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r k` KEI-P86-084A-1 April 15 , 1987 Page 3 LABORATORY ANALYSES Soil and water .samples were submitted to the Sequoia Analytical Laboratory for chemical analyses . Samples were analyzed using EPA methods 5020, 8015 , 8020 and 602 . Results of the analyses as reported by Sequoia Analytical Laboratory are attached . The analytical results are summarized in the accompanying Table 1 . DISCUSSION The analyses of groundwater samples from the six wells indicated presence of dissolved gasoline constituents in all wells except well I.1W-1 which continued to show non-detectable levels . A comparison of the data for well MW-4 for- February , 1987 and September , 1986 showed a significant decrease in dissolved hydrocarbon concentrations. This decrease may be due to adsorption , dilution and natural degradation . As indicated in our previous report , the presence of dissolved gasoline constituents in the shallow groundwater in our opinion does not pose any public health risk. The shallow groundwater is not used for domestic purposes , as the City of Tracy and local agricultural industries rely on a deeper confined aquifer for their useable water . The deeper aquifer occurs at depths ranging from 400 feet to over 1 , 000 feet . In summary , it is obvious from our recent investigation that the shallow groundwater has been impacted with dissolved hydrocarbons beyond the property . However , at this time , we do not feel that Mobil Oil Corporation should undertake full scale cleanup of the shallow groundwater for the following reasons . 1 . It is unclear whether the Mobil Service Station is the primary source of impact . Since there are two other service stations within 100 feet of the Mobil property , it is conceivable that inadvertent spillage from these stations may have occurred and impacted the shallow water table .