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California bional Water Quality Con; Board <br /> `- <br /> Central Valley Region �"� <br /> Katherine Hart,Chair ���£ <br /> Arnold <br /> Linda S.Adams 11020 Sun Center Drive#200,Rancho Cordova,California 95670-6114 <br /> Schwarzenegger <br /> Secretaryfor <br /> Phone(916)464-3291 •FAX(916)464-4645 Governor <br /> Environmental http://www.waterboards.ca.gov/centralvalley <br /> Protection <br /> D <br /> 8 April 2010 <br /> AIP;1 i 3 i0 <br /> Mr. Joe Lentini ENVIRUWOENT HEALTH <br /> Shell oil Products US FERMiT%SER'JIUES <br /> 20945 S. Wilmington Avenue <br /> Carson, CA 90810 <br /> SUBSURFACE INVESTIGATION AND THIRD QUARTER 2009 GROUNDWATER <br /> Iw,J!©"!lTOR!NG REPORT, FORMER SHELL CENTRAL PIPELINES, NEIGHBORHOODS B, C <br /> & D, MOUNTAIN HOUSE, SAN JOAQUIN COUNTY <br /> Regional Water Quality Control Board — Central Valley Region (Central Valley Water Board) <br /> staff reviewed the 30 November 2009 Subsurface Investigation and Third Quarter 2009 <br /> Groundwater Monitoring Report (Report) for Mountain House Neighborhoods B, C and D (Site) <br /> in Tracy, California. The Report was submitted by Conestoga-Rovers & Associates (CRA) on <br /> behalf of Equilon Enterprises LLC doing business as Shell Oil Products US (Shell). <br /> This letter also provides notification that Mr. Brian Taylor has assumed project management <br /> duties from Mr. Nathan Casebeer for this site. <br /> The Site is north and south of Grant Line Road, about one-half mile west of Mountain House <br /> Parkway. The purpose of the Report is to present the results of additional soil and <br /> groundwater investigation and well installation activities for areas of potential concern <br /> previously identified through investigation and soil remediation at the Site. <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 in Neighborhoods B, C, and D at the Site. The <br /> Department of Toxic Substances Control, Schools Unit (DISC) provided review comments for <br /> a portion of Neighborhood D where construction of a high school is planned. <br /> The Report provides the results of monitoring well installations at the Site to further investigate <br /> the lateral extent of shallow groundwater pollution. Between January and September 2009, <br /> CRA advanced 35 borings to depths ranging from 16 to 40 feet below ground surface (bgs) <br /> using a hollow stem auger drill rig. Depth to first encountered groundwater ranged from 24 to <br /> 33 feet bgs. Total petroleum hydrocarbons as crude (TPHc) and diesel (TPHd) were detected <br /> at maximum concentrations of 23,000 milligrams per kilogram (mg/kg) and 11,000 mg/kg, <br /> respectively, at a depth of 25 feet bgs. The highest concentrations were observed in boring <br /> MW-6 in Neighborhoods C and D and exceeded Central Valley Water Board staff's 5,000 <br /> mg/kg cleanup level for this Site. Sulfate and sulfur were ubiquitous with concentrations that <br /> averaged 61 mg/kg and 407 mg/kg, respectively. <br /> California Environmental Protection Agency <br /> 0a Recycled Paper <br />