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GROUND-WATER
ACTIVITIES
FOR WATER YEARS 1996-98
Land-Use Survey
Land-use studies assess the effects of specific land
use on shallow ground water. This focus on recently recharged ground
water allows for the direct assessment of the effects of land-use activities
on ground-water quality. In the Upper Colorado River Basin, the land
use of concern was identified as increasing urbanization in many rural
and mountain communities in the eastern portion of the basin within
the Southern Rocky Mountains physiographic province. Twenty-five newly
constructed ground-water monitoring wells located in alluvial aquifers
in areas of increasing urbanization in the Southern Rocky Mountains
physiographic province were sampled in April and May 1997.
• Objectives:
1. Assess the concentrations and distributions
of water-quality constituents in recently recharged (shallow) ground water
associated with areas of increasing residential and commercial development.
2. Determine natural and anthropogenic factors associated with observed
ground-water quality conditions in the areas of increasing urban development.
• Approach:
During fall 1996 and spring 1997, 25 ground-water
monitoring wells were installed in alluvial aquifers in areas of increasing
urbanization in the Southern Rocky Mountains Physiographic Province.
Five wells were randomly located in each of five growing towns: Crested
Butte and Gunnison, Gunnison County; Fraser, Grand County; Silverthorne,
Summit County; and Vail, Eagle County.
• Timing:
Each well was sampled once in April or May 1997.
• Targeted Constituents:
Physical properties, major ions, nutrients, dissolved
organic carbon, pesticides, trace elements, volatile organic compounds,
radon, tritium, and chlorofluorocarbons.
• Results:
Selected results of the sampling of the 25 urban
land-use ground-water monitoring wells in alluvial aquifers in the Southern
Rocky Mountain physiographic province are presented in the study unit
summary report:
Spahr, N.E., Apodaca, L.E., Deacon, J.R.,
Bails, J.B., Bauch, N.J., Smith, C.M., and Driver, N.E., Water Quality
in the Upper Colorado River Basin, Colorado, 1996-98: U.S. Geological
Survey Circular 1214, 33 p.
Sub-Unit Survey
Sub-unit
surveys assess the water quality of major aquifers in a subregion of
the study unit. Each sub-unit is considered to have homogeneous water-quality
characteristics. All wells sampled for a sub-unit survey are preexisting
wells. In the Upper Colorado River Basin, alluvial aquifers in the Southern
Rocky Mountains physiographic province that are used predominately for
water supply were the focus of the sub-unit survey. Water-quality samples
were collected from 45 ground-water sites (43 preexisting wells and
2 springs) in alluvial aquifers in the Southern Rocky Mountains physiographic
province in August and September 1997. Twenty-three of the 45 sites
were located in or near mining districts. (Map of sub-unit survey ground-water
site locations).
• Objectives:
1. Assess ground-water quality conditions in alluvial aquifers utilized
predominantly for domestic or public water supply.
2. Assess ground-water quality conditions in alluvial aquifers in mining-impacted
areas.
3. Relate observed ground-water quality conditions to natural and anthropogenic
factors.
• Approach:
Domestic and public water-supply wells in select alluvial aquifers in
the Southern Rocky Mountains Physiographic province were randomly chosen
for sampling. Mining-impacted areas included the drainage basins or
parts of the basins of the Blue, Eagle, Roaring Fork, East, Lake Fork
of the Gunnison, and Uncompahgre Rivers. Two springs were selected for
sampling in locations where wells could not be identified.
• Timing:
Each ground-water site was sampled once in August or September 1997.
• Targeted Constituents:
Physical properties, major ions, nutrients, dissolved organic carbon,
pesticides, trace elements, volatile organic compounds, radon, bacteria,
and methylene blue active substances.
• Results:
Results of the study are presented in:
1. Apodaca, L.E., and Bails, J.B., 2000,
Water Quality in Alluvial Aquifers of the Southern Rocky Mountains physiographic
province, Upper Colorado River Basin, Colorado, 1997: U.S. Geological
Survey Water-Resources Investigations Report 99-4222, 68 p.
2. Apodaca, L.E., Bails, J.B.,
and Smith, C.M, 2002, Water Quality in Shallow Alluvial Aquifers, Upper
Colorado River Basin, Colorado, 1997: Journal of the American Water
Resources Association, v. 38, no. 1, p. 133-149.
Ground Water in the French Gulch Drainage
The French Gulch drainage, located 2 miles east of Breckenridge, Colorado,
had undergone extensive placer and underground metals mining from the
late 1850’s until the 1970’s. In cooperative efforts with
the Colorado Division of Minerals and Geology and the U.S. Environmental
Protection Agency, sampling of ground water and seeps in the French Gulch
area was conducted in June 1996 to investigate high trace-element concentrations
in the mining-impacted French Gulch drainage. (Map
of French Gulch ground-water site locations).
• Objectives:
1. Assess the difference in ground-water quality between sites unaffected
and affected by metals mining.
2. Determine sources of metal loading within the basin.
3. Evaluate interactions between unaffected and affected waters through
mass-balance modeling.
• Approach:
Nine ground-water sites were selected for sampling. This included 5
wells selected from 20 wells installed by the Colorado Division of Minerals
and Geology, a mine pool, and 3 seeps. Site selection was based on well
screening within a single hydrologic unit and site characterization
as representing mining-affected or unaffected waters within the French
Gulch drainage.
• Timing:
Each ground-water site was sampled once in June 1996.
• Targeted Constituents:
Physical properties, major ions, dissolved organic carbon, trace elements,
and tritium.
• Results:
Results of the sampling of the wells and seeps in the French Gulch drainage
are presented in:
1. Apodaca, L.E., 1996, Sources of high trace-element
concentrations in the French Gulch drainage, Breckenridge, Colorado: The
Geological Society of America, 1996 Annual Meeting, October 28-31, 1996,
Denver, Colorado, 1 p.
2. Bails, J.B., 1998, Water-Quality
Characteristics and Mass-Balance Modeling of the French Gulch Drainage,
Breckenridge, Colorado: Master of Science Thesis, University of Colorado,
Boulder, Department of Geology, 97 p. (Unpublished).
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