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Water Quality 9 River and its tributaries are given the highest (class 1) aquatic life and recreational qualifications allowable. In 2000, USEPA established recommended nutrient crite- ria for rivers and streams in ecoregion II-Western Forested Mountains, including the Fraser River watershed. The intent of these criteria is to identify baseline conditions for rivers and streams that are minimally affected by human activities and protect against nutrient enrichment from cultural eutrophication (U.S. Environmental Protection Agency, 2000a). These criteria are guidance that States and tribes may use as a starting point in establishing their water-quality standards (U.S. Envi- ronmental Protection Agency, 2000a). For ecoregion II, the rec- ommended criterion for total phosphorus in rivers and streams is 0.010 mg/L (U.S. Environmental Protection Agency, 2000a). Because the total phosphorus criterion only is a guidance for establishing standards and is not a legally enforceable criterion, it will be excluded from the discussions about ground- and sur- face-water quality in the Fraser River watershed. Water Quality Water-quality data for ground water and surface water include field properties, dissolved solids and(or) major ions, selected trace elements, nutrients, organic carbon, and bacteria. Ground-water data also include MBAS and radon-222. Ground- water data are related to aquifer type, type of land use, and the presence or absence of ISDS's and are examined for changes over time. To the extent required, interpretation of water-qual- ity data is limited or qualified by quality-control factors, as described in Appendix II-"Quality-Control Methods and Analysis" at the end of this report. Ground Water All water-quality constituents for ground water are in the dissolved form except for total coliform bacteria, MBAS, and radon-222. A statistical summary of selected ground-water data, USEPA and State of Colorado water-quality standards, and NWQL reporting levels is listed in table 2. A full listing of ground-water-quality data is in table 5 in Appendix I. Field Properties Water temperature for 86 percent of the wells was less than 10°C. Temperatures above 10°C were measured only in two wells (sites 5 and 11) near Tabernash. Well 5 is 120 ft deep in the Troublesome Formation, and well 11 is 105 ft deep in the Precambrian fractured granite. Water temperature from site 5 generally was about two times higher than temperatures from the other wells. Sample collection for this well took place at an outside household spigot, and the temperature of the water may have increased as the water traveled through the pressure tank and plumbing system. There is no known hydrothermal activity in the area. No statistical relation was detected between well depth and water temperature. There was a statistically signifi- cant difference in water temperature between the alluvial and the Troublesome Formation aquifers (table 3); the median water temperature was cooler in the alluvial aquifer. Specific conductance, defined as the ability of water to conduct an electric current at 25°C, provides an indication of ion concentration. As ion concentrations increase, specific con- ductance increases (Hem, 1992). Specific conductance for ground water in the Fraser River watershed was low to moder- ate, ranging between 88 and 430 µS/cm (table 2). Median val- ues of specific conductance were lowest in the vicinity of Fraser and Winter Park and were highest in the Tabernash area. Well 8 had the highest median specific conductance, 392 ltS/cm. Most (76 percent) dissolved-oxygen concentrations mea- sured in ground water for this study were greater than 1.0 mg/L. Dissolved-oxygen concentrations less than 1.0 mg/L, which can be indicative of reducing conditions, were measured in three wells, one in the Troublesome Formation aquifer near Fraser (well 2) and two in the alluvial aquifer near Tabernash (wells 7 and 9). Some metals such as iron and manganese are more sol- uble under reducing conditions (Hem, 1992). Dissolved-oxygen concentrations in sites 7 and 9 were particularly low-less than or equal to 0.7 mg/L for all samples. Dissolved-oxygen concen- trations below 1.0 mg/L are considered low for the Fraser River watershed (Apodaca and Bails, 1999). Statistically significant differences in dissolved-oxygen concentrations were detected for aquifer type and land use (table 3); median dissolved- oxygen concentrations were lower in the alluvial aquifer and in urban areas than in the Troublesome Formation aquifer and nonurban areas. Ground water is supplied with dissolved oxy- gen through recharge and the movement of air through the unsaturated zone above the water table (Hem, 1992). Low dissolved-oxygen concentrations may result from the interac- tion of ground water with oxidizable materials (organic matter and reduced minerals) along the flow path of the water and(or) from microbiological activities. The lower dissolved-oxygen concentrations in the alluvial aquifer and urban wells may represent natural conditions or may indicate the addition of organic matter through human activities, including fertilizers or septic systems. Of the three wells with low dissolved-oxygen concentrations, only site 7 is in an ISDS area. Almost all pH values were within the USEPA SDWR of 6.5 to 8.5 (table 2). The exception was site 1, where pH in the water samples ranged from 6.1 to 6.5. A pH of 7.0 indicates neutral pH, less than 7.0 indicates the water is acidic, and pH greater than 7.0 indicates the water is basic. Site 1 is very shal- low-only 18 ft deep, and ground water is frequently in contact with the soil horizon. Humic acids from the soil horizon decrease pH in the ground water. Values of pH were statistically different for aquifer types and land use (table 3). Median pH was lower in alluvial aquifer and urban well-water samples than in water samples from the Troublesome Formation aquifer and nonurban areas. It is not known why urban wells had a generally lower pH than did nonurban wells.