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y <br /> PROPOSED SCOPE OF WORK <br /> FOR <br /> SUBSURFACE INVESTIGATION <br /> AND <br /> REMEDIAL PLANNING STUDY <br /> Mobil Oil Corporation <br /> Former Service Station 10-NP4 <br /> Tracy Blvd. and Grantline Rd. <br /> Tracy, California <br /> INTRODUCTION <br /> This work plan presents the proposed scope of work to conduct <br /> a supplemental site investigation of subsurface contamination <br /> and remedial planning study at the former. Mobil Oil Station <br /> 10-NP4, located at the corner of Tracy Blvd. and Grantline <br /> Rd. , Tracy, California. The scope of work proposed herein <br /> was based on the results of the preliminary site <br /> investigation work completed to date to determine the extent <br /> of hydrocarbon contamination in the subsurface soil and <br /> ground water. <br /> The primary intent of the proposed supplemental investigation <br /> work and feasibility study is to: (1) obtain additional <br /> information to conduct the 5-step investigative process of <br /> RWQCB, (2) define the nature and extent of ground water <br /> contamination, and (3) develop the appropriate and <br /> cost-effective course of action for remediation. <br /> PROJECT BACKGROUND <br /> Following removal of four underground storage tanks at the <br /> site, . a preliminary assessment of potential subsurface <br /> contamination was undertaken in August 1986. Analysis of <br /> soil and ground water samples collected from the fuel tank <br /> area indicated the presence of detectable concentrations of <br /> petroleum hydrocarbon constituents. <br /> To determine the extent of subsurface contamination, four <br /> ground water monitoring wells were installed in September <br /> 1986. Ground water was encountered at a depth of about 7 <br /> feet below grade while the flow direction was determined to <br /> be towards the north/northeast . Dissolved hydrocarbon <br /> constituents were detected at levels higher than the <br /> established state drinking water standards in two of the <br /> water samples collected from the four monitoring wells. <br /> Hydrocarbon contamination of the soil was found to be limited <br /> to the subsurface zone above the shallow aquifer. <br /> 1 <br />