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{ E Pacific Gas&Electric Co. Page 4 - - ' The low levels of petroleum hydrocarbons reported in:the native soil beneath the tanks does not suggest a high residual concentration of,petroleum hydrocarbons present:This condition is interpreted as.a low potential for • groundwater impact,therefore,we believe that there is no need for groundwater<investigation at this time-. U Based upon this assumption,we propose that PG&E excavate approximately five additional feet of soil from the bottom of the tank removal pit.Dames&Moore could arrange for:excavation"equipment to accomplish this task at the site if so requested by PG&E. Since the tank removal sampling analyses reported such low levels of hydrocarbons present,it seems likely that.the limited additional excavation"could achieve the removal of remaining low-level petroleum hydrocarbons in the soil within the tank removal area At the culmination of the overexcavation a set of soil samples which duplicate the original sampling could be obtained from the tank pit bottom to evaluate the effectiveness of:this effort.In the event non-detected results are obtained in these"samples from laboratory analyses;the excavation could be backfilled and properly compacted,and excavated soils could be disposed of in a proper manner. U In the event the soil samples obtained'from the limits of the over-excavation continue to report detectable levels t..l of hydrocarbons,-the tank pit will need to be backfilled in-order to provide access for drilling equipment: Drilling will be necessary to evaluate the vertical and horizontal distribution of residual petroleum hydrocarbons. In this eventuality,we propose to advance three"exploratory soil borings directly through the backfilled tank ° removal pit location,to:a maximum depth of 40 feet below.the existing grade.The tank removal excavation will need to be backfilled in order to allow drilling equipment access to the area which requires'investigation.The proposed I ; soil boring locations have been selected to assess the vertical and lateral migration of petroleum hydrocarbons from the previous.tanks at the site. The samples from these soil borings should confirm if limited contamination' conditions exist. The proposed exploratorysoil'borings locations are shown on the site plan which:is.included as Figure 2 of this proposal. The purpose of those soil borings would be to provide data regarding the presence of Proposal Stockton Service Center i �,; DAMES-6i MOORS '.