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Den's Auto Repair Page 2 <br /> 308 South EI Dorado Street February 18, 2011 <br /> Stockton, California 95203 <br /> groundwater samples OB-1/MW-1A and OB-2/MW-2A, respectively, on the <br /> seventh and final day of ozonation. These concentrations exceed the California <br /> Environmental Protection Agency Maximum Contaminant Level (MCL) of 10 pg/L. <br /> In comparison, bromate was not generated in either of the groundwater samples <br /> collected from MW-1A and MW-2A after undergoing oxygen sparging. <br /> • On the seventh and final day of ozonation, concentrations of total chromium, <br /> vanadium, molybdenum, selenium, antimony, and arsenic increased in both <br /> soil/groundwater samples with total chromium and arsenic detected above their <br /> respective MCL of 50 pg/L. <br /> • Benzene, ethylbenzene, total xylenes, and total petroleum hydrocarbons quantified <br /> as gasoline (TPH-g) were reported at significant concentrations in both initial <br /> groundwater samples; however, these contaminants of concern were not detected <br /> above the laboratory reporting limits in either soil/groundwater sample collected on <br /> the seventh day of the ozone injections. Also, the two groundwater samples <br /> collected from MW-1A and MW-2A underwent oxygen sparging following which <br /> concentrations of TPH-g and total xylenes were detected at 160 pg/L and 0.61 <br /> pg/L, respectively, in MW-1A while contaminants of concern were not detected in <br /> MW-2A. <br /> Based on the findings submitted in the ozone bench scale test, AGE has recommended the <br /> preparation and submittal of a Corrective Action Plan (CAP) that will present a comparison <br /> of groundwater and soil remedial methods to determine the most cost effective remedial <br /> method to mitigate the petroleum hydrocarbon contaminants at this site. The EHD concurs <br /> with this recommendation and directs that a CAP be submitted to this department by 18 May <br /> 2011. <br /> The EHD also approves the quarterly monitoring and sampling of monitoring wells MW-8 <br /> through MW-10, installed in October 2010, through the third quarter 2011. If analytical <br /> results for groundwater collected from these wells are non-detect, then these wells may be <br /> sampled annually; otherwise, sample these wells semi-annually following the third quarter <br /> 2011. <br /> Please contact Vicki McCartney at (209) 468-9852 or by email at vmccartney sicehd com if <br /> you have any questions concerning this letter. <br /> Sincerely, <br /> Victoria L. McCartney, REHS Nuel C. Henderson, Jr., PG <br /> Senior Registered Environmental Health Specialist Engineering Geologist <br />