GROUND-WATER ACTIVITIES FOR WATER YEARS 1996-98
Land-use studies assess the effects of specific land use on shallow groundwater. 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.
- Assess the concentrations and distributions of water-quality constituents in recently recharged (shallow) groundwater associated with areas of increasing residential and commercial development.
- Determine natural and anthropogenic factors associated with observed ground-water quality conditions in the areas of increasing urban development.
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.
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.
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 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).
- Assess ground-water quality conditions in alluvial aquifers utilized predominantly for domestic or public water supply.
- Assess ground-water quality conditions in alluvial aquifers in mining-impacted areas.
- Relate observed ground-water quality conditions to natural and anthropogenic factors.
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.
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 of the study are presented in:
- 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.
- 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.
Groundwater 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 groundwater 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).
- Assess the difference in ground-water quality between sites unaffected and affected by metals mining.
- Determine sources of metal loading within the basin.
- Evaluate interactions between unaffected and affected waters through mass-balance modeling.
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.
Each ground-water site was sampled once in June 1996.
- Targeted Constituents:
Physical properties, major ions, dissolved organic carbon, trace elements, and tritium.
Results of the sampling of the wells and seeps in the French Gulch drainage are presented in:
- 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.
- 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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