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1.11, %.a <br />HORIZON ENVIRONMENTAL INC. <br />'• �� Specialists in Site Assessment, Remedial Testing, Design and Operation <br />May 5, 2012 F?ECEIVED <br />Mr. Harlin Knoll MAY 0 8 2012 <br />San Joaquin County Environmental Health Department <br />600 East Main Street EN AEANMENTAL 11Stockton, California 95202-3029 M►7�5ER.� <br />VICE$ <br />Subject: Work Plan for DPE Well Installation and Soil Gas Investigation <br />Abdelwahed Facility, Ultramar Site No. 13792 <br />2255 South Airport Way, Stockton, California <br />Mr. Knoll: <br />On behalf of Ultramar Inc. (Ultramar), Horizon Environmental Inc. (Horizon) is submitting <br />this work plan for installation of a dual-phase extraction (DPE) well, a contingency DPE <br />remediation event and a soil gas investigation (SGI) at the subject site (Site). Horizon and <br />Ultramar introduced the premise for similar work at this and other sites overseen by the San <br />Joaquin County Environmental Health Department (EHD) during a meeting with EHD staff <br />on 27 June 2011. The EHD requested that proposals for work be formalized in a work plan. <br />Horizon recommended this work in the Fourth Quarter 2011 Groundwater Monitoring / <br />Remediation Status Report dated 11 January 2012, <br />Site Description and Background <br />The Site is located in San Joaquin County, California as shown on Figure 1. Current Site <br />features include the former station building in the western portion of the Site as shown on <br />Figure 2. There are eleven groundwater monitoring wells (MW -1 through MW -4 and MW -6 <br />through MW -12), five vapor extraction wells (VW -1 through VW -5) and two sparge wells <br />(SW -1 and SW -2) associated with the Site as shown on Figure 2. Wells MW -6, MW -7, <br />MW -10, MW -11 and MW -12 are located off site to the east and south. Monitoring well <br />MW -5 was destroyed in March 2008. <br />The site was operated as retail gasoline station circa 1964 to 1981. Formerly, multiple <br />underground storage tanks (USTs) were installed in a common basin in the southern portion <br />of the Site and former dispenser islands were located in the eastern portion of the Site. The <br />Site, including the former station building, has been and currently is used as an auto repair <br />shop. <br />Groundwater monitoring has been conducted since first quarter 2004 with the most recent in <br />November 2011. Depth to groundwater was approximately 33 feet below surface grade <br />(bsg) and the groundwater flow direction was eastward under a gradient of approximately <br />0.001 as shown on Figure 2. An analytical summary is shown on Figure 3. <br />4970 Windplay Drive, #C5 • EI Dorado Hills, CA 95762 • (916) 939-2170 • FAX (916) 939-2172 <br />PO. Box 5283 • Bakersfield, CA 93388 • (661) 589-8389 • FAX (661) 589-1456 <br />