SITE INFORMATION AND CORRESPONDENCE

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y � r San Joaquin County Pu!" Environmental Health Department o. •0 Q• c DIRECTOR 2. „�?y�, •G Donna Heran, REHS Q. z� 600 East Main Street Stockton, California 95202-3029 PROGRAM COORDINATORS ' Robert McClellon,REHS Jeff Carruesco, REHS,RDI cqC f F p �P Website: www-sjgov.org/ehd Kasey Foley, REHS Phone: (209) 468-3420 Fax: (209)464-0138 February 18, 2010 Thrifty Oil Company Mr. Chris Panaitescu 13116 Imperial Hwy. Santa Fe Springs, CA 90670 Subject: Thrifty Gas Station #171 LOP Case#: 1299 1250 N. Wilson Way APN: 117-310-01 Stockton, CA 95205 Geotracker ID#: T0607700132 The San Joaquin,,County Environmental Health Department (EHD) has reviewed Feasibility Study (FS), which had been submitted to Geotracker. The FS was required by the EHD in correspondence dated November 4, 2009, after Thrifty Oil Company (TOC) concluded that groundwater extraction was too costly and only soil vapor extraction would be utilized as the remedial action for the site. Included in the FS were estimated costs and time requirements for a variety of remedial alternatives. TOC concluded that soil vapor extraction with ORC Socks installed inside three wells for one year would be the most cost-effective and feasible method for cleaning up the site. TOC has determined that the use of an oxygen releasing compound, ORC, would enhance bioremediation of petroleum hydrocarbons in groundwater and reduce the contaminant mass and concentrations in groundwater to levels that could qualify the site for a no further action status. Currently, residual groundwater contamination is centered in the southwest corner of the site where three monitoring/extraction wells (TB-7, EW-5S, EW-5D) are located. Monitoring well TB-7 and extraction wells EW-5S and EW-5D are located in the plume of contaminated groundwater and are the wells proposed for ORC sock installation. The groundwater in this area is impacted by elevated concentrations of dissolved total petroleum hydrocarbons quantified as gasoline (TPHg), methyl tert-butyl ether (MtBE), and tert-butyl alcohol (TBA) that the EHD believes cannot remain in place without remediation. The proposed use of ORC socks as detailed in the FS does not address the following issues and the EHD can not approve the plan until they are adequately addressed: • With the ORC socks in each of the three wells, groundwater samples cannot be collected, and there would be no monitoring points within the contaminated plume to evaluate the effectiveness of the ORC. Either additional monitoring points or injection points are to be installed.