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i 1444 MARIPOSA ROAD WKA No. 2938 07 January 18, 2001 Page 5 informed us that the water obtained from the well is used for domestic purposes and was recently tested. Our response to the San Joaquin County Pubhc Health Services Department's inquiry regarding the disposition of the previously stockpiled soil generated from the former underground storage tank(UST)excavation is as follows• • On October 29 and November 2, 1992 our firm observed the excavation of approximately 1,500 cubic yards of soil from the vicinity of the former underground storage tanks • On December 1, 1993 a workplan addendum was submitted to SCPHSD discussing our proposal to put the stockpiled soil back into the UST excavation • Based on analytical results of stockpile soil samples, Mr Michael Collins of SJCPHSD suggested that the stockpiled soil be used to backfill the excavation with the understanding that a soil venting system be installed in or adjacent to the excavation . The excavation was backfilled with this approved soil in January of 1994. A soil venting system was constructed in the excavation prior to and during backfilling procedures. The soil venting system consisted of three horizontal, perforated squares o£4-rich diameter PVC pipe laid on the bottom of the excavation in a bed of pea gravel The squares were approximately 15 feet on each side and were plumbed to the surface each with a 4-mch diameter perforated PVC nser. The risers were surrounded with a 12-inch diameter,removable collar that was filled with pea gravel as the excavation was backfilled with the on-site soil Lifting the pea gravel-filled collar as the excavation was backfilled essentially provided a gravel pack around a vertical well. Once the excavation was backfilled to subgrade depth(approxunately 2 feet below top of asphalt),the vertical risers were plumbed to a common location, a shut off valve was installed then the three soil venting squares described above were mamfolded together Use of the shut off valves enabled each circuit of the soil venting system to be control independently once a vacuum was applied to the system. Use of the originally excavated material for backfill was documented in our December 15, 1993 Prelinunary Investigation and Evaluation Report and was reiterated in our September 6,2000 Request for Site Closure Report. i