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· Concentrations of trace elements, such as cadmium, zinc, copper, and lead, in streambed sediments in many historical mining areas were greater than guidelines for the protection of aquatic life (p. 11-12). · Pesticides were commonly detected in streams in agricultural areas of the Colorado Plateau during the growing season; however, the concentrations were typically low. Pesticide concentrations that exceeded guidelines for the protection of aquatic life were detected in only 5 of 90 samples (p. 16). Not all detected pesticides have established guidelines. · The herbicides atrazine and alachlor were detected in more than one-half of the water samples collected in agricultural areas of the Colorado Plateau. These compounds, commonly used for weed control in corn, were also commonly detected in agricultural areas nationwide (p. 17). · Nutrient and suspended-sediment concentrations in streams in the Colorado Plateau were typically greater than concentrations found in streams in other areas of the UCOL (p. 18-19). These concentrations can generally be associated with a more degraded status of algae, invertebrates, and fish (p. 19). Major Influences on Streams and Rivers .Urban development .Abandoned/inactive mines .Agricultural return flows Ground-Water Highlights Historical ground-water-quality data for the UCOL are limited. The studies completed in the UCOL by NA WQA provide baseline information that can be used for identifying future water-quality changes. With the exception of radon, ground-water quality in the urban areas of the Southern Rocky Mountains gener- ally met Federal and State standards for drinking water. The presence of a few elevated nitrate concen- trations, a few pesticides, and generally low concentra- tions of volatile organic compounds indicate some influence on the quality of ground water from human activities. Bacteria were detected in ground-water samples and can occur naturally or indicate human influences. · A concentration of nitrate greater than the U.S. Envi- ronmental Protection Agency (USEPA) drinking- water standard was found in 1 of 57 shallow ground- water samples collected in urban land-use settings (p.8). 2 Water Quality in the Upper Colorado River Basin · Ground water in urban areas recharged in the late 1980s or 1990s tends to have higher concentrations of nitrate than ground water recharged before the 1980s (p. 10). · Pesticides and volatile organic compounds were detected infrequently and generally at concentrations less than drinking-water standards. In only one sample, dichloromethane and tetrachloroethene, which are sol- vents, were detected at concentrations greater than their drinking-water standards (p. 10). Low concentra- tions of methyl tert-butyl ether (MTBE), a gasoline additive, were detected in shallow ground water in four of the five urban areas sampled (p. 9). · Total coliform bacteria were detected in 21 percent of the shallow ground-water samples collected in urban areas in the Southern Rocky Mountains; none of the samples contained the potentially pathogenic Escheri- chia coli (E. coli) bacteria (p. 10). · Radon, a naturally occurring radioactive gas, was detected in all wells sampled in urban areas in the Southern Rocky Mountains. Concentrations were greater than the proposed USEPA drinking-water stan- dard of 300 picocuries per liter. Currently (2000), radon in drinking water is not regulated; however, if a new drinking-water regulation is implemented, treat- ment of drinking water for radon may be required in the UCOL (p. 9). Major Influences on Ground Water · Urban development in the Southern Rocky Mountains · Natural background conditions Selected Indicators of Ground-Water Quality Shallow Ground Water Supply Wells Urban Urban Forest Rangeland Pesticides ~ ~ e ~ A ~ r 4.,...;" 'ifi1 e ~ e ~ e o CD .. Nitrate t9 e \0 tit Radon Volatile Organics Trace Elements Bacteria . . . Percentage of samples with concentrations greater than or equal to health-related national guidelines for drinking water Percentage of samples with concentrations less than health-related national guidelines for drinking water Percentage of samples with no detection