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San Joaquin County <br /> Environmental Health Department DIRECTOR <br /> Donna Heran,REHS <br /> 600 East Main Street <br /> N: < Stockton, California 95202-3029 PROGRAM COORDINATORS <br /> Robert McClellon,REHS <br /> Jeff Carruesco,RENS,RDI <br /> Website:www.sjgov.org/ehd Kasey Foley,REHS <br /> ��FOR Phone: (209)468-3420 Linda Turkatte,REHS <br /> Fax: (209)464-0138 <br /> November 8, 2010 <br /> Mr. Ken Hilliard <br /> 7-Eleven, Incorporated <br /> Post Office Box 711 NOV 1 0 2010 J <br /> Dallas, Texas 75221-0711 <br /> ray <br /> Subject: 7-Eleven Store No. 19976 ---- - <br /> 1399 North Main Street <br /> Manteca, California 95336 <br /> By letter dated 13 July 2009, the San Joaquin County Environmental Health Department <br /> (EHD) directed you to reduce sampling of the monitoring wells at the above-referenced <br /> subject site in accordance with the recently adopted State Water Resources Control Board <br /> Resolution 2009-0042. The EHD directed that monitoring wells MW-1 and MW-2 be sampled <br /> semi-annually, and the remaining nine monitoring wells be sampled annually. The EHD also <br /> directed that groundwater samples collected from MW-1, MW-2, and MW-5 be analyzed for <br /> total petroleum hydrocarbons quantified as gasoline (TPH-g), benzene, toluene, <br /> ethylbenzene, and total xylenes (BTEX), methyl tertiary-butyl ether (MTBE), tertiary-amyl <br /> methyl ether (TAME), and tertiary-butyl alcohol (TBA); and groundwater from the remaining <br /> wells be analyzed for MTBE only. Since the EHD issued the directive, your consulting firm, <br /> Stantec Consulting Corporation (Stantec), has continued to collect groundwater quarterly from <br /> all 11 wells and analyze the samples for TPH-g, BTEX, MTBE, TAME, TBA, ethyl tertiary-butyl <br /> ether (ETBE), and di-isopropyl ether (DIPS). Stantec has stated that quarterly sampling is <br /> necessary to observe the effectiveness of the remediation by periodic oxygen injection. <br /> Utilizing the site data, submit a report to the EHD by 27 December 2010, demonstrating that <br /> the additional data collection is technically justified. <br /> The EHD has reviewed the analytical results from the most current sampling event conducted <br /> on 20 July 2010. With few exceptions, concentrations of chemicals of concern, including <br /> TPH-g, BTEX, MTBE and TBA, have decreased significantly in groundwater samples <br /> collected from the two most-impacted wells, MW-1 and MW-2, since March 2003, when <br /> oxygen was first injected as a remediation method. Groundwater samples collected from the <br /> remaining on- and off-site monitoring wells show a similar decrease in concentrations of <br /> petroleum hydrocarbon contaminants. By 27 December 2010, provide the EHD an evaluation <br /> of the effectiveness of past and continued oxygen injection and a recommendation as to <br /> whether rebound testing should commence. <br /> By letter dated 22 September 2009, the EHD directed you to submit an evaluation of the <br /> potential for vapor intrusion into structures at this site. To date, the EHD has not received this <br />