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- - _ AMM <br /> s <br /> Harding Lawson Associates <br /> f VII CONCLUSIONS <br /> a� <br /> Our interpretations of data collected during Phases I, II, and III have <br /> Yielded the following conclusions concerning hydrogeologic conditions and <br /> distribution of gasoline constituents chemicals at the 455 West Grant Eine <br /> Road site. <br /> j 1. On the basis- of our review of the distribution of gasoline consti- <br /> tuents in the area of the tanks, we conclude that the tank leak <br /> identified in November, 1986, appears to be the primary cause of the <br /> presence of free-phase gasoline on-site. <br /> 2• Naparently gasoline constituents are migrating northeast toward the <br /> sit, boundaries. <br /> 3. The upward hydraulic gradient caused by artesian pressure in the <br /> shallow sand stratum will inhibit free-phase gasoline from moving <br /> into this zone. Free-phase gasoline will probably migrate horizon- <br /> tally at or near the top of the capilsa,;y fringe, somewhere in the <br /> clayey sails above the shallow sand `stratum. 6 <br /> 4. Because oft x <br /> he artesian-induced upward gradient in the shallow sand <br /> h stratum, gasoline can only migrate down into the sand zone, through a <br /> diffusive (molecular) process that occurs at."the gasoline-water <br /> interface. The magnitude of the gasoline,constituents that can <br /> i <br /> therefore reach the sand zone is believed to be relatively small. <br /> $° 5, Because of the shallow ground water and the artesian condition in the <br /> f, sand stratum, we conclude that .a French drain in conjunction with <br /> a <br /> some.pumping from the tank backf ill would-be feasilble methods for <br /> a` source control. A pumping test is required to help determine the . <br /> oetimal <br /> �> approach. <br /> 12 <br /> - I � <br />