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'#eh. ,+> _ ,.-a - - - ' <br /> WWIRa ME <br /> IN <br /> f <br /> SUMMARY OF FINDINGS AND RECOMMENDATIONS <br /> • Gasoline initially migrated radially outward from the tank <br /> source an unknown distance beyond the property limits. <br /> e The extraction system is operating properly and has a <br /> radius of influence (capture) of approximately 100 feet. <br /> This well appears to influence the majority of the impacted <br /> area (on and off site). <br /> a Since activation of the extraction system in August 1984, <br /> floating product thickness at the site has been reduced <br /> from over 3 feet, to nearly non-detectable. <br /> e little or no additional floating product is anticipated to <br /> be captured by the extraction system. However, high <br /> concentrations of dissolved constituents still remain in <br /> most site monitoring walls. <br /> A review of data from nearby water supply wells indicates a <br /> moderately low potential for migration of contaminated <br /> s water to deeper water supply aquifers. <br /> a Based on the findings of this investigation EMCON recom- <br /> mends the following course of action: (1) sample nearby <br /> - water supply wells for gasoline constituents as a precau- <br /> ".� tionary measure, and (2) continue operation of the <br /> extraction system until acceptable clean-up limits of both <br /> floating and dissolved gasoline can be established with the <br /> Regional Water Qualitv Control Board. <br /> HYDROGEOLOGICAL SETTING <br /> The City of Stockton is located in the San Joaquin Valley which is <br /> underlain by alluvial sedime'A s up to 1,000 feet thick. The principal <br /> source of recharge to the ground water in the valley is the Sierra <br /> Nevada mountains to the east. According to the Department of Water <br /> Resources Bulletin 146, ground water historically flowed from the base <br /> of the Sierra Nevada Mountains westward,;towards the San Joaquin Sacra- <br /> mento River delta. However, increased municipal use of ground viater in <br /> Stockton has developed a ground-water depression changing the regional <br /> gradient away from the delta and towards the municipal wells. This has <br /> �i <br /> caused an easterly migration of poor quality saline ground water from <br /> �. . PJD 438-22.04 2 <br /> emco(l Ass0d0t9s <br /> u <br />