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Federal regulation 40 CFR Part 144.3 defines an Underground Source of Drinking Water (USDW) as an aquifer or its portion: (a)(1) which supplies any public water system; or (a)(2) which contains a sufficient quantity of groundwater to supply a public water system; and (i) currently supplies drinking water for human consumption; or (ii) contains fewer than 10,000 mg/I total dissolved solids; and (b) which is not an exempt aquifer. A USDW is considered to have TDS concentrations less than 10,000 ppm. Water quality data collected while drilling test solution mining well 20-3 indicate that the potential USDW is restricted to the Uinta Formation at this site, i.e., down to depths of 700 to 750 feet, which is approximately 800 to 850 feet above the top of the mining interval (for a well with a ground surface elevation of approximately 6,200 feet). Conductivity measurements taken in the field after every 30 feet of drilling showed that water quality deteriorated significantly between 694 feet depth (conductivity 1,500 limhos/cm) and 758 feet (conductivity 12,000 pmhos/cm). Salinity increases rapidly as the A-Groove is approached, with TDS values in excess of the 10,000 ppm USDW limit in the lowest parts of the Upper Aquifer (Table G-2). A water quality sample taken just above the A- Groove at a depth of 811 feet below surface at the solution mining well 20-3 site recorded a TDS level of 15,900 mg/1 (Table G-2). Therefore, the only aquifer at the Piceance Site that meets the definition of a USDW is the Uinta Formation (upper) portion of the Upper Aquifer. G.2 Potential Water System Effects G.2.1 Surface Water Quality Effects Surface water quality could be affected by fill during construction activities and by discharges during commercial mine operations. Fill activities during construction are regulated by the U.S. Army Corps of Engineers (ACOE), and discharges to the surface waters during mine operations are primarily regulated by the Colorado Department of Public Health and Environment (CDPHE). Where the pipeline crosses a surface water body, a Clean Water Act Section 404 permit will be obtained from the ACOE. The permit would regulate discharge of dredged or fill materials into "waters of the U.S." Certain requirements will be included in the permit, including sediment control measures and restoration of the affected areas in accordance with BLM and ACOE requirements. A pipeline breach, although unlikely, could result in contamination of surface waters if the breach occurred in or near a stream. Where the pipeline crosses a perennial surface G-8