ARCHIVED REPORTS BIOTREATMENT BEDS POST REMEDIATION INVESTIGATION REPORT

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' ARCADIS Ms. Kathryn Dominic August 24, 2010 ' Soil TPH-d concentrations were also compared to alternative cleanup requirements (e.g., SFB-RWQCB ESLs)as previously discussed. Two soil samples (HA-5 and ' HA-6) collected at 1 ft bgs exceed the ESL of 500 mg/kg for gross contamination and the risk-based ESL of 450 mg/kg based on an HQ of 0.2. However, all 12 TPH-d sample results are well below the risk-based ESL of 2,200 mg/kg that is based on a HQ of 1. As discussed previously, the ESL of 2,200 is most applicable in the absence of other CDCs and industrial land uses. In addition to the direct comparison of soil sample results to these cleanup requirements, the 95% upper confidence limit of the mean (95% UCL)concentration was also calculated for comparison. Use of the 95% UCL is appropriate for sample ' populations greater than S; 12 samples are available for this calculation. The 95% UCL was calculated using the US Environmental Protection Agency ProUCL (Version 4.00.05) statistical software (USEPA 2009). The 95% UCL for TPH-d in the ' 12 soil samples is 417 mg/kg, which is below the more stringent ESL of 450 mg/kg based on a HQ of 0.2. ' In summary, the maximum detected concentration of 620 mg/kg is well below the ESL of 2,200 mg/kg, which is based on an HQ of 1, and the 95% UCL concentration ' of 417 mg/kg is lower than the ESL of 450 mg/kg, which is based on an HQ of 0.2. These comparisons demonstrate that current soil conditions do not pose an environmental or human health risk. ' As shown in the data validation report included in Appendix D, analytical data were reviewed by CRA and no data qualifiers were assigned as a result of the data review. ' Conclusions ' Based on the results of the post remediation investigation, the biotreatment of the TPCA pond soil/sludge was effective, has not adversely affected the environment, and has achieved the substantive requirements of the CAO based on the following information: Soil TPH-d residuals remaining in surface soils within the biotreatment beds are not leaching into deeper subsurface soil and groundwater based on results from the ' several recent groundwater sampling events and post-remediation soil sampling. Although TPH-d was detected in biotreatment bed soil samples, there is a general Page: ' 9/12