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I 1 recreation, freshwater habitat, wildlife, fish migration, and fish spawning (CRWQCB Water Quality Control Plan, 1991) The existing and potential uses of groundwater in the area include irrigation, private and municipal water supply, stock watering, process water, and service supply (CRWQCB Water Quality Control Plan, 1991) The "older alluvium" is the most extensively developed geologic unit in the area and hosts both unconfined and confined zones The unconsolidated, mostly coarse grained nature of the aquifer material results in high well yields Specific capacities of ' wells completed in the older alluvium average 42 GPM/ft (USGS Professional Paper 1401-D, 1989) Regional groundwater flow in the site area is generally in a northwesterly direction, toward the San Joaquin River Delta and a regional groundwater depression centered about 4 miles east of Stockton (San Joaquin County Flood Control and Water Conservation District, Spring 1991) ' Published data from the San Joaquin Flood Control and Water Conservation District (Fall 1990) indicate that the average long term depth to groundwater at the site is approximately 60 feet below grade The continuing drought has, however, lowered water levels valley wide and at the site Current depth to groundwater at the site is approximately 68 feet below grade ' 4.0 PREVIOUS WORK ' 4.1 Underground Tank Removal On April 17, 1991, six underground storage tanks (USTs) were removed from the project site ' by RPSNA The USTs consisted of one 550-gallon diesel tank, two 2,000-gallon gasoline tanks, one 4,000-gallon gasoline tank, one 10,000-gallon gasoline tank and one 350-gallon waste oil ' tank Soil samples collected from beneath the gasoline and diesel tanks contained elevated levels of petroleum hydrocarbons Analytical results are summarized in Table 1 and sample locations ' are shown on Plate 2 1500471REP0RTSICAP 0694 FNL 3