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27 <br /> • 7-Eleven/Stockton <br /> November 1989 <br /> SOIL-v7EN`f SYSTE14 <br /> Four vapor-extraction points are located near the <br /> e connected to a high-vacuum vapor- <br /> underground tank pit and arremove <br /> control system designed to ventilate the ubsurf <br /> soil. The four points are daremanif°lded <br /> hydrocarbon vapors from the <br /> -adsorption canisters todecrease <br /> air <br /> to four vapor-phase carbon r million (pPm <br /> emissions to levels below 1.o part Pe ) volatile <br /> organics, which is deemed acceptable by the San Soaquin county <br /> Air pollution Control District. <br /> The soil-vent system is currently operational and is <br /> vapors at an approximate flow rate of go-cubic feet <br /> withdrawing prefilter, vapor-phase <br /> Iyer minute (cfm) . Monitoring of the two <br /> carbon canisters with a photo-ionization detector (piD) is <br /> -• rbon breakthrough. Upon <br /> conducted weekly for detection of ca <br /> detection of hydrocarbon vapors in the emissions from the two <br /> prefilter carbon canistersreplaced. Spent <br /> , the can are <br /> prefilter carbon canisters at thesite <br /> 21er1989p1aThasomel <br /> th°d f <br /> August 20, September 7, and Sem <br /> emission treatment and monitoring ensure� that mntheewotfinal <br /> hydrocarbons are emitted to the atmosphere <br /> carbon canister's in the soil-'vent system. <br /> SUhIIKARY <br /> During this reporting period, one monitoring-well cluster <br /> ing well were installed. Sestuthate <br /> face <br /> and one individual monitorthe <br /> materials encountered during <br /> the recant drilling suggest <br /> subsurface stratigraphy at the site is composed °f two distinct <br /> dominated by laterally <br /> sequences. The upper sequence is <br /> is marked <br /> t its base by <br /> continuous permeable sand intervals and unit. The alower sequence <br /> -` a highly permeable gravelly coarse son <br /> iikul SIr111:E'.et <br /> a., TLIH�erE.rrta Iii <br />