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it <br /> San Joaquin County DIRECTOR <br /> Donna Her an, REHS <br /> ASSISTANT Department DIRECTOR <br /> 600 East Main Street Laude cn ono, REHS <br /> Stockton , California 95202-3029 <br /> PROGRAM COORDINATORS <br /> - Carl Borgman, REHS <br /> Mike Huggins, REHS, RDI <br /> C . . <br /> Website: wwwsjgov. org/ehd Margaret Lagorio, REHS <br /> Phone: (209) 468-3420 Robert McClellon , REHS <br /> Fax: (209) 464-0138 Jeff Carruesco, REHS, RDI <br /> Kasey Foley, REHS <br /> March 26, 2009 <br /> Stacie Frerichs <br /> Chevron Environmental Management Company <br /> 6111 Bollinger Canyon Road , Room 3596 <br /> San Ramon , CA 94583 <br /> Subject: Former Chevron Service Station #9-8632 <br /> 575 W . Grant Line Road <br /> Tracy, CA <br /> The San Joaquin County Environmental Health Department (EHD) has reviewed "Site <br /> Conceptual Model and Closure Request" dated December 29 , 2008 , prepared by Conestoga- <br /> Rovers and Associates for the above subject site, discussed the site with the Central Valley <br /> Regional Water Quality Control Board and provides the following comments. <br /> Contaminant concentrations in the water samples from the monitoring wells appear to be <br /> generally decreasing . The concentrations of total petroleum hydrocarbons as gasoline (TPH-g) <br /> and benzene in the water samples from monitoring wells MW4 and MW7 exceed water quality <br /> goals . The concentrations of MTBE in the water samples from monitoring wells MW 1 , MW2 <br /> and MW3 also exceed water quality goals. An estimate as to when the concentrations of TPH- <br /> g , benzene and MTBE will reach water quality goals must be prepared for this site. <br /> There was a significant rise in contaminant concentrations in the water samples from monitoring <br /> well MW 4 (7700 ug/I benzene , 35, 000 ug/I TPH-g ) on January 24, 2008, and the concentrations <br /> have declined each quarter since that time . In January 2009 the water sample from monitoring <br /> well MW7 had increased contaminant concentrations . The statements that off-site sources are <br /> suspected for the contamination (soil and groundwater) in these wells are not supported by <br /> data . An explanation for these increases in contaminant concentrations must be provided . <br /> Soil samples collected from the site at depths shallower than 10 feet exceed the San Francisco <br /> Bay Regional Water Quality Control Board Environmental Screening Levels not only for <br /> residential exposure but for commercial/industrial exposure as well . A soil gas survey has not <br /> been conducted at this site . Although, there are no buildings currently on the site , there may be <br /> buildings constructed on the site in the future. Direct exposure and gross contamination issues <br /> have not been addressed for future workers at the site. The EHD recommends that at a <br /> minimum a soil gas survey be conducted so there is data to support that vapor intrusion will not <br /> be a risk at this site . All of these environmental concerns must be addressed for future use of <br /> the site in a report. <br />