SITE INFORMATION AND CORRESPONDENCE_CASE 2

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San Joaquin County DIRECTOR Po u/NDonna Heran, REHS Environmental Health Department ASSISTANT DIRECTOR 600 East Main Street Laurie Cotulla, REHS " Stockton, California 95202-3029 r PROGRAM COORDINATORS Mike Huggins,REHS,RDI C4</FOR�`P • Website: www.s ov.or /ebd Margaret Lagorio, REHS J9 9 Robert McClellon,REHS Phone: (209) 468-3420 Jeff Carruesco, REHS, RDI Fax: (209) 464-0138 Kasey Foley, REHS March 27, 2009 Ms. Jennifer Sedlachek Mr. Kevin Meeks ExxonMobil Environmental Services Company Mr. Pat and Ms. Kathleen Meeks 4096 Piedmont Avenue #194 25355 Highway 99 Oakland, California 94611 Acampo, California 95220 Subject: Meeks RV (former Pacific Auto Center) 25355 North Highway 99 Acampo, California 95220 On March 13, 2009, personnel from the San Joaquin County Environmental Health Department (EHD) and Environmental Resolutions, Inc. (ERI) met by teleconference call to discuss petroleum hydrocarbon contamination detected at the above-referenced site. The purpose of the meeting was to identify data gaps and establish a clear direction for moving this site toward closure consideration. The EHD and ERI concurred that the main contaminant of concern at this site is 1,2- dichloroethane (1,2-DCA). This contaminant has historically been detected at significant concentrations in groundwater samples collected quarterly from monitoring wells MW-1, and MW-3, and at concentrations less than or equal to 12 micrograms per liter (µg/L) in groundwater collected from MW-4 and MW-5. Discussions focused on the 1,2-DCA plume and the general concurrence that the plume did not appear to be defined toward the southwest, northeast, nor southeast of MW-3, the well most impacted by 12,-DCA with concentrations currently at approximately 180 µg/L. The EHD recommended the installation of additional monitoring wells screened within the first water zone to define the lateral extent of the 1,2-DCA plume. To identify data gaps and thereby determine if or where additional monitoring wells are needed, the EHD recommended submittal of a preliminary site conceptual model (SCM). The general purposes of an SCM are to demonstrate where the contaminants came from, where they are at the present time, how they move through the subsurface, how they will respond to changes in the groundwater flow characteristics or to potential remediation efforts, what the contaminants' ultimate environmental fate will be, and to help evaluate the risk posed by the contaminants to groundwater supplies and sensitive receptors. To be sure that the SCM will adequately address the assessment, remediation and, ultimately, final closure requirements for this site, the following should be included in the SCM: