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1 <br /> ' ARCADIS Ms. Kathryn Dominic <br /> November 5, 2010 <br /> ' TPH-d cleanup goals were based on a VLEACH model developed to calculate the <br /> maximum allowable TPH-d soil concentrations, as described in the, "Pre-Excavation <br /> ' Soil Investigation Results for OU-3 and OU-4 Technical Memorandum, Union Pacific <br /> Railroad Company, Former Tracy Maintenance Facility," prepared by ARCADIS and <br /> dated May 2, 2008 (ARCADIS 2008). The VLEACH model results suggested that <br /> ' TPH-d concentrations of 11,300 milligrams per kilogram (mg/kg) or less in shallow <br /> soil are protective of groundwater. <br /> ' Following a similar approach, a site-specific VLEACH model was developed to <br /> assess whether TPH-d in the biotreatment beds would impact groundwater for this <br /> Site at a concentration that would exceed beneficial use protective concentrations <br /> ' (beneficial use protective concentration is 100 micrograms per liter[Ng/1] based on <br /> Environmental Screening Level for TPH-d [SFRWQCB 2008]). <br /> ' Results from the site-specific VLEACH model indicate that the proposed TPH-d <br /> cleanup goal concentration for soil (2,200 mg/kg)would result in a TPH-d <br /> concentration in groundwater less than 41 pg/I. Furthermore, results from the <br /> ' VLEACH model indicate that the maximum concentration of TPH-d in soil (620 <br /> mg/kg) detected during the biotreatment bed investigation would result in a TPH-d <br /> concentration in groundwater less than 12 ug/I. Both VLEACH model simulations <br /> demonstrate that TPH-d concentrations in soil are incapable of leaching to <br /> ' groundwater at levels that exceed the beneficial use protective concentration (100 <br /> pg/1).A summary of the site-specific VLEACH model is included in Attachment 1. <br /> ' In addition, TPH-d has not been detected in samples collected from groundwater <br /> wells located near the biotreatment beds and TPH-d has not been detected in <br /> samples collected from,wells MW-4A and MW-5A(which are located within the <br /> ' biotreatment bed boundary) since March 2003. <br /> Therefore, TPH-d affected soils remaining in the biotreatment bed appear to be <br /> incapable of leaching to groundwater at levels that exceed beneficial use protective <br /> concentrations based on the site-specific VLEACH model and soil and groundwater <br /> sampling results for the Site. <br /> ' RWQCB Comment Summary tables and discussion of historical sampling results for <br /> semi-volatile organic compounds (including PAHs and naphthalene) and metals in <br /> ' soil and groundwater in the biotreatment area must be provided. This information is <br /> necessary to support the claims made in the Report that these compounds are <br /> present below cleanup goals, or(in the case of metals)are consistent with samples <br /> ' collected elsewhere on site. <br /> Page: <br /> PWRGpS DfldPIGxbA[WaWmn FxNOPeYOWtCfi9-i,ery ANIFm10MMre,61M]AI0.1181o0emnwA OM B�msa IOAW00010MAmL0e65JITGy%1115-1u1 3/ <br /> 1 <br />