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�� <br /> Working To Restore Nature <br /> nature of the aquifer material results in high well yields Specific capacities of wells completed <br /> in the older alluvium average 42 GPM/ft (USGS Professional Paper, 1401-D, 1989) <br /> iRegional groundwater flow in the site area is generally in a northwesterly direction, toward the <br /> San Joaquin River Delta and a regional groundwater depression centered about 4 miles east of <br /> ' Stockton (San Joaquin County Flood Control and Water Conservation District, Spring 1991) <br /> Published data from the San Joaquin Flood Control and Water Conservation District (Fall 1990) <br /> indicate that the average long term depth to groundwater at the site is approximately 60 feet <br /> below grade The continuing drought has, however, lowered water Ievels valley wide and at the <br /> ' site Current depth to groundwater at the site is approximately 68 feet below grade <br /> 4.0 PREVIOUS WORK <br /> On April 17, 1991, six underground (u/g) storage tanks were removed from the project site by <br /> RESNA Industries Inc (RESNA) The u/g tanks consisted of one 550-gallon diesel tank, two <br /> 2,000-gallon gasoline tanks, one 4,000-gallon gasoline tank, one 10,000-gallon gasoline tank, <br /> ' and one 350-gallon waste oil tank Soil samples were collected in accordance with PHS/EHD <br /> guidelines and analyzed for one or more of the following, benzene, toluene, ethylbenzene, <br /> xylenes(BTEX), total petroleum hydrocarbons as gasoline(TPHg), total petroleum hydrocarbons <br /> as diesel (TPHd), organic lead, and the metals cadmium, chromium, lead, and zinc, by Sequoia <br /> ' Analytical Laboratories, Inc , utilizing appropriate EPA and DHS methodologies The tank <br /> removal sampling points are depicted on Plate 2 The analytical results are summarized on <br /> Table 1. The presence of elevated concentrations of hydrocarbons in the soil samples collected <br /> from beneath the gasoline and diesel tanks indicated further investigation was necessary to <br /> ' determine the lateral and vertical extent of soil contamination at the project site <br /> On October 16 and 17, 1991, RESNA personnel advanced one angle and five vertical soil <br /> bonngs to assess subsurface conditions at the project site (Plate 2) Analytical results of <br /> 1 15004718-WIS94 FNL 3 <br />