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1 <br /> Idlewild Market <br /> July 2, 1996 <br /> Page -2- <br /> ethyl benzene at the capillary fringe is 0 8 µg/ml dissolved, 1 0 µg/g adsorbed, and 0 23 }tg/cm3 air in <br />' pores (see Ethyl Benzene, attached) The primary MCL for ethyl benzene, as defined in the California <br /> Code of Regulations, Title 22, Drinking Water Regulatory Criteria, is 0 7 µg/ml <br />' Xylene <br /> I Xylene was modeled using two simulations The first simulation for xylene was a 50 year run with <br /> volatilization at 0 2 and without applying a degradation rate The second simulation for xylene was a 30 <br /> year iun using a degradation rate of 1% of the published biological degradation rate for xylene (attached) <br /> and volatilization at 0 2 The input values for biodegradation for xylene were 0 0000192/day in <br /> groundwater and 0 0002476/day in soil <br /> SESOIL predicted that it would take approximately 16 to 22 years for xylene to reach the capillary fringe <br /> for both simulations, regardless of biodegradation The predicted concentration of xylene without <br /> biological degradation, at the capillary fringe is 10 0 µg/ml dissolved, 6 3 µg/g adsorbed, and 2 5 µg/cm3 <br /> air in pores (see Xylene, No Bio-Rate,attached) The predicted concentration of xylene, with degradation, <br />' at the capillary fringe is 1 65 µg/ml dissolved, 1 0 µg/g adsorbed, and 0 4 µg/cm3 air in pores (see Xylene, <br /> Bio-Rate 1 0% attached) The primary MCL for xylenes, as defined in the California Code of <br /> Regulations, Title 22, Drinking Water Regulatory Criteria, is 1 75 dig/ml <br /> CONCLUSIONS <br /> IThe results of the SESOIL modeling indicate that without biological degradation and with 0 2 <br /> volatilization, toluene, ethyl benzene, and xylene, would reach the capillary fringe, within approximately <br /> 12 to 45 years at concentrations exceeding their respective primary MCL's as defined in the California <br /> Code of Regulations, Title 22, Drinking Water Regulatory Criteria The results of the modeling are based <br /> on the assumption that no surface pavement exists at the site A sensitivity analysis for a biological <br /> degradation rate was run using a degradation rate of 0 01 or I% of the published rate for xylene The <br /> results yielded a concentration of xylene at the capillary fringe, below the primary MCL(Xylene Bio-Rate <br /> 1%, attached) Similar results are obtained with toluene and ethyl benzene utilizing 1% of their respective <br /> Ipublished biological degradation rate <br /> RECOMMENDATIONS <br /> Condor's recommendations, provided in the report titled "Sesoil Modeling Results, Fate and Transport <br /> I within the Vadose Zone", dated May 23, 1996, remain unchanged The upper portion of the excavation <br /> should be filled with road base material Compaction testing should be performed after the placement of <br /> the road base to ensure the structural integrity of the backfill All compaction and paving work should <br /> be conducted by a licensed contractor Upon completion of the site paving, on behalf of the property <br /> owner, Condor requests that the site be closed <br /> If the excavated area is not paved, Condor recommends that a groundwater fate/transport and risk <br /> assessment study be conducted In addition, a receptor survey should be conducted to determine if there <br /> L� CONDOR <br />