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ow California Regional Water Quality �� and Central Valley Region Robert Schneider,Chair � Alan C.Lloyd,Ph.D. A S L006 Arnold Agency Secretary Sacramento Main OfficeHEALTH Schwarzenegger 11020 Sun Center Drive#200,Rancho Cordova,California 9V"R@NNIENT Governor Phone(916)464-3291 •FAX(916)464-4645 ��PERf�IT�SEVICES http://www.waterboards.ca.gov/centralvalley 13 March 2006 Mr. John MacLeod Chevron Environmental Management Company 6001 Bollinger Canyon Road Room K2276 San Ramon, CA 94583 REQUEST FOR REVISED MRP, CORRAL HOLLOW AND GRANT LINE ROADS SITE, TRACY, SAN JOAQUIN COUNTY Staff of the Central Valley Regional Water Quality Control Board (Regional Water Board) have reviewed the 2005 Annual Groundwater Monitoring_Report, Corral Hollow ad Grant Line Roads Site, Tracy, California (Report) submitted on your behalf by Blasland, Bouck& Lee, Inc. (BBL)and dated January 2006. You submitted the Report in compliance with Monitoring and Reporting Program No. 96-814 (MRP). The MRP requires monitoring of groundwater at the site of gasoline and diesel petroleum hydrocarbon release (TPHd and TPHg), and associated fuel oxygenates benzene, toluene, ethyl benzene and xylene (BTEX) and polynuclear aromatic compounds (PNAs) subsequent to rupture of a refined petroleum pipeline in 1987 near the referenced intersection. Chevron estimated that about 870 barrels were released from the rupture, and about 840 barrels were recovered during emergency response and soil excavation, leaving about 30 barrels or 1,260 gallons remaining in the environment. Chevron operated a dual phase extraction system (soil vapor and groundwater) from about August 1997 to November 1997 and recovered another 533 pounds of volatile organic compounds (VOCs). Chevron completed several rounds of site assessment investigations since 1987 and completed a Health Risk Assessment (HRA) in 1998. The file contains a 26 January 1999 letter from the Department of Toxic Substances Control concurring with the HRA and stating that the cancer risk from exposure to the released chemicals was substantially below the 1 x 10-6 level. Historically, monitoring wells MW-2, MW-9, MW-10, MW-11, MW-13 and MW-14 were in the down- gradient direction. Most of these wells did not contain any of the chemicals of concern, and have been decommissioned with Regional Board concurrence. Of these, MW-10 appears to have been most directly downgradient, about 100 feet from the spill site. It was sampled 18 times between 1991 and 2001 and contained BTEX 3 time times in 1996 and 1997 (240 ug/1 benzene in May 1997) and once in 2001 (4.9 ug/l benzene in May 2001) before it was destroyed in 2002. MW-13, located about 15 feet side-gradient to existing well MW-8, contained 200 ug/1 benzene once in 1994,then varied from non- detect to 2.8 ug/l from 1995 until it was destroyed in 1999. From our analysis of the data, it appears that the hydrocarbons are limited to the soils and groundwater adjacent to the release. The property where the downgradient wells previously existed is vacant but proposed to be developed into a retail complex. California Environmental Protection Agency Ca Recycled Paper