SITE INFORMATION AND CORRESPONDENCE

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California .Regional Water Quality Control Board .e Central Valley RegionQW; Karl E.Longley,ScD,P.E.,Chair Linda S.Adams 11020 Sun Center Drive#200,Rancho Cordova,California 95670-6114 Arnold Secretaryfor Phone(916)464-3291 •FAX(916)464-4645 Schwarzenegger Environmental http://www.waterboards.ca.gov/centralvalley Governor Protection !-� - - V 17 September 20091 S_r 1 8 20119 Mr. John MacLeod EWVIRONNIF!11, Chevron Environmental Management Company 6001 Bollinger Canyon Road, Room K2276 San Ramon, CA 94583 2008 ANNUAL GROUNDWATER MONITORING REPORT, CHEVRON CORRAL HOLLOW AND GRANT LINE ROADS, TRACY, SAN JOAQUIN COUNTY California Regional Water Quality Control Board, Central Valley Region (Central Valley Water Board) staff reviewed the following reports: • 28 April 2009 Site Closure Report (Closure Report) • 29 July 2009 2009 Semiannual Groundwater Monitoring Report (Monitoring Report) ARCADIS prepared these reports on behalf of Chevron Environmental Management Company (Chevron) for the site at Corral Hollow and Grant Line Roads in Tracy (Site). The Closure Report was submitted in response to our 16 January 2009 letter which requested that Chevron submit a No Further Action Report pursuant to Section 6.0 of the 16 April 2004 Tri-Regional Board Staff Recommendations for Preliminary Investigation and Evaluation of Underground Tank Sites Appendix A — Reports (Appendix A). Groundwater monitoring at the Site is conducted in accordance with Monitoring and Reporting Program No. R5-2006-0804 (MRP). Maximum soil concentrations in 1995 for total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, and xylene (BTEX) were 1,500 milligrams per kilogram (mg/kg), 5.6 mg/kg, 75 mg/kg, 57 mg/kg, and 390 mg/kg, respectively. Monitoring well MW-6 has contained the maximum historical groundwater concentrations of TPHg, TPH as diesel (TPHd), benzene and naphthalene at 120,000 micrograms per liter (pg/L), 39,000 pg/L, 17,000 pg/L, and 250 pg/L, respectively. Chevron previously destroyed 10 of the 15 monitoring wells at the Site to facilitate Site development. The five remaining monitoring wells are parallel to Grant Line Road. Past remedial actions at the Site include an air sparge pilot test in July 1994, a one-month pump and treat operation between July and August 1994, and dual phase extraction (DPE) between July and December 1997. Chevron estimates that 440 pounds (lbs) of hydrocarbon vapors were destroyed during operation of the DPE system. The DPE operation was discontinued after influent concentrations became asymptotic. On 28 May 2009, Chevron conducted the second quarter 2009 groundwater monitoring event and the results are summarized in the Monitoring Report. Groundwater flow was to the east, California Environmental Protection Agency 0a Recycled Paper