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Mr. James Barton,PG 25 July 2013. Page 2 previously operated and removed, from the Site have been -adequately investigated. In response to Comment 3, Geosyntec proposes a third location for soil vapor sampling in the forthcoming investigation, located east of the pump house near the groundwater sample from 2006 labeled `B-21" (see Figure 4 of Work Plan). The location of the proposed soil vapor sample, as well as the sample locations originally proposed in the Work Plan, are presented in the attached Figure 1. , The need for any additional soil gas .samples in the future will be evaluated based upon the results from the forthcoming investigation and the historical sub-slab and soil vapor data. (2) Clarification of the maximum soil concentrations reported in the CPT-13 Area Investigation Report and Work Plan The table summarizing the maximum soil concentrations observed during the CPT-13 Area Investigation presented on page 2 of the RWQCB's comments to the Work Plan should be revised as follows: ' Concentration Drinking Water Non-Drinking Constituent Location/Depth (mg/kg) ESL(mg/kg) Water ESL(mg/kg) Toluene CO—15'bgs 3,070 2.9 9.3 Naphthalene CO—15' bgs 0.0168 1.2 4.8 Xylenes CO—15'bgs 1.63 2.3 11 Benzene B1+-20'bgs 0.0152 0.044 1.2 ESL = May 2013 San Francisco Bay Region Water Quality Control Board EnvironmentalScreening Level for Leaching Concerns(Table G) (3) Confirmation of the List of Analytes in the Forthcoming Investigation With regard to the analyte list, groundwater and soil samples will be analyzed by EPA Method 8260, and soil vapor samples will be analyzed by EPA Method TO-15; benzene, xylenes, and naphthalene, in addition to toluene, are included in the analyte lists for both methods. Addendum 2 to CPT-13 Area Investigation Report and Work Plan engineers I scientists I innovators