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.` California Regional Water Quality Control Board <br /> vCentral Valley Region <br /> Alan C.Lloyd,PhD Robert Schneider Chair <br /> (a <br /> Secretary for Sacramento Main Office Arnold Schwarzenegger <br /> Environmental Internet Address: http://www.swrcb.ca,gov/rwgcb5 Governor <br /> Protection 11020 Sun Center Drive#200 Rancho Cordova,CA 95670-6114 <br /> Phone(916)464-3291 (� �/J <br /> 23 February 2005 H D D IS� 1% �D <br /> Mr. John Fray Mr. Jay Allen FEB 2 5 7005 <br /> Union Oil Company of California Stone Brothers Management Company ENVIRONMENT HEAUH <br /> 276 Tank Farm Road. 1024 W. Robinhood Dr. PERMIT/SERVICES <br /> P.O.Box 1069 Stockton, CA 95207 <br /> San Luis Obispo, CA 93406 <br /> REPORT REVIEWS, CLEANUP AND ABATEMENT ORDER(CAO)NO. 5-00-707,- <br /> FORMER UNION OIL COMPANY OF CALIFORNIA (UNOCAL)STATION#5098 AT <br /> 5606 PACIFIC AVENUE,AND FORMER MONTGOMERY WARDS AUTO SERVICE AT <br /> 5400 PACIFICA VENUE,STOCKTON, SAN JOAQUIN COUNTY, <br /> I reviewed the Updated Site Conceptual Model, Quarterly Monitoring and Remediation Status, Fourth Quarter <br /> 2004(4Q2004 Report) and the Ozone Sparging Bench Scale Testing Results Report(BST Report). Both reports <br /> were received 31 January 2004 and submitted by ENSR International (ENSR) on behalf of Unocal. Additionally, <br /> I met with ENSR staff at my office on 1 February 2005 to discuss project management and the above two reports <br /> (see enclosed Memorandum). <br /> The 4Q2004 Report provides quarterly groundwater analytical results from monitoring well samples collected <br /> between 19 and 22 October 2004, and groundwater analytical results of Reduction-Oxidation(Redox) analyses <br /> collected on 17 December 2004 to confirm whether natural attenuation of petroleum hydrocarbons is occurring in <br /> site groundwater. Maximum groundwater monitoring concentrations were reported from monitoring well MW-3 <br /> as: total petroleum hydrocarbons as gasoline(TPH-g), 23,000 micrograms per Liter(µg/L); benzene, 4,000 µg/L; <br /> ethylbenzene, 1,100 µg/L; toluene,2,400 µg/L; and xylenes, 3,800 gg/L. Redox results are typical of petroleum <br /> hydrocarbon release undergoing natural attenuation, in that the interior of the groundwater plume appears highly <br /> reduced(depleted in dissolved oxygen by biological activity), while groundwater outside of the plume appears <br /> slightly reduced. The 4Q2004 Report recommends: <br /> • Continued pulse (week on, week off) operation of the Air Sparging(AS) system. <br /> • Deleting ethane and ethene from the list of groundwater parameters for natural attenuation, since they do <br /> not relate to petroleum hydrocarbon degradation. <br /> • Move towards permitting of the modified Soil Vapor Extraction(SVE) system by San Joaquin Valley <br /> Air Pollution Control District(SCVAPCD). <br /> • Stop "...moving towards... "in-situ chemical oxidation(ozone injection—see review of BST Report). <br /> • Installing two additional air sparging wells, one near MW-3 and into MW-23S, to the Soil Vapor <br /> Extraction/Air Sparging(SVE/AS) Treatment System, to address deeper aquifer contamination <br /> emanating from UNOCAL's former station. <br /> I concur to all recommendations listed above from the 4Q2004 Report, except for the continued pulsing of the AS <br /> system. Your consultant notified me by email on 17 February 2005 that ENSR changed the AS system to <br /> continuous operation, which I approved(attached emails). Note that the SVE system was inspected by <br /> SCVAPCD and restarted on 17 February 2005. Also, in the meeting on 1 February 2005, ENSR agreed to submit <br /> the Workplan to install additional AS wells by 31 March 2005. <br /> California Environmental Protection Agency <br /> Co Recycled Paper <br />