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1.0 INTRODUCTION <br /> Conestoga-Rovers & Associates (CRA) prepared this document on behalf of Equilon <br /> Enterprises LLC dba Shell Oil Products US (Shell) in response to the August% 2011 <br /> letter from the San Joaquin County Environmental Health Department (EHD). In the <br /> above-referenced letter, the EHD requested that a contingency plan to remediate the <br /> source area of petroleum impacts to groundwater be submitted by September 30, 2011. <br /> This document summarizes the constituents of concern in groundwater, their <br /> concentration trends, the previous remedial activities, an evaluation of remedial <br /> alternatives, a recommended remedial approach, and a work plan for additional deep <br /> groundwater monitoring wells. <br /> 2.0 CONSTITUENTS OF CONCERN IN GROUNDWATER <br /> Historical groundwater monitoring data shows that the groundwater beneath the site <br /> has been impacted by petroleum hydrocarbons (total petroleum hydrocarbons as <br /> gasoline (TPHg), benzene, toluene, ethylbenzene, and xylenes (BTEX)). The fuel <br /> oxygenates methyl tertiary butyl ether (MTBE) and tertiary butyl alcohol (TBA) have <br /> been identified in groundwater starting in 1996; however, MTBE and TBA are not <br /> constituents of concern (COC) at this site due to their infrequent detection and low <br /> concentrations. <br /> As mentioned in CRA's June 10,2011 Updated Site Conceptual Model (SCM),groundwater <br /> monitoring data suggest that the extent of TPHg is defined to the west (MW-5), north <br /> (MW-2), northeast (MW-1), the east (MW-12), and to the south (MW-14 and MW-3). <br /> Benzene is defined to the west(NM-5),north (MW-2),northeast(MW-1), east (MW-12), <br /> southeast (MW-8), and south (MW-3). Toluene, ethylbenzene and xylenes are below <br /> their respective maximum contaminant levels (MCUs) in all wells except VEW-2, <br /> VEW-4,and VEW-7. <br /> 3.0 COC CONCENTRATION TRENDS <br /> CRA evaluated TPHg and benzene concentration trends in wells MW-3, MW-4, MW-7, <br /> MW-8, MW-12, MW-14, VEW-2, VEW-3, VFW-4, and VEW-7. Graphs were not <br /> prepared for the remaining wells because they did not contain detectable levels TPHg or <br /> benzene. Some of the wells that were not graphed have reported TPHg detections that <br /> have been classified as false positive detections due to the presence of tetrachloroethene <br /> 2403M(29) 1 CONESTOGA-ROVERS&ASSOCIATES <br />