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Show Water Quality in the Great Salt Lake Basins, Utah, Idaho, and Wyoming, 1998- 2001 exceeded for total DDT ( 2 sites) and PCBs ( 4 sites). The use of most of these compounds has been discontinued for decades, but they continue to persist in the environment. ( See page 18) • At 9 of 15 sites sampled for streambed sediment and 11 of 14 sites sampled for fish tissue, concentrations of at least 1 trace element were greater than 90 percent of the samples collected in all NAWQA studies nationally in 1993- 2000. Aquatic- life guidelines for arsenic, cadmium, copper, lead, mercury, silver, and zinc were exceeded in bed- sediment samples from stream reaches that were affected by mine tailing deposits and smelters ( including some on urbanized streams). ( See pages 21 and 24) Major Influences on Streams and Rivers • Urban and agricultural land use • Historical mining activities • Water development and management Ground- Water Highlights Ground water is a major source of public supply in the Great Salt Lake Basins Study Unit. The basin- fill aquifers receive recharge from precipitation on the mountains through subsurface inflow and from infiltration of precipitation, irrigation, or seepage from streams and canals in the valleys. Shallow ground water in Salt Lake Valley contains elevated concentrations of nitrate; and pesticides and VOCs were detected in many samples from the shallow aquifer, indicating that the shallow aquifer is affected by human activities at the land surface. Water from the deeper underlying basin- fill aquifers generally meets existing Federal and State standards and regulations for drinking water. • The median nitrate concentration of 6.8 mg/ L for shallow water from 30 monitoring wells in recently developed residential and commercial areas in Salt Lake Valley is the highest of 34 studies done across the Nation as part of the NAWQA Program. These wells are in areas with high potential for downward movement of water to the underlying basin- fill aquifer used for public supply. ( See page 11) • Tetrachloroethene ( PCE) was detected more frequently in shallow ground water underlying residential and commercial areas in Salt Lake Valley than in most ground water sampled by NAWQA across the Nation. PCE was detected in water from 16 of 30 monitoring wells. Water from one monitoring well exceeded the USEPA drinking- water standard of 5 [ ig/ L ( micrograms per liter) for PCE, although water from the shallow aquifer is not used for drinking. ( See pages 14 and 15) Selected Indicators of Ground Water Quality Shallow Ground Water Deeper Aquifers Water- Supply Wells Mixed Land Use Urban Pesticides Nitrate Arsenic Volatile organics1 Radon m m \ B Proportion of samples with detected concentrations greater than or equal to health- related national guidelines for drinking water | J Proportion of samples with detected concentrations less than health- related national guidelines for drinking water I I Proportion of samples with no detections 1 Solvents, refrigerants, fumigants, and gasoline compounds. VOCs were frequently detected in water from the basin- fill aquifers in both agricultural and urban areas. Chloroform, likely formed as a byproduct of water disinfection, was the most frequently detected VOC, but at concentrations much less than the USEPA drinking- water standard. ( See page 15) Atrazine was the most frequently detected pesticide ( 77 percent of samples) in shallow ground water underlying Salt Lake Valley, but mostly at concentrations much less than the USEPA drinking- water standard of 3 u. g/ L. Atrazine was detected in 23 percent of samples collected from wells in the basin- fill aquifers throughout the Study Unit. ( See page 15) The age ( time since recharge) of water from 31 public- supply wells in Salt Lake Valley ranged from 3 to more than 50 years. Manmade compounds generally were detected in water that was less than 50 years old, but not in water more than 50 years old. ( See page 16) Concentrations of arsenic in water from about 20 percent of wells ( primarily domestic wells) in the basin- fill aquifers underlying recharge areas exceeded the USEPA drinking- water standard of 10 ug/ L. Arsenic in basin- fill aquifers likely is derived naturally from geo- chemical reactions between aquifer minerals and water. ( Seepage 21) Major Influences on Ground Water • Urban and agricultural land use • Aquifer properties and characteristics • Sources of ground- water recharge |