U.S. Department of the Interior

U.S. Geological Survey

Ground-Water-Quality Assessment of Selected Wells in the

Fraser River Watershed, Colorado, August 1998

INTRODUCTION

The Fraser River watershed is located in the southeastern

part of Grand County, Colorado. The Fraser River flows about

28 river miles from its headwaters along the Continental Divide

in the Arapaho National Forest through the towns of Winter Park,

Fraser, Tabernash, and Granby and into the Colorado River

(fig. 1). Grand County covers 1,869 square miles; the Fraser

River watershed comprises about 16 percent of the county (about

302 square miles).The annual precipitation in the watershed

ranges from 20 inches per year north and west of Fraser to more

than 40 inches per year in the higher peaks near the Continental

Divide. Land use/land cover in the watershed is 71 percent forested land; 14 percent agriculture and rangeland; 11 percent tundra, bare ground, or exposed rock; 2 percent urban; and 2 percent

other land-use classifications (fig. 1; Fegeas and others, 1983).

USGS WRIR 99–4243

January 2000

In cooperation with Grand County

 

1

2

3

4 5

6 7

8

9

10

11

12

13

14

16 15 17

18

19

20

Fraser

River

Basin

Denver

COLORADO

Arapaho

National

Forest

Tabernash

Fraser

Winter Park

106°00' 105°52'30"

105°45'

Tabernash

0

0

2

2

4

4

6

6

8 KILOMETERS

8 MILES

40

40

COLORADO R IVER

Granby

Divide

Conti nental

Fraser

River

40° 00'

39° 52'

30"

LAND USE

Urban

Other urban

Transitional areas

Agriculture

Forest

Rangeland

Wetland

Tundra, bare ground,

 or exposed rock

Lakes and reservoirs

Basin boundary

U.S. Highway 40

Arapaho National

 Forest boundary

Sampling site

EXPLANATION

Figure 1. Location of the study area, ground-water sampling sites, and land use/land cover. All land-use/land-cover classifications were determined

during the late 1970's (Fegeas and others, 1983) and refined with 1990 population data (Hitt, 1995).
The population of Grand County (estimated 1997 population of 9,879) has increased 138 percent between 1970 and 1997

(U.S. Bureau of the Census, 1970, 1997). In the upper part of the

watershed upgradient from Tabernash, there are three wastewater-treatment facilities and public water supplies that serve the

larger urban centers. Homes located outside the urban centers

rely on well water and individual septic disposal systems

(ISDS’s). With the increase in population, local agencies are

concerned about a high density of ISDS's and their potential

effects on the future water quality in the watershed. In addition,

the increased use (withdrawal) of ground water in the study

area also is a factor that may affect the water quality. The U.S.

Geological Survey (USGS), in cooperation with Grand County,

began a 5-year study in 1998 to evaluate the ground-water

quality in the Fraser River watershed. Twenty wells (18 domestic, 1 municipal, and 1 monitoring) were randomly selected in

the watershed upgradient from Tabernash to determine baseline

ground-water-quality conditions in this part of the watershed.

The majority of the sites were randomly selected by using a

stratified random selection computer program (Scott, 1990). The

results from this study and the continued monitoring of 10 wells

are intended to aid land-use planners in preserving water quality

of the Fraser River watershed for Grand County residents and

visitors.

DATA COLLECTION

The 20 wells used in this study were sampled in August

1998. In addition to the samples collected to determine groundwater quality, eight quality-assurance samples were collected

and analyzed to determine bias and variability in the data. The

20 wells were selected to represent water-quality characteristics associated with overlying land use/land cover, lithology,

and well depth. The major land-use classifications within a

radius of 1,640 feet (ft) from the wells are forested and urban

(primarily residential) lands. Wells in this study ranged in

depth from 25 to 295 ft and were completed in the alluvium of

Quaternary age, in the Troublesome Formation sedimentary

rocks of Tertiary age, and in fractured rocks of Precambrian

age. Water samples were analyzed for major ions, iron, manganese, nutrients, dissolved organic carbon (DOC), bacteria (total

coliform and Escherichia coli [E. coli]), methylene blue active

substances (MBAS), radon, chlorofluorocarbons (CFC’s), and

oxygen and hydrogen isotopes. The results from these samples

were compared to U.S. Environmental Protection Agency

(USEPA) drinking-water standards.

The USEPA drinking-water standards are defined as the

permissible level of a contaminant in water as delivered to

users of a public water system. The drinking-water standards

consist of a maximum contaminant level (MCL) that is health

related and legally enforceable, a secondary maximum contaminant level (SMCL) that applies to the esthetic qualities of

water and is a recommended level, and a proposed maximum

contaminant level (PMCL) that is not currently (2000) enforceable. A maximum contaminant level goal (MCLG) is a nonenforceable level of a drinking-water contaminant and is intended

for protection against adverse human health effects. A USEPA

health advisory (HA) used in this report is defined as the concentration of a contaminant in drinking water that is expected

to cause adverse, but noncarcinogenic, effects over a lifetime

of typical exposure. The typical exposure assumes that a

154-pound adult drinks about 0.5 gallon of such contaminated

water per day for 70 years (U.S. Environmental Protection

Agency, 1996).

The water-quality samples were analyzed at the USGS

National Water Quality Laboratory (NWQL) in Denver, Colorado. The year the ground water was recharged was determined

by measuring CFC’s (manmade compounds used mainly as

refrigerants) present in the water using the method of Busenberg and Plummer (1992). The source of the ground water was

evaluated by analyzing oxygen and hydrogen stable isotopes.

The CFC's and stable isotopes were analyzed at a USGS laboratory in Reston, Virginia. The field properties measured at

each site were water temperature, specific conductance, dissolved oxygen, pH, alkalinity, and turbidity. Sampling protocols and procedures used in this study are described in Koterba

Urban development and others (1995).

Ground-water quality in the Fraser River

watershed is generally suitable for domestic

and municipal uses.
QUALITY ASSURANCE/QUALITY CONTROL

Quality assurance of water-quality samples is needed to

assess bias and variability in the analytical results. The qualityassurance samples included four field blanks and four replicate

samples. Field blanks are obtained by using a blank solution that

is subjected to all aspects of sample collection, field processing,

preservation, transportation, and laboratory handling to test for

high bias in the data, which may result from the introduction of

contaminants into the water-quality sample. Source water for the

field blanks is documented by the NWQL to be essentially free

of constituents of concern; if constituents are present in the

source water, they are generally near the reporting limit. Results

from field blanks indicate that a high bias on the water-quality

data is unlikely. The few constituents detected were near the

reporting limit and were at concentrations of less than 10 percent

of the water-quality sample.

Sequential replicate samples were collected to assess the

variability in chemical constituents as a result of sampling and

analytical procedures. Relative percent differences were calculated for all replicate samples. Results indicate that differences

between the water-quality samples and the replicate samples

were less than 10 percent for approximately 90 percent of the

constituents analyzed. A relative percent difference of greater

than 10 percent occurred when the sample and the replicate concentrations were at or near the reporting limit. Results from the

quality-assurance samples indicated that the water-quality sample data show low variability and that a high bias is unlikely.

The major-ion data were quality assured by examining the

differences between the total-cation and total-anion charge balance. Differences between the charge balance for all samples

were less than 5 percent, which was acceptable for this study.

GEOLOGIC AND HYDROLOGIC

CHARACTERISTICS

The geology of the Fraser River watershed varies from

rocks of Precambrian age to unconsolidated alluvial deposits of

Quaternary age (fig. 2). The oldest rocks are of Precambrian age

and are exposed in the eastern and southern parts of the watershed. Fractured Precambrian rocks generally yield small quantities of water that are adequate only for domestic supplies.

Sedimentary rocks of Triassic, Jurassic, and Cretaceous age in

the northwestern part of the watershed generally yield little

water; however, well yields from these sedimentary rocks probably are sufficient for most domestic uses. The geologic units in

the watershed that yield the most water are Tertiary or younger

in age (Voegeli, 1965). These units include the Troublesome

Formation and alluvial deposits in the lower altitudes of the

watershed, which provide water for residential and municipal

use. The Troublesome Formation is predominantly siltstone with

some interbedded sandstones and conglomerates and is as much

as 1,000 ft thick. The alluvial deposits, which can be 200 ft

thick, consist of unconsolidated sands and gravels and older

glacial drift.

GROUND-WATER QUALITY

The quality of the ground water in the Fraser River watershed

is important because many individuals rely on ground water for

drinking water. The ground-water-quality conditions in the Fraser

River watershed can be characterized by assessing the dissolved

constituents and other physical properties (table 1).

Some measured properties that are significant in assessing

water-quality conditions and that also may indicate effects by

ISDS’s are specific conductance, dissolved oxygen, and pH.

 

Fraser

Unconsolidated alluvial

 deposits of Quaternary age

Igneous rocks of Tertiary age

 or Cretaceous age, or both

Troublesome Formation—Siltstone,

 sandstone and conglomerate

 of Tertiary age

Coalmont Formation—Sandstone,

 shale, coal beds, and conglomerate

 of Tertiary age

Sedimentary rocks of

 Cretaceous age

Sedimentary rocks of

 Cretaceous and Jurassic age

Sedimentary rocks of mainly

 Cretaceous, Jurassic, and

 Triassic age

Igneous and metamorphic

 rocks of Precambrian age

Basin boundary

U.S. Highway 40

Arapaho National Forest

 boundary

EXPLANATION

40

40

COLORADO

RIVER

Granby

106°00' 105°52'30"

105°45'

Arapaho

National

Forest

40°00"

39°52'30"

Tabernash

Winter Park

Fraser

River

C

Divide

onti nental

0

0

2

2

4

1 3 5 MILES 4

1 3 5 KILOMETERS

Figure 2. Generalized geology of the Fraser River watershed (Tweto, 1979;

Green, 1992).
Table 1. Summary of measured properties and analyzed constituents for water samples from 20 wells in the Fraser River

watershed, August 1998

[USEPA, U.S. Environmental Protection Agency; oC, degrees Celsius; μS/cm, microsiemens per centimeter at 25 degrees Celsius;

mg/L, milligrams per liter; μg/L, micrograms per liter; NTU, nephelometric turbidity units; col/100 mL, colonies per 100 mL; pCi/L,

picocuries per liter; MCL, maximum contaminant level; SMCL, secondary maximum contaminant level; PMCL, proposed maximum

contaminant level; MCLG, maximum contaminant level goal; HA, health-advisory level; <, less than; ---, no standard]

Properties, constituents, and reporting units Minimum Median Maximum

USEPA drinking-water

standards or health

advisoriesa

Field properties

Water temperature (oC) 6.0 7.8 14 ---

Specific conductance (μS/cm) 106 236 436 ---

Oxygen, dissolved (mg/L) 0.1 4.5 7.6 ---

pH, field (standard units) 6.1 7.4 8.1 6.5–8.5 (SMCL)

Alkalinity (mg/L as CaCO3) 39 109 206 ---

Turbidity (NTU) 0.06 0.42 3.17 5.0

Major ions

Bromide, dissolved (mg/L) <0.01 0.02 0.06 ---

Calcium, dissolved (mg/L) 14.2 33.7 71.1 ---

Chloride, dissolved (mg/L) 0.33 1.78 16.4 250 (SMCL)

Fluoride, dissolved (mg/L) <0.10 0.19 1.40 4.0 (MCL)

Magnesium, dissolved (mg/L) 1.26 2.55 5.84 ---

Potassium, dissolved (mg/L) 1.03 2.00 6.30 ---

Silica, dissolved (mg/L) 11.1 28.1 46.6 ---

Sodium, dissolved (mg/L) 4.02 7.07 19.1 ---

Sulfate, dissolved (mg/L) 1.62 3.14 10.9 250 (SMCL)

Dissolved solids (mg/L) 82 129 281 500 (SMCL)

Trace elements

Iron, dissolved (μg/L) <10 <10 244 300 (SMCL)

Manganese, dissolved (μg/L) <4 <4 436 50 (SMCL)

Nutrients

Ammonia, dissolved as N (mg/L) <0.002 <0.002 0.010 30 (HA)

Ammonia plus organic, dissolved as N (mg/L) <0.10 <0.10 0.13 ---

Nitrite, dissolved as N (mg/L) <0.001 <0.001 0.002 1.0 (MCL)

Nitrate plus nitrite, dissolved as N (mg/L) <0.005 0.256 4.678 10 (MCL)

Orthophosphate, dissolved as P (mg/L) 0.003 0.035 0.131 ---

Phosphorus, dissolved as P (mg/L) 0.001 0.036 0.126 ---

Other constituents

Carbon, organic, dissolved as C (mg/L) 0.2 0.6 2.3 ---

Coliform bacteria, total, m-ENDO agar (col/100 mL) <1.0 <1.0 2.0 0 (MCLG)

Methylene blue active substances (mg/L) <0.02 <0.02 0.03 0.5 (SMCL)

Radon-222, total (pCi/L) 365 867 6,378 300 (PMCL)

a U.S. Environmental Protection Agency (1996).
0

1.0

2.0

3.0

4.0

5.0

Forest Urban

NITRATE, IN MILLIGRAMS PER LITER

LAND USE

Detection

Median

Number of

 samples 

(6)

(14)

(6) 

Specific conductance ranged from 106 to 436 microsiemens per

centimeter at 25 degrees Celsius (μS/cm). Dissolved oxygen

ranged from 0.1 to 7.6 milligrams per liter (mg/L). Dissolvedoxygen concentrations of less than 1.0 mg/L can be considered

low for the Fraser River watershed (Apodaca and Bails, 1999).

Low dissolved oxygen in the ground water may be a result of the

presence of organic material in the water, which allows microorganisms to grow and consume oxygen. The pH values measured

at 19 of the 20 wells (6.1 to 8.1) were in the range of the USEPA

SMCL drinking-water standard of 6.5 to 8.5 for pH.

Major ions, which compose the bulk of dissolved constituents in ground water, generally occur naturally. Major ions in

ground water most commonly result from interactions between

the water and soil and rock. All major ions were less than the

USEPA drinking-water standards. On the basis of the major ions

present in the water, ground water in the Fraser River watershed is

predominantly a calcium bicarbonate type water.

Dissolved-solids concentrations for all 20 wells were less

than the USEPA SMCL of 500 mg/L in drinking water. Water

containing amounts of dissolved solids above the USEPA SMCL

is usually hard. High concentrations of dissolved constituents in

the ground water can result from natural sources or ISDS contamination.

A major ion that may be associated with ISDS's is chloride

(Canter and Knox, 1985). Chloride is present in all natural waters,

usually in relatively small amounts; however, chloride also can be

derived from human sources. Chloride is not effectively removed

by the septic systems and, therefore, remains in their effluent.

Chloride concentrations detected in the ground water of the Fraser

River watershed did not exceed the USEPA SMCL standard of

250 mg/L. The chloride concentrations detected cannot be related

to ISDS’s in the study area.

Manganese, which is a trace element, exceeded the USEPA

SMCL drinking-water standard of 50 micrograms per liter (μg/L)

at three wells near the Tabernash area. The presence of elevated

manganese concentrations in drinking water can cause a brown

discoloration of the water and can affect the taste of the water

(Hem, 1992).

Nitrogen and phosphorus are nutrients in ground water that

can occur naturally. However, elevated nutrient concentrations

may result from human activity, such as lawn fertilizer and animal and human waste. In areas containing ISDS’s, the infiltration

of septic system effluent can cause elevated nutrient levels in the

ground water. For the 20 wells sampled, nutrient concentrations

were less than USEPA drinking-water standards. However, nitrate

was detected at two wells at concentrations greater than 2.0 mg/L.

Nitrate concentrations greater than 2.0 mg/L may indicate that the

concentrations are affected by human activities (U.S. Geological

Survey, 1999). The concentrations of nitrate were generally

higher in the urban setting (median = 0.40 mg/L) than in the forested setting (median = 0.14 mg/L) (fig. 3). Both of these factors

suggest the effects of human activities.

Although no USEPA drinking-water standards or health

advisories apply to phosphorus, the amount of phosphorus in

ground water is important. Ground water that has elevated

phosphorus concentrations can discharge into surface water and

accelerate the process of eutrophication in rivers and lakes.

Eutrophication is the process by which water becomes enriched

with plant nutrients, most commonly phosphorus and nitrogen.

Concentrations greater than 0.1 mg/L were present at 10 wells for

orthophosphate.

Most of the DOC in ground water results from biological

processes. The source of the DOC may be organic matter in the

aquifer or may be related to human activities such as the use

of fertilizers and ISDS’s. Dissolved organic carbon was detected

at all wells and ranged in concentration from 0.2 to 2.3 mg/L

(table 1). The presence of DOC in water can affect the dissolvedoxygen concentration, which in turn can affect the nutrients and

trace elements present in the ground water.

Figure 3. Nitrate concentrations by land-use classifications.

Of the 20 wells sampled:

• water samples from 3 wells exceeded the

U.S. Environmental Protection Agency

secondary maximum contaminant level

drinking-water standard of 50 micrograms

per liter for manganese;

• nitrate concentrations were elevated in

2 wells;

• total coliform bacteria were detected in

2 wells;

• methylene blue active substances were

detected in 4 wells;

• all wells had radon concentrations greater

than the U.S. Environmental Protection

Agency proposed maximum contaminant

level drinking-water standard of 300 picocuries per liter.
Total coliform bacteria are used to assess the sanitary quality of the drinking water because they can be correlated with

water-borne diseases. Total coliform bacteria were detected at

two wells in this study area at concentrations of 1 and 2 colonies

per 100 milliliters (col/100 mL). The USEPA MCLG in drinking

water for bacteria is 0 col/100 mL (U.S. Environmental Protection Agency, 1996). Total coliform bacteria may occur naturally

in the soils or may be related to human or animal waste. The

bacteria detected in this study probably are related to the soils

because E. coli, which originates from warm-blooded animals,

was not detected.

Methylene blue active substances are natural or synthetic

anionic surfactants; the synthetic surfactants are found in many

types of laundry detergents as optical brighteners. Methylene

blue active substances are water soluble and may be transported

from septic system effluent into the ground water (Thurman and

others, 1986).The surfactants were detected at four wells at a

concentration greater than the reporting limit of 0.02 mg/L. The

USEPA SMCL for MBAS is 0.5 mg/L, and none of the wells

exceeded this concentration. The presence of detergents in drinking

water may cause an unpleasant taste and may create foaming.

Radon-222 is a natural decay product of uranium and occurs

in soils and rocks. Radon can enter a home from seepage of air

through dirt floors, cracks in concrete floors or walls, floor drains,

or from the use of water from wells. All of the wells sampled

exceeded the USEPA PMCL of 300 picocuries per liter (pCi/L)

(table 1), which is currently under review (U.S. Environmental

Protection Agency, 1996). The higher radon concentrations generally occurred in the samples from wells west of Fraser. Radon is a

concern because it has been identified as a human carcinogen.

Radon concentrations in ground water for the Fraser River watershed are comparable to concentrations from selected wells sampled

in other parts of the Upper Colorado River Basin, Colorado,

which ranged in concentration from 305 to 4,030 pCi/L

(L.E. Apodaca, U.S. Geological Survey, unpub. data, 1997).

Table 2. Well information, estimated ground-water recharge date, and stable-isotope data for the 20 wells sampled in the

Fraser River watershed, August 1998

[USGS, U.S. Geological Survey; ft, feet; F, forest; U, urban (primarily residential); CFC, chlorofluorocarbons; δ18O, oxygen

isotopes; δD, hydrogen isotopes; Fm, formation; N/A, not available; data in bold type indicated sites with continued monitoring]

Site number

(figure 1)

USGS station

identification

Altitude

(ft) Aquifer a

Well

depth

(ft)

Land

use b

CFC

estimated

recharge

date

δ18O

per mil

δD

per mil

1 395411105464500 8,920 Granite 185 F 1981 –18.3 –138

2 395658105485400 8,568 Troublesome Fm 110 U 1983 or

younger

–17.8 –135

3 395642105500700 8,685 Troublesome Fm 145 U 1968 –18.5 –141

4 395647105500500 8,680 Alluvium 100 U 1990’s –18.2 –138

5 395649105501500 8,680 Alluvium 120 U 1990’s –18.3 –142

6 395657105500300 8,640 Alluvium 120 U 1961 –18.5 –140

7 395657105495300 8,610 Alluvium 85 U 1980 –18.0 –137

8 395704105500700 8,660 Alluvium 91 U 1990’s –18.1 –139

9 395750105515800 8,665 Troublesome Fm 120 F 1979 –18.3 –139

10 395921105472300 8,531 Alluvium 75 F 1991 –17.7 –134

11 395942105502000 8,332 Alluvium 65 U 1969 or

younger

–17.8 –135

12 395925105503100 8,377 Alluvium 45 U 1981 –18.2 –138

13 395934105503600 8,345 Troublesome Fm N/A U 1968 –17.4 –132

14 395937105500500 8,342 Alluvium 25 U 1990’s –18.0 –138

15 395930105505500 8,348 Alluvium 25 U 1974 –17.9 –137

16 395929105510300 8,320 Alluvium 28 U 1976 –17.7 –134

17 395934105521700 8,410 Alluvium 200 F 1973 –18.6 –143

18 395928105533500 8,592 Troublesome Fm 295 F 1968 –18.6 –143

19 395907105540100 8,582 Granite 105 F 1955 –18.7 –143

20 400013105540600 8,670 Alluvium 80 U 1989 –18.3 –142

a

 Tweto (1979) and Green (1992).

b

 Fegeas and others (1983).
On average, ground-water recharge takes

18 to 38 years. The recharge age of the

ground water is an important factor when

devising land-management practices.

GROUND-WATER AGE AND SOURCE

Measurement of CFC's in the ground water has been

useful in dating ground water recharged within the last 50 years.

Chlorofluorocarbons are manmade organic compounds used as

refrigerants, aerosol propellants, cleaning agents, solvents, and

blowing agents used in the production of foam rubber and plastics. Concentrations of CFC’s in the atmosphere have steadily

increased from the 1940’s through the early 1990's (Busenberg

and Plummer, 1992). Ground water acquires CFC's through

recharge; on the basis of knowledge of the temporal variations in

the CFC concentrations in the atmosphere, the date of the

ground-water recharge can be estimated.

Ground-water ages in the Fraser River watershed ranged

from the mid-1950’s to 1990’s (table 2). Water samples that

were dated in the 1990’s were collected from the alluvial aquifers. Most of the ground water sampled ranged in age from

the late 1960’s to early 1980’s, indicating that the interval

from the time the water recharged the aquifer to the time it

was withdrawn from the aquifer was about 18 to 38 years. The

two wells that had nitrate concentrations greater than 2.0 mg/L

had water of 1990’s age (fig. 4).

These dates indicate that changes in the land use in

recharge areas may not affect the ground-water quality in the

Fraser River watershed for 20 to 40 years; correspondingly,

land-management practices may take 20–40 years to cause

changes in ground-water quality. Supplementing water-quality

data with the age of the ground water helps provide a better

understanding of the link between current land use and water

quality in the underlying aquifers.

Analyses of δ18O (oxygen isotopes) and δD (hydrogen

isotopes) can be useful in identifying the probable source of the

ground water. If the ground-water isotopic compositions plot

close to the local meteoric water line, then the source of the

ground water is likely from local precipitation (Drever, 1988).

If the data plot to the right of the meteoric water line, then the

precipitation may have undergone evaporation. Also, the precipitation may have infiltrated through the land surface and chemically interacted with the surrounding soils and sediment, as it

moved through the aquifer. Ground water in the Fraser River

watershed had δ18O values ranging from –17.4 to –18.7 per mil

and δD concentrations ranging from –132 to –143 per mil

(fig. 5). An alpine basin northeast of the Fraser River watershed

had δ18O values of the snowpack ranging from –25.9 to

–16.5 per mil and had an average δ18O value of the snowmelt of

–18.6 per mil (Mast and others, 1995). The comparable δ18O

values indicate that the Fraser River watershed ground water is

probably derived from snowmelt.

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

YEAR/DATE RECHARGE OCCURRED

NITRATE, IN MILLIGRAMS PER LITER

Detection

Figure 4. Nitrate concentrations as related to the age of the ground

water.

-150

-145

-140

-135

-130

-20 -19 -18 -17 -16

Meteoric Water Line δD=8δ18

O+10 

δD PER MIL

δ18O PER MIL

Figure 5. Hydrogen (deuterium) and oxygen (18O) isotopic

compositions of selected ground-water wells sampled in the

Fraser River watershed.

Recharge of the ground water is most

likely from snowmelt.
SUMMARY AND CONCLUSIONS

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

County, began a 5-year study in 1998 to evaluate the groundwater quality in the Fraser River watershed. Because of the

increase in population, the county is concerned about a high

density of ISDS's and their potential effects on the future water

quality in the watershed. In addition, the increased use (withdrawal) of ground water in the study area also may affect water

quality. In August 1998, 20 randomly selected wells in the

Fraser River watershed were sampled upgradient from Tabernash as part of the 5-year study. The results indicated that the

ground water is of suitable quality for a drinking-water resource.

The ground water in the Fraser River watershed is probably

derived from snowmelt. The presence of nitrate and methylene

blue active substances in modern waters may indicate that current (1998) land-use practices are affecting the water quality.

The age of most of the ground water sampled is between 18 to

38 years, indicating that present-day land use may not affect the

ground-water quality for many years. Therefore, the development and implementation of land-use planning strategies are

important for maintaining the ground-water quality for future

use.

REFERENCES CITED

Apodaca, L.E., and Bails, J.B., 1999, Fraser River watershed, Colorado

assessment of available water-quantity and water-quality data

through water year 1997: U.S. Geological Survey WaterResources Investigations Report 98–4255, 58 p.

Busenberg, Eurybiades, and Plummer, L.N., 1992, Use of chlorofluorocarbons (CCl3F and CCl2F2) as hydrologic tracers and age-dating

tools—The alluvium and terrace system of central Oklahoma:

Water Resources Research, v. 28, no. 9, p. 2257–2283.

Canter, L.W., and Knox, R.C., 1985, Septic effects on ground water

quality: Michigan, Lewis Publishing Inc., 336 p.

Drever, J.I., 1988, The geochemistry of natural waters, (2d ed.): Englewood Cliffs, N.J., Prentice Hall, 437 p.

Fegeas, R.G., Claire, R.W., Guptil, S.C., Anderson, K.E., and Hallam,

C.A., 1983, U.S. Geological Survey digital cartographic data

standards—Land use and land cover digital data: U.S. Geological

Survey Circular 895–E, 21 p.

Green, G.N., 1992, The digital geological map of Colorado in Arc/Info

format: U.S. Geological Survey [Revised April 12, 1995] OpenFile Report 92–507, scale 1:500,000.

Hem, J.D., 1992, Study and interpretation of the chemical characteristics of natural water: U.S. Geological Survey Water-Supply Paper

2254, 263 p.

Hitt, K.J., 1995, Refining 1970's land-use data with 1990 population data

to indicate new residential development: U.S. Geological Survey

Water-Resources Investigations Report 94–4250, 15 p.

Koterba, M.T., Wilde, F.D., and Lapham, W.W., 1995, Ground-water datacollection protocols and procedures for the National Water-Quality

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Acknowledgments—We thank the homeowners and local

agencies who allowed the USGS personnel access to their properties for the purpose of sampling their wells. We also thank Eurybiades Busenberg and L. Neil Plummer of the U.S. Geological

Survey for the chlorofluorocarbon analyses and interpretation of

the ground-water ages.

—Lori E. Apodaca, C. Michelle Smith, and Jeffrey B. Bails

U.S. Geological Survey, Water Resources Division

Denver Federal Center, Bldg. 53

P.O. Box 25046, MS 415

Denver, CO 80225–0046

e-mail: lapodaca@usgs.gov

 carlam@usgs.gov

 jbbails@usgs.gov

The effects of individual septic disposal

systems on the ground-water quality are not

definitive or substantial; but with current and

future urban growth of the watershed, ongoing

monitoring would be beneficial to evaluate

human effects.

Design: Loretta Ulibarri

Editing: Mary Kidd

Manuscript and Layout: Alene Brogan