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<br />, , <br /> <br />) <br /> <br />. <br /> <br />. <br /> <br />U.S. Geological Survey, Water Resources Division <br />Jefferson County Mountain Ground-Water Resources Study <br /> <br />A. Title <br /> <br />Hydrologic assessment of ground-water resources in the mountainous areas of' Jefferson <br />County, Colorado. <br /> <br />B. Location <br /> <br />The study area includes all or parts of the mountainous areas of Jefferson County, Colorado <br />which includes about 385 square miles (excluding about 165 square miles within Pike National <br />Forest) and ranges in elevation from about 6,000 to 11,000 feet (fig. 1). The pilot study area <br />encompasses the Turkey Creek drainage area which includes the State Highway 285 corridor and the <br />towns of Conifer, Aspen Park, and Indian Hills. The pilot study area is about 47 square miles and <br />ranges in elevation from about 6,000 to 10,000 feet. <br /> <br />C. Problem <br /> <br />The lure of suburban mountain living within commuting distance of Denver has led to a rapid <br />population growth in the mountainous parts of Jefferson County. Residential development in this <br />region typically relies on individual domestic wells and septic sewage systems. Household wells in <br />this area normally are drilled into fractured crystalline rock and produce water from depths of 100 to <br />400 feet. Individual septic systems discharge effluent to leach fields from which effluent percolates <br />into the upper 10 feet of soil and a percentage of the effluent ultimately returns to the ground-water <br />system. Rapid growth in the mountainous areas results in increased demands on the ground-water <br />supply, increased septic system effluent returning to the ground-water system, and heighte'nedpublic <br />concern about the adequacy and quality of the ground-water supply. <br /> <br />An understanding of the mountain ground-water system is complicated by the heterogeneous <br />nature of the fractured, crystalline bedrock and the variable nature of precipitation in the semi-arid <br />west. Water production and' quality can vary dramatically in ground-water wells located within several <br />feet of each other because offracture locations. Consecutive high precipitation years can raise <br />ground-water levels, resulting in overconfidence about ground-water supplies. Ineyitable low <br />precipitation years can lower the ground-water levels, leaving pump intakes above the, water table <br />(dry wells). <br /> <br />Ground-water supplies are a, function of not only the quantity of water, but also the availability <br />of that water. In the mountainous parts of Jefferson County ground-water availability can be limited <br />by the location of fractures and the quality of the water. Techniques are currently being used to <br />enhance the fractures in a new well, but the life of these artificial fractures and their effect on <br />surrounding wells is still unknown. Natural and manmade contaminants can affect water availability <br />when the concentrations affect human health or impart a bad taste or odor to the water. Fluoride, <br />nitrate, radon, uranium, and high total dissolved solids have affected water availability in this area in <br />the past. ' <br /> <br />Water supply and growth issues are of concern to Jefferson County officials who must <br />balance the needs of current residents with the requests for additional development of living space <br />and water resources. Knowledge of the current status of the ground-water resources of the <br />mountainous parts of Jefferson County is needed to provide a basis for County planning and zoning <br />decisions that will allow reasonable development without causing undue harm to the area's vital water <br />resources. <br /> <br />Appendix A to Contract C153855 <br />