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_ <br /> ze a <br /> .t R[SNA Cnmp,,,nr' t'jY0rwwWr'hd1 Soludiun.s <br /> Through Applied Science, <br /> &ghwerh q A Construcfrun <br /> :1 I6•t Geld Grmtl D1 M.,tiuilc 20D <br /> Kanrho Cordova,CA 97)6711 <br /> I'Itnne'91fi} <br /> r/1X f9161 8i2-6{fff� <br /> December 18. 1991 <br /> Mr. Bob Boust <br /> Unocal Corporation <br /> P.O. Box 5155 <br /> San Ramon. California 94583 <br /> Subject: Quarterly Ground-Water%lonitoring,fourth Quarter 1991,at Former Unocal <br /> 5 Pacific Avenue. Stockton, California. <br /> Service Station No. 2859. 166 <br /> *.vIr. Sisk: <br /> This report summarizes rte results of the fourth quarter 1991 groundwater monitoring that <br /> RESNA Industries (RESNA, formerly Applied GeoSysterns) conducted at the request of <br /> Unocal Corporation (Unocal) at the subject site. Tile site location is shown on tite Site <br /> Vicinity :Flap (Plate 1). The purpose of quarterly sampling is to monitor changes in <br /> concentrations of dissolved gasoline hydrocarbons in the ground water and changes in the <br /> ground-water gradient. <br /> The work for this monitoring phase included subjectively analyzing ground water in two <br /> monitoring wells (wells NIW-4 and AIW-5) and collecting and analyzing ground-water <br /> ft samples for dissolved hydrocarbon constituents. We did not collect water samples from <br /> wells MW-1 through MW-3 or measure depths to water because these wells were dry. As <br /> a result, we could not evaluate the groundwater gradient beneath the site. The locations <br /> of the monitoring wells are shown on the Generalized Site Plan (Plate 2). � <br /> BACKGROUND <br /> Five soil borings were drilled at the site in January 1988 as part of a subsurface <br /> environmental investigation conducted by J.H. Kleinfelder & associates (Kleinfelder) of <br /> hat investigation <br /> dicated that <br /> present int <br /> tsoil ulnderlying he site (Klults of teinfelder, March 3, 198S. ReportlNor24 20815ocarbonre <br /> 01). <br /> p <br /> Applied GeoSystems began an environmental investigation in conjunction with underground <br /> storage tank removal in March and April 1988. During this investigation, a geologist <br /> observed removal of the underground storage tanks and collected soil samples for laboratory <br /> analysis of hydrocarbons. Results of analyses indicated that hydrocarbons were present in <br /> 1112rsis <br /> „x 38012-7 <br />