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California&gional Water Quality Cobol Board <br /> Central Valley Region = <br /> Katherine Hart, Chair ( k .' <br /> Linda S.Adams '� '' Arnold <br /> Secretary for 11020 Sun Center Drive#200, Rancho Cordova,California 9567 �ahwerzenegger <br /> Environmental Phone(916)464-3291 •FAX(916)464-4645 Governor <br /> Protection http:lMrvw.waterboards.ca.gov/centralvalley FEB. O 3 2010 <br /> 2 February 2010 ENVIRONMENT HEALTH <br /> PERMIT/SERVICESMs. Stephanie McKenna Mr. Jay Allen <br /> Chevron Environmental Management Company Stone Brothers Management Company <br /> 6001 Bollinger Canyon Road 1024 W. Robinhood Dr. <br /> San Ramon, CA 94583 Stockton, CA 95207 <br /> DIRECTIVE LETTER, MONTGOMERY WARDS AND UNOCAL STATION#5098, 5400-5606 <br /> PACIFIC AVENUE, STOCKTON, SAN JOAQUIN COUNTY, CASE NOS. 390258 AND 390014 <br /> On 21 January 2010, representatives from Chevron Environmental Management Company (Chevron), <br /> their consultant AECOM, Downey Brand representing Stone Brothers Management Company (SBMC), <br /> their consultant Geocon Inc. (Geocon), and Regional Board staff (staff) met to discuss the rebound <br /> testing of the soil vapor extraction/air sparging (SVE/AS) treatment system, and steps needed to move <br /> the case towards closure. AECOM stated that when rebound occurred in October 2009, the SVE/AS <br /> system was restarted and ran until 28 December 2009, when a second rebound test was initiated. <br /> Chevron proposes restarting the SVE/AS system if the February 2010 groundwater data exceed the <br /> 2009 maximum concentration of 30,000 micrograms per Liter (ug/L) for total petroleum hydrocarbons <br /> as gasoline (TPHg); or start biosparging mode (no SVE and low air pressure to AS) if concentrations <br /> reach TPHg, 2,000 ug/L and benzene, 40 ug/L. They will stop treatment if groundwater concentrations <br /> are below biosparging levels. Staff concurred with the AECOM's proposal as reasonable, and <br /> reserved final approval for stopping SVE/AS pending review of the February 2010 data, and added that <br /> if the February data shows slightly higher, equal to, or lower than proposed biosparging mode <br /> concentrations, the Responsible Parties may submit a no further action report with applicable additional <br /> rationale why case closure is appropriate, including an evaluation of risk from vapor intrusion to the <br /> current building occupants and future workers. Staff also suggested that AECOM might want to <br /> conduct limited quarterly monitoring to speed up the closure process. <br /> Review of all data indicates that are a couple of data gaps: 1) potential soil vapor intrusion (discussed <br /> above), and 2) lack of delineation in Robinhood Drive. Chevron replied that it is their policy to not <br /> expose their consultants to potential traffic hazards, but will provide an agreement for Geocon (Stone <br /> Brothers consultant) to conduct the requested work on behalf of Chevron. Regional Board staff agreed <br /> that these actions (further investigation and on behalf agreement) are reasonable and necessary. <br /> Therefore, in order to expedite the case towards closure in a timely, cost-effective manner, by <br /> 26 February 2010, please submit a workplan for soil vapor investigation for the all potential areas of <br /> concern, such as the Macaroni Grill (former Wards) and the bank (former Unocal), and for a direct <br /> push soil and groundwater investigation under Robinhood Drive. You may contact me regarding <br /> questions by hone at (916) 464-4615; or by e-mail at ibartonCcilwaterboards.ca.gov. <br /> James L.L. Barton, P.G. <br /> Engineering Geologist <br /> California Environmental Protection Agency <br /> C1*Recycled Paper <br />