SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Moore Petroleum y Page 2 of 2 5491 F Street August 5, 2010 Banta, California Monitoring well MW-18 was installed to confirm detection of total petroleum hydrocarbons quantified as motor oil (TPHmo) detected in grab groundwater samples obtained from cone penetration testing (CPT) borings CPT-1 at 78 feet below surface grade (bsg) and CPT-2 at 28 feet bsg, 2 feet bsg, 57 feet bsg and 78 feet bsg. Due to high groundwater usage in the immediate area, the EHD considered it necessary to evaluate the CPT data before closure consideration for your site. Failure to detect any CDCs in MW-18, screened at 60 to 80 feet bsg, the most intensely impacted depths in CPT-2, indicates to the EHD that the contaminant is not likely to be present at detectable concentrations at that depth and may represent cross- contamination from TPHmo encountered at shallower depth. By inference, the same would apply to the THmo detected in CPT-1 at 78 feet bsg. The EHD discussed the status of your site with a representative of the Central Valley Regional Water Quality Control Board (CVRWQCB) on 14 July 2010; the representative agreed with the EHD that preparation of a site closure summary report (SCSR) would be appropriate at this time. Therefore, if the results of the confirmation soil gas sampling event and associated vapor intrusion evaluation are favorable, you are directed to prepare and submit an SCSR to the EHD. The results of the soil gas sampling event can be rolled into the SCSR or submitted as a separate report. The SCSR should follow the guidance provided in the Tri-Regional Guidelines, Appendix A, issued by the CVRWQCB. In addition to the information elicited by Appendix A, the SCSR should also address the following issues: • Total residual mass in soil; • Comparison of residual COCs concentrations against the Environmental Screening Levels (ESLs) established by the San Francisco Bay Regional Water Quality Control Board and against the California Human Health Screening Levels (CHSSLs) established by the Office of Environmental Health Hazard Assessment, to assess the risk and hazard to human health posed by the residual contaminant masses; • Estimated time to achieve water quality objectives (WQOs) for any CDCs currently exceeding WQOs; and • The results and conclusions from rebound testing following suspension of soil vapor extraction and ozone sparging. If any of the above noted issues have already been addressed, AEI can simply reference the report and restate the main conclusion or interpretation in the SCSR. Questions or comments may be directed to Nuel Henderson at (209) 468-3436. Sincerely, V-14-7 i�' Nuel C. Henderson, Jr., PG Adrienne Ellsaesser, REHS Engineering Geologist Acting Program Coordinator C: J. Barton, PG —CVRWQCB; 11020 Sun Center Dr. #200, Rancho Cordova, CA 95670 D. Lafontaine, PE —AEI; 11244 Pyrites Way, Gold River, CA 95670 Directive Letter 0810