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1117 Lone Palm Ave., Suite B <br /> Modesto, California 95351 <br /> www.atc-enviro.com <br /> 209.579.2221 <br /> r{ a s s o c a a r e s i N c Fax 209.579.2225 <br /> July 30, 2002 <br /> 54.17292.0002 <br /> Mr. Jeff Wong <br /> San Joaquin County Environmental Health Department <br /> 304 E. Weber Street, Third Floor <br /> Stockton, California 95202 <br /> Subject: Mass Balance of Petroleum Hydrocarbons, Stagg High School, 1621 Brookside <br /> Road, Stockton, California <br /> Dear Mr. Wong: <br /> ATC Associates Inc., on behalf of the Stockton Unified School District, has prepared this letter <br /> report the mass balance for the subject site (Figures 1 and 2). <br /> • <br /> Mass Balance Calculations <br /> Using the analytical results from the subsurface investigations presented in Table 1, ATC <br /> estimated the lateral extent of TPHg concentrations in the unsaturated zone beneath the site as <br /> depicted on Figure 2. The isoconcentration shown on Figure 2 was then used by ATC to perform <br /> mass balance calculations to estimate the mass of TPHg impacted soil. The total mass of TPHg <br /> originally present in the soil is estimated to be approximately 47 kilograms. Since benzene and <br /> methyl tert butyl ether (MTBE) have not been detected in soil, the total mass of benzene and <br /> MTBE remaining in the soil is estimated to be less than one tenth of a kilogram. Toluene, <br /> ethylbenzene, and total xylenes were detected at low concentrations. The total mass originally <br /> present in the soil is estimated to be less than 5 kilograms. Since petroleum hydrocarbons were <br /> not detected in groundwater samples for the previous four sampling events, the mass balance of <br /> TPHg, benzene, toluene, ethyl benzene, xylenes, and MTBE does not represent a concern to the <br /> site. Mass balance calculations are included in Attachment 1. j <br /> w Awordpro117292.00021reportslmass_bal_rpt.doc <br /> ENVIRONMENTAL, GEOTECHNICAL AND MATERIALS PROFESSIONALS <br />