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r � � <br /> HORIZON ENVIRONMENTAL INC. <br /> Specialists In Site Assessment,Remedial Testing,Design and operation <br /> April 10,2008 <br /> Mr. Michael J. Infurna Jr. <br /> San Joaquin County l <br /> Environmental Health Department <br /> 304 East Weber Avenue,Third Floor <br /> Stockton,California 95202-2708 <br /> Subject: Letter Work Plan for Additional Groundwater Investigation <br /> Quik Stop Station No. 39 <br /> 2285 East Fremont Street, Stockton,California <br /> Mr. Infurna: <br /> At the request of Quik Stop Markets(Quik Stop), Horizon Environmental Inc. (Horizon)has <br /> prepared this letter work plan for an additional groundwater investigation at the Quik Stop <br /> Station No. 39 (site) located in San Joaquin County, California. The work plan was <br /> requested by the San Joaquin County Environmental Health Department (SJCEHD) in the <br /> attached letter dated February 7,2008. <br /> The purpose of the proposed investigation is to evaluate the lateral extent of 1,2- <br /> dichloroethane (DCA) in groundwater in the south and southwest of wells MW-1 and MW- <br /> 2. This work plan was developed in general accordance with the Regional Water Quality <br /> Control Board (RWQCB) document Tri-Regional Board Staff Recommendations for <br /> Preliminary Invesligalion and Evaluation of Underground Tank Sites. <br /> Site Description and Background <br /> The Quik Stop site is a convenience market and retail gasoline station located on the <br /> northwestern corner of the intersection of East Fremont Street and E Street in a commercial <br /> and residential area of Stockton, California as shown on Figure 1. Structures and <br /> installations at the site include a station building, gasoline dispenser islands under a canopy, <br /> and two 12,000-gallon gasoline USTs as shown on Figure 2. The site elevation is <br /> approximately 22 feet above mean sea level (msl) and is underlain by alternating silty sand <br /> (SM)and clayey to sandy silt(ML)to approximately 61 feet below surface grade(bsg), <br /> Horizon has conducted quarterly groundwater monitoring at the site since December 1999. <br /> Monitoring data indicate groundwater flow directions have been variable under gradients <br /> ranging from 0.03 to 0.001. Monitoring data for first quarter 2008 indicated depth to <br /> groundwater of approximately 44 feet bsg and north to northwestward groundwater flow <br /> direction under a gradient of approximately 0.005 as shown on Figure 2. Monitoring data <br /> are summarized in Table 1. <br /> 4970 Windplay Drive,#C5 - EI Dorado Hills,CA 95762 • (916)939-2170 - FAX(916)939-2172 <br /> P.O.Box 5283 - Bakersfield.CA 93388 - (661)589-8389 - FAX(661)589-1456 <br />