Nitrate and Ammonia in Shallow Ground Water, 

Carson City Urban Area, Nevada, 1989

A product of the 

National Water-Quality 

Assessment Program 

Carson River Basin, 

Nevada and California

UNITED STATES GEOLOGICAL SURVEY 

Water-Resources Investigations Report 96-4224

NATIONAL WATER - QUALITY ASSESSMENT PROGRAM
Nitrate and Ammonia in Shallow Ground Water, 

Carson City Urban Area, Nevada, 1989 

By STEPHEN J. LAWRENCE 

U.S. GEOLOGICAL SURVEY 

Water-Resources Investigations Report 96-4224 

A product of the 

National Water-Quality 

Assessment ProgramCarson River Basin, 

Nevada and California 

Carson City, Nevada 

1996 
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

GORDON P. EATON, Director

Any use of trade names in this publication is for descriptive purposes 

only and does not constitute endorsement by the U.S. Government

For additional information Copies of this report can be

write to: purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

333 West Nye Lane, Room 203 Box 25286

Carson City, NV 89706-0866 Denver, CO 80225-0286
FOREWORD

The mission of the U.S. Geological Survey 

(USGS) is to assess the quantity and quality of the 

earth resources of the Nation and to provide information that will assist resource managers and policymakers at Federal, State, and local levels in making sound 

decisions. Assessment of water-quality conditions and 

trends is an important part of this overall mission.

One of the greatest challenges faced by waterresources scientists is acquiring reliable information 

that will guide the use and protection of the Nation's 

water resources. That challenge is being addressed by 

Federal, State, interstate, and local water-resource 

agencies and by many academic institutions. These 

organizations are collecting water-quality data for a 

host of purposes that include: compliance with permits 

and water-supply standards; development of remediation plans for specific contamination problems; operational decisions on industrial, wastewater, or watersupply facilities; and research on factors that affect 

water quality. An additional need for water-quality 

information is to provide a basis on which regionaland national-level policy decisions can be based. Wise 

decisions must be based on sound information. As a 

society we need to know whether certain types of 

water-quality problems are isolated or ubiquitous, 

whether there are significant differences in conditions 

among regions, whether the conditions are changing 

over time, and why these conditions change from 

place to place and over time. The information can be 

used to help determine the efficacy of existing waterquality policies and to help analysts determine the 

need for and likely consequences of new policies.

To address these needs, the U.S. Congress appropriated funds in 1986 for the USGS to begin a pilot program in seven project areas to develop and refine the 

National Water-Quality Assessment (NAWQA) Program. In 1991, the USGS began full implementation of 

the program. The NAWQA Program builds upon an 

existing base of water-quality studies of the USGS, as 

well as those of other Federal, State, and local agencies. 

The objectives of the NAWQA Program are to:

 Describe current water-quality conditions 

for a large part of the Nation's freshwater 

streams, rivers, and aquifers.

 Describe how water quality is changing 

over time.

 Improve understanding of the primary 

natural and human factors that affect 

water-quality conditions.

This information will help support the development 

and evaluation of management, regulatory, and monitoring decisions by other Federal, State, and local 

agencies to protect, use, and enhance water resources.

The goals of the NAWQA Program are being 

achieved through ongoing and proposed investigations 

of 60 of the Nation's most important river basins and 

aquifer systems, which are referred to as study units. 

These study units are distributed throughout the 

Nation and cover a diversity of hydrogeologic settings. More than two-thirds of the Nation's freshwater 

use occurs within the 60 study units and more than 

two-thirds of the people served by public water-supply 

systems live within their boundaries.

National synthesis of data analysis, based on 

aggregation of comparable information obtained from 

the study units, is a major component of the program. 

This effort focuses on selected water-quality topics 

using nationally consistent information. Comparative 

studies will explain differences and similarities in 

observed water-quality conditions among study areas 

and will identify changes and trends and their causes. 

The first topics addressed by the national synthesis are 

pesticides, nutrients, volatile organic compounds, and 

aquatic biology. Discussions on these and other waterquality topics will be published in periodic summaries 

of the quality of the Nation's ground and surface water 

as the information becomes available.

This report is an element of the comprehensive 

body of information developed as part of the NAWQA 

Program. The program depends heavily on the advice, 

cooperation, and information from many Federal, 

State, interstate, Tribal, and local agencies and the 

public. The assistance and suggestions of all are 

greatly appreciated.

Robert M. Hirsch 

Chief Hydrologist
CONTENTS

Abstract ........................................................................................................................_^ 1

Introduction ......................................................................................................................^ 1

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

Acknowlegdments ..................................................................................................................................................... 3

Environmental Setting .......................................................................................................................................................... 3

Physical Setting, Population, and Climate ............................................................................................................... 3

Soils ..........................................................................._^ 5

Hydrogeology............................................................................................................................................................ 5

Nitrogen Cycle in Natural and Stressed Systems ................................................................................................................. 9

Methods Used in the Study ................................................................................................................................................... 10

Well Construction .....................................................................................................................................................^ 10

Sampling Methods .................................................................................................................................................... 11

Statistical Analysis of Water-Quality Data ............................................................................................................... 11

General Ground-Water Quality ............................................................................................................................................. 13

Nitrate and Ammonia in Shallow Ground Water.................................................................................................................. 18

Areal and Temporal Differences in Nitrate Concentrations ...................................................................................... 18

Areal and Temporal Differences in Ammonia Concentrations ................................................................................. 20

Relations Among Nitrate, Ammonia, and Other Properties and Constituents .......................................................... 22

Areal Relations Among Nitrate, Ammonia, and Other Properties and Constituents ................................................ 27

Relations Among Nitrate, Ammonia, and Well Depth .............................................................................................. 31

Summary ...........................................................................................................................^^ 31

References Cited .................................................................................................................................................................. 34

Appendix............................................................................................................ ^ 37

Figures

1-3. Maps of Carson City, Nev., urban study area showing:

1. Location of study area............................................................................................................................. 4

2. Well locations, water-table altitudes, and generalized direction of ground-water flow,

January-March 1989................................................................................................................................ 6

3. Depth to ground water, January-March 1989.......................................................................................... 8

4. Diagram of nitrogen cycle...................................................................................................................................... 9

5-7. Maps showing areal distribution of:

5. Specific conductance in shallow ground water, January-March 1989..................................................... 14

6. Nitrate concentrations in shallow ground water for January-March and May-June 1989 ...................... 19

7. Ammonia concentrations in shallow ground water for January-March and May-June 1989.................. 21

8-9. Graphs showing:

8. Principal component loadings (varimax rotation) for hydrologic properties and chemical

constituents at shallow wells, January-March and May-June 1989 ........................................................ 24

9. Relation between dissolved-oxygen concentrations and sample scores for principal

components............................................................................................................................................. 26

10-11, Maps showing estimated areal distribution of sample scores for principal components in shallow ground 

water, January-March 1989:

10. Principal components 1 (carbonate dissolution) and 2 (evaporite dissolution)....................................... 29

11. Principal component 3 (nitrification or denitrification/nitrate reduction)................................................ 30

12. Graph showing relations between well depth and nitrate, trichloroethylene, ammonia, dissolved-oxygen, 

dissolved-iron, and dissolved-manganese concentrations and specific conductance for wells a, b, c, and d 

at well cluster 13, January-March and May-June 1989......................................................................................... 32

CONTENTS Mi
Tables

1. Land-surface altitude, well depth, and water-level data, Carson City, Nev., urban study area,

January-March and May-June 1989....................................................................................................................... 7

2. Water-quality data from shallow wells, 1989......................................................................................................... 15

3. Robust multiple-regression equations for water-quality constituents in shallow ground water,

January-March and May-June 1989...................................................................................................................... 23

4. Loading coefficients from a varimax-rotated principal components analysis of rank-transformed

well-depth and water-quality measurements at shallow ground-water sampling sites.......................................... 25

5. Principal component sample scores calculated for shallow ground-water samples, Carson City, Nev.,

urban study area..................................................................................................................................................... 28

CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATED UNITS

Multiply By To obtain

foot (ft) 0.3048 meter

inch (in.) 25.4 millimeter

mile (mi) 1.609 kilometer

square mile (mi2) 2.590 square kilometer

Temperature: Degrees Celsius (°C) can be converted to degrees Fahrenheit (°F) by using the formula °F = [1.8(°C)]+32. Degrees Fahrenheit 

(°F) can be converted to degrees Celsius (°C) by using the formula °C = 0.556(°F-32).

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929, formerly called "Sea-Level 

Datum of 1929"), which is derived from a general adjustment of the hrst-order leveling networks of the United States and Canada.

Abbreviated water-quality units:

Ug/L (microgram per liter) Um (micrometer) 

uS/cm (microsiemens per centimeter at 25 °C) mL (milliliter) 

mg/L (milligram per liter)

iv Nitrate and Ammonia in Shallow Ground Water, Carson City Urban Area, Nevada, 1989
Nitrate and Ammonia in Shallow Ground Water, 

Carson City Urban Area, Nevada, 1989

By Stephen J. Lawrence 

Abstract

As part of the National Water-Quality 

Assessment program (NAWQA) of the 

U.S. Geological Survey, a network of 26 wells at 

20 sites was established in 1989 to investigate the 

quality of shallow ground water beneath the oldest 

and most developed part of the Carson City urban 

area. Nitrate was detected in water samples from 

16 of the sites. The nitrate, as nitrogen, concentration was between 0.1 and 3.0 mg/L (milligrams per 

liter) at four sites, greater than 3.0 mg/L but less 

than 10 mg/L at six sites, and 10 mg/L, the Nevada 

drinking-water standard, or greater, at six sites; the 

highest concentration measured during the study 

was 38 mg/L. Ammonia, as nitrogen, concentrations exceeded 0.15 mg/L at 2 of the 20 sites; the 

highest concentration detected during the study 

was 0.26 mg/L. Nitrate concentrations were positively correlated with dissolved-oxygen concentrations, and negatively correlated with ammonia, 

dissolved-iron, and dissolved-manganese concentrations. Ammonia concentrations were positively 

correlated with calcium, magnesium, potassium, 

bicarbonate, iron, manganese, strontium, and dissolved organic carbon concentrations, and were 

negatively correlated with nitrate and dissolvedoxygen concentrations. Principal components 

analysis identified five groups of water-quality 

constituents that suggest that the ammonia or 

nitrate source might be nitrogen-based fertilizers, 

septic systems, or leaking municipal sewer lines, 

and that nitrification and denitrification, or nitrate 

reduction, control nitrate and ammonia concentrations as well as dissolved-oxygen, iron, and manganese concentrations in the shallow ground water 

beneath the Carson City urban area.

INTRODUCTION

Nitrogen is present in various forms throughout 

the natural environment and is needed to sustain biological life. Biological processes are dependent on an 

abundant and usable supply of nitrogen because nitrogen is a vital component of genetic material, proteins, 

and enzymes. Nitrate (NO^ ) and ammonia (NH4 ) are 

the nitrogen forms most easily used by organisms. In 

this report, nitrate and ammonia concentrations are 

reported as N (nitrogen). NH4 is referred to as ammonia because the laboratory analytical procedure used 

for this study converted NH4 (ammonium) to NH3 

(ammonia) prior to analysis. Both forms are rapidly 

cycled through the biosphere by a complex series of 

transformations. Because of human activities related to 

agriculture and urbanization, however, the amounts of 

nitrate and ammonia produced can exceed the assimilative capacity of the environment. When this capacity 

is exceeded, nitrate can enrich or, if concentrations are 

higher than 10 mg/L, contaminate ground-water 

resources.

Every State in the United States has some part of 

its ground-water resource contaminated by nitrate. Furthermore, the number of contaminated wells is increasing rapidly across the country (Hallberg, 1989, p. 38, 

66). Extensive areas of nitrate-contaminated ground 

water exist in the northeastern part of the United States 

because of poultry manure, agricultural fertilizers, and 

a dense rural population that uses septic-tank systems. 

Contaminated ground water is found in the midwestern 

grain belt because of intensive agricultural use of 

ammonia fertilizers and in the southern Central Valley

Abstract 1
of California and parts of Texas because of fertilized 

crops coupled with widespread, intensive agricultural 

irrigation (Madison and Brunett, 1985).

By the early 1980's, water from 20 percent of all 

wells sampled in the United States contained nitrate 

concentrations greater than 3 milligrams per liter 

(mg/L), and samples from 6 percent had concentrations 

greater than 10 mg/L, as N (Madison and Brunett, 

1985). The maximum nitrate concentration recommended in drinking water supplies in the United States 

(U.S. Environmental Protection Agency, 1986a) and 

allowed in Nevada (Nevada Bureau of Health Protection Services, 1992) is 10 mg/L, as N. The 10 mg/L 

value is a conservative threshold designed to safeguard 

human health. One human-health problem related to 

high nitrate concentrations is "blue baby" disease 

(methemoglobinemia) in infants (U.S. Environmental 

Protection Agency, 1986b). Generally, infants younger 

than 1 year lack the enzyme in the intestinal tract that 

degrades nitrate. When nitrate is absorbed into the 

blood stream, hemoglobin in red-blood cells preferentially combines with nitrate rather than with dissolved 

oxygen and the body becomes oxygen deficient; hence, 

the name blue baby disease. Although uncommon, blue 

baby disease can be fatal (U.S. Environmental Protection Agency, 1986b). Moreover, nitrate is converted to 

nitrosamines in the intestinal tracts of adults and 

infants older than 1 year. Although this prevents blue 

baby disease, medical research has shown that high 

concentrations of nitrosamines are carcinogenic, 

mutagenic, and teratogenic to humans (U.S. Environmental Protection Agency, 1973).

As of 1985, about one-half of all waterborne illness in the United States was related to contaminated 

ground water (Yates, 1985). This contamination was 

most frequently traced to effluent from septic-tank systems (Yates, 1985). High nitrate or ammonia concentrations in ground water could indicate that an aquifer 

is contaminated with sewage effluent (LeBlanc, 1984; 

Canter and Knox, 1985; Hallberg, 1989; Wilhelm and 

others, 1994). Besides indicating possible sewage contamination, ammonia concentrations that exceed 0.2 

mg/L, as N, may cause objectionable taste and odor in 

ground water used for drinking (Hallberg, 1989).

Nitrate- and ammonia-contaminated ground 

water can discharge to and adversely affect rivers, 

lakes, and estuaries (surface water). One adverse effect 

is increased eutrophication caused by large increases in 

algae and plant biomass. Algae and aquatic plants in 

nitrogen-depleted water may grow rapidly when nitrate

and ammonia concentrations increase. Large increases 

in plant biomass can impair aesthetics and beneficial 

uses, and can disrupt ecological communities in surface water through changes in the pH and dissolvedoxygen regimes (Hynes, 1970, p. 48-49). The increase 

in primary production of algae in Chesapeake Bay is 

thought to be caused, in part, by high nitrate concentrations in the Columbia Aquifer, which discharges into 

some tributaries of Chesapeake Bay (Weil and others, 

1990).

Nitrate and ammonia in ground water are from 

three major sources: (1) natural (not affected by human 

activities); (2) agricultural; and (3) urban and domestic. 

Natural sources of nitrate and ammonia commonly 

result in nitrate concentrations less than 1 mg/L and 

ammonia concentrations less than about 0.05 mg/L 

(Hallberg, 1989, p. 66). Studies by Bormann and others 

(1968), Likens and others (1977, p. 102), Vitousek and 

Melillo (1979), Verry and Timmons (1982), and 

Lawrence and Wigington (1987) show that nitrogen 

cycling within undisturbed ecosystems is a conservative process. Most of the nitrogen entering the ecosystem is retained and cycled among various inorganic, 

organic, and biological compartments. As a result, 

nitrogen losses from undisturbed ecosystems are small. 

Although naturally elevated nitrate concentrations are 

uncommon in ground water, elevated nitrate in water 

samples from wells in Las Vegas Valley, Nev., may be 

from buried spring mounds containing large amounts 

of organic matter (Patt and Hess, 1976). Moreover, 

high nitrate concentrations in water-saturated soil cores 

from an unaltered alluvial fan in the eastern Mojave 

Desert, Calif., may be the result of natural processes 

during the Pleistocene or leaching of decomposed local 

volcanic rocks that contain high nitrate concentrations 

(Marrett and others, 1990). Natural nitrate concentrations between 3 and 6 mg/L and dissolved-oxygen concentrations greater than 4 mg/L (Whitney, 1994, table 

25) were measured in ground-water samples from 

wells deeper than 100 ft below land surface in Dayton 

and Churchill Valleys, Nev. Assuming a closed system, 

carbon-isotope methods estimated that this water was 

between 3,700 and 24,000 years old (Thomas and 

Lawrence, 1994, table 6).

Hallberg (1989, p. 36) states "research since the 

1970's has clearly shown that the most extensive source 

of nitrates to ground water and surface water worldwide is agriculture." Hallberg further states "considering the U.S. as a whole, nitrogen from fertilizers 

represents at least 60 percent of the total nitrogen

Nitrate and Ammonia in Shallow Ground Water, Carson City Urban Area, Nevada, 1989
applied to land if all the nitrogen from animal and poultry wastes were reclaimed and applied to land." A 

direct relation between nitrate concentration in ground 

water and rates of fertilizer application in agricultural 

areas has been shown by Hallberg (1989), Milburn and 

others (1990), and Weil and others (1990).

Nitrogen fertilizers and septic-tank effluent have 

contaminated shallow ground water in many urban 

areas including Long Island, N.Y. (Eckhardt and 

others, 1989), Michigan (D'ltri and others, 1985), 

and Minnesota (Komor and Anderson, 1993). High 

density septic-tank systems probably cause the high 

nitrate concentrations in shallow ground water near 

Topaz Lake, west-central Nevada (Nowlin, 1982) and 

in Washoe Valley, 15 mi. south of Reno, Nev. (Armstrong and Fordham, 1977).

Purpose and Scope

In 1986, the U.S. Geological Survey began a program to determine the current conditions and long-term 

trends in the quality of the Nation's water resources 

(Hirsch and others, 1988). One component of this program was to evaluate the effect of human activity on 

water quality. The program, known as the National 

Water-Quality Assessment (NAWQA), included a 

ground-water study in the Carson River Basin of westcentral Nevada (Welch and Plume, 1987). One aspect 

of this study was an examination of shallow groundwater quality beneath an urban area, Carson City, Nev., 

which is in the Carson River Basin. The study was 

completed in 1989 and encompassed the oldest part of 

the Carson City urban area and the uppermost part of 

the shallow aquifer beneath the city.

The purposes of this report are to (1) describe the 

areal and temporal distribution of nitrate and ammonia 

in shallow ground water beneath the Carson City urban 

area and (2) attempt to identify the source or sources of 

elevated concentrations of nitrate and ammonia. The 

report is based on data from a network of 26 shallow 

observation wells at 20 sites that was established 

within a small part of the Carson City urban area. A single well was constructed at each of eighteen sites. A 

clustered set of four nested wells was constructed at 

two additional sites. All single wells and the shallowest 

wells at both nested sites penetrated the upper 15 ft of 

saturated sediments in the basin-fill aquifer. Water from 

the 26 wells was sampled twice during the first 6 

months of 1989. Samples were analyzed for nitrate,

ammonia, major cations and anions, trace elements, 

volatile organic compounds, and dissolved organic carbon. Field measurements included depth to water table, 

pH, specific conductance, and dissolved oxygen. Data 

were interpreted using nonparametric statistics, robust 

multiple regression, and a factor analysis using principal components.

Acknowledgments

The author thanks the Nevada State Capital 

Building and Grounds Department, Nevada Department of Conservation and Natural Resources, Nevada 

Department of Transportation, Carson City Parks and 

Recreation Division, Carson City School District, 

Samuel Lompa, Paul Larquier, Homer Angelo, John 

Serpa, I.R. Anderson, Joseph Bensinger, and St. 

Theresa's Catholic Church for allowing the construction of observation wells on property they own or 

manage.

ENVIRONMENTAL SETTING

Physical Setting, Population, and Climate

Carson City is a small but rapidly expanding 

urban area in west-central Nevada, approximately 30 

mi south of Reno and 14 mi east of Lake Tahoe. The 

study area encompasses 13 mi2 of the most urbanized 

part of the city (fig. 1). The boundaries of the entire 

Carson City consolidated municipality enclose an area 

of 143.5 mi2 that includes Eagle Valley (71 mi2), parts 

of three adjacent basins, and a small part of the Sierra 

Nevada.

Eagle Valley is typical of the basin and range 

topography in Nevada. The area west of Carson City is 

the eastern escarpment of the Carson Range of the 

Sierra Nevada (maximum altitude, 9,214 ft above sea 

level). To the north of the city is the Virginia Range 

(maximum altitude, 5,297 ft) and to the east is the Pine 

Nut Mountains (maximum altitude, 7,629 ft). The 

southern hydrographic boundary is a subtle topographic high (maximum altitude, 5,000 ft). The altitude 

of the Carson City urban study area ranges from 4,760 

ft on the west to 4,600 ft on the east.

ENVIRONMENTAL SETTING
119°

EXPLANATION 

I Consolidated rocks

Basin-fill deposits

/y/y/ Carson City consolidated

^/^ municipality

&&&& Carson City urban study £

.. Boundary of Eagle Valley 

Hydrographic area

^^^V*\ /i 0 10 20 Kilometers

\ ) L STOREY / j.

iA/ACurn=Y( J / Lahontan^+ll WASHOEM , / peservoirXrrFigure 1 . Location of Carson City, Nev., consolidated municipality and the urban study area.

4 Nitrate and Ammonia in Shallow Ground Water, Carson City Urban Area, Nevada, 1989
As of 1988, approximately 43 percent of the snidy 

area in Carson City was residential, 11 percent was 

commercial, 9 percent was industrial, 2 percent was 

public land (parks and schools), and 35 percent was 

pasture or undeveloped land (Carson City Zoning Map, 

1979 base, including amendments as of April 4,1988). 

The population of Carson City has increased from 

4,500 in 1950 to about 41,000 in 1990 (Maud Naroll, 

University of Nevada, Reno, Bureau of Business and 

Economics Research, oral commun., 1990) with 

growth continuing at a rate of 2-4 percent per year.

The semiarid climate of Carson City is affected 

by the rain shadow of the Sierra Nevada. The west 

slope of the Sierra Nevada captures most of the precipitation from frontal storms that originate over the 

Pacific Ocean, leaving the east slope much drier. During 1951-73, the average daily maximum temperature 

in the Carson City urban area was 85.4°F during the 

summer, and the average daily minimum temperature 

was 21.8°F during the winter. The average annual precipitation was 11.1 in., and the average annual snowfall 

was 29.6 in. (Candland, 1979, table 1). Most of the precipitation falls between December and March. The prevailing wind is from the west-northwest.

Soils

Because nearly all water entering ground-water 

flow systems must pass through the soil zone, soils can 

have a large effect on ground-water quality. The soils in 

the urban study area may impede or promote the movement of precipitation, urban runoff, or irrigation water 

into the shallow aquifer. Soils in the uroan study area 

belong primarily to the Bishop group (about 92 percent) and the Dalzell group (about 8 percent; Candland, 

1979, p. 9). Soils of the Bishop group are loamy in the 

upper layer; a sandy, clayey loam in the lower layers; 

slightly saline and alkaline in all layers; and have low 

to very low permeability (Candland, 1979, p. 11). The 

Dalzell soils are a saline loam in the upper layers; a 

saline, sandy-clay loam in the lower layers; and a silica-cemented hardpan at about 40 in. below land surface. This hardpan effectively prevents water at land 

surface from moving into deeper layers (Candland, 

1979, p. 15). During well drilling for this study, alfisol, 

or perhaps mollisol, soils were found at sites that were 

landscaped with grass. Aridosols were found at sites 

with native vegetation such as sagebrush and rabbitbrush. Alfisol and mollisol soils have definite soil

horizons including a highly organic "A" horizon and 

are commonly found in humid, high rainfall areas such 

as the grasslands of the midwestern United States. Mollisols have somewhat more organic matter and a higher 

supply of base ions than alfisols and also are commonly 

found in more humid environments (Birkeland, 1974, 

p. 47). Aridosols are soils low in organic matter, have 

accumulations of silica at depth, and are usually dry 

for more than 6 months of the year (Birkeland, 1974, 

p. 47). Irrigated lawns in Carson City may simulate the 

leaching environments that create mollisol or alfisol 

soils in the midwestern grassland areas.

Hydrogeology

The hydrogeology of the shallow aquifer beneath 

the study area generally controls the flow of ground 

water and, thus, the movement of contaminants within 

the aquifer. The primary aquifer underlying Eagle 

Valley is a mixture of basin-fill sedimentary deposits. 

These deposits consist of unconsolidated to partly consolidated lenses of gravel, sand, silt, and clay (Worts 

and Malmberg, 1966, table 1). The aquifer is thickest 

along the east-central edge of Eagle Valley and may 

extend to a depth of 2,000 ft below land surface 

(Arteaga, 1986, p. 23). A consolidated-rock basement 

complex (bedrock) underlies the basin-fill deposits and 

makes up the bordering hills and mountains. The bedrock is composed of sedimentary, volcanic, granitic, 

and metamorphic rocks (Worts and Malmberg, 1966, 

table 1).

Ground water in the basin-fill aquifer underlying 

the floor of Eagle Valley is recharged by seepage losses 

from streams that drain the Sierra Nevada and cross 

alluvial fans west of the city (Worts and Malmberg, 

1966, p. 14; Arteaga, 1986, p. 13; Maurer and Fischer, 

1988, p. 34). Recharge by direct infiltration of precipitation on the valley floor is assumed to be minor except 

during infrequent, sustained rainstorms. Landscape 

watering and agricultural irrigation probably recharge 

the shallow ground-water system beneath the valley 

floor to a greater extent than direct precipitation. The 

flow of shallow ground water in the basin-fill deposits 

beneath the urban area is generally southeastward 

(fig. 2). Depths to water measured during the first half 

of 1989 ranged from 2.8 to 16.7 ft below land surface 

(fig. 3 and table 1).

ENVIRONMENTAL SETTING
119°47' 119°44'

39°09'

EXPLANATION 

Urban study area

Area served by septic-tank systems

 4,630 Water-table contour Shows altitude of water 

table, March 1989. Dashed where approximated. 

Contour interval, 10 feet. Datum is sea level. Contours 

constructed by simple interpolation

Generalized direction of ground-water flow

o Single well and site number (table 1)

13

Well cluster and site number (table 1)

Figure 2. Well locations, water-table altitudes, and generalized directions of ground-water flow, 

Carson City, Nev., urban study area, January-March 1989.

6 Nitrate and Ammonia in Shallow Ground Water, Carson City Urban Area, Nevada, 1989
Table 1. Land-surface altitude, well depth, and water-level data, Carson 

City, Nev., urban study area, January-March and May-June 1989

Well 

number 

(figure 2)

1

2

3

4

5

6

7

8

9

10

11

12

13a

13b

13c

13d

14

15a

15b

15c

15d

16

17

18

19

20

Attitude of 

land surface 1 

(feet above

4,723

4,721

4,702

4,668

4,641

4,636

4,633

4,660

4,679

4,719

4,760

4,712

4,667

4,667

4,667

4,667

4,659

4,637

4,637

4,637

4,637

4,634

4,643

4,650

4,655

4,661

Feet below land surface

Depth 

to well 

screen

18

21

19

35

11

18

21

19

19

21

30

20

35

30

25

20

21

30

25

20

15

18

15

16

14

20

Depth to water 

(measurement period 2)

(1)

6.6

14.2

14.8

4.7

4.6

3.3

10.2

12.8

14.0

8.3

16.7

10.5

12.4

11.7

11.6

11.5

9.9

4.4

5.6

2.8

2.9

11.0

7.2

4.6

5.7

10.0

(2)

6.5

8.9

13.4

4.6

4.3

3.4

7.7

10.8

11.5

11.2

9.9

10.2

11.7

11.2

11.2

11.1

9.1

3.9

3.5

3.2

2.9

10.2

6.0

3.6

4.9

16.5

Site 

- number3

54

45

42

48

47

49

32

37

38

33

34

25

28

29

30

31

24

20

21

22

23

14

17

15

11

13

1 Altitudes surveyed from benchmarks.

2 Measurement periods: (1), January-March 1989; (2), May-June 1989.

3 Site number used by Whitney (1994).

ENVIRONMENTAL SETTING
119°47' 119°44'

39°09'

o

7.2

2.9

EXPLANATION 

Urban study area

Area served by septic-tank systems

Line of equal depth to water Depth to water, in feet below 

land surface, January-March 1989. Interval, 4 feet. Lines 

constructed using simple interpolation

Single well and depth to water, In feet below land surface

Well cluster and depth to water, In feet below land surface, 

for shallowest well

Figure 3. Depth to ground water, Carson City, Nev., urban study area, January-March 1989.

8 Nitrate and Ammonia in Shallow Ground Water, Carson City Urban Area, Nevada, 1989
ORGANIC 

NITROGEN

ATMOSPHERIC 

LOSS

NITROUS OXIDES

AND 

NITROGEN GAS

NITRIFICATION

Figure 4. Nitrogen cycle (modified from Snoeyink and Jenkins, 1980, p. 405).

NITROGEN CYCLE IN NATURAL AND 

STRESSED SYSTEMS

The nitrogen cycle is a complex phenomenon 

with many processes taking place simultaneously, 

depending on local conditions. The cycle consists of 

oxidation and reduction reactions involving various 

nitrogen forms. Reactions are catalyzed by specific 

bacterial populations, depending on the presence or 

absence of oxygen (Snoeyink and Jenkins, 1980, p. 44,

407-411). A catalyst is any substance that increases the 

rate of a chemical reaction and is itself unchanged in 

the process. The reactions proceed slowly or not at all 

in the absence of bacterial populations. Bacteria produce an enzyme that either "shortcuts" the reaction 

pathways or reduces the activation energy to a level 

that allows the reaction to proceed (Snoeyink and Jenkins, 1980, p. 44-48). The activation energy can be 

thought of as an energy "dam" that prevents a chemical 

reaction. Organic nitrogen is converted to the nitrate 

ion, chemically the most stable form of nitrogen,

NITROGEN CYCLE IN NATURAL AND STRESSED SYSTEMS
through a series of oxidation steps. A depiction of the 

nitrogen cycle is shown in figure 4. The following 

description of the nitrogen cycle is summarized from 

Drever (1988, p. 310) and Snoeyink and Jenkins (1980, 

p. 405-407).

Organic nitrogen is decomposed to amine groups 

(R-NHX, where R is a carbon-hydrogen chain or ring, 

N is nitrogen, and x is the number of hydrogen atoms, 

which depends on the number of R groups directly 

bonded to the nitrogen atom). This decomposition, 

called deamination, is catalyzed by bacteria in both 

oxic (oxygenated) and anoxic (no oxygen) environments. In an oxic environment, bacteria catalyze the 

oxidation of amine groups to ammonia (Nt^) in a process called ammonification. Further bacterial oxidation 

converts ammonia to nitrite, then rapidly to nitrate, in a 

process called nitrification. If conditions are anoxic, no 

nitrification occurs.

Nitrification begins whenever ammonia and dissolved oxygen (greater than 1.0 mg/L) are present with 

appropriate bacteria (generally nitrobactor and 

nitrosomonas species), such as occur in soil or aquifer 

materials. During nitrification, ammonia, dissolvedoxygen, and dissolved organic carbon concentrations 

decrease while nitrate concentrations increase. Nitrification commonly proceeds until one of the reactants 

becomes limiting. When ammonia fertilizers are 

applied to agricultural or urban landscapes, nitrification 

is often limited by ammonia concentrations (Hallberg, 

1989). When ammonia is the limiting factor, nitrate 

concentrations will be elevated, dissolved-oxygen concentrations will be above 1.0 mg/L, and ammonia concentrations will be below laboratory reporting limits 

(Hallberg, 1989). However, when manure or sewage 

effluent is nitrified, the large amounts of proteinaceous 

organic matter promote large increases in microbial 

respiration that will deplete dissolved-oxygen concentrations. Nitrification ceases when dissolved-oxygen 

concentrations fall below 1.0 mg/L.

When dissolved oxygen declines below 1.0 

mg/L, reducing conditions exist and nitrate concentrations are depleted by denitrification (Lowrance and 

Pionke, 1989, p. 377). Microbes need electrons to 

metabolize nitrogen; when dissolved-oxygen concentrations are greater than 1.0 mg/L, microbes use the 

electrons in the oxygen molecule. However, under 

anoxic conditions, microbes use the next readily available source of electrons, which is oxygen within the 

nitrate molecule. As a result, oxygen atoms are 

removed from the nitrate molecule; nitrate is reduced

and converted to various nitrous oxide gases or gaseous 

nitrogen (N2; Drever, 1988). This process is denitrification. As nitrate is reduced, electrons become so scarce 

that the nitrogen atom itself is reduced and reacts with 

hydrogen ions to form ammonia. This process is nitrate 

reduction. Nitrate reduction can increase ammonia 

concentrations in ground water and also create conditions that liberate iron and manganese ions that are 

attached to oxide coatings on aquifer grains. Thus, 

ground water can lose ammonia and gain nitrate by 

nitrification under aerobic conditions, and in the 

absence of dissolved oxygen, can lose nitrate by denitrification, or lose nitrate and gain ammonia by 

nitrate reduction.

Under anoxic conditions, bacteria reduce nitrate 

to nitrogen gas or various nitrous oxides that are lost to 

the atmosphere (denitrification) or convert nitrate to 

ammonia in the reverse of nitrification (nitrate reduction). Generally, denitrification takes place before 

nitrate reduction because bacteria get more energy 

from denitrification than from nitrate reduction. Nitrogen gas can be converted to ammonia by certain plants 

in a process called nitrogen fixation. Ammonia can 

then be incorporated into plants by root uptake or into 

animals by ingestion and converted to protein in a process called biosynthesis.

METHODS USED IN THE STUDY

Well Construction

An aligned square-grid design (Gilbert, 1987, 

p. 93) was used to locate 20 sampling sites within the 

most densely developed part of the Carson City urban 

area. The distance between grid lines was 1/2 mi, 

which fixed the total number of sites at 20. The grid 

was placed over a map of the urban study area and the 

first well site was picked at random. This first well site 

was the reference point from which all subsequent well 

sites were located using the 1/2-mi grid spacing. 

Twenty-six wells were constructed at the 20 sites (table 

1 and fig. 2); most were in or downgradient from residential areas. At 18 sites, a single well was screened 

no deeper than 35 ft below land surface (most of these 

wells were screened within the upper 15 ft of the saturated zone); at two sites, clusters of four nested wells 

were constructed. The deepest well in the cluster was 

screened within the upper 25 ft of the saturated zone,

10 Nitrate and Ammonia in Shallow Ground Water, Carson City Urban Area, Nevada, 1989
but less than 35 ft below land surface (well "a"). Each 

subsequent well in the cluster (wells b, c, and d) was 

screened 5 ft shallower than the previous well. At each 

cluster site, well designations "a, b, c, d" identify both 

the well-construction sequence and the sampling 

sequence. Well "a," the deepest, was constructed and 

sampled first, then well "b," and so on, to prevent shallow ground water from contaminating the deeper wells. 

All wells were drilled with either a 4-in.-diameter, solid-stem auger or an 8-in.-diameter, hollow-stem 

auger using methods of Hardy and others (1989). Each 

well was cased with threaded, 2-in.-diameter, polyvinyl chloride (PVC) pipe. At the 18 single well sites, the 

bottom section of well casing was a 5-ft length of 0.01- 

in. slotted PVC screen. At the two well cluster sites, the 

bottom section of the well casing was a 2-ft length of 

0.01 in. screen. At all sites, including the shallowest 

well at each cluster site, the screen was set 5-10 ft 

below the water table.

Sampling Methods

Two water samples were collected from each 

well, the first during January-March 1989 and the second during May-June 1989. Before sampling, each 

well was pumped for 10-20 minutes with a positivedisplacement, nitrogen-driven, Teflon bladder pump. 

During that time, approximately 20 casing volumes of 

water were removed from each well. Specific conductance and pH measurements had stabilized before the 

end of pumping. Measurements of pH, specific conductance, dissolved oxygen, and temperature were taken 

from a flow-through chamber on site.

Water was pumped from the well to sample bottles through Teflon tubing attached to the bladder 

pump. Samples were analyzed by the U.S. Geological 

Survey National Water-Quality Laboratory in Arvada, 

Colo., for dissolved ammonia, nitrite, nitrate plus 

nitrite, major cations and anions, trace elements, volatile organic compounds, and dissolved organic carbon 

(DOC), using methods described by Fishman and 

Friedman (1989) and Wershaw and others (1987). 

Before sample bottles were filled, ground water was 

filtered through a membrane filter with a pore size of 

0.45 (im. Before filtering, membrane filters were rinsed 

with 500 mL of ground water. Samples for volatile 

organic analysis were not filtered. All samples were 

chilled and nutrient samples were preserved with mercuric chloride. Samples for trace-element analysis were

preserved with nitric acid. Whitney (1994) compiled 

the data collected for this study. Data used in this report 

are in table 2.

Statistical Analysis of Water-Quality Data

Several methods were used to explore possible 

interactions among water-quality constituents and 

properties. Scatterplots were constructed for pairs of 

constituents 'see appendix). Specific conductance, 

nitrate, and ammonia concentrations were plotted on 

maps of the urban study area. Nonparametric statistics, 

robust multiple-regression analysis (RMRA), and a 

factor analysis using principal components (PCA) 

were used to explore associations among the data. 

These data consist of nitrate, ammonia, major cation 

and anion, selected trace-element, and dissolvedoxygen concentrations, and pH, well depth, and depth 

to water.

Nonparametric statistical methods transform the 

original data to ranks, then use the ranks in the analysis. 

Before rank transformation, the concentrations of 

major cations, major anions, and trace elements were 

normalized by converting to milliequivalents per liter 

(meq/L). The following discussion on rank-transformation is from Conover (1980, p. 250-256) and Ott 

(1988, p. 319-323). Data are sorted from the lowest to 

the highest value. The rank of the lowest value is 1 and 

the rank of the highest value is equal to the total number of samples for that constituent. Each constituent is 

ranked. Values below a laboratory reporting limit are 

given the lowest ranks. Samples that have the same 

value, including values below a laboratory reporting 

limit, are given the mean of their ranks. For example, if 

three samples have a constituent value below its laboratory reporting limit, their ranks will be 2 (the average 

of 1,2, and 3).

The Mann-Whitney Rank-Sum test and Spearman's rank-correlation analysis were used to analyze 

the data. The Mann-Whitney method is the nonparametric counterpart to the parametric t-test and compares the medians, rather than the means, of 

constituents in two data sets. The Mann-Whitney 

method tests whether the data fit one of two possible 

hypotheses: (1) The medians of the data sets are equal; 

therefore, the data sets belong to the same population; 

or (2) the medians are not equal; therefore, they do not 

belong to the same population.

METHODS USED IN THE STUDY 11
The Spearman rank-correlation analysis tests the 

independence of a variable X from a variable Y by comparing their ranks rather than their measured values. 

Therefore, the method can include censored values 

reported as above or below a threshold value. The 

method tests for changes in the value of one constituent 

as the value of another constituent changes and can 

detect linear or curvilinear relations between two constituents. For this study, the Statistical Analysis System 

(SAS Institute Inc., 1990) was used to compute the 

Spearman correlation coefficients (r) and a value (p) 

that measures the probability of an association between 

two constituents. If high ranks of one constituent are 

associated with high ranks of another constituent, then 

the correlation coefficient will be close to +1 and the 

constituents are positively correlated. If high ranks of 

one constituent are associated with low ranks of 

another constituent, then the correlation coefficient will 

be close to -1 and the constituents are negatively correlated. If the ranks of one constituent are random with 

respect to the ranks of another constituent, then the correlation coefficient will be close to zero and the constituents are considered not correlated.

The statistical significance, or strength, of a correlation between two constituents is determined using 

the p-value; the smaller the p-value, the greater the 

likelihood of correlation (Conover, 1980, p. 254; Ott, 

1988, p. 150). Thus, a p-value of 0.001 indicates stronger correlation than a p-value of 0.05. Correlations 

between two constituents in this report are considered 

statistically significant if the p-value is 0.05 or less.

Robust multiple-regression analysis (RMRA), 

along with factor analysis using principal components 

(PCA), are used in this report as exploratory tools to 

identify multivariate relations among data from each 

well in the urban study area. RMRA was also used as a 

check on the PCA. RMRA is a multiple linear-regression of rank-transformed data (Conover, 1980, p. 338). 

The method is robust because it is insensitive to outliers, nonnormally distributed data, and censored data 

(Conover, 1980, p. 338). The set of independent constituents that maximized the coefficient of determination, r% and minimized Mallow's Cp were used in the 

regression analysis. The coefficient of determination is 

the proportion of the total variability in the dependent 

constituent that is accounted for by variability in the 

independent constituents (Ott, 1988, p. 320). Mallow's 

Cp is a value that helps identify the optimal regression 

equation (Montgomery and Peck, 1982, p. 251). Mallows Cp identifies the best combination of independent

variables (constituents) that maximize r1 (minimize 

bias) while minimizing the standard error of the regression. A large number of variables can account for 

nearly 100 percent of the variance in Y, the dependent 

variable, but the standard error of the regression is then 

so high that the equation is useless as a predictive tool.

The PCA for this study used the same rank-transformed data used in the correlation and multiple regression analyses; the set of Spearman rank-correlation 

coefficients was the initial matrix for the PCA. Except 

where noted, the following explanation of PCA is from 

Afifi and Clark (1984, p. 328-360).

PCA provides a way to examine the interrelations 

among data. The output from PCA consists of four 

major elements a set of components, a set of communalities, a set of loading coefficients, and a partitioning 

of variance.

The set of components is a set of new, uncorrelated variables that contain the original correlated constituents. The PCA computes components so they 

account for as much of the total variance as possible. 

The analysis can produce 20 or more components, but 

the first 3 to 6 generally account for most (as much as 

95 percent or more) of the variance and are considered 

the principal components of the data set. The first component accounts for most of the total variance and is 

commonly the most stable. Subsequent components 

account for smaller proportions of the total variance 

and are less stable. A component is stable when adding 

or removing constituents or observations from the data 

set does not change the variance of the component or 

alter the constituent groupings within the component. 

Because the goal of PCA is to reduce the complexity of 

a data set, only the principal components are used for 

interpretation.

Varimax rotation was used to optimize the association of original constituents with the principal components (table 4). This rotation changes the component 

loadings so that the original constituents are either very 

high (as close to +1.0 or -1.0 as possible) or close to 

zero. It changes the relation between constituents and a 

component axis, but does not change the relations 

among the constituents (Davis, 1986, p. 555). Varimax 

rotation helps the interpretation of the principal components by identifying more discrete groups of constituents.

The PCA associates two values, the communality 

and the loading coefficient, with each constituent (table 

4). The communality is "the proportion of the variance 

for each original constituent accounted for by the

12 Nitrate and Ammonia In Shallow Ground Water, Carson City Urban Area, Nevada, 1989
retained components" (Puckett and Bricker, 1992). 

Thus, the communality is an index of the amount of 

total variance that a constituent contributes to the data 

set. The more variance contributed, the more important 

thai constituent is to the data set and to the interpretation of the PCA. The importance of a constituent 

increases as the communality approaches 1.0 (table 4). 

Constituents with a communality greater than 0.60 are 

used for the interpretation of components. Varimax 

rotation does not change the communality of a constituent.

Loading coefficients range between -1 and +1; 

values close to ±1 indicate strong correlation with a 

particular component. Values from -0.5 to +0.5 indicate 

weak or no correlation; therefore, constituents with 

loading coefficients from -0.5 to +0.5 are not included 

in the interpretation. Constituents with loading coefficients from -0.75 to -0.5 and from +0.50 to +0.75 are 

important to the interpretation of a component, and 

constituents with loading coefficients from -1 to -0.75 

and from +0.75 to +1 are the most important (Puckett 

and Bricker, 1992). A constituent, such as sulfate in 

table 4, can be represented in more than one component. Loading coefficients can be depicted graphically 

several ways; for example, figure 8 is the visual equivalent to table 4 and shows those constituents that are 

correlated with each component in this study.

PCA partitions the total variance in a data set 

among the components. The total variance is the sum 

of variances for each constituent in the data set. The 

variance for each constituent, a measure of variability 

among the samples, is calculated as the square of the 

positive and negative deviations from the constituent 

mean. In PCA, the first component contains the correlated constituents that have the greatest variance in the 

data set. Thus, the first component accounts for the 

largest proportion of the total variance and each subsequent component accounts for a smaller proportion.

Because each component is a group of related 

constituents, each component may represent sources or 

processes common to all constituents within the component. However, PCA can force functionally unrelated data into components, thereby leading to 

erroneous interpretations (Rexstad and others, 1988). 

The correct interpretation, therefore, depends on 

knowledge of hydrologic, geochemical, and physical 

factors. Since 1966, PCA has been used in several 

water-quality studies; Meglen and Sistko (1985) used 

PCA on a large data set to distinguish anomalous samples, samples from three different aquifers, samples

that represented a mixture of water from different aquifers, and samples that identified a leak in one of the 

three holding ponds in the study area; Ruiz and others 

(1990) used PCA to detect saltwater intrusion in a 

coastal aquifer in Spain and Puckett and Bricker (1992) 

used PCA to examine regional chemistry patterns in 

low-order streams in the Blue Ridge Mountains of 

Virginia and Maryland.

PCA can be used to areally map each component 

by assigning a score (sample score) to each sample or 

observation in the data set. The sample score indicates 

the relation between the sample and a principal component and, by extension, those constituents important to 

the component. The sample score is the sum of all the 

constituent scores for a particular sample and specific 

component; the constituent score is a constituent's 

original value multiplied by its loading coefficient for 

the component.

For example, the sample score for sample 1, well 

1, and component 1 in table 5 was computed as follows: For each sample, the component 1 loading coefficients (second column, table 3) for each constituent 

were multiplied by the constituent's original value. The 

resulting constituent scores were then summed to get 

the sample score. Principal components that are interpreted as depicting either the presence of a contaminant 

in an aquifer, or a geochemical process, or a particular 

source of water can be delineated on a map. For example, Ruiz and others (1990) mapped sample scores to 

delineate an area of seawater intruding into a coastal 

aquifer.

GENERAL GROUND-WATER QUALITY

Water-quality data used in this report are listed in 

table 2. The specific conductance and dominant cations 

and anions were markedly different in different parts of 

the urban study area. Specific conductance ranged from 

380 (iS/cm to 1,970 (iS/cm (table 2). The highest specific conductance was measured in the southwestern 

part of the area and the second highest was measured in 

the northeastern part (fig. 5). With several exceptions, 

the dominant ions in shallow ground water in the urban 

study area were calcium and bicarbonate. The codominant ions at sites 3,4, and 13d were sodium, calcium, 

and bicarbonate. The dominant ions at sites 5 and 18 

were sodium and bicarbonate, and sodium and sulfate, 

respectively.

GENERAL GROUND-WATER QUALITY 13
119°47' 119°44'

39°09'

EXPLANATION

Urban study area

Area served by septic-tank systems

 1000 Line of equal specific conductance Specific conductance 

of shallow ground water, in microsiemens per centimeter at 25 

degrees Celsius diS/cm), January-March 1989. Interval, 250 |xS/cm. 

Dashed where approximated. Lines constructed by simple 

interpolation 

13 

O Single weil and well number

3 

PI Well cluster and well number

Figure 5. Areal distribution of specific conductance in shallow ground water, Carson City, Nev., 

urban study area, January-March 1989.

14 Nitrate and Ammonia in Shallow Ground Water, Carson City Urban Area, Nevada, 1989
Table 2. Water-quality data from shallow wells in the Carson City, Nev., urban study area, 1989

[Sampling period indicated by "1" or "2": 1, January-March 1989; 2, May-July 1989. All concentrations in milligrams per liter, except where indicated; jig/L, micrograms per liter; 

US/cm, microsiemens per centimeter at 25 degrees Celsius.]

O 

mm

O 3D 

OC

3D 

O

Well 

number 

(figure 2)

1

2

34

56789

10

11

12

13a

13b

13c

13d

14

15a

15b

15c

15d161718

19

20

Specific 

conductance, 

field GiS/cm)

1

720550

900510

17301300

390

470

1090

640380

460

770

1050

1130

10701060

460

730730

1280

370

«

1940

780540

2

720580

880

630

1730

1180

390670750

~

240

500

810

1110

1140

1170

1010

470

720700960

380

1020

2050

760

540

Laboratory 

pH 

(units)

1

7.47.17.28.0

7.67.2

7.46.56.9

7.3

6.66.8

6.7

6.86.97.06.77.27.07.2

7.37.27.16.97.37.0

2

7.07.27.27.67.47.1

7.36.6

6.7

7.3

6.3

6.6

6.7

6.6

6.7

6.96.8

7.27.27.2

7.37.27.06.87.36.8

Dissolved

Oxygen

1

3.8

3.1

1.2

4.0

.4

1.7

.4

2.1

~

.6

3.9

.5

.5.5

3.9

1.11.31.0

.8

.9

3.4

.5.4

4.94.5

2

3.72.62.4

5.4

1.8

2.0

1.6

4.3

2.4

~

2.0

4.5

1.2

1.01.11.2

1.9

1.1

.7.6

1.5

6.0

1.7

2.1

4.5

5.6

Calcium

1

9370775473

120

51

48

110

8433

53

95

120

120

100130

55

85

79

120

37

130

160

7967

2

89

69

717074

120

53

81

68

94

2958

95

110110110

120

53

7976

87

39

130170

7965

Magnesium

1

23

2023

9.3

14

55

11

10

2626

7.5

17

23

28282231

19

3029

33

12

33

32

21

17

2

2220

21

12

14

53

11

18

16

27

5.9

18

22

27262231

18

272650

11

303520

16

Sodium

1

3826

110

43

310

94

22

24

6623

41

20

3872

88

95

602137

46

97

2662

260

5738

2

3826

9950

330

100

21

30

6225

14

21

40

73

88

97

682138

39

69

25

61

310

57

37

Potassium

1

1.8

2.3

4.0

2.3

1.8

5.4

1.1

5.85.0

3.74.0

1.1

3.9

4.6

5.4

4.0

3.7

1.9

2.42.3

1.41.3

3.4

4.5

.7.9

2

1.6

2.2

3.3

2.0

1.6

5.5

1.0

6.5

3.6

4.2

2.5

1.1

4.1

4.9

5.5

3.9

3.3

1.9

2.42.4

1.11.0

2.73.3

.7.7

Bicarbonate

1

363289

512220682504

239200

265

420

148

172

290

350380390

490

250

540

550

680

180

480

520

386

250

2

376

405

390395

857

574312

218

249

467

161

229347

515380

400

530

290

405

400

420

240560510370340
O)

Table 2. Water-quality data from shallow wells in Carson City, Nevada urban study area, 1989 Continued

3 

o

I5'

CO

o 

3

ai

?CO 

Oo

cII0)*

Well 

number 

(figure 2)

1

2345678

9

10

11

12

13a

13b

13c

13d

14

15a

15h

15c

15d161718

19

20

Sulfate

1

5028

49

34

260220

7.7

16

140

11

16

32

78

110110

100100

12

29

28

38

25

110

670

76

39

2

47

25

40

51

240220

9.0

18

61

8

5

32

79

110110

110100

12

2625

532796

760

74

37

Chloride

1

13

8.8

272385

43

8.2

2588

6.4

49

19

63

110

120

93

68

17

313789

9

71

5331

12

2

12

8.8

44

2983

40

9.0

9773

5.75.0

2463

120

120

92

65

17

3535

76

13

67

63

36

11

Silica 

(Si02)

1

53

4240

29

545835

28

24

3829

44

393431293531

32

3238

41

32

36

5450

2

52

41

382952

59

33

2622

40

30

43

383229

293230313139

41

31

36

56

49

Dissolved

Nitrate, 

asN

1

8.5

7.2

3.2

5.4

<.l

11

<.l

1.9

17

.1.3

12

<.l<.l<.l

38

<.l

.3

<.l

<.l<.l

3.25.7

<.l

1815

2

8.68.4

2.7

7.3

<.l

10

<.l

2.4

5.4

<.l<.l

11

<.l

<.l

.2

3.7

<.l<.l<.l<.l<.l

3.3

4.7

<.l

17

5.5

Ammonia, 

asN

1

0.03

<.01

.01.04.03

.02

.04.01.04.08.04

<.01

.21.26

.19

.03.24

<.01

.05.04.03

<.01

.05.09.02.01

2

0.03

.01.02.01.02.04

.05

<.01<.01

.09.02.01.21.18.17

.02.18

<.01

.04.02

<.01

<.01

.04.09.01.02

Orthophosphorus 

as P

1

0.04

.07.04.05.13.05

.19

.06.05

.01

.01.03.06.09.10

.09.39

.14.19.19.23.05

.26.19.19.13

2

0.05

.07.04.04.15.07.20.05.05.01

<.01

.03.04

<.01

.04

.10.02.15.10.08.22

.07

.25

<.01

.18.12

Boron

1

40

0

150

20

2,900

260

20

20

120

30

10

20

10

50

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GENERAL GROUND-WATER QUALITY 17
NITRATE AND AMMONIA IN SHALLOW 

GROUND WATER

The most likely sources of nitrate and ammonia in 

shallow ground water beneath an urban area are anthropogenic, such as urban runoff, sewage effluent, and 

nitrogen-based fertilizers (Madison and Brunett, 1985; 

Hallberg, 1989; Eckhardt and others, 1989; and Komor 

and Anderson, 1993). Urban runoff was not a likely 

source of nitrate or ammonia to the shallow aquifer in 

the urban study area because the amount of surface runoff is generally small and soil permeability is low. 

Also, no detention ponds where urban runoff could 

accumulate and infiltrate were in or upgradient from 

the study area in 1989. Thus, sewage effluent or nitrogen fertilizers were more likely sources. Municipal 

sewer pipes contribute sewage effluent to shallow 

ground water if these pipes leak. In addition, septictank systems northeast and south of the urban study 

area (fig. 2) might be a source because they are upgradient from the study area. Nitrogen-based fertilizers 

may be a major source of nitrate or ammonia in landscaped areas in residential parts of the urban study area. 

Residential areas, including public parks, have large 

expanses of lawn and landscaping, and probably 

receive nitrogen-based fertilizers regularly.

Nitrate and ammonia concentrations are presented as the nitrogen form (NO3-N) and (NH4-N), 

respectively, and the terms "nitrate" and "ammonia" 

are used in the rest of this report. Nationwide data indicate that nitrate concentrations below 3.0 mg/L represent background, or "natural," conditions in ground 

water (Hallberg, 1989, p. 66). Therefore, in this report, 

ground-water samples with nitrate concentrations 

below 3.0 mg/L are assumed to represent natural concentrations in the shallow aquifer, samples with nitrate 

concentrations between 3.0 and 10.0 mg/L are assumed 

to be nitrate-enriched, and samples with nitrate concentrations at or above 10.0 mg/L are considered contaminated.

Areal and Temporal Differences in Nitrate 

Concentrations

Shallow ground-water samples from the urban 

study area contained nitrate concentrations that were 

highly variable, both areally and temporally (fig. 6). 

Nitrate concentrations for the study as a whole ranged 

from less than 0.1 to 38 mg/L and had a coefficient of

variation of 153 percent. The median concentration of 

1.1 mg/L was similar to the median nitrate concentration of 1.2 mg/L measured near Topaz Lake, about 30 

mi south of the study area (Nowlin, 1982, p. 69-73). 

The maximum nitrate concentration in the urban study 

area was nearly eight times higher than the maximum 

concentration measured near Topaz Lake, where nitrate 

ranged from 0.02 to 5.0 mg/L (Nowlin, 1982, p. 69- 

73). Septic-tank systems were the suspected source of 

nitrate in shallow ground water near Topaz Lake.

A nonparametric t-test showed that nitrate concentrations in the urban area's shallow ground water 

during sampling period one (January-March 1989) 

were not statistically different (p=0.38) from those 

measured in sampling period two (May and June 

1989), even though nitrate concentrations at some 

wells changed markedly between the two sampling 

periods. During the first sampling period, nitrate concentrations ranged from less than 0.1 to 38 mg/L (fig. 

6); the median concentration and coefficient of variation were 1.1 mg/L and 155 percent, respectively. During this same period, samples from 12 of the 20 shallow 

wells contained more than 3.0 mg/L of nitrate (fig. 6A). 

Six of the first-period samples equaled or exceeded the 

Nevada drinking-water standard of 10 mg/L (Nevada 

Bureau of Health Protection Services, 1992). Wells 9, 

13d, 19, and 20 contained particularly high nitrate concentrations during the first sampling period (table 2).

During the second sampling period, nitrate concentrations ranged from less than 0.1 to 17 mg/L; the 

median concentration and coefficient of variation were 

1.3 mg/L and 130 percent, respectively. Water from 

two shallow wells had higher nitrate concentrations, 

from eight shallow wells had lower nitrate concentrations, and from ten shallow wells had nitrate concentrations that were unchanged (within 1 mg/L) from those 

measured in first-round samples (table 2). Most samples that contained more than 3.0 mg/L of nitrate in the 

first sampling period also had concentrations greater 

than 3.0 mg/L in the second period (fig. 6). However, 

in the second sampling period, water from only 3 of 20 

shallow wells had nitrate concentrations that equaled or 

exceeded 10 mg/L (fig. 65), and water from 3 of 

20 shallow wells had concentrations that were at least 

3 mg/L lower than first-round samples (fig. 6).

The decrease in nitrate concentrations between 

sampling periods might be caused by a number of factors: (1) ground-water flow paths changed or concentrations were diluted as the water table rose before the 

second round of sampling; (2) the amount of nitrogen

18 Nitrate and Ammonia in Shallow Ground Water, Carson City Urban Area, Nevada, 1989
119°47' 119°44'

39°09'

39°11

39°09'

5 -

2.4

o

3.7

D

EXPLANATION 

Urban study area

Area served by septic-tank 

systems

Line of equal nitrate concentration, in milligrams per liter 

as N Dashed where approximated. Constructed by simple 

interpolation.

Single well and nitrate concentration, in milligrams per liter, 

asN

Well cluster and nitrate 

concentration, in milligrams 

per liter, as N, for shallowest well

Figure 6. Areal distribution of nitrate concentrations in shallow ground water for (A) January-March 1989 and (B) May-June 1989, 

Carson City, Nev., urban study area.

NITRATE AND AMMONIA IN SHALLOW GROUND WATER 19
entering the aquifer decreased; or (3) denitrification 

began or increased. The water table at 18 of 20 sites 

was closer to land surface during the second round of 

ground-water sampling than during the first round. The 

decrease in depth to water ranged from 0.3 to 6.8 ft, but 

the average decrease among all 26 wells was about 1 ft 

(table 1). Although a rising water table might change 

ground-water flow paths and divert contaminated water 

away from specific wells, broad changes in groundwater flow were not apparent. Moreover, the well network was not dense enough to detect changes in 

ground-water flow at or near individual wells.

Decreases in nitrate concentrations with a rising 

water table are commonly attributed to dilution (Hallberg, 1989, p. 48). Chloride and boron concentrations 

from both sampling periods were compared to see if 

dilution was likely in the urban study area. Chloride 

and boron are commonly used as tracers in groundwater studies because they are highly mobile, do not 

interact with other chemical constituents, and are not 

attenuated by cation exchange (LeBlanc, 1984; Canter 

and Knox, 1985; Hallberg, 1989). Decreases in chloride, boron, and nearly all other dissolved constituents 

between the two sampling periods indicated that nitrate 

concentrations (table 2) at 3 wells (9,11, and 14) might 

have been diluted as the water table rose (table 1). 

However, changes in chloride and boron concentrations were not consistent with changes in nitrate concentrations in samples from most wells in the urban 

study area. In the second sampling period, chloride 

concentrations were more than 1 mg/L lower at eight 

shallow wells, higher at six shallow wells, but 

unchanged at six wells (table 2). Boron concentrations 

were lower at 5 shallow wells (2 of these also had lower 

chloride concentrations), higher at 5 shallow wells (2 

of these also had higher chloride concentrations), but 

unchanged at 10 shallow wells (table 2). Furthermore, 

nonparametric correlation showed that changes in 

depth to water between sampling periods were not 

associated with changes in dissolved oxygen, chloride, 

nitrate, ammonia, or boron concentrations (p greater 

than 0.20). In addition, when samples from both sampling periods were combined, depth to water did not 

correlate with dissolved oxygen, chloride, nitrate, 

ammonia, or boron concentrations (see appendix).

The decreases in nitrate concentrations in the second sampling period might be caused by seasonal 

application of nitrogen fertilizers to grass in residential 

landscapes. According to several local gardeners, lawn 

fertilizer is applied in both spring and autumn, but

commonly is applied at a higher rate in autumn. Hallberg (1989) noted that in many areas of the U.S. where 

agricultural fertilizers were applied seasonally, 

changes in ground-water nitrate concentrations were 

seasonal. In contrast, water from a well contaminated 

by septic-tank effluent near Topaz Lake showed neither 

short- nor long-term changes in nitrate concentration 

(Nowlin, 1982). Similarly, water from a well in western 

Iowa that was contaminated by septic-tank effluent 

contained high nitrate concentrations that changed little during a 40-year period (Hallberg, 1989, p. 57). 

Thus, seasonal changes in nitrate concentrations can 

result from seasonal applications of fertilizer and concentrations that remain elevated through time can result 

from a constant source of nitrogen, such as sewage 

effluent.

Areal and Temporal Differences in Ammonia 

Concentrations

Ammonia concentrations were variable in water 

from the 20 shallow wells in the urban study area. 

Ammonia concentrations for all samples ranged from 

less than 0.01 to 0.26 mg/L (table 2). The median 

ammonia concentration and coefficient of variation 

were 0.03 mg/L and 128 percent, respectively. Ammonia concentrations in the urban study area were markedly higher than those in the Topaz Lake study area, 

most of which were less than the 0.01 mg/L laboratory 

reporting limit (Nowlin, 1982, p. 69-73).

Based on a nonparametric t-test, ammonia concentrations between the two sampling periods were not 

statistically different (p=0.63). The ammonia concentrations for sampling period one ranged from less than 

0.01 to 0.26 mg/L (table 2); the median ammonia concentration and coefficient of variation were 0.035 mg/L 

and 127 percent, respectively. Ammonia concentrations for sampling period two ranged from less than 

0.01 to 0.21 mg/L (table 2); the median concentration 

and coefficient of variation were 0.02 mg/L and 130 

percent. Ammonia concentrations at five wells (4,9, 

13b, 14, and 15d) decreased between the first and second sampling periods (table 2). The largest decrease in 

ammonia concentration, 0.08 mg/L, was measured at 

well 14. The difference in ammonia concentrations 

between the two sampling periods (fig. 7) was associated neither with differences in depth to water nor with 

differences in dissolved oxygen, chloride, nitrate, or 

boron concentrations (p greater than 0.73).

20 Nitrate and Ammonia in Shallow Ground Water, Carson City Urban Area, Nevada, 1989
119°47' 119°44'

39°09'

39°09'

EXPLANATION 

Urban study area 

Area served by septic-tank systems

 0.02 Line of equal ammonia concentration, 

in milligrams per liter, as N Dashed 

where approximated. Constructed by 

simple interpolation

0.01

O Single well and ammonia concentration, in milligrams per liter, as N

0.02

[J Well cluster and ammonia concentration, in milligrams per liter, as N 

for shallowest weii

Figure 7. Area! distribution of ammonia concentrations in shallow ground water for (A) January-March 1989 and 

(B) May-June 1989, Carson City, Nev., urban study area.

NITRATE AND AMMONIA IN SHALLOW GROUND WATER 21
Relations Among Nitrate, Ammonia, and 

Other Properties and Constituents

Nitrate, ammonia, well depth, depth to water, pH, 

dissolved oxygen, major cations, major anions, 

selected trace elements, and selected organic compounds were measured in ground-water samples collected in the Carson City urban study area (table 2) and 

compared statistically (see appendix). Concentrations 

of nitrate and ammonia generally are highly variable 

within the urban study area because of the variety of 

pathways available during nitrogen cycling. Because 

nitrate and ammonia concentrations in the first sampling period were not statistically different from those 

in the second, samples for each well from both periods 

were combined for statistical analysis.

Strong correlations among several constituents in 

the urban study were consistent with correlations 

reported for other areas for ground water contaminated 

with sewage effluent and nitrogen fertilizer (LeBlanc, 

1984; Canter and Knox, 1985). Nonparametric correlation showed that several constituents were statistically 

correlated to nitrate and ammonia (see appendix). 

Nitrate concentrations were positively correlated with 

dissolved oxygen and negatively correlated with 

ammonia, iron, ana manganese concentrations. 

Ammonia concentrations were positively correlated 

with calcium, magnesium, bicarbonate, iron, manganese, strontium, and dissolved organic carbon (DOC). 

Ammonia concentrations were negatively correlated 

with nitrate and dissolved oxygen. Because of the number of correlated constituents, particularly with ammonia, robust multiple-regression analysis (RMRA) was 

used to search for multivariate relations in the data set.

RMRA indicated that nitrate and ammonia concentrations are related to some of the same constituents 

as in the nonparametric correlation analysis. RMRA 

indicated that nitrate had a positive relation with potassium and sulfate, a negative relation with sodium, iron, 

and manganese, and no relation with ammonia (table 

3). This contrasts with the results from the correlation 

analysis, which indicates that iron and manganese correlated with nitrate, but sodium, potassium, and sulfate 

were not correlated (see appendix). RMRA indicated 

that ammonia concentrations were positively related to 

well depth and to calcium, manganese, and DOC concentrations (table 3). The correlation analysis indicated 

that ammonia was positively correlated to calcium, 

manganese, and DOC, but not to well depth (see appendix). RMRA indicated that some relations were consistent with the correlation results; the differences could 

result partially from the Mallow's Cp method used to 

select the variables for RMRA.

Varimax rotation was used to optimize the relation between constituents and components that were 

defined in the initial PCA. Because dissolved oxygen 

was not measured for three samples (two sites), it was 

not included in the PCA. Table 3 lists the principal 

components and their related constituents, and figure 8 

depicts those constituents that are most important to the 

principal components. Varimax rotated PCA resulted in 

five principal components that accounted for 74 percent of the total variance in the data (fig. 8; table 4).

Principal component 1 explains 24 percent of the 

total variance and may represent carbonate dissolution 

because calcium, magnesium, bicarbonate, and strontium, which are present in carbonate or plagioclase 

feldspar minerals, group within that component (Hem, 

1985, p. 89; Welch, 1994). Component 1 may describe 

water affected by dissolution of soil minerals during 

landscape irrigation or dissolution of aquifer minerals. 

DOC also groups with the carbonate elements, 

although its contribution is minor (table 4). Correlation 

analysis showed that DOC is correlated with well 

depth, dissolved oxygen, calcium, magnesium, 

sodium, bicarbonate, sulfate, ammonia, barium, boron, 

manganese, and strontium (see appendix). Correlation 

coefficients for most of the relations with DOC were at 

least 0.60 and p-values were less than 0.001. Some of 

these relations with DOC might indicate that these constituents have a common source, such as sewage effluent, a rising water table that intercepts shallow organicrich layers in the unsaturated zone, or leaching of 

organic acids (humic and fulvic acids) from landscape 

areas. Detergents containing anionic or ionic surfactants can make large contributions to DOC (LeBlanc, 

1984). However, principal component 1 provides no 

other indication that sewage effluent is the source of 

carbonate constituents or nitrate concentrations in the 

study area. Scatterplots and correlation results show a 

strong correlation among the elements in component 1 

(see appendix).

Principal component 2 explains 18 percent of the 

total variance and may represent evaporite dissolution 

because of its relation to sodium, boron, sulfate, and 

chloride (fig. 8; table 4). Evaporites consist of minerals 

such as halite (sodium and chloride), thenardite 

(sodium and sulfate), trona, soda, or nahcolite (various 

combinations of sodium carbonate and sodium bicarbonate minerals), and gypsum (calcium and sulfate).

22 Nitrate and Ammonia in Shallow Ground Water, Carson City Urban Area, Nevada, 1989
Table 3. Robust multiple-regression equations for water-quality constituents in shallow ground water, Carson City, Nev., 

urban study area, January-March and May-June 1989

[Measurements of water-quality constituents were rank transformed before robust multiple regression analysis. The procedure is robust in that it is 

insenstitive to outliers, censored values, and data that is not normally distributed (Conover, 1980, p. 338). Mallow's Cp was used to select the 

constituents that formed the regression equation. Mallow's Cp is a coefficient that optimizes the balance between minimum bias with minimum total 

error of an equation (Montgomery and Peck, 1982, p. 253) The best equation is one that minimizes bias while minimizing the total error in the 

regression. Bias in a regression equation is the tendency to overestimate or underestimate the true value. Explanation: Form of regression equations, 

Y = a + b(depth) + c(pH) + d(DO) + e(Ca) + f(Na) + g(K) + h(HCO3) + i(SO4) + j(Cl) + k(NO3) + 1(NH4) + m(PO4) + n(Silica) + o(Boron) + p(Fe) + 

q(Mn) + r(Sr) + s(DOC); pH, rank of the negative log of hydrogen ion concentration; depth, rank of well depth in feet below land surface; DO, rank of 

dissolved-oxygen concentration; Ca, rank of calcium concentration; Na, rank of sodium concentration; K, rank of potassium concentration; HCX>3 

rank of bicarbonate concentration; SO4, rank of sulfate concentration; Cl, rank of chloride concentration; NO3, rank of nitrate as N concentration; 

NH4, rank of ammonia concentration; PO4, rank of orthophosphorous concentration; Silica, rank of silica concentration; Boron, rank of boron 

concentration; Fe, rank of iron concentration; Mn, rank of manganese concentration; Sr, rank of strontium concentration; DOC, rank of dissolved 

organic-carbon concentration; , not included in regression; r2, coefficient of determination, the amount of variance in Y accounted for by the b to s 

constituents up to a maximum of 100 percent.]

Dependent constituents (Y)

vucniwiciii:

a

b

c

d

e

f

g

h

i

j

k

1

m

n

o

P

q

r

s

r2

DO

39.78

~

_

-.290

--

.301

~

__

~

~

~

-.422

~

-.530

.68

Ca

1.556

~

~

_

~

~

0.221

~

_.

0.174

-0.238

~

--

0.767

__

.91

Na

-4.747

.219

~

_

.209

.302

.274

-0.163

~

.391

-

__

.90

K

34.27

-.330

-.453

~

.388

~

0.300

~

-.251

-.325

~

-

__

.60

HCO3

3.534

.220

~

^814

_

~

~

-0.206

~

-

__

.68

Cl

26.58

-.369

~

~

.569

~

__

-0.496

~

-

__

.72

N03

31.87

~

~

~

-.937

.209

~

1.009

~

_.

~

-0.242

-.594

__

.63

NH4

-7.978

.362

--

~

.338

_

~

-

-

__

~

~

~

0.438

.252

.62

Mn

28.36

-.324

~

-.621

~

~

.659

-

-0.438

.340

~

~

~

~

__

.70

DOC

21.60

-.554

.272

__

-.187

~

-

-

0.415

-

-

__

.68

1 The coefficient is for magnesium rather than calcium.

These minerals can be found in the unsaturated zone 

within arid and semiarid environments (Doner and 

Lynn, 1977, p. 77). Sodium, chloride, and sulfate were 

the most important constituents in component 2. 

Although boron accounts for only a minor part of the 

total variance explained by component 2, it may indicate the presence of sewage effluent (LeBlanc, 1984; 

Canter and Knox, 1985). Boron is a common ingredient in detergents and is a good tracer of sewage effluent 

(LeBlanc, 1984). LeBlanc reported boron concentrations averaged about 500 (ig/L in the center of a sewage 

plume in Cape Cod, Mass., or about 8 times higher than 

ambient concentrations. Boron concentration in the 

Carson City urban study area ranged from less than 

10 \ig/L to 2,200 \ig/L (table 2).

Principal component 3 explains 13 percent of 

the total variance and may represent the oxidation/ 

reduction of nitrogen by nitrification, denitrification, 

or nitrate reduction (fig. 8; table 4). Principal component 3 shows a positive relation between ammonia and

NITRATE AND AMMONIA IN SHALLOW GROUND WATER 23
PRINCIPAL COMPONENTS 

(VARIMAX ROTATION)

I.U

0.8 

0.6 

0.4

o 0-2

1 °

o 

-1 -0.2

-0.4

-0.6

-0.8 

-1.0

Ca

HCOg

DOC SO4

-

-

-

-

-

1.0 

0.8 

0.6

0.4 

1 °

° -0.2

-0.4

-0.6

-0.8 

-1.0

4

Cl Na S04 " 

. B

-

-

-

- WDEPTH

-

SiO2 - 

PHLAB

-

-

-

- K

5

Mn 

NH3

" Fe

-

-

-

-

N03

TCE

-

-

-

-

-

Figure 8. Principal component loadings (varimax rotation) for hydrologic properties and chemical constituents at 

shallow wells in the Carson City, Nev., urban study area, January-March and May-June 1989. Abbreviations: B, boron; 

Ca, Calcium; Cl, chloride; DOC, dissolved organic carbon; Fe, iron; HCO3, bicarbonate; K, potassium; Mg, 

magnesium; Mn, manganese; Na, sodium; NH3, ammonium; NO3, nitrate; PHLAB, laboratory measured pH; Si02, 

Silica; SO4, sulfate; Sr, strontium; TCE, trichloroethylene; WDEPTH, well depth.

24 Nitrate and Ammonia In Shallow Ground Water, Carson City Urban Area, Nevada, 1989
Table 4. Loading coefficients from varimax-rotated principal components 

analysis of rank-transformed well-depth and water-quality measurements at 

shallow ground-water sampling sites, Carson City, Nev., urban study area

[Coefficients in bold indicate constituent or property important to interpretation of a principal 

component. The closer the coefficient is to one (positive or negative), the stronger the association 

between the constituent or property and the component and, thus, the more important the constituent 

or property to the interpretation of the principal component. Abbreviations and symbol: DOC, dissolved 

organic carbon; TCE, trichloroethylene; PCE, tetrachloroethylene; , constituent or property not 

included in interpretation of component]

Constituent or 

property

Depth of well . . . 

pH.. ..........

Calcium .......

Magnesium. .... 

Sodium. .......

Potassium. .....

Bicarbonate .... 

Sulfate ........

Chloride .......

Silica .........

Nitrate ........

Ammonia ......

Orthophosphorus 

Barium ........

Boron .........

Iron. ..........

Manganese .....

Strontium ......

DOC..........

TCE ..........

PCE ..........

Principal component 1

1

-0.33 

-.11 

.83 

.89

.36

.26 

.72 

.52 

.17 

.37

.24 

.45

.45

.30 

.90

.51

.14

2

-0.60 

.38 

.38 

.21 

.86

.15 

.27 

.74 

.86 

-.13

-.08 

-.03

.64

-.02 

.22 

.42 

.17

3

0.08 

-.07 

.23 

.13 

.11

.12

.32 

-.02 

.01

-.24

-.86 

.69

-.07

.80

.04 

.44 

.29

4

-0.37 

.69

-.18 

-.08 

.03

-.79

.10 

.04 

-.35 

.78

.01 

-.15

.31

-.17 

.09 

.08 

-.04

5 Communality2

0.25 

-.13 

.01 

.08 

.20

.18 

.11 

.12 

-.05 

.07

-.10 

.10

.27

-.11 

.07 

-.09 

.80

0.68 

.66 

.92 

.86 

.92

.76 

.72 

.84 

.89 

.82

.82 

.70

.55 

.51 

.78

.56 

.76 

.86 

.65 

.77 

.51

Variance, in percent 24 18 13 11 8

1 Each principal component explains part of the data set's total variance. The first component 

commonly accounts for most of the variance; each subsequent component accounts for part of the 

remainder. Each component is a collection of constituents or properties from the original data set. Each 

constituent or property has an associated loading coefficient for each component. Loading coefficients 

with an absolute value of 0.5 or greater are most important to a component (that is, account for most of 

the component's variance). Each principal component might relate to a process or a source of the 

constituents within it.

Principal component 1 represents ground water affected by carbonate dissolution. Principal 

component 2 represents water affected by evaporite dissolution. Principal component 3 represents 

ground water affected by tne oxidation/reduction of nitrogen. Principal component 4 represents ground 

water affected by potassium, silica, and pH. Principal component 5 represents ground water affected by 

trichloroethylene.

2 The communality is "the proportion of the variance for each original variable accounted for by 

the retained components" (Puckett and Bricker, 1992). Thus, the communality is an index of the amount 

of total variance that a constituent contributes to the data set. The closer the communality is to 1.0, the 

more variance contributed by the constituent and the more important that constituent is to the data set 

and to the interpretation of the principal component analysis. Constituents with a communality greater 

than 0.60 are used to interpret components.

NITRATE AND AMMONIA IN SHALLOW GROUND WATER 25
manganese, and a negative relation with nitrate concentrations (fig. 8; table 4). Correlation analysis and 

RMRA also support the relations in principal component 3 (table 3; appendix). Nitrification of ammonia is 

indicated by the positive correlation between dissolved-oxygen concentrations and nitrate concentrations in scatterplots (appendix), the relation between 

dissolved oxygen and principal component 3 sample 

scores (fig. 9), and the negative correlations between 

nitrate and ammonia and between ammonia and dissolved oxygen (appendix). These relations indicate 

nitrification (Snoeyink and Jenkins, 1980, p. 405-407; 

Ceazan and others, 1984; LeBlanc, 1984; Drever, 

1988, p. 310; Druliner, 1989, Hallberg, 1989). For 

more details about the processes in the nitrogen cycle, 

see section titled "Nitrogen Cycle in Natural and 

Stressed Systems."

Figure 9 shows that low dissolved-oxygen concentrations correspond to positive component 3 scores. 

Positive component 3 scores were related to positive 

correlations among ammonia, iron, and manganese 

concentrations. Negative correlations between dissolved oxygen and ammonia concentrations (appendix) and between ammonia and nitrate concentrations, 

and positive correlations among ammonia, iron, and 

manganese indicate denitrification (Snoeyink and Jenkins, 1980, p. 405-407; LeBlanc, 1984; Smith and 

Duff, 1984; Trudell and others, 1986; Drever, 1988, 

p. 310; Hallberg, 1989; Weil and others, 1990; Starr 

and Gilham, 1993) or nitrate reduction, particularly at 

wells where iron and manganese concentrations are 

very high (Drever, 1988, p. 310; Ceazan and others, 

1984). Iron and manganese concentrations were probably regulated by the oxidation/reduction conditions 

created by the nitrification/denitrification reactions and 

solubility constraints of siderite (FeCC^) and rhodochrosite (MnCO3 ; Welch, 1994, p. 88).

Principal component 4 explains 11 percent of the 

total variance and is not easily interpreted. Silica and 

pH are positively related, and potassium is negatively 

related with this component. Component 4 might represent nitrogen fertilizer used on residential lawns in 

the urban study area because potassium is an ingredient 

in the nitrogen fertilizers commonly used on lawns

0

LU h5! CL

o

C/D 

C/D

Q

ELEVATED NITRATE 

CONCENTRATIONS 

(NITROGEN OXIDATION)

O

o

o

-2

I

ELEVATED AMMONIA, 

MANGANESE, AND IRON 

CONCENTRATIONS 

(NITROGEN REDUCTION)

O

-1 0 1 

PRINCIPAL COMPONENT 3 SAMPLE SCORES

Figure 9. Relation between dissolved-oxygen concentrations and sample scores for principal component 3. Scores 

below -0.5 indicate nitrification; scores above 0.5 indicate nitrogen reduction (denitrification or nitrate reduction).

26 Nitrate and Ammonia in Shallow Ground Water, Carson City Urban Area, Nevada, 1989
(Berg, 1984). Potassium concentrations can be elevated in ground water beneath fertilized agricultural 

areas (Hallberg, 1989, p. 53; Weil and others, 1990). 

The silica might be related to dissolution of the silicacemented hardpan in Dalzell soils (Candland, 1979, 

p. 15) when lawns and other landscape areas are 

irrigated.

Principal component 5 explains 8 percent of the 

total variance and represents trichloroethylene (TCE) 

concentrations in the study area. No other constituent is 

related to this component. TCE is an organic compound commonly used in degreasing operations, dry 

cleaning, and offset-printing businesses. TCE is also 

commonly found in sewage-contaminated areas, particularly where there are septic-tank systems (Canter 

and Knox, 1985, p. 82), because it is commonly contained in commercial products used to rejuvenate septic-tank systems. TCE was detected at three sites (3,14, 

and 18) in the urban study area at concentrations of 0.2, 

0.3, and 20 |Hg/L (table 2). The ground-water samples 

from site 14 had the highest concentration of TCE in 

the urban study area, 44 |Hg/L (table 2).

Areal Relations Among Nitrate, Ammonia, and 

Other Properties and Constituents

Principal component sample scores (table 5) were 

used to map the estimated areal extent of principal 

components 1, 2, and 3 in the urban study area. These 

are illustrated in figures 10 and 11. Principal components depict constituents and properties that might be 

found together because they have the same source or 

are affected by the same processes. The component 

sample scores provide a way to relate individual 

ground-water samples to a principal component. These 

scores can be used to identify wells where the water 

quality might be affected by the source or process identified by the principal component. However, a sample 

might have high concentrations of several constituents 

that are not correlated and, therefore, will not associate 

with a component. A principal component will only 

consist of correlated data and not necessarily those 

with the highest values.

Figure 10 shows the estimated areal extent of 

sample scores for principal component 1, carbonate 

dissolution, in the first sampling period. This map indicates that ground water at wells 1,2,6, 9,10, and 13d 

(only the shallowest of each cluster well was used for

mapping), 14,15d, 17,18, 19, and 20 was strongly 

affected by carbonate dissolution (sample scores equal 

to or greater than 0.75; table 5).

Figure 10 also shows the estimated areal extent of 

sample scores for principal component 2, evaporite dissolution, in the first sampling period. These sample 

scores indicate that ground water at wells 3, 5,9,13d, 

15d, 17, and 18 was strongly affected by evaporite dissolution (sample scores equal to or greater than 0.75; 

table 5). Ground water at wells 4, 6, and 19 was moderately affected by evaporite dissolution (sample score 

between 0.5 and 1.00). Ground water at 10 sites was 

not affected by evaporite dissolution (sample scores 

less than 0.50). However, ground water was affected by 

both carbonate and evaporite dissolution at wells 6, 9, 

13d, 15d, 17,18, and 19.

Figure 11 shows the estimated areal extent of 

sample scores for principal component 3, nitrogen oxidation or reduction, in the first sampling period. Nitrification appears to strongly affect ground water at wells 

2,6,9,12,13d, 16,19, and 20 (sample scores equal to 

or smaller than -0.75; table 5); ground water was moderately affected at wells 1, 3, and 8 (sample scores 

between 0.50 and 0.75). Denitrification or nitrate 

reduction appears to have strongly affected ground 

water at wells 5, 7,10,14,15d, and 18 (sample scores 

equal to or greater than 1:00; table 5); ground water 

was moderately affected at well 17 (sample score 

between 0.50 and 1.00). Nitrate reduction may have 

affected the nitrate and ammonia concentrations in 

ground water at wells 10,14, and 18 as indicated by the 

relations among ammonia, iron, and manganese concentrations (table 2). Large iron and manganese concentrations have been related to nitrate reduction 

(Potsma and others, 1991). Some studies suggest that 

denitrification or nitrate reduction is uncommon in 

ground water because labile DOC concentrations are 

not high enough to sustain microbial populations 

(Smith and Duff, 1984; Starr and Gillham, 1993; 

Wilhelm and others, 1994). However, other research 

has shown that the requirement for labile DOC is not 

universal because reactions involving sulfide and iron 

may serve as a surrogate for DOC (Potsma and others, 

1991; Komor and Anderson, 1993). Also, Smith and 

Duff (1984) and Trudell and others (1986) show that 

denitrification depends more on organic carbon from 

soil than on DOC in ground water.

NITRATE AND AMMONIA IN SHALLOW GROUND WATER 27
Table 5. Principal component sample scores calculated for shallow ground-water samples, Carson City, Nev., urban study 

area

[Principal component score is a unitless, numerical index that associates each ground-water sample with a principal component (table 4). For each principal 

component, the score is calculated as follows: each constituent or property (chemical concentration, depth to water, well depth) associated with a sample is 

multiplied (normalized) by its loading coefficient (table 4); the new values are summed.]

Well 

number 1 

(figure 2)

1 

1

2 

2

3 

3

4 

4

5 

5

6 

6

7 

7

8 

8

9 

9

10 

10

11 

11

12 

12

13a 

13a

Principal component

1

1.70 

1.80

.80 

.80

.40 

-.40

-1.70 

-.80

-.10 

-.80

3.40 

3.70

-.80 

-.70

-1.10 

-.20

1.70 

-.70

1.50 

1.90

-1.50 

-1.30

-.20 

.20

1.30 

.90

2

-0.60 

-1.00

-1.4 

-1.5

1.40 

1.80

.50 

.70

2.90 

3.20

.70 

.60

-.60 

-.90

.10 

.70

1.60 

1.90

-1.80 

-1.90

-.20 

-1.80

-1.10 

-1.10

-.80 

-.40

3

-0.60 

-.80

-1.00 

-.50

-.70 

-.40

-.10 

-1.00

1.60 

.90

-1.90 

-1.40

2.00 

1.50

-.60 

-1.30

-1.50 

-1.30

1.90 

2.30

.30 

.50

-1.30 

-1.30

1.40 

1.80

4

1.70 

1.20

.60 

.90

1.00 

1.00

-.03 

.06

2.40 

2.10

.40 

.20

2.00 

1.70

-2.00 

-3.10

-2.30 

-1.70

.50 

.60

-2.10 

-1.00

.50 

.20

-1.40 

-1.30

5

0.30 

.20

.10 

.70

4.40 

2.90

1.40 

.90

.70 

.40

1.30 

1.30

-.40 

-.60

.40 

-.40

1.20 

.20

.60 

.50

.90 

1.30

1.10 

.90

.40 

2.30

Well 

number 1 

(figure 2)

13b 

13b

13c 

13c

13d 

13d

14 

14

15a 

15a

15b 

15b

15c 

15c

15d 

15d

16 

16

17 

17

18 

18

19 

19

20 

20

Principal component

1

1.20 

1.40

1.00 

1.00

1.20 

.90

2.30 

2.20

-.50 

-.80

1.70 

.70

1.20 

.50

1.50 

.70

-.50 

-.70

2.40 

2.20

2.10 

1.60

1.50 

1.30

.90 

.80

2

1.00 

.80

1.70 

1.50

1.90 

2.10

.20 

0.10

-.80 

-.50

-.70 

-.10

.10 

.30

1.60 

1.80

-.40 

-.30

1.00 

1.00

1.50 

1.40

.70 

.80

-.30 

-.60

3

1.70 

1.50

1.50 

.90

-1.00 

-.60

1.80 

1.70

-.10 

.30

1.80 

1.50

1.90 

1.30

1.40 

.50

-.80 

-.80

.60 

.40

2.30 

2.30

-1.40 

-2.00

-1.50 

-1.30

4

-1.20 

-1.70

-1.30 

-2.20

-1.70 

-1.40

-.60 

-0.60

.10 

.20

-.10 

.04

.40 

.20

1.40 

1.60

1.40 

1.50

-.60 

-.50

-.20 

.10

2.30 

2.30

1.70 

1.60

5

2.50 

3.10

2.20 

2.60

-.20 

-.30

3.20 

4.20

-.20 

-.10

-.40 

.30

-.40 

.10

-.70 

-.40

.40 

.50

-1.90 

-1.90

-.40 

3.00

.10 

1.70

.20 

.50

1 Samples collected twice at each well: January to March 1989 and May to June 1989

28 Nitrate and Ammonia In Shallow Ground Water, Carson City Urban Area, Nevada, 1989
119°47 119°44'

39°09'

EXPLANATION

Urban study area No carbonate or evaporite 

dissolution

Area served by septic-tank systems

Principal component 1 Carbonate dissolution. 

Area estimated by simple interpolation

Principal component 2 Evaporite dissolution. 

Area estimated by simple interpolation

Principal components 1 and 2 Evaporite and 

carbonate dissolution. Area estimated by simple 

interpolation

o Well G Well cluster 

Constituent concentrations, 

in milligrams per liter

90

40

10

50

Well number

Calcium 

Sodium 

Chloride 

Sulfate

Figure 10. Estimated areal distribution of sample scores for principal component 1 (carbonate 

dissolution) and principal component 2 (evaporite dissolution) in shallow ground water beneath the 

Carson City, Nev., urban study area, January-March 1989.

NITRATE AND AMMONIA IN SHALLOW GROUND WATER 29
119°47' 119°44'

39°09'

EXPLANATION

Urban study area Neither oxidation nor 

reduction of nitrogen

Area served by septic-tank systems

o Well D Well cluster

Constituent concentrations, 

in milligrams per liter

Principal component 3 Denitrification / reduction 

of nitrogen; area estimated by simple interpolation

Principal component 3 Nitrification of nitrogen; 

area estimated by simple interpolation

Figure 11. Estimated area! distribution of sample scores for principal component 3 (nitrification or 

denitrification/nitrate reduction) in shallow ground water beneath the Carson City, Nev., urban study 

area, January-March 1989.

1

0.03 

8.5 

0.07 

3.8

Well number

Ammonia, as N 

Nitrate, as N 

Manganese 

Dissolved oxygen

30 Nitrate and Ammonia in Shallow Ground Water, Carson City Urban Area, Nevada, 1989
Relations Among Nitrate, Ammonia, and Well 

Depth

The well clusters at sites 13 and 15 (fig. 2) were 

constructed to measure nitrate and ammonia concentrations at increasing depths within the shallow part of the 

basin-fill aquifer. At these two sites, only water samples from site 13 had nitrate concentrations greater than 

background levels and showed distinct differences in 

concentration with depth. Site 13 is within the landscaped areas of a city park that receives nitrogen-based 

fertilizers and site 15 is in an irrigated pasture. The 

shallowest well (d) at site 13 had 38 mg/L of nitrate in 

a water sample collected during the first sampling 

period (table 2).

In both sampling periods, at site 13, nitrate and 

dissolved-oxygen concentrations were highest in well 

13d while TCE, specific conductance, ammonia, iron, 

and manganese concentrations were lowest (fig. 12). 

Nitrate and dissolved-oxygen concentrations were 

lowest in wells 13a, b, and c, while TCE, specific conductance, ammonia, iron, and manganese were highest 

(fig. 12). The highest ammonia concentrations were in 

samples from well 13b; the highest iron concentrations 

(12 mg/L) were in water samples from well 13a, the 

deepest well in this cluster (fig. 12).

PCA showed that ground-water samples from 

well 13d were related to principal component 1 (carbonate dissolution), principal component 2 (evaporite 

dissolution), the nitrification part of principal component 3, and to potassium in principal component 4 

(table 5). PCA showed that water samples from well 

13c were related to components 1 and 2 (carbonate and 

evaporite dissolution), the denitrification/reduction 

part of component 3, the potassium part of component 

4, and component 5 (TCE). PCA showed that water 

samples from well 13b and 13a were related to component 1 (carbonate dissolution), the nitrogen reduction 

part of component 3, the potassium part of component 

4, and component 5 (TCE). Water samples from well 

13b were related to component 2 (evaporite dissolution), but water samples from well 13a were not (table 

5).

The elevated ammonia, TCE, and specific conductance; the apparent relations among dissolved oxygen, nitrate, ammonia, iron, and manganese relative to 

well depth; and PCA suggest that sewage effluent is 

undergoing denitrification or nitrate reduction, perhaps 

in a plume, about 20 ft below land surface at site 13. 

Nitrate reduction, the microbial mediated conversion

of nitrate to ammonia under anoxic conditions, is commonly associated with high iron or manganese concentrations (Stumm and Morgan, 1981, p. 516-517; 

Drever, 1988, p. 310-314). The strong PCA signature 

for potassium in water samples from wells 13c and b 

was similar to that in samples from well 13d. This 

potassium signature is difficult to interpret, but could 

be associated with either sewage effluent or shallow 

ground water containing potassium from fertilizers that 

mixes with deeper water, possibly as a result of fertilizer and lawn irrigation applied upgradient from site 

13.

Although PCA seems to be capable of identifying 

sources of nitrogen in wells, ambiguities and uncertainties in the interpretation remain. A more definitive 

identification of nitrate and ammonia sources in the 

ground water beneath the Carson City urban area 

would require more study. Information on nitrogen and 

oxygen isotopes in the nitrate ion and sewage-related 

constituents, such as caffeine, ascorbic acid, or derivatives of fecal steroids, could determine sources of 

nitrate and ammonia. Data from additional wells would 

help define the ground-water flow regime and determine nitrate and ammonia sources.

SUMMARY

A network of 26 shallow observation wells at 20 

sites was established within a small part of the Carson 

City urban area. Single wells were constructed at 18 

sites. Clustered sets of four nested wells were constructed at 2 sites. All single wells and the shallowest 

wells at both nested sites penetrated the upper 15 ft of 

saturated sediments in the basin-fill aquifer. All 26 

wells were sampled twice during the first 6 months of 

1989.

Water-table altitudes increased an average of 1 ft 

between the first and second sampling periods in the 

urban study area. Specific conductance ranged from 

380 to 1,970 nS/cm. The highest specific conductance 

was measured in the southwestern part of the study area 

and the second highest was measured in the northeastern part of the study area.

Water samples collected from the wells in 1989 

contained concentrations of nitrate, as nitrogen, that 

ranged from below the laboratory reporting limit of 0.1 

mg/L to 38 mg/L. A nonparametric t-test showed that 

nitrate concentrations measured in the shallow ground 

water during sampling-period one (January-March

SUMMARY 31
LU

o

2

CC 

^ 

CO 

Q

I

LU 

CO

LU 

LJJ 

LL

10

15

20

25

30

35

40

- b

- a LABORATORY REPORTING' 

LIMIT

MILLIGRAMS PER 

LITER

MICROGRAMS PER 

LITER

- SPECIFIC

CONDUCTANCE

MICROSIEMENS PER 

CENTIMETER AT 25° C

£E 

LJJ

Q 

LU

CO 

LL 

O

LU 

Q

10

15

20

25

30

35

40 ,

<y

AMMONIA, AS N DISSOLVED 

OXYGEN

DISSOLVED 

IRON

DISSOLVED 

MANGANESE

fa.

MILLIGRAMS PER LITER

EXPLANATION

D January-March 1989

 May-June 1989

Figure 12. Relations between well depth and nitrate, trichloroethylene, ammonia, dissolved-oxygen, dissolved-iron, and 

dissolved-manganese concentrations, and specific conductance for wells a, b, c, and d at well cluster 13, Carson City, Nev., 

urban study area, January-March 1989 and May-June 1989. Concentrations of iron and manganese are shown only for 

March 1989 because concentrations were equal for both sampling periods. Some X-axis scales are logarithmic.

32 Nitrate and Ammonia in Shallow Ground Water, Carson City Urban Area, Nevada, 1989
1989) were not statistically different from those measured in sampling-period two (May-June 1989). The 

first-period samples from 12 of the 20 shallow wells 

contained more than 3.0 mg/L of nitrate. Samples from 

six of the first-period wells and three of the secondperiod wells had nitrate concentrations that exceeded 

the Nevada drinking-water standard of 10 mg/L. 

Nitrate concentrations decreased by an average of 2 

mg/L between the first and second sampling periods. 

This difference in nitrate concentrations was not 

related to changes in the depth to water between the 

two sampling periods. A comparison of chloride and 

boron concentrations between the two sampling periods showed that the higher water table during the second sampling period generally did not affect nitrate 

concentrations.

Ammonia concentrations for all samples ranged 

from less than 0.01 to 0.26 mg/L. Concentrations were 

not statistically different in the two sampling periods 

and were not affected by the higher water table in the 

second period, although concentrations were lower in 

second-period samples from five wells.

Scatterplots and nonparametric correlation 

showed many statistically significant relations among 

nitrate and ammonia concentrations and the other constituents and properties measured during the study. 

Robust multiple regression showed relations similar to 

those of the correlation analysis; the differences were 

probably partly caused by the method used to select the 

regression variables (Mallow's Cp).

A principal components analysis with varimax 

rotation resulted in five principal components that 

accounted for 74 percent of the data-set variance. The 

first component represents carbonate dissolution (24 

percent of total variance), the second represents 

evaporite dissolution (18 percent of the total variance), 

the third represents nitrification/denitrification or nitrogen reduction (13 percent of the total variance), the 

fourth component represents potassium, silica, and pH 

relations (11 percent of the total variance), and the fifth 

component represents trichloroethylene (TCE; 8 percent of the total variance).

The estimated area! extent of principal component scores in the urban study area is shown on maps 

(figs. 10,11). Sample scores for principal component 1 

(carbonate dissolution) indicate that calcium, magnesium, bicarbonate, and dissolved organic carbon

(DOC) were strongly related in samples from 12 wells 

during the first sampling period of the urban study. 

Scores for principal component 2 (evaporite dissolution) from the first sampling period indicate that 

sodium, sulfate, chloride, and boron were strongly 

related in samples from seven wells and moderately 

related in samples from three wells. Seven of those 

samples were also related to calcium, magnesium, 

bicarbonate, and DOC. Sample scores for principal 

component 3 (nitrification/denitrification or reduction) 

showed that nitrification affected nitrate and ammonia 

concentrations at 11 wells dunng the first sampling 

period. Ammonia, iron, and manganese were related in 

samples from seven wells. This indicates that reducing 

conditions exist that favor either denitrification or 

nitrate reduction. Samples from three wells had high 

iron and manganese concentrations that may indicate 

nitrate reduction. Samples scores for principal components 4 and 5 could not be interpreted and therefore 

were not mapped.

Clusters of four wells screened at different depths 

were installed at two sites to assess nitrate and ammonia concentrations in the shallow part of the basin-fill 

aquifer. Of water samples from the two sites, only those 

from site 13 had measurable concentrations of nitrate 

and distinct differences in nitrate with depth. In both 

sampling periods, nitrate and dissolved-oxygen concentrations were highest in the shallowest well (20 ft 

below land surface), whereas TCE, specific conductance, ammonia, iron, and manganese concentrations 

were lowest. In contrast, nitrate and dissolved-oxygen 

concentrations were lowest in the three deepest wells, 

whereas TCE, specific conductance, ammonia, iron, 

and manganese were highest. The highest ammonia, 

iron, and manganese concentrations were in samples 

from the second deepest well at site 13. The associations among nitrate, ammonia, iron, and manganese 

concentrations in the principal components analysis 

(PCA) indicate that nitrate concentrations in samples 

from the shallowest well were related to nitrification. 

The source of nitrate may be fertilizer application. The 

PCA associations indicate that ammonia, iron, and 

manganese concentrations may be related to denitrification or nitrate reduction in the deeper wells at site 13. 

The elevated TCE, specific conductance, ammonia,

SUMMARY 33
iron, and manganese values in water from the deeper 

wells at site 13 suggest that those wells may be affected 

by sewage.

Correlation analysis, robust multiple regression 

analysis, and principal components analysis were used 

to evaluate water-quality data collected from the Carson City urban area shallow aquifer. Wells where 

ground-water quality is affected by carbonate and 

evaporite constituents and where nitrification or nitrogen reduction has affected nitrogen concentrations 

were identified. However, the source or sources of 

nitrate ana ammonia concentrations could not be identified.

REFERENCES CITED

Afifi, A.A., and Clark, Virginia, 1984, Computer-aided 

multivariate analysis: Belmont, Calif., Lifetime 

Learning Publications, 458 p.

Armstrong, A.T., and Fordham, J.W., 1977, Investigation of 

ground-water quality and its effect on suburban development in Washoe Valley, Nevada: University of 

Nevada, Desert Research Institute Project Report 

41048, 60 p.

Arteaga, F.E., 1986 [1990], Mathematical model analysis of 

the Eagle Valley ground-water basin, west-central 

Nevada: Nevada Division of Water Resources, Bulletin 

45, 53 p.

Berg, G.L., 1984, Farm Chemicals Handbook: Willoughby, 

Ohio, Meister Publishing Co,, 508 p.

Birkeland, P.W., 1974, Pedology, weathering, and geomorphological research: New York, Oxford University 

Press, 285 p.

Bormann, F.H., Likens, G.E., Fisher, D.W, and Pierce, R.S., 

1968, Nutrient loss accelerated by clear-cutting of a 

forest ecosystem: Science, v. 159, p. 882-884,

Candland, D.M., 1979, Soil survey of Carson City area, 

Nevada: U.S. Soil Conservation Service and Forest 

Service, 169 p.

Canter, L.W, and Knox, R.C., 1985, Septic tank system 

effects on ground water quality: Chelsea, Mich., Lewis 

Publishers, 336 p.

Ceazan, M.L., Updegraff, D.M., and Thurman, E.M., 1984, 

Evidence of microbial processes in sewage-contaminated ground water, in LeBlanc, D.R., ed., Movement 

and fate of solutes in a plume of sewage-contaminated 

ground water, Cape Cod, Massachusetts: U.S. Geological Survey Toxic Waste Ground-water Contamination 

Program, U.S. Geological Survey Open-file Report 84- 

475, 175 p.

Conover, W.J., 1980, Practical nonparametric statistics 

(2d ed.): New York, John Wiley, 493 p.

Davis, J.C., 1986, Statistics and data analysis in geology 

(2d ed): New York, John Wiley, 646 p.

D'ltri, F.D., Kittleson, K.M., Kruska, R.L., 1985, Spatial 

analysis of Michigan Department of Public Health 

nitrate data: East Lansing, Mich., Michigan State 

University, Institute of Water Resources, 21 p.

Doner, H.E., and Lynn, W.C., 1977, Carbonate, halide,

sulfate, and sulfide minerals, in Dixon, J.B., and Weed, 

S.B., eds., Minerals in soil environments: Madison, 

Wis., Soil Science Society of America, 909 p.

Drever, J.I., 1988, The geochemistry of natural waters

(2d ed.): Englewood Cliffs, N. J., Prentice-Hall, 437 p.

Druliner A.D., 1989, Overview of the relations of nonpointsource agricultural chemical contamination to local 

hydrogeologic, soil, land-use, and hydrochemical characteristics of the High Plains aauifer of Nebraska, in 

Mallard, G.E., and Ragone, S.E., eds., U.S. Geological 

Survey Toxic Substances Hydrology Program, Proceedings of the Technical Meeting, Phoenix, Ariz., September 26-30, 1988: U.S. Geological Survey WaterResources Investigations Report 88-4220, p. 411-435.

Eckhardt, D.A.V., Flipse, W.J., Jr, and Oaksford, E.T., 1989, 

Relation between land use and ground-water quality in 

the upper glacial aquifer in Nassau and Suffolk Counties, Long Island, New York: U.S. Geological Survey 

Water-Resources Investigations Report 86-4142, 35 p.

Fishman, M.J., and Friedman, L.C., eds., 1989, Methods for 

the determination of inorganic substances in water and 

fluvial sediments: U.S. Geological Survey Techniques 

of Water-Resources Investigations, book 5, chap. Al, 

545 p.

Gilbert, R.O., 1987, Statistical methods for environmental 

pollution monitoring: New York, Van Nostrand Reinhold, 320 p.

Hallberg, G.R., 1989, Nitrate in ground water in the United 

States, in Follett, R.F., ed., Nitrogen management and 

ground water protection: New York, Elsevier, Developments in Agricultural and Managed-Forest Ecology 21, 

p. 35-74.

Hardy, M.A., Leahy, P.P., and Alley, W.M., 1989, Well

installation and documentation, and ground-water sampling protocols for the pilot National Water-Quality 

Assessment Program: U.S. Geological Survey OpenFile Report 89-396, 36 p.

Hem, J.D., 1985, Study and interpretation of the chemical 

characteristics of natural water [3d ed].: U.S. Geological Survey Water-Supply Paper 2254,264 p.

Hirsch, R.M., Alley, W.M., and Wilbur, W.G., 1988, Concepts for a National Water-Quality Assessment Program: U.S. Geological Survey Circular 1021,42 p.

Hynes, H.B.N., 1970, The ecology of running waters: Liverpool, Great Britain, Liverpool University Press, 555 p.

34 Nitrate and Ammonia in Shallow Ground Water, Carson City Urban Area, Nevada, 1989
Komor, S.C., and Anderson, H.W., Jr., 1993, Nitrogen isotopes as indicators of nitrate sources in Minnesota sandplain aquifers: Ground Water, v. 31, p. 260-270.

Lawrence, S.J., and Wigington, P.J., Jr., 1987, Oxidized 

nitrogen in precipitation, throughfall, and streamflow 

from a forested watershed in Oklahoma: Water 

Resources Bulletin, v. 23, p. 1069-1076.

LeBlanc, D.R., 1984, Sewage plume in a sand and gravel 

aquifer, Cape Cod, Massachusetts: U.S. Geological 

Survey Water-Supply Paper 2218, 28 p.

Likens, G.E., Bormann, F.H., Pierce, R.S., Eaton, J.S., and 

Johnson, N.M., 1977, Biogeochemistry of a forested 

ecosystem: New York, Springer-Verlag, 146 p.

Lowrance, R.R., and Pionke, H.B., 1989, Transformations 

and movement of nitrate in aquifer systems, in Follett, 

R. E, ed., Nitrogen management and ground water protection: New York, Elsevier, Developments in Agricultural and Managed-Forest Ecology 21, p. 373-392.

Madison, R.J., and Brunett, J.O., 1985, Overview of the 

occurrence of nitrate in ground water of the United 

States, in National water summary 1984 Hydrologic 

events, selected water-quality trends, and ground-water 

resources: U.S. Geological Survey Water-Supply Paper 

2275, p. 93-105.

Marret, D.J., Khattak, R.A., Elseewi, A.A., Page, A.L., 

1990, Elevated nitrate levels in soils of the eastern 

Mojave Desert: Journal of Environmental Quality, 

v. 19, p. 658-663.

Maurer, D.K., and Fischer, J.M., 1988, Recharge to the Eagle 

Valley ground-water basin by streamflow in Vicee 

Canyon, west-central Nevada: U.S. Geological Survey 

Water-Resources Investigations Report 88-4158, 61 p.

Meglen, R.R, and Sistko, R.I., 1985, Evaluating data quality 

in large data bases using pattern-recognition techniques, in Environmental applications of chemometrics: American Chemical Society, 80 p.

Milburn, P., Richards, J.E., Gartley, C, Pollock, T., O'Neill, 

H., and Bailey, H., 1990, Nitrate leaching from systematically tiled potato fields in New Brunswick, Canada: 

Journal of Environmental Quality, v. 19, p. 448-454.

Montgomery, D.C., and Peck, E.A., 1982, Introduction to 

linear regression analysis: New York, John Wiley, 

504 p.

Nevada Bureau of Health Protection Services, 1992, Public 

water system Quality: Nevada Administrative Code, 

Chapter 445, p. 49-52.

Nowlin, J.O., 1982, Ground-water levels and water quality 

in an area near Topaz Lake, Douglas County, Nevada: 

U.S. Geological Survey Open-File Report 80-2046, 

76 p.

Ott, Lyman, 1988, Introduction to statistical methods and 

data analysis, 3d. ed.: Boston, Mass., PWS-Kent Publishing Co., 835 p.

Part, R.O., and Hess, J.W, 1976, Characterization of nitrogen sources contaminating shallow ground water in an 

arid basin, Las Vegas area, Nevada: University of 

Nevada, Desert Research Institute Technical Report 

HW-26,44 p.

Potsma, D., Boesen, C., Kristiansen, H., and Larsen, F, 

1991, Nitrate reduction in an unconfined sandy aquifer: 

Water Resources Research, v. 27, p. 2027-2045.

Puckett, L.J., and Bricker, O.P, 1992, Factors controlling the 

major ion chemistry of streams in the Blue Ridge Valley 

and Ridge physiographic provinces of Virginia and 

Maryland: Hydrological Processes, v. 6, p. 79-98.

Rexstad, E.A., Miller, D.D., Flather, C.H., Anderson, E.M., 

Hupp, J.W., Anderson, D.R., 1988, Questionable multivariate statistical inference in wildlife habitat and community studies: Journal of Wildlife Management, v. 52S 

p. 794-798.

Ruiz, F., Gomis, V, and Blasco, P., 1990, Application of factor analysis to the hydrogeochemical study of a coastal 

aquifer: Journal of Hydrology, v. 119, p. 169-177.

SAS Institute, Inc., 1990, Statistical analysis system users 

guide, SAS/STAT: Raleigh, N.C., SAS Institute, Inc., 

vol. 1 and 2, version 6,4th ed., 851 p.

Smith, R.L, and Duff, J.H., 1984, Preliminary study of denitrification in a plume of sewage-contaminated ground 

water, in LeBlanc, D.R., ed., Movement and fate of solutes in a plume of sewage-contaminated ground water, 

Cape Cod, Massachusetts: U.S. Geological Survey 

Toxic Waste Ground-water Contamination Program, 

U.S. Geological Survey Open-file Report 84-475, 

175 p.

Snoeyink, V.L., and Jenkins, David, 1980, Water chemistry: 

New York, John Wiley, 463 p.

Starr, R.C., and Gillham, R.W, 1993, Denitrification and 

organic carbon availability in two aquifers: Ground 

Water, v. 31, p. 934-947.

Stumm, Werner, and Morgan, J.J., 1981, Aquatic chemistry An introduction emphasizing chemical equilibria 

in natural waters, 2d ed.: New York, John Wiley, 780 p.

Thomas, J.M., and Lawrence, S.J., 1994, Ground-water 

quality and geochemistry in Dayton, Stagecoach, and 

Churchill Valleys, western Nevada: U.S. Geological 

Survey Open-File Report 93-356, 69 p.

Trudell, M.R., Gillham, R.A., and Cherry, J.A., 1986, An insitu study of the occurrence and rate of denitrification in 

a shallow unconfined sand aquifer: Journal of Hydrology, v. 83, p. 141-268.

U.S. Environmental Protection Agency, 1973, Nitrogenous 

compounds in the environment: Washington, D.C., U.S. 

Government Printing Office, EPA-SAB-73-001, 

unpaginated.

REFERENCES CITED 35
U.S. Environmental Protection Agency, 1986a, Maximum 

contaminant levels (subpart B of part 141, National 

interim primary drinking-water regulations): U.S. Code 

of Federal Regulations, Title 40, parts 100 to 149, 

revised as of July 1, 1986, p. 524-528.

U.S. Environmental Protection Agency, 1986b, Quality criteria for water: Washington, D.C., U.S. Government 

Printing Office, EPA 440/5-86-001, unpaginated.

Verry, E.S., and Timmons, T.R., 1982, Waterborne nutrient 

flow through an upland-peatland watershed in Minnesota: Ecology, v. 63, p. 1456-1467.

Vitousek, P.M., and Melillo, J.M., 1979, Nitrate losses from 

disturbed forests Patterns and mechanisms: Forest 

Science, v. 25, p. 605-619.

Weil, R.R., Weismiller, R.A., and Turner, R.S., 1990, Nitrate 

contamination of ground water under irrigated coastal 

plain soils: Journal of Environmental Quality, v. 19, 

p. 441-448.

Welch, A.H., 1994, Ground-water quality and geochemistry 

in Carson and Eagle Valleys, western Nevada and eastern California: U.S. Geological Survey Open-File 

Report 93-33, 99 p.

Welch, A.H., and Plume, R.W, 1987, Water-quality assessment of the Carson River ground-water basin, Nevada 

and California Project description: U.S. Geological 

Survey Open-File Report 87-104, 27 p.

Wershaw, R.L., Fishman, M.J., Grabbe, R.R., and Lowe, 

L.E., eds., 1987, Methods for the determination of 

organic substances in water and fluvial sediments: U.S. 

Geological Survey Techniques of Water-Resources 

Investigations, book 5, chap. A3, 80 p.

Whitney, Rita, 1994, Data on ground-water Quality in the 

Carson River Basin, western Nevada and eastern California, 1987-90: U.S. Geological Survey Open-File 

Report 94-39, 139 p.

Wilhelm, S.R., Schiff, S.L., and Cherry, J.A., 1994, Biogeochemical evolution of domestic waste water in septic systems 1. Conceptual model: Ground Water, 

v. 32, p. 905-916.

Worts, G.F., Jr., and Malmberg, G.T., 1966, Hydrologic 

appraisal of Eagle Valley, Ormsby County, Nevada: 

Nevada Department of Conservation and Natural 

Resources, Water Resources - Reconnaissance Report 

39, 55 p.

Yates, M.V, 1985, Septic tank density and ground-water 

contamination: Ground Water, v. 23, p. 586-591.

36 Nitrate and Ammonia in Shallow Ground Water, Carson City Urban Area, Nevada, 1989
Appendix

Scatterplots of well depth, depth to water, and hydrogeologic and water-quality properties in shallow 

ground water, Carson City, Nev., urban study area, January-March 1989. r, Spearman's rank-correlation 

coefficient; p, p-value (probability that correlation is due to chance), p-value of 0.05 or less indicates 

statistically significant correlation.

APPENDIX 37
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CONCENTRATION, IN MILLIGRAMS PER LITER

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p _,. O p p p o IL -L o b '-* iv> co 

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CALCIUM

25 50 75 0 125 250 375 0 2 4 6 8 10

MAGNESIUM SODIUM POTASSIUM 

CONCENTRATION, IN MILLIGRAMS PER LITER

APPENDIX 47
CONCENTRATION, IN MILLIGRAMS PER LITER

AMMONIA, AS N NITRATE, AS N CHLORIDE SULFATE

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DISSOLVED ORGANIC

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0 0.1 0.2 0.3 0.0 0.1 0.2 0.3 0.4 0.5 0.0 0.1 0.2 0.3 0.4 0.01 0.1 1 1

AMMONIA, AS N ORTHOPHOSPHATE, AS P BARIUM BORON

CONCENTRATION, IN MILLIGRAMS PER LITER

APPENDIX 51
CONCENTRATION, IN MILLIGRAMS PER LITER

DISSOLVED ORGANIC 

CARBON SILICA

DQ.

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01234 0.0 0.5 1.0 1.5 2.0

MANGANESE STRONTIUM 

CONCENTRATION, IN MILLIGRAMS PER LITER

0 20 40 60 80 

SILICA

APPENDIX 53