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- " CLOSURE CLU'T TQN.S, NC. <br /> September 8, 2011 <br /> Ms. Victoria McCartney <br /> San Joaquin County Environmental Health Department <br /> 600 E. Main Street ` <br /> Stockton, CA 95202 <br />�r <br /> Re: Supplemental Calculations for Closure Review <br /> Former BP Station No..11193 <br /> I 3202 West Hammer Lane <br /> Stockton,California 95209 <br /> SJCLOP .Case No. 1129 <br /> CVRWQCB Case No. 390779 <br /> Dear Ms. McCartney, <br /> Closure Solutions, Incorporated (Closure Solutions) 'is. submitting this Supplemental <br /> Calculations for Closure Review for Former BP Station No. 11193, located at 3202 West <br /> Hammer Lane,'Stockton; California (the Site). This document has been prepared to provide <br /> additional information as requested in your email dated August 11, 2011. <br /> ESTIMATED TIME TO REACH WATER QUALITY OBJECTIVES <br /> As stated in the Closure Report, results of recent groundwater monitoring events show that the <br /> highest concentrations of methyl tertiary butyl ether (MTBE) at the -Site were detected in up- <br /> gradient wells MW-4 and MW-9. Concentrations of MTBE at"the. up-gradient Parkinson's <br /> Hammer I-5 ARCO station are routinely one to two orders of magnitude higher than:at the <br /> subject Site, strongly suggesting that' MTBE ismigrating onto the subject Site from the <br /> Parkinson's Hammer 1-5 ARCO station. This is especially evidenced by MTBE analytical <br /> results for MW-4 at the subject Site, which is located outside the influence of the former ozone <br /> sparge system, and recent MTBE is o concentration maps which show theencroaching plume. <br /> With exception to the MTBE concentrations reported in up-gradient wells MW-4 and MW-9, <br /> which Closure Solutions believes are from,the encroaching plume, MTBE has not been detected <br /> in wells monitoring the onsite release at concentrations above'the water quality objective of 5 <br /> micrograms per liter (ug/L) since April.2010. Therefore, Closure Solutions believes the water <br /> quality objective for MTBE related to the onsite release has been met. <br /> In addition, as stated in our Closure Report, results of-recent groundwater monitoring events <br /> show that the highest concentrations of diesel range organics (DRO) were detected in well <br /> MW-9 and deep zone well MW-13. The source of the DRO is unclear since both wells are <br /> 4600 No rthgate Boule)ard'• Suite 230 •Sacramento. CA 95834 <br /> j 800) 958-?88() <br /> r -u•.Cla s�zz•cSc�?€,�i,i,o�.s.e urn <br /> F. <br /> F - <br />