SITE INFORMATION AND CORRESPONDENCE

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San Joaquin County DIRECTOR Donna Heran,REHS PQtJiN Environmental Health Department ASSISTANT DIRECTOR 600 East Main Street G Laurie Cotulla, REHS 2 � •2 W < Stockton, California 95202-3029 PROGRAM COORDINATORS Carl Borgman,REHS Mike Huggins,REHS,RDI 0,9•. "..:.j�P Website: www.sjgov.org/ehd Margaret Lagorio, REHS /FOR Phone: (209)468-3420 Robert McClellon, REHS Fax: (209)464-0138 Jeff Carruesco, REHS,RDI DENIS L BROWN OCTK1e F206ey 7EHs SHELL OIL PRODUCTS US 20945 S WILMINGTON AVE CARSON, CA 90810 RE: SHELL SERVICE STATION 2320 N. EL DORADO STREET STOCKTON CA 95204 The San Joaquin County Environmental Health Department (EHD) has reviewed Groundwater Monitoring Report — First Quarter 2007 (QR) dated March 6, 2007, Third Quarter 2005 Groundwater Monitoring Report and Site Conceptual Model (SCM), dated November 2, 2005, both prepared by your consultant Cambria Environmental Technology Inc. (CET), and other historical site data for the above referenced site. The EHD also reviewed site data for the Castle Motors site located at 2315 N. El Dorado Street. EHD has the following comments: • Source of contamination. CET states in the SCM that the groundwater data from the Shell site and the Castle Motors site suggest that the total petroleum hydrocarbons quantified as gasoline (TPH-g), benzene, toluene, ethylbenzene, and xylenes (BTEX), and fuel oxygenates detected in on-site wells likely originated at the Castle Motors site. This may in part be correct, especially along the northern portion of the site. The core of the plume appears to be near Castle Motors MW-3 (screened 43 to 63 feet bsg) with 220,000 micrograms per liter (µg/1) TPH-g detected in groundwater during the first quarter 2007. The groundwater flow direction is consistent with an elongated Castle Motors plume oriented predominantly toward the northeast across the northern portion of the Shell site. The major source area at the Shell site appears to be the southeast dispenser area, with 1,200 milligrams per kilogram (mg/kg) total petroleum hydrocarbons (TPH) detected in soil collected from SS-8 during the underground storage tank (UST) system removal in 1990. Soil collected from the down- gradient MW-2, was nearly non-detect for TPH-g. Additionally, Shell's old tank pit soil samples were all non-detect. Utilizing your SCM with cross-sections, maps, and data from the Castle Motors site, prepare a model of the dissolved plumes showing migration pathways and probable areas of distinct and commingled plumes. Include a discussion of the technical basis for the plume designations (i.e, Shell plume, Castle Motors plume and commingled plume). Submit this model to the EHD by December 3,2007. • Further site assessment needed. Site Investigation Workplan, dated October 4, 2004 prepared by CET proposed four cone penetration testing (CPT) borings to 75 feet bgs to define the vertical and lateral extent of contamination. This work was approved by the EHD as adequate and necessary for your site investigation; however this proposed work was postponed by CET due to their concern for potential on-site migration of off-site contaminants from Castle Motors. To date, this work has not been implemented. Your site must be fully characterized and contaminant plumes fully delineated to properly manage the contaminants. By January 2, 2008 either implement the approved workplan, submit another workplan, or show how the investigation objectives of the approved plan have already been met.