SITE INFORMATION AND CORRESPONDENCE_FILE 2

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San Joaquin County DIRECTOR QD N Donna Heran,REHS P O. '' C Environmental Health Department ASSISTANT DIRECTOR 600 East Main Street Laurie Cotulla,REHS a: Stockton, California 95202-3029 PROGRAM COORDINATORS Carl Borgman,REHS Mike Huggins,REHS, RDI Website: www.sjgov.org/ehd Margaret Lagorio,REHS Phone: (209)468-3420 Robert McClellon,REHS Fax: (209) 464-0138 Jeff Carruesco,REHS, RDI Kasey Foley,REHS May 6, 2008 Eric Hetrick Conoco Phillips Risk Management & Remediation 76 Broadway Sacramento, CA 95818 Subject: 76 Service Station No. 5886 SITE CODE: 1176 2701 March Lane Stockton, CA San Joaquin County Environmental Health Department (EHD) has reviewed "Quarterly Status and Remediation Summary Report — First Quarter 2008" (Report) dated April 23, 2008, and "Work Plan for Additional Off-Site Assessment, and Hydrogen Peroxide Benchscale Testing" (Work Plan) dated March 20, 2008, prepared by Secor International Inc. for the above subject site. The Report explains that TRC was monitoring and sampling a tank pit well instead of monitoring well MW3 and that this mistake has been corrected in response to the EHD letter dated December 28, 2007. The Work Plan proposes installation of three monitoring wells (MW11 D/I/S) down-gradient of monitoring wells MW9 D/I/S and constructed similar to the MW9 wells. This work is approved as adequate and necessary. The Work Plan also proposes a bench scale test to evaluate injection of hydrogen peroxide. A rational for use of the hydrogen peroxide was provided. The test as proposed appears to be adequate to evaluate the effectiveness for degrading the TPH and MTBE; however the ITRC guidance document indicates that using permanganate to determine the oxidant demand can lead to an overestimation so this should be considered. The test may be inadequate to address the Central Valley Regional Water Quality Control Board evaluation for Waste Discharge Requirements. The following items should be considered: • Adding analyses for cadmium and barium on the soil pretest samples; • Adding analyses for pH, TDS, chloride, sulfate, nitrate, fluoride, chemical oxygen demand, aluminum, antimony, arsenic, beryllium, total chromium and hexavalent chromium on the groundwater samples; • Using results of the general mineral analyses of soil and groundwater to evaluate if naturally occurring minerals will move into or precipitate out of groundwater as a result of the injection;