (UMUT, 2004). 

The UMUT specifically focused their assessment of 

vulnerability on natural risk and land-use susceptibility 

to contamination (UMUT, 2004). Three classifications of 

natural risk—low, moderate, and high—were developed by 

the UMUT; an area’s risk is based on its natural conditions, 

including geology and aquifer properties, and soil properties 

(leaching and run-off potential) (UMUT, 2004). A high natural 

risk to contamination occurs, for example, when aquifer 

properties and leaching through soil favor the movement of 

a pesticide or other anthropogenic chemical from the land 

surface to the water table. 

The susceptibility of a given area of land to contamination was determined by land-use sensitivity and resource use 

(UMUT, 2004). The use of land by the UMUT and the level of 

care required to prevent adverse effects to groundwater affect 

land-use sensitivity (UMUT, 2004). A high sensitivity ranking, 

for example, is applied to springs because of their importance 

for Tribal ceremonial activities, and a low-sensitivity ranking is applied to rangeland because of low pesticide use and 
Table 18. Summary of chlorofluorocarbon (CFC) and apparent age for water samples collected by the Ute Mountain Ute Tribe in 2017 for one spring Mountain Ute Reservation in Colorado.[Samples were analyzed at the U.S. Geological Survey Reston Groundwater Dating Laboratory in Reston, Virginia. fig., figure; ID, identification; pptv, parts per trillion by volumcould not be determined]

Site

(see fig. 5, site ID

in parentheses

is used on figure)

Sample

date

CFC-11,

range of calculated atmospheric mixing 

ratio

(pptv)

CFC-12,

range of calculated atmospheric mixing 

ratio

(pptv)

CFC-13,

range of calculated atmospheric mixing 

ratio

(pptv)

Piston-flow 

model age basis

Piston-flow model

apparent age 

Lopez 2 Spring (S8) 5/23/2017 243–248 538–556 70.4–73.8 CFC-11, 12, 13 Late 1990s or younger 5000 Block well (W3) 5/03/2017 0.0–0.5 93.5–162.2 11.4–13.4 None cnbd Cottonwood Spring well (W8) 5/24/2017 2.4–5.8 18.9–22.1 0.5–2.0 CFC-11, 12, 13 Mid-1950s1 Goodknight well (W10) 5/10/2017 0.2–0.5 106.4–120.8 12.3–13.3 None cnbd SE Toe well (W20) 5/02/2017 0.8–2.2 87.8–95.2 13.4–14.9 None cnbd 

1Likely anomalous value. Tritium and carbon-14 data indicate that recharge occurred before the early 1950s (see table 17). Tritium was not detected in the sample.

Table 19. Summary of dissolved gas data for water samples collected by the Ute Mountain Ute Tribe in 2017 for one spring and four wells on the Ute in Colorado, with estimated recharge dates and concentrations of total recoverable ammonia and sulfate.[Dissolved gas samples were analyzed at the U.S. Geological Survey Reston Groundwater Dating Laboratory in Reston, Virginia. fig., figure; ID, identification; mg/L, milligramless than]

Site

(see fig. 5, site ID

in parentheses

is used on figure)

Sample

date

Dissolved gases Estimated re

charge date

Methane 

(mg/L)

Carbon dioxide

(mg/L)

Nitrogen

(mg/L)

Oxygen

(mg/L)

Argon

(mg/L)

Laboratory 

comment

Lopez 2 Spring (S8) 5/23/2017 0.0 0.0 11.9 11.2 15.4 15.3 6.0 6.9 0.57 0.56 — Post-1950s 

5000 Block well (W3) 5/03/2017 39.2 39.6 10.2 10.0 0.62 0.65 0.001 0.0005 0.033 0.036 Gas stripping2 Pre-1950s Cottonwood Spring well (W8) 5/24/2017 0.096 0.094 1.2 1.2 19.9 20.1 0.28 0.29 0.67 0.68 — Pre-1950s Goodknight well (W10) 5/10/2017 27.2 27.6 22.1 23.8 6.4 6.4 0.060 0.050 0.29 0.29 Gas stripping2 Pre-1950s SE Toe well (W20) 5/02/2017 27.0 25.9 1.2 1.2 9.9 9.9 0.060 0.076 0.35 0.36 Gas stripping2 Pre-1950s 

1Post-1950s: recharge after the early 1950s. Pre-1950s: recharge before the early 1950s. Estimated dates based on tritium and carbon-14 concentrations. See table 17.2Degassing (separation of a gas from a liquid) of a sample, likely due to high methane concentration.
Table 20. Summary of noble gas data for water samples collected by the Ute Mountain Ute Tribe in 2017 for one spring and four wells on the Ute MoColorado. [Samples were analyzed at the U.S. Geological Survey Noble Gas Laboratory in Lakewood, Colorado. fig., figure; ID, identification; cm3STP/g[H20], cubic centimeters at stand

per gram of water; R/Ra, measured helium-3/helium-4 isotopic ratio relative to the helium isotopic ratio of air; —, no laboratory comment] Site (see fig. 5, site ID in parentheses is used on figure) Sample date Helium-4 (cm3STP/ g[H20]) Neon (cm3STP/ g[H20]) Argon (cm3STP/ g[H20]) Krypton (cm3STP/ g[H20]) Xenon (cm3STP/ g[H20]) R/Ra 

Lopez 2 Spring (S8) 5/23/2017 4.06E-8 0.000 3.29E-4 8.00E-8 1.24E-8 0.906 5000 Block well (W3) 5/03/2017 13.24E-08 1.32E-8 1.64E-5 4.98E-9 9.96E-10 0.197 Cottonwood Spring well (W8) 5/24/2017 6.29E-7 1.82E-7 3.57E-4 8.75E-8 1.31E-8 0.149 Goodknight well (W10) 5/10/2017 3.85E-6 5.62E-8 1.56E-4 4.04E-8 5.97E-9 0.140 SE Toe well (W20) 5/02/2017 2.03E-7 0.000 1.86E-4 4.24E-8 5.04E-9 0.130 

1Value is lower than expected because of gas stripping of the sample (degassing [separation of a gas from a liquid], likely due to high methane concentration).
Vulnerability Assessment 57

no irrigation. Some areas are more susceptible to contamination because of resource use. Irrigated land and roadways, for 

example, are susceptible areas because of a greater potential of 

a chemical to contaminate water resources as compared to land 

that is not susceptible because of the lack of development. 

Natural risk and land-use susceptibility to contamination 

were combined by the UMUT to develop an overall groundwater vulnerability ranking of high, moderate, or low (table 21) 

(UMUT, 2004). A high vulnerability ranking for potential contamination, for example, is given to culturally significant springs 

because of the short residence time of water in the spring and 

Tribal ceremonial use. A ranking of low vulnerability is given 

to rangeland because of the limited amount of recharge to the 

subsurface and lack of exposure to potential toxic or hazardous 

chemicals. The groundwater vulnerability ranking is used by the 

UMUT to focus monitoring, target prevention measures, and 

implement a strategy for responding to detections of pesticides 

and other anthropogenic chemicals (UMUT, 2004). 

Areas with oil and gas development are given a high 

vulnerability ranking (table 21). Abandoned wells in the 

northwest portion of the UMUR have been an issue of concern 

for several years (Clarren, 2018). Concerns include a legacy of 

contamination from surface activities and injection wells with 

casing failure. Hydrocarbons and metals in soils and unlined 

pits, and other surface contamination at abandoned wells sites, 

have the potential to migrate farther into in the subsurface, 

to the water table, or to McElmo Creek during large runoff 

events. It is estimated that cleanup costs for seven abandoned 

wells could range from $1 to $5 million or more (Clarren, 

2018). Lack of financial and human resources greatly limit the 

amount of cleanup that can be undertaken (Clarren, 2018).

Vulnerability of groundwater to contamination can also be 

assessed for different types of groundwater resources. Springs 

and surficial deposits are more vulnerable to contamination 

than deeper bedrock wells because of proximity to the land 

surface, porous aquifer materials, shallow depths to water, 

young groundwater age, and lack of a confining layer. Based 

on groundwater-age results, for example, recharge to springs on 

Ute Mountain and to groundwater in the surficial deposits of the 

Farm and Ranch Enterprise area has occurred primarily since 

the early 1950s. These results indicate that contamination at 

the land surface could potentially affect groundwater quality in 

springs and surficial deposits in these areas. Chemicals applied 

or spilled at the land surface can move with recharge water to 

springs and surficial deposits because of the absence of a confining layer. Similarly, bedrock aquifers are vulnerable to contamination where the geologic formations containing the aquifers 

are exposed (outcrop) at the land surface. Overlying confining 

layers and the long residence time of groundwater in deep 

bedrock aquifers, such as that for the SE Toe well that is likely 

thousands of years old, minimize the likelihood of contamination from present-day land uses. However, the natural protection offered by overlying, unfractured confining layers may be 

negated if chemicals on the land surface or poor-quality surficial 

groundwater contact bedrock aquifers through abandoned wells, 

as described previously, or through well bores (EPA, 2015). 

Deeper groundwater could be vulnerable if activity resumes 

in areas of oil and gas development. Historically, oil and gas 

development on the UMUR in Colorado has occurred in the far 

northwest and southeast corners of the reservation and in areas 

near the confluence of Navajo Wash and the Mancos River. An 

anthropogenic chemical in deep, old groundwater would not be 

diluted by new recharge because of the slow rate of infiltration 

to deep groundwater. The introduction of oxic groundwater to 

deep anoxic groundwater could change redox conditions and 

mobilize redox-sensitive contaminants such as uranium.

The vulnerability of the shallow groundwater system in 

agricultural areas to nitrate is greatly increased with the application of irrigation water and nitrogen-containing fertilizer to the 

land surface. Downward-flowing irrigation water can transport 

fertilizers through the subsurface to the water table and can also 

mobilize and transport naturally occurring nitrate in materials 

derived from Mancos Shale (Morrison and others, 2012; Mills 

and others, 2016). Total nitrate concentrations in samples from 

some AP wells collected in 2011 and 2013–14 were 40 mg/L or 

more, and depth to water during these sample years was from 

3.3 to 24.9 ft bls (table 2). Overall, the deep groundwater system 

is not vulnerable to nitrate or nitrate plus nitrite because of the 

absence of a nitrate source, the overlying Mancos Shale confining layer, long residence time, and geochemical processes that 

would reduce nitrate to nitrogen gas. Most (12 of 13) concentrations of nitrate plus nitrite in samples of deep groundwater were 

0.23 mg/L or less (fig. 12B). The deep groundwater system, 

however, may be vulnerable to ammonia when reducing conditions are present. Ammonia concentrations >1 mg/L in the deep 

groundwater system (fig. 12A) were only detected in anoxic 

samples from the 5000 Block, Goodknight, and SE Toe wells.

Detection of a pesticide or VOCs in well samples collected from the irrigated area, even though concentrations were 

well below human-health benchmarks, also indicate vulnerability of surficial deposits. The presence of E. coli and detections 

of aluminum and arsenic at concentrations greater than Tribal 

cultural-use standards in samples from culturally significant 

Table 21. Land use and natural risk in groundwater vulnerability 

for the Ute Mountain Ute Reservation.

[Modified from Ute Mountain Ute Tribe (2004). HV, high vulnerability; MV, 

moderate vulnerability; LV, low vulnerability]

Land

use

High

natural risk

Moderate

natural risk

Low

natural risk

Cultural HV HV MV

Irrigated agriculture HV MV MV

Urban HV MV LV

Highways HV MV LV

Oil and gas HV MV LV

Agriculture MV LV LV

Rangeland LV LV LV
58 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

springs indicates vulnerability to contamination from bacteria 

and trace elements. The UMUT water-quality standards for use 

of surface water for agriculture, irrigation, and (or) livestock 

watering, and the CDPHE standards for the agricultural use of 

groundwater, were exceeded for some constituents.

Groundwater is vulnerable not only to anthropogenic 

chemicals from various land uses but also to naturally occurring 

salts and minerals (Focazio and others, 2002). In the absence of 

anthropogenic influences, detections of dissolved solids, major 

ions, and trace elements in spring and well samples indicate 

naturally occurring constituents in groundwater. Groundwater 

vulnerability to naturally occurring salts and minerals is affected 

by natural factors such as water movement, rock-water interactions, geochemical processes, and residence time and by the 

sources, locations, fate, and transport of the salts and minerals. For example, the application of freshwater to irrigate land 

in the Farm and Ranch Enterprise area likely has dissolved 

naturally occurring salts in the subsurface and increased their 

downward movement to the water table where groundwater has 

become enriched with dissolved solids (Tuttle and other, 2014b, 

Mills and others 2016). For shallow wells, most (77 percent) 

TDS concentrations between the 25th (3,456 mg/L) and 90th 

(6,722 mg/L) percentile concentrations on figure 9 were for 

samples from AP wells. The trace elements arsenic and selenium, which are often present in materials derived from Mancos 

Shale (Morrison and others, 2012; Tuttle and others, 2014a), 

can readily dissolve from surficial deposits when in contact with 

oxic recharge water. Detected concentrations of total recoverable arsenic and total recoverable and dissolved selenium 

were greatest in samples from AP wells. Deep groundwater is 

highly vulnerable to naturally occurring salts and minerals. For 

example, about 75 percent of samples from deep wells had TDS 

concentrations >2,000 mg/L (fig. 9).

An area of concern for the UMUT is the effect of 

climate change on water resources and other ecological 

characteristics on the UMUR. Climate studies indicate that 

southwest Colorado warmed by 2 °F between 1977 and 2007 

and could warm an additional 2.5–5.5 °F by 2050 (Mountain Studies Institute, 2014). A warmer environment would 

increase the rate at which water evaporates or transpires 

from snow, surface water, the water table, soil, and vegetation. Decreases in snowpack and water content of snow and 

earlier snowmelt and peak streamflow have already been 

observed in western Colorado as temperatures have warmed 

(EPA, 2016). It is estimated that snowmelt in western Colorado now occurs 2 weeks earlier than it did in the late 1970s 

(Clow, 2010). Other potential effects of warmer temperatures 

include a decrease in groundwater recharge, which results 

in decreased flow of springs; a decrease in soil moisture for 

natural vegetation and crops; an increase in invasive vegetation and pests; changes in irrigation and crop production; 

reduced vegetation coverage; shifts in the altitudinal distribution of plants and animals; and increased occurrence of wildfires and forest mortality (Mountain Studies Institute, 2014; 

EPA, 2016). Particularly for the UMUT, climate change 

could potentially affect medicinal and culturally important 

plants and springs. Climate studies indicate that precipitation could decrease annually, occur more often in winter, and 

(or) be more variable with more frequent extreme storms 

(Mountain Studies Institute, 2014). Periods of drought 

are a natural occurrence in southwest Colorado (fig. 15), 

but their frequency, length, and intensity are expected to 

increase throughout the southwestern United States, including Colorado. In MVNP, 90 percent of high-altitude pinyon 

pines (Pinus edulis) have died recently because of drought 

(National Park Service, 2011). 

15

20

–10

–5

0

10

5

Total annual precipitation, departure from average, in inches –15

1930

Year

1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015

No data

Figure 15. Precipitation departure from average for meteorological station 051886 at Cortez, 

Colorado, 1930–2016 (Western Regional Climate Center, 2018b). The dashed line indicates no data.
Summary 59

Information Needs

During the compilation and interpretation of data for this 

report, several items were identified where additional information would aid in understanding the groundwater resources of 

the UMUR. Some pertain to ancillary information and others 

pertain to data collection. 

The lack of ancillary information for most bedrock 

wells, including well-completion data such as lithology, 

lithologic thickness, well depth, and screen interval, limited 

the interpretation of groundwater-chemistry data for bedrock 

wells. In most instances, for example, groundwater chemistry could not be correlated to specific geologic formations 

(aquifers) underlying the UMUR. Information provided by 

a downhole camera, such as well depth and screen interval, 

could aid in understanding the source and, therefore, the 

quality of groundwater.

Collection of environmental tracer data was conducted 

by the UMUT at six sites in May 2017. The identification of 

additional sites appropriate for environmental tracer sampling and the sampling of these sites would expand information on recharge, processes affecting groundwater quality, 

geochemical conditions, groundwater age, methane occurrence, and recharge temperature. This information would 

increase understanding of where groundwater is old and 

vulnerable to the effects of human activity occurring in the 

deep subsurface or younger and vulnerable to human activities occurring at the land surface. 

Analysis of elevated dissolved methane concentrations in samples from the 5000 Block, Goodknight, and SE 

Toe wells indicate that methanogenesis likely has occurred 

in parts of the groundwater system. Methane can also be 

introduced into groundwater during oil and gas activities 

(McMahon and others, 2018). Collection of groundwater 

samples for analysis of methane and additional hydrocarbons 

(ethane, propane, butane, and pentane) and analysis of methane isotopes at the three wells and other wells could provide 

a baseline understanding for the origin of methane, especially if there is Tribal interest in resuming development of 

hydrocarbon resources in Colorado. Thermogenic gas, which 

is gas that is produced under high temperature and pressure 

conditions, is more enriched with ethane, propane, butane, 

and pentane relative to methane than microbial gas, which 

is enriched with methane (Kulongoski and others, 2018; 

McMahon and others, 2018). 

The resampling of some sites could aid in further understanding of groundwater resources. Some springs and wells 

were last sampled in 2002 or earlier, whereas others have been 

sampled only since 2010. The resampling of springs and wells 

with data collected from 1996 through 2002, such as that for 

East Toe Spring and the AW Hwy 141 well, would update the 

temporal coverage of groundwater-chemistry data. 

Summary

Water sustains the cultural, spiritual, and economic 

health of the Ute Mountain Ute Tribe (UMUT) and the Ute 

Mountain Ute Reservation (UMUR) in the semiarid Colorado Plateau region of Colorado, New Mexico, and Utah. 

The U.S. Geological Survey, in cooperation with the UMUT, 

initiated a study in 2016 to compile and analyze hydrogeologic and groundwater-chemistry information for the UMUR 

in Colorado and Utah and, in 2017, assisted the UMUT in 

developing and implementing a sampling plan for environmental tracers in spring and well water that was executed by 

the UMUT. The study was designed to increase understanding of the hydrogeology and groundwater chemistry of the 

groundwater system within select areas the UMUR, identify 

vulnerabilities to the system and other natural resources, and 

outline information needs to aid in groundwater resource 

understanding and protection. The results presented for this 

study can be used to support the UMUT’s goal of protecting 

their vital groundwater resources on the UMUR. This report 

includes (1) characterization of hydrogeologic conditions for 

selected aquifers within the UMUR in Colorado; (2) compilation and analysis of groundwater-chemistry data for springs 

and wells, focusing primarily on data collected by the UMUT 

in Colorado and Utah from 1996 through 2017; (3) analysis 

of environmental tracer data collected by the UMUT in Colorado in 2017; (4) assessment of the vulnerability of resources 

to contamination and climate change; and (5) identification of 

information needs to advance the protection and understanding of groundwater resources.

The UMUR encompasses about 597,000 acres 

(933 square miles) of trust land in Colorado, New Mexico, and 

Utah in the Four Corners region of the Colorado Plateau; most 

is in southwestern Colorado. Geology of the UMUR includes 

Cretaceous-age sandstones, shales, and mudstone, prominently 

the Mancos Shale and Dakota Sandstone; Late Cretaceousand Tertiary-age igneous rocks that form the Ute Mountains; 

and Quaternary-age unconsolidated surficial deposits. Groundwater primarily occurs in the surficial aquifer contained in 

unconsolidated surficial deposits and in aquifers contained in 

sandstone geologic formations, such as the Dakota Sandstone. 

Some springs in the Ute Mountains are culturally significant 

for the UMUT and have ceremonial use.

Characterization of hydrogeologic conditions in Colorado 

include (1) determining depth to the water table below land 

surface and direction and gradient of the water-table slope for 

the surficial aquifer in two areas of the UMUR and (2) mapping 

depth to the top of the Dakota Sandstone. The median depth to 

water in the surficial aquifer in the Farm and Ranch Enterprise 

area ranged from 5.4 to 17.2 feet (ft) below land surface (bls), 

and the water surface slopes to the southwest away from the 

Ute Mountains with a mean gradient of about 94 ft per mile. 

Near Towaoc, the depth to water ranged from about 11 to 34 ft 

bls, and the water-table slopes generally southward with mean 

gradient of about 143 ft per mile. Within the boundaries of the 

UMUR in Colorado, depths to the top of the Dakota Sandstone 
60 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

range from zero in outcrop areas to about 1,500 ft bls in the 

western part of the UMUR and to more than 3,000 ft bls on 

mesas in the southeastern part of the UMUR.

Groundwater-chemistry data collected by the UMUT 

in Colorado and Utah were the focus of the groundwaterchemistry assessment. Analysis was supplemented with 

historical data from the U.S. Geological Survey and Colorado 

Oil and Gas Conservation Commission. The UMUT collected 

data from 13 springs and 31 wells in 1996 through 2017 for 

physical properties, total dissolved solids (TDS), major ions, 

nutrients, trace elements, uranium, coliform bacteria, and environmental tracers. Quality-assurance procedures were applied 

to the data prior to analysis. 

Specific conductance values for UMUT data were much 

lower for samples of spring water than well water; median 

values were 512 and 6,024 microsiemens per centimeter at 

25 degrees Celsius, respectively. Most pH values were within 

water-quality standards established for cultural use of water, 

aquatic-life criteria, and agricultural use of surface water and 

groundwater. Dissolved oxygen concentrations in a few well 

samples were low, less than 0.5 milligrams per liter (mg/L), 

which could indicate reducing conditions in the aquifer. 

Overall, spring samples collected by the UMUT were 

less mineralized than well samples. About 72 percent of 

spring samples had fresh water (TDS concentrations less than 

1,000 mg/L), whereas most (85 percent) of well samples had 

brackish or highly saline water (TDS concentrations greater 

than 1,000 mg/L). The UMUT cultural-use standard for TDS 

of 500 mg/L was exceeded for five springs, including the culturally significant Whiskers Draw Spring. 

Samples from springs on the Ute Mountains were calcium-bicarbonate type water, whereas lower-altitude springs 

with more mineralization were a calcium-sulfate type water. 

Most well samples had sodium as the dominant cation and 

sulfate, bicarbonate, and chloride as the dominant anions. 

Alkalinity concentrations less than 100 mg/L in some 

UMUT samples from springs on the Ute Mountains indicate that some spring water is not well buffered and could 

be susceptible to input of acidic water. Of the well samples, 

about 45 percent had fluoride concentrations greater than the 

Colorado agricultural-use standard for groundwater of 2 mg/L, 

which could adversely affect animal health if water were to 

be used for livestock supply. Most ammonia concentrations in 

spring and well samples collected by the UMUT were similar 

to or less than the estimated natural background concentration in groundwater of 0.2 mg/L. Concentrations greater than 

1 mg/L were detected in well samples that were anoxic. Most 

concentrations of nitrate plus nitrite in spring and well samples 

were 1.6 mg/L or less. Concentrations were elevated (maximum of 78.5 mg/L) in samples from wells in the Farm and 

Ranch Enterprise area of the UMUR. 

About 50 percent of samples collected by the UMUT for 

trace elements had concentrations less than laboratory reporting 

limits. Total recoverable aluminum, arsenic, and selenium in 

spring samples, and dissolved boron and selenium in well samples, were detected at concentrations greater than water-quality 

standards established by the UMUT or the Colorado Department of Public Health and Environment. Samples from three 

culturally significant springs, Hanna, Ute, and Whiskers Draw, 

exceeded the UMUT surface-water cultural-use standards for 

aluminum and (or) arsenic. Only the pesticides alachlor and 

atrazine and the volatile organic compound di(2-ethylhexyl) 

phthalate were detected in well samples. The detected concentrations for wells in the Farm and Ranch Enterprise area were 

less than drinking-water standards.

Coliform bacteria (total coliform and E. coli) were more 

commonly detected in well samples (77 percent) than in spring 

samples (30 percent). Detections of E. coli were more common for well samples (47 percent) than for spring samples 

(23 percent). Exceedances of the UMUT cultural-use standard 

of total absence of the E. coli in spring water included samples 

from the culturally significant Hanna, Lopez 2, and Whiskers 

Draw Springs. 

Water samples from Lopez 2 Spring and AP–1, 

5000 Block, Cottonwood Spring, Goodknight, and SE Toe 

wells were analyzed for environmental tracers, including stable isotopes, tritium, chlorofluorocarbons, dissolved gases, and 

noble gases. Concentrations of the stable isotope of hydrogen 

and oxygen of water in the spring and well samples indicate 

that recharge primarily was derived from precipitation. Tritium 

and carbon-14 were the primary tracers used for interpreting 

groundwater ages. Recharge to Lopez 2 Spring was post1950s in age, and recharge to 5000 Block, Cottonwood Spring, 

Goodknight, and SE Toe wells was pre-1950s in age. Recharge 

to the AP–1 well was a mixture of pre- and post-1950s water. 

Helium-4 data support the tritium and carbon-14 ages for 

Lopez 2 Spring and Cottonwood, Goodknight, and SE Toe 

wells but not the 5000 Block well because of high methane 

concentrations in the water. 

Springs and surficial deposits are more vulnerable to contamination from anthropogenic chemicals than deeper bedrock 

wells because of proximity to the land surface, porous aquifer 

materials, and shallow depths to water. Bedrock aquifers are 

vulnerable in areas where the geologic formations containing these aquifers are exposed (outcrop) at the land surface. 

Groundwater in deep bedrock aquifers is likely thousands of 

years old and is not currently affected by present-day land 

uses. Deeper groundwater could be vulnerable to contaminants 

from surface activities or poor-quality shallow groundwater 

if chemicals can move to deeper groundwater through abandoned wells or through well bores. Both shallow and deep 

groundwater is vulnerable to naturally occurring salts and 

minerals, including TDS, major ions, nitrate, and trace elements. Water resources and other ecological characteristics 

of the UMUR are vulnerable to a changing climate. Possible 

effects could include changes in evapotranspiration, a decrease 

in snowpack, decreased aquifer recharge and flow of springs, 

a decrease in soil moisture, changes in irrigation and crop 

production, and increased occurrence of wildfires and forest 

mortality. Of particular interest for the UMUT are possible 

effects of a changing climate on medicinal and culturally 

important plants and springs.
References Cited 61

Several information needs were identified that would aid 

in understanding the groundwater resources of the UMUR. 

Ancillary information for bedrock wells, including wellcompletion data such as lithology, well depth, and screen interval, would increase understanding of the source and quality 

of groundwater. The collection of environmental tracer data at 

additional wells and collection of well samples for methane and 

hydrocarbon analysis would expand information on recharge, 

processes affecting groundwater quality, geochemical conditions, groundwater age, and methane occurrence. Resampling 

of seven springs and wells that were last sampled in 2002 or 

earlier would update the temporal coverage of groundwaterchemistry data.

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Toccalino, P.L., Norman, J.E., and Schoephoester, K.M., 2014, 

Health-Based Screening Levels for evaluating water-quality 

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3, 2017, at https://doi.org/10.5066/F71C1TWP.
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Tuttle, M.L.W., Fahy, J.W., Elliot, J.G., Grauch, R.I., and 

Stillings, L.L., 2014a, Contaminants from Cretaceous black 

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66 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

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organic compounds in the Nation’s ground water and 

drinking-water supply wells: U.S. Geological Survey 

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https://doi.org/10.3133/cir1292.
Appendix 1 67

Appendix 1. Hydrogeologic Characterization

Table 1.1. Description of wells used for measuring water levels in the surficial aquifer contained in unconsolidated surficial deposits on 

the Ute Mountain Ute Reservation in Colorado, with sources of data, period of water-level record, and select water-level measurements.

[ID, identification; figs., figures; USGS, U.S. Geological Survey; LatitudeDD, latitude in decimal degrees; LongitudeDD, longitude in decimal degrees; DatumDD, 

datum for decimal degrees; DEM, digital elevation model; ft; feet; NAVD88, North American Vertical Datum of 1988; bls, below land surface; UTEMTN, Ute 

Mountain Ute Tribe; na, not applicable; NAD27, North American Datum of 1927; NWIS, National Water Information System; NAD83, North American Datum of 

1983; —, no information]

Site ID

(see 

figs. 5 

and 6)

Unique site

identifier

USGS

station

name

Latitude

DD

Longitude

DD

Datum

DD

DEMderived 

altitude

(ft above 

NAVD88)1

Well 

depth

(ft bls)2

Waterlevel 

period of 

record

USGS

water

level

(ft bls)

Ute Mountain Ute Tribe, Farm and Ranch Enterprise wells

AP−1 3UTEMTN-AP−1 na 37.1896 −108.95114 NAD27 5,228 26.6 2008–14 na

AP−2 UTEMTN- AP−2 na 37.181417 −108.96471 NAD27 5,162 15.2 2008, 2010 na

AP−3 UTEMTN- AP−3 na 37.176026 −108.97301 NAD27 5,113 15 2008–10 na

AP−4 UTEMTN- AP−4 na 37.173375 −108.97961 NAD27 5,086 14 2009–12 na

AP−5 3UTEMTN- AP−5 na 37.171144 −108.99418 NAD27 5,015 11 2008–14 na

AP−10 3UTEMTN- AP−10 na 37.18558 −108.9329 NAD27 5,308 22.6 2008–14 na

AP−14 3UTEMTN-AP−14 na 37.159029 −108.92268 NAD27 5,245 14.2 2008–14 na

AP−15 3UTEMTN-AP−15 na 37.149655 −108.95784 NAD27 5,059 18.3 2010–14 na

AP−16 3UTEMTN-AP−16 na 37.152035 −108.93392 NAD27 5,170 13.4 2008–14 na

AP−17 UTEMTN- AP−17 na 37.163943 −108.91495 NAD27 5,300 18.4 2008–14 na

AP−22 UTEMTN- AP−22 na 37.209428 −108.97165 NAD27 5,273 6.4 3/1/2010 na

AP−24 3UTEMTN-AP−24 na 37.195571 −108.96395 NAD27 5,214 11.6 2010, 2012, 

2014 na

USGS NWIS, USGS (2016b)

NW31 4370946108423801 NB03301729UDAA 37.16278 −108.71056 NAD83 5,457 36.4 5/25/1982 12.3

USGS, Geldon (1985)

NW20 3,4371204108434301 NB33501707DDA B−15 37.20111 −108.72926 NAD83 5,875 65.8 4/4/1983 26.3

NW29 — NB03301729UADD 537.18944 5−108.72812 — 5,476 36.4 4/7/1983 11.4

NW30 4370928108433101 NB03301729UCCA 37.15778 −108.725277 NAD83 5,446 34 4/7/1983 15.2

NW32 4371208108433501 NB03301708UCCB 37.20222 −108.72639 NAD83 5,883 36 4/4/1983 17.4

USGS, Irwin (1966)

NW11 3,4371003108451301 NB33501825UABCC B–2 37.16749 −108.75426 NAD83 5,686 77.0 9/3/1956 30.1

NW28 — B–4 537.186 5−108.727 — 5,691 29.5 — 25

NW19 3,4371204108433801 NB33501707DDA B−14 37.20111 −108.72787 NAD83 5,873 98 2/7/1954 33.5

1

Altitude data are from USGS DEMs, which are available at https://www.usgs.gov/core-science-systems/ngp/3dep/about-3dep-products-services (USGS, 2019).

2

Well depths for the Ute Mountain Ute Tribe wells are approximate.

3

See table 4.

4

USGS NWIS site number.

5

Approximate latitude or longitude.
68 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

Table 1.2. Description of wells used for determining lithology and depth to the top of the Dakota Sandstone on the Ute Mountain Ute 

Reservation in Colorado.—Continued

[LatitudeDD, latitude in decimal degrees; LongitudeDD, longitude in decimal degrees; DatumDD, datum for decimal degrees; NAD83, North American Datum 

of 1983; na, not applicable; —, no data; No., number; S, section; T, township; N, north; R, range; W, west; ffnl, feet from north line; ffwl, feet from west line; 

ffsl, feet from south line; ffel, feet from east line; SW, southwest; NW, northwest; NE, northeast; SE, southeast; USGS, U.S. Geological Survey; NGVD29, 

National Geodetic Vertical Datum of 1929]

Well

identifier

Well

name

Latitude

DD

Longitude

DD

Datum

DD

Township

and range

Depth to top 

of Dakota 

Sandstone

(feet below 

land surface 

datum)

Altitude

datum

Colorado Oil and Gas Conservation Commission1

05–067–05038 1 SOUTHERN UTE 37.026 −108.239 NAD83 na 3,094 —

05–067–05063 1 STEWARD 37.014 −108.198 NAD83 na 3,165 —

05–067–05148 9 UTE 37.007 −108.308 NAD83 na 3,002 —

05–067–05176 2 UTE 37.028 −108.332 NAD83 na 2,840 —

05–067–05177 2 UTE 37.017 −108.302 NAD83 na 3,160 —

05–067–05204 1–A UTE 37.026 −108.222 NAD83 na 3,104 —

05–067–05235 1 HUTCHINSON 37.063 −108.172 NAD83 na 3,230 —

05–067–05259 1E GOVT 37.069 −108.292 NAD83 na 3,225 —

05–067–05359 1 NORTH BARKER DOME—GOV 37.088 −108.321 NAD83 na 3,480 —

05–067–05422 1 LLOYD-BENTON 37.106 −108.244 NAD83 na 3,160 —

05–067–05717 5 UTE 37.027 −108.283 NAD83 na 3,215 —

05–067–05727 C−11−1 S. UTE I–22–2818 37.085 −108.184 NAD83 na 3,268 —

05–067–05733 3 UTE MOUNTAIN 37.092 −108.316 NAD83 na 3,310 —

05–067–05734 4 UTE MOUNTAIN 37.092 −108.321 NAD83 na 3,460 —

05–067–05819 3 UTE 37.012 −108.283 NAD83 na 3,128 —

05–067–06011 1 SOUTHERN UTE 37.029 −108.153 NAD83 na 4,001 —

05–067–06034 1 NORTH BARKER UNIT 37.042 −108.331 NAD83 na 3,258 —

05–067–06040 1 AZTEC UTE 37.052 −108.307 NAD83 na 3,273 —

05–067–06044 2 UTE 37.062 −108.315 NAD83 na 3,238 —

05–067–06052 1 BARKER DOME 37.025 −108.330 NAD83 na 3,134 —

05–067–06068 1 FEDERAL ""B"" 37.218 −108.231 NAD83 na 3,025 —

05–067–06071 34 UTE 24–D 37.085 −108.315 NAD83 na 3,318 —

05–067–06087 1 STORY A 37.189 −108.252 NAD83 na 3,090 —

05–067–06195 1 BARKER CANYON 37.023 −108.325 NAD83 na 3,160 —

05–067–06245 1 RED HORSE GULCH 37.103 −108.315 NAD83 na 3,426 —

05–067–06273 1 MENEFEE FEDERAL 37.228 −108.270 NAD83 na 3,024 —

05–067–06279 1 UTE MOUNTAIN TRIBAL P 37.002 −108.257 NAD83 na 3,134 —

05–067–06354 1 ROACH 37.157 −108.213 NAD83 na 2,825 —

05–067–06491 1 WEST ALKALI GULCH 37.132 −108.230 NAD83 na 3,156 —

05–067–06493 1 WILDWATER CANYON FEDERAL37.230 −108.241 NAD83 na 3,034 —

05–067–06562 1 DECKER 37.005 −108.189 NAD83 na 3,790 —

05–067–06782 1 CHERRY CREEK-UTE 37.164 −108.203 NAD83 na 3,090 —

05–067–07820 1 UTE COM 37.020 −108.263 NAD83 na 3,178 —
Appendix 1 69

Table 1.2. Description of wells used for determining lithology and depth to the top of the Dakota Sandstone on the Ute Mountain Ute 

Reservation in Colorado.—Continued

[LatitudeDD, latitude in decimal degrees; LongitudeDD, longitude in decimal degrees; DatumDD, datum for decimal degrees; NAD83, North American Datum 

of 1983; na, not applicable; —, no data; No., number; S, section; T, township; N, north; R, range; W, west; ffnl, feet from north line; ffwl, feet from west line; 

ffsl, feet from south line; ffel, feet from east line; SW, southwest; NW, northwest; NE, northeast; SE, southeast; USGS, U.S. Geological Survey; NGVD29, 

National Geodetic Vertical Datum of 1929]

Well

identifier

Well

name

Latitude

DD

Longitude

DD

Datum

DD

Township

and range

Depth to top 

of Dakota 

Sandstone

(feet below 

land surface 

datum)

Altitude

datum

05–067–07821 16 Ute 37.002 −108.289 NAD83 na 3,028 —

05–067–07920 2R Ute 37.011 −108.299 NAD83 na 3,220 —

05–067–07974 19 UTE 37.007 −108.315 NAD83 na 3,108 —

05–067–07975 9A UTE 37.004 −108.307 NAD83 na 3,065 —

05–067–08010 31 UTE 37.029 −108.294 NAD83 na 3,203 —

05–067–08012 30 UTE 37.022 −108.291 NAD83 na 3,215 —

05–067–08726 58 UTE 37.016 −108.288 NAD83 na 3,208 —

05–067–08786 66 UTE MOUNTAIN UTE 37.021 −108.273 NAD83 na 3,207 —

05–067–08791 63 UTE MOUNTAIN UTE 37.007 −108.292 NAD83 na 3,197 —

05–067–08825 67 UTE MOUNTAIN UTE 37.014 −108.265 NAD83 na 3,153 —

05–067–08861 65 UTE MOUNTAIN UTE 37.002 −108.283 NAD83 na 3,095 —

05–067–09027 64 UTE MOUNTAIN UTE 37.002 −108.298 NAD83 na 3,168 —

05–067–09028 61 UTE MOUNTAIN UTE 37.014 −108.283 NAD83 na 3,130 —

05–067–09029 68 UTE MOUNTAIN UTE 37.027 −108.265 NAD83 na 3,192 —

05–067–09030 62 UTE MOUNTAIN UTE 37.007 −108.283 NAD83 na 3,093 —

05–067–09052 71 UTE MOUNTAIN UTE 37.004 −108.307 NAD83 na 3,071 —

05–067–09053 72 UTE MOUNTAIN UTE 37.008 −108.275 NAD83 na 3,167 —

05–067–09319 86 UTE MOUNTAIN UTE 37.014 −108.273 NAD83 na 3,153 —

05–067–09320 85 UTE MOUNTAIN UTE 37.028 −108.272 NAD83 na 3,226 —

05–067–09321 88 UTE MOUNTAIN UTE 37.002 −108.271 NAD83 na 3,116 —

05–067–09358 87 UTE MOUNTAIN UTE 37.020 −108.282 NAD83 na 3,226 —

05–067–40011 2 UTE 37.044 −108.392 NAD83 na 2,840 —

05–083–05008 2 UTE TRIBE 37.001 −108.484 NAD83 na 2,639 —

05–083–05013 C−1 UTE 37.005 −108.889 NAD83 na 362 —

05–083–05020 1 PHILMO UTE 37.012 −108.698 NAD83 na 1,738 —

05–083–05039 2 UTE MOUNTAIN 37.023 −108.849 NAD83 na 530 —

05–083–05042 5 UTE 37.024 −108.791 NAD83 na 598 —

05–083–05058 1 UTE 37.032 −108.789 NAD83 na 615 —

05–083–05060 B−1 UTE 37.034 −108.821 NAD83 na 675 —

05–083–05065 368 STRAT TEST VA 37.027 −108.852 NAD83 na 515 —

05–083–05068 367 STRAT TEST VA 37.042 −108.834 NAD83 na 667 —

05–083–05072 1 MESA A 37.051 −108.642 NAD83 na 2,360 —

05–083–05073 366 VA STRAT TEST 37.051 −108.822 NAD83 na 720 —

05–083–05081 6 UTE MOUNTAIN TRIBAL 37.067 −108.834 NAD83 na 645 —
70 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

Table 1.2. Description of wells used for determining lithology and depth to the top of the Dakota Sandstone on the Ute Mountain Ute 

Reservation in Colorado.—Continued

[LatitudeDD, latitude in decimal degrees; LongitudeDD, longitude in decimal degrees; DatumDD, datum for decimal degrees; NAD83, North American Datum 

of 1983; na, not applicable; —, no data; No., number; S, section; T, township; N, north; R, range; W, west; ffnl, feet from north line; ffwl, feet from west line; 

ffsl, feet from south line; ffel, feet from east line; SW, southwest; NW, northwest; NE, northeast; SE, southeast; USGS, U.S. Geological Survey; NGVD29, 

National Geodetic Vertical Datum of 1929]

Well

identifier

Well

name

Latitude

DD

Longitude

DD

Datum

DD

Township

and range

Depth to top 

of Dakota 

Sandstone

(feet below 

land surface 

datum)

Altitude

datum

05–083–05084 1 MARIANNA WASH 37.078 −108.963 NAD83 na 184 —

05–083–05089 1 UTE MOUNTAIN TRIBAL 37.085 −108.785 NAD83 na 877 —

05–083–05097 1 UTE TRIBAL 37.096 −108.907 NAD83 na 410 —

05–083–05103 D−1 UTE MOUNTAIN INDIAN 37.111 −108.967 NAD83 na 413 —

05–083–05118 1 UTE 37.114 −108.393 NAD83 na 3,220 —

05–083–05125 4 UTE 37.121 −108.803 NAD83 na 714 —

05–083–05141 2 PORTER 37.231 −108.665 NAD83 na 912 —

05–083–05159 1 HARE 37.255 −108.311 NAD83 na 1,474 —

05–083–05177 24−14X MENEFEE MOUNTAIN 

UNIT

37.284 −108.255 NAD83 na 1,882 —

05–083–05182 1 WILBURN 37.298 −108.363 NAD83 na 854 —

05–083–05184 1 WILLBURN (DAY) 37.300 −108.369 NAD83 na 715 —

05–083–05214 1 STEPHANSON 37.337 −108.402 NAD83 na 745 —

05–083–05222 1 HALLER 37.343 −108.411 NAD83 na 515 —

05–083–05225 2 STEPHANSON 37.345 −108.394 NAD83 na 645 —

05–083–05328 2 PHILMO UTE 37.002 −108.690 NAD83 na 1,746 —

05–083–05356 1 UTE TRIBE 37.003 −108.476 NAD83 na 2,721 —

05–083–05402 1 UTE MTN TRIBAL B 37.102 −108.943 NAD83 na 350 —

05–083–05419 1 LEE W & JAMES C SHEEK 37.269 −108.363 NAD83 na 1,200 —

05–083–06016 1 UTE 37.126 −108.694 NAD83 na 1,485 —

05–083–06027 1 FEDERAL 37.240 −108.281 NAD83 na 1,660 —

05–083–06040 1 MOBIL UTE 37.033 −108.970 NAD83 na 196 —

05–083–06134 1 CITIES SERVICE-FEE 37.330 −108.393 NAD83 na 570 —

05–083–06152 1 BEARD-FEDERAL 37.335 −108.398 NAD83 na 555 —

05–083–06170 3 BEARD-FEDERAL 37.326 −108.367 NAD83 na 470 —

05–083–06178 1 LEULLAN 37.319 −108.388 NAD83 na 815 —

05–083–06192 14–24 UTE MOUNTAIN 37.172 −108.325 NAD83 na 3,198 —

05–083–06276 4 DOERFER 37.301 −108.298 NAD83 na 1,275 —

05–083–06316 2 LEE RATTLER 37.337 −108.495 NAD83 na 70 —

05–083–06317 3 SHEEK 37.282 −108.365 NAD83 na 1,000 —

05–083–06318 2 SHEEK 37.284 −108.368 NAD83 na 985 —

05–083–06319 4 SHEEK 37.295 −108.367 NAD83 na 1,015 —

05–083–06320 1 LUELLEN 37.306 −108.372 NAD83 na 730 —

05–083–06351 1–3 STATE HINDMARSH 37.327 −108.482 NAD83 na 260 —

05–083–06352 1–2 STATE HINDMARSH 37.326 −108.469 NAD83 na 305 —
Appendix 1 71

Table 1.2. Description of wells used for determining lithology and depth to the top of the Dakota Sandstone on the Ute Mountain Ute 

Reservation in Colorado.—Continued

[LatitudeDD, latitude in decimal degrees; LongitudeDD, longitude in decimal degrees; DatumDD, datum for decimal degrees; NAD83, North American Datum 

of 1983; na, not applicable; —, no data; No., number; S, section; T, township; N, north; R, range; W, west; ffnl, feet from north line; ffwl, feet from west line; 

ffsl, feet from south line; ffel, feet from east line; SW, southwest; NW, northwest; NE, northeast; SE, southeast; USGS, U.S. Geological Survey; NGVD29, 

National Geodetic Vertical Datum of 1929]

Well

identifier

Well

name

Latitude

DD

Longitude

DD

Datum

DD

Township

and range

Depth to top 

of Dakota 

Sandstone

(feet below 

land surface 

datum)

Altitude

datum

05–083–06353 1−1 STATE 37.323 −108.453 NAD83 na 510 —

05–083–06354 1–36 STATE 37.328 −108.462 NAD83 na 345 —

05–083–06363 3 MONTEZUMA REVENGE 37.331 −108.364 NAD83 na 455 —

05–083–06394 1−1 FEDERAL 37.324 −108.461 NAD83 na 470 —

05–083–06414 1–30 FEDERAL 37.343 −108.433 NAD83 na 505 —

05–083–06463 30−12 COYOTE WASH 37.163 −108.961 NAD83 na 132 —

05–083–06475 6−11 BADGER 37.140 −108.743 NAD83 na 804 —

05–083–06476 23–32 NIGHTHAWK 37.093 −108.771 NAD83 na 932 —

05–083–06493 6–22 UTE MOUNTAIN TRIBAL 37.050 −108.739 NAD83 na 1,192 —

05–083–06495 31−13 CANYON 37.059 −108.636 NAD83 na 1,660 —

05–083–06498 23–43 NIGHTHAWK 37.089 −108.768 NAD83 na 932 —

05–083–06551 BB 1 STATE - ODOM 37.290 −108.294 NAD83 na 1,200 —

05–083–40032 — 37.002 −108.861 NAD83 na 560 —

New Mexico Oil Conservation Division2

30–045−10963 PRE-ONGARD WELL No. 001 — — — S 10, T 31 N, R 19 W, 1650 ffnl,

1650 ffwl

834 —

30–045−11022 PRE-ONGARD WELL No. 001 — — — S 1, T 31 N, R 16 W, 1650 ffsl,

990 ffel 3,363 —

30–045−11065 PRE-ONGARD WELL No. 001 — — — S 3, T 31 N, R 16 W, 2310 ffsl,

1650 ffwl

2,340 —

30–045−11120 PRE-ONGARD WELL No. 001 — — — SW S 31, T 32 N, R 15 W, 990 ffsl, 

910 ffwl of sec 31

3,345 —

30–045−11151 PRE-ONGARD WELL No. 001 — — — S 36, T 32 N, R 18 W, 660 ffsl,

660 ffwl

1,480 —

30–045−11188 PRE-ONGARD WELL No. 001 — — — SW NW S 32, T 32 N, R 18 W, 

1980 ffnl, 660 ffwl of S 32

1,425 —

30–045−11276 PRE-ONGARD WELL No. 001 — — — S 25, T 32 N, R 18 W, 2510 ffnl, 

1980 ffel

1,544 —

30–045−11322 UTE No. 007 — — — NE SW S 19, T 32 N, R 14 W, 

1685 ffsl, 1945 ffwl of sec 19

2,846 —

30–045−11328 PRE-ONGARD WELL No. 001 — — — SE SW S 20, T 32 N, R 13 W, 660 

ffsl, 1980 ffwl of sec 20

3,215 —

30–045−11332 PRE-ONGARD WELL No. 001 — — — S 21, T 32 N, R 19 W, 660 ffsl,

660 ffel 735 —

30–045−11392 PRE-ONGARD WELL No. 001 — — — S 14, T 32 W, R 16? W, 800ffsl, 

890 ffel

3,312 —

30–045−11413 PRE-ONGARD WELL No. 001 — — — S 15, T 32 N, R 15 W, 1650 ffsl, 

790 ffwl of sec 15

3,252 —

30–045−11469 PRE-ONGARD WELL No. 001 — — — S 17, T 32N, R 18 W, 1980 ffnl, 

660 ffwl

940 —

30–045−11476 PRE-ONGARD WELL No. 001 — — — S 13, T 32 N, R 17 W,990 ffnl, 

1980 ffwl

3,330 —

30–045−11479 UTE No. 004 — — — S 10, T 32 N, R 14 W, 510 ffsl, 

2030 ffwl

3,150 —
72 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

Table 1.2. Description of wells used for determining lithology and depth to the top of the Dakota Sandstone on the Ute Mountain Ute 

Reservation in Colorado.—Continued

[LatitudeDD, latitude in decimal degrees; LongitudeDD, longitude in decimal degrees; DatumDD, datum for decimal degrees; NAD83, North American Datum 

of 1983; na, not applicable; —, no data; No., number; S, section; T, township; N, north; R, range; W, west; ffnl, feet from north line; ffwl, feet from west line; 

ffsl, feet from south line; ffel, feet from east line; SW, southwest; NW, northwest; NE, northeast; SE, southeast; USGS, U.S. Geological Survey; NGVD29, 

National Geodetic Vertical Datum of 1929]

Well

identifier

Well

name

Latitude

DD

Longitude

DD

Datum

DD

Township

and range

Depth to top 

of Dakota 

Sandstone

(feet below 

land surface 

datum)

Altitude

datum

30–045−13183 PRE-ONGARD WELL No. 001 — — — NW NW S 4, T 31 N, R 18 W, 660 

ffnl, 660 ffwl of S 4

1,428 —

30–045−13193 PRE-ONGARD WELL No. 001 — — — NW NW S 33, T 32 N, R 19 W, 660 

ffnl, 660 ffwl of S 33

642 —

30–045–20043 PRE-ONGARD WELL No. 002 — — — S 30 T 32 N, R 17 W, 2310 ffsl, 670 

ffel

2,255 —

30–045–20354 PRE-ONGARD WELL No. 001 — — — S 36, T 32 N, R 18 W, 990 ffnl, 990 

ffel

1,658 —

30–045–20364 PRE-ONGARD WELL No. 001 — — — S 32, T 32 N, R 19 W, 660 ffsl, 

1980 ffwl

618 —

30–045–20389 PRE-ONGARD WELL No. 001 — — — S 25, T 32 N, R 18 W, 330 ffsl,

1610 ffwl

1,569 —

30–045–20570 PRE-ONGARD WELL No. 002 — — — S 14, T 32 N, R 15 W, 1980 ffsl, 

660 ffel 3,242 —

30–045–20658 PRE-ONGARD WELL No. 003 — — — S 14, T 32 N, R 15 W, 2190 ffnl, 

900 ffwl 3,265 —

30–045–20692 PRE-ONGARD WELL No. 001 — — — S 31, T 32 N, R 17 W, 650 ffnl, 

1549 ffwl 1,610 —

30–045–22179 PRE-ONGARD WELL No. 001 — — — S 35, T 32 N, R 16 W, 1980 ffsl, 

1980 ffwl 3,555 —

30–045–23003 PRE-ONGARD WELL No. 001 — — — NW NE S 27, T 32 N, R 15 W, 

1175 ffnl, 1650 ffel 2,939 —

30–045–23237 PRE-ONGARD WELL No. 001 — — — S 13, T 32 N, R 14 W, 1840 ffsl, 

1180 ffwl 3,134 —

30–045–23542 PRE-ONGARD WELL No. 001 — — — S 26, T 32 N, R 15 W, 1160 ffnl, 

790 ffel 3,218 —

30–045–29262 UTE COM No. 025 — — — S 19, T 32 N, R 14 W, 475 ffsl, 

1415 ffwl 3,196 —

30–045–29264 PRE-ONGARD WELL No. 026 — — — S 18, T 32 N, R 14 W, 1270 ffnl, 

655 ffel 2,540 —

30–045–29265 UTE COM No. 023 36.976 −108. 34693 — na 2,550 —

30–045–29395 UTE No. 022 36.990 −108. 32944 — na 2,403 —

30–045–29547 UTE MOUNTAIN UTE No. 051 36.985 −107. 28000 — na 3,117 —

30–045–33760 UTE INDIANS B No. 001 — — — S 13 T 32 N, R 14 W, 793 ffnl, 

885 ffwl 3,024 —

30–045–34471 UTE MOUNTAIN UTE No. 078 — — — SE SW S 16, T 32 N, R 14 W, 

1075 ffsl, 1340 ffwl 2,406 —

30–045–34488 UTE MOUNTAIN UTE No. 084 — — — NW SE NW S 29, T 32 N, R 14 W, 

1330 ffnl, 1465 ffwl 2,454 —

U.S. Geological Survey, Irwin (1966)3

370518108540601 NB03301922ADCB A–4 37.092 −108.896 NAD83 na 546 NGVD29

370612108424001 NB03301716BCCC B–7 37.106 −108.710 NAD83 na 1,258 NGVD29

370717108532501 NB03301911BBBB A–3 37.126 −108.891 NAD83 na 659 NGVD29

370806108485801 NB03301804BCDA A−1 37.135 −108.815 NAD83 na 722 NGVD29

371006108530402 NB33501926ABBB2 B–6 37.169 −108.882 NAD83 na 275 NGVD29

371112108443401 NB33501718CCAC B−10 37.188 −108.743 NAD83 na 328 NGVD29
Appendix 1 73

Table 1.2. Description of wells used for determining lithology and depth to the top of the Dakota Sandstone on the Ute Mountain Ute 

Reservation in Colorado.—Continued

[LatitudeDD, latitude in decimal degrees; LongitudeDD, longitude in decimal degrees; DatumDD, datum for decimal degrees; NAD83, North American Datum 

of 1983; na, not applicable; —, no data; No., number; S, section; T, township; N, north; R, range; W, west; ffnl, feet from north line; ffwl, feet from west line; 

ffsl, feet from south line; ffel, feet from east line; SW, southwest; NW, northwest; NE, northeast; SE, southeast; USGS, U.S. Geological Survey; NGVD29, 

National Geodetic Vertical Datum of 1929]

Well

identifier

Well

name

Latitude

DD

Longitude

DD

Datum

DD

Township

and range

Depth to top 

of Dakota 

Sandstone

(feet below 

land surface 

datum)

Altitude

datum

371115108432001 NB33501717CCA B−18 37.187 −108.723 NAD83 na 560 —

371152108435401 NB33501718ABA B−17 37.198 −108.732 NAD83 na 260 —

371159108434801 NB33501707UDDC B−16 37.200 −108.731 NAD83 na 273 —

371217108435701 NB33501707UDBA B−13 37.205 −108.733 NAD83 na 220 —

371218108433301 NB33501708CBB B−19 37.205 −108.726 NAD83 na 320 —

371248108402201 NB33501703DDDA A–9 37.216 −108.674 NAD83 na 986 NGVD29

1

Colorado Oil and Gas Conservation Commision data are from Colorado Oil and Gas Conservation Commision (2016). Well identifier is the Colorado Oil 

and Gas Conservation Commision Well API. On the Commission website https://cogcc.state.co.us/data.html, select "Facility" under "Inquiry". On the "Facility 

Inquiry" page, using well 9 Ute as an example, type 67 as the county code and type 5148 as the sequence code. After entering, select "Well" to obtain well information. Well name is from the Colorado Oil and Gas Conservation Commision (2016).

2

Well identifier is the New Mexico Oil Conservation Division API number (New Mexico Oil Conservation Division, 2016). Well name is from the New 

Mexico Oil Conservation Division (2016).

3

Well identifier and well name for the USGS, Irwin (1966) wells are the National Water Information System site number and site name, respectively (USGS, 

2016b).
74 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

Appendix 2. Supplemental Information for Data-Quality Assurance

This appendix contains supplemental information for 

data-quality assurance. Included is information for duplicate 

sample results, zero values, inconsistent results, data outliers, data pairs with total and dissolved concentrations for the 

same constituent in a sample, field blanks, field replicates, and 

cation-anion balance percent difference for samples collected 

by the Ute Mountain Ute Tribe (UMUT). Data for field blanks 

and field replicates were not available for the historical U.S. 

Geological Survey, National Uranium Resource Evaluation, 

and Colorado Oil and Gas Conservation Commission data. 

Groundwater-chemistry data were first checked for duplicate sample results, zero values, inconsistent results, and outliers. The duplicated sample results were excluded; the same 

analytical result for one of two samples collected on the same 

date was excluded. Select chemical data with a reported result 

of zero also were excluded from analysis if the meaning of the 

zero value could not be determined. Zero values were retained 

if the laboratory reported limit for a concentration was a zero 

value or were changed to the known laboratory reporting limit, 

described as a “less-than” value or concentration. Zero values 

for physical properties such as specific conductance and pH 

were assumed erroneous and were excluded. Inconsistent 

results, such as specific conductance values of 150 microsiemens per centimeter at 25 degrees Celsius or less for Lagoon 

1 wells 1 and 3 that were not consistent with related total 

dissolved solids (TDS) concentrations of 3,400 milligrams per 

liter (mg/L) or more for the same sample, were excluded from 

analysis. Data from multiple samples of a constituent at a site 

were checked for outliers, and extreme outliers were excluded 

from analysis. For example, a TDS concentration of 66 mg/L 

for a sample from Navajo Spring was excluded because all 

other reported TDS concentrations for the spring ranged from 

747 to 1,272 mg/L. 

Of the trace-element data pairs collected by the UMUT, 

40 contained total and dissolved concentrations of the same 

chemical constituent. Because a total concentration should be 

greater than a dissolved concentration, a comparison of the two 

concentrations for each data pair was used as a check on data 

quality. These data were evaluated by calculating the relative 

percent difference of concentrations for each data pair (RPDtd) 

using equation 2.1 (modified from Mueller and others [2015], 

p. 40, table 47): 

RPDtd = ABS[(total result – dissolved result)/

 ((total result + dissolved result) /2)] x 100, (2.1)

where

RPDtd is the relative percent difference of 

concentrations for each data pair, and 

ABS is the absolute value.

The total concentration was less than the dissolved concentration in about 18 percent (7 of 40) of the trace-element 

data pairs. For six of the data pairs, total concentrations were 

substantially less than dissolved concentrations; the RPDtd

values ranged from 27.4 to 81.3 percent. Each of these data 

pairs was excluded for analysis, including total and dissolved 

concentrations of arsenic, manganese, nickel, selenium, and 

zinc for Lagoon 1 well 1 and selenium for Lagoon 1 well 3. 

Field-blank data were only available for samples collected by the UMUT. Field-blank samples were processed 

using inorganic- or organic-free water that contained no 

detectable concentrations of the constituents of interest. The 

blank water was processed through the same sampling equipment and handled and analyzed in the same manner as the 

environmental samples. Data for field blanks retrieved from 

the National Water Quality Monitoring Council Water Quality Portal were collected at three springs and eight wells, and 

included data for physical properties (alkalinity, hardness), 

major ions, nutrients, trace elements, pesticides, volatile 

organic compounds, and coliform bacteria (National Water 

Quality Monitoring Council, 2017). Field-blank samples 

with concentrations greater than laboratory reporting limits were collected from one spring (Whiskers Draw Spring) 

and four wells (AP–14, AP–15, Lagoon 1 well 3, and Wing 

well) (table 2.1). Detected constituents in field-blank samples 

included TDS, nitrate plus nitrite, total phosphate, manganese, 

nickel, selenium, zinc, and alachlor (table 2.1). Concentrations 

of unfiltered nitrate plus nitrite (0.02 mg/L), total phosphate 

(0.082 mg/L), unfiltered selenium (1 microgram per liter 

[μg/L]), dissolved zinc (5.8 μg/L), and unfiltered zinc (7 μg/L) 

in field blanks were substantially lower than paired environmental concentrations (9 mg/L, 0.886 mg/L, 15.2 μg/L, 

11.5 μg/L, and 32 μg/L, respectively), and the field-blank 

detections would not affect interpretation of environmental 

data. Concentrations of dissolved manganese and dissolved 

nickel (0.5 μg/L for each) in one field-blank sample also were 

less than the environmental sample concentrations of 1 and 

1.4 μg/L, respectively. These blank detections could affect 

interpretation of environmental data for the sample, and the 

environmental concentrations were subsequently excluded 

from analysis because of replicate-sample results. Detections of TDS (24 mg/L), unfiltered selenium (2.4 μg/L), and 

alachlor (0.3 μg/L) in field blanks could not be evaluated; no 

environmental samples were collected at the same site and 

date. A detected concentration of dissolved zinc in a field 

blank is described in the “Groundwater Chemistry” section.

Replicate data were only available for samples collected 

by the UMUT. By comparing the analytical results of the first 

sample (environmental concentration) with the second sample 

(replicate concentration), replicate data provide information on 

the variability in constituent detection and concentration. For 

the 185 replicate pairs, both the environmental and replicate 

concentrations were greater than the laboratory reporting limit 

in 105 pairs and less than the laboratory reporting limit in 

63 pairs, and 17 pairs had inconsistent detections (a detected 

concentration and a concentration less than the laboratory 
Table 2.1. Select quality-assurance data for field-blank samples collected by the Ute Mountain Ute Tribe for springs and wells on the Ute Mountain Colorado and Utah, 2001–13.[Detected concentrations are in bold. fig., figure; ID, identification; dis, dissolved; mg/L, milligrams per liter; unfil, unfiltered; N, nitrogen; P, phosphorus; μg/L, micrograms per no data; <, less than]

Site

(see fig. 5, site ID

in parentheses

is used on figure)

Site

type

Sample

date

Total dis

solids

(mg/L)

Nitrate plus 

Nitrite, unfil

(mg/L as N)1

Phosphate, 

total

(mg/L as P)

Manganese, dis

 (μg/L)

Nickel, dis

(μg/L)

Selenium, 

unfil trec

(μg/L)

Zinc, dis

(μg/L)

Whiskers Draw Spring (S13)2 Spring 8/28/2013 — <0.01 0.082 <0.4 — <0.4 5.8 AP–14 Well 10/31/2001 — — — — — — — AP–15 Well 7/25/2011 24 <0.6 — — — 2.4 — Lagoon 1 well 3 (W13) Well 9/15/2010 <10 — — 0.5 0.5 <1 9 Wing well (W23) Well 7/22/2003 — — — — — 1 — Wing well (W23) Well 8/16/2012 <10 0.02 — — — <1 — 

1Includes "Inorganic nitrogen (nitrate and nitrite), total."2Spring is shown on figure 1.
76 Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation

reporting limit). All concentrations for pesticide and volatile 

organic compound replicate pairs were less than laboratory 

reporting limits.

When a sufficient number of replicate pairs have been 

collected for a particular constituent over a range of concentrations, variability in constituent concentration can be estimated 

using a two-range model—the mean standard deviation for 

replicate pairs with low concentrations and the mean relative 

percent difference for replicate pairs with high concentrations 

(Mueller and others, 2015). The standard deviation over a 

range of low concentrations generally is constant but increases 

at higher concentrations (Mueller and others, 2015), which 

can overestimate variability. For example, a replicate pair with 

concentrations of total phosphorus of 0.20 and 0.29 mg/L has 

a standard deviation of 0.04 and a relative percent difference 

of the replicate pairs (RPDrep) of 37 percent. For a range of 

high concentrations, the RPDrep is generally constant (Mueller and others, 2015). Eight replicate pairs had RPDrep values 

greater than (>) 100 percent. Environmental concentrations for 

seven pairs were excluded from analysis, including carbonate, unfiltered lead, and dissolved chromium for Toe Windmill 

(sample date September 2016); dissolved barium for LF well 

1 (March 2009); and unfiltered iron, dissolved manganese, and 

dissolved nickel for Lagoon 1 well 3 (September 15, 2010). 

For the Hanna Spring sample collected in May 2015, the unfiltered iron concentration of 82 μg/L was retained for analysis 

because it was similar to other report unfiltered iron concentrations for the spring. 

For this report, charge-balance differences of less 

than 5 percent were deemed acceptable, and the data were 

retained for analysis. Only 3 of 34 well samples had chargebalance differences of >10 percent. Differences of 11.7 and 

11.4 percent for wells AP–5 and AP–14, respectively, may 

reflect analytical precision at the time of same collection in 

2000 or 1999, respectively. The difference of 51.7 percent for 

a Mariano-FW well sample collected in 2013 reflected a much 

larger cation sum (27.3 milliequivalents [meq]) than the anion 

sum (8.7 meq). This is the only sample collected at the well, 

so it is not known why the difference is so large. Nine samples 

had charge-balance differences between 5 and 10 percent, four 

of which had TDS concentrations >2,300 mg/L, and three 

of which had a total cation-anion sums of less than 5.0 meq 

per liter. Hem (1985) reports that water with TDS values 

>1,000 mg/L tend to have a few constituents with high concentrations. For such water, the charge-balance difference does 

not adequately account for constituents with lower concentrations (Hem, 1985), which can skew the accuracy determination. Hem (1985) also reports that charge-balance differences 

of more than a few percentages for samples with total sums of 

less than 5.0 meq per liter are acceptable. All major-ion data 

collected by the UMUT were retained for analysis.
Publishing support provided by the Science Publishing Network, 

Denver Publishing Service Center

For more information concerning the research in this report, contact the

Director, USGS Colorado Water Science Center

Box 25046, Mail Stop 415

Denver, CO 80225

(303) 236-4882

Or visit the Colorado Water Science Center website at

https://co.water.usgs.gov/
Bauch and Arnold—Hydrogeologic Characterization, Groundwater Chemistry, and Vulnerability Assessment, Ute Mountain Ute Reservation—SIR 2019–5122

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20195122