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ERI <br /> ENVIRONMENTAL RESOLUTIONS, INC. <br /> July 14, 1997 <br /> (� ERI 205503.W02 <br /> Mr. Ed Ralston �JN <br /> Tosco Marketing Company11 <br /> �Q f� <br /> p <br /> 2000 Crow Canyon Place, Suite 400 <br /> San Ramon, California 94583 <br /> Subject: Work Plan for Supplemental Environmental Investigation at Unocal Service Station <br /> 5886, 2701 March Lane, Stockton, California. <br /> Mr. Ralston: <br /> At the request of Tosco Marketing Company (Tosco), Environmental Resolutions, Inc. (ERI) is <br /> submitting this work plan describing the tasks to further evaluate soil and groundwater conditions at <br /> and in the vicinity of Unocal Service Station 5886 in Stockton, California. The purpose of the work <br /> is to evaluate the extent of residual and dissolved methyl tert-butyl ether (MTBE) in soil and <br /> groundwater detected beneath the site. The San Joaquin County Public Health Services Department, <br /> Environmental Health Division, requested Tosco submit a plan to investigate and abate any potential, <br /> suspected, or known discharges of hazardous materials including petroleum hydrocarbons and <br /> delineate the extent of MTBE detected beneath the subject site. <br /> To abate a potential on-site source of MTBE, and as requested by the San Joaquin County Public <br /> Health Services Department, Tosco recently decommissioned on-site drains which were installed at <br /> the site during reformatting in 1995. <br /> Tasks for the present investigation will be performed in a phased approach. The tasks include: 1) <br /> obtaining and reviewing any available MTBE data from previous investigations; 2) performing two <br /> additional groundwater monitoring and sampling events and interpreting the data to further evaluate <br /> the extent of dissolved MTBE in groundwater and select additional well locations (if necessary); 3) <br /> drilling three soil borings adjacent to former drains; 4) obtaining appropriate permit(s) and access <br /> agreement(s), drilling off-site soil boring(s); collecting soil samples; constructing groundwater <br /> monitoring well(s); developing and purging the new well(s); collecting groundwater samples; <br /> analyzing selected soil and groundwater samples; and 5) preparing a report. <br /> BACKGROUND <br /> The site is immediately west of Interstate I-5 on the northwestern corner of March Lane and the I-5 <br /> offramp in Stockton, California, as shown on the Site Vicinity Map (Plate 1). The locations of <br /> existing underground storage tanks (USTs), dispenser islands, and other selected site features are <br /> shown on the Generalized Site Plan (Plate 2). Properties in the vicinity of the site are generally <br /> occupied by commercial developments. <br /> 74 Digitai Drive,Suite 6, Novato, California 94949 415-382-9105 (FAX 415-382-1856) <br /> Irvine • Novato • Seattle <br />