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w r <br /> KEI-J86-084 <br /> September 12 , 1986 <br /> Page 3 <br /> LABORATORY ANALYSES <br /> Soil and water samples were submitted to the Sequoia Analytical <br /> Laboratory for chemical analyses . Samples were analyzed using <br /> EPA methods 5020, 8010 and 8020. Results of the analyses as <br /> reported by Sequoia Analytical Laboratory are attached . The <br /> analytical results are summarized in the accompanying Table 1 . <br /> ANALYTICAL RESULTS <br /> Analytical results indicate that gasoline constituents are <br /> present in the shallow ground water. Ground water analyses <br /> indicate low to moderate concentrations of dissolved gasoline <br /> constituents are present in wells MW-3 and MW-4. The <br /> concentrations in well MW-3 and MW-4 exceed minimum Department of <br /> Health Services (DOHS) drinking water standards , and Regional <br /> Water Quality Control Board guidelines. Dissolved gasoline <br /> constituents were non detectable in wells MW-1 and MW-2. <br /> CONCLUSION <br /> No free product was observed in any of the wells, and dissolved <br /> gasoline constituents were evident in two wells (MW-3 and MW-4) <br /> only. According to the City of Tracy Utility Department , the <br /> shallow ground water is of poor quality and has very limited use <br /> (i.e. used for irrigation only) . The City of Tracy and local <br /> agricultural industries rely on their water source from a deeper <br /> aquifer which extends to a depth greater than 400 feet and some <br /> exceed 1000 feet. <br /> The presence of moderate concentrations of gasoline constituents <br /> in the shallow ground water , in our opinion, does not pose any <br /> public health risk. An extensive clay deposit, known as corcoran <br /> clay , overlies the deeper confined fresh water aquifer . <br /> Gasoline contamination of soil on the site is restricted to the <br /> subsurface zone between the ground surface and a depth of 7 feet. <br /> Therefore , it is unlikely that gasoline contamination of the <br /> lower aquifer has occured or would occur from vertical migration. <br /> The extent to which possible lateral , downgradient migration of <br /> contaminated ground water has occurred is unknown and may require <br /> further investigation. <br />