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3 <br /> E.A �. <br /> WI RODUCTION <br /> The following report presents the results of an investigation to evalu- <br /> ate the affectiv-ness of a gasoline recovery system located at the ARCO <br /> service statir. 3 located at, 908 Benjamin }colt Drive in Stockton, Cali <br /> fornia (see Figure 1). The report includes (1) a description of the <br /> regional and local hydrogeologic setting, (2) a review of EMCON's <br /> previous site investigation, (3) a discussion of the installation of the <br /> remedial-action system, (4) evaluation of the systems performance, and <br /> (5) conciusions and recommendations. A brief site history follows. <br /> Or. May 24, 1984 a broken leak detector was discovered in a submersible <br /> pump near the tank complex. The leak reportedly ,resulted in an <br /> estimated loss of 2,000 gallons of gasoline. As a result of the loss, a <br /> site investigation. was irnediately initiated by EMCON and Gettler-Ryan <br /> in late May 1984. All piping was tested, and the underground tanks and <br /> surrounding soil fill were excavated. Nei tanks were installed in the <br /> IF same area on June 1, 1984. <br /> ` r <br /> ti EMCON's site investigation consisted of drilling,12 exploratory wells to <br /> determine the local hydrogeologic conditions (` .e., geology, ground- <br /> water flow direction, and extent of hydrocarbon contamination). <br /> Floating product was detected in seven wells varying in thickness from <br /> .16 to over 3 feet. Based on the results of the investigation- a hydro- <br /> carbon recovery well was ins:;alled in late July 1984 to remove the <br /> floating product on top of the ground-,rater table. <br /> ' The results of EMCON's investigation show that the recovery well is <br /> propes,ly functioning and capturing floating product beneath the ARCO <br /> service station. Documented product recovery has been approximately <br /> 640 gallons since the loss was discovered. An unknown amount of product <br /> may have been recovered during tank replacement activities. Currently <br /> small amounts (1/4 inch or less) of floating product have been detected <br /> in five monitoring wells. Total dissolved gasoline constituents in <br /> wells without floating product range from 430 to 80,000 parts per <br /> billion (ppb) in:the:-other:wel-ls: <br /> PX) 438-22.04 1 <br /> Mon Associates <br />