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I I San Joaquin County DIRECTOR u Pp U, I N Donna Heran, REHS Environmental Health Department ASSISTANT DIRECTOR 600 East Main Street Laurie Golub, REHS Stockton , California 95202-3029 m � PROGRAM COORDINATORS Carl Borgman, REHS . _ Mike Huggins, REHS, RDI 4 . i , Website: wwwv. .sjgoorg/ehd FOR Phone: (209) 468-3420j3n cClellon, REHS Fax: (209) 464-0138 esco, REHS, RDI iey, REHS March 26 , 2009 M;ARStacie Frerichs Chevron EnvironmentalManagement Company 6111 Bollinger Canyon Road , Room 3596 San Ramon, CA 94583 Subject: Former Chevron Service Station #9-8632 575 W. Grant Line Road Tracy, CA The San Joaquin County Environmental Health Department ( EHD) has reviewed "Site Conceptual Model and Closure Request' dated December 29, 2008 , prepared by Conestoga- Rovers and Associates for the above subject site, discussed the site with the Central Valley Regional Water Quality Control Board and provides the following comments . Contaminant concentrations in the water samples from the monitoring wells appear to be generally decreasing . The concentrations of total petroleum hydrocarbons as gasoline (TPH-g) and benzene in the water samples from monitoring wells MW4 and MW7 exceed water quality goals, The concentrations of MTBE in the water samples from monitoring wells MW 1 , MW2 and MW3 also exceed water quality goals. An estimate as to when the concentrations of TPH- g , benzene and MTBE will reach water quality goals must be prepared for this site . There was a significant rise in contaminant concentrations in the water samples from monitoring well MW 4 (7700 ug/I benzene , 35, 000 ug/I TPH-g ) on January 24, 2008, and the concentrations have declined each quarter since that time. In January 2009 the water sample from monitoring well MW7 had increased contaminant concentrations. The statements that off-site sources are suspected for the contamination (soil and groundwater) in these wells are not supported by data. An explanation for these increases in contaminant concentrations must be provided . Soil samples collected from the site at depths shallower than 10 feet exceed the San Francisco Bay Regional Water Quality Control Board Environmental Screening Levels not only for residential exposure but for commercial/industrial exposure as well. A soil gas survey has not been conducted at this site. Although , there are no buildings currently on the site, there may be buildings constructed on the site in the future. Direct exposure and gross contamination issues have not been addressed for future workers at the site. The EHD recommends that at a minimum a soil gas survey be conducted so there is data to support that vapor intrusion will not be a risk at this site. All of these environmental concerns must be addressed for future use of the site in a report,