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.` California Regional Water Quality Control Board ` ' r <br /> Central Valley Region z, <br /> Terry Tamminen Robert Schneider,Chair a <br /> Secretary for Sacramento Main Office Arnold zenegger <br /> Environmental Internet Address: hup://www.swrcb.ca.gov/rwgcb5 Goovernvers or <br /> Protection 11020 Sun Center Drive 4200 Rancho Cordova,CA 95670-6114 <br /> Phone(916)464-3291 n <br /> 11 August 2004 RECEIVED <br /> AUG 1 6 2004 <br /> Mr. Bob Hopkins Mr. Jay Allen ENVIRONMENT HEALTH <br /> Union Oil Company of California Stone Brothers Management Company PERMIT/SERVICESILAMENTHEAL <br /> 276 Tank Farm Road,P.O.Box 1069 1024 W. Robinhood Dr. <br /> San Luis Obispo, CA 93406 Stockton,CA 95207 <br /> REPORT REVIEWS, CLEANUP AND ABATEMENT ORDER(CAO)NO. 5-00-707, FORMER UNOCAL <br /> STATION #5098 AT 5606 PACIFIC AVENUE,AND FORMER MONTGOMERY WARDS AUTO SERVICE <br /> AT 5400 PACIFICA VENUE,STOCKTON,SANJOAQUIN COUNTY, <br /> We reviewed the 12 July 2004 Updated Site Conceptual Model, Monitoring and Remediation Status Report, <br /> Second Quarter 2004 (Quarterly Report) and the 30 July 2004 Monitoring Well Installation Report and Summary <br /> of Efforts to Cease Plume Movement(Summary Report) submitted by ENSR International (ENSR) on behalf of <br /> Unocal. <br /> The Quarterly Report maximum contaminant groundwater concentrations in April 2004 were: total petroleum <br /> hydrocarbons as gasoline (TPHg, 17,000 gg/L),benzene(2,800 µg/L), ethylbenzene(930 Itg/L),toluene <br /> (490 µg/L),xylenes(3,000 µg/L), and methyl tert-butyl ether(0.81 µg/L). The Air Sparging system,repaired in <br /> June 2004,is currently operating. The Quarterly Report recommends restarting the soil vapor extraction(SVE) <br /> system,due to soil vapor contaminant concentrations rising up to three orders of magnitude in the SVE wells <br /> since shutdown in 2003 (for example,TPHg increased from 1.3 to 1,300 µg/L in SVE well VEW-IA). <br /> The Summary Report provides the soil and groundwater analytical data and boring logs for three new <br /> groundwater monitoring wells (MW-28 to MW-30)installed on 6 to 7 July 2004 to define the lateral extent of the <br /> expanding groundwater plume. The Summary Report fulfills the requirements of my letter dated 18 June 2004, <br /> requiring installation of the new monitoring wells by 15 July 2004 and a report of the limits of the groundwater <br /> plume by 1 August 2004. The Summary Report also recommends restarting the SVE system. <br /> Based on the reported rising concentrations in the SVE wells and my discussion with ENSR on 27 July 2004, <br /> we concur to the recommendation to restart the SVE treatment system. Please focus the SVE remediation on the <br /> SVE wells show g at least two orders of magnitude increase in 2004. <br /> You may call J es Barton at(916)464-4615 for questions or additional information. <br /> GORDON L E OGGS <br /> UST Progr anager <br /> cc: r. Mark Owens,UST Cleanup Fund, SWRCB, Sacramento <br /> Mr.Mike Infuma, San Joaquin County Environmental Health Division, Stockton <br /> Ms. Jill Tracy,Esq.,UNOCAL,Brea <br /> Mr. Ben Henningburg, ENSR International, Sacramento <br /> California Environmental Protection Agency <br /> Ca Recycled Paper <br />