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San Joaquin County DIRECTOR <br /> Donna Heran,REHS <br /> N. Environmental Health Department <br /> ASSISTANT DIRECTOR <br /> 600 East Main Street Laurie Cotulla,REHS <br /> N < Stockton, California 95202-3029 PROGRAM COORDINATORS <br /> Carl Borgman, REHS <br /> Mike Huggins,REHS,RDI <br /> Website: www.sjgov.org/ehd Margaret Lagorio,REHS <br /> 4�rFORt� Phone: (209) 468-3420 Robert McClellan, REHS <br /> Fax: (209) 464-0138 Jeff Carruesco,REHS, RDI <br /> Kasey Foley,REHS <br /> STEPHANIE FURGAL DEC 2 0 2007 <br /> CHEVRON ENVIRONMENTAL MANAGEMENT COMPANY <br /> 6001 BOLLINGER CANYON RD ROOM K2050 <br /> SAN RAMON CA 94583 <br /> RE: Former Unocal #0187 <br /> 437 E. Miner Street <br /> Stockton, CA <br /> The San Joaquin County Environmental Health Department (EHD) has reviewed the <br /> "Sample Frequency and Analyte Reduction Request" (Request) dated November 28, <br /> 2007 and the "Proposal for Site Assessment and Remedial Alternative Evaluation" <br /> (Proposal) dated December 3, 2007, both prepared by ENSR for the above referenced <br /> site and provides the following comments. <br /> In the Request, ENSR proposed to reduce the sampling frequency for monitoring wells <br /> U-7, U-16, U-18, U-22, U-23, U-24, U-25 and U-26 to annual and that the annual <br /> sampling for these wells would be in the first quarter of each year while the groundwater <br /> monitoring program continues at the site. The EHD approves this reduction of sampling <br /> frequency for the above listed wells. <br /> In the Request, ENSR also requested discontinuing analysis of all oxygenates and 1,2- <br /> DCA from water samples from all monitoring wells. The detection limits used for the <br /> analysis of the water samples from U-3 were above the maximum contaminant limit <br /> (MCL) for 1,2-DCA in public drinking water except once. The water samples from U-12, <br /> U-21, and NP-1-22 have had detections of 1,2-DCA above the MCL. The EHD <br /> approves discontinuing of analysis for oxygenates on water samples from all the <br /> monitoring wells. The analysis for 1,2-DCA on water samples from the monitoring wells <br /> can be discontinued except the water samples from U-3, U-12, U-21 and NP-1-22 which <br /> must continue to be analyzed for 1,2-DCA. The Central Valley Regional Water Quality <br /> Control Board (CVRWQCB) has a site located at 601 E. Miner Street and ethanol has <br /> been detected in water samples from the B zone wells at that site. The CVRWQCB has <br /> requested that you include analysis for ethanol in the water samples from the wells at <br /> your site in the first quarter of 2008. <br /> In the Proposal, ENSR discussed using a Membrane Interface Probe (MIP) to identify <br /> locations and depth of potential remaining petroleum hydrocarbon sources in the <br /> vadose zone soil but also stated that the total depth of the MIP investigation would be to <br /> 50 feet below ground surface (bgs) because depth to groundwater in the early 1990's <br /> was 40 to 48 feet bgs. There are 17 MIP locations identified on figure 4 included in the <br /> Proposal. The Proposal stated a maximum of five confirmation soil samples would be <br />