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California egional Water Quality Cool Board <br /> .t, <br /> Central Valley Region <br /> Katherine Hart,Chair <br /> Linda S.Adams Arnold <br /> Secretrrr or 11020 Sun Center Drive#200.Rancho Cordova, a 95670-61 14 Sehwarzenegger <br /> f Phone(916)464-3291 •FAX(1)16) <br /> Environmental http://www.waterboards.ca.gov/centra vE I Governor <br /> Proter•tiai Vcc <br /> Nps CD <br /> 0920 10 <br /> 5 November 2010 <br /> 04%RM fk, gC <br /> tT�gFALIt ENN <br /> Mr. Joe Lentini <br /> Shell Oil Products US <br /> 20945 S. Wilmington Avenue <br /> Carson, CA 90810 <br /> SOIL VAPOR SAMPLING REPORT AND THIRD QUARTER 2010 GROUNDWATER <br /> MONITORING REPORT, FORMER SHELL CENTRAL PIPELINES, NEIGHBORHOODS B, C <br /> AND D, MOUNTAIN HOUSE, SAN JOAQUIN COUNTY <br /> Regional Water Quality Control Board — Central Valley Region (Central Valley Water Board) <br /> staff reviewed the 26 October 2010 Soil Vapor Sampling Report (Report) and the <br /> 29 October 2010 Groundwater Monitoring Report— Third Quarter 2010 (Third QMR) for <br /> Mountain House Neighborhoods B, C and D in Tracy (Site). The Third QMR was submitted by <br /> Conestoga-Rovers & Associates (CRA) on behalf of Equilon Enterprises LLC doing business <br /> as Shell Oil Products US (Shell). <br /> The Report was prepared in response to the Department of Toxic Substances Control (DTSC) <br /> Schools Unit's comments on a portion of Neighborhood D where construction of Mountain <br /> House High School is planned. The DTSC recommended collecting soil gas samples at five <br /> and 15 feet bgs out of concern that previous soil vapor samples may have been collected <br /> before source area vapors equilibrated following soil removal activities in 2006. In <br /> September 2009, Shell installed one soil vapor well (SVP-1) in Neighborhood D and originally <br /> estimated that that it would be sampled during the first quarter of 2010. However, rainy <br /> weather and other factors delayed sampling until 15 July. <br /> Soil vapor samples collected from five and 15 feet bgs were submitted for laboratory analysis <br /> for the constituents of concern (COCs) benzene, toluene, ethylbenzene, and total xylenes <br /> (collectively BTEX), naphthalene, and the tracer gas helium. Laboratory analytical results <br /> showed that no CDCs were detected. Helium was detected in the 16-foot sample at <br /> 28,200 micrograms per cubic meter (pg/m3). Shell explained that since the helium was <br /> introduced to the sampling train at a 50% concentration and detected at 0.0173%, it is not <br /> indicative of an unacceptable leak. <br /> Between January and September 2009, Shell installed 15 monitoring wells (MW-2 through <br /> MW-16) in Neighborhoods C and D, and 19 monitoring wells (MW-1 through MW-19) in <br /> Neighborhood B. The monitoring wells were generally screened between 20 and 40 feet bgs. <br /> Depth to first encountered groundwater ranged from 24 to 33 feet bgs. <br /> Groundwater monitoring at the Site has been voluntarily conducted for five consecutive <br /> quarters starting in September 2009. During the third quarter 2010, depth to static <br /> California Environmental Protection Agenq, <br /> Rccrchgd Mlper <br />