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14. "1 quantities is believed to first occur beneath the site at an estimated depth of 90 to 100 feet (Department of water Resources, ilistorical Groundwater Levels in San Joaquin County - April 1990) . Beneficial uses of groundwater in this area include domestic supply and agricultural supply. Criteria established in the Leaking Underground Fuel. Tank Field Manual (LUFT Manual - 1989) wera used as a guideline in determining the potential environmental impact on grourlwater at the site. Table 2-1 from the LUFT Manual, Leaching Potential Analysis for Gasoline and Leaching Potential Analysis for Diesel [using Total Petzoleum Hydrocarbons (TPH) and BTEX) I was designed to permit estimating concentrations of TPH and BTEX that can be left in place without threatening groundwater. A summary of the site evaluation data for LUFT analysis shows the following: the depth to groundwater is between 90 and 100 feet; average annual precipitation is less than 25 inches per year; there are no man- made conduits which increase vertical migration of leachate; and no qualifying unique site features or subsurface fractures are present in the soils beneath the site. summation of the "scores" (see Figure 5) for these site features indicate that the maximum allowable levels of contamination that can be left in place is 100 ppm for gasoline-range hydrocarbons and .3 ppm, .3 ppm, 1 ppm, and 1 ppm for benzene, toluene, xylenes, and ethylbenzene, respectively. None of the verification soil samples from borings B1, B2, and stockpiles SP-1 and SP-2 exceed these levels. Verification soil sample VS-1, from the 30 foot level of the TP-2 excavation, was also below the LUFT Manual action levels. Eastern sidewall sample VS-2 indicated that only the toluene (2.0 ppm) and xylenes (3.0 ppm) exceeded the allowable levels. The residual hydrocarbons associated with tank pit TP-2 appears to be largely limited to the shallow (30 to 35 feet) soils along the eastern sidewall of the excavation. Because the depth to groundwater in this region may exceed loo feet and since the impacted area will be paved with asphalt (eliminating much of the potential for rain water infiltration) TPE believes that adverse impact to the underlying groundwater is unlikely.