HIGHLIGHTS

✔ The stable summer low-flow period is a time of good water quality in the watershed—dissolved-oxygen concentrations are high, and constituent

concentrations are low.

✔ Nine of 17 trace elements were detected. Concentrations were related to weathering of crystalline and sedimentary rocks rather than to urban or

recreational land uses.

✔ Although four U.S. Environmental Protection Agency (USEPA) trace-element priority pollutants were detected in stream samples, they were

present only in low concentrations.

✔ Nutrient concentrations did not exceed stream standards, but were somewhat elevated downstream through the Town of Vail.

 Gore Creek, which flows through Vail, Colorado,

originates in pristine alpine headwaters and is

designated a gold-medal trout fishery. The creek

drains an area of about 102 square miles and is a

tributary to the Eagle River. Gore Creek at the mouth

near Minturn (site 13 in fig. 1) is one of the 14 sites

in the UCOL network. This site was selected to

evaluate water quality resulting from urban development and recreational land use.

 The Gore Creek watershed has undergone rapid

land-use changes since the 1960’s as the Vail area

shifted from traditional mountain ranchlands to a

four-season resort community. Residential, recreational, commercial, and transportation development

continues near Gore Creek and its tributaries to

support the increasing permanent and tourist

population of the area. Interstate 70 runs through

the watershed from Vail Pass near site 14, along the

eastern side of Black Gore Creek, and along the

northern side of the main stem of Gore Creek to the

mouth of the watershed (fig. 1). A major local

concern is how increasing urbanization/recreation

affects the water quality, gold-medal trout fishery,

and aesthetic values of Gore Creek. An evaluation of

the spatial characteristics of water quality in the

watershed upstream from site 13 at the mouth of

Gore Creek (fig. 1) can provide local water and land

managers with information necessary to establish

water policy and make land-use planning decisions to

maintain or improve water quality. Historical data

collected at the mouth of Gore Creek provide

National Water-Quality Assessment U.S. Department of the Interior - U.S. Geological Survey

Upper Colorado River Basin NAWQA

 

FACTSHEET

LOW-FLOW WATER-QUALITY CHARACTERIZATION OF THE GORE CREEK

WATERSHED, UPPER COLORADO RIVER BASIN, COLORADO, AUGUST 1996

—Kirby H. Wynn and Norman E. Spahr

information about water quality

resulting from land use, but a

synoptic sampling is needed to

determine the distribution and

sources of water-quality constituents at one point in time.

 In August 1996, a low-flow

synoptic sampling for analyses of

water-quality properties and

constituents at sites in the Gore

Creek watershed was done by the

U.S. Geological Survey, in

cooperation with the Town of

Vail, Eagle River Water and

Sanitation District, Upper Eagle

River Water Authority, and

Northwest Colorado Council of

Governments, to evaluate the

water quality of Gore Creek.

 The August low-flow period can be important

from water-quality and stream ecology perspectives.

There is less water available to dilute any contaminants entering the streams, and stream temperatures

are highest during August. Physical habitat for

aquatic plants and animals is smaller than during

most other times of the year. To address these more

extreme water-quality and ecological conditions, the

synoptic sampling was conducted during the summer

low-flow period.

 Specific objectives of this sampling included:

1. Establish a current data set representing the

spatial characteristics of low-flow waterquality conditions in the Gore Creek

watershed, and

2. Develop some understanding of land-use and

 water-quality relations in the watershed.

 This fact sheet presents hydrologic background

information and an analysis of general water-quality

properties and constituents, trace elements, and

nutrients collected in water samples during low-flow

synoptic sampling of the Gore Creek watershed.

 The U.S. Geological Survey also is conducting a

study of the algae and macroinvertebrate communities and physical habitat of streams in the Gore

Creek watershed during low flow. This study is

designed to provide information about land-use and

stream ecology relations in the watershed.

INTRODUCTION

 The Upper Colorado River Basin (UCOL) is one

of 59 National Water-Quality Assessment (NAWQA)

study units designed to assess the status and trends of

the Nation’s water quality (Leahy and others, 1990).

The UCOL study unit began operation in 1994, and

surface-water-quality data collection at a network of

14 sites began in October 1995 (Apodaca and

others, 1996; Spahr and others, 1996).

Upper Colorado

River Basin

Gore Creek

Watershed

Photograph by Kirby H. Wynn
DATA COLLECTION

 Water-quality samples were collected from August 19 through August

23, 1996, at 24 sites (fig. 1). The sites included 4 on Black Gore Creek, 13 on

Gore Creek, and 7 at the mouths of tributaries. Sites 1 through 13 are on the

main stem of Gore Creek and were chosen to represent any effects of urban land

use on water quality as water flows from the headwaters through the Town of

Vail. Sites 5 and 7 bracket the golf course. The wastewater-treatment-plant outfall

is located between sites 8 and 9, upstream from the confluence of Red Sandstone

and Gore Creeks. Sites 16 and 1 (Polk and Gore Creeks) represent background

(undeveloped land use) conditions, whereas sites 19, 20, 21, and 23

(Bighorn, Pitkin, Booth, and Middle Creeks) also generally represent background

conditions, but are relatively close to Interstate 70 and some minor land

development.

 Water samples were collected using an equal-width interval method, and

samples were processed using standard NAWQA surface-water protocols

(Shelton, 1994). Analytical results from the synoptic sampling are reported in

Crowfoot and others (1996). Synoptic-sampling results included in Crowfoot and

others (1996), but not summarized in table 1 are streamflow, alkalinity, and

concentrations of major ions (calcium, chloride, fluoride, magnesium, potassium,

silica, sodium, and sulfate).

RESULTS

 Selected analytical results for the synoptic sampling are summarized in

table 1. The lowest applicable stream-quality standards have been calculated for

Gore Creek using the methods of the Colorado Department of Health (1996) and

are listed for properties and constituents in table 1. The stream-quality standards

are the chronic aquatic-life, acute aquatic-life, or drinking-water standards, if

available.

HYDROLOGY

 The synoptic sampling was conducted during stable, low-flow

conditions. Streamflow at the mouth of Gore Creek during the synopticsampling period (August 19–23) was near the low flow for water year 1996,

gradually declining from 64 to 43 cubic feet per second (ft3/s) (fig. 2). No

significant precipitation occurred during the sampling period or in the week prior

to sampling.

 Flow from the primary point source, the wastewater-treatment plant,

accounted for less than 10 percent of the streamflow at the mouth of Gore Creek

(Caroline Byus, Eagle River Water and Sanitation District, written commun.,

1997); therefore, dilution had a strong mitigating effect on any chemical

constituents discharging into Gore Creek from this point source during the

synoptic sampling. No additional point sources were observed near sampling

sites during the synoptic-sampling period.

GENERAL WATER QUALITY

 Water in the Gore Creek watershed generally was of good quality at

synoptic-sampling sites. Concentrations of dissolved oxygen and dissolved

solids, pH, specific conductance, and suspended-sediment concentrations,

which are indicators of overall stream water quality, did not exceed applicable

stream standards. Dissolved-oxygen concentrations were near saturation at all

sites. Dissolved-solids concentrations generally were low in Gore Creek (fig. 3),

but gradually increased in a downstream direction from 29 milligrams per liter

(mg/L) at site 1 (background site) to 165 mg/L at the mouth of Gore Creek.

Tributaries draining sedimentary rock formations in undeveloped areas and in

the ski area probably contributed most of this increase in dissolved-solids

concentrations. Suspended-sediment concentrations were very low at all sites,

ranging from 1 to 3 mg/L (table 1).

OND J FMAMJ J A S

Gore Creek at mouth, site 13

Synoptic-sampling period

0

500

1995 1996 DATE

DAILY MEAN STREAMFLOW,

IN CUBIC FEET PER SECOND 1,000

1,500

Figure 2.—Streamflow during the synoptic period compared to water year

1996 hydrograph.

Figure 3.—Concentrations of selected constituents. Symbol colors correspond to explanation in figure 1.

0 2 4 6 8 10 12 14 16 18 20

200

150

100

50

0

Site

14

Site

16

Site

1

Site

3

Site

5

Site

8

Site

10

Site

13 Lakes

CONCENTRATIONS, IN

MILLIGRAMS PER LITER

DISSOLVED SOLIDS

DISTANCE UPSTREAM FROM MOUTH, IN MILES

Photograph by Richard J. Szmajter
0

0

1

1

2

2

3

3

4

4

5 MILES

5 KILOMETERS

Gore Creek site without trace-element analysis

Gore Creek site with trace-element analysis

Tributary site without trace-element analysis

Tributary site with trace-element analysis

Town of Vail Corporate limit

EXPLANATION 70

Minturn

Vail

Pass

R

ed

S

andstone

Cr.

Middle

Cr.

Booth

Pitkin

Cr.

Bighorn Cr.

Gore

Creek

Black

Gore Cr.

Polk Cr.

Cr

1

14

13 12

11 10

9 8

23

22

7

6

5

21

4

20

19

3 2

18

17 16

15

24

Figure 1.—Gore Creek watershed sampling sites.
TRACE ELEMENTS

 Concentrations of trace elements did not exceed the stream standards

established by the Colorado Department of Health (Colorado Department of

Health, 1996), except for manganese at site 14 (fig. 1), where Black Gore Creek

flows into Black Lake. The locations where samples for trace elements were

collected are shown in figure 1.

 Four of the USEPA trace-element priority pollutants (U.S. Environmental

Protection Agency, 1994) listed in table 1 were detected at low concentrations.

They are, in descending order of detection frequency, nickel, zinc, chromium, and

copper. Zinc had the highest concentration, 5 micrograms per liter (μg/L), of the

four priority trace elements detected. Zinc and copper concentrations were highest

at the background site on Gore Creek (site 1), indicating that weathering of

crystalline rock in the headwaters was the source of these elements. Priority trace

elements that were not detected in the watershed were arsenic, cadmium, lead,

and silver.

 Five other dissolved trace elements—aluminum, barium, iron, manganese, and

uranium—were detected during the low-flow synoptic sampling (table 1). The

highest manganese concentrations were on Black Gore Creek; concentrations

ranged from 530 μg/L at site 14, the farthest upstream site on Black Gore

Creek,to 22 μg/L at site 18, just upstream from the confluence with Gore

Creek. Weathering of sedimentary rock greatly contributes to these elevated

manganese concentrations (Steele and others, 1991). The two lakes on Black

Gore Creek downstream from site 14 probably removed most of the manganese from the creek through precipitation and deposition processes. All other

manganese concentrations in the watershed were less than 20 μg/L. The

pattern for iron concentrations in the watershed was similar to the pattern for

manganese; the highest iron concentrations (14, 20, and 150 μg/L) were in

Black Gore Creek, and all other iron concentrations were less than 10 μg/L.

Aluminum and barium were detected in all analyses, but each of these

detections was less than stream standards (table 1). Dissolved uranium was

detected 7 times in low concentrations ranging from 1 to 2 μg/L. Antimony,

beryllium, cobalt, and molybdenum were not detected.

 Weathering of crystalline and sedimentary rocks seemed to be the primary

source of dissolved trace elements in the watershed. Land uses associated with

urban development and recreation did not measurably affect concentrations of

trace elements in Gore Creek during the synoptic sampling.

Table 1.-- Summary of water-quality analyses for water samples collected in the Gore Creek watershed, August 1996

[USEPA, U.S. Environmental Protection Agency; *, no detections greater than laboratory reporting limit; — , no data; mg/L, milligrams per liter;

°C, degrees Celsius; microsiemens per centimeter at 25 degrees Celsius; μS/cm, μg/L, micrograms per liter; N, nitrogen; P, phosphorus]

Property

or constituent

Number of

detections/total

number of samples

Range of detected

concentrations

Laboratory

reporting limit

 Stream

standard1

General water quality

Dissolved oxygen, mg/L 24/24 6.7–9.0 — 6.0

Dissolved solids, mg/L (calculated) 24/24 26–199 — —

pH, standard units 24/24 7.5–8.9 — 6.5–9.0

Specific conductance, μS/cm 24/24 45–397 — —

Suspended sediment, mg/L 12/24 1–3 — —

Water temperature,°C

Trace-element priority pollutants 2, dissolved ( μg /L)

Arsenic 0/12 * 1 3 50

Cadmium 0/12 * 1 1.1

Chromium 4/12 2–3 1 3 50

Copper 3/12 1–2 1 11.8

Lead 0/12 * 1 3.9

Nickel 9/12 1–3 1 96

Silver 0/12 * 1 0.08

Zinc 6/12 1–5 1 106

Other trace elements, dissolved (μg/L)

Aluminum 12/12 3–10 1 87

Antimony 0/12 * 1 3 6

Barium 12/12 19–170 1 3 1,000

Beryllium 0/12 * 1 3 4

Cobalt 0/12 * 1 —

Iron 21/24 4–150 3 300

Manganese 17/24 1–530 1 50

Molybdenum 0/12 * 1 —

Uranium 7/12 1–2 1 1,500

Nutrients (mg/L)

Ammonia, ionized + un-ionized, dissolved, as N 3/24 0.02–0.22 0.01 —

Ammonia, un-ionized (calculated), dissolved, as N, 3/24 0.0009–0.004 — 0.02

Nitrite, dissolved, as N 0/24 * 0.01 0.05

Nitrate, dissolved, as N, 19/24 0.05–0.61 0.05 10

Ammonia plus organic nitrogen, dissolved, as N 1/24 0.5 0.2 —

Orthophosphate, dissolved, as P 5/24 0.05–0.08 0.01 —

Phosphorus, dissolved, as P 6/24 0.02–0.09 0.01 —

Total phosphorus as P 5/24 0.06–0.10 0.01 —

1Colorado Department of Health (1996): standards are for Gore Creek.

2U.S. Environmental Protection Agency (1994).

3Stream standard is for total recoverable material.

24/24 7–16 — —
NUTRIENTS

 Nutrient concentrations did not exceed applicable stream standards in

the Gore Creek watershed. Because ammonia is reported as ionized plus unionized ammonia, but only the un-ionized part of ammonia is considered harmful

to fish and has a stream standard, the ammonia and the calculated un-ionized

ammonia concentrations (Thurston and others, 1974) are listed individually in

table 1. The highest concentration for ammonia was just 0.22 mg/L at site

14,the farthest site upstream on Black Gore Creek. Un-ionized ammonia

concentrations were very low in the watershed.

 Nitrate concentrations in the main stem of Gore Creek gradually increased

from 0.07 mg/L as N at the background site (site 1) to 0.17 mg/L as N at site 8

upstream from the wastewater-treatment-plant outfall (fig. 4). This slight increase

occurs as Gore Creek flows past the golf course and through areas draining

increasingly urban land uses. Concentrations of nitrate and other nutrients were

less than the applicable stream standards downstream from the treatment-plant

outfall. However, figure 4 shows the somewhat elevated concentrations of nitrate

and total phosphorus at the Gore Creek sites downstream from site 8 and the

treatment-plant outfall.

 Nitrate and total phosphorus concentrations in Gore Creek were fairly

low when compared to data compiled for a study of regional and national

nutrient-concentration patterns (Mueller and others, 1995). The concentrations in Gore Creek were comparable to concentrations measured in streams

draining mostly undeveloped areas.

SUMMARY

 Surface water in the Gore Creek watershed was of good quality during the

summer low-flow synoptic sampling. Recreational and urban land uses did not

substantially affect water quality. Weathering of rocks seemed to be the primary

source of dissolved-solids and trace-element concentrations in the watershed.

Zinc and copper were highest at site 1 on Gore Creek, which drains igneous,

crystalline bedrock. Tributaries draining sedimentary rocks had the higher

concentrations of manganese, iron, and dissolved solids. Nutrient concentrations

increased in a downstream direction through the Town of Vail, but remained

relatively low.

 Results of the synoptic sampling indicate that the stable summer low-flow

period is a time of good water quality in the watershed—dissolved-oxygen

concentrations are high, and constituent concentrations are low. Additional data

collected during higher flow runoff events, such as snowmelt or thunderstorms,

would be beneficial in evaluating effects of land use on water quality.

REFERENCES

Apodaca, L.E., Driver, N.E., Stephens, V.C., and Spahr, N.E., 1996, Environmental setting and implications on water quality, Upper Colorado

River Basin, Colorado and Utah: U.S. Geological Survey WaterResources Investigations Report 95–4263, 33 p.

Colorado Department of Health, 1996, Classifications and numeric standards

for Upper Colorado River Basin and North Platte River (planning

region 12) 3.3.0: Denver, Water Quality Control Commission, 72 p.

Crowfoot, R.M., Paillet, A.V., Ritz, G.F., Smith, M.E., Jenkins, R.A., and

O’Neill, G.B., 1996, Water resources data, Colorado, water year

1996, v. 2, Colorado River Basin: U.S. Geological Survey WaterData Report CO-96-2, 551 p.

Leahy, P.P., Rosenshein, J.S., and Knopman, D.S., 1990, Implementation

plan for the National Water-Quality Assessment Program:

U.S. Geological Survey Open-File Report 90–174, 10 p.

Mueller, D.K, Hamilton, P.A., Helsel, D.R., Hitt, K.J., and Ruddy, B.C., 1995,

Nutrients in ground water and surface water of the United States—

An analysis of data through 1992: U.S. Geological Survey WaterResources Investigations Report 95–4031, 74 p.

Shelton, L.R., 1994, Field guide for collecting and processing stream-water

samples for the National Water-Quality Assessment Program:

U.S. Geological Survey Open-File Report 94–455, 42 p.

Spahr, N.E., Driver, N.E., and Stephens, V.C., 1996, The Upper Colorado

River National Water-Quality Assessment Program surface-watermonitoring network: U.S. Geological Survey Fact Sheet 191-96, 4 p.

Steele, T.D., Weaver, R.M., and Mott, D.E., 1991, Temporal and spatial

patterns in trace-metal concentrations of a mountain stream in westcentral Colorado, USA, in Peters, N.E., and Walling, D.E., eds.,

Sediment and stream water quality in a changing environment; trends

and explanation—Proceedings of symposium, International Union of

Geodesy and Geophysics, Vienna, Austria, August 11–24, 1991:

International Association of Hydrological Sciences Publication 203,

p. 293–302.

Thurston, R.V., Russo, R.C., and Emerson, Kenneth, 1974, Aqueous ammonia

equilibrium calculations: Bozeman, Montana State University,

Fisheries Bioassay Laboratory Technical Report 74-1, 18 p.

U.S. Environmental Protection Agency, 1994, Water quality standard hand

book (2d ed.): U.S. Environmental Protection Agency Report

EPA-823-B-94-005b, appendix p, 3 p.

Manuscript and Layout: Alan M. Duran

Design: Alan M. Duran, Loretta J. Ulibarri, and Anthony Sanchez

Final illustrations: Alan M. Duran and Anthony Sanchez

January 1998

Figure 4.—Concentrations of selected constituents. Symbol colors correspond to explanation in figure 1.

Information on technical reports and hydrologic

data related to the NAWQA program

can be obtained from:

Upper Colorado River NAWQA Manager

U.S. Geological Survey,

Water Resources Division

Bldg. 53, Denver Federal Center

Mail Stop 415, Box 25046

Denver, CO 80225-0046

email: nedriver@usgs.gov

Photograph by Richard J. Szmajter

0.75

1.00

0.50

0.25

0.00 0 2 4 6 8 10 12 14 16 18 20

0.75

1.00

0.50

0.25

0.00

Site

14

Site

16

Site

1

Site

3

Site

5

Site

8

Site

10

Site

13 Lakes

CONCENTRATIONS, IN

MILLIGRAMS PER LITER

DISTANCE UPSTREAM FROM MOUTH, IN MILES

TOTAL PHOSPHORUS

NITRATE

FS-167-97