SITE INFORMATION AND CORRESPONDENCE

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Di Salvo-Lathrop Hydropunch Letter �., March 11,1995 Page-.z- On May 6, 1994, a total of 3 soil samples were collected following over-excavation of soil along the east sidewall of the former locations of TK3, TK4 and TK5 One soil sample was collected from the floor of the over-excavation at a depth of approximately 15.5 feet b s. Two soil samples were collected from the east sidewall approximately 15 feet bgs and approximately 12 feet apart. Laboratory analyses of the soil sample collected from the floor of the over-excavation detected 6.2 ug/kg toluene and 10 gg/kg xylene. Total I petroleum hydrocarbons quantified as kerosene, diesel and motor oil were not detected at or above the reported laboratory detection limits in the soil sample tolled ed from the floor of the over-excavation. Laboratory analyses of the soil samples collected from the e ist sidewall indicated no evidence of hydrocarbon contamination at or above the reported laboratory detection imits. No petroleum staining, odors or OVA readings were noted during the over-excavation. Based or.-the results of field observations and laboratory analyses, Condor concluded that the lateral extent of soil contamination at the site had been evaluated. the complete descriptions of the results of the UST removal and the over-excavation are in Underground Storage Tank Removal - Soil Sampling Results, Condor Earth Techn logies, Inc., October 14, 1993, and Over- excavation Soil Sampling Results, Condor Earth Technologies, Inc., June 21, 1994, respectively. DISCUSSION The draft version of the Water Quality Site Assessment for Soil and Groundwater (WQSA document) prepared by the California Regional Water Quality Control Board, Central Valley Region (CRWQCB,CVR), states that a contaminate detected in soil does not threaten water quality if the soil leachate concentration for that sample is less than or equal to the background groundwater concentration, regardless of whether background is greater than or less than the numerical water quality limit. The May, 1993, Recommended Limiting Water Quality Goals for Components of Petroleu -Based Fuels prepared by the CRWQCB indicates that, for the hydrocarbon constituents detected at the Di Salvo - Lathrop site, the following water quality goals are applicable: benzene = 1.0 gg/l, toluene = 42.0 gg/l, ethyl benzene = 29.0 gg/1 and xylene = 17 pig/1 hydrocarbon mixtures of kerosene and diesel— 10 g/l for lifetime health advisory. To evaluate if hydrocarbon constituents detected in the soil may leach into groundwater, a soil sample collected from above the water table, may be analyzed using Title 22 CCR Waste Extraction Test (WET). By performing a WET on a soil sample collected from above the water table, a quantitative assessment of the leachable hydrocarbon constituents that present a risk to gr undwater quality can be assessed. The detectable `� CONDOR