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California lVional Water Quality Cool Board <br /> Central Valley Region <br /> v Katherine Hart, Chair e.. <br /> Arnold <br /> Linda S. Adams 11020 Sun Center Drive#200;Rancho Cordova,California 95670-6114 chwarzenegger <br /> Secretary for Phone(916)4643291 •FAX(916)464-4645 RECEIVE Governor <br /> Environmental nttp://vwvw.waterboardS.Ca.govicentralvalley <br /> Protection <br /> NOV 0 5 2010 <br /> 3 November 2010 <br /> ENVIRONMENTAL HEALTH <br /> Mr. Ja <br /> Ms. Stephanie McKenna y Allen PERMIT/SERVICES <br /> Chevron Environmental Management Company StonP Brothersfic Avenue, Suite Management Company <br /> 6001 Bollinger Canyon Road 5757 <br /> San Ramon, CA 94583 Stockton, CA 95207 <br /> DOCUMENT REVIEW, MONTGOMERY WARDS AND UNOCAL STATION#5098, 5400-5606 <br /> PACIFIC AVENUE, STOCKTON, SAN JOAQUIN COUNTY, CASE NOS. 390258 AND 390014 <br /> 1 reviewed the Semi-Annual Groundwater Monitoring and Remediation Status Report for Third Quarter <br /> 2010 (Report) received 2 November 2010 from Chevron Environmental Management's consultant <br /> AECOM. The Report provides the results of the 27 August 2010 groundwater monitoring event. <br /> Maximum groundwater monitoring results were total petroleum hydrocarbons as gasoline, <br /> 500 micrograms per Liter(ug/L); benzene, 56 ug/L; toluene, 15 ug/L; ethylbenzene, 16 ug/L; and <br /> xylenes, 44 ug/L. Groundwater flow direction varied from northeast to southeast, and gradients varied <br /> from 0.020 ft/ft to 0.064 ft/ft by aquifer zone (A/B, C, and D). The Report recommends discontinuing <br /> semi-annual monitoring and permanently shutting down the soil vapor extraction/air sparging treatment <br /> system. <br /> The recommendation to discontinue semi-annual monitoring is approved with the condition that a <br /> closure report is submitted before the next monitoring report is due on 30 April 2011. If a closure <br /> report is not received by the due date, then semi-annual monitoring will resume during the second <br /> quarter of 2011. 1 have discussed the requirements for the closure report with AECOM, and was <br /> informed that a schedule for submittal of the closure report would be provided in the soil vapor risk <br /> assessment report that is due 3 December 2010. However, due to potential soil vapor threats that <br /> were identified by two rounds of vapor sampling outside of the bank now occupying the former Unocal <br /> site, the decommissioning of the soil vapor extraction/air sparging system is postponed until completion <br /> of my review of the risk assessment. At that time, I will approve or disapprove the second request. <br /> You may contact me regarding questions by phone at(916) 464-4615; or by e-mail at <br /> ibarton(a�waterboards.ca.gov. <br /> James L.L. Barton, P.G. <br /> Engineering Geologist <br /> cc: Judy Reid, SWRCB, UST Cleanup Fund (Commingled Plume Program), Sacramento <br /> Mike Infurna, San Joaquin County Environmental Health Division, Stockton <br /> Nichole Gleason, Downey Brand, 621 Capitol Mall, 18"' Floor, Sacramento 95814 <br /> Breda Miller, AECOM, 1220 Avenida Acaso, Camarillo 93012 <br /> Jim Brake, Geocon Inc., 3160 Gold Valley Dr., Ste. 800, Rancho Cordova 95742 <br /> California Environmental Protection Agency <br /> 0 Recycled Paper <br />