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California*egional Water Quality Co*1 Board <br /> Central Valley Region &; „ <br /> Karl E.Longley,ScD,P.E.,Chair N11 "I''11 tt ;� . ,,.„.. <br /> Linda S.Adams 11020 Sun Center Drive#200,Rancho Cordova,California 9567 1 I'�� U Arnold <br /> EnvSecironmental <br /> Schwarzene <br /> Environmental Phone(916)4643291•FAX(916)464-4645 gger <br /> Protection http://www.waterbowds.ca.gov/centralvalley SEP 1 0 2009 Governor <br /> 8 September 2009 ENVIRONMENT HEALTH <br /> PERMIT/SERVICES <br /> Ms. Stephanie Furgal 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 /> DOCUMENTS 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 Quarterly Groundwater Monitoring and Remediation Status Report and Updated Site <br /> Conceptual Model for Second Quarter of 2009 (2Q2009) and Proposed Remediation System Rebound <br /> Testing Schedule (Rebound Test), received 13 July 2009 and 3 September 2009, respectively, from <br /> Chevron Environmental Management Company consultant AECOM Environment (AECOM). The <br /> 2Q2009 reported the groundwater concentration for Total Petroleum Hydrocarbons as gasoline <br /> (TPHg), at 110 micrograms per Liter (ug/L). During the second quarter of 2009, the soil vapor <br /> extraction/air sparge (SVE/AS) system removed 69 pounds of petroleum hydrocarbons, with an <br /> estimated 5.9 pounds of TPHg remaining in groundwater. The Rebound Test proposes shutting down <br /> the SVE/AS treatment system during the fourth quarter of 2009, and; after 6 weeks;conducting a <br /> focused groundwater sampling event (TPHg, benzene, toluene, ethylbenzene, and xylenes) to evaluate <br /> the effectiveness of the July 2008 treatment system upgrades in post-remediation mode. The <br /> Rebound Test proposes restarting treatment for 6 weeks (followed by a second 6-week rebound test) if <br /> groundwater concentrations increase to 10% or more of the pre-upgrades (April 2008) maximum <br /> groundwater concentrations for any one of monitoring wells MW-2, MW-3, MW-8D, and MW-11. If <br /> rebound does not occur after 6 weeks, then a second focused groundwater sampling will be conducted <br /> during the first quarter of 2010 for an evaluation of the post-remediation data. Semi-annual <br /> groundwater monitoring and reporting for the 2nd and 4d' quarters, with submittal of status reports of the <br /> work conducted during the 1at and 3`d quarters, was approved in my letter dated 8 July 2009. <br /> 1 concur to the proposed rebound test for the SVE/AS treatment system. If rebound has not occurred <br /> after conducting the focused first quarter 2010 sampling event, then you are to submit a closure report <br /> by 30 April 2010, per the Regional Board guidance Appendix A - Tri-Regional Board Staff <br /> Recommendations for Preliminary Investigation and Evaluation of Underground Tank Sites, which may <br /> be downloaded electronically from the Internet at <br /> ham://www.waterboards.ca.gov/centraIvalley/water issues/underground storage tanks/tri- <br /> regionals appendix a.pdf. You may contact me regarding questions by phone at (916) 464-4615; or <br /> f r questions and status report submittals, by e-mail at Ibarton(o)waterboards.ca.gov. <br /> aures L.L. Barton, P.G. <br /> Engineering Geologist <br /> cc: Ms. Judy Reid, SWRCB, UST Cleanup Fund (Commingled Plume Program), Sacramento <br /> Mr. Mike Infurna, San Joaquin County Environmental Health Division, Stockton <br /> Ms. Jennifer Johnston, AECOM, 10461 Old Placerville Rd, Ste 170, Sacramento 95827 <br /> California Environmental Protection Agency <br /> ped Recycled Paper <br />