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Ground Water <br /> Quality and <br /> Usage: Ground water in San Joaquin County is designated by the California <br /> Regional Water Quality Control Board in the Basin Plan to have beneficial <br /> or potentially beneficial use. Currently, however, the uppermost water- <br /> bearing zone does not yield water used for domestic, industrial, or <br /> municipal purposes; this may be attributed to the degraded nature of this <br /> shallow aquifer. Background ground water quality tests performed on <br /> ground water from upgradient and downgradient wells in December 1992, <br /> indicates that EPA Secondary MCLS were exceeded by the following <br /> constituents: chloride, sulfate, aluminum, iron, and manganese. <br /> 3.0 BACKGROUND SITE CONDITIONS <br /> • 64 onsite and 12 offsite soil borings have been drilled at the site between 1988 and 1993, <br /> and 12 onsite test holes were excavated by backhoe in 1989. The maximum <br /> concentrations of total petroleum hydrocarbons as gasoline (TPH-G) and total petroleum <br /> hydrocarbons as diesel (TPH-D) detected at the site prior to remedial efforts were 590 <br /> and 3,700 parts per million (ppm), respectively. <br /> • Eight onsite and 4 offsite ground water monitoring wells are present at the site. <br /> • Onsite, hydrocarbon concentrations in soil were excavated to the standing water level in <br /> July 1990. Greater than 6,000 cubic yards of soil were hauled to appropriate disposal <br /> facilities. Approximately 7,300 cubic yards of clean, imported fill was then compacted <br /> and brought to grade. Figure 2 indicates the approximate limits of the area of excavation. <br /> • Dissolved-phase hydrocarbons have historically been detected in Monitoring Wells AW-3 <br /> and AW-9, along the northern margin of the site. A dissolved-phase concentration of 51 <br /> ppb TPH-D was detected on January 21, 1994. No other dissolved-phase TPH-G, TPH- <br /> D, or BTEX concentrations were detected in any other wells at the site during the January <br /> 21, 1994 sampling event. <br /> • Free product has not been observed in wells at this site. <br /> 4.0 PLANNED SITE ASSESSMENT ACTIVITIES <br /> 4.1 PRE-FIELD WORK ACTIVITIES <br /> Boring permits, encroachment permits, and property access will be acquired prior to drilling. <br /> Underground Service Alert(USA)will be notified approximately 10 days prior to field activities, <br /> and a geophysical survey will be performed to mark potential underground utilities at the <br /> proposed drilling locations. <br /> 4 <br />