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Ms. Vicki McCartney Project No. 8800401A.0201 <br /> October 26, 2004 <br /> Page 5 <br /> Based omthe 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 of the mass of contaminants remaining in soil and groundwater. <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 /> 1 l 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 /> i 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; 0.03 1, 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. 31jsi's <br /> 1 California RW <br /> QCB water quality goals G(W are 50 µg/1-for TPHg, 1.0 µg/1 <br /> f �� 9 µg/1 for eth lbenzene <br /> for benzene, .42 µg/1 for toluene andA�ynes, y , and <br /> 13 µg/1 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 appropriate for this site. <br /> -t <br /> 1 <br /> i_ <br /> N:IsacDP12oo41Pr�1sso1s8004o1A.4ad.doc Shaw Environmental,.Inc. <br />