U.S. Department of the Interior USGS Fact She

U.S. Geological Survey 

Foothills

Floodplain

Boise Terrace

Whitney Terrace

Sunrise Terrace

Gowen Terrace

Fivemile Creek

 surface

Amity Terrace

Tenmile Terrace

Wilder Terrace

Deer Flat Terrace

Basalt surface—undivided

EXPLANATION

Figure 1. Location of the lower Boise River Basin, northern Ada County, selected geologic features, and hydrologic cond

March and April 1996.

Line of equal water-level altitude—Interval

 100 feet. Datum is land surface

Line of equal water-level altitude—Interval

 25 feet. Datum is land surface

Generalized direction of ground-water movement

Geothermal well

Hydrologic Unit Code (HUC) 17050114 boundary

2400

0

0

5

5 

2400

2300

2200

2400

2400

2500

2400

2500

2400

2300

2500

2700

2700

2600

2600

2700

2700

3200

3400

3600

3500

3300

3100

2900

3000

2800

PAYETTE GEM

BOISE

CANYON

ADA

ELM

2600

Terrac

modifi

Othber

Lower Bois

River Basin

116° 15' 116° 30'

116° 00'

116° 00'

116° 15'

116° 30' 116° 45'

116° 45'

43° 45 43° 45' '

43° 30' 

43° 43° 15' 15'

117° 00'

117° 00'

Lucky

Peak

Lake

Boise

River

River

Lowell

Lake

Boise

INTRODUCTION

In October 1992, the U.S. Geological 

Survey (USGS), in cooperation with the 

Idaho Division of Environmental Quality, 

Boise Regional Office (IDEQ-BRO), began 

a comprehensive study of ground-water 

quality in the lower Boise River Basin. The 

study in northern Ada County has been completed, and this report presents selected 

results of investigations in that area. Results 

and discussion presented herein are based on 

information in publications listed under 

“References Cited” on the last page of this 

Fact Sheet.

DESCRIPTION OF THE AREA

Northern Ada County is located in 

southwestern Idaho (fig. 1). The area is in the 

lower Boise River Basin and comprises 

about 560 square miles. Regional slope of 

the valley floor generally is we

northwestward; the slope of th

floodplain is about 13 feet per m

receives about 12 inches of pre

annually.

Northern Ada County incl

populated rangeland and farmla

the city of Boise and some of t

densely populated and rapidly 

urban and suburban areas of Id

Ground-Water Quality in Northern Ada County, Lower Boi

River Basin, Idaho, 1985–96

Prepared in cooperation with Idaho Division of Environmental Quality
2

about 1985, rates of land-use change were 

highest on the floodplain and adjacent terraces. In recent years, urbanization has accelerated throughout the area. Changes in 

land and water uses that accompany development (such as irrigation methods or home, 

well, and septic-tank drainfield densities) 

have affected ground-water recharge and 

quality.

Occurrence, movement, and quality of 

ground water in northern Ada County are 

determined, in part, by geologic environment. Geologic features in the area include 

the foothills, floodplain, steplike terraces 

(ranging in age from the approximately 

10,000-year-old Boise Terrace to the 

2,000,000-year-old Tenmile Terrace), and 

faults at the base of the foothills and at depth 

in terraces. These geologic features are the 

result of a complex history of valley-floor 

subsidence, glacial episodes, and volcanism. 

Foothills are composed of granite, basalt, 

and consolidated sedimentary rocks. Floodplain and most terrace sediments have been 

weathered from nearby foothills and mountains. These sediments are composed primarily of varying thicknesses of soil overlying 

beds and lenses of clay, sand, and gravel. 

Although types of sediments are similar in 

all terraces, distribution of beds and lenses of 

sediments is heterogeneous and erratic within each terrace and probably discontinuous 

from one terrace to another. Basalt is exposed at land surface or interbedded at depth 

in older terrace sediments. Older regional 

sedimentary and volcanic rocks underlie 

floodplain and terrace sediments.

Ground water is the primary source of 

private and public drinking water. Large 

amounts of ground water also are used for 

irrigation, stock, commercial, industrial, and 

air-conditioning supplies. Ground water is 

present at varying depths in floodplain and 

terrace sediments. Layers of water-bearing 

zones are less than 30 feet to more than 

1,000 feet below land surface, and wells 

throughout the area are open to one or several water-bearing zones. Water-bearing 

zones within a local ground-water system 

(floodplain and terrace sediments—depth to 

water near land surface to several hundred 

feet below land surface) overlie a regional 

ground-water system. Geothermal water 

(temperature greater than 29 degrees Celsius,°C; 84 degrees Fahrenheit,°F) occurs 

along faults at the base of the foothills. The 

extent of local, regional, and geothermal systems currently has not been determined. 

Major sources of recharge to waterbearing zones within the first few hundred 

feet of land surface are seepage from the 

Boise River, streams, canals, and ditches, 

and underflow from adjacent areas. In some 

near-surface zones, water is unconfined 

(water table); there can be large changes in 

depth to water during the irrigation season; 

and there can be seasonal change in direction 

of ground-water movement. Ground water in 

most deeper zones of the local ground-water 

system is confined (artesian); there is some 

seasonal change in depth to water; and direction of water movement is relatively constant. Information on the regional system is 

sparse because few wells are completed in 

deepest water-bearing zones. Most of the 

deepest wells are used for public supply or 

irrigation, and in order to increase water production, these wells are open to multiple 

zones in local and regional systems.

Ground water in most zones generally 

moves northwestward. Contours of waterlevel altitude and general directions of 

ground-water movement are shown in figure 

1. Contours are based on static water-level 

measurements in 335 wells throughout the 

lower Boise River Basin during March and 

April 1996. Water-level altitude was calculated by subtracting depth to water (feet 

below land surface) from land

tude. Total well depths range f

to more than 1,000 feet below 

Ground-water movement gene

areas of recharge to areas of di

arrows showing the direction o

are drawn perpendicular to con

water-level altitude.

GROUND-WATER QUALI

CHARACTERISTICS

Water samples collected fr

representing all major water-b

throughout northern Ada Coun

lyzed from 1985 through Decem

summarized in this report. Wid

temperature and chemical con

occur naturally in northern A

ground water. Water tempera

from 9° to 79.5°C (about 48° t

about 80 percent of ground wat

to 16°C (55° to 61°F). More th

of ground water is warm, 16.5

(62° to 83°F), the result of inc

temperature with depth or, mo

ing of geothermal and nontherm

fault zones. At least 25 wells p

thermal water (fig. 1). 

Ground water in northern 

generally is characterized by p

calcium and bicarbonate, calci

fate, or sodium and bicarbonat

Nonthermal water (temperatur

29°C) generally is enriched in 

bicarbonate ions, but relative p

cations and anions vary in non

from predominantly calcium a

ate to calcium and sulfate ions

eralized water commonly is en

cium and sulfate ions. Geother

characteristically is enriched in 

bicarbonate ions, and concentr

ride are distinctively large. Wa

Sodium and bicarbonate

(Geothermal) Calcium (Ca)

Magnesium (Mg)

Sodium plus potassiu

Carbonate (CO3)

Nitrite plus nitrate a

 (NO2 + NO3 as N)

Bicarbonate (HCO3)

Fluoride (F)

Sulfate (SO4)

Chloride (Cl)

Figure 2. Proportions of major ions in nonthermal and geothermal ground water in northern Ada County. (Proportions 

on total milliequivalents per liter)

Calcium and sulfate

(Nonthermal)

Calcium and bicarbonate

(Nonthermal)

EXPLANATION
3

Figure 3. Wells in which one or more volatile organic compounds were de

general areas of known point-source contamination, northern Ada County.

Star

Eagle

Boise

Garden

Meridian

Kuna

Lucky

Peak

Lake

Boise

River Boise River

R 3 E

R 2 E

R 1 W R 1 E

R 4 

T

4

N

T

3

N

T

2

N

T

5

N

ADA COUNTY

116° 22' 30" 116° 15' 116° 07' 30" 116° 00

116° 30'

43° 3

43° 45'

General area of known 

 of volatile organic co

 (VOC) contaminatio

Well in which one or m

 organic compounds 

 See figure 1 for expl

 geologic features (co

Base from U.S. Geological Survey

digital data, 1:100,000, 1980

Albers Equal-Area projection

Standard parallels 43° 30', 47° 30'

and -114° 00', 41° 45'

No false easting or false northing

0

0 4

2 

2

EXPLANATION

R 3 E

R 2 E

R 1 W R 1 E

R 4 

T

4

N

T

3

N

T

2

N

T

5

N

City

produced by many wells completed in deep 

water-bearing zones and generally has a calcium and bicarbonate or calcium and sulfate 

composition. Small concentrations of fluoride indicate that water temperature in these 

wells probably is not the result of a mixing of 

nonthermal and geothermal water.

Radiochemical analyses of water for 

carbon-14, chlorofluorocarbon, tritium, and 

isotopes of carbon, hydrogen, oxygen, sulfur, chlorine, nitrogen, or helium can be used 

to delineate ground-water flowpaths, define 

sources of recharge and contamination, or 

characterize water from various water-bearing zones. A few analyses for carbon-14, tritium, and isotopes of carbon, hydrogen, and 

oxygen are available for ground water in 

northern Ada County. No carbon-14 analyses are available for nonthermal wells less 

than 500 feet total depth. Ages of water from 

four deeper nonthermal wells range from 

about 2,000 to 11,000 years before present, 

but these ages might represent a mixture of 

younger and older water from local and regional systems. Ages of water from five geothermal wells range from about 15,000 to 

28,000 years before present. Few isotope 

data currently are available for nonthermal 

water. Isotope data are available for water 

from most geothermal wells, however, and 

have been used to define at least two geothermal circulation systems along foothills faults 

in northern Ada County.

On the basis of U.S. Environmental 

Protection Agency (EPA) standards for public water supplies, ground water in northern 

Ada County is suitable for most public and 

private drinking-water uses. Water from 

some water-bearing zones in a few areas, 

however, contains contaminants—components that can limit the water's suitability for 

use or can represent degradation of water 

quality. Contaminants can be naturally 

occurring or can be the result of land- and 

water-use activities (table 1, last page of 

report).

Naturally Occurring Contaminants

The most common naturally occurring 

water-quality contaminant in northern Ada 

County is large concentrations of total dissolved solids (TDS), a measure of the total 

amount of minerals dissolved in the water. 

TDS can be calculated from concentrations 

of major ions or estimated from specific conductance measurements. Water containing 

TDS concentrations of less than 500 mg/L 

(milligrams per liter, equivalent to parts per 

million) is preferred for home use and many 

industrial processes. Water containing TDS 

concentrations of more than 500 mg/L might 

require treatment for taste, color, or hardness, or might contain one or more ions of 

specific concern.

In northern Ada County, TDS concentrations in water from about 10 percent of 

wells exceeds the EPA drinking-water standard of 500 mg/L. These wells are distributed throughout the area, and highly mineralized water generally is from wells less 

than 400 feet total depth. Water hardness and 

large concentrations of dissolved sulfate, fluoride, iron, or manganese are the most common problems in mineralized water. Hydrogen sulfide odor ('rotten egg' or 'swampy' 

smell) is present in water from some wells, 

an esthetically objectionable trait for some 

domestic water uses.

Radon is a naturally occurring, odorless, tasteless, inert gas formed by the natural 

radioactive decay of uranium, present to 

some extent in nearly all rocks and soil. 

Household activities that heat, aerate, or 

expose ground water to air release dissolved 

radon from the water and increase the radon 

concentration in indoor air. To keep radon 

concentrations in indoor air to a minimum, 

the EPA has proposed that radon concentrations in water not exceed 300 picocuries per 

liter (pCi/L). This proposed lim

under review, and other sugges

limits are 1,000 pCi/L or a ran

5,000 pCi/L.

In northern Ada County, r

trations in water from more th

of wells exceed 300 pCi/L, an

tions from about 25 percent of 

1,000 pCi/L. Radon concentra

ground-water supplies are dete

mineral content of water-beari

soil and by well location and c

For most ranges of concentratio

tion has been observed betwee

centrations and physical prope

(temperature, specific conduct

alkalinity, or pH), major ion co

or well depth. However, all wa

that contain concentrations e

1,800 pCi/L (26 samples from 

from wells less than 125 feet de

temperatures less than 16.5°C

Contaminants Related to 

Water Uses 

Potential pathways of con

movement to water-bearing zo

seepage, leakage, or dumping 
4

Figure 4. Wells in which nitrate as nitrogen concentrations were greater than or equal to

5.5 milligrams per liter, and wells in which one or more pesticides were detected,

northern Ada County.

Star

Eagle

Boise

Garden City

Meridian

Kuna

Lucky

Peak

Lake

Boise

River Boise River

R 3 E

R 2 E

R 1 W R 1 E

R 4 E

T

4

N

T

3

N

T

2

N

T

5

N

ADA COUNTY

116° 22' 30" 116° 15' 116° 07' 30" 116° 00'

116° 30'

43° 30'

43° 37' 30"

43° 45'

Well in which nitrate as nitrogen

 concentration was 5.5 to 9.9

 milligrams per liter

Well in which nitrate as nitrogen

 concentration was equal to or

 greater than 10 milligrams

 per liter

Well in which one or more

 pesticides were detected

 See figure 1 for explanation

 of geologic features

 (colored areas)

0 EXPLANATION

0 4

4

6 KILOMETERS

2 6 MILES

2

nants at or near land surface; downward 

flushing of contaminants by infiltration of 

precipitation, floodwater, or applied irrigation water; flushing of contaminants from 

soil and unsaturated rocks by seasonal variations in ground-water levels; leakage around 

or into well casings or dumping of contaminants into wells; backflushing contaminants 

to wells through water-supply systems; and 

transport from upgradient sources. Contamination from land and water uses can be localized (point source) or widespread (nonpoint 

source).

Point-source contamination in northern 

Ada County is mainly the result of leakage, 

spillage, or dumping of chemicals at land 

surface; leakage from underground storage 

tanks; leakage and infiltration of chemicals 

at dump sites or landfills; and dumping of 

chemicals around or into wells. In most areas 

where contaminated soil or unsaturated 

rocks have been identified, contaminated 

materials were removed before ground water 

was affected. In some areas, ground-water 

contamination from point sources has been 

identified (fig. 3), and these point-source 

problems are under investigation by local, 

State, or Federal regulatory agencies.

Two groups of nonpoint-source contaminants are pesticides and volatile organic 

compounds (VOCs). Because laboratory 

analyses for pesticides and VOCs are relatively expensive, nonquantitative methods 

for determining the presence or absence of 

these compounds were used as preliminary 

screening tools. When preliminary screening 

indicated that compounds were present, 

duplicate samples were sent for laboratory 

confirmation of contamination. Quality 

assurance samples were sent for laboratory 

analyses without preliminary screening.

Water samples from 148 wells were 

screened for pesticides, and pesticide compounds were detected in water from 45 wells 

(fig. 4). In general, very small concentrations 

of pesticide compounds were detected, and 

the most commonly detected compounds 

were triazine herbicides. Distribution of pesticide detections is similar to that of elevated 

nitrate concentrations. Land-use sources and 

pathways of contaminant movement probably are similar for both groups of compounds.

Water samples from 847 wells were 

screened for presence of VOCs, and VOCs 

were detected in water from 96 wells (fig. 3). 

Concentrations of VOCs generally were very 

small except in areas affected 

source contamination. The mo

detected compounds were tetr

ene (PERC) and trichloroethyl

components of many cleaning 

in businesses and homes. Mos

detected in the floodplain in th

Garden City areas and from B

ian in south Whitney Terrace a

point-source VOC contaminati

is the result of long-term use o

products at many locations rat

age or leakage of chemicals fro

tions. History of suburban and 

development, densities of sept

field systems, and length of tim

version from septic tanks to mu

systems probably are importan

distributions of small concentra

in floodplain and terrace areas

Another indicator of wate

radation resulting from land an

is change in nitrate concentratio

reported in milligrams per liter a

During 1985–96, the median c

(50th percentile) of nitrate in g

from all areas of Idaho was 1.5 

northern Ada County, about 63 

concentrations exceeded 1.5 m

median concentration was 2.2 

Concentrations of nitrate in sa

about 10 percent of the wells w

than or equal to 5.5 mg/L(N) (fi

alous concentrations of nitrate 

from many wells completed w

three hundred feet of land surfa

active exchange of water from 

to water-bearing zones. Many 

taining elevated nitrate concen

from wells outside city bounda

concentrations in these wells po

result of large numbers and de

homes with septic-tank drainfi

and primary land uses related t

practices.

Few data currently are av

assess seasonal or long-term tre

concentrations. Boxplots (fig. 

tistical summary of nitrate dat

grouped by major geologic fea

thermal systems. Each boxplo

the variability of nitrate in gro

from a broad variety of hydrog

ronments and historical water-

ences. Smallest median concen

from ground water in foothills

and floodplain areas. Greatest 

centrations are from ground w

ney Terraces north and south o

River. Median concentrations 

water in all terraces south of th
5

25

20

15

10

5

0

CONCENTRATION OF NITRATE

AS NITROGEN, IN

MILLIGRAMS PER LITER

99th percentile

75th percentile

Median

25th percentile

1st percentile

Concentrations in

 upper 1% of data

37 milligrams

36 milligrams

Foothills

27 wells

Geothermal

17 wells

Whitney Terrace,

north of river

62 wells

Boise Terrace,

north of river

116 wells

Floodplain

120 wells

Boise Terrace,

south of river

20 wells

Whitney Terrace,

south of river

293 wells

Sunrise Terrace 81 wells

Gowen Terrace 47 wells

Fivemile Creek surface

19 wells

Amity Terrace

24 wells

Basalt surface

undivid

34 

Figure 5. Nitrate as nitrogen data for wells grouped by major geologic feature and geothermal system, northern Ada Cou

See figure 1 for

 explanation of

 geologic features

 (colored areas)

ally are larger than from ground water in terraces north of the river.

When nitrate data were grouped by 

selected geologic feature and generalized 

direction of ground-water movement (fig. 6), 

nitrate concentrations decrease from east to 

west and down valley in ground water in the 

Boise Terrace north of the Boise River (north 

Boise Terrace) and floodplain. In contrast, 

ranges and median concentrations increase 

in ground water in the south Whitney Terrace, confirming trends indicated in figure 4. 

Distribution of nitrate concentrations shown 

in figures 4, 5, and 6 reflects effects of a 

long-term history of changing land uses and 

development.

ADDITIONAL INFORMATION 

NEEDED 

Effects of several hydrogeologic and 

environmental factors on ground-water quality are not well understood at this time. For 

example, little information is available on 

hydrogeologic relations between surface 

water and ground water; near-surface waterbearing zones and deeper zones in the local 

ground-water system; local and regional 

ground-water systems; or geothermal systems and adjacent or overlying nonthermal 

water. Areal and vertical extent of local and 

regional systems currently is not defined. 

Few data currently are available on seasonal 

variation in ground-water movement in 

water-bearing zones or ground-water systems. Few chemical analyses a

for water from wells complete

water-bearing zones. Documen

torical land use and developme

progressive changes in uses an

ment, is fragmentary and spars

hensive studies of hydrogeolog

ronmental factors are needed to 

stand historical and current gro

quality and to estimate future e

development on water quality. 

currently are available on gene

water chemistry in the area, bu

cal analyses of water from disc

bearing zones could help defin

ground-water systems, sources 

and flowpaths.

20

15

10

5

0

CONCENTRATION OF NITRATE

AS NITROGEN, IN

MILLIGRAMS PER LITER

3N-2E

28 wells

4N-2E

46 wells

4N-1E

27 wells

4N-1W

15 wells

3N-2E

79 wells

4N-1E

15 wells

4N-1W

26 wells

3N-2E

86 wells

4N-1E

63 wells

4N-1W

29 well

Figure 6. Nitrate as nitrogen data for wells grouped by townships within selected geologic features, northern Ada County

(N, township north; E, range east; W, range west)

BOISE TERRACE,

NORTH OF BOISE RIVER

WHITNEY TERRA

SOUTH OF BOISE R

FLOODPLAIN

Generalized direction of

ground-water movement
6

ACKNOWLEDGMENTS

Special thanks are extended to the City 

of Boise for providing information and assistance with segments of the ground-water 

study in northern Ada County and financial 

support for this report.

—D.J. Parliman and J.M. Spinazola

REFERENCES CITED

Boyle, Linda, 1995, Determination of nature 

and extent of ground water contamination 

in Boise City and Boise Urban Planning 

areas, Ada County, Idaho: Boise, Idaho 

Department of Health and Welfare, Division of Environmental Quality, Water 

Quality Status Report no. 114, 24 p., 4 

apps.

———1996, Ground water study of the lower 

Boise River Valley, Ada and Canyon 

Counties, Idaho: Boise, Idaho Department of Health and Welfare, Division of 

Environmental Quality, Water Quality 

Status Report no. 118, 37 p., 5 apps.

———1997, Ground water investigation of 

nitrate and pesticides in northwest Ada 

County, Idaho: Idaho Division of Environmental Quality, Ground Water Quality 

Technical Report no. 10, 21 p., 3 apps.

Cecil, L.D., Parliman, D.J., Edwards, D.D., and 

Young, H.W., 1994, Concentrations of 

dissolved radon-222 in water from 

selected wells and springs in Idaho, 

1989–91: U.S. Geological Survey, OpenFile Report 94–66, 40 p.

Kjelstrom, L.C., 1995, Data for and adjusted 

regional regression models of volume and 

quality of urban stormwater runoff in 

Boise and Garden City, Idaho, 1993–94: 

U.S. Geological Survey Water-Resources 

Investigations Report 95–4228, 36 p.

Mariner, R.H., Young, H.W., Parliman, D.J., 

and Evans, W.C., 1989, Geochemistry of 

thermal water from selected wells, Boise, 

Idaho: Geothermal Resources Council 

Transactions, v. 13, p. 173–178.

Neely, K.W., and Crockett, J.K., 1998, Ground 

water quality characterization and initial 

trend analyses for the Treasure Valley 

shallow and deep hydrogeologic subareas: Boise, Idaho Department of Water 

Resources, Water Information Bulletin 

no. 50, Part 3, 76 p., 5 apps.

Newton, G.D., 1991, Geohydrology of the 

regional aquifer system, western Snake 

River Plain, southwestern Idaho: U.S. 

Geological Survey Professional Paper 

1408–G, 52 p., 1 pl.

Othberg, K.L., 1994, Geology and geomorphology of the Boise Valley and adjoining areas, western Snake River Plain, 

Idaho: Moscow, Idaho Geological Survey 

Bulletin 29, 54 p.

Othberg, K.L., and Stanford, L.R., 1992, Geologic map of the Boise Valley and adjoining area, western Snake River Plain, 

Idaho: Moscow, Idaho Geological Survey 

Geologic Map Series, 1 sheet, scale 

1:100,000.

Parliman, D.J., 1983, Compilation of groundwater quality data for selected wells in 

Elmore, Owyhee, Ada, and Canyon 

Counties, Idaho, 1945 through 1982: U.S. 

Geological Survey Open-F

83–39, 152 p.

———1996, Radon in ground w

1989–95: U.S. Geological 

Sheet FS–143–96, 2 p.

Parliman, D.J., Boyle, Linda, an

Sabrina, 1996, Selected we

water chemistry data for th

Valley, southwestern Idaho

U.S. Geological Survey O

Report 96–246, 199 p.

Parliman, D.J., and Young, H.W

pilation of selected data fo

water wells and springs in 

through 1991: U.S. Geolog

Open-File Report 92–175

U.S. Environmental Protection A

Drinking Water Regulation

Advisories: U.S Environm

tion Agency, Office of Wat

96–002, 18 p. 

Young, H.W., Parliman, D.J., an

R.H., 1988, Chemical and 

data for selected thermal-w

nonthermal springs in the 

southwestern Idaho: U.S. G

Survey Open-File Report 8

For additional information, contac

D.J. Parliman

U.S. Geological Survey

Water Resources Division

230 Collins Road

Boise, ID 83702-4520

(208) 387-1326

toluene

1,2,3-trimethylbenzene

1,2,4-trimethylbenzene

(pseudocumene)

1,3,5-trimethylbenzene

(mesitylene)

benzene

ethylbenzene

xylene

dichlorobromomethane

chlorodibromomethane

bromoform

chloroform

trichlorofluoromethane

dichlorodifluoromethane

PERC (tetrachloroethylene, 

PERK, PCE, perchloroethylene)

TCE (trichloroethylene)

1,1,1-TCA (1,1,1-trichloroethane)

1,1,2-TCA (1,1,2-trichloroethane)

1,1-DCA (1,1-dichloroethane)

1,2-DCA (1,2-dichloroethane)

1,1-DCE (1,1-dichloroethylene)

1,2-DCE (1,2 [cis- and trans-]

dichloroethene)

1,2-DCB (1,2-dichlorobenzene)

1,3-DCB (1,3-dichlorobenzen

1,4-DCB (1,4-dichlorobenzen

1,2-DCP (1,2-dichloropropan

1,2,3-TCP (1,2,3-trichloropro

MTBE (methyl tert-butyl eth

vinyl chloride

carbon tetrachloride

methylene chloride 

(dichloromethane)

carbon disulfide

ethyl acetate

naphthalene

phenanthrene

Table 1. Contaminants1 in northern Ada County ground water

Naturally Occurring

pH, hardness, sulfate, fluoride, total dissolved solids, iron, manganese, gross alpha and beta radioactivity, radon

Related to Land and Water Uses

Nutrients (nitrogen and phosphorus compounds) 

Total dissolved solids

Bacteria (total coliform, fecal coliform, fecal streptococci, and additional “opportunistic” noncoliform bacteria)

Pesticides

Herbicides (primarily triazine compounds but including dacthal, dicamba [Banvel], diuron, and metolachlor)

Insecticides (including chlorpyrifos and p,p’DDE)

Organic compounds, including:

1

 Water-quality component(s) that can limit the water’s suitability for use or can represent degradation of water quality.