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_ California Regional Water Quality Control Board Central Valley Region Robert Schneider, Chairr*, C Lloyd PhD Arnold Schwil aeggei Secretary For Sacramento Maui Off cer� Governor Environmental Internet Address hnp Ywww swrcb ca gov/rwycb5 DEC G 7 2004 Protection 11020 San Center Dnve#200 Rancho Cordova,CA 9567MI 14 Phone(916)464-3291 23 December 2004 Mr Bob Hopkins Mr Jay Allen Union Oil Company of California Stone Brothers Management Company 276 Tank Farm Road 1024 Vii Robinhood Dr P 0 Box 1069 Stockton, CA 95207 San Luis Obispo, CA 93406 REPORT REVIEW, CLEANUP AND ABATEMENT ORDER (CAO)NO. 5-00-707, FORMER UNOCAL STATION #5098 AT 5606 PACIFICA VENUE,AND FORMER MONTGOMERY WARDS AUTO SERVICE AT 5400 PA CIFIC A VENUE, STOCKTON, SAN JOAQUIN COUNTY, I reviewed the 3 December 2004 Remedial System Evaluation/Comparative Analysis of Changes in Contaminant Concentrations, Distribution and Mass within the Aquifer Beneath the Site (Report), submitted by ENSR International (ENSR) on behalf of Unocal The Report reviews the performance of the current soil and groundwater remediation system, consisting of Soil Vapor Extraction (SVE) and Air Sparging(AS), in order to recommend potential remediation system enhancements or modifications for accelerating site closure The Report states the US Army Corps of Engineers(USACE) guidelines were followed in writing the document The Report also references a quantitative profiling method, the RCP-4 Showcase Pilot, Region 4, An Eiczeni Method for Demonstrating Plume Stability (USEPA Guidance) developed by Veliscol Chemical Corporation for the groundwater cleanup at the US Environmental Protection Agency's Veliscol Superfund Site in Memphis, TN The Report-referenced 3 USACE guidance documents,In-situ Air Sparging Subsurface Performance Checklist, Vapor Extraction Subsurface Performance Checklist and Remedzation System Evaluation Checklist (USACE Checklists) Comment 1) The Report is incomplete The USACE Checklists were not included in the Report, nor was the USEPA Guidance While I was able to download the USACE Checklists and USEPA Guidance from the Internet,I could not complete the USACE Checklists with the information provided in the Report In a phone conversation on 16 December 2004, Ben Heningburg, ENSR promised to provide the completed USACE Checklists as soon as possible Please provide the completed USACE Checklists by 31 December 2004 ENSR utilized SURFER®Version7, Golden Software, a computer contouring program cited in the USEPA Guidance, to graph groundwater analytical results of specific contaminants of concern and calculate the volume and average concentration for each contaminant, to provide evidence for a determination whether the groundwater plume exhibited stability between 1998 and 2004 Because the USEPA Guidance requires at least three monitoring wells in each zone (not present in C- and D-zones) and detectable contaminant concentrations (not present in A-zone) to produce contaminant contours, the spatial (plume area, volume and average concentration) and temporal (annual) trends were only calculated for the B-zone ENSR designated 5 µg/L Benzene and 60 gg/L Total Petroleum Hydrocarbons as Gasoline for the lowest value concentration contour The Report graphically depicts the central mass of the existing groundwater plume (Figures B-15 & B-16) as being under Robinhood Drive (Figure 3), in an area currently not within the radius of influence of the existing SVE/AS remediation system The Report states the average contaminant concentrations have declined in the two montns following the restart of SVE The Report cautions that SVE has not operated for sufficient duration to evaluate SVE perform?nce although preliminary data shows a declining trend similar to startup in prior years, with a recent California Environmental Protection Agency ��y Recycled Paper pr.l n(�4 n , y}01