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WESTERN GEO-ENGINEERS SECTION 8.0 DISCUSSION AND SUMMARY 1 Desert Petroleum has owned and operated the project site as a gas station facility since 1979, this site has been an active service station prior to Desert Petroleum ownership. On April 19, 1988 the station was undergoing remodeling for Desert Petroleum, Inc. The existing tanks, piping, islands, and overall station was to be upgraded and remodeled by Walton Engineering of West Sacramento, CA. Upon tank removal hydrocarbon odors were noticed and the construction operation was discontinued, except for removal of known contaminated soil from the tank excavation area; until assessment of the possible contamination to soil and water could be performed (see figure 4A and Appendix J). Tank removal was performed on this date in which four underground storage tanks were removed done regular gasoline, one unleaded gasoline, one super unleaded asoline and one waste oil . a $ 9 9 I� 9 ) Shortly after tank removal, Western Geo-Engineers along with Walton Engineering proceeded with the initial phase of the investigation by installing three 2 inch ground r water monitoring wells (MW 1 through MW 3) on May 5 and 6, 1988 on site (see figures 4A and Appendices A. H, K and L). These welts were installed to a total depth of 29 feet. Monitor well 1 was installed north and closest to the tank excavation and sampling showed ground water contamination with hydrocarbons. Monitor well 2 was installed southeast of the excavation behind the station builiding yum and Monitor well 3 was installed east of the excavation and pre-existing p p islands. Sampling of monitor wells 2 and 3 indicate no ground water contamination . exists in this area Soil samples taken from the base and sidewalls of the fuel tank excavation m 1 indicate that all soil contamination associated at on and from bor g i (MW ) with the fuel tanks was removed during initial tank removal. The waste oil tank excavation had to be re- excavated, a soil sample taken at the base of the original excavation indicated that soil contaminated with oil type hydrocarbons still existed. e- v it site was performed June 6 1888 under the The re-excavation anon of the waste ® p , supervision of Western Geo-Engineers and San Joaquin Local Health inspectors. The excavation at this time was expanded in anorth-south and east- west direction } r 't les taken at the base and deepened oximatel 1112 to 2 fee . The fou soil samples of each ) of the excavation indicate that all contaminated soil has been removed. Total hydrocarbon concentrations that were present in the soil at the fuel tank . excavation ranged from non-detected in the native soil left after excavation to 33 parts per millon, gasoline range, in the spoil soil pile. Total hydrocarbon concentrations that were present in the waste oil excavation ranged from non-detected in the re-excavation to 32 parts per million. motor oil range, in the original excavation. Hydorcarbon concentrations in the ground water exposed in the fuel tank excavation range from 20.5 parts per million in the north end and 77.7 parts per million in the south end, gasoline range, Hydocarbon concentrations in the soil taken from the borings (MW 1, 2 and 3) are non-detected. Hydrocarbon concentrations in the ground water sampled from the monitor wells range from non-detected in MW 2 & 3 and non-detected to 40 parts per million, gasoline range, in MW 1. No floating product was observed in the excavations or the monitor wells durinWestern Geo-Engineers investigation (other than the thin fluorescent skim bor from ing of MW#1). page 36 I