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Working To Restore Nature <br /> Quality Control Plan, 1991). The "older alluvium" is the most extensively developed geologic <br /> unit in the area and hosts both unconfined and confined zones. The unconsolidated, mostly <br /> ' coarse grained nature of the aquifer material results in high well yields Specific capacities of <br /> wells completed in the older alluvium average 42 GPM/ft (USGS Professional Paper 1401-D, <br /> 1989). <br /> Dnnk mg wells in the region are generally completed at depths greater than 100 feet below <br /> ground surface due to the relatively poor quality of near surface groundwater. <br /> Regional groundwater flow in the site area is generally in a southwesterly direction toward the <br /> ' San Joaquin River Delta, or easterly toward a regional groundwater depression centered about <br /> 4 miles east of Stockton (San Joaquin County Flood Control and Water Conservation District, <br /> ' Spring 1991). <br /> Published data from the San Joaquin Flood Control and Water Conservation District indicate that <br /> the average long term depth to groundwater at the site has vaned from approximately 65 feet <br /> ' below grade (Fall 1991) to 35 feet below grade (Spring 1986). Current depth to groundwater <br /> at the site is approximately 47 to 49 feet below grade. <br /> 4.0 PREVIOUS WORK <br /> 9A Underground Tank Removal <br /> ' All buildings, pump islands, underground fuel storage tanks, and associated product lines were <br /> removed on or before March 17, 1987. Residual hydrocarbons were observed an soils beneath <br /> ' the former tanks Analytical results of soil samples are summarized in Table 1. <br /> 4_2 ub rface Investigation <br /> The uuhal subsurface investigation was performed by Groundwater Technology, Inc. (GTI) <br /> 1 On April 10, 1987, GTI collected confirmation soil samples (SS-1, SS-2, SS-3) from beneath <br /> 15MMEPoR' WAP-079a DRF 3 <br />