SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Mr. Ken Gillies Page 2 of 3 Gillies Trucking • 23 January 2009 3931 Newton Road, Stockton Dissolved TPH-d concentrations appear to have a direct relationship to the depth to groundwater, increasing when the groundwater elevation rises and decreasing when the groundwater elevation drops. Groundwater in the First Riverbank sand is impacted, commonly by low to moderate concentrations of TPH-d, groundwater in some periphery wells vary between less than detectable concentrations to moderate concentrations of dissolved TPH-d. Your previous consultant identified over 30 water supply wells within a 2,000-foot radius of your site. You stated during the meeting that a new well has been recently installed on the opposite side of Newton Road from your property, but the EHD has not been able to verify that. The main concern with your site is the potential effect on groundwater supplies in the area during periods of high groundwater elevation that would put groundwater in contact with additional impacted soil, which could result in higher dissolved concentrations and may make the plume of impacted groundwater expand and impact the local water supply wells; indeed this may have happened on your site based on the TPH-d recently detected in a groundwater sample collected from your water supply well. To bring your site toward closure, the following concerns must be addressed: • The threat to groundwater supplies must be minimized, which may require that significantly impacted soil be actively remediated to reduce the transfer rate of contaminant from soil to groundwater, thereby reducing the dissolved TPH-d concentrations and reduce the areal extent of the dissolved plume; • The potential for soil vapor intrusion into structures on your site must be evaluated, and if found to be excessive, must be ameliorated; • The lateral extent of impacted groundwater must be assessed to demonstrate minimal risk to water wells on nearby sites, especially in the down-gradient direction; • Contaminant concentrations left in soil must be compared to the San Francisco Bay Regional Water Quality Control Board's (SFBRWQCB) Environmental Screening Levels (ESLs); it must be shown that any contaminant concentrations found to exceed the ESLs do not pose a significant risk to human health, groundwater supplies or the environment; and • Your consultant should be able to predict and demonstrate the time required for contaminant concentrations in groundwater to decline below concentrations of regulatory concern. At the meeting it was agreed that your consultant will: • Prepare and submit a work plan for a soil vapor extraction (SVE) test on existing well GT-10 to determine if hydrocarbon vapor can be extracted from the impacted soil in the GT-10 area at a sustainable and sufficient rate to warrant installation of additional wells for further testing SVE to remediate the deep impacted soil; and • Prepare and submit a work plan to complete the lateral assessment of impacted groundwater. Meeting Summary Directive Letter 0109