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San Joaquin County Environmental Health Department 600 East Main Street Stockton, California 95202-3029 DIRECTOR Donna Heran, REHS PROGRAM COORDINATORS Robert McClellon, REHS Jeff Carruesco, REHS, RDI Kasey Foley, REHS Website: www.sjgov.org/ehd Phone: (209) 468-3420 Fax: (209) 464-0138 March 11,2010 Eric Mar California Water Service 1550W. Fremont Street Ste 100 Stockton, CA 95203 Subject: Unauthorized Release from Underground Storage Tank System at Waterloo Food & Fuel, 3032 E. Waterloo Rd., Stockton, that May Have Potential to Impact the California Water Service Well at Filbert Street and Cherokee Road. As you were informed on May 9, 2010, by telephone, the San Joaquin County Environmental Health Department (EHD) is providing regulatory oversight of the investigation and corrective action needed to mitigate an unauthorized release from an underground storage tank (UST) system at 3032 E. Waterloo Road, Stockton, California (the subject site). The unauthorized release may have the potential to impact your municipal well near the intersection of Filbert Street and Cherokee Road in Stockton, reported to the EHD to be Well #75. The subject site has been under investigation since early 1999, impacted groundwater has been monitored since February 2000. Groundwater has been intensely impacted by total petroleum hydrocarbons quantified as gasoline (TPHg), benzene, toluene, ethylbenzene and total xylenes (BTEX), methyl tert-butyl ether (MTBE), and other chemicals of concern (COCs). The inferred flow direction of shallow groundwater has been predominantly toward the northwest and west. The site at 1905 Broadway (WFS) has a wide groundwater monitoring system; WFS's third quarter 2009 report states that the predominant groundwater flow direction in the area is toward the west, varying from southwest to northwest. Your Well #75, west of the subject site, is in the general down-gradient direction. The plume of impacted groundwater associated with the subject site is not well delineated in the down-gradient direction. Monitoring wells on the site at 3012 E. Waterloo Road impacted by MTBE are believed to be part of the subject site plume. MTBE was encountered in a monitoring well that is part of the WFS monitoring network in Gilchrist Road (WFS MW-20B). The well, screened between 95 and 110 feet below surface grade, is between 800 and 1,000 feet (depending on which map is used) from the tank pit on the subject site. MTBE was first encountered in the well in January 2006, peaked at a concentration of 870 parts per billion in July 2007, and has since declined to 4.3 parts per billion (September 2009). There has not been sufficient assessment of the plume to definitively associate the MTBE in MW-20B with the subject site plume, but EHD believes there is a significant likelihood that it is. Your Well #75, Eric Mar Letter 0310