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Water-Quality Characteristics and Ground-Water Quantity <br />of the Fraser River Watershed, Grand County, Colorado, <br />1998-2001 <br />Nancy J. Bauch and Jeffrey B. Bails <br />Abstract <br />The U.S. Geological Survey, in cooperation with the <br />Grand County Board of County Commissioners, conducted a <br />4-year study to assess ground- and surface-water-quality condi- <br />tions and ground-water quantity in the 302-square-mile Fraser <br />River watershed in north-central Colorado. The Fraser River <br />flows north about 28 miles from the headwaters near the Conti- <br />nental Divide, through the towns of Winter Park, Fraser, Taber- <br />nash, and Granby, and is one of the major tributaries to the <br />Upper Colorado River. Increasing urban development, as well <br />as the seasonal influx of tourists, is placing more demands on <br />the water resources in the Fraser River watershed. <br />A ground-water sampling network of I 1 wells was <br />established to represent different aquifer systems (alluvial, <br />Troublesome Formation, Precambrian granite), land uses <br />(urban, nonurban), and areas with or without individual septic <br />disposal system use. The well network was sampled for ground- <br />water quality on a semiannual basis from August 1998 through <br />September 2001. The sampling included field properties and the <br />collection of water samples for analysis of major ions, trace <br />elements, nutrients, dissolved organic carbon, bacteria, methyl- <br />ene blue active substances, and radon-222. One surface-water <br />site, on the Fraser River just downstream from the town of <br />Tabernash, Colorado, was sampled bimonthly from August <br />1998 through September 2001 to assess the cumulative effects <br />of natural and human processes on water quality in the upper <br />part of the Fraser River watershed. Surface-water-quality sam- <br />pling included field properties and the collection of water-qual- <br />ity samples for analysis of major ions, trace elements, nutrients, <br />organic carbon, and bacteria. <br />Ground water was a calcium-bicarbonate type water and is <br />suitable as a drinking-water, domestic, municipal, industrial, <br />and irriuation source. In general, no widespread ground-water- <br />quality problems were indicated. All pH values and concentra- <br />tions of dissolved solids, chloride, fluoride, sulfate, nitrite, and <br />nitrate in the ground-water samples met or were substantially <br />less than U.S. Environmental Protection Agency drinking- <br />water standards and health advisories or State of Colorado <br />water-quality standards. Federal standards for turbidity and <br />concentrations of iron, manganese, methylene blue active sub- <br />stances, and radon-222 were not met in water samples from at <br />least one well. The only ground-water-quality concern assessed <br />by this study is radon-222, which was detected in all radon- <br />analyzed samples from 10 wells at levels exceeding the pro- <br />posed U.S. Environmental Protection Agency drinking-water <br />standard of 300 picocuries per liter. <br />Concentrations of chloride, magnesium, and sulfate were <br />statistically different (higher) in ground-water samples from <br />wells completed in the alluvial aquifer, urbanized areas, and <br />areas with individual septic disposal system use than those from <br />wells completed in the Troublesome Formation, nonurban <br />areas, and areas without individual septic disposal system use. <br />Dissolved organic carbon concentrations were statistically <br />higher in ground-water samples from wells completed in the <br />alluvial aquifer and areas without individual septic disposal sys- <br />tem use than those from wells completed in the Troublesome <br />Formation and areas with individual septic disposal system use. <br />Differences in dissolved organic-carbon concentrations <br />between the latter category and areas without septic systems <br />likely had no environmental significance. <br />Surface water at the site Fraser River below Crooked <br />Creek at Tabernash was a calcium-bicarbonate type water and <br />is suitable as a drinking-water, residential, commercial, and irri- <br />gation resource. All pH values and concentrations of dissolved <br />oxygen were within the State of Colorado instream water-qual- <br />ity standards, and all concentrations of chloride, sulfate, iron, <br />manganese, un-ionized ammonia, nitrite, nitrate, and fecal <br />coliform bacteria met State standards. Seasonal changes in the <br />values or concentrations of field properties and constituents in <br />the surface water were detected. For most constituents, maxi- <br />mum concentrations typically occurred during winter with low <br />streamflow conditions, and minimums typically occurred dur- <br />ing spring as a result of dilution by snowmelt runoff. <br />Ground-water quantity was estimated for the alluvial and <br />Troublesome Formation aquifers in the upper portion of the <br />Fraser River watershed, the most likely area for future ground- <br />water use. The estimated average volume of available ground <br />water in the alluvial aquifer was about 150,000 acre-feet, with <br />seasonal fluctuations of about 7 percent. The Troublesome <br />Formation aquifer, which consists of siltstone and interbedded <br />sandstone and conglomerate, has approximately 370,000 acre- <br />feet of available water in the upper 500 feet of the aquifer.