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k encountered in the excavation at about 9.25 feet below grade. Strong hydrocarbon odors were noted in the open excavation and a sheen was observed on the surface of the water in the excavation. stained, Gravel fill removedmingwas otthe observled onstheiexcavation walls A ut hydrocarbon staining b total xylenes. water sample collected from the pit contained 1.1 pp Y The pea gravel containing fuel hydrocarbons was returned to the excavation. Three monitoring wells (MW-1 through MW-3) were installed between August 12 and 14, 1987 (Figure 1-3), No petroleum hydrocarbons were detected groundwater any romof these subsequentsduring sampling oflthe activities or in the gran wells. eMarch 12 and 15, 1988, eleven soil samples were collected from one-half to one foot below the concrete slab and analyzed for r In o10, 1988 to Gordon Boggs of the Centrai Valley letter dated June Regional Water Quality Control Board (CVRWQCB), WA requested permission the on to leave the concrete slab in the excavation argued that analytical results of the March 1988 soil sampling. � an hydrocarbons, which had leaked from the tanks, had migrated laterally and downward away from. the edges of the slab and are the southwestern corner of the contained in soil adjacent to - excavation. WA removed s soil al Between July sand g way along the outhen and western wallof the excavation to a ! depth of 24 feet. In a proposal to the county datec'i November 22, 1988, Precision Instruments of Stock oval in December 988, the entirel on of the excavation. Upon app excavation was backfilled. 989, Western Geologic lon w Resources, Inc. Inas performed by y September near the former ltank another investigation w locations. Six boreholes were drilled(B-10 through B-15) from which soil samples were collected for chemical analysis (Figureof the Groundwater was observed at 26.8 feet below gr boreholes (B-10) was completed as a four-inch monitoring well (MW-4). Groundwater samples from wells MW-1 through MW-4 were collected on October 3, 1989. The soil analytical results are summarized in Table 1-1. Total purgeable petroleuin hydrocarbons(TPes from 25 to raze feet below #2, were detected only in the soil P - - _ grade in borings B-111 B-14, and B-15,_located-on_t�e andt�,400 ppm, - nd south sides of the former tank locations at 28 pp pp 12