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Former Beacon Station No 12419 June 27,2002 <br /> Stockton California Groundwater Groundwater Monitoring Re ort <br /> t (BTEX), and the fuel oxygenates methyl-tert-butyl ether (MTBE), diisopropyl ether (DIPE), <br /> • ethyl-butyl ether (ETBE), tert-amyl methyl ether (TAME), tert-butanol (TBA), methanol, <br /> ethanol, 1,2-dichloroethane (EDC) and 1,2-dibromoethane (EDB) by Environmental <br /> Protection Agency(EPA) Method 8260B <br /> I <br /> Groundwater Monitoring Results <br /> Depth-to-groundwater measurements were subtracted from the surveyed TOC elevations to <br /> calculate groundwater elevations Groundwater elevation data were used to construct a <br /> groundwater contour map as shown on Figure 2 <br /> Groundwater analytical results are summarized in Table 1 Benzene concentration data from <br /> this sampling event were used to construct a benzene isoconcentration map as shown on <br /> Figure 3 Copies of the Iaboratory data sheets and chain-of-custody documents are included <br /> as Attachment C <br /> Recommendations <br /> Horizon recommends continued quarterly monitoring be performed to evaluate trends in the <br /> groundwater gradient and concentrations of dissolved hydrocarbons over time Horizon is <br /> developing a revised Problem Assessment Report / Corrective Action Plan for the site which <br /> describes the nature and extent of petroleum hydrocarbons in soil and groundwater, and <br /> • contains recommendations for remedial actions <br /> f <br /> Report Distribution <br /> We recommend a copy of this report be forwarded to <br /> Mr Michael J Infurna, R E H S Mr Gordon Boggs <br /> Environmental Health Division CRWQCB - CentraI Valley Region <br /> San Joaquin County Public Health Services 3443 Routier Road, Suite A <br /> P O Box 2009 Sacramento, California 95827-3098 <br /> Stockton, California 95201 <br /> If you have any questions, please contact Horizon at (916) 939-2170 <br /> Sincerely, <br /> HORIZON ENVIRO r �� <br /> yV REXFORD K SMITH l <br /> 0 530 (( , <br /> Rexford Smith `�.� Flo;�� Craig J Roth <br /> Registered Geologist No t`7�f CA��E� Staff Geologist <br /> 419gmr02Q2 doc <br /> 141945 2 HORIZON ENVIRONMENTAL INC. <br />