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April 1 , 2009 Foppiano Investments Ernest Foppiano 5313 Knox Drive Linden , CA 95236 Subject: Stockton City Taxi Service Site Code : 1117 2085 Fremont Street Stockton, CA 95205 The San Joaquin County Environmental Health Department (EHD) has reviewed Ozone Bench-Scale Treatability Study (Study), dated February 26 , 2009, submitted on your behalf by ATC Associates Inc. (ATC) and has the following comments . The Study documents the results of an ozone infusion bench scale test performed on soil and groundwater samples collected from your site. The results of the bench scale test indicate that while ozone infusion would be a very effective remedial method for destruction of the petroleum hydrocarbon contamination remaining at your site, it would also produce unwanted secondary byproducts of hexavalent chromium and bromate . Attenuation tests indicated the bromate would naturally attenuate in both the treatment area and downgradient of the treatment area, but the hexavalent chromium may not readily attenuate back to trivalent chromium in the treatment area , though it did attenuate downgradient of the treatment area . In the Study, ATC proposes to conduct an insitu ozone infusion pilot test per the Pilot Test Work Plan dated May 8 , 2008. However, in correspondence dated July 1 , 2008, the EHD did not approve the pilot test as proposed because a bench scale test for ozone infusion had not been completed . Please proceed with submittal of a work plan to conduct an insitu pilot test for ozone infusion . Address in the work plan the following points : 1 . Installation of infusion points; the EHD recommends a limited number of points to conduct a test, located near the former underground storage tank pit (UST). This would allow for monitoring of the hexavalent chromium downgradient of the test treatment area without going offsite. 2. In the May 8, 2008 work plan the proposed screen interval depths of the sparge points was 60-65 feet below surface grade (bsg) and 80-85 feet bsg , but there are no monitoring wells set at total depth 85 feet bsg . The middle depth monitoring wells at your site which are impacted with petroleum hydrocarbons have screen intervals set from 85-90 feet bsg . The ozone sparge points should be set in this same water bearing unit.