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0 • <br /> California Regional Water Quality Control Board <br /> Central Valley Region <br /> Robert Schneider,Chair <br /> Terry Tamminen Arnold Schwarzenegger <br /> Secretary for Sacramento Main Office Governor <br /> Environmental Internet Address: http://www.swrcb.ca.gov/rwgcb5 <br /> Protection 11020 Sun Center Drive#200 Rancho Cordova,CA 95670-6114 ^ ��r �.� <br /> Phone(916)464-3291 II��JJUlllllll L <br /> 5 November 2004 NOV 0 8 2004 <br /> Mr. John Fray Mr. Jay Allen ENVIRONMENT HEALTH <br /> Union Oil Company of California Stone Brothers Management Company PERMIT/SERVICES <br /> 276 Tank Farm Road. 1024 W.Robinhood Dr. <br /> P.O. Box 1069 Stockton, CA 95207 <br /> San Luis Obispo, CA 93406 <br /> WORKPLAN APPROVAL AND REPORT REVIEWS, CLEANUP AND ABATEMENT ORDER(CAO) <br /> NO. 5-oo-7o7,FORMER UNOCAL STATION#5098 AT 5606 PACIFIC AVENUE,AND <br /> FORMER MONTGOMERY WARDS A UTO SERVICE AT 5400 PACIFIC AVENUE, STOCKTON, <br /> SANJOAQUIN COUNTY, <br /> I reviewed the 3 November 2004 Work Plan to Evaluate Potential SVE/AS System Enhancements and Additional <br /> Well Installation within the Deeper Aquifer Units(Workplan)and 29 October 2004 Updated Site Conceptual <br /> Model, Quarterly Monitoring and Remediation Status, Well Installation, and Well Destruction Report, Third <br /> Quarter 2004 (3Q2004 Report), submitted by ENSR International(ENSR)on behalf of Unocal. I also reviewed <br /> the 8 October 2004 MW-1 Redevelopment Report(MW-1 Report), submitted by GHH Engineering Ino. (GHH)on <br /> behalf of Stone Brothers Management Company. <br /> The Workplan proposes a time schedule that correlates to the dates listed in my 4 October 2004 Letter Request to <br /> evaluate additional enhancements to the existing treatment systems, and the installation of monitoring wells <br /> MW-31 and MW-32, in order to better define the plume limits and flow direction of groundwater in the C-zone <br /> and D-zone within the footprint of the Former Montgomery Wards Auto Service(Wards). The Workplan states <br /> that the Air Sparging(AS)well AS-26 airflow rate was adjusted downward to prevent further movement of the <br /> B-zone groundwater plume to the north and east of Former Unocal Station#5098 (Unocal). <br /> The 3Q2004 Report provides groundwater results from monitoring well samples collected from <br /> 14 to 22 July 2004. Total Petroleum Hydrocarbons (TPH) as gasoline and benzene groundwater concentrations <br /> increased in the treatment area at Wards (MW-1 through MW-9) and to the north and east of Unocal (MW-14 <br /> and MW-18D). As a result of my 18 June 2004 Notice of Violation,three new monitoring wells (MW-28 through <br /> MW-30)were installed to redefine the limits of the groundwater plume at Wards. On 24 September 2004,the <br /> Soil Vapor Extraction (SVE) System was restarted and the AS System reverted from pulsed operation back to <br /> continuous operation. ENSR conducted monthly groundwater sampling and analysis on selected monitoring <br /> wells in August and September of 2004,to facilitate better understanding of the hydrodynamics of the restarted <br /> SVE/AS systems. Due to pending new construction,MW-9R was installed and MW-9 was abandoned on 16 <br /> August 2004. An attempt to rehabilitate MW-1,which was contaminated by intrusion of a parking lot oil-based <br /> sealant, occurred on 22 September 2004. <br /> The MW-1 Report stated that redevelopment activities (scrubbing and groundwater purging) failed to remove all <br /> traces of the oil-based sealant. MW-1 confirmation analyses reported TPH as motor oil (TPHmo)in the primary <br /> (1,900 µg/L)and split(5,500 µg/L)groundwater samples. TPHmo was not present in MW-1 prior to the <br /> incident. <br /> California Environmental Protection Agency <br /> CO Recycled Paper <br />