Magnitude, Extent, and Potential Sources of 

Nitrate in Ground Water in the 

Gallatin Local Water Quality District, 

Southwestern Montana, 1997-98

U.S. Department of the Inferior 

U.S. Geological Survey

U.S. Department of the Interior 

U.S. Geological Survey

Magnitude, Extent, and Potential Sources of 

Nitrate in Ground Water in the 

Gallatin Local Water Quality District, 

Southwestern Montana, 1997-98

By Eloise Kendy

Water-Resources Investigations Report 01-4037

In cooperation with the

GALLATIN LOCAL WATER QUALITY DISTRICT
U.S. Department of the Interior

GALE A. NORTON, Secretary

U.S. Geological Survey

Charles G. Groat, Director

Any use of trade, product, or firm name in this publication is for 

descriptive purposes only and does not imply endorsement by the 

U.S. Government

Helena, Montana 

March 2001

For additional information write to:

District Chief 

U.S. Geological Survey 

3162 Bozeman Avenue 

Helena, MT 59601-6456

Copies of this report may be purchased from:

U.S. Geological Survey 

Branch of Information Services 

Box 25286 

Denver, CO 80225-0286
CONTENTS

Page

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

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

Purpose and scope...................................................................................................................................................... 2

Site-numbering system ............................................................................................................................................. 2

Acknowledgments..................................................................................................................................................... 2

Methods of data collection and analysis ............................................................................................................................... 4

Well inventory and water-level measurement........................................................................................................... 4

Water-quality sampling and analysis......................................................................................................................... 4

Stable isotopes of water.................................................................................................................................. 5

Nitrogen isotopes of nitrate............................................................................................................................ 6

Chlorofluorocarbons....................................................................................................................................... 7

Description of the study area ................................................................................................................................................ 7

Physiography, drainage, and climate......................................................................................................................... 7

Land and water use.................................................................................................................................................... 9

Hydrogeology........................................................................................................................................................................ 11

Hydrogeologic units................................................................................................................................................... 12

Basin-fill deposits........................................................................................................................................... 12

Bedrock.......................................................................................................................................................... 13

Ground-water occurrence, movement, and recharge................................................................................................. 16

Ground-water quality................................................................................................................................................. 21

Magnitude and extent of nitrate in ground water.................................................................................................................. 23

Potential sources of nitrate in ground water.......................................................................................................................... 26

Timber harvests ......................................................................................................................................................... 27

Atmospheric deposition............................................................................................................................................. 27

Livestock waste ......................................................................................................................................................... 27

Fertilizer and soil organic nitrogen............................................................................................................................ 29

Domestic septic-system effluent................................................................................................................................ 32

Summary..................................................................................................................................................................^ 36

References cited .................................................................................................................................................................... 37

Data....................................................................................................................................................................................... 42

ILLUSTRATIONS

Figure 1. Map showing location of the Gallatin Local Water Quality District, Montana............................................ 3

2. Diagram showing site-numbering system..................................................................................................... 4

3. Map showing topographic features and average annual precipitation in the Gallatin Local Water

Quality District, Montana.......................................................................................................................... 8

4. Graph showing mean monthly air temperature and precipitation at the Belgrade Airport Weather

Station, Montana....................................................................................................................................... 9

5. Map showing generalized land uses in the Gallatin Local Water Quality District, Montana....................... 10

6. Graph showing acres of farmland in Gallatin County, Montana, 1929-92................................................... 11

7. Map showing generalized hydrogeologic units in the Gallatin Local Water Quality District, Montana ..... 14

8. Map showing water-level contours and approximate direction of ground-water flow in the basin-fill

deposits in April 1998, and approximate ground-water recharge dates, Gallatin Local Water Quality

District, Montana....................................................................................................................................... 17

9. Perspective view and diagrammatic hydrogeologic section showing ground-water recharge and flow in

the basin-fill deposits in the Gallatin Local Water Quality District, Montana ......................................... 18

CONTENTS iii
ILLUSTRATIONS-Continued

Page

Figure 10. Hydrographs of selected wells in the Gallatin Local Water Quality District, Montana............................... 19

11. Graph showing relation between S18O and 8D in ground water and the Gallatin River, Gallatin

Local Water Quality District, Montana, 1998........................................................................................... 20

12. Modified trilinear diagram showing percentages of major ions in ground water, Bozeman Hot

Springs, and the Gallatin River in the Gallatin Local Water Quality District, Montana.......................... 22

13. Map showing nitrate concentrations in ground water and the Gallatin River, Gallatin Local Water

Quality District, Montana, 1998................................................................................................................ 24

14. Boxplots showing range of nitrate concentrations in ground water in relation to hydrogeologic

unit and land use, Gallatin Local Water Quality District, Montana, 1998................................................ 25

15. Graph showing seasonal changes in nitrate concentrations in water from selected wells in the

Gallatin Local Water Quality District, Montana....................................................................................... 26

16. Graph showing relation between nitrate concentrations and 8 15NN03 values for ground water in the

Gallatin Local Water Quality District, Montana....................................................................................... 28

17. Graphs showing nitrate concentrations of hypothetical mixed waters as a function of 6J 5NNO3................. 30

18. Map showing nitrate concentrations and 8 15NNO3 values in ground water in the western half of the

Royal Arabian subdivision, Gallatin Local Water Quality District, Montana, 1998................................ 33

19. Graph showing relation between chloride and bromide concentrations in ground water, Gallatin

Local Water Quality District, Montana, 1998........................................................................................... 35

TABLES

Table 1. Well data and chloride and nitrate concentrations in ground water in the Gallatin Local Water

Quality District, Montana.......................................................................................................................... 43

2. Summary of water-level data for wells in the Gallatin Local Water Quality District water-level

monitoring network, Montana................................................................................................................... 53

3. Water-quality data for ground and surface water in the Gallatin Local Water Quality District,

Montana, 1998........................................................................................................................................... 56

4. Chlorofluorocarbon (CFC) data and estimated recharge dates for ground water in the Gallatin

Local Water Quality District, Montana, 1998........................................................................................... 64

5. 'Drinking-water standards and guidelines for public-water supply ............................................................... 66

iv Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
CONVERSION FACTORS, VERTICAL DATUM, ABBREVIATED WATER-QUALITY UNITS, ABBREVIATED 

HYDROGEOLOGIC UNITS, AND ACRONYMS

Multiply _________ By _______To obtain

acre

cubic foot per second (ft3/s)

foot (ft)

foot per foot (ft/ft)

foot per mile (ft/mi)

foot squared per day (ft2/d)

gallon per minute (gal/min)

gallon per minute per foot

[(gal/min)/ft]

inch (in.)

mile (mi)

. ounce

pound (Ib)

pound per acre (Ib/acre)

square mile (mi )

0.4047

0.028317

0.3048

1.0

0.1894

0.09290

0.06309

0.2070

25,400

1.609

28.35

453.6

1.121

2.59

hectare

cubic meter per second

meter

meter per meter

meter per kilometer

meter squared per day

liter per second (L/s)

liter per second per meter

micrometer (|im)

kilometer

gram (g)

gram

kilograms per hectare

square kilometer

Temperature can be converted to degrees Celsius (°C) or degrees Fahrenheit (°F) by the following equations:

°C = 5/9 (°F - 32) 

°F = 9/5 (°C) + 32

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929) a geodetic datum derived 

from a general adjustment of the first-order level nets of both the United States and Canada, formerly called Sea Level Datum of 1929.

Chemical concentration in water is reported in milligrams per liter (mg/L) or micrograms per liter (ng/L). Milligrams per liter is a unit 

expressing the solute mass (milligram) per unit volume (liter) of water and is about the same as parts per million unless concentrations are 

more than 7,000 milligrams per liter (Hem, 1985, p. 55). One thousand micrograms per liter is equivalent to 1 milligram per liter. 

Specific conductance of water is a measure of the ability of water and dissolved constituents to conduct an electrical current and is an indication of the ionic strength of the solution. Specific conductance is expressed in microsiemens per centimeter at 25°C (|iS/cm) and increases 

with the concentration of dissolved constituents.

Abbreviated water-quality units used in this report:

	microsiemens per centimeter at 25 degrees Celsius 

mg/L milligrams per liter 

mL milliliter 

mm millimeter 

Jim micrometer 

%o permil (or parts per thousand) 

pg/kg picogram per kilogram

CONTENTS
Abbreviated hydrogeologic units used in this report:

Cenozoic basin-fill deposits:

Qal Quaternary alluvium

QTd Quaternary and Tertiary deposits, undifferentiated

Tb Tertiary Bozeman Group

Bedrock

TV Volcanic rocks (Eocene)

TYsaq Sedimentary bedrock potential aquifers (Paleocene through Middle Proterozoic)

KGscu Sedimentary bedrock typically confining units (Cretaceous through Cambrian)

Am Metamorphic rocks (Archean)

Acronyms used in this report:

CFCs chlorofluorocarbons.

CFC-11 trichlorofluoromethane

CFC-12 dichlorodifluoromethane

CFC-113 trichlorotrifluoroethane

GIRAS Geographic Information Retrieval and Analysis System

GIS Geographic Information System

GLWQD Gallatin Local Water Quality District

MCL Maximum Contaminant Level

NWQL National Water Quality Laboratory, Denver, Colo.

SLAP Standard Light Antarctic Precipitation

SMCL Secondary Maximum Contaminant Level

TIGER Topologically Integrated Geographic Encoding and Referencing

USGS U.S. Geological Survey

VSMOW Vienna Standard Mean Ocean Water

vi Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
Magnitude, Extent, and Potential Sources of Nitrate in Ground 

Water in the Gallatin Local Water Quality District, 

Southwestern Montana, 1997-98

By Eloise Kendy

Abstract

The population of Gallatin County, Montana, has 

increased rapidly in recent years, and much of the associated new development has been concentrated in the 

northern part of the county. In response to increasing 

public concerns about the sustainability of the local 

water resources, the Gallatin Local Water Quality District (GLWQD) was established in 1995 to preserve, 

protect, and improve the quality of surface and ground 

water in the District. This report, prepared in cooperation with the GLWQD, describes the magnitude, 

extent, and potential sources of nitrate in ground water 

in the GLWQD.

The GLWQD encompasses most of the Gallatin 

Valley, which is an approximately north-south-trending 

intermontane basin about 520 square miles in area, consisting of a broad alluvial plain flanked on the west by 

the Madison Plateau and on the east and south by 

smaller benches. Mountainous areas compose almost 

one-half of the GLWQD. Land use in the GLWQD is 

predominantly agricultural.

Water-level, oxygen-isotope, and chlorofluorocarbon (CFC) data indicate that Cenozoic basin-fill 

aquifers beneath the irrigated and subirrigated parts of 

the GLWQD are recharged primarily by the Gallatin 

River and its irrigation diversions. Recharge to basinfill deposits beneath the benches originates more 

locally as low-altitude snowmelt, seepage from ephemeral streams, and summer rainfall. On the basis of CFC 

data, estimated recharge dates for 27 ground-water 

samples collected in 1998 from the Gallatin Valley 

range from the 1960s to the 1990s.

Nitrate concentrations generally were low in 

ground water of the GLWQD and in 1998 ranged from 

<0.05 to 13 milligrams per liter (mg/L). Nitrate concentrations (10 and 13 mg/L) equaled or exceeded the 

U.S. Environmental Protection Agency drinking-water 

standard of 10 mg/L in water from 2 of the 96 sites, sampled. Median nitrate concentrations in water from 

basin-fill deposits where many residents obtain their

water were less than about 3 mg/L. Median nitrate concentrations in water from wells located within all landuse categories were less than 3 mg/L. Seasonal variations in nitrate concentrations were determined in 

water from some wells.

Potential sources of nitrate to ground water 

include runoff or infiltration from areas of timber harvests, atmospheric deposition, livestock waste, fertilizer, soil organic nitrogen, and domestic septic-system 

effluent. However, fertilizers and soil organic nitrogen 

probably contribute most of the nitrate to ground water 

in the GLWQD. Irrigation can facilitate the movement 

of nitrogen from fertilizers through permeable soils and 

into underlying aquifers, although nitrate concentrations in ground water in the GLWQD are not as high as 

in similar agricultural areas of the United States, where 

nitrate concentrations frequently exceed 10 mg/L. 

Some higher nitrate concentrations in water beneath 

the eastern benches probably are related more to the 

quantity of ground-water recharge than to the source of 

the nitrate. With limited recharge and flow, nitrate in 

water beneath the benches is not diluted to the same 

extent as the irrigated and subirrigated areas. On the 

basis of water-quality data from three subdivisions, 

domestic septic-system effluent does not appear at 

present to be a major source of nitrate to ground water 

in the GLWQD.

INTRODUCTION

The population of Gallatin County has increased 

from about 21,900 in 1950 to 60,170 in 1996 (Montana 

Department of Commerce, 2000). Much of the associated new residential and commercial development has 

been concentrated in the northern part of the county. 

This development has resulted in concerns regarding 

the sustainability of local water resources. Of particular concern are the potential effects of development on 

the quality of water in the underlying aquifers because 

much of the population increase has been outside of 

established cities and towns, in housing areas where

Abstract
each dwelling or commercial development has its own 

well and septic system. Septic systems and application 

of pesticides and fertilizers to lawns and gardens could 

increase the potential for ground-water contamination. 

The occurrence of higher nitrate concentrations in 

ground water beneath more densely developed areas 

can indicate a probable influence of increased development on ground-water quality (Slagle, 1995a).

Nutrients, including nitrate, are associated with 

certain land uses. Nationally, nitrate concentrations in 

natural waters typically are less than 2 mg/L (Mueller 

and others, 1995), although background concentrations 

vary locally. Nitrate concentrations that exceed background levels commonly are due to human activities 

such as sewage disposal and fertilizer application, and 

the occurrence of elevated nitrate concentrations might 

indicate a potential for the presence of pesticides, 

pathogenic bacteria, and viruses. The U.S. Environmental Protection Agency (1991) has established a 

Maximum Contaminant Level (MCL) of 10 mg/L for 

nitrate (as nitrogen) for public drinking-water supplies 

in the United States. Infants can be seriously and occasionally fatally poisoned by ingestion of water containing more than 10 mg/L of nitrate, which inhibits the 

ability of hemoglobin to release oxygen to cells, resulting in cell asphyxiation, or methemoglobinemia ("blue 

baby syndrome").

In response to increasing public concerns about 

the sustainability of the local water resources, the Gallatin Local Water Quality District (GLWQD) was 

established in 1995 to preserve, protect, and improve 

the quality of surface and ground water in an 816 mi 

area of the District (fig. 1). In 1997, the U.S. Geological Survey (USGS) began a study, in cooperation with 

the GLWQD, to provide the GLWQD with hydrogeologic information needed to make sound decisions 

regarding the local water resources. A primary objective of the study was to determine the magnitude, 

extent, and sources of nitrate in ground water in the 

GLWQD.

Purpose and Scope

This report describes the magnitude, extent, and 

potential sources of nitrate in ground water in the 

GLWQD. The magnitude and extent of nitrate in 

ground water were determined by sampling 96 sites, 

including one hot spring, and the Gallatin River in 

1998. Potential sources of nitrate were determined by 

analyzing the spatial patterns of various water-quality 

constituents (major ions, nutrients, and stable isotopes), comparing land uses to ground-water quality, 

and age-dating ground water using chlorofluorocarbons (CFCs). Interpretations presented herein are 

based on previously published data; well-inventory, 

water-level, and water-quality data collected from July 

1997 through November 1998; and unpublished data 

obtained from the GLWQD in 1997-98.

Site-Numbering System

Sites are assigned location numbers according to 

geographic position within the rectangular grid system 

used for the subdivision of public lands (fig. 2). The 

location consists of as many as 14 characters. The first 

three characters specify the township and its position 

north (N) or south (S) of the Montana Base Line. The 

next three characters specify the range and its position 

east (E) of the Montana Principal Meridian. The next 

two characters are the section number. The next three 

to four characters designate the quarter section (160- 

acre tract), quarter-quarter section (40-acre tract) quarter-quarter-quarter section (10-acre tract), and quarterquarter-quarter-quarter section (2 1/2-acre tract), 

respectively, in which the site is located. These four 

subdivisions of a section are designated A, B, C, and D 

in a counter-clockwise direction, beginning in the 

northeast quadrant. The last two characters are a 

sequence number assigned to distinguish multiple 

wells in a single 2 1/2-acre tract. For example, well 

01S04E04ACDC01 (fig. 2) is the first well inventoried 

in the SW1/4SE1/4SW1/4NE1/4 of sec. 4, T. 1 S., 

R. 4E.

Acknowledgments

The author acknowledges with appreciation 

David N. Whitson, Kerri Fleming, and Cynthia Crayton of the Gallatin Local Water Quality District for 

technical guidance, water-level measurement, and 

assistance with sample collection. Stewart A. Dixon 

and Stephan G. Custer of Montana State University are 

gratefully acknowledged for their hydrogeologic map 

compilation. Appreciation also is extended to Johnkarl 

F. Bohlke of the U.S. Geological Survey for suggesting 

the use of oxygen isotopes to distinguish sources of 

ground-water recharge and to Lee M. Shanklin of the 

U.S. Environmental Protection Agency for explaining 

Geographic Information System (GIS) applications. 

Finally, many thanks to the citizens of the Gallatin 

Local Water Quality District who generously allowed 

access to their wells for water-level measurement and 

sample collection.

2 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
Base map from U.S. Geological Survey digital data, 1:24,000, 

1961-89 (streams), Gallatin County, 1997 (roads. 1:12,000 and 

public land survey, 1:24,000).

0246 MILES

0246 KILOMETERS

Figure 1. Location of the Gallatin Local Water Quality District, Montana.

FIGURE 1 3
Well 01S04E04ACDC01

Figure 2. Site-numbering system.

METHODS OF DATA COLLECTION AND 

ANALYSIS

GLWQD staff. Table 2 summarizes water-level data 

for wells in the network.

Well Inventory and Water-Level Measurement

In June 1997 through July 1998, private wells 

throughout the study area were inventoried or revisited 

to augment the existing database of wells (table I all 

tables are at the back of this report) that were inventoried for previous studies (Hackett and others, 1960; 

Slagle, 1995a,b). Well-construction information 

(Lapham and others, 1997) and information about land 

use were obtained during the inventory because of the 

potential effect of these aspects on nitrate in ground 

water.

In 1997, a long-term water-level monitoring network of 101 wells was established. Many of the wells 

in the network had been previously monitored; other 

wells were included to expand the network spatially to 

represent most of the aquifers in the GLWQD. Water 

levels generally were measured eight times a year by

Water-Quality Sampling and Analysis

Ground-water samples were collected from 96 

sites using the existing submersible pumps. Thirtyeight of the sites were sampled only once for field 

parameters and nitrate during the well inventory (table 

1). Nitrate concentrations were determined either 

using an onsite spectrophotometer or by chemical analysis by the USGS National Water Quality Laboratory, 

Denver, Colo., using methods described by Fishman 

(1993). Fifty-eight sites, including Bozeman Hot 

Springs, were resampled for additional constituents 

(table 3) (fig. 1). All wells were pumped until at least 

three well volumes of water were removed and field 

parameters (specific conductance, pH, water temperature, and dissolved oxygen) had stabilized. Specific 

conductance, dissolved oxygen, and alkalinity were 

measured onsite according to standard methods

4 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
described by Knapton (1985). Water samples were collected from a flow-through chamber using a peristaltic 

pump. Bottles and equipment were prepared in the laboratory, and samples were processed, filtered, and preserved in the field as described by Knapton (1985) and 

Horowitz and others (1994). An individual, disposable 

0.45-fim capsule filter was used for each site. Water 

sampled for stable isotopes of oxygen, hydrogen, and 

nitrogen was not filtered.

Most ground-water samples were collected from 

domestic wells that were completed well below the 

water table to obtain drinking water. However, most 

potential sources of nitrate originate at or near the land 

surface and effects of various land uses on groundwater quality presumably would be more pronounced 

near the water table than at the depths from which 

domestic supplies generally are obtained. Thus, the 

ground-water quality data presented in this report represent water that is being used by residents, rather than 

shallower water that might be more affected by land 

use. Over time, effects near the water table could 

migrate deeper into the aquifer if inputs to the groundwater system continued or increased.

Two surface-water samples were collected from 

the Gallatin River (table 3) from a bridge by depth and 

width integration at multiple stream verticals according 

to methods described by Knapton (1985) and Horowitz 

and others (1994). These samples were collected in a 

glass bottle using a D-74 sampler with a 0.25-in. nylon 

nozzle, and composited in a polyethylene churn splitter. A sample also was collected from unchlorinated 

effluent from the Bozeman Wastewater Treatment 

Plant (fig. 1, table 3). Field processing, including sample filtration and preservation, was performed in the 

same manner for surface-water samples as for groundwater samples.

Data-collection and analytical procedures used 

in this study incorporated practices designed to assure, 

control, verify, and assess the quality of sample data. 

Analyses for major ions and nutrients were performed 

by the USGS National Water Quality Laboratory 

(NWQL), Denver, Colo., using methods described by 

Fishman and Friedman (1989) and Fishman (1993). 

Methods and associated quality control for collection 

and processing of water samples are described by 

Knapton (1985), Knapton and Nimick (1991), and 

Horowitz and others (1994). Quality-assurance and 

quality-control procedures used by the NWQL are 

described by Pirkey and Glodt (1998), Friedman and 

Erdmann (1982), and Jones (1987). All sample bottles,

standard solutions, and preservatives for water samples 

analyzed by the NWQL were provided by the NWQL 

and were systematically tested by internal quality control for conformance with criteria described in BenchLevel Protocols on file in the Quality Control Office of 

the laboratory.

Quality-control data to document sample contamination and reproducibility of analytical results 

were provided by test samples that consisted of either a 

field-blank sample of deionized water or a replicate 

environmental sample. Quality-control samples comprised 11 percent of the total number of samples submitted for analysis. A field-blank sample is a volume 

of deionized water that is treated as an environmental 

sample in all aspects, including contact with sampling 

equipment, sample containers, filtration apparatus, and 

chemical preservatives in the field, and to holding 

times and laboratory processing. Five field-blank samples were collected and concentrations of nitrate 

(nitrite plus nitrate, dissolved) were determined to be 

less than the minimum reporting level of 0.05 mg/L in 

all five. Results of chemical analyses of field blanks 

are presented at the end of table 3. A replicate environmental sample is a volume of sampled water split into 

subsamples in such a manner that the physical and 

chemical characteristics of each subsample are considered to be essentially identical in composition. To 

assess the degree to which sample collection and laboratory analytical methods affected nitrate concentration 

data, 10 replicate samples were collected and submitted 

for laboratory analysis. The differences in the concentration of nitrate between the replicates ranged from 0.0 

mg/L to 0.1 mg/L. Results of chemical analyses of 

replicate samples are presented in tables 1 and 3.

Stable Isotopes of Water

Ratios of the stable isotopes of oxygen (oxygen18/oxygen-16, or 18O/ 16O) and hydrogen (deuterium/ 

hydrogen, or D/H) can be used as natural tracers of 

ground-water recharge if the different recharge sources 

are isotopically distinct. Isotopically distinct recharge 

sources are common in mountainous areas, where 

recharge originates as precipitation over a large range 

of altitudes (Clark and Fritz, 1997). Precipitation 

becomes progressively depleted in 18O and D (the 

ratios become more negative) as an air mass is transported to lower temperature and higher altitude on the 

windward side of a mountain (Coplen, 1993). ThereMETHODS OF DATA COLLECTION AND ANALYSIS
18 1 f\ fore, ratios of O/ O and D/H in ground water can 

reflect the values in the local precipitation that 

recharged the aquifer. Alternatively, ground water or 

surface water originating at high altitude may transport

1 8O-depleted water to aquifers at lower altitudes (Deak 

and others, 1995). Thus, spatial variations in isotopic 

content of ground water can be used to distinguish local 

from regional sources of recharge to aquifers in the 

Gallatin Valley.

18O/ 16O and D/H were analyzed by the USGS at 

laboratories in Reston, Va. Oxygen-isotope ratios were 

determined using the carbon-dioxide equilibration 

technique at 25°C (Epstein and Mayeda, 1953). 

Hydrogen-isotope ratios were determined by equilibration with hydrogen gas at 30°C (Coplen and others, 

1991).

Isotopic data are reported as ratios, which are 

more precisely determined than abundances, and are 

expressed as delta (8) values in units of parts per thousand, or permil (%o), relative to a standard. This ratio 

is calculated as follows:

Rstandard

- 1 X 1000 (1)

where R^ and Rstandard are tne atomic ratios of the 

sample and standard, respectively. For example, a 

sample with a 818O value of-10%o is depleted in 18O 

by 1 percent, or 10%o, relative to the standard.

The standard for 818O and SD is Vienna Standard 

Mean Ocean Water (VSMOW). Oxygen and hydrogen 

isotopic results are normalized (Gonfiantini, 1984; 

Hut, 1987; Coplen, 1988,1994) on scales such that the 

oxygen and hydrogen isotopic values of SLAP (Standard Light Antarctic Precipitation) are -55.5%o and 

-428%o, respectively.

Nitrogen Isotopes of Nitrate

Ratios of the stable isotopes of nitrogen 

( N/ N) in nitrate can, in many circumstances, be 

used to determine the source of nitrate in ground water 

or pore water (for example, Kreitler, 1975; Gormly and 

Spalding, 1979; Flipse and Bonner, 1985; Bottcher and 

others, 1990; and Wassenaar, 1995, among many others). Comparison of 8 15NN03 (815N of the nitrogen in 

nitrate) values in nitrate sources to 8 15NN03 values in 

ground water can be made only if the isotopic composition of the nitrate has remained unchanged along the

ground-water flow path. Denitrification (the conversion of reduced or organic nitrogen into gaseous nitrogen) is the most likely process that might change 

8 NNCM values. Ifdenitrification occurs, then 8 NNOS 

values in the residual nitrate increase (Bottcher and 

others, 1990;NimickandThamke, 1998). Typically, 

denitrification is not significant in shallow, transmissive aquifers with oxic water (Gillham and Cherry, 

1978; Gormly and Spalding, 1979; Starr and Gillham, 

1993), like most aquifers in the Gallatin Valley.

Interpretation of nitrate sources requires caution 

because the ranges of isotope ratios from different 

sources may overlap. 815NNos values for precipitation 

range from about -7 to +2.5%o and are typically lower 

than values for other sources (Hubner, 1986; LeTolle, 

1980; Heaton, 1986). 815NNos values for inorganic fertilizers depend on the form of nitrogen in the fertilizer 

(Shearer and others, 1974; Spalding and others, 1982; 

Heaton, 1986; Hubner, 1986). Urea and ammoniumbased fertilizers have values that typically range from 

-4 to +2%o; nitrate fertilizers have slightly higher values, typically ranging from 0 to +6%o (Spalding and 

others, 1982). Nitrate derived from ammonium fertilizer may retain the original 8 15NN03 value if little or no 

volatilization of ammonia occurs. Alkaline conditions 

promote volatilization and can result in 815NN03 enrichment of 2 to 5%0 (Fenn and Kissel, 1973; Feigin and 

others, 1974; Kreitler, 1975). 8 15NNo3 values for nitrate 

derived from mineralization or oxidation of organic 

nitrogen in soil typically are between +4 and +9%o 

(Boyce and others, 1976; Gormly and Spalding, 1979; 

Wolterink and others, 1979; Heaton, 1986), and the 

range in a given area typically is small, often within 

+l%o, when derived from soil of uniform type (Heaton, 

1986). Nitrate derived from livestock waste and 

domestic septic-system effluent generally has 815NN03 

values between +9 and +22%o (Kreitler, 1975; Gormly 

and Spalding, 1979; Heaton, 1986).

15N/ 14N in nitrate was analyzed by Global 

Geochemistry, Canoga Park, Calif., by distillation with 

NaOH and Dvarda's alloy to reduce the nitrate to 

ammonium, then NaOBr oxidation to convert ammonium to nitrogen gas. The nitrogen was then purified 

in a Cu-CuO furnace at 700°C (Miyake and Wada, 

1967) and analyzed by mass spectrometry.

The isotopic ratio of nitrogen is calculated using 

equation 1. The standard for 8 15N is atmospheric nitrogen.

6 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
Chlorofluorocarbons

Nitrate concentrations in shallow ground water 

commonly can be associated with land use. Because 

land uses change in response to economics and other 

factors, understanding the relation between specific 

land uses and ground-water recharge dates can provide 

useful information for analyzing current water-quality 

conditions. The recent development of a technique 

using Chlorofluorocarbons (CFCs, or Freons) to estimate the recharge date of ground water less than about 

50 years old (Plummer and others, 1993) allows comparison of recharge dates, land use, and nitrate concentrations for water from shallow aquifers (Bohlke and 

Denver, 1995).

The stability of CFCs in water has led to their 

effective use as conservative tracers to estimate the 

date that ground water was recharged during the past 50 

years (Plummer and others, 1993). CFCs are synthetic 

compounds whose atmospheric concentrations have 

steadily increased since they were first manufactured in 

the 1930s and are stable in aerobic conditions, but subject to degradation processes in anaerobic conditions. 

Detectable concentrations are present in post-1950 

ground water or mixtures of older ground water and 

post-1950 water. CFC concentrations in recharge 

water depend on the atmospheric concentration of 

CFCs and the temperature at the bottom of the unsaturated zone during recharge. Recharge temperature can 

be estimated from mean annual air temperature and 

concentrations of argon and nitrogen gas dissolved in 

ground water. The estimated age of ground water is the 

difference between the time when the water became 

isolated from the unsaturated zone (and recharged the 

aquifer) and the time when the water sample was collected.

Ground-water ages were estimated for 27 samples collected in May-June 1998. Samples were collected for CFC analysis using equipment and methods 

described in Busenberg and Plummer (1992). A copper-tube discharge line was connected directly to a 

spigot as close to the well as possible to ensure samples 

were not contaminated with atmospheric CFCs. Five 

glass ampules were filled and sealed at each site. While 

the samples were being collected, field parameters 

were monitored in a flow-through chamber.

Concentrations of CFCs and associated dissolved gases used to estimate ground-water recharge 

dates were analyzed by the USGS CFC Laboratory, 

Reston, Va. The analytical methods are described in

Busenberg and Plummer (1992). CFC concentrations 

are reported in table 4.

DESCRIPTION OF THE STUDY AREA

Physiography, Drainage, and Climate

The Gallatin Local Water Quality District 

(GLWQD) encompasses most of the Gallatin Valley 

(fig. 1). In addition, the GLWQD includes undeveloped mountains that are probable recharge zones for 

aquifers near and in the Gallatin Valley.

The Gallatin Valley is an approximately north-

^

south-trending intermontane basin about 520 mi in 

area consisting of a broad alluvial plain flanked on the 

west by the Madison Plateau and on the east and south 

by smaller benches (fig. 3). West of the alluvial plain, 

the Madison Plateau (also known as the Madison 

Bluffs or the Camp Creek Hills) is a broad bench with 

an altitude of more than 5,000 ft that drains northeastward into the Gallatin River. Most of the eastern edge 

of the Madison Plateau lies within the GLWQD. Some 

of the smaller benches, or terraces, that flank the eastern and southern basin margins are mantled by alluvial 

fans, the largest of which extends well into the alluvial 

plain between Hyalite and Bozeman Creeks. The Gallatin Valley ranges in altitude from about 4,100 ft 

where the Gallatin River leaves the basin, to about 

6,300 ft at the southeastern mountain front. In the rest 

of this report, "Gallatin Valley" refers to that part of the 

intermontane basin that is located within the GLWQD.

Mountainous areas compose almost one-half of 

the GLWQD. East and south of the Gallatin Valley, the 

sparsely populated Bridger and Gallatin Ranges rise 

from the valley floor. The crest of the Gallatin Range, 

with an altitude of more than 10,000 ft, is the highest 

part of the GLWQD. East of the Bridger Range, 

Bridger Creek drains the mountainous Bridger Canyon 

area.

The Gallatin River and its tributaries drain the 

GLWQD, except for about 20 mi2 in the northeastern 

part, which drain to the Shields River (fig. 1). The 

Gallatin River originates in Yellowstone National Park 

and flows northward about 80 mi through a bedrock 

canyon before entering the Gallatin Valley near Gallatin Gateway. From there, the river flows northward 

to the northern valley margin, then westward out of the 

valley. After leaving the Gallatin Valley, the Gallatin 

River joins the Madison and Jefferson Rivers to form

DESCRIPTION OF THE STUDY AREA
R.3E 111°15' R. 4 E. R.5E. R.7 E.

T. 1 N.

-20- LINE OF EQUAL AVERAGE 

ANNUAL PRECIPITATION 

BASED ON 1 961-90 PERIOD 

OF RECORD-Contour interval 

2 inches

BELGRADE AIRPORT WEATHER 

STATION-Located at Gallatin 

Field Airport

SMILES

6 KILOMETERS

Base map from U.S. Geological Survey digital data. 1:24,000, 

1961-89 (streams), Gallatin County, 1997 (roads, 1:12,000 and 

public land survey, 1:24,000). Hillshade base from U.S. Geological 

Survey digital data, 1:24,000, 1979. Universal Transverse Mercator 

Projection Standard, zone 12.

Figure 3. Topographic features and average annual precipitation in the Gallatin Local Water Quality District, Montana. Digital precipitation data 

compiled bythe Oregon Climate Service (George Taylor, unpub. data, 1995).

8 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
the Missouri River. The East Gallatin River, which is 

the principal tributary to the Gallatin River, meanders 

northwesterly near the northern edge of the Gallatin 

Valley and joins the mainstem about two miles north 

of Manhattan. Mean annual flow of the Gallatin River 

near Gallatin Gateway (USGS streamflow-gaging 

station 06043500, drainage area 825 mi2) is 818 ft3 /s 

for water years 1894-1997 (during periods of 

operation; U.S. Geological Survey, 1998). About 1 

mi downstream from the GLWQD, mean annual flow 

of the Gallatin River at Logan (USGS station 

06052500; drainage area 1,795 mi2) is 1,077 ft3/s for 

water years 1893-1997 (during periods of operation; 

U.S. Geological Survey, 1998). Inflow from 

tributaries and discharge from ground water contribute 

to the downstream increase in flow.

The climate of the Gallatin Valley is typical of 

mid-altitude intermontane basins of the Northern 

Rocky Mountains east of the Continental Divide, with 

cold winters and mild summers. On the basis of the 

1961-90 period of record, the average annual temperature is 41.9 °F at the Belgrade Airport Weather Station 

located at Gallatin Field Airport (altitude 4,450 ft) and 

44.2 °F at Bozeman (altitude 4,860 ft) (National Oceanic and Atmospheric Administration, 1992). The 

average last occurrence of frost (32 °F) is June 3 in Belgrade and May 27 in Bozeman, and the average first 

occurrence is September 13 in Belgrade and September 

18 in Bozeman (Natural Resources Conservation Service, U.S. Department of Agriculture, unpub. data., 

1994). Mean monthly climatic data for the Belgrade 

Airport Weather Station are shown in figure 4. Average annual precipitation in the GLWQD ranges from 

less than 14 in. near Manhattan to more than 44 in. on 

mountaintops in the Gallatin and Bridger Ranges (fig. 

3). The average annual precipitation in the valley area 

ranges from less than 14 in. to more than 20 in. (George 

Taylor, unpub. data, National Oceanic and Atmospheric Administration, 1992).

Land and Water Use

Land use in the Gallatin Valley is predominantly 

agricultural (fig. 5). In 1996, Gallatin County farmers 

harvested crops from 170,230 acres, 89,630 acres of 

which were irrigated (Montana Agricultural Statistics 

Service, 1997). On the Madison Plateau, the principal 

crop is irrigated potatoes; hay and grains also are 

important crops, as well as native grasses used for cattle grazing. On the intensively irrigated and subirrigated alluvial plain, hay and grains are the principal 

crops; on the eastern benches, dryland grains are the 

principal crops. Most of the dryland farmers use cropfallow rotations to increase moisture storage on the relatively dry benches. For the period 1964-92, farmland 

acreages have declined by more than 300,000 acres 

(fig. 6) in all of Gallatin County (U.S. Department of 

Commerce, issued periodically). Residential and commercial development in the GLWQD have accounted 

for some of this decline, particularly on the alluvial 

plain and the eastern benches. Most new residential 

developments contain lots ranging in size from about 

0.25 to 10 acres. The mountainous parts of the 

GLWQD are mostly forested and the primary land uses

EXPLANATION

MEAN MONTHLY AIR TEMPERATURE FOR 

1961-90 PERIOD OF RECORD

MEAN MONTHLY PRECIPITATION FOR 

1961-90 PERIOD OF RECORD

Figure 4. Mean monthly air temperature and precipitation at the Belgrade Airport Weather Station, Montana. Data from National Oceanic and 

Atmospheric Administration (1992).

DESCRIPTION OF THE STUDY AREA
R.3E. 11f15' R.4 E. R.5E. 111° R. 6. E. R. 7E.

T. 1 N.

EXPLANATION 

PRIMARY LAND USE

IRRIGATED HAY AND GRAIN

IRRIGATED POTATOES

DRYLAND GRAIN

SUBIRRIGATED HAY

RANGELAND

FOREST

TUNDRA 

URBAN OR SUBDIVIDED AREA

BOUNDARY OF SELECTED

SUBURBAN POPULATION AREAS

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

1:24,000,1961 -89 (streams), Gallatin County, 1997 

(roads, 1:12,000 and public land survey, 1:24,000). 

Universal Transverse Mercator Projection Standard, 

zone 12.

0246 MILES

6 KILOMETERS

Agricultural land uses modified from Slagle (1995a, scale 1:100,000); 

boundaries of Manhattan, Belgrade, and Bozeman from U.S. Census 

Bureau Topographically Integrated Geographic Encoding and Referencing (TIGER) Line Files (Washington D.C., 1992, scale 1:100,000; subdivisions from Galfatin County Geographic Information System (GIS) 

Department (June 1998, scale 1:63,360); rangeland, forest, and tundra 

from U.S. Geological Survey Geographic Information Retrieval and 

Analysis System (GIRAS) files, Bozeman quadrangle (1972, scale 

1:250,000).

1 HYALITE HEIGHTS SUBDIVISION

2 BAXTER CREEK SUBDIVISION

3 ROYAL ARABIAN SUBDIVISION

4 SPRING HILL ROAD (Detailed 

inset shown on Fig. 13)

Figure 5. Generalized land uses in the Gallatin Local Water Quality District, Montana.

JO Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
1,050,000

1,000,000

950,000

900,000

cc 850,000

800,000

750,000

700,000

650,000

* \

1920 1950 1960 1970 1980 1990 2000

Figure 6. Acres of farmland in Gallatin County, Montana, 1929-92. Data from U.S. Department of Commerce (issued periodically).

are timber harvesting, cattle grazing, and recreation. 

Residential development has recently spread into these 

mountainous areas, especially in Bridger and Bear 

Canyons.

Water use in the GLWQD is primarily for municipal and domestic supply, irrigation, and livestock. 

Municipal-supply water for the City of Bozeman is 

obtained from Hyalite Reservoir and diversions from 

Bozeman Creek. Ground water provides domestic supplies for about 17,000 residents of the GLWQD and 

also provides irrigation water for about 2,800 acres 

(Parrett and Johnson, 1988). The Gallatin River is the 

major source of irrigation water in the GLWQD (Parrett and Johnson, 1988; [Montana] State Engineer's 

Office, 1953a,b).

HYDROGEOLOGY

Several investigators have described the general 

hydrogeology of the Gallatin Valley or detailed hydrogeology of small areas (Donohue, 1984; Kendy and 

Tresch, 1996). Murdock (1926) investigated ground 

water, focusing on irrigation and drainage problems in 

the Gallatin Valley. Hackett and others (1960) measured water levels and streamflow, mapped basin fill, 

and sampled wells to provide the first comprehensive

hydrogeological assessment of the Gallatin Valley. 

Earth Science Services, Inc. (1978) sampled ground 

water and measured water levels in wells throughout 

the Gallatin Valley. Custer (1991) reexamined the 

water-yielding potential of the unconsolidated deposits 

west of Bozeman. Slagle (1995b) appraised the 1992- 

93 hydrologic conditions throughout the Gallatin Valley, focusing on hydrologic changes resulting from 

changes in land use. Erickson (1995) and Hay (1997) 

estimated water budgets for unconsolidated aquifers 

underlying the benches north of Bozeman. Moore 

(1984) examined ground-water quality and availability 

in bedrock aquifers of the Bridger Canyon area.

Structurally, the Gallatin Valley intermontane 

basin composes the eastern two-thirds of an eastwardtilted graben (Robinson, 1961). The southwestern 

basin boundary is not flanked by obvious faults and 

might be a depositional contact between Cenozoic 

basin fill and pre-Cenozoic bedrock. The eastern 

boundary of the Gallatin Valley is a series of steep normal faults along the fronts of the Bridger and Gallatin 

Ranges (Robinson, 1961). Gravity data indicate that 

more than 6,000 ft of Cenozoic sediments fill the basin 

at its deepest point, east of Bozeman Hot Springs 

(Noble and others, 1982). Tertiary deformation is evidenced by several broad folds (Custer, 1991) and by

HYDROGEOLOGY 11
possible faulting along the western margin of the 

Madison Plateau (Schneider, 1970).

Hydrogeologic Units

In general, geologic units of the GLWQD consist 

of poorly consolidated Cenozoic basin-fill deposits in 

the Gallatin Valley and complexly folded and faulted 

Tertiary through Archean bedrock in the mountains. 

These geologic units can be grouped into seven hydrogeologic units on the basis of major lithology, waterbearing characteristics, and geomorphologic relations. 

Figure 7 is a generalized map of these hydrogeologic 

units.

Basin-Fill Deposits

Cenozoic basin-fill deposits are subdivided into 

three hydrogeologic units: Quaternary alluvium (Qal), 

Quaternary and Tertiary undifferentiated deposits 

(QTd), and Tertiary Bozeman Group (Tb).

Basin-fill deposits can contain aquifers that are 

unconfined, leaky confined, or confined. Aquifers in 

basin-fill deposits that consist of Quaternary alluvium 

commonly are unconfined and highly productive (Briar 

and others, 1996). Fine-grained layers within Tertiary 

deposits (QTd or Tb) can restrict flow into or out of 

more permeable layers, which result in leaky-confined 

or confined aquifers. With depth, these fine-grained 

layers become more consolidated and, therefore, less 

permeable. However, some Tertiary basin-fill deposits 

contain productive aquifers (Briar and others, 1996).

Quaternary alluvium (Qal) was deposited by the 

Gallatin River and its tributaries and extends across the 

northern part of the alluvial plain between the Gallatin 

and East Gallatin Rivers. This unit is mostly composed 

of moderately sorted cobbles and pebbles, but sand, 

silt, and clay also are present. The proportion of finegrained material generally increases to the north. Estimates of the thickness of the alluvium range from 70 ft 

near Bozeman Hot Springs to more than 800 ft near 

Belgrade (Hackett and others, 1960). Quaternary alluvium generally is the most permeable hydrogeologic 

unit and the most reliable source of ground water in the 

GLWQD. Typical wells completed in alluvium are less 

than 100 ft deep and provide sufficient supplies for 

most uses, including irrigation (Button and others, 

1995). Based on 24 aquifer tests, transmissivity ranges 

from 5,100 to 90,000 ft2/d and averages 27,000 ft2/d for

alluvium of the Gallatin and East Gallatin Rivers; 

based on four multiple-well aquifer tests, storage coefficients range from 0.01 to 0.06 (Hackett and others, 

1960).

Quaternary and Tertiary undifferentiated deposits (QTd) consist of unconsolidated Quaternary 

alluvial-fan deposits overlying Tertiary sedimentary 

pediments that form benches and underlie the southcentral part of the alluvial plain and the eastern benches 

(fig. 7). Alluvial-fan deposits, probably of late Pleistocene age, extend into the Gallatin Valley from the 

Bridger and Gallatin Range fronts and consist of a heterogenous mixture of unconsolidated to consolidated, 

poorly sorted rock fragments in a sand, silt, and clay 

matrix with some carbonate cement (Hay, 1997; Erickson, 1995; Custer, 1991; Hackett and others, 1960). 

Typically, grain sizes decrease toward the toes of the 

fans. Likewise, fan thicknesses decrease from more 

than 150 ft at the heads to zero thickness at the toes of 

the fans (Custer, 1991; Hackett and others, 1960). Tertiary sediments in the Gallatin Valley belong to the 

nonmarine Bozeman Group described by Fields and 

others (1985). In general, Tertiary sediments that 

underlie the Quaternary alluvial fans grade from moderately well-cemented conglomerate along the Bridger 

and Gallatin Range fronts to finer-grained, tuffaceous 

siltstone and sandstone to the northwest. However, 

within this general framework, the Tertiary sediments 

are extremely heterogeneous and include laterally discontinuous beds of volcanic ash; tuffaceous marl, siltstone, and sandstone; limestone; cemented and 

uncemented conglomerate; and cross-bedded sandstone (Hackett and others, 1960; Custer, 1991; Hanneman and Wideman, 1991). Owing to their similar 

compositions, Quaternary alluvial-fan deposits cannot 

easily be distinguished from the underlying Tertiary 

sediments. Therefore, the thickness of these deposits at 

any location is uncertain. The depths of wells completed in QTd range from 40 to 375 ft, with the deeper 

wells located on topographically higher benches. In 

some areas with low aquifer permeability, landowners 

have reported difficulties in obtaining ground water. 

The hydraulic characteristics of QTd vary widely, 

reflecting the heterogeneity of the deposits. Based on 

aquifer tests of six wells completed on alluvial fans, the 

transmissivity of QTd ranges from 3,500 to 8,700 ft2/d 

and averages 6,400 ft2/d (Hackett and others, 1960).

The Tertiary Bozeman Group (Tb) consists of the 

Tertiary Sixmile Creek and Renova Formations (Fields 

and others, 1985) where they crop out as pediments on

12 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
the Madison Plateau, east of Bozeman, and 5 mi north 

of Belgrade (fig. 7). The Miocene Sixmile Creek Formation consists of three unconformable cyclic units. 

The basal part of each unit is a fluviatile, cross-bedded, 

andesitic conglomerate with coarse-grained sandstone. 

Each unit grades upward into sediments that vary laterally from lacustrine beach sands to laminated clays 

with tuffaceous claystone. The entire formation is rich 

in tuffaceous siltstone and sandstone and contains 

numerous ash beds ranging in thickness from 0.5 to 12 

ft (Schneider, 1970). The Eocene to Oligocene Renova 

Formation (Fields and others, 1985) is not wellexposed in the Gallatin Valley. However, the formation crops out extensively to the west of the GLWQD. 

These fine-grained, dominantly lacustrine, tuffaceous 

sediments underlie the Sixmile Creek Formation in 

most, if not all, of the Gallatin Valley (Hackett and others, 1960; Robinson, 1961). North of Belgrade and 

east of Bozeman, wells completed in Tb typically have 

low well yields. Specific-capacity values for 16 wells 

completed in Tb north of Belgrade and east of Bozeman range from 0.2 to 47.6 (gal/min)/ft with a median 

value of 0.78 (gal/min)/ft (Slagle, 1995a). Transmissivity values determined from four aquifer tests range 

from 40 to 2,300 ft2/d (Hackett and others, 1960). In 

contrast, wells completed in Tb on the Madison Plateau 

tap a permeable zone capable of yielding as much as 

2,800 gal/min to irrigation wells. These wells are 

about 200 to more than 500 ft deep, with well depths 

increasing to the south. Specific-capacity values estimated from data from drillers' logs can be as high as 59 

(gal/min)/ft (Button and others, 1995). Hackett and 

others (1960) calculated a transmissivity of 3,500 ft2/d 

for a 225-ft well on the Madison Plateau 

(01N03E33DD).

Bedrock

Mountains within the Gallatin Local Water Quality District are composed of complexly folded and 

faulted bedrock that can be grouped into four hydrogeologic units: Tertiary (Eocene) volcanic rocks (Tv), 

Tertiary through Middle Proterozoic sedimentary bedrock that contains potential aquifers (TYsaq), Cretaceous through Cambrian sedimentary bedrock that 

contains confining units (KGscu), and Archean metamorphic rocks (Am).

Tertiary volcanic rocks (Tv) mostly are present 

in the topographically highest parts of the GLWQD.

These rocks include andesite and basalt flows, breccia, 

agglomerate, and tuff of the Gallatin-Absaroka Volcanics. Owing to their poorly accessible locations and 

dense, crystalline nature, the volcanic rocks have not 

been developed as a ground-water source.

Tertiary through Proterozoic sedimentary bedrock units that contain potential aquifers (TYsaq) 

include the Paleocene to Upper Cretaceous Fort Union 

Formation; Upper Cretaceous Hoppers Formation, 

Miner Creek Formation, Cokedale Formation, Eagle 

Sandstone, Telegraph Creek Formation, and Frontier 

Formation; the lower part of the Lower Cretaceous 

Kootenai Formation; Permian Phosphoria Formation; 

Pennsylvanian Quadrant Formation; Mississippian 

Mission Canyon Limestone; Cambrian Flathead Sandstone; and the Middle Proterozoic Belt Supergroup 

(S.G. Custer, Montana State University, written commun., 1998). Sandstone, conglomerate, and limestone 

predominate the lithologies of TYsaq. Because these 

units have not been extensively developed, they are 

considered only potential aquifers. Permeability of 

these formations depends on grain size and sorting, 

degree of cementation, and fracturing, which are not 

uniform throughout a formation. Rugged terrain and 

deep water tables may restrict development of these 

potential aquifers.

Cretaceous through Cambrian sedimentary bedrock units that contain confining units (KGscu) include 

the Upper Cretaceous Billman Creek Formation, Miner 

Creek Formation, Cokedale Formation, and Cody 

Shale; Lower Cretaceous Mowry and Thermopolis 

Shales; the upper part of the Lower Cretaceous 

Kootenai Formation; Upper Jurassic Morrison Formation; Upper to Middle Jurassic Ellis Group; Pennsylvanian to Mississippian Amsden Formation; 

Mississippian Big Snowy Group, Charles Formation, 

and Lodgepole Limestone; Devonian Three Forks 

Shale, Jefferson Dolomite, and Maywood Formation; 

and the Cambrian Snowy Range Formation, Pilgrim 

Limestone, Park Shale, Meagher Limestone, and Wolsey Shale. Fine-grained sandstone, shale, mudstone, 

siltstone, and chert predominate the lithologies of 

KGscu. Structural relations might prevent these rocks 

from actually confining underlying aquifers in some 

areas, but they are termed "typically confining units" to 

distinguish them from the potential aquifers included in 

TYsaq. Even with its poor water-yielding characteristics, more ground-water development has occurred in 

KGscu than in TYsaq. However, ground water generally is not readily available in many areas where this

HYDROGEOLOGY 13
R. 3E. 111°15' R. 4E. R.5E. 111° R. 6. E. n.7 E.

T. 1 N.

lase map from U.S. Geological Survey digital data, 1:24,000, 

1961-89 (streams), Gallatin County, 1997 (roads. 1:12,000 and 

public land survey, 1:24,000). Universal Transverse Mercator 

Projection Standard, zone 12.

Hydrogeologic units modified from 

S.G. Custer, Montana State University 

(unpublished digital data, 1998) and 

Hackett and others (I960).

6 MILES

Figure 7. Generalized hydrogeologic units in the Gallatin Local Water Quality District, Montana.

14 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
CORRELATION OF HYDROGEOLOGIC UNITS

. ;.;QTd;v

u

KGscu

Qal . -

Unconformity

' . :Tb-:::i:-;:

iconformity

TYsaq

-

TV

'- , « '

- Holocene

- Pleistocene

- Pliocene

- Miocene

- Oligocene

- Eocene

- Paleocene

- Quaternary

- Tertiary

Cretaceous

through

Cambrian

- CENOZOIC

Unconformity

- MESOZOIC

- PALEOZOIC

MIDDLE 

PROTEROZOIC

- ARCHEAN

EXPLANATION

| Qal | ALLUVIUM (Quaternary)

[. .Qjd.yJ UNDIFFERENTIATED DEPOSITS (Quaternary and Tertiary)

[i.:'::JTb-;'-:-:j BOZEMAN GROUP (Eocene through Miocene)

| TV | VOLCANIC ROCKS (Eocene)

| TYsaq | SEDIMENTARY BEDROCK-Potential aquifers (Paleocene through Middle Proterozoic)

| KGscu | SEDIMENTARY BEDROCK-Typically confining units (Cretaceous through Cambrian)

METAMORPHIC ROCKS (Archean)

CONTACT-Approximately located

FIGURE 7 EXPLANATION 15
unit is found. Most drillers' logs indicate that wells 

completed in KGscu provide inadequate supplies for 

sustained pumping that is required for domestic 

supplies.

Archean metamorphic rocks (Am) are present in 

undeveloped areas of the Gallatin and Bridger Ranges, 

and probably underlie Cenozoic basin-fill deposits in 

much of the Gallatin Valley. These rocks are mainly 

biotite gneiss, with some schist, quartzite, and marble. 

If the rocks were fractured and the fractures interconnected, this unit could potentially yield water to wells.

Ground-Water Occurrence, Movement, and 

Recharge

Comprehensive records of water levels in wells 

in the Gallatin Valley begin in 1947. Periodic waterlevel measurements in more than 100 wells from 1947 

to 1954 were used to draw the first map of the water 

table (Hackett and others, 1960). In 1978, water levels 

were remeasured in 76 of those wells and no long-term 

trends were observed (Earth Science Services, Inc., 

1978). Likewise, Slagle (1995a) determined no substantial long-term water-level changes for the period 

1947 to 1993. Contours of water levels measured in 

April 1998 (fig. 8) are similar to previous maps (Murdock, 1926; Hackett and others, 1960; Earth Science 

Services, Inc., 1978; Slagle, 1995a), and indicate that 

the direction of regional ground-water flow in the 

basin-fill deposits generally is from the south, west, 

and east margins of the Gallatin Valley toward the Gallatin or East Gallatin Rivers (fig. 9). However, heterogeneities caused by discontinuous beds and lenses in 

the basin-fill deposits can result in complex local 

ground-water flow patterns. Therefore, local flow 

directions may be somewhat different from those 

shown in figure 8. In most parts of the GLWQD, water 

levels fluctuate seasonally. Water levels generally rise 

from spring through mid-summer, peak in June or July, 

and gradually recede until about April or May, when 

snowmelt, seepage from streams, and summer rainfall 

begin to recharge aquifers. The greatest fluctuations in 

developed aquifers occur in Quaternary and Tertiary 

undifferentiated deposits along the western flank of the 

Bridger Range front (Hay, 1997), where seasonal fluctuations of more than 40 ft occur. In contrast, wells 

completed in Quaternary alluvium near the Gallatin 

and East Gallatin Rivers typically fluctuate less than 10 

ft seasonally (fig. 10).

Depths to ground water vary considerably within 

the GLWQD. In subirrigated areas (fig. 5), the water

table is usually less than about 5 ft below land surface. 

Also, much of the area southwest of Bozeman and east 

of Hyalite Creek has a shallow water table within about 

8 ft of land surface. In contrast, ground water in some 

mountainous areas outside of the GLWQD is hundreds 

of feet below land surface.

Generalized recharge sources may be determined 

on the basis of water-level contours, which are perpendicular to the ground-water flow direction. For example, contours that are parallel to mountain fronts (fig. 8) 

indicate that mountain bedrock aquifers recharge 

basin-fill deposits in the Gallatin Valley. Basin-fill 

deposits in the Gallatin Valley are recharged by subsurface flow from bedrock, direct infiltration of precipitation, seepage from some streams and canals, and 

infiltration of applied irrigation water. In general, bedrock aquifers in the mountains are recharged by precipitation.

Spatial variations in the ratios of stable isotopes 

of oxygen (8 18O) and hydrogen (8D) in ground water 

were used to further delineate sources of recharge to 

basin-fill deposits in the Gallatin Valley. 8 18O and 5D 

values in ground water reflect the values in the precipitation that recharged the ground water, unless some 

process or reaction caused the isotopes to be fractionated. One such process is evaporation, which results in 

deuterium enrichment relative to hydrogen (reflected in 

a higher 5D value), because water lost to the atmosphere has a slightly greater proportion of the hydrogen 

isotope relative to the heavier deuterium isotope (that 

is, a lower 6D value) (Coplen, 1993). Most of the 8 18O 

and 8D values (fig. 11) plot between the meteoric water 

line for North American continental precipitation 

described by the equation 8D = 8(818O) + 6%o (Gat, 

1980) and the global meteoric water line described by 

the equation SD = 8(818O) + 10%o (Craig, 1961), indicating that most of the isotopic compositions have not 

been affected by evaporation. Data for 5 of the 8 wells 

completed beneath unirrigated benches plot below both 

lines, indicating some isotopic fractionation caused by 

evaporation, as might be expected for dryland farming 

areas.

In this study, the stable-isotope data (fig. 11) 

were used primarily to distinguish recharge sources for 

ground water in different areas. The sample collected 

from the Gallatin River in 1998 had a 8 18O value of 

-18.74%o. The other value (818O value of-18.45%o and 

SD value of-137) from the Gallatin River plotted in 

figure 11 represents a sample collected in June 1993

16 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
R.3E R.7E.

T. 1 N.

EXPLANATION

 4,950- WATER-LEVEL CONTOUR-Dotted

where approximately located. Contour 

interval 50 and 100 feet. Datum is sea 

level

APPROXIMATE DIRECTION OF 

GROUND-WATER FLOW

 WELL USED FOR CONTROL IN 

CONTOURING WATER LEVELS 

1960s

O WELL LOCATION WITH APPROXIMATE 

RECHARGE DATE BASED ON 

CHLOROFLUOROCARBON(CFC) 

CONCENTRATIONS

Base map from U.S. Geological Survey digital data, 1:24,000, 

1961-89 (streams), Gallatin County, 1997 (roads, 1:12,000 and 

public land survey, 1:24,000). Universal Transverse Mercator 

Projection Standard, zone 12.

6 MILES

6 KILOMETERS

Figure 8. Water-level contours and approximate direction of ground-water flow in the basin-fill deposits in April 1998, and approximate groundwater recharge dates, Gallatin Local Water Quality District, Montana.

FIGURE 8 17
mmvKl «f*» Jfcfr, « . ..-.. -« ' : >..i * i rfi\|U?M

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

1:24,000, 1979. Perspective surface vertical exaggeration x2.5 

Universal Transverse Mercator Projection Zone 12.

EXPLANATION

° BASIN-FILL DEPOSITS

^=^ BEDROCK

GROUND WATER 

GROUND-WATER RECHARGE

APPROXIMATE DIRECTION OF 

GROUND-WATER FLOW

Figure 9. Perspective view and diagrammatic hydrogeologic section showing ground-water recharge and flow in the basin-fill deposits in the 

Gallatin Local Water Quality District, Montana.

18 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
Wells completed in Quaternary and Tertiary undifferentiated deposits (QTd) along 

the western flank of the Bridger Range. Data for 1995-96 from Hay (1997).

ou

5

q

EJ 80

00

L_ 111

LLJ O

£2: 100

2 £

3- co

j£j g 120

CE

y 140

1

1fiO

I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I

-

-* .

*.,

* » .

* "* -.

" '* """*-- ,''' ~

\ % % 01S06E08CAAB 01S06E09CBAA «v

\x'-». *v*v^ s'''

**, '**. NO DATA ^^^

"' .._ "* - 01S06E09CBAA ***'

""* - 01S06E08CCBC

-

I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I

ASONDJFMAMJJASONDJFMAMJJASONDJFMAMJJ

Well 02S04E13CCBC01 completed in Quaternary alluvium (Qal) 0.5 mile from the Gallatin River

 Z. DC

CO 

Q 8

10

12

I I | I I I \ \ \ \ \ \ I I I I | I I I I | I I I I

NO DATA

<

G 

I I I 1947 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 1998

Figure 10. Hydrographs of selected wells in the Gallatin Local Water Quality District, Montana.

from an overflow channel about 6 mi downstream 

from the GLWQD (location number 

02N02E17DDCC01; U.S. Geological Survey, unpub. 

data). 6 O values for ground water collected from 12 

wells completed beneath the irrigated or subirrigated 

parts of the Gallatin Valley (fig. 5) range from 

-18.07%o to -18.69%o and are similar to the values for 

the Gallatin River (fig. 11). Thus, the Gallatin River 

and water diverted from the river for irrigation 

probably are the primary sources of ground-water 

recharge in the irrigated and subirrigated areas. The 

importance of irrigation water in recharging basin-fill 

deposits and sustaining aquifer storage is supported by 

the water table rising to maximum altitudes during 

periods of intense irrigation rather than during periods 

of intense precipitation (Brustkern, 1977; Slagle, 

1995a).

Conversely, water levels beneath the unirrigated 

benches rise in response to intense precipitation (Slagle, 1995a). 8 18O values from eight samples collected from these areas spanned a much larger range 

(-16.21%0 to -18.93%0) than samples collected from 

irrigated and subirrigated areas. Higher (less negative) 

8 O values indicate enrichment in 18O, which results 

from fractionation at a lower altitude or a higher temperature. The larger range of 8 18O values suggests that 

some combination of factors, including evaporation 

and the altitude and season of the precipitation that 

recharged the aquifer, varies throughout the unirrigated 

bench areas. In contrast to the irrigated and subirrigated areas, which apparently have a common recharge 

source, the unirrigated benches probably are recharged 

from a variety of sources, including low-altitude snow 

melt, seepage from ephemeral streams, and summer 

rainfall. The recharge area and resultant quantity of

FIGURE 10 19
-126

-128

-130

-132

-134

£ -136 

QL

Q -138 

<~o

-140

-142

-144

-146

-148

-19.0

 GROUND WATER BENEATH IRRIGATED OR 

SUBIRRIGATED ALLUVIAL PLAIN

o GROUND WATER BENEATH UNIRRIGATED BENCH 

A GALLATIN RIVER

-18.5 -18.0 -17.5

g' 8 0, IN PERMIL

-17.0 -16.5 -16.0

Figure 11. Relation between 8180 and 8D in ground water and the Gallatin River, Gallatin Local Water Quality District, Montana, 1998.

recharge for aquifers beneath these unirrigated benches 

are small compared to the recharge area for aquifers 

beneath the subirrigated and irrigated areas. Only limited ground-water supplies are reported by drillers and 

residents of the unirrigated benches, despite the relatively high transmissivities of potential aquifers 

(Custer, 1991). Furthermore, the large seasonal waterlevel fluctuations probably result from seasonal infiltration of precipitation rather than recharge ffom a 

major perennial surface-water source, which could sustain more consistent water levels throughout the year.

Water from the Tertiary Bozeman Group (Tb) 

beneath the Madison Plateau has an isotopic composition distinct from the other unconsolidated deposits. 

Water from samples collected in 1991 from depths of 

710, 289, and 245 ft, had 518O values of-21.0%o, 

-19.2%0 , and -18.5%o, respectively (U.S. Geological 

Survey, unpub. data). This apparent trend of O depletion with well depth might indicate that deeper wells 

are recharged at higher altitudes and have longer, more 

regional recharge flowpaths than shallower wells. 

Similarity between isotopic composition of water from

the two shallower wells with that of the Gallatin River 

could indicate recharge from the Gallatin River. But 

hydraulic gradients (K.B. Waren, Montana Department 

of Natural Resources and Conservation, written commun., 1991;Slagle, 1995a) indicate that direct recharge 

from the river is unlikely. However, recharge from irrigation water diverted from the Gallatin River is likely, 

based on water-level mounds beneath canals (Slagle, 

1995a). In contrast, 8 18 0 values for ground water from 

Tb beneath the Madison Plateau are different from the 

Madison River (5 spring and summer samples with values ranging from -16.8%o to -17.9%oj and shallow alluvial ground water west of the Madison Plateau (11 

samples with values ranging from -17.2%o to -17.9%o; 

Tuck and others, 1997). Therefore, based on hydraulic 

gradients and the isotopic composition of water, Tb 

beneath the Madison Plateau probably is recharged by 

irrigation water diverted from the Gallatin River, and 

not by the Madison River. Precipitation, seepage from 

streams, and subsurface flow from bedrock to the south 

probably also provide recharge (K.B. Waren, written 

commun., 1991).

20 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
To understand the timing of ground-water 

recharge, ground-water ages were estimated using CFC 

data for water collected from 27 sites in May-June 1998 

(fig. 8, table 4). All samples had detectable concentrations of CFCs, indicating recharge dates ranging from 

the 1960s to the 1990s. In general, ground water near 

the Gallatin River was recharged during the 1980s and 

1990s. In places along the western flank of the Bridger 

Range, ground water also was recharged during the 

1980s. These recent ground-water ages support the 

interpretations that the Gallatin River recharges nearby 

Quaternary alluvium (Qal) and that local infiltration 

recharges aquifers beneath the eastern benches on the 

western flank of the Bridger Range.

CFC data also demonstrate that local groundwater flow patterns can be different from the regional 

flow pattern. If local flow paths corresponded exactly 

to the regional flow paths depicted in figure 8, then the 

approximate recharge dates based on CFC data would 

become older downgradient. For example, south of 

Bozeman between Hyalite and Bozeman Creeks, 

recharge dates progress downgradient from the 1990s 

to the 1980s. In contrast, along the western flank of the 

Bridger Range (T.I N., R. 5 E.), coalescing alluvial 

fans consisting of heterogeneous, laterally discontinuous sediments locally control ground-water flow such 

that younger water (1970s) was sampled down hill 

from older water (1960s). The 1970s water was sampled from a 47-ft well, and the 1960s water was sampled from 80- and 120-ft wells. These age and depth 

relations suggest that either the shallower deposits 

were recharged closer to the wells or that the shallower 

deposits are more permeable than the deeper deposits, 

allowing ground water to flow faster from the same 

recharge source. Similar 8 18O values (-18.3 l%o and 

-18.76%o) for the 47-ft and 120-ft wells indicate that 

water from both wells has a common recharge source. 

Conversely, 1980s ground water sampled from the center of the Gallatin Valley (T. 1 S., R. 5 E.) had different 

8 18O values (-18.19%o and -18.46%o) from regional 

ground water sampled upgradient, along the basin margin (T. 3 S., R. 5 E; -17.48%o and -17.79%). The 

younger water probably represents infiltrated irrigation 

water rather than precipitation and stream seepage that 

infiltrated along the valley margin and flowed downvalley. Therefore, in this case, the 8 18O values indicate 

that the age relations probably result from distinct 

recharge sources.

Water from basin-fill deposits discharges to 

streams, irrigation drains, wells, and evapotranspiration, particularly in the northern part of the valley 

where the water table is very shallow. Pumpage from 

wells is a small component of ground-water discharge. 

Water that'does not evapotranspire eventually flows out 

of the GLWQD along the Gallatin River, either as surface water or as ground water. Discharge from the 

Gallatin Valley exceeds recharge throughout the fall, 

winter, and early spring (Hackett and others, 1960). 

Water from bedrock aquifers discharges to streams and 

as subsurface flow to basin-fill deposits.

Ground-Water Quality

The major-ion chemistry of ground and surface 

water sampled in the GLWQD (table 3) is shown in figure 12. Wells completed in Quaternary alluvium (Qal) 

and Quaternary and Tertiary undifferentiated deposits 

(QTd) beneath the alluvial plain of the Gallatin Valley 

produce calcium bicarbonate or calcium-magnesium 

bicarbonate water. Water from Quaternary and Tertiary 

undifferentiated deposits (QTd) and the Tertiary Bozeman Group (Tb) beneath the eastern benches (fig. 7) 

has major-ion chemistry similar to that of the alluvial 

plain. Concentrations of dissolved solids from these 

hydrogeologic units ranged from 149 to 405 mg/L. 

Generally, water from Tb beneath the Madison Plateau 

has similar anion chemistry, but with a larger percentage of sodium than ground water from basin-fill deposits to the east (table 3; Slagle, 1995a). Water from two 

samples from the Gallatin River also are a calcium 

bicarbonate type.

Wells completed in sedimentary bedrock (TYsaq 

and KGscu, fig. 7) east of the Gallatin Valley have a 

wide variety of water types (fig. 12) owing to the different rock types that compose these units. Dissolvedsolids concentrations for seven wells sampled in 1998 

ranged from 127 to 438 mg/L. Some Cretaceous rocks 

in Bridger Canyon contain thin beds of sulfur-rich lignite and coal which, under reducing conditions, impart 

an unpleasant "rotten egg" odor to ground water 

(Moore, 1984).

The presence of Bozeman Hot Springs 

(02S04E14DADC01 and 02; fig. 1) indicates subsurface flow of geothermal water from Archean metamorphic bedrock (Am) (Chadwick and Leonard, 1979). 

Water discharges with a temperature of 53.0°C and a 

dissolved-solids concentration of 456 mg/L at a rate of 

74 gal/min. A 685-ft flowing well at the same location 

produces 1,000 gal/min of 55°C water (Sonderegger

HYDROGEOLOGY 21
o o 

CALCIUM

-O T> <?> <^,

CHLORIDE PLUS FLUORIDE PLUS NITRATE

EXPLANATION 

SOURCE OF SAMPLE 

A Qal--ALLUVIUM (Quaternary)

+ QTd- UNDIFFERENTIATED DEPOSITS (Quaternary and Tertiary) 

O Tb-- BOZEMAN GROUP (Eocene through Miocene)

V TYsaq--SEDIMENTARY BEDROCK-Potential aquifers (Paleocene through Middle Proterozoic) 

D KCscu-SEDIMENTARY BEDROCK-Confining units (Cretaceous through Cambrian) 

O Am--METAMORPHIC ROCKS (Archean), Bozeman Hot Springs 

X GALLATIN RIVER

Figure 12. Modified trilinear diagram showing percentages of major ions in ground water, Bozeman Hot Springs, and the Gallatin River in the Gallatin 

Local Water Quality District, Montana. Data were converted from milligrams per liter to milliequivalents per liter before computing percentages.

22 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
and Bergantino, 1981). However, subsurface flow 

from metamorphic bedrock probably does not 

substantially recharge basin-fill deposits, based on the 

dissimilarity between the chemistry of the thermal 

water and that of ground water from Qal and QTd (fig. 

12).

Concentrations of constituents in water samples 

(tables 1 and 3) were compared to standards and guidelines established by the Montana Department of Environmental Quality (1995) and the U.S. Environmental 

Protection Agency (1996) for the protection of human 

health (table 5). Constituents in most samples were 

present at concentrations considered safe for human 

consumption. The standards and guidelines for fluoride were exceeded in water from Bozeman Hot 

Springs (11 mg/L as F), which is not used for drinking.

Fluoride is present naturally in most ground 

water and can reduce the incidence of tooth decay in 

children when the water is consumed during the period 

of enamel calcification. Fluoride concentrations in 

ground water of the GLWQD ranged from <0.1 to 11 

mg/L and commonly were less than the 0.8 to 1.2 

mg/L fluoride that is considered optimum for dental 

health (Centers for Disease Control and Prevention, 

1985).

Much of the ground water in the GLWQD is considered hard because it has a relatively high proportion 

of calcium and magnesium. Hard water consumes soap 

before a lather will form, leaves soap deposits, and 

forms scale in boilers, water heaters, and pipes. The 

hardness of water is expressed in terms of an equivalent 

amount of calcium carbonate the principal constituent 

of limestone. Water is considered soft if it contains 0 to 

60 mg/L of hardness, moderately hard if it contains 61 

to 120 mg/L of hardness, hard if it contains 121 to 

180 mg/L of hardness, and very hard if it contains more 

than 180 mg/L of hardness (Hem, 1985). Hardness of 

ground water of the GLWQD ranged from 6 to 

340 mg/L. Many GLWQD residents use water softeners to reduce the hardness of their well water.

MAGNITUDE AND EXTENT OF NITRATE 

IN GROUND WATER

In 1998, samples collected from 96 sites in the 

GLWQD were analyzed in the laboratory for nitrate

concentrations (tables 1 and 3; figure 13). Most samples were collected from domestic wells; therefore, the 

water-quality data represent the water that residents 

drink, rather than the shallower water that might be 

more affected by land use. Concentrations of nitrite 

plus nitrate were determined and reported in units of 

mg/L as nitrogen (N). All nitrite concentrations in this 

study were at or less than the minimum reporting level 

of 0.01 mg/L (table 3). The concentration of nitrate is 

equal to the difference between the concentration of 

nitrite plus nitrate and the concentration of nitrite. 

Because nitrite concentrations were negligible, nitrite 

plus nitrate concentrations are considered essentially 

equivalent to nitrate concentrations in this report.

Nitrate concentrations for ground-water samples 

collected from the GLWQD in 1998 ranged from less 

than the minimum reporting level of 0.05 to 13 mg/L 

(tables 1 and 3). Nitrate concentrations (10 and

13 mg/L) equaled or exceeded the U.S. Environmental 

Protection Agency drinking-water standard (10 mg/L) 

in water from 2 of the 96 sites sampled. Figure 14 illustrates the range of nitrate concentrations (data from 

table 3 only) and the relations between nitrate concentrations, hydrogeologic unit, and land use 1 . However, 

some nitrate concentrations (table 3) are from water 

near suburban population areas adjacent to irrigated 

and subirrigated areas and dryland grain. For these 

data sites, nitrate concentrations were plotted in figure

14 as "Suburban population areas."

Figure 14 shows that nitrate concentrations generally are low in water from the most of the hydrogeologic units of the GLWQD. Nitrate concentrations in 

water from basin-fill deposits where many residents 

obtain their water (hydrogeologic units Qal, QTd, and 

Tb) ranged from 0.18 to 8.1 mg/L (table 3). Median 

nitrate concentrations for these three units were less 

than about 3 mg/L. Nitrate concentrations in water 

from Quaternary and Tertiary undifferentiated deposits 

(QTd) have a wider range of values and a slightly 

higher median value than nitrate concentrations in 

water from Quaternary alluvium (Qal) and the Tertiary 

Bozeman Group (Tb). Nitrate concentrations in water 

from sedimentary bedrock (hydrogeologic units TYsaq 

and KGscu) ranged from <0.05 to 10 mg/L (fig. 14, 

table 3), with three of the highest nitrate concentrations 

(8.0, 8.8, and 10 mg/L) detected in samples from one 

well (well 02S06E36BDBB01).

Land-use information is not available for most sites from table 1.

23
111° R.6. E. R.7E.

T. 1 N.

1.7 NITRATE CONCENTRATION, IN 

MILLIGRAMS PER LITER-Range 

of concentrations shown for 

wells that were sampled more 

than one time in 1998

T.5S.

Base map from U.S. Geological Survey digital data, 1:24,000, 

1961-89 (streams), Gallatin County, 1997 (roads, 1:12,000 and 

public land survey, 1:24,000). Universal Transverse Mercator 

Projection Standard, zone 12.

6 MILES

0246 KILOMETERS

Figure 13. Nitrate concentrations in ground water and the Gallatin River, Gallatin Local Water Quality District, Montana, 1998. Samples collected 

and analyzed by U.S. Geological Survey.

24 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
12

10

CC o UJ ° 

0. 

CO

< 

cc 

o

Zi 6

8 4

GENERALIZED HYDROGEOLOGIC UNIT

(6)

(41)

These three values 

from well 

02S06E36BDBB01

(30)

(4)

EXPLANATION

(23) Number of observations 

i Maximum value 

 75th percentile 

I - Median 

" 25th percentile 

 Minimum value

 Values for which percentiles 

were not calculated

12

10

_i ft 6

4

PRIMARY LAND USE

(10)

(7)

(7)

(2)

(39)

v^ ^

00* &

<P~ ^ jSf r£ oT^

^

.&

Figure 14. Range of nitrate concentrations in ground water in relation to hydrogeologic unit and land use, Gallatin Local Vteter Quality District, 

Montana, 1998. Nitrate concentrations reported as less than the minimum reporting level (0.05 mg/L) are plotted as one-half the minimum reporting 

level. Several sites include multiple analyses. Samples collected and analyzed by the U.S. Geological Survey (table 3).

FIGURE 14 25
Figure 14 also shows that nitrate concentrations 

generally are low in water from wells in all land-use 

categories. Median nitrate concentrations for all 

land-use categories were less than 3 mg/L. Nitrate 

concentrations in water from wells in irrigated and 

subirrigated parts of the GLWQD ranged from 0.67 

and 2.8 mg/L. Nitrate concentrations in water from 

wells in areas where dryland grain production, rangeland, and forests were the dominant land-use categories 

varied widely and ranged from <0.05 to 10 mg/L. 

However, for these three land-use categories, the 

median nitrate concentration was about 1.2 mg/L (the 

combined concentrations). Three of the four highest 

nitrate concentrations (8.0, 8.8, 10 mg/L) in these 

three categories were determined from one well (well 

02S06E36BDBB01). Nitrate concentrations in water 

from suburban population areas ranged from 0.26 

to 5.0 mg/L, with a median concentration of about 2.3 

mg/L (fig. 14, table 3).

Nitrate concentrations in ground water can fluctuate seasonally owing to changing environmental conditions such as fertilizer application, quality of

recharge water, and water-table levels (Hallberg and 

Keeney, 1993). Examples of seasonal changes in 

nitrate concentrations in water from four wells located 

in the Gallatin Valley during 1998 are shown in figure 

15. The cause of the minor degree of seasonal variability in nitrate concentration (generally less than 

1.5 mg/L) cannot be determined from the available 

data.

POTENTIAL SOURCES OF NITRATE IN 

GROUND WATER

Potential sources of nitrate to ground water in the 

GLWQD include runoff from areas of timber harvests, 

atmospheric deposition, livestock waste, fertilizer, soil 

organic nitrogen, and domestic septic-system effluent. 

Generally, the more permeable the soil and the shallower the water table, the greater the likelihood that 

nitrate from these sources will percolate to ground 

water. However, additional factors specific to each 

potential source also control the movement of nitrate. 

The sources discussed below have not been quantified

o

UJ 

O 2 z. 

O 

O 

UJ

01N05E36BADD01

01N05E35ADBA01

01S04E04ACDD02

01S04E04ACCA02

APR MAY JUNE JULY AUG SEPT OCT NOV

1998

Figure 15. Seasonal changes in nitrate concentrations in water from selected wells in the Gallatin Local Water Quality District, Montana.

26 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
in terms of their relative contribution to nitrate in 

ground water but are presented in a general manner to 

conceptually support the potential relation between 

nitrate concentrations and spatial variations in land use.

Timber Harvests

Timber has been harvested from forests in Gallatin County for more than 100 years ([Montana] State 

Engineer's Office, 1953a). Timber harvests can accelerate soil erosion which might generate nitrogen-rich 

runoff (Likens and others, 1970). Harvests also reduce 

the amount of nitrogen uptake from soils by trees, 

thereby increasing the amount of nitrogen available for 

infiltration to aquifers (Hallberg and Keeney, 1993). 

Data are insufficient to describe nitrogen-rich runoff 

resulting from timber harvests as a potential source of 

nitrate in ground water. However, nitrogen-rich runoff 

from logged areas might be a source of nitrate in 

ground water in permeable basin-fill deposits downslope from areas where timber has been harvested in 

the GLWQD.

Atmospheric Deposition

Nitrogen oxides in the atmosphere are present 

naturally and from the combustion of fossil fuels. 

These oxides undergo various chemical alterations that 

produce nitrate (Hem, 1985). In 1995, precipitation in 

the GLWQD had an average nitrate concentration of 

about 0.1 mg/L, or a total annual wet deposition of 

200,000 Ib of nitrogen (900,000 Ib of nitrate) over the 

816-mi2 area of the GLWQD. An additional 0.1 mg/L, 

or 200,000 Ib, of nitrogen was deposited in the form of 

wet ammonium (NH4+) (National Atmospheric Deposition Program/National Trends Network, 1996). Measurements of nitrogen in dry deposition are not 

available for Montana but may be as much as 1.5 times 

the amount contained in wet deposition (D.L. Sisterson, Argonne National Laboratory, oral commun., 

1998). Using this ratio and assuming that all the nitrogen in atmospheric precipitation both wet and drydirectly recharged ground water, then about 0.5 mg/L 

nitrate in ground water could be derived from atmospheric deposition. Lower nitrate concentrations in 

ground water could result if this nutrient is used by vegetation; higher concentrations could result from evapoconcentration if nitrate concentrations increase as 

water evaporates from the land surface, especially in 

fallow parts of fields used for dryland grain production.

815NN03 values for precipitation range from 

about -7 to +2.5%o and are typically lower than values 

for other sources (Hubner, 1986; LeTolle, 1980; 

Heaton, 1986). Well01S06E06ABCB01 is completed 

in alluvial-fan deposits upgradient from any human 

activity and produced water with a nitrate concentration of 0.18 mg/L and a 8 15NN03 value of+1.6%o (fig. 

16, table 3). These data indicate that water from this 

well probably was recharged by precipitation and not 

subsequently influenced by human activity. Water 

from two shallow wells (01S04E04ACAC01 and 

01S04E04ACCA02) that were recharged in the 1990s 

(fig. 8) by the Gallatin River also had low nitrate concentrations (range of 0.26 to 0.84 mg/L) and 8 N values (+1.1 and +2.4%o). Although s"5NN03 was not 

determined for water from the Gallatin River, atmospheric precipitation in the Gallatin River watershed 

(970 mi above Manhattan; 825 mi2 above the Gallatin 

Valley) probably is the major source of nitrate to the 

river and would impart a low 8 15NiM03 value to Gallatin 

River water, similar to values in these wells. Water 

from nearby wells (SW1/4 NE1/4 sec. 4, T. 1 S., 

R. 4 E.) had nitrate concentrations ranging from 0.08 to 

1.3 mg/L (table 1 and Montana Microbiological Services, Bozeman, Mont., written commun., 1998). In 

addition, water from bedrock wells that were sampled 

east of the Gallatin Valley had a nitrate concentration of 

less than 0.5 mg/L, indicating a nitrate source attributable primarily, if not completely, to atmospheric deposition.

Although the several wells described above had 

8 NNOS values indicative of recharge from precipitation, most ground water sampled during this study had 

nitrate concentrations that exceeded what could be 

expected from atmospheric deposition or precipitation 

(fig. 16). Therefore, an additional source or sources 

can be inferred to have contributed nitrate to ground 

water. These other potential sources include livestock 

waste, fertilizer, soil organic nitrogen, and domestic 

septic-system effluent.

Livestock Waste

Livestock produce nitrogen-rich organic waste 

that can oxidize to form nitrate. Cattle have been the 

primary stock raised in Gallatin County since about 

1944 (Montana Agricultural Statistics, issued annually). In 1992, farm operators in Gallatin County raised 

61,960 cattle and calves, 1,980 horses and ponies, and

POTENTIAL SOURCES OF NITRATE IN GROUND WATER 27
Fertilizer

Atmosphere

Soil organic 

nitrogen Livestock waste or septic effluent

tr

01 _ 

QL 7

Z LU 3° 

O

o

O 2

HI

o

10 12 14 16

S15NN03 , IN PERMIL

EXPLANATION

PRIMARY LAND USE AND GENERAL LOCATION 

O Irrigated or subirrigated alluvial plain

 Dryland farming, rangeland, or forested bench 

@ Also within suburban population areas

 Forested Bear Canyon area

Figure 16. Relation between nitrate concentrations and 615 NNos values for ground water in the Gallatin Local Water Quality District, Montana. All 

wells were completed in Cenozoic basin-fill deposits (Qal, QTd, and Tb) except for one well in forested Bear Canyon area, which was completed in 

Cretaceous shale (KGscu). Patterns indicate typical ranges of 815 l\lN03 values for various nitrate sources (Kreitler, 1975; Boyce and others, 1976; 

Gormly and Spalding, 1979; Wolterink and others, 1979; LeTolle, 1980; Spalding and others, 1982; Heaton, 1986; Hubner, 1986).

3,650 hogs and pigs (U.S. Department of Commerce, 

1994). If the average cow, horse, and pig excrete 

156, 128, and 150 Ib of nitrogen per year, respectively 

(Van Vuren, 1949, p. 158), then waste from these 

animals produced about 10.5 million Ib of nitrogen in 

Gallatin County in 1992. Livestock waste from 

concentrated feeding operations is applied to 

farmland, whereas waste from range livestock is not 

managed. The quantity of nitrate leached from

livestock waste to ground water depends on the 

quantity of nitrate in the waste, the infiltration rate, the 

soil texture, and the ambient air temperature (National 

Academy of Sciences, 1978).

515NN03 values of nitrate from livestock waste 

typically range from +9 to +22%o (fig. 16; Kreitler, 

1975; Gormly and Spalding, 1979; Lindau and Spalding, 1984; Heaton, 1986). Water from one well com28 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
pleted in alluvium and 1,500 ft downgradient from a 

livestock waste land-application area (well 

01S04E04ADDD01) had a nitrate concentration of 3.4 

mg/L and a 515NNos value of +4.0%o (fig. 16). However, the S 15NN03 value for this well is within the 

reported range for fertilizer and soil organic nitrogen 

(fig. 16).

Conceivably, the observed 8 15NN03 value of 

+4.0%o might have resulted from the mixing of atmospheric nitrate with livestock waste-derived nitrate. To 

assess this possibility, hypothetical mixing curves were 

calculated. The 8 15NN03 value of a water sample that is 

a mixture of water from two sources is:

and the concentration of nitrate in the mixture is:

(3)

where 8 15N is the 8 15NN03 value, C is the nitrate

concentration, and P is the percent by volume, 

and the subscripts m, a, and b represent mixed, 

source a, and source b water, respectively 

(Davidson and Bassett, 1993).

The curves shown in figure 17A represent the 

mixing of two waters, as calculated using these equations. The first water is atmospheric water (source a, 

equations 2 and 3) with a nitrate concentration of 0.28 

mg/L and a 815NN03 value of+2.4%o (as sampled from 

well 01S04E04ACCA02, which is located about 2,000 

ft (0.4 mi) west of well 01S04E04ADDD01). The second water is wastewater from livestock (source b, equations 2 and 3). Because the wastewater is hypothetical, 

its nitrate concentration and 8 15NN03 values are 

unknown. Therefore, two plausible wastewaters were 

used to generate separate mixing curves that bracket 

possible mixtures of atmospheric water with livestock 

wastewater. The two plausible livestock wastewaters 

have nitrate concentrations of 5 and 50 mg/L and 

8 NNOS values of+9 and +15%o, respectively. The 

point having a nitrate concentration of 3.4 mg/L and a 

8 NN03 value of+4.0%o, representing the sample from 

well 01S04E04ADDD01, does not plot between the 

two mixing curves shown in figure 17A. Therefore, 

based on the nitrogen isotopic values, fertilizer or soilorganic nitrogen not livestock waste are more likely 

sources of nitrate in the sample from this well.

Fertilizer and Soil Organic Nitrogen

Fertilizers contain nitrogen as nitrate or in other 

forms which, if not used by plants, contribute nitrate to 

the soil. Nitrate is soluble in water and can easily leach 

to the water table. Over-application of fertilizers to 

cropland has resulted in extensive nitrate contamination of aquifers in many agricultural areas of the United 

States (Bohlke and Denver, 1995; Nolan and others, 

1997). Dissolved constituents in fertilizers, including 

nitrate, can percolate and infiltrate through the permeable, gravelly loam soils into the basin-fill deposits.

The acreage of fertilized farmland in Gallatin 

County has increased more than 5-fold since 1954 (U.S 

Department of Commerce, issued periodically), even 

as the total acreage of farmland has decreased (fig. 6). 

In 1992, a wide variety of commercial fertilizers was 

applied to about 127,650 acres of cropland in Gallatin 

County (U.S. Department of Commerce, 1994). Irrigated wheat typically receives 80-100 Ib of nitrogen 

per acre in the form of ammonium nitrate or urea, irrigated barley requires somewhat less nitrogen, and 

alfalfa fertilizers contain no nitrogen. Seed potatoes, 

which are cultivated on the northern part of the Madison Plateau, are the most heavily fertilized crop in the 

GLWQD. Most potato farmers apply about 150 to 200 

Ib of nitrogen per acre in the form of ammonium-nitrate 

fertilizer every fall. Dryland wheat and barley fields 

are fertilized with 60-70 Ib of nitrogen per acre in the 

form of urea (D.E. Heck, CCA, Crop Production Specialist, Gallatin Farmers Cooperative, Belgrade, Mont., 

oral commun., 1998). Assuming a uniform nitrogen 

application rate of 60 Ib per acre to all fertilized cropland in the county, roughly 7.7 million Ib of nitrogen 

may be applied annually to cropland in the form of fertilizer.

Fertilizers also are applied to lawns, gardens, and 

golf courses, primarily in the form of urea. Hantzche 

and Finnemore (1992) estimated that lawn fertilization 

in residential subdivisions and rural communities contributes about 1 to 3 Ib of nitrogen to ground water per 

year from each developed acre. The acreage of developed land in the GLWQD has not been determined. 

However, if one-fifth of the 33 mi2 (21,000 acres) of 

urban and subdivided land (fig. 5) is developed, then as 

much as 12,600 Ib of nitrogen might be applied to 

lawns annually. The amount of nitrogen contributed to

POTENTIAL SOURCES OF NITRATE IN GROUND WATER 29
A. MIXTURE OF ATMOSPHERIC WATER AND 

HYPOTHETICAL LIVESTOCK WASTEWATER

3-

Sample from well 

01S04E04ADDD01

0.8 percent 

wastewater

10 915N,

N03, IN PERMIL

B. MIXTURE OF FERTILIZER-AFFECTED WATER AND 

HYPOTHETICAL SEPTIC-EFFLUENT WASTEWATER

/8.5 percent 

/ wastewater

Sample from well 

01S05E21BCDD01 100 percent 

wastewater

100 percent 

fertilizer-affected 

water

G15N, 10 12

N03, IN PERMIL

EXPLANATION 

HYPOTHETICAL WASTEWATER COMPOSITION

NITRATE CONCENTRATION OF 5 MILLIGRAMS PER LITER AND

£ NNOS, VALUE OF +9 PERMIL 

NITRATE CONCENTRATION OF 50 MILLIGRAMS PER LITER AND

£15NN03, VALUE OF +15 PERMIL

15* Figure 17. Nitrate concentrations of hypothetical mixed waters as a function of 8 NNOS. In example A, atmospheric water has a nitrate 

concentration of 0.28 mg/L and a 5 NNOS value of +2.4 permil (as sampled from well 01S04E04ACCA02). In example B, fertilizer-affected water 

has a nitrate concentration of 3.1 mg/L and a 8 NNOS value of +4.7 permil (as sampled from well 01S05E21CDDB01). Several hypothetical 

wastewater compositions are plotted to show plausible ranges. These mixing curves assume that nitrate is conservative (non-reactive) in ground 

water.

ground water toy fertilizers depends on the type and 

amount of fertilizer applied, the pH and texture of the 

soil, the air temperature at the time of application, the 

amount of water applied after fertilization, and the 

acreage of fertilized land (Seiler, 1996; Nolan and 

others, 1997).

Decay of natural organic matter in soil can contribute nitrate to ground water (Nimick and Thamke, 

1998). Most of the cropland on the eastern benches of 

the Gallatin Valley (fig. 5) has been used for growing 

wheat and barley using crop-fallow rotation. Typically, one-half the farmland in a rotation is left

uncropped and weed-free for one growing season. This 

rotation allows moisture to be stored in the soil below 

the surficial evaporation zone during the fallow period 

to complement the cropping-season rainfall. During 

the fallow period, nitrogen from decaying organic matter is mineralized, resulting in nitrate accumulation in 

the soil, which provides valuable crop nutrients. However, the added soil moisture can increase the percolation of nitrate into ground water (Power, 1970; Cassel 

and others, 1971). The quantity of nitrate loading from 

crop-fallow farming depends on the timing and magnitude of precipitation and the quantity of organic matter 

and

30 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
crop residue remaining on the ground after harvest 

(Nimick and Thamke, 1998).

Nitrogen also is released from natural organic 

matter when soil is plowed, vegetation is removed, or 

deep-rooted plants are replaced by shallow-rooted 

plants, especially if the soil has a large organic component (Lamb and others, 1985). For example, alfalfa is 

extensively grown in the Gallatin Valley. As a natural 

nitrogen fixer, alfalfa stores a large quantity of nitrogen 

in its rhizomes, which may extend as deep as 15 ft 

below the land surface. When alfalfa fields are converted to other land uses such as residential development, the stored nitrogen in the remnant roots oxidizes 

to nitrate and can leach into soils and aquifers if not 

used by .other vegetation (Spalding and others, 1982; 

Hallberg and Keeney, 1993).

Most of the ground-water samples collected in 

the GLWQD had 8 15NN03 values within the +2.5 to 

+9%o range, which coincides with the range expected 

for nitrate derived from fertilizer or soil organic nitrogen (fig. 16). Eight samples had values indicating fertilizer (+2.7 to +3.6%o), seven samples had values 

indicating soil organic nitrogen (+6.2 to +8.7%o), and 

12 samples had values that could indicate either source 

(+4.0 to +5.7%o). Owing to the possibility of mixed 

sources, nitrate from soil organic nitrogen cannot be 

distinguished from fertilizer nitrate in these samples on 

the basis of 8 15NN03.

CFC data (table 4, fig. 8) indicate that water from 

wells completed in basin-fill deposits in unirrigated 

areas along the eastern benches was recharged prior to 

the 1990s, when the quantity of nitrogen in fertilizers 

increased to allow for continuous cropping. Also in the 

1990s, subdivision development increased on the 

benches. Where continuous-cropped agricultural land 

is converted to subdivisions, increased loading of 

nitrate from the unconsumed soil organic nitrogen 

could result in increased concentrations of nitrate in 

ground water. However, if crop-fallow farming is the 

main source of soil organic nitrate, then concentrations 

might decrease following the decline in crop-fallow 

practices and the associated decrease in deep percolation of water in fallow fields.

Irrigation can facilitate the movement of nitrogen from fertilizers through the permeable Gallatin 

Valley soils and into underlying aquifers. However, 

nitrate concentrations in ground water in the Gallatin 

Valley are not as high as in other agricultural areas of 

the United States, where nitrate concentrations frequently exceed 10 mg/L (Hem, 1985; Hallberg and

Keeney, 1993). Relatively low fertilizer application 

rates and dilution from snowmelt-derived irrigation 

water could result in the relatively low nitrate concentrations in ground water of the Gallatin Valley.

In contrast to the irrigated and subirrigated alluvial plain, the eastern benches are not irrigated. 

Although most of the wells on these unirrigated 

benches yielded water with relatively low nitrate concentrations, some samples with higher nitrate concentrations (from about 4 to 13 mg/L; fig. 13) were 

obtained from wells completed beneath these benches. 

The wells with higher nitrate concentrations were 

located downgradient from dryland farming areas and, 

in some cases, in subdivisions where land use changed 

from rangeland or dryland farms to residential development. Many of these wells are completed beneath thick 

(40 to 150 ft), fine-grained, unsaturated zones that 

might have been expected to decrease nitrate concentrations by denitrification of recharge water from the 

land surface.

The higher nitrate concentrations in some water 

beneath the eastern benches relative to the alluvial 

plain (fig. 13) probably are related more to the quantity 

of ground-water recharge than to the source of the 

nitrate. As stable-isotope data indicate (fig. 11), 

ground water beneath the irrigated and subirrigated 

alluvial plain is recharged by the Gallatin River or irrigation water. In contrast, ground water beneath the 

eastern benches is recharged locally by snowmelt, 

seepage from ephemeral streams, and summer rainfall. 

Low well yields in the eastern bench areas (Custer, 

1991) indicate that ground-water flow is limited. With 

limited recharge and flow, nitrate in water beneath 

these benches is not diluted to the same extent as the 

irrigated and subirrigated areas. Moreover, limited stable-isotope data (fig. 11; water from three wells) indicate that some of the recharge to the aquifer is affected 

by evaporation. Transpiration by plants likely concentrates some dissolved constituents in water. Although 

nitrate was the focus of this investigation, evapoconcentration and limited recharge also could result in 

higher concentrations of any conservative (non-reactive) constituent that infiltrates to ground water beneath 

the unirrigated benches compared to the irrigated alluvial plain.

Based on the interpretations presented in this 

section, fertilizers and soil organic nitrogen probably 

contribute most of the nitrate found in ground water 

beneath the Gallatin Valley. However, if 515NNoa values exceeded 9%o, then livestock waste or domestic

POTENTIAL SOURCES OF NITRATE IN GROUND WATER 31
septic-system effluent would be inferred as the major 

source of nitrate to ground water. 8 15NNoa values in the 

range of+2.5 to 9%o can result from a mixture of 

sources. For example, using equations 2 and 3, water 

with a nitrate concentration of 3.1 mg/L and a S15NN03 

value of+4.7%o (well 01S05E21CDDB01) might have 

originated as fertilizer, soil organic nitrogen (fig. 16), 

or a mixture of 95 percent fertilizer nitrogen (hypothetical nitrate concentration of 2.8 mg/L and +3%o 

S 15Ni\io3) and 5 percent domestic septic-system effluent 

(hypothetical nitrate concentration of 9 mg/L and 

+15%o815NNo3).

Domestic Septic-System Effluent

Domestic septic systems are designed to reduce 

the amount of nitrogen in human waste by ammonia 

volatilization, denitrification, sorption onto sediments, 

and retention in organic matter. In recent years, Gallatin County has issued more than 500 septic permits 

per year. Approximately 7,000 septic systems served 

residences in the GLWQD in 1998 (S.G. Custer, oral 

commun., 1998) The average home in rural Gallatin 

County houses 2.7 people, and the average per capita 

discharge is about 45 gallons of wastewater per day 

(Hay, 1997). Average total-nitrogen concentrations in 

septic-tank effluent range from about 35 to 90 mg/L 

(Walker and others, 1973; U.S. Environmental Protection Agency, 1980; Alhajjar and others, 1989). On the 

basis of these estimates, septic systems in the GLWQD 

discharge about 91,000 to 230,000 Ib of nitrogen per 

year. The quantity of nitrate contributed to ground 

water depends on the actual quantity of wastewater, the 

depth to ground water, soil characteristics, and the 

design and upkeep of septic tanks and drainfields.

Soil properties are critical to septic system function. Clayey soils that shrink and swell, such as those 

derived from weathered Cretaceous shales in the 

Bridger and Bear Canyon areas, can impede septic system performance by clogging drainfields and possibly 

cracking septic tanks and associated plumbing. 

Sodium chloride from water softeners can make this 

problem worse by causing clayey soils to expand irreversibly (Gretchen Rupp, Montana State University 

Extension Service, oral and written commun., 1998).

In the absence of other nitrate sources, 8 15NN03 

values for ground water affected by domestic septicsystem effluent fall in the same +9 to +22%o range (fig. 

16) as water affected by livestock waste (Kreitler, 

1975; Gormly and Spalding, 1979; Lindau and Spalding, 1984; Heaton, 1986). The only water sample from 

the GLWQD that fell within that range was collected 

from the 75-ft domestic well in Bear Canyon 

(02S06E36BDBB01) with a 815NN03 value of+14.9%o 

and a history of elevated nitrate concentrations (8 to 50 

mg/L; D.N. Whitson, oral commun., 1998; and Cynthia 

Crayton, oral commun., 1998, 1999). Based on the 

nitrate concentrations and 8 NNOS value, and in consideration of the local soil properties and possible sources 

of nitrate, this sample is probably affected by livestock 

waste or domestic septic-system effluent.

To evaluate the effects of domestic septic-system 

effluent on ground-water quality in other areas, waterquality data were collected from domestic wells on 

both the upgradient and downgradient edges of three 

subdivisions with lot sizes of 1 acre or less: Hyalite 

Heights, Baxter Creek, and Royal Arabian subdivisions (fig. 5).

In the Hyalite Heights subdivision (SW1/4, sec. 

36, T. 2 S., R. 5 E.), the two sampled wells are located 

about 0.5 mi apart with six rows of intervening houses, 

each with an individual well and septic system. In May 

1998, nitrate concentrations measured in upgradient 

(well 02S05E36CCCD01) and downgradient (well 

02S05E36CAAB01) ground water were 2.3 and 4.1 

mg/L, respectively. In May and August the corresponding 8 NNOS values in water from these two wells 

were +4.6 (May) and +4.9%o (August). According to 

drillers' logs, the wells were constructed with openended steel casing instead of screens, and completed in 

sand and gravel at depths of 51.5 and 45 ft, respectively. Interpretations of CFC data indicate that the 

ground water was recharged in the 1980s artd 1990s 

(fig. 8), more than a decade after most of the homes in 

the subdivision were constructed.

In the Baxter Creek subdivision (SW1/4, 

sec. 21, T. 1 S., R. 5 E.), the two sampled wells 

also are located about 0.5 mi from one another. 

In May 1998, nitrate concentrations in upgradient 

(well 01S05E21CDDB01) and downgradient (well 

01S05E21BCDD01) ground water were 3.1 and 4.4 

mg/L, respectively. The corresponding 8 15Nwo3 values 

were +4.7 and +5.1%o. The wells were constructed 

with open-ended steel casing and completed in a sand 

and gravel lens of a gravelly, clayey sand sequence that 

extends upward to the topsoil. Both wells are 83 ft 

deep. Interpretation of CFC data indicate ground water 

was recharged in the 1980s (fig. 8). Homes in the 

upgradient part of the subdivision were constructed in

32 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
the 1970s and 1980s, and homes in the downgradient 

part were constructed in the 1990s.

Water in Quaternary alluvium (Qal) beneath the 

western part of the Royal Arabian subdivision 

(SW1/4NE1/4 sec. 4, T. 1 S., R. 4 E.) was sampled to 

describe the magnitude and extent of nitrate in water of 

a densely developed subdivision. The approximately 

50-acre focus area is located on mostly level ground 

about 0.5 mi east of the Gallatin River. Prior to residential development in 1992-94, the area was used as

farmland and irrigated with water diverted from the 

Gallatin River ([Montana] State Engineer's Office, 

1953b). In 1992-94, the land was subdivided into 1- 

acre residential lots. Each residence has a well, septic 

system, and drainfield. These wells were constructed 

with open-ended steel casing at depths ranging from 57 

to 80 ft (median depth of 60 ft) in gravel and sand. 

Water levels in the Royal Arabian subdivision range 

from about 20 to 40 ft below land surface (table 1). 

Locally, ground water flows to the northeast (fig. 18).

45°47' 

45"46'30" 

1

0.24 041 0.72 +2.9 0.84 *°'75

_ 0 0

SHEEPSHANK DRIVE

0.16

0.23

O

0.21

0.32 V

_ 0.90

 O

0.29

0.55

0.27 +1.1 m

 W

0.62

0 

0.28

0.26 f}

%+2.4 7/0.43

LU

cc

a

in

1.25

0.67 O

0.55 0.43

0.38 1.3 * 

 +3.4

LU

tr

D

0

ir

LU

o

 z.

m

1.0

o

£ \^ // SHATTO DRIVE

0-15 ^ o 

°'°0 0.34 0.37 0.44 0.62

0.19 -

Base modified from Gallatin County, 1980, 0 100 200 300 400 500 FEET

50 100 METERS

EXPLANATION 

0.15 NITRATE CONCENTRATION, IN MILLIGRAMS PER LITER

 Sample collected April 20-21, 1998 

by U.S. Geological Survey

O Sample collected February 22,1998

by Gallatin Local Water Quality District and 

analyzed by Montana Microbial Services 

(written commun., 1998)

+2.4 £15NN03 , IN PERMIL-Sample collected May 20-21, 1998

CIl£> APPROXIMATE DIRECTION OF GROUND-WATER FLOW-- 

Water-level data determined April 20-21, 1998, from sites 

with surveyed land-surface altitudes

Figure 18. Nitrate concentrations and 8 NNOS values in ground water in the western half of the Royal Arabian subdivision, Gallatin Local Water 

Quality District, Montana, 1998. Location of Royal Arabian subdivision is shown in figure 5.

FIGURE 18 33
Based on water-level, CFC, and oxygen-isotope data, 

alluvium (Qal) underlying the western part of the 

Royal Arabian subdivision probably was recharged by 

seepage from the Gallatin River in the early 1990s. 

Although nitrate concentrations in ground-water samples from the western part of the subdivision are not 

high, they generally increase in a downgradient direction from about 0.2 to as much as 1.3 mg/L (fig. 18), 

suggesting that infiltration from the subdivision might 

contribute some nitrate to the underlying aquifer. 

Potential sources of nitrate include lawn fertilizers, 

organic soil nitrogen that has oxidized after the land 

use changed from agriculture to residential development, and domestic septic-system effluent. 8 15Ni\io3 

values (range of+1.1 to 3.4%o) for samples collected 

from the western part of the Royal Arabian subdivision 

(fig. 18) indicate atmospheric 

deposition (or the Gallatin River) and fertilizer as 

sources of nitrate in ground water (fig. 16).

The 8 15NN03 values for ground-water samples 

from the three subdivisions ranged from +1.1 to 

+5.1%o, which is well below the +9%o minimum associated with domestic septic-system effluent, but within 

the reported range for atmospheric deposition, fertilizers, and soil organic nitrogen. If the background isotopic composition is caused either by atmospheric deposition or by fertilizers, and domestic septic-system 

effluent contributes additional nitrate to ground water 

beneath the subdivisions, then 8 15NN03 values would be 

expected to increase downgradient. However, mixtures of background water and septic wastewater cannot explain the downgradient increases. To illustrate, 

figure 17B shows mixing curves for upgradient ground 

water beneath Baxter Creek subdivision ("fertilizeraffected water" sample from well 01S05E21CDDBO1, 

3.1 mg/L nitrate and +4.7%o 8 15NN03) mixed with two 

plausible septic-effluent wastewaters. The downgradient sample from beneath Baxter Creek subdivision 

(well 01S05E21BCDDO 1,4.4 mg/L nitrate and+5.1%0 

8 15NN03) does not plot on or near these curves, indicating that the hypothetical mixtures could not produce 

the sample.

In contrast, nitrogen from fertilizers or soil 

organic nitrogen can explain the downgradient increase 

in nitrate concentrations. From equations 2 and 3, a 

mixture of 50 percent water from upgradient well 

01S05E21 CDDBO land 50 percent fertilizer-affected 

water from a hypothetical source (5.7 mg/L nitrate and 

+5.3%o 8 15NN03) produces the water from downgradient well 01S05E21BCDDO1. Based on analogous calculations, ground-water samples collected from the 

Royal Arabian and Hyalite Heights subdivisions also 

were not affected by domestic septic-system effluent.

The ratio of chloride to bromide concentrations 

in ground water can be used to help identify water that 

has been affected by domestic septic-system effluent. 

Because humans consume and dispose of salt, or 

sodium chloride, effluent from septic systems commonly has elevated concentrations of chloride. Both 

chloride and bromide tend to be conservative (or nonreactive) and can originate from atmospheric deposition or mineral dissolution, but only chloride is usually 

associated with domestic septic-system effluent. A 

high ratio of chloride to bromide compared to other 

waters from an area may indicate the presence of 

domestic septic-system effluent (Davis and others, 

1998; Vengosh and Pankratov, 1998) and, therefore, 

can be used to trace discharge from septic systems.

The ratios of chloride to bromide concentrations2 

in most of the samples collected from the GLWQD in 

1998 average about 90:1 (fig. 19). This ratio is typical 

for atmospheric deposition in inland areas such as the 

GLWQD (Davis and others, 1998). Therefore, the 

chloride and bromide in most of these samples probably originate from this source. Evapoconcentration is 

the likely principal reason for the order-of-magnitude 

range in concentrations. Hence, the chloride and bromide data provide additional evidence that domestic 

septic-system effluent has not affected most ground 

water of the GLWQD.

Chloride to bromide ratios higher than the average (90:1) indicate that ground water might be affected 

by domestic septic-system effluent. For four wells, the 

chloride to bromide ratio in water ranged from 147 to

2Some bromide concentrations in ground water were reported as less than the minimum reporting level of 0.01 mg/L. For these analyses, the ratios of chloride 

to bromide were not used to calculate the average ratio of 90:1. In addition, the chloride and bromide concentrations in water from wells 

01S05E21 BCDDO 1, 02S04E16BCCA01, 02S06E36BDBB01, and 02S05E36CAAB01 were not used to calculate the average ratio of 90:1 because the 

water from these wells might be affected by domestic septic-system effluent.

34 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
Well 02S05E36CAAB01 

Hyalite Heights Subdivision 

(downgradient) 

Nitrate concentration 4.1 mg/L

Well02S04E16BCCA01 

Nitrate concentration 1.2 mg/L

Well 02S06E36BDBB01 

Bear Canyon area 

Nitrate concentration 10 mg/L

Well01S05E21BCDD01 

Baxter Creek Subdivision 

(downgradient) 

Nitrate concentration 4.4 mg/L

Well 02S05E36CCCD01 

Hyalite Heights Subdivision 

(upgradient) 

Nitrate concentration 2.3 mg/L

Well01S05E21CDDB01 

Baxter Creek Subdivision 

(upgradient) 

Nitrate concentration 3.1 mg/L

0.02 0.04 0.06 0.08 0.10 0.12 0.14 

BROMIDE CONCENTRATION, IN MILLIGRAMS PER LITER

0.16 0.18 0.20

Figure 19. Relation between chloride and bromide concentrations in ground water, Gallatin Local Water Quality District, Montana, 1998. Diagonal 

line through data represents the average ratio of chloride to bromide in all samples except those with bromide concentration less than the minimum 

reporting level and the four outliers noted in the text. Bromide concentrations below the minimum reporting level of 0.01 mg/L are plotted as 0.005 

mg/L

1,100. A chloride to bromide ratio of 550, elevated 

nitrate concentrations, and the 5 15NN03 value indicate 

that water from well 02S06E36BDBB01, located in 

Bear Canyon, is affected by livestock waste or domestic septic-system effluent. Well02S04E16BCCA01 is 

completed in the Tertiary Bozeman Group, in a subdivision consisting of 20-acre lots located on the eastern 

edge of the Madison Plateau. The 8 15NN03 value for 

this water is unknown, but specific conductance and 

concentrations of chloride and nitrate were greater in 

1998 than in 1992 (table 1).

Two wells (02S05E36CAAB01 and 

01S05E21BCDD01) are located on the downgradient 

edges of the Hyalite Heights and Baxter Creek subdivisions. The ratios of chloride to bromide concentrations 

were 1,100 and 320, respectively, which seems to indicate that water from these two wells is affected by 

domestic septic-system effluent. However, low 

8 15NN03 values (+5.1 and +4.9 %o) for these wells indicate that nitrate from domestic septic-system effluent 

has not affected these samples. Possible sources of 

chloride to ground water beneath these subdivisions 

include water softeners (which discharge sodium chloride as domestic septic-system effluent) and fertilizers, 

which contain varying amounts of chloride.

Although high chloride concentrations relative to 

bromide concentrations can indicate possible effects of 

domestic septic-system effluent on ground-water
quality, 8 15NN03 values are a better indicator of the 

nitrate source in ground water. Analysis of nitrate, 

chloride, and bromide concentrations in ground water 

can provide reconnaissance data to identify potential 

areas of septic contamination, which can then be used 

to reduce the number of samples subsequently 

collected for more definitive identification by 615NN03 

analysis.

SUMMARY

The population of Gallatin County has increased 

rapidly in recent years, and much of the associated new 

development has been concentrated in the northern part 

of the county. In response to increasing public concerns about the sustainability of the local water 

resources, the Gallatin Local Water Quality District 

(GLWQD) was established in 1995 to preserve, protect, and improve the quality of surface and ground 

water of the District. This report, prepared in cooperation with the GLWQD, describes the magnitude, 

extent, and sources of nitrate in ground water in the 

GLWQD. The magnitude and extent of nitrate in 

ground water were determined by sampling 96 sites 

and the Gallatin River in 1998. Sources of nitrate were 

determined by analyzing the spatial patterns of various 

water-quality constituents (major ions, nutrients, and 

stable isotopes); comparing land uses to ground-water 

quality; and age-dating ground water using chlorofluorocarbons (CFCs).

The GLWQD encompasses most of the Gallatin Valley, which is an approximately north-southtrending intermontane basin about 520 mi2 in area consisting of a broad alluvial plain flanked on the west by 

the Madison Plateau and on the east and south by 

smaller benches. West of the alluvial plain, the Madison Plateau is a broad bench at an altitude of more than 

5,000 ft that drains northeastward into the Gallatin 

River. Some smaller benches, or terraces, that flank the 

eastern and southern parts of the valley are mantled by 

alluvial fans, the largest of which extends well into the 

alluvial plain between Hyalite and Bozeman Creeks. 

The Gallatin River and its tributaries drain most of the 

GLWQD. Mountainous areas compose almost onehalf of the GLWQD. East and south of the Gallatin 

Valley, the sparsely populated Bridger and Gallatin 

Ranges rise from the valley floor. The crest of the Gallatin Range, with an altitude of more than 10,000 ft, is 

the highest part of the GLWQD. East of the Bridger

Range, Bridger Creek drains the mountainous Bridger 

Canyon area.

Land use in the GLWQD is predominantly agricultural. Irrigated and dryland farm crops include hay, 

grain, potatoes, and native grass. Residential and commercial developments have replaced farmland on both 

the alluvial plain and the benches. The mountainous 

parts of the GLWQD are forested and are used for timber harvesting, cattle grazing, and recreation.

In general, geologic units of the GLWQD consist 

of poorly consolidated Cenozoic basin-fill deposits and 

complexly folded and faulted Tertiary through Archean 

bedrock in the mountains. These geologic units can be 

grouped into seven hydrogeologic units. Basin-fill 

deposits can contain aquifers which are unconfined, 

leaky confined, or confined. Aquifers in basin-fill 

deposits that consist of Quaternary alluvium commonly are unconfined and highly productive. Finegrained layers within Tertiary deposits can restrict flow 

into or out of more permeable layers, which result in 

leaky-confined or confined aquifers. With depth, these 

fine-grained layers become more consolidated and, 

therefore, less permeable. However, some Tertiary 

basin-fill deposits contain productive aquifers.

Some bedrock units also are aquifers but have 

not been extensively developed in the GLWQD. Many 

of these bedrock units contain fine-grained sandstone, 

shale, mudstone, siltstone, or chert that generally are 

confining units. Ground water generally is not readily 

available in many areas where some bedrock units are 

found.

Water-level, oxygen-isotope, and CFC data indicate that Cenozoic basin-fill aquifers beneath the irrigated and subirrigated parts of the GLWQD are 

recharged primarily by the Gallatin River and its irrigation diversions. Recharge to basin-fill deposits 

beneath the benches originates more locally as lowaltitude snowmelt, seepage from ephemeral streams, 

and summer rainfall. On the basis of CFC data, estimated recharge dates for 27 ground-water samples collected in 1998 from the Gallatin Valley range from the 

1960s to the 1990s.

Nitrate concentrations generally were low in 

ground water of the GLWQD and in 1998 ranged from 

<0.05 to 13 mg/L. Nitrate concentrations (10 and 13 

mg/L) equaled or exceeded the U.S. Environmental 

Protection Agency drinking-water standard of 10 mg/L 

in water from 2 of the 96 sites sampled. Median nitrate 

concentrations in water from basin-fill deposits where 

many residents obtain their water were less than about

36 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
3 mg/L. Median nitrate concentrations in water from 

wells located within all land-use categories were less 

than 3 mg/L. Seasonal variations in nitrate concentrations were determined in water from some wells.

Potential sources of nitrate to ground water 

include runoff or infiltration from areas of timber harvests, atmospheric deposition, livestock waste, fertilizer, soil organic nitrogen, and domestic septic-system 

effluent. However, fertilizers and soil organic nitrogen. 

probably contribute most of the nitrate to ground water 

in the GLWQD, based on nitrogen isotopic ratios in 

nitrate. Irrigation can facilitate the movement of nitrogen from fertilizers through permeable soils and into 

underlying aquifers, although nitrate concentrations in 

ground water in the GLWQD are not as high as in other 

agricultural areas of the United States, where nitrate 

concentrations frequently exceed 10 mg/L. Relatively 

low fertilizer application rates and dilution from irrigation water could be the reasons for the relatively low 

nitrate concentrations in ground water. Some samples 

with higher nitrate concentrations were obtained from 

wells completed beneath the unirrigated eastern 

benches. The higher nitrate concentrations in water 

beneath the eastern benches probably are related more 

to the quantity of ground-water recharge than to the 

source of the nitrate. With limited recharge and flow, 

nitrate in water beneath these benches is not diluted to 

the same extent as the irrigated and subirrigated areas. 

On the basis of water-quality data from three subdivisions, domestic septic-system effluent does not appear 

at present to be a major source of nitrate to ground 

water in the GLWQD.

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DATA

42 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
Table 1. Well data and chloride and nitrate concentrations in ground water in the Gallatin Local Water Quality District, Montana

[Data type: I, inventory only; Q, water quality (1997-98); W, water-level monitoring network. Hydrogeologic unit: Qal, Quaternary alluvium; QTd, 

Quaternary and Tertiary undifferentiated deposits; Tb, Tertiary Bozeman Group; TYsaq, Tertiary through Proterozoic sedimentary bedrock (potential 

aquifers); KGscu, Cretaceous through Cambrian sedimentary bedrock (typically confining units); Am, Archean metamorphic rocks. Abbreviations: 

ft, feet below or above (+) land surface; (iS/cm, microsiemens per centimeter at 25 degrees Celsius; lab, laboratory; mg/L, milligrams per liter; (D), 

depth to water reported by driller. Symbols: --, no data; <, less than minimum reporting level]

Location number

02N03E33DADD01

02N05E34DDDD01

01N03E03CADD01

01N03E06BBBB01

01N03E07CDDA01

01N03E10ABBA01

01N03E10BDCD01

01N03E11BAAA01

01N03E16CABB01

01N03E19ADBB01

01N03E19DADC01

01N03E20CADA01

01N03E21AAAB01

01N03E21ADDD01

01N03E23DBBA01

01N03E27AACC01

01N03E28DCAA01

01N03E28DCBB01

01N03E33AAAC01

01N03E33ABCC01

01N03E33BADD01

01N03E33BDBB01

01N03E33BDBB02

01N03E33CCBC01

01N03E33DDAA01

01N03E34ABBA01

01N03E35DDBB01

01N04E01DBAB01

01N04E01DDBC01

01N04E03BBAA01

01N04E05DDDD01

01N04E06CBBB01

01N04E10AADD01

Data type

W

1

I

W

Q,W

I

Q,w

i

w

i

i

i

i

i

Q

i

i

i

Q

w

i

i

i

w

I

I

w

I

Q,W

W

1

I

I

Hydrogeologic 

unit

Tb

Tb

Tb

Tb

Tb

Tb

Tb

Tb

Tb

Tb

Tb

Tb

Tb

Tb

Tb

Tb

Tb

Tb

Tb

--

Tb

Tb

Tb

Tb

Tb

Tb

Qal

Tb

Tb

Qal

Qal

Qal

Qal

Depth of 

well

(ft)

61

92

--

118

-

327

47.5

40

400

526

581

530

240

212

50

196

289

284

114

--

275

340

230

378

135

174

72

123

157

48

65

82

5.8

Date of 

measurement

09-09-1951

07-30-1997

04-07-1998

09-09-1997

11-04-1992

06-03-1998

05-02-1991

07-31-1997

05-27-1998

04-13-1998

05-14-1991

10-08-1980

05-06-1986

05-02-1991

05-02-1991

05-02-1991

04-13-1998

05-27-1998

05-15-1991

05-14-1991

06-14-1991

- -1997

06-03-1998

11-21-1994

05-14-1991

05-14-1991

12-01-1984

05-14-1991

09-10-1997

05-15-1991

05-15-1991

06-20-1991

07-08-1993

05-28-1998

08-05-1992

06-24-1991

06-18-1992

06-18-1992

Depth to 

water 

(ft)

34.43

7.24

-

83.29

227.89

232.87

23.25

10.68

18.76

15.93

84.56

310(D)

350 (D)

299.48

66.87

151.20

17.84

17.47

14.36

77.30

115.39

48 (D)

-

69.22

78.92

17.42

70 (D)

145.08

-

18.47

11.45

75.73

122.98

124.18

14.26

8.21

4.99

2.66

Specific 

conductance, 

field

(|iS/cm)

-

496

447

484

-

399

~

500

475

734

~

~

--

-

-

-

523

503

-

~

~

-

428

-

~

~

~

~

512

-

-

309

~

424

-

462

~

-

pH, 

field 

(standard 

units)

~

7.4

7.9

7.5

-

7.5

-

7.6

7.4

7.6

~

~

-

-

~

-

7.5

7.3

-

-

~

-

7.5

~

~

-

~

~

7.8

-

-

7.6

~

7.3

~

7.5

-

-

Nitrite Chloride, Nitrate, . 

.... , ,1 nitrate, dissolved, field 1 .. , ' 

. .. dissolved, lab (mg/L 

, n ° lab (mg/L as as N) * (mg/L as

CJ N)

1.5

1.1

2.1

-

5.6 -- 1.4

..

1.1

6.6 - .67

1.7

..

..

--

..

..

1.5

8.7 -- 1.7

..

-

-.

-

1.5 - 1.9

..

..

--

.9

-.

..

..

2.3 -- .19

..

~

-

..

TABLE 1 43
Table 1. Well data and chloride and nitrate concentrations in ground water in the Gallatin Local Water Quality District, Montana (Continued)

Location number

01N04E12CDCC01

01N04E15DDAA01

01N04E17BAAA01

01N04E18DBCC01

01N04E19CBCC01

01N04E25BBCC01

01N04E25DCDD01

01N04E26BCCC01

01N04E26CCCC01

01N04E28ABBB01

01N04E28ABBD01

01N04E31CAAA01

01N04E33CDCC01

01N05E02AAAC01

01N05E02BAAD01

01N05E04DDAD01

01N05E04DDAD02

01N05E14ACDD01

01N05E16DAAA01

01N05E20DBAA01

01N05E27CCDD01

01N05E28DCAD01

01N05E29CDAB01

01N05E30DDAA01

01N05E34ABAB01

01N05E34ADAD01

01N05E34ADDA01

01N05E34ADDC01

01N05E34CDBD01

01N05E34DAAB01

01N05E34DAAC01

01N05E34DCBB01

Data type

I

W

W

W

W

Q

W

W

I

I

I

I

W

W

I

W

I

Q,W

I

W

I

I

W

I

I

Q

i

i

Q

I

I

I

Hydrogeologic 

unit

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

QTd

QTd

Qal

Qal

QTd

QTd

Qal

QTd

Qal

Qal

Qal

QTd

QTd

QTd

QTd

Qal

QTd

QTd

QTd

Depth of 

well 

(ft)

7.0

225

28

33

81

45

101

51

63

44

10

--

101

78

40

13

68

109

120

33

40

39

10

40

47

95

103

90

120

100

80

Date of 

measurement

08-14-1992

07-14-1992

06-11-1992

07-15-1992

09-01-1953

07-30-1997

05-27-1998

12-07-1951

07-28-1997

07-14-1992

07-14-1992

07-14-1992

06-18-1992

06-19-1991

07-22-1992

06-20-1991

07-17-1992

07-17-1992

07-31-1992

05-28-1998

06-21-1991

07-15-1992

05-13-1998 

05-13-19982

07-08-1992

07-08-1993

07-07-1951

05-13-1998

07-28-1997

05-12-1998

06-23-1998

08-26-1998

11-18-1998

07-28-1997

05-12-1998

07-16-1986

05-12-1998

07-29-1997

05-13-1998

06-24-1998

05-12-1998

05-12-1998

05-13-1998

Depth to 

water 

(ft)

5.43

3.35

3.75

5.63

4.00

5.11

8.59

10.57

8.02

17.94

3.54

4.00

2.96

21.85

6.12

5.91

11.37

7.46

86.32

94.19

43.30

12.86

;;

4.45

6.27

3.00

6.17

2.42

2.85

1.20

3.05

-

+.69

3.56

26 (D)

-

18.29

-

~

36.29

37.32

25.96

Specific 

conductance, 

field

(^iS/cm)

~

-

411

364

~

430

406

-

410

-

426

608

298

~

185

240

-

650

429

412

461

348

428

435

-

-

320

308

304

285

290

291

287

278

~

315

346

344

331

282

297

349

pH, 

field 

(standard 

units)

-

-

7.2

7.6

~

7.8

7.4

~

7.7

-

7.6

7.4

7.3

-

7.0

7.0

-

7.6

7.6

7.4

7.1

7.8

7.5

7.7

-

~

7.7

7.8

7.8

7.7

7.5

7.7

7.8

7.7

-

7.7

7.8

7.9

7.7

8.1

7.9

7.8

Chloride, 

dissolved, 

lab 

(mg/L as CD

-

-

-

-

-

-

2.3

~

~

-

-

~

-

-

-

-

~

~

~

1.0

-

-

2.6 

2.6

2.7

-

-

1.3

-

.9

.7

~

-

-

.7

-

.8

-

1.1

1.0

.6

.7

1.7

Nitrate, 

field 1 

(mg/L

asN)

-

-

.6

.9

-

1.8

-

-

.9

-

1.5

.9

<.5

-

.9

-

~

1.3

1.0

~

-

1.6

;;

~

-

-

-

1.0

~

-

-

~

.5

~

-

-

2.8

-

~

~

-

-

Nitrite 

plus 

nitrate, 

dissolved, 

lab 

(mg/L as 

N)

-

-

-

-

-

-

1.7

~

-

~

~

-

-

-

-

-

-

--

-

1.1

-

-

3.0 

3.0

~

-

1.0

-

1.6

1.5

1.6

1.5

-

.69

-

1.4

~

4.6

4.4

.78

1.2

4.6

44 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
Table 1. Well data and chloride and nitrate concentrations in ground water in the Gallatin Local Water Quality District, Montana (Continued)

Location number

01N05E34DCCD01

01N05E34DDAD01

01N05E34DDDC01

01N05E35ADBA01

01N05E35ADDB01

01N05E35CCAD01

01N05E35CCCC01

01N05E35DABB01

01N05E35DABD01

01N05E35DDBA01

01N05E35DDCA01

01N05E35DDDC01

01N05E36BAAD01

01N05E36BADD01

01N05E36BBBB01

01N05E36BCCC01

01N05E36BDAA01

01N06E17CDCB01

01N06E30BCBB01

01N07E20ABBA01

01N07E20CDDA01

01N07E29BDCD01

01S03E36BCCD01

Data type

I

I

W

Q,W

I

I

I

I

I

Q

i

i

I

Q

i

i

i

Q,W

W

Q,W

I

Q,W

W

Hydrogeologic 

unit

QTd

QTd

Qal

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

KGscu

K scu

K scu

Tb

Depth of 

well 

(ft)

--

102

102

80

-

108

--

120

80

78

100

122

85

120

57

61

101

60

154

135

--

485

113

Date of 

measurement

05-12-1998

07-29-1997

05-12-1998

06-20-1991

07-22-1992

05-12-1998

05-12-19982

06-23-1998

06-23-19982

08-26-1998

08-26- 19982

11-18-1998

11-18-19982

05-11-1998

07-29-1997

05-12-1998

05-12-1998

05-11-1998

05-12-1998

05-12-1998

06-24-1998

08-27-1998

11-18-1998

05-12-1998

05-12-1998

05-11-1998

05-11-1998

06-23-1998

08-27-1998

11-18-1998

- -1971

05-11-1998

05-11-1998

05-11-1998

06-20-1991

05-28-1998

07-16-1992

07-09-1997

06-04-1998

07-09-1997

07-09-1997

06-04-1998

10-14-1952

Depth to 

water 

(ft)

33.10

38.65

44.03

64.35

25.59

18.15

-

13.92

--

14.29

-

15.05

-

25.04

.35

11.01

57.06

-

27.15

44.02

42.41

41.55

-

51.94

60.43

56.04

57.86

-

-

-

27 (D)

-

34.34

66.12

10.77

11.10

116.72

11.50

8.20

41.78

139.49

113.32

14.20

Specific 

conductance, 

field

(US/cm)

364

328

327

315

427

450

~

424

453

431

~

432

--

448

292

289

310

402

358

322

312

307

313

329

307

418

421

392

398

402

~

416

406

511

328

314

570

226

212

422

353

342

pH,

field 

(standard 

units)

7.7

7.9

8.0

7.7

7.9

7.7

-

7.7

7.8

7.5

--

7.6

7.6

--

7.7

7.7

7.6

7.7

7.7

7.8

7.5

7.6

7.7

7.7

7.7

7.7

7.7

7.6

7.6

--

7.7

7.6

7.7

7.4

7.6

7.6

7.0

6.9

7.4

8.0

7.9

..

Chloride, Nitrate, 

dissolved, field' 

lab (mg/L 

(mg/L as as N) 

Cl)

1.8

1.7

.8

..

3.1

3.0

2.9

2.8

2.8

..

1.7

<.5

.5

.7

.9

.7

.4

.5

..

..

.7

.5

4.3

7.9

8.1 4.0

..

..

..

4.6

.9

4.2

--

.6

3.5

.6

.1

.8

2.9

2.2

Nitrite 

plus 

nitrate, 

dissolved, 

lab 

(mg/L as 

N)

3.6

--

2.8

--

--

3.5

3.5

3.2

3.3

3.5

3.5

3.1

3.1

3.4

--

.74

2.4

4.6

4.6

3.7

3.7

3.7

4.0

3.2

2.2

7.1

5.0

4.7

4.7

4.7

--

6.2

4.7

13

-

1.7

--

--

.15

--

-

3.7

TABLE 1 45
Table 1. Well data and chloride and nitrate concentrations in ground water in the Gallatin Local Water Quality District, Montana (Continued)

Location number

01S04E01ACCA01

01S04E01DCBD01

01S04E01DDCC01

01S04E04ACAA01

01S04E04ACAA02

01S04E04ACAB01

01S04E04ACAC01

01S04E04ACAC02

01S04E04ACBA01

01S04E04ACBA02

01S04E04ACBB01

01S04E04ACBC01

01S04E04ACBD01

01S04E04ACCA01

01S04E04ACCA02

01S04E04ACCB01

01S04E04ACCC01

01S04E04ACCD01

01S04E04ACDA01

01S04E04ACDB01

01S04E04ACDB02

01S04E04ACDB03

01S04E04ACDC01

01S04E04ACDD01

01S04E04ACDD02

01S04E04ADCC01

01S04E04ADDB01

01S04E04ADDD01

Data type

I

I

I

Q

I

I

Q

I

I

I

I

I

I

I

Q

I

I

I

I

I

I

I

I

i

Q

i

I

Q

Hydrogeologic 

unit

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Depth of 

well 

(ft)

85

185

205

57

--

63

60

63

80

60

60

60

60

60

--

60

60

--

--

--

60

--

--

--

60

-

58

64

Date of 

measurement

06-19-1991

06-19-1991

05-27-1983

10-27-1992

04-21-1998

05-20-1998

08-27-1998

11-18-1998

04-21-1998

09-17-1992

04-21-1998

04-21-1998

05-21-1998

08-27-1998

04-21-1998 

04-21-19982

04-20-1998

04-20-1998

04-20-1998

04-20-1998

04-20-1998

04-20-1998

04-21-1998

05-21-1998

08-27-1998

11-18-1998

04-20-1998

04-20-1998

04-21-1998

04-21-1998

04-21-1998

04-21-1998

04-21-1998

04-21-1998

04-21-1998

04-21-1998 

04-21-19982

05-21-1998

08-27-1998

11-18-1998

04-21-1998

07-31-1997

05-12-1998

Depth to 

water 

(ft)

47.64

54.73

57 (D)

21 (D)

-

-

-

-

34.85

30 (D)

-

38.67

-

-

34.83

32.70

31.46

32.07

30.84

29.59

30.23

29.87

27.40

24.74

-

27.02

28.57

29.79

36.71

33.94

35.35

-

37.40

35.26

36.29

33.27

30.01

~

37.20

32.36

39.56

Specific 

conductance, 

field 

(|iS/cm)

450

-

-

-

357

342

340

343

352

~

342

333

312

315

342

316

313

290

298

305

308

308

298

298

298

290

304

301

332

319

333

323

315

328

362

286

339

350

339

377

417

pH, 

field 

(standard 

units)

7.6

~

~

-

7.2

6.9

6.9

6.9

7.4

-

7.2

7.2

7.0

6.9

7.1

7.2

7.3

7.3

7.2

7.3

7.2

7.2

6.9

6.8

6.8

7.2

7.2

7.1

7.0

7.2

7.1

7.1

7.2

7.0

7.0

6.9

6.8

6.8

7.2

7.1

7.0

Chloride, Nitrate, 

dissolved, field 1 

lab (mg/L 

(mg/L as as N)

CD

-

-

-

-

1.6

1.4 1.1

..

1.8

-

1.3

1.4

1.3

..

1.3 

1.3

2.2

1.5

1.7

1.5

1.4

1.7

1.6

1.5

-

..

1.8

1.6

1.2

1.3

1.4

1.3

1.1

1.2

1.3

2.0 

2.2

1.6

..

1.5

1.6

3.0 2.9

Nitrite 

plus 

nitrate, 

dissolved, 

lab 

(mg/L as 

N)

~

-

-

-

.96

.91

1.5

1.4

.75

-

.72

.55

.46

.59

.67 

.62

.41

.29

.16

.23

.27

.28

.26

.28

.84

.78

.15

.32

.19

.43

.43

.55

.38

.34

.37

1.3 

1.3

.61

1.8

2.1

.62

-

3.4

46 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
Table 1. Well data and chloride and nitrate concentrations in ground water in the Gallatin Local Water Quality District, Montana (Continued)

Location number

01S04E09BAAA01

01S04E10DDDD01

01S04E12BDDC02

01S04E12CAAB01

01S04E17DCDD01

01S04E18BCB01

01S04E25AAA03

01S04E25ADDD01

01S04E26CDDD01

01S04E26CDDD02

01S04E29BCDD01

01S05E05CCBB01 3

01S05E09ACCC01

01S05E09CCAD01

01S05E09DCCC01

01S05E12BCCC01

01S05E12BCCC02

01S05E13DBCB01

01S05E13DDDA01

01S05E13DDCB01

01S05E14ACDD01

01S05E14DDCB01

01S05E15BCBA01

01S05E16DBCC01

01S05E16DBCC02

01S05E16DBDD01

01S05E17CCDC01

01S05E21BCDD01

01S05E21CDDB01

01S05E22AADD01

01S05E22ADDD01

01S05E24BACB01

01S05E24CACD01

Hydro-

~ eeo- Data type , . Jr logic

unit

W

Q,W

W

I

Q,W

W

I

W

Q,W

I

W

I

I

I

W

W

I

I

Q

i

Q

I

I

I

I

I

w

Q

Q

I

i

i

i

Qal

Qal

Qal

Qal

Tb

Tb

Qal

Qal

Qal

Qal

Tb

Qal

Qal

Qal

Qal

QTd

QTd

QTd

QTd

QTd

QTd

Qal

Qal

QTd

Qal

Qal

Qal

QTd

QTd

Qal

Qal

QTd

Qal

Depth of Date of 

well meas- 

(ft) urement

97

107

146

260

50

318

50.5

34

37

27

~

47

28

80

141

112

120

275

260

224

140

36

60

58.5

80

60

42

83

83

52

33

60

37

03-27-1953

07-30-1992

06-02-1998

09-09-1997

02-04-1988

06-19-1991

06-18-1992

01-05-1998

01-21-1989

03-07-1953

07-29-1992

07-30-1992

05-27-1998

05-27-19982

07-13-1993

01-30-1986

07-23-1992

07-09-1992

07-28-1997

07-09-1992

07-09-1992

07-09-1992

07-30-1997

07-30-1997

01-06-1998

09-09-1997

09-10-1997

05-19-1998

09-09-1997

07-13-1993

06-18-1991

07-29-1997

07-29-1997

07-29-1997

07-31-1992

07-31-1997

05-20-1998

07-31-1997

05-20-1998

07-23-1992

09-10-1997

08-01-1997

07-29-1992

Depth to 

water 

(ft)

22.58

12.15

32.35

43.44

53. 4 (D)

~

6.52

-

70.64 -

15.97

7.76

4.76

6.96

~

6.62

-67 (D)

17.86

19.93

12.24

21.89

100.73

-

159.87

111.08

-

109.56

107.46

106.15

11.67

28.87

37.24

23.66

24.45

25.88

9.05

37.61

-

49.51

60.82

3.86

2.58

19.49

27.73

Specific 

conductance, 

field

(^S/cm)

-

379

444

-

-

432

553

643

-

-

374

457

443

457

431

-

403

465

551

~

-

375

487

504

488

444

462

454

650

532

575

614

590

505

347

598

533

548

540

623

572

502

553

__ Chlo- pH, 

« .1 nde, field ,. . ' dissolved, (stan- 

, , lab dard 

... x (mg/L as units) * 1}

-

7.5

7.2 2.7

~

-

7.6

7.6

7.8 9.9

..

..

7.3

7.5

7.3 4.5

7.5 4.8

7.7

-

7.6

7.5

7.4

~

-

7.6

7.7

7.7

7.0 13

7.4

7.6

7.5 13

7.3

7.3

7.3

7.6

7.5

7.6

7.2

7.4

7.1 16

7.3

7.1 4.6

7.6

7.5

7.9

7.5

Nitrite

Nitrate, .pluS field 1 "ltrfte' 

._ dissolved, ("£ ""> as N) . ._ (mg/L as

N)

-

.8

-

-

-

~

1.5

1.4

~

-

1.0

.6

~

2.4

~

1.4

1.8

2.1

-

-

3.9

4.1

4.4

3.8

3.8

3.1

-

4.8

2.9

-

2.9

3.3

1.5

1.0

3.9

~

3.2

-

2.8

1.7

4.1

4.5

-

-

.94

-

-

~

-

2.8

~

-

~

-

1.5

1.5

-

-

-

-

-

~

-

-

-

~

7.1

-

-

4.4

-

-

-

-

-

~

-

-

4.4

-

3.1

~

~

-

-

TABLE 1 47
Table 1. Well data and chloride and nitrate concentrations in ground water in the Gallatin Local Water Quality District, Montana (Continued)

Location number

01S05E25ADAD01

01S05E27CBDC01

01S05E35CAAB01

01S06E06ABCB01

01S06E07CCBA01

01S06E08CBAA01

01S06E17CCDD01

01S06E18BBBB01

01S06E20BCDB01

01S06E20BDAA01

01S06E20BDAA02

01S06E20BDAB01

01S06E20CAAD01

01S06E20CBDD01

01S06E20CCDD01

01S06E28DABD01

01S06E32BADC01

01S06E32DCAB01

01S06E33DACD01

01S06E36ADDC01

01S07E09CCCA01

01S07E16BBBA01

01S07E16CCDA01

01S07E17AACA01

01S07E17BDCB01

01S07E21BDAB01

01S07E21CABA01

01S07E27CCAB01

01S07E27DBDC01

HydroData type . . logic

unit

W

Q,W

W

Q

w

W

Q

i

I

w

Q

I

i

i

i

w

Q,W

I

I

I

I

I

I

W

W

I

I

I

Q

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

KGscu

QTd

Qal

Qal

K scu

KGscu

KGscu

TYsaq

KGscu

TYsaq

TYsaq

TYsaq

TYsaq

TYsaq

Depth of Date of 

well meas- 

(ft) urement

150

115

67

375

100

200

115

285

173

110

128

166

307

230

173

620

157

102

97

--

17

220

320

50

107

340

100

165

80

01-27-1998 

04-14-1998

04-20-1998

08-06-1992

05-27-1998

08-18-1992

07-16-1992

05-13-1998

09-10-1991

08-09-1997

09-09-1997

05-19-1998 

05-19-19982

06-20-1991

09-10-1997

06-20-1991

11-04-1992

07-21-1993

05-19-1998

06-20-1991

07-17-1997

06-20-1991

07-17-1997

03-24-1992

07-16-1997

07-17-1997

05-28-1998

07-17-1997

07-17-1997

07-10-1997

04-14-1998

07-09-1997

07-08-1997

01-26-1998

04-14-1998

04-20-1998

01-26-1998

04-14-1998

04-20-1998

07-08-1997

07-08-1997

06-04-1998

07-08-1997

Specific 

Depth to conducwater tance, 

(ft) field

(jiS/cm)

2.16

2.04

46.31

41.60

19.08

281.45

283.39

62 (D)

106.75

64.58

84.51

213.91

74.37

39.39

45.62

43.08

48.73

38.4

65.15

88.4

.79.92

320 (D)

-

57.06

57.63

17.97

11.17

-

5.71

5.29

93.50

43.47

34.89

29.35

'--

43.47

231.58

20.95

21.28

34.30

405

-

598

593

505

290

266

-

~

375

399 

407

405

554

-

-

285

296

276

~

502

 458

-

415

365

336

494

278

671

331

262

178

-

393

~

'

433

~

218

582

60

296

pH, 

field 

(standard 

units)

7.6

~

7.6

7.3

7.5

7.8

7.8

~

-

7.6

7.6 

7.8

7.4

7.4

-

-

8.1

7.9

7.8

-

7.4

7.4

-

7.8

7.7

7,5

7.7

7.6

7.3

7.8

8.9

9.9

-

8.0

~

-

7.6

-

9.3

7.3

9.0

7.4

Nitrite Chlo-

 J XT'* * PlUS ride, Nitrate, 

,. , , ~ ..i nitrate, dissolved, field ,. , , 

. . , .. dissolved,

lab (mg/L lab

, ,T -T-. laO (mg/L as as N) . _ 

 (mg/L as

j N)

.6

..

1.6

21

3.3

<.5

.44 .5

..

-

1.3

1.3 2.0 

1.3

--

9.7

~

-

_. 

1.3 .8 .

..

-

-

5.1

~

.8

.6

2.1

.9

2.4

1.2

.6

.5

<.5

..

.9

..

~

.7

..

.7

1.1

.6

.7

-

~

2.6

~

-

.18

-

~

-

2.1

2.2

-

-

~

.--

-

.90

~

-- 

-

~

~

-

-

.23

~

~

~

-

~

~

-

-

-

-

~

-

~

~

~

-

48 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
Table 1. Well data and chloride and nitrate concentrations in ground water in the Gallatin Local Water Quality District, Montana (Continued)

Location number

01S07E30BAAA01

01S07E33DABD01

02S04E01BABC01

02S04E01CCCD01

02S04E05BCBB01

02S04E10ACCA01

02S04E11ADDD01

02S04E12CADA01

02S04E13BADA01

02S04E13BBAC01

02S04E13BBDA01

02S04E13CBDC01

02S04E13CCBC01 

02S04E14DADC01 4 

02S04E14DADC024

02S04E16BCCA01

02S04E16DADA01

02S04E23ACDC01

02S04E29CDDC01

02S04E35ABBB01

02S05E05ABBB01

02S05E05ABBD01

02S05E10AABB01

02S05E11ADAB01

02S05E12DACC01

02S05E13BDCD01

02S05E14CDBA01

Data type

Q,W

I

I

Q,W

I

W

I

I

Q,W

I

Q

I

w 

i 

Q

Q,W

W

I

I

W

I

w

Q

w

I

w

w

Hydrogeologic 

unit

TYsaq

K scu

Qal

Qal

Tb

Tb

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Am 

Am

Tb

Tb

Qal

QTd

Qal

QTd

QTd

QTd

QTd

QTd

QTd

QTd

Depth of 

well 

(ft)

118

180

44.5

40

178

119

26

42

40

35

30

38

11

148

177

50

56

31

40

125

55

75

80

185

113

Date of 

measurement

06-04-1998

07-09-1997

06-05-1998

07-08-1997

07-24-1997

07-23-1997

05-27-1998

06-23-1991

01-06-1998

04-14-1998

04-24-1998

08-11-1992

07-24-1997

07-23-1997

01-05-1998

07-24-1997

07-23-1997

05-11-1998

06-02-1998

07-23-1997

06-21-1947 

03-23-1991 

06-23-1991

01-05-1998

08-11-1992

09-11-1992

05-26-1998

01-06-1998

04-13-1998

04-24-1998

07-23-1997

06-22-1991

08-17-1992

06-23-1991

06-23-1991

08-18-1992

05-20-1998

10-24-1988

07-14-1993

06-17-1988

06-11-1988

04-07-1989

05-11-1989

Depth to 

water 

(ft)

36.50

49.89

53.03

174.81

11.87

18.57

14.50

58.00

39.82

-

45.29

12.96

15.92

20.29

-

13.15

9.66

15.90

12.04

10.81

3.30

~

108.25

-

-

72.46

-

80.52

10.86

39.35

4.78

6.25

2.79

10.41

~

12.80

-

26 (D)

11.10

2.60

3.08

Specific 

conductance, 

field

(|iS/cm)

297

510

463

196

482

522

514

711

~

462

-

~

452

452

437

485

494

491

458

498

681 

704

681

440

446

571

~

427

-

440

199

419

420

268

~

474

-

520

-

~

.--

412

pH, 

field 

(standard 

units)

7.4

7.1

7.1

9.6

7.3

7.1

7.2

7.5

-

7.7

-

~

7.1

7.1

7.1

7.2

7.2

7.1

7.2

7.0

8.9 

9.0

9.3

7.8

7.9

7.4

-

7.6

~

7.4

6.7

7.6

7.2

7.7

~

7.3

-

7.2

~

~

-

8.7

Chlo- ruf

ride, Nitrate, .*; . 

j- j r- ui nitrate, dissolved, field ,. , ' 

. . , ,, dissolved, lab (mg/L

(mg/L as as ]N) , ._ 

rn (mg/L as

Vxll m.T\ N)

.6 -- .33

.9

4.2 -- .84

1.0

.7

1.6

4.8 -- 2.0

..

..

1.4

..

--

1.3

1.3

4.2 1.0 1.6

1.6

.6

5.7 .6 1.1

1.0

1.8

--

54 <.5

<.5

9.8 -- .46

28 -- 1.2

1.1

..

1.1

-

1.0

-

--

-

2.7 1.7 1.7

-

..

~

--

..

TABLE 1 49
Table 1. Well data and chloride and nitrate concentrations in ground water in the Gallatin Local Water Quality District, Montana (Continued)

Location number

02S05E17BBAA01

02S05E18BCDD01

02S05E19BACC01

02S05E20DDCC01

02S05E22CCDC01

02S05E23AADD01

02S05E23CCCB01

02S05E31ADDA01

02S05E35DCDC01

02S05E36BACD01

02S05E36CAAB01

02S05E36CCCD01

02S06E08ADDA01

02S06E12DCAA01

02S06E19BBBB01

02S06E20CABD01

02S06E20CACA01

02S06E21BBAA01

02S06E21BCDD01

02S06E23ABCC01

02S06E23DCAD01

02S06E24ACAB01

02S06E26ADAD01

02S06E26DDBA01

02S06E33ADAC01

02S06E33BABD01

02S06E33BDDC01

02S06E36BDBB01

Data type

W

I

Q

I

I

I

Q,W

Q

w

i

Q

Q

i

Q,W

W

Q,W

I

W

I

w

I

w

I

w

I

I

w

Q

Hydrogeologic 

unit

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

Tb

TYsaq

QTd

QTd

QTd

Tb

QTd

Qal

Qal

KGscu

TYsaq

QTd

QTd

QTd

QTd

KGscu

Depth of 

well 

(ft)

39

55

152

30

165

49

80

125

156

138

45

51.5

550

39

--

300

238

145

220

42

120

342

80

70

176

305

159

75

Date of 

measurement

08-18-1992

07-23-1997

04-14-1998

05-11-1998

06-23-1991

03-09-1953

08-13-1992

08-19-1992

01-27-1998

04-14-1998

05-13-1998

06-02-1998

08-17-1992

05-26-1998

05-14-1951

10-26-1988

07-31-1997

05-18-1998

07-31-1997

05-18-1998

08-26-1998

06-24-1991

07-10-1997

06-04-1998 

06-04- 19982

10-27-1992

06-22-1991

06-05-1998

06-22-1991

07-30-1997

07-30-1997

07-30-1997

07-30-1997

01-26-1998

07-30-1997

06-23-1991

06-22-1991

06-22-1991

06-22-1991

07-30-1997

01-06-1998

10-19-1998

10-19-1998

Depth to 

water 

(ft)

18.65

27.84

57.95

59.97

5.22

10.78

9.60

5.89

6.96

3.89

5.48

4.24

30.58

-

35.68

11.31

9.92

11.51

22.22

-

-

223.05

11.40

6.42

23.59

140.90

143.87

167

86.85

94.91

4.27

9.36

22.11

43.91

23.26

88.37

126

31.71

39.09

-

-

Specific 

conductance, 

field

(^iS/cm)

472

364

542

~

433

~

455

-

-

487

461

454

596

459

-

-

507

507

346

334

346

372

456

394 

414

-

345

-

472

661

346

714

580

~

523

647

-

364

-

1,080

683

692

741

pH, 

field 

(standard 

units)

7.6

6.8

7.3

~

7.3

-

7.6

-

-

7.4

7.5

7.3

8.0

7.8

~

-

7.3

7.3

7.7

7.3

7.1

7.7

7.0

6.8 

7.0

-

7.8

-

7.5

7.6

7.5

6.9

7.9

-

7.4

7.0

-

7.5

-

6.9

6.8

6.9

6.8

Chloride, 

dissolved, 

lab 

(mg/L as 

Cl)

-

-

-

6.1

--

-

~

~

-

-

1.2

~

-

1.3

~

-

-

22

-

3.8

-

~

~

2.7 

2.9

~

-

6.9

-

-

~

-

-

-

-

-

~

~

-

-

19

~

22

Nitrate, 

field 1 

(mg/L

asN)

<.5

.6

1.7

1.5

-

-

1.0

~

-

1.9

2.1

-

1.5

'--

-

-

-

-

1.6

~

-

-

2.8

~

-

~

-

~

4.1

.8

.5

1.1

-

2.6

~

-

-

-

25

5.5

-

Nitrite 

plus 

nitrate, 

dissolved, 

lab 

(mg/L as 

N)

-

-

~

2.4

-

~

-

-

-

-

2.6

2.5

-

.75

~

-

-

4.1

-

2.3

2.8

~

~

1.7 

1.7

~

-

2.0

-

-

-

-

~

-

-

~

-

-

~

-

8.0

8.8

10

50 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
Table 1. Well data and chloride and nitrate concentrations in ground water in the Gallatin Local Water Quality District, Montana (Continued)

Location number

02S07E02ACDC01

02S07E06ADBD01

02S07E10DDAD01

02S07E12BBAD01

02S07E24CCAC01 

02S07E24CDCB01

02S07E26CACD01

03S04E02DCAD01

03S04E03ABAA01

03S04E09ABBC01

03S04E11BCAD01

03S04E11BDCD01

03S04E11CAAA01

03S04E11CBBA01

03S04E11DCCB01

03S04E11DDBC01

03S04E21DDBD01

03S04E23AADC01

03S04E23CABB01

03S04E23CCBD01

03S04E25DBBD01

03S04E32DADA01

03S04E34ABBB01

03S04E36ABDD01

03S04E36ACAC01

03S04E36BABB01

03S05E04AAAD01

03S05E06DAAA01

03S05E07BCCC01

03S05E10CCCB01

Data type

Q

I

w

w

w

Q,W

W

I

I

Q,W

Q

I

I

w

w

Q

i

i 

Q

w

w

w

Q,W

I

Q

w

i

w

w

w

Hydrogeologic 

unit

K scu

TYsaq

K scu

K scu

TYsaq 

TYsaq

TYsaq

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

QTd

Qal

Qal

Qal

K scu

QTd

QTd

QTd

QTd

QTd

QTd

Qal

QTd

Depth of 

well 

(ft)

111

900

65

66

220 

125

395

48

22.8

96

80

45

58.5

40

50

65

105

208

100

80

50

71

92

150

197

312

54

178

36

70

Date of 

measurement

07-08-1997

06-03-1998

- - 1994

07-10-1997

07-07-1997

07-07-1997

07-07-1997 

07-07-1997

06-03-1998

07-07-1997

08-04-1992

07-13-1993

07-29-1992

05-26-1998

07-22-1997

05-12-1998

06-02-1998

07-22-1997

07-22-1997

06-18-1991

07-22-1997

07-22-1997

05-13-1998

03-31-1971

06-18-1991

07-29-1992

07-22-1997

05-26-1998

07-22-1997

06-18-1991

09-10-1997

06-18-1991

07-28-1992

05-26-1998

09-11-1997

09-11-1997

05-19-1998

06-18-1991

09-10-1997

08-19-1992

06-03-1998

06-18-1991

06-22-1991

Depth to 

water 

(ft)

15.80

16.46

300 (D)

-

3.39

1.42

60.29 

49.54

~

51.38

26.95

8.19

23.99

24.87

11.53

14.55

13.84

9.47

30.97

5.48

27.69

30.19

36.17

26 (D)

-

130.02

56.28

60.49

43.82

15.81

17.85

53.28

46.11

44.49

59.17

136.66

135.82

233.40

229.41

4.79

157.37

3.87

41.66

Specific 

conductance, 

field

((iS/cm)

397

366

-

273

345

320

612 

693

697

509

360

371

387

406

471

397

405

447

447

541

--

440

426

-

310

374

412

434

331

299

349

576

354

369

714

658

643

340

318

300

496

235

464

pH, 

field 

(standard 

units)

7.2

7.1

-

6.6

7.1

7.5

7.3 

7.9

8.1

7.3

7.7

7.7

7.5

7.1

7.4

7.3

7.3

7.4

7.6

7.2

~

7.6

7.5

-

7.5

7.8

7.5

7.2

7.7

7.2

7.4

7.2

7.4

7.1

7.5

7.6

7.5

7.2

7.5

7.1

7.7

7.5

7.5

Nitrite Chloride, Nitrate, ."* 

.. , , ~ ,,i nitrate, dissolved, field ,. , ' 

, . / ,r dissolved, lab (mg/L , , 

, ;T - T, lab (mg/L as as N)

ci) mgN) as

2.4

1.9 - 1.4

--

3.6

2.5

1.6

.9 \ --

\ ..

.6 -- '<.05

.8

1.7

1.5

1.1

8.1 -- .41

1.4

3.2 1.5 1.5

1.6

3.8

1.8

..

~

1.6

2.8 2.1 2.6

~

..

2.1

1.0

1.5 -- 1.2

.6

~

.6

..

2.4

1.5 -- 1.1

4.9

4.8

2.0 -- 8.1

-

.5

3.0

2.6

-

..

TABLE 1 51
Table 1. Well data and chloride and nitrate concentrations in ground water in the Gallatin Local Water Quality District, Montana (Continued)

Location number

03S05E11BCAD01

03S05E11DAAC01

03S05E11DAAC02

03S05E15DCCA01

03S05E21BBBA01

03S05E21CCCC01

03S05E27BCBB01

03S05E27CBBD01

03S06E01AACB01

03S06E05CBAA01

04S04E18ACAA01

04S04E28CBDA01

04S04E33DBBA01

04S04E33DBDA01

05S04E36DBDB01

05S05E30ACCC01

Data type

I

I

Q,W

Q,W

I

W

W

I

W

W

W

W

W

W

W

W

Hydrogeologic 

unit

QTd

QTd

QTd

QTd

Qal

QTd

KGscu

K scu

K scu

QTd

Qal

Qal

K scu

Qal

Qal

Qal

Depth of 

well 

(ft)

95

74

--

220

22

263

50 .

77

51

128

40

104

100

80

38

40

Date of 

measurement

07-31-1997

06-22-1991

01-17-1998

05-18-1998

06-22-1991

05-13-1998

08-04-1992

04-15-1998

01-27-1998

- -1965

07-30-1997

08-19-1992

07-20-1993

06-18-1991

11-02-1992

07-29-1997

07-23-1997

07-24-1997

07-29-1997

07-29-1997

Depth to 

water 

(ft)

62.63

60

101.49

210.13

~

8.27

185.99

7.03

29 (D)

20.91

82.14

81.95

~

24.71

23.14

50.65

52.75

9.14

8.00

Specific 

conductance, 

field 

(liS/cm)

308

-

-

215

219

222

315

813

-

-

610

~

262

135

-

296

285

250

382

232

pH, 

field 

(standard 

units)

7.9

--

-

6.5

7.3

7.2

7.7

7.5

-

-

7.2

-

7.4

6.7

~

7.4

8.2

8.0

7.8

7.6 '

Chloride, 

dissolved, 

lab 

(mg/L as 

Cl)

-

-

-

6.9

-

1.4

-

-

-

~

-

~

-

-

-

-

-

~

-

-

Nitrate, 

field 1 

(mg/L

asN)

.9

--

-

1.6

~

1.1

.6

5.0

-

~

.9

-

~

-

~

<.5

<.5

<.5

.5

<.5

Nitrite

plus 

nitrate, 

dissolved, 

lab 

(mg/L as 

N)

~

-

-

2.0

-

.71

~

-

-

-

~

~

-

-

~

~

-

-

-

~

Nitrate concentrations determined on unfiltered samples using a spectrophotometer by USGS personnel. 

Replicate sample. 

3Well destroyed. 

Bozeman Hot Springs.

52 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
Table 2. Summary of water-level data for wells in the Gallatin Local Water Quality District water-level monitoring network, Montana

[Hydrogeologic unit: Qal, Quaternary alluvium; QTd, Quaternary and Tertiary undifferentiated deposits; Tb, Tertiary Bozeman Group; TYsaq, Tertiary 

through Proterozoic sedimentary bedrock (potential aquifers); K scu, Cretaceous through Cambrian sedimentary bedrock (typically confining units). 

Abbreviation: ft, feet below land surface. Symbol: , no data]

Location number

02N03E33DADD01

01N03E06BBBB01

01N03E07CDDA01

01N03E10BDCD01

01N03E16CABB01

01N03E33ABCC01

01N03E33CCBC01

01N03E35DDBB01

01N04E01DDBC01

01N04E03BBAA01 

01N04E15DDAA01

01N04E17BAAA01

01N04E18DBCC01

01N04E19CBCC01

01N04E25DCDD01

01N04E26BCCC01

01N04E33CDCC01

01N05E02AAAC01

01N05E04DDAD01

01N05E14ACDD01

01N05E20DBAA01

01N05E29CDAB01

01N05E34DDDC01

01N05E35ADBA01

01N06E17CDCB01

01N06E30BCBB01

01N07E20ABBA01

01N07E29BDCD01

01S03E36BCCD01

01S04E09BAAA01

01S04E10DDDD01

01S04E12BDDC02

01S04E17DCDD01

01S04E18BCB01

01S04E25ADDD01

01S04E26CDDD01

Hydrogeologic 

unit

Tb

Tb

Tb

Tb

Tb

Tb

Tb

Qal

Tb

Qal 

Qal

Qal

Qal

Qal

Qal

Qal

Qal

QTd

Qal

QTd

Qal

Qal

Qal

QTd

QTd

QTd

K scu

KGscu

Tb

Qal

Qal

Qal

Tb

Tb

Qal

Qal

Well depth

(ft)

61

118

~

47.5

400

-

378

72

157

48 

225

28

33

81

101

51

101

78

13

109

33

39

102

80

60

154

135

485

113

97

107

146

50

318

34

37

Period of 

record 

(calendar 

year)

1951-98

1997-98

1992-98

1997-98

1989-98

1989-98

1986-98

1986-98

1993-98

1992-98 

1992-98

1992-98

1992-98

1953-98

1951-98

1997-98

1991-98

1992-98

1992-98

1992-98

1992-98

1993-98

1991-98

1992-98

1991-98

1992-98

1997-98

1997-98

1952-98

1953-98

1992-98

1997-98

1992-98

1989-98

1992-98

1992-98

Number of 

measurements

21

8

6

10

24

32

26

21

21

21

22

11

9

22

203

9

11

11

19

15

14

18

13

13

23

10

7

6

22

25 

13

8

11

21

13

24

Water level (ft)

Highest

34.00

83.30

227.89

10.70

73.59

39.23

139.80

6.36

122.98

14.26 

3.02

3.40

5.27

3.29

5.92

7.95

21.60

5.60

2.24

77.92

11.27

5.74

47.92

13.22

9.36

102.99

3.12

113.32

14.20

17.04

12.15

43.44

5.63

70.50

6.35

2.78

Date of 

highest

09-09-51

09-09-97

11-04-92

07-31-97

10-04-97

10-16-95

04-26-86

10-14-98

07-08-93

08-05-92 

04-15-93

08-07-98

06-09-98

05-04-93

08-06-52

10-08-97

08-03-93

08-02-93

06-10-93

07-02-97

04-22-98

07-07-98

10-06-97

11-01-93

07-09-93

10-06-97

04-20-98

06-04-98

10-14-52

07-09-93

07-30-92

09-09-97

09-09-92

11-05-92

07-07-98

07-07-98

Lowest

42.37

85.86

241.68

20.83

86.05

78.52

174.46

13.92

125.59

21.17 

3.93

6.86

8.91

4.82

16.91

13.69

27.64

7.04

11.37

95.10

13.03

8.81

52.21

26.10

14.38

117.14

20.05

139.00

39.72

25.50

53.29

64.79

11.71

89.39

14.31

11.55

Date of 

lowest

04-15-93

10-08-97

10-08-97

04-22-98

07-29-91

11-06-91

10-08-97

02-13-92

05-19-94

02-25-93 

01-12-98*

03-06-98

10-08-97

06-11-92

05-04-94

04-22-98

04-22-98

05-03-93

07-17-92

04-22-98

09-03-92

02-15-95

06-09-98

05-04-93

02-25-93

05-04-93

03-02-98

07-09-97

06-11-98

04-04-98

04-24-98

04-24-98

05-05-93

10-14-98

03-06-98

03-06-98

TABLE 2 53
Table 2. Summary of water-level data for wells in the Gallatin Local Water Quality District water-level monitoring network, Montana 

(Continued)

Location number

01S04E29BCDD01

01S05E09DCCC01

01S05E12BCCC01

01S05E17CCDC01

01S05E25ADAD01

01S05E27CBDC01

01S05E35CAAB01

01S06E07CCBA01

01S06E08CBAA01

01S06E20BDAA01

01S06E28DABD01

01S06E32BADC01

01S07E17AACA01

01S07E17BDCB01

01S07E30BAAA01

02S04E01CCCD01

02S04E10ACCA01

02S04E13BADA01

02S04E13CCBC01

02S04E16BCCA01

02S04E16DADA01

02S04E35ABBB01

02S05E05ABBD01

02S05E11ADAB01

02S05E13BDCD01

02S05E14CDBA01

02S05E17BBAA01

02S05E23CCCB01

02S05E35DCDC01

02S06E12DCAA01

02S06E19BBBB01

02S06E20CABD01

02S06E21BBAA01

02S06E23ABCC01

02S06E24ACAB01

02S06E26DDBA01

02S06E33BDDC01

02S07E10DDAD01

Hydrogeologic 

unit

Tb

Qal

QTd

Qal

QTd

QTd

QTd

QTd

QTd

QTd

KGscu

QTd

K scu

TYsaq

TYsaq

Qal

Tb

Qal

Qal

Tb

Tb

Qal

QTd

QTd

QTd

QTd

QTd

QTd

QTd

TYsaq

QTd

QTd

Tb

Qal

K scu

QTd

QTd

KGscu

Period of 

Well depth record 

(ft) (calendar 

year)

-

141

112

42

150

115

67

100

200

110

620

157

50

107

118

40

119

40

11

148

177

31

125

75

185

113

39

80

156

39

-

300

145

42

342

70

159

65

1986-98

1992-98

1992-98

1992-98

1998

1992-98

1992-98

1998

1997-98

1991-98

1997-98

1997-98

1998

1998

1997-98

1997-98

1998

1997-98

1947-98

1992-98

1998

1992-98

1991-98

1988-98

1988-98

1989-98

1992-98

1998

1951-98

1997-98

1992-98

1991-98

1997-98

1997-98

1998

1991-98

1991-98

1997-98

Number of 

measurements

37

20

21

12

5

14

11

1

6

7

3

8

5

5

9

8

5

5

370

13

3

14

14

19

10

10

13

7

18

9

22

14

6

7

3

11

23

8

Water level (ft)

Highest

58.22

15.19

75.72

7.55

1.00

30.38

16.29

54.14

95.12

36.19

280.69

57.06

24.54

28.25

49.89

8.71

28.15

16.75

2.54

106.59

72.50

-3.69

.72

10.83

11.10

1.90

15.69

3.89

11.64

6.11

22.99

121.58

84.20

3.88

19.32

18.82

18.83

3.29

Date of 

highest

11-21-89

11-01-93

10-04-97

08-02-93

10-13-98

11-01-93

04-24-98

07-06-98

06-30-98

06-10-93

10-06-97

07-17-97

06-04-98

06-04-98

07-09-97

06-11-98

08-11-98

06-11-98

06-27-52

06-08-98

01-06-98

06-10-98

08-07-98

08-02-93

06-11-88

04-23-98

08-03-93

04-15-98

10-04-97

04-15-98

06-11-93

07-20-93

06-08-98

04-15-98

04-15-98

10-06-97

07-02-97

01-17-98

Lowest

104.06

30.33

103.99

25.57

2.31

48.50

21.56

54.14

130.31

39.39

325.77

60.76

43.47

31.33

57.47

23.35

45.29

22.10

10.40

124.55

80.52

8.72

2.83

22.85

14.17

5.22

20.32

6.96

43.99

11.40

25.74

182.58

87.02

9.02

22.10

26.98

35.43

6.90

Date of 

lowest

07-02-97

02-25-93

11-03-92

03-02-98

06-08-98

11-03-92

08-02-93

07-06-98

01-30-98

06-20-91

10-13-98

10-06-97

01-26-98

10-13-98

10-06-97

03-06-98

04-24-98

02-23-98

02-20-71

11-02-92

04-24-98

01-08-98

03-02-98

02-25-93

04-11-98

03-01-98

05-03-93

01-27-98

05-03-93

07-10-97

04-15-93

05-04-93

07-31-98

03-02-98

01-26-98

05-04-93

02-25-93

01-17-98

54 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
Table 2. Summary of water-level data for wells in the Gallatin Local Water Quality District water-level monitoring network, Montana 

(Continued)

Location number

02S07E12BBAD01

02S07E24CCAC01

02S07E24CDCB01

02S07E26CACD01

03S04E09ABBC01

03S04E11CBBA01

03S04E11DCCB01

03S04E23CCBD01

03S04E25DBBD01

03S04E32DADA01

03S04E34ABBB01

03S04E36BABB01

03S05E06DAAA01

03S05E07BCCC01

03S05E10CCCB01

03S05E11DAAC02

03S05E15DCCA01

03S05E21CCCC01

03S05E27BCBB01

03S06E01AACB01

03S06E05CBAA01

04S04E18ACAA01

04S04E28CBDA01

04S04E33DBBA01

04S04E33DBDA01

05S04E36DBDB01

05S05E30ACCC01

Hydrogeologic 

unit

K scu

TYsaq

TYsaq

TYsaq

Qal

Qal

Qal

Qal

Qal

KGscu

QTd

QTd

QTd

Qal

QTd

QTd

QTd

QTd

KGscu

KGscu

QTd

Qal

Qal

KGscu

Qal

Qal

Qal

Period of 

Well depth record 

(ft) (calendar 

year)

66

220

125

395

96

40

50

80

50

71

92

312

178

36

70

--

220

263

50

51

128

40

104

100

80

38

40

1997-98

1997-98

1997-98

1997-98

1992-98

1991-98

1997-98

1997-98

1991-98

1991-98

1992-98

1991-98

1998

1991-98

1991-98

1998

1991-98

1998

1998

1997-98

1992-98

1992-98

1997-98

1997-98

1997-98

1997-98

1997-98

Number of 

measurements

9

5

2

4

24

13

9

9

22

8

13

11

1

12

13

5

2

3

5

7

12

10

9

9

5

7

8

Water level (ft)

Highest

.50

60.29

49.54

51.38

23.46

5.45

27.69

35.69

13.80

50.21

40.75

229.41

157.37

2.02

27.80

78.82

199.34

178.99

6.55

19.01

77.22

19.97

22.61

49.84

52.63

8.56

8.00

Date of 

highest

04-17-98

07-07-97

07-07-97

07-07-97

06-10-98

08-03-93

07-22-97

10-15-98

07-07-98

05-03-93

10-07-97

10-07-97

06-03-98

06-10-98

08-12-98

08-12-98

05-13-98

10-19-98

06-10-98

04-15-98

10-06-97

10-14-98

06-08-98

06-08-98

06-08-98

06-08-98

07-29-97

Lowest

4.96

74.81

70.49

85.71

29.68

9.06

39.03

59.54

20.29

55.74

49.96

253.08

157.37

14.72

41.66

101.49

210.13

185.99

7.03

25.85

92.03

25.18

25.30

58.19

56.70

10.46

9.55

Date of 

lowest

12-13-97

12-13-97

10-13-98

12-13-97

02-23-98

10-07-97

04-24-98

02-23-98

11-02-92

11-02-92

08-03-93

11-02-92

06-03-98

02-23-98

06-22-91

01-17-98

06-22-91

04-15-98

01-27-98

03-02-98

05-09-93

04-13-98

11-24-98

04-26-98

02-23-98

11-24-97

10-07-97

TABLE 2 55
Table 3. Water-quality data for ground and surface water in the Gallatin Local Water-Quality District, Montana, 1998

[All sites are private wells unless otherwise indicated. Primary land use: DG, dryland grain; F, forest; IHG, irrigated hay and grain; IP, irrigated potatoes; R, rangeland; SH, subirriga

Qal, Quaternary alluvium; QTd, Quaternary and Tertiary undifferentiated deposits; Tb, Tertiary Bozeman Group; TYsaq, Tertiary through Proterozoic sedimentary bedrock (potential a

Cretaceous through Cambrian sedimentary bedrock (typically confining units); Am, Archean metamorphic rocks. Abbreviations: ft, feet below land surface; °C, degrees Celsius; (O.S/c

centimeter at 25°C; mg/L, milligrams per liter; permil, parts per thousand. Symbols: , no data; <, less than minimum reporting level ]

O

HydroPrimary 

Location number geologic 

land use 

unit

Depth of 

well Date 

(ft)

Depth to 

water 

(ft)

Specific 

conductance

(uS/cm)

pH, 

field 

(standard 

units)

Water Oxygen, Hardness, 

temperature, dissolved, dissolved 

field field (mg/L as 

(°C) (mg/L) CaC03)

Cal- 

cium, 

dissolved 

(mg/L 

as Ca) 

WELLS

01N03E07CDDA01 IHG Tb

01N03E10BDCD01 IHG Tb

01N03E23DBBA01 IP Tb

01N03E33AAAC01 IHG Tb

01N04E01DDBC01 DG Tb

01N04E25BBCC01 SH Qal

01N05E14ACDD01 DG QTd

01N05E34ADAD01 1 DG QTd

01N05E34CDBD01 1 DG Qal

01N05E35ADBA01 1 DG QTd

01N05E35DDBA01 1 DG QTd

06-03-98

47.5 05-27-98

50 05-27-98

1 14 06-03-98

157 05-28-98

45 05-27-98

109 05-28-98

47 05-12-98

06-23-98

08-26-98

11-18-98

90 05-13-98

06-24-98

80 05-12-98

05-12-982

06-23-98

06-23-982

08-26-98

08-26-982

11-18-98

11-18-982

78 05-12-98

06-24-98

08-27-98

11-18-98

232.87

18.76

17.47

~

124.18

8.59

94.19

2.85

1.20

3.05

-

-

-

18.15

~

13.92

~

14.29

-

15.05

-

44.02

42.41

41.55

399

475

503

428

424

406

412

304

285

290

291

344

331

450

-

424

453

431

-

432

-

322

312

307

313

7.5

7.4

7.3

7.5

7.3

7.4

7.4

7.8

7.7

7.5

7.7

7.9

7.7

7.7

~

7.7

7.8

7.5

~

7.6

-

7.7

7.8

7.5

7.6

21.0

10.0

11.0

10.5

12.0

10.0

9.5

9.5

9.0

9.5

9.0

9.0

9.0

11.0

-

11.0

~

11.0

-

10.5

9.0

. 8.5

9.0

8.5

4.4 120

7.0 190

5.8 220

7.9 170

5.2 200

6.0 200

9.8 220

9.5

9.6 150

10.1

10.1

10.5

10.0 170

9.6

..

8.7 210

9.9

..

10.1

-

11.2

11.0 160

11.2

11.8

35 

52 

56 

44._._ .

53 

56 

61 

~

42 

--

-

48 

..

55 

55 

_.

..

..

47 

'
Table 3. Water-quality data for ground and surface water in the Gallatin Local Water Quality District, Montana, 1998 (Continued)

Alkalinity, 

field 

(mg/L as 

CaCO3)

162

185

204

202

222

184

214

--

146

--

-

169

~

-

211

3 211

-

~

-

-

-

144

--

Sulfate, 

dissolved 

(mg/L as 

S04)

30

38

46

24

6.5

24

9.2

-

7.9

-

-

-

8.3

-

--

15

15

-

~

--

-

-

7.5

-

Chloride, 

dissolved 

(mg/L 

asCl)

5.6

6.6

8.7

1.5

2.3

2.3

1.0

.9

.7

--

-

1.1

1.0

3.0

2.9

2.8

2.8

-

--

--

-

.4

.5

-

Fluo- Broride, mide, 

dissolved dissolved 

(mg/L (mg/L as 

as F) Br)

0.8 0.05

.3 .06

.3 .10

.4 .03

.5 .05

.1 .03

<.l .02

..

<.l .01

--

..

<.l .02

..

..

.1 .03

.1 .03

-

-

~

..

<.l .01

Solids, Ammo- Phos- Deuterium/ Oxygen-18

Silica, Nitrite, Nitrite plus 

sum of nia, phorus, hydrogen oxygen-16 

dissolved dissolved nitrate, 

constituents, dissolved ortho, stable- stable- 

(mg/L as (mg/L as dissolved 

dissolved (mg/L as dissolved isotope ratio isotope rati

SiO2) N) (mg/L as N) 

2 (mg/L) * N) (mg/L as P) (permil) (permil) 

88

44

40

54

55

22

9.9

-

12

~

-

--

11

~

~

20

20

-

-

-

-

-

12

-

..

316 O.01

302 .01

324 <01

300 <01

284 <.01

245 .01

234 .01

<01

174 <.01

-

..

<.01

205 <.01

<01

<.01

251 <.01

265 <.01

-

--

-

<.01

184 <01

--

WELLS

1.4 <0.02 <0.01

.67 <.02 .01

1.7 .02 .03

1.9 <.02 <.01

.19 <.02 <.01

1.7 <02 .03

1.1 .03 <.01

1.6

1.5 .06 <.01 -137

1.6

1.5

4.6

4.4 .06 .01

3.5

3.5

3.2 .05 .03

3.3 .04 .03

3.5

3.5

3.1

3.1

3.7

3.7 .05 .02

3.7

4.0

-18.31 

-

..

--

--

-

-
Table 3. Water-quality data for ground and surface water in the Gallatin Local Water Quality District, Montana, 1998 (Continued)

Magnitude, Extent

, and Potential So

c

s

o *>

Z

89

n

9*

O

c 

o.

ta

 t

5°

~

n

O

 

ET

3*

r

o

£0

i

85

J?

O

c 

E.

0

S3.

o"

t/i

0

1

re

3

O

35^

HydroPrimary 

Location number geologic 

land use 

unit

01N05E36BADD01 1 DG

01N06E17CDCB01 DG

01N07E20ABBA01 F

01N07E29BDCD01 F

01S04E04ACAA01 1 SH

01S04E04ACAC01 1 SH

01S04E04ACCA02 1 SH

01S04E04ACDD02 1 SH

01S04E04ADDD01 SH

01S04E10DDDD01 SH

01S04E17DCDD01 IHG

01S04E26CDDD01 IHG

QTd

QTd

KGscu

KGscu

Qal

Qal

Qal

Qal

Qal

Qal

Tb

Qal

Depth of 

well Date 

(ft)

120 05-11-98 

06-23-98 

08-27-98

11-18-98

60 05-28-98

135 06-04-98

485 06-04-98

57 04-21-98

05-20:98

08-27-98

11-18-98

60 04-21-98

05-21-98

08-27-98

60 04-21-98

05-21-98

08-27-98

11-18-98

60 04-21-98

04-2 1-982

05-21-98

08-27-98

11-18-98

64 05-12-98

107 06-02-98

50 01-05-98

37 05-27-98

05-27-982

Depth to 

water 

(ft)

57.86

-

11.10

8.20

113.32

-

--

-

~

38.67

_

29.87

27.40

24.74

_

36.29

-

33.27

30.01

39.56

32.35

6.96

Specific 

conductance

(uS/cm)

pH, 

Water 

field 

temperature, 

(stanfield 

dard 0

units)

WELLS-continued

421 7.7 10.5 

392 7.7 10.5 

398 7.6 11.0

402

314

212

342

357

342

340

343

333

312

315

308

298

298

298

362

-

286

339

350

417

444

643

443

457

7.6

7.6

6.9

7.9

7.2

6.9

6.9

6.9

7.2

7.0

6.9

7.2

6.9

6.8

6.8

7.0

-

6.9

6.8

6.8

7.0

7.2

7.8

7.3

7.5

10.5

7.0

6.0

8.5

9.0

9.0

8.5

8.5

9.0

8.0

8.5

8.0

7.5

8.0

8.0

9.5

-

9.0

9.0

9.0

10.0

10.5

8.5

9.0

Oxygen, 

dissolved, 

field 

(mg/L)

9.5 

9.0 

9.4

9.8

9.2

8.4

4.4

7.4

6.9

9.1

8.7

2.8

5.3

7.1

6.6

6.3

8.5

7.6

7.6

-

8.2

8.8

8.6

7.3

8.5

9.9

7.6

Hardness, 

dissolved 

(mg/L as 

CaCO3)

190

-

160

97

77

-

170

~

-

160

_

-

150

-

-

140

-

210

220

290

210

210

Calcium, 

dissolved 

(mg/L

asCa)

53

-

45

28

27

-

44

-

-

41

..

--

39

-

--

-

38

-

56

63

62

61

61
Table 3. Water-quality data for ground and surface water in the Gallatin Local Water Quality District, Montana, 1998 (Continued)

Alkalinity, 

field 

(mg/L as 

CaCO3)

ChloSulfate, 

ride, 

dissolved 

dissolved 

(mg/L as 

(mg/L 

S04) V W 

4 as Cl)

Fluo- BroSilica, 

ride, mide, 

dissolved 

dissolved dissolved 

(mg/L as 

(mg/L (mg/L as

as F) Br) L

Solids, 

sum of 

constituents, 

dissolved 

(mg/L)

Ammo- PhosNitrite, Nitrite plus 

nia, phorus, 

dissolved nitrate, 

dissolved ortho, 

(mg/L as dissolved 

(mg/L as dissolved 

N) (mg/L as N) 

N) (mg/L as P)

Deuterium/ Oxygen-1

hydrogen oxygen-1

stable- stable- 

isotope ratio isotope rat

(permil) (permil) 

WELLS-continued

-

174

-

-

155

113

160

--

171

-

-

-

152

-

-

121

~

-

--

-

128

-

--

218

193

3 289

> 205

03

r

fa

-

12

-

-

9.5

3.3

6.2

-

29

-

-

-

29

-

~

34

~

-

~

-

21

-

-

30

25

44

25 

24

7.9

8.1

-

-

.6

.1

2.2

1.6

1.4

-

-

1.4

1.3

-

1.6

1.5

--

-

2.0

2.2

1.6

-

-

3.0

2.7

9.9

4.5 

4.8

..

<.l .07 20

-

..

<1 .02 13

.1 <.01 13

1.3 <01 16

.1 .02 20

~

..

.2 .02 19

..

.2 <01 17

-

-

:.

..

.1 <.01 18

-

..

.1 .02 21

.3 .02 23

.4 -- 41

.4 .04 22 

.4 .04 22

-

245

-

-

186

127

-

-

223

~

-

-

202

~

184

-

-

--

176

-

-

283

259

405

269

271

<.01 5.0

<.01 4.7 .05 .05

4.7

4.7

.01 1.7 <.02 <.01

<.01 .15 <.02 <.01

<.01 3.7 <.02 <.01

<.01 .96

<01 .91 .04 <.01

1.5

1.4

<01 .55

<01 .46 .05 .01

.59

<.01 .26

<.01 .28 .05 <01

.84

.78

<.01 1.3

<.01 1.3

<.01 .61 .05 <.01

1.8

2.1

<.01 3.4 .03 .02

<.01 .94 <.02 .02

<.01 2.8 <.02 .03

.01 1.5 <.02 .02 

.01 1.5 <.02 .02

-147 -18.76 

-

-

-142 -18.68 

-

..

-

-

-141 -18.61 

-

~

-140 -18.52 

208
Table 3. Water-quality data for ground and surface water in the Gallatin Local Water Quality District, Montana, 1998 (Continued)

Magnitude, Extent,

SS

3

Q.

0

re

3

E!

0

e

re

re

O

Z

I

re

5'

O

3

3 

Q.

ES

re

5"

re

O

ET

5'

r

0

f)

i»

re

Os

g

1re'

W5

o 

c

3"

re

re

3

2e

3

3

Location number

HydroPrimary 

geologic 

land use 

unit

Depth of 

well

(ft)

Date

Depth to 

water 

(ft)

Specific 

conductance

(uS/cm)

pH, 

field 

(standard 

units)

Water Oxygen, 

temperature, dissolved, 

field field 

(°C) (mg/L)

Hardness, 

dissolved 

(mg/L as 

CaCO3)

Calcium, 

dissolved 

(mg/L 

asCa)

WELLS-continued

01S05E13DDDA01

01S05E14ACDD01

01S05E21BCDD01 1

01S05E21CDDB01 1

01S05E27CBDC01

01S06E06ABCB01

01S06E17CCDD01

01S06E20BDAA02

01S06E32BADC01

01S07E27DBDC01

01S07E30BAAA01

02S04E01CCCD01

02S04E13BADA01

02S04E13BBDA01

02S04E14DADC02

02S04E16BCCA01

02S05E10AABB01

02S05E19BACC01

02S05E23CCCB01

02S05E31ADDA01

02S05E36CAAB01 1

02S05E36CCCD01 1

02S06E12DCAA01

DG

DG

IHG

IHG

IHG

R

DG

R

DG

F

F

IHG

IHG

IHG

IHG

IHG

IHG

IHG

IHG

IHG

IHG

R

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

QTd

TYsaq

TYsaq

Qal

Qal

Qal

Am

Tb

QTd

QTd

QTd

QTd

QTd

QTd

TYsaq

260

140

83

83

115

375

115

128

157

80

118

40

40

30

148

55

152

80

125

45

51.5

39

01-06-98

05-19-98

05-20-98

05-20-98

05-27-98

05-13-98

05-19-98

05-19-982

05-19-98

05-28-98

06-04-98

06-05-98

05-27-98

01-05-98

05-11-98

06-02-98

01-05-98

05-26-98

05-20-98

05-11-98

05-13-98

06-02-98

05-26-98

05-18-98

05-18-982

05-18-98

08-26-98

06-04-98

06-04-982

-

106.15

60.82

41.60

283.39

84.51

_

48.73

57.63

36.50

53.03

14.50

-

15.90

12.04

-

59.97

5.48

4.24

-

11.51

-

-

_

6.42

488

454

533

540

593

266

399

407

296

336

297

463

514

437

491

458

681

571

474

-

461

454

459

507

-

334

346

394

414

7.0

7.5

7.1

7.1

7.3

7.8

7.6

7.8

7r9

7.5

7.4

7.1

7.2

7.1

7.1

7.2

9.3

7.4

7.3

-

7.5

7.3

7.8

7.3

-

7.3

7.1

6.8

7.0

9.1

9.5

10.0

10.5

10.5

8.0

13.0

9.5

9.0

7.0

8.0

9.5

10.5

9.0

8.5

53.0

10.0

8.5

10.5

7.5

7.5

-

9.0

-

9.0

8.5

6.5

10.1

9.4

7.8

7.9

3.8

14.0

10.8

5.7

9.5

6.5

5.2

7.0

8.2

5.3

5.5

9.0

2.3

4.5

2.8

2.2

~

8.6

-

9.1

11.3

7.8

240

230

230

240

290

140

210

210

150

160

130

190

250

190

230

._

6

210

240

-

230

180

240

-

170

_

170

65

61

68

69

82

32

59

59

36

43

38

59

72

52

64

..

2.4

55

70

--

67

35

67

-

51

_

50

50
Table 3. Water-quality data for ground and surface water in the Gallatin Local Water Quality District, Montana, 1998 (Continued)

Alkalinity, 

Held 

(mg/Las 

CaCO3)

Sulfate, 

dissolved

(mg/Las 

S04)

Chloride, 

dissolved 

(mg/L 

asCl)

Fluoride, 

dissolved 

(mg/L 

asF)

Bromide, 

dissolved 

(mg/L as 

Br)

Silica, 

dissolved 

(mg/L as 

Si02)

Solids, 

sum of 

constituents, 

dissolved 

(mg/L)

Nitrite, Nitrite plus 

dissolved nitrate, 

(mg/L as dissolved 

N) (mg/L as N)

Ammonia, 

dissolved 

(mg/L as

N)

Phosphorus, 

ortho, 

dissolved 

(mg/L as P)

Deuterium/ 

hydrogen 

stableisotope ratio 

(permil)

Oxygen-

oxygen-1

stableisotope ra

(permil

WELLS-continued

TABLE

U)

3 207

203

228

253

222

150

202

3 204

158

160

138

202

255

3 207

265

217

3 88

176

265

260

252

240

226

212

161 

196

3204

12

11

18

23

50

8.0

10

10

3.6

16

20

45

17

19

29

130

54

8.4

37

5.6

~

25

8.0

-

5.2 

9.2

9.2

13

13

16

4.6

21

.44

1.3

1.3

1.3

2.1

.6

4.2

4.8

4.2

5.7

-

54

28

2.7

6.1

1.2

--

1.3

22

-

3.8 

2.7

2.9

<.l

.1

.2

.2

.1

.1

.1

.1

.3

.2

.1

.5

.1

.3

.2

-

11

.6

.1

<.l

<1

~

.8

.2

-

.2 

.1

.2

-

.09

.05

.06

.19

.01

.03

.03

.02

.02

.02

.02

.05

-

-

~

.19

.02

.07

.01

-

.03

.02

-

.02 

.02

.02

11

14

35

41

31

12

18

18

30

19

12

14

25

31

33

66

44

29

42

30

-

21

32

-

34 

16

16

284

266

334

348

362

163

240

240

191

199

176

285

311

275

333

456

352

304

-

293

-

280

308

-

217 

233

238

<01 7.1

<.01 4.4

<.01 4.4

<.01 3.1

.01 2.6

<01 .18

<.01 2.1

<.01 2.2

<.01 .90

<.01 .23

<.01 .33

<.01 .84

<.01 2.0

<.01 1.6

<.01 1.1

1.0

..

.01 1.2

<.01 1.7

<.01 2.4

<01 2.6

<.01 2.5

.01 .75

<.01 4.1

<.01 2.3 

2.8 

<.01 1.7

<.01 1.7

<.02

.05

.03

.03

.02

<.02

.05

.04

.02

.03

<.02

<.02

<.02

<.02

.04

-

<02

.04

.03

.03

<.02

<.02

.03

-

.05 

<.02

<.02

.02

<01

.04

.04

.02

<.01

.01

.01

.03

.01

<.01

<.01

.03

.06

.06

-

.06

.05

.07

.04

.04

.04

.12

-

.09

<.01

-

-147

-138

-139

~

-137

-140

~

~

-

~

/--

-

-141

-

~

-141

-143

-138

~

-

-

-137

-

-18.93

-18.19

-18.46

-

-18.14

-18.10

-

--.

-

-

-

-

~

-18.69

-

-

--

-18.46

-18.63

-18.46

-

~

~

-

-18.07
Table 3. Water-quality data for ground and surface water in the Gallatin Local Water Quality District, Montana, 1998 (Continued)

00

! Hydros Primary 

n Location number geologic 

" land use 

g1 unit

£

D3

a

2? 02S06E20CABD01 IHG

1 02S06E36BDBB01 F

E!

c/3 ' o

e

s

1 02S07E02ACDC01 R

|. 02S07E24CDCB01 R

| 03S04E09ABBC01 R

=[ 03S04E11BCAD01 IHG

O

0

M

o. 03S04E11DDBC01 IHG

| 03S04E23CABB01 IHG

» 03S04E34ABBB01 IHG

f 03S04E36ACAC01 R

£ 03S05E11DAAC02 F

| 03S05E15DCCA01 F

S*

n

EL

» 01S04E09BAAB01 4

0 01S05E26ACDD01 5 -

| 04S04E07DDDA01 6 -

O

5-

o'

00

o

e

rt

n

a 

Depth of Depth to 

well Date water 

(ft) (ft)

Specific 

conductance 

(uS/cm)

pH, 

Water Oxygen, 

field 

temperature, dissolved, 

(stanfield field 

dard 

(°C) (mg/L) 

units)

Hardness, 

dissolved 

(mg/L as 

CaC03)

Calcium, 

dissolved 

(mg/L 

asCa)

WELLS-continued

QTd

K scu

KGscu

TYsaq

Qal

Qal

Qal

Qal

QTd

QTd

QTd

QTd

300 06-05-98 143.87

75 01-06-98

10-19-98

10-19-98

111 06-03-98 16.46

125 06-03-98

96 05-26-98 24.87

80 05-12-98 14.55

06-02-98 13.84

65 05-13-98 36.17

100 05-26-98 60.49

92 05-26-98 44.49

197 05-19-98 135.82

05-18-98

220 05-13-98

06-02-98

-

683

692

741

366

697

406

397

405

426

434

369

643

215

222

218

-

6.8

6.9

6.8

7.1

8.1

7.1

7.3

7.3

7.5

7.2

7.1

7.5

6.5

7.2

7.2

9.5

6.0

7.5

7.5

6.5

7.0

8.0

10.0

9.5

9.0

8.5

8.0

7.5

7.0

7.0

7.0

10.8

4.8

2.5

2.7

5.7

-

5.2

6.1

7.1

12

8.5

8.5

8.0

8.8

10.2

9.3

~

340

~

160

100

190

190

~

210

220

160

280

96

91

-

94

-

48

22

62

56

-

63

73

47

80

24

27

OTHER SITES

-

-

05-12-98

01-05-98

01-06-98

188

617

322

8.4

7.0

7.4

7.2

10.5

0.0

..

-

11.6

86

180

160

24

47

41

FIELD BLANKS

-

__

-

-

-

03-31-98

05-12-98

05-26-98

06-04-98

06-24-98

1

2

2

2

2

-

5.3

5.2

-

5.5

15.0

-

-

-

7.5

-

-

-

.04

<.02

<.02

<02

.08

1 Also within suburban population areas, see figures 5 and 14.

2Replicate sample. Specific conductance, pH, and alkalinity (if shown) were measured in the laboratory.

Alkalinity measured in the laboratory.

4Gallatin River at Amsterdam Road, near Belgrade.

5Bozeman Wastewater Treatment Plant effluent prior to chlorination.

Gallatin River near Gallatin Gateway.
Table 3. Water-quality data for ground and surface water in the Gallatin Local Water Quality District, Montana, 1998 (Continued)

Alka- ChloSulfate, 

Unity, ride, 

dissolved 

field dissolved 

(mg/L as 

(mg/L as so (mg/L

CaCO3) 4 as Cl)

164

2 307

2307

-

186

363

184

195

192

252

236

168

309

87

107

88

282

2 149

2 116

1.7

2 1.9

2 1.8

2<1.0

2 1.7

H

co 

pi

10 6.9

20 19

22

12 1.9

41 .6

22 8.1

18 3.2

9.6 2.8

4.0 1.5

6.7 1.5

. 3.7 2.0

5.3 6.9

5.6 1.4

15 .6

20 53

53 1.2

<.l <.l

<.l <1

<1 <.l

<.l <.l

<1 <.l

Fluo- Broride, mide, 

dissolved dissolved 

(mg/L (mg/L as 

as F) Br)

.5 .07

.3

..

.04

.2 .02

.4 .04

.2 .05

.2 .04

..

.1 .03

.1 .02

.2 .03

.8 .04

.1 .04

.5 .02

.1 <.01

1.0

.3

<.l

<. 1 <.01

<.l <.01

<01

<. 1 <.01

Solids, 

Silica, 

sum of 

dissolved 

constituents, 

(mg/L as 

dissolved 

SiO2) 

(mg/L)

46

16

-

-

13

10

37

38

~

27

21

44

38

34

55

13

26

14

<.l

<1

<.l

.1

<.l

409

-

-

221

438

263 '

264

-

290

263

236

403

149

176

113

309

199

-

-

Ammo- Phos- Deuterium/ Oxygen-

Nitrite, Nitrite plus 

nia, phorus, hydrogen oxygen-

dissolved nitrate, 

dissolved ortho, stable- stable- 

(mg/L as dissolved 

(mg/L as dissolved isotope ratio isotope ra

N) (mg/L as N) 

N) (mg/L as P) (permil) (permil

WELLS-continued

<.01 2.0

<.01 8.0

8.8

10

<.01 1.4

<.01 <.05

<.01 .41

<.01 1.5

1.6

<.01 2.6

<.01 1.2

.01 1.1

.01 8.1

<.01 2.0

<.01 .71

.70

OTHER SITES

<.01 .09

<.01 .08

FIELD BLANKS

<.01 <.05

<.01 <.05

<01 <.05

<.01 <.05

<.01 <05

<.02 .03

<.02 .02

..

-

<.02 .01

.26 <.01

.03 .08

.02 .04 -141

..

.04 .03 -140

.05 .04

<.02 .07

.03 .04 -128

.04 .05 -135

.02 .09 -136

<.02 .02 -143

<.02 <.01

.03 <.01

<.02 <.01

<.02 <.01

<.02 <.01

.04 <.01

-

..

-18.45 

-18.38 

-16.21 

-17.79 

-17.48 

-18.74 
Table 4. Chlorofluorocarbon (CFC) data and estimated recharge dates for ground water in the Gallatin Local Water Quality 

District, Montana, 1998

[Estimated recharge dates are based on CFC concentrations and estimated recharge temperatures and altitudes (U.S. Geological Survey, 

unpublished data). Abbreviation: pg/kg, picograms per kilogram of solution; CFC-11, chlorofluorocarbon-11; CFC-12, chlorofluorocarbon-12; 

CFC-113, chlorofluorocarbon-113. Symbol: -, not determined]

Location number

01N05E34ADAD01

01N05E34CDBD01

01N05E35ADBA01

01N05E35DDBA01

01N05E36BADD01

01S04E04ACAA01

01S04E04ACAC01

01S04E04ACCA02

01S04E04ACDD02

01S04E04ADDD01

01S05E14ACDD01

01S05E21BCDD01

01S05E21CDDB01

Sampling date

06-23-98

06-24-98

06-23-98

06-24-98

06-23-98

05-20-98

05-21-98

05-21-98

05-21-98

05-12-98

05-19-98

05-20-98

05-20-98

CFC-1 1

825.1

822.7

828.5

1,236.8

1,239.3

1,253.4

119.7

119.5

118.1

734.2

737.3

729.4

39.0

39.3

39.8

712.6

718.0

716.1

666.5

666.3

675.6

692.2

694.9

698.9

618.4

616.6

614.8

629.4

630.9

626.2

273.2

274.6

268.1

2,144.1

2,208.1

2,559.5

555.0

554.5

559.1

Concentration (pg/kg)

CFC-12

29,764.5

1,045.1

1,371.8

568.2

565.3

570.3

52.9

52.9

51.5

681.8

677.3

651.4

26.9

28.3

26.5

390.7

383.2

370.4

572.1

571.9

602.3

522.1

511.7

498.2

334.3

332.4

311.9

349.0

354.2

335.6

126.9

137.3

127.4

287.3

286.5

276.7

260.3

262.4

266.0

CFC-113

13.8

13.1

14.4

33.2

32.6

32.9

0.0

3.4

4.2

59.0

59.5

59.1

0.0

2.8

2.6

102.6

110.1

104.6

97.0

96.6

96.8

109.7

102.9

111.1

101.9

106.0

89.6

101.2

99.5

95.3

21.3

19.9

10.7

53.5

62.0

56.4

63.4

Estimated recharge

date 

(year)

1970s

1980s

1960s

1980s

1960s

1990s

1990s

1990s

1990s

1990s

1970s

1980s

1980s

64 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98
Table 4. Chlorofluorocarbon (CFC) data and estimated recharge dates for ground water in the Gallatin Local Water Quality 

District, Montana, 1998 (Continued)

Location number

01S06E06ABCB01

01S06E17CCDD01

01S06E20BDAA02

02S04E13BBDA01

02S05E19BACC01

02S05E23CCCB01

02S05E36CAAB01

02S05E36CCCD01

03S04E11BCAD01

03S04E11DDBC01

03S04E36ACAC01

03S05E11DAAC02

03S05E15DCCA01

Sampling date

05-13-98

05-19-98

05-19-98

05-11-98

05-11-98

05-13-98

05-18-98

05-18-98

05-12-98

05-13-98

05-19-98

1

05-18-98

05-13-98

CFC-11

726.1

704.8

717.9

599.4

602.3

617.8

218.4

170.8

197.5

546.0

546.5

553.5

27.6

28.5

27.8

445.1

444.5

444.3

638.8

639.2

636.5

625.6

625.1

617.4

560.1

563.3

559.9

539.8

548.5

545.8

34.1

34.4

34.9

875.4

906.7

896.8

392.9

260.6

266.0

261.7

Concentration (pg/kg)

CFC-12

317.0

315.0

304.5

327.1

337.6

343.3

12.6

11.4

12.4

4,200.4

4,189.6

4,271.4

41.7

45.1

42.9

260.1

255.7 '

252.9

352.9

354.2

354.6

354.2

354.3

352.7

340.6

340.1

342.7

299.1

314.0

312.5

28.5

30.4

27.4

381.1

399.1

387.3

123.5

66.5

55.3

64.1

CFC-113

77.9

69.1

74.2

69.3

76.0

79.8

0.0

0.0

0.0

62.0

63.8

68.8

0.0

0.0

0.0

61.7

61.4

61.7

95.0

84.3

115.5

97.0

100.4

110.6

62.4

63.2

60.5

74.6

85.2

86.1

0.0

0.0

0.0

114.5

111.3

113.2

26.4

6.4

4.3

5.4

Estimated recharge

date 

(year)

1980s

1980s

1970s

1980s

1960s

1980s

1980s

1990s

1980s

1980s

1960s

1990s

1970s

TABLE 4 65
Table 5. Drinking-water standards and guidelines for public-water supply

[Abbreviations: mg/L, milligrams per liter. Symbol: , no standard or guideline concentration has been adopted]

Constituent

pH (standard pH units)

Sulfate (mg/L as S04)

Chloride (mg/L as Cl)

Fluoride (mg/L as F)

Dissolved solids (mg/L)

Nitrite (mg/L as N)

Nitrate (mg/L as N)

Montana 

Human Health

Standard1

'

-

-

4

-

1

10

Maximum 

Contaminant Level

(MCL)2

~

4500

-

4

~

1

10

Secondary 

Maximum Contaminant

Level 

(SMCL)2

3 6.5-8.5

250

250

2

500

--

--

! Montana Department of Environmental Quality (1995).

2National Primary Drinking-Water Regulations are established for contaminants which, if present in drinking water, may cause 

adverse human health effects. Either a Maximum Contaminant Level (MCL) or an action level with a treatment technique is 

specified by these regulations for regulated contaminants for public drinking-water supplies. MCLs are health-based and 

enforceable; proposed MCLs are nonenforceable. Secondary Drinking-Water Standards are established for contaminants 

that can adversely affect the taste, odor, or appearance of water and result in discontinuation of use of the water. These regulations specify Secondary Maximum Contaminant Levels (SMCL), which are esthetically based and nonenforceable (U.S. 

Environmental Protection Agency, 1996). 

Ideal range; not a maximum level (U.S. Environmental Protection Agency, 1996).

Proposed MCL.

66 Magnitude, Extent, and Potential Sources of Nitrate in Ground Water in the Gallatin Local Water Quality District, Southwestern Montana, 1997-98

 k U.S. GOVERNMENT PRINTING OFFICE: 2001 674-573 / 45005 Region No. 8
Kendy-MAGNITUDE, EXTENT, AND POTENTIAL SOURCES OF NITRATE IN GROUND WATER IN THE GALLATIN LOCAL WATER QUALITY DISTRICT, SOUTHWE