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California ,gional Water Quality Con 1 Board <br /> Central Valley Region <br /> Katherine Hart,Chair Wim°'-`` <br /> Linda S.Adams 11020 Sun Center Drive#1200,Rancho Cordova.California 95670.6114 Arnold <br /> Secretary for Schwarzenegger <br /> Environmentalhttp://www.",aterboards.ca.gov/centralvalleN <br /> (916)464-3291 •FAX(916)464-4645 <br /> http://www.waterboards.ca.gov/centralvalleN Governor <br /> Protection <br /> 11 August 2010 cr',,E E'=' <br /> AUG 12 �UIO <br /> Mr. Joe Lentini ENV1KUfvl�t?.�fU HEALTH <br /> Shell Oil Products US PER MMSERVIriES <br /> 20945 S. Wilmington Avenue <br /> Carson, CA 90810 <br /> SECOND QUARTER 2010 GROUNDWATER MONITORING REPORT, FORMER SHELL <br /> CENTRAL PIPELINES, NEIGHBORHOODS B, C & D, MOUNTAIN HOUSE, SAN JOAQUIN <br /> COUNTY <br /> Regional Water Quality Control Board — Central Valley Region (Central Valley Water Board) <br /> staff reviewed the 30 July 2010 Groundwater Monitoring Report - Second Quarter 2010 <br /> (Second QMR) for Mountain House Neighborhoods B, C and D in Tracy (Site). The Second <br /> QMR was submitted by Conestoga-Rovers & Associates (CRA) on behalf of Equilon <br /> Enterprises LLC doing business as Shell Oil Products US (Shell). <br /> In 2006 and 2007, about 165,000 cubic yards of soil contaminated with petroleum <br /> hydrocarbons from two former pipelines, which were removed from operation in the 1960s, <br /> were excavated from 25 areas of concern at the Site. Between January and September 2009, <br /> Shell installed 15 monitoring wells (MW-2 through MW-16) and one soil vapor well (SVP-1- <br /> 6/16) 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 conducted for four consecutive quarters starting <br /> in September 2009. Table 1 of the Second QMR includes the laboratory analytical results for <br /> total petroleum hydrocarbons (TPH), benzene, toluene, ethylbenzene, and total xylenes <br /> (collectively BTEX), and naphthalene, which have been non-detect (ND) in all wells. Sulfate <br /> and sulfur were detected in all wells during the September 2009 sampling round, which is the <br /> only time they were analyzed. <br /> The monitoring results appear to indicate that the most of the petroleum hydrocarbon pollution <br /> mass is either sorbed to the porous media solids or generally insoluble. During the fourth <br /> quarter of 2009, Shell conducted a background analysis of the soil and groundwater sulfate <br /> and sulfur concentrations. The results of the study demonstrated that sulfate and sulfur <br /> concentrations are similar between background and source area samples, so sampling for <br /> these constituents was discontinued. In our 8 April 2010 letter, Central Valley Water Board <br /> staff required Shell to conduct groundwater monitoring and submit reports for at least four <br /> consecutive quarters. We stated that if monitoring results were consistently ND or below water <br /> quality objectives, we would be willing to consider developing a regulatory decision for this <br /> Site. <br /> California Divirotimoital Protection Agency <br /> rT, Renrleci Paper <br />