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1 <br /> ARCADIS Ms. Kathryn Dominic ' <br /> August 24, 2010 <br /> • 500 mg/kg—Gross contamination ceiling value (Odors, etc)— ESL Table B-2 ' <br /> • 450 mg/kg—Direct contact exposures based on a target hazard quotient(HQ)of <br /> 0.2— ESL Table K-2 ' <br /> • 2,200 mg/kg— Direct contact exposures based on a target HQ of 1.0— ESL <br /> Table K-2 <br /> The ESLs summarized above are most applicable for determining the effectiveness , <br /> of biotreatment and for ensuring that post-remediation soil conditions are protective <br /> of human health and the environment. Therefore, the most current soil TPH-d data , <br /> collected in March 2010 are compared to alternative cleanup requirements proposed <br /> in this report. <br /> The ESL of 450 mg/kg is based on an HQ of 0.2 which is conservatively set to ' <br /> account for the possible additive effect of other CDCs. The ESL of 2,200 mg/kg <br /> accounts for potential exposure only to TPH-d. At this time, there are no other ' <br /> known COCs in biotreatment bed soils. Therefore, the ESL of 2,200 mg/kg is most <br /> applicable for comparison to biotreatment bed soil results in this case. <br /> Responses to RWQCB Requests in February 19, 2009 Letter ' <br /> This section summarizes previous data relevant to the former TPCA pond and the ' <br /> Biotreatment Beds and, where appropriate, presents the corresponding RWQCB <br /> request as outlined in the February 19, 2009 letter and appropriate justification for <br /> modifying the requested sampling of the Biotreatment Beds. Additional details and ' <br /> analytical data regarding this information are provided in the Work Plan. <br /> Volatile Organic Compounds(VOCs) ' <br /> VOC data collected during previous investigations relevant to the TPCA pond and <br /> the Biotreatment Beds include the following: ' <br /> • As documented in the 1994 Remedial Investigation(RI) Report(Industrial <br /> Compliance 1994a), several site wide investigations for VOCs have been ' <br /> completed. VOCs contamination has been attributed to a source or sources other <br /> than the TPCA pond. As stated in the 1994 Feasibility Study(FS) Report(Industrial <br /> Compliance 1994b), VOCs are found primarily in soil and groundwater around the ' <br /> engine house and former concrete pad areas. <br /> • Since 1990, site groundwater wells have been regularly sampled for VOCs. In ' <br /> March 2009, VOCs were below detection limits in wells sampled. <br /> I <br /> Page: <br /> 4/12 ' <br />