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Ms Vicki McCartney Project No 8800401A 0201 <br /> iOctober 26, 2004 <br /> Page 5 <br /> Based on the analytical results for both soil and groundwater samples collected to <br /> date, the primary contaminants appear to be gasoline constituents Material <br /> Safety Data Sheets (MSDSs) for unleaded gasoline are included in Appendix B <br /> The MSDS sheets describe the physical and chemical characteristics of the fuel <br /> and its components <br /> ■ An estimate o the mass o contaminants remaining in soil and groundwater <br /> f f g <br /> Appendix C contains calculations of total mass of dissolved TPHg, benzene, and <br /> MtBE in groundwater beneath the site These calculations are based on <br /> groundwater analytical data collected on August 12, 2004 Since the majority of <br /> dissolved hydrocarbons appear present in the sand horizon between <br /> approximately 28 to 40 feet bgs, the volumes used for mass calculations are <br /> based on a zone 15 feet thick The average concentrations used in the <br /> calculations are based on the mean of each contoured zone in Figures 3 through <br /> 5, or an approximate mean if only one or no data points were in the zone, which <br /> may slightly overestimate the actual concentrations present in that zone The <br /> total mass of dissolved TPHg, benzene, and MtBE in groundwater is <br />' approximately 0 52, 0 031, and 0 57 pounds, respectively <br /> ■ Identification of applicable cleanup levels for affected or threatened <br /> groundwater and surface water, and a rationale for selecting these levels %JYA SIW"s <br /> California RWQCB water quality goals (W& re 50 µg/l for TPHg, 1 0 µg/l <br /> for benzene, 42 pgll for toluene and, y nes, 29 µg/l for ethylbenzene, and <br /> 13 µg/l for MtBE The WQGs are based on taste and odor threshold levels, not <br />' on levels that pose a threat to human health Because the hydrocarbon/oxygenate <br /> plume beneath the site is limited in extent and it is very unlikely that <br /> groundwater within this area will be used as a drinking water source, these <br /> clean-up levels do not appear appropnate for this site <br /> i <br /> r <br />! N 1sacDPQ0041Pr1188018800401A 4ad doc Shaw Environmental,Inc <br />