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California gional Water Quality Con` I Board <br /> Central Valley Region <br /> Karl E. Longley,ScD, P.E.,Chair <br /> Linda S. Adams Arnold <br /> 11020 Sun Centcr Drive X200. Rancho Conov <br /> ia.California 9�67461 la <br /> Set IeIon /or Schwarzenegger <br /> Phone(916)464-3291 •FAX(91(,)464-464 <br /> l:nvn onmenra! Governor <br /> 1'rurr<nn http://NcNcNc.waterboards.ca.eov/cenhtraallcN <br /> 13 August 2008 I_�("( (I�f] <br /> ifiEk L�IJ �"/ ED <br /> Mr. Joe Lentini AUG Z 5 2008 <br /> Shell Oil Products US <br /> 20945 S. Wilmington Avenue ENVIRONi��E"+T 11i ALTH <br /> Carson, CA 90810 oG4!y,7;T��GRt�lr`�� <br /> REVIEW OF WORK PLAN, FORMER SHELL CENTRAL VALLEY CRUDE OIL PIPELINES, <br /> NEIGHBORHOODS C AND D, MOUNTAIN HOUSE, SAN JOAQUIN COUNTY <br /> Staff of the Regional Water Quality Control Board — Central Valley Region (Regional Water <br /> Board) has reviewed the 17 June 2008 Groundwater Monitoring Well Installation Work Plan <br /> (Work Plan) for the Mountain House Neighborhoods C and D submitted by Science <br /> Applications International Corporation (SAIC) on behalf of Shell Oil Products US (Shell). The <br /> purpose of the Work Plan is to propose additional groundwater investigation activities for <br /> areas of potential concern previously identified through investigation and soil remediation <br /> within Neighborhoods C and D. The Department of Toxic Substances Control, Schools Unit <br /> (DTSC) provided review comments for a portion of Neighborhood D where construction of <br /> Mountain House High School is planned. <br /> In 2006, soil impacted with petroleum hydrocarbons was excavated from 13 areas in <br /> Neighborhoods C and D. The excavations ranged in depth from 10 feet to about 26 feet <br /> below ground surface (bgs), the approximate depth of the water table. Soil was removed that <br /> was impacted as evidenced by visual staining, or that exceeded a concentration of 5,000 <br /> milligrams per kilogram total petroleum hydrocarbons as crude oil (TPHcr), a remedial <br /> excavation goal provided by Regional Water Board staff. Approximately 130,000 cubic yards <br /> of soil were removed from the site for disposal. <br /> Shell proposes to install 14 monitoring wells in the vicinity of 6 of the 13 previously excavated <br /> areas within neighborhoods C and D. The purpose of the monitoring wells is to further <br /> delineate the lateral extent of shallow groundwater contamination as well as determine the <br /> groundwater flow direction and gradient. The monitoring wells will be installed using a hollow <br /> stem auger drill rig equipped with 8-inch diameter hollow stem augers. Soil samples for <br /> lithological characterization will be collected at 5-foot intervals from the boreholes using an 18- <br /> inch long California modified split spoon sampler. Selected soil samples may also be <br /> collected for laboratory analysis. The monitoring wells will be constructed with 2-inch diameter <br /> schedule 40 PVC blank and slotted casing. Screen intervals are anticipated to extend from 20 <br /> to 35 feet below ground surface. After developing and surveying the monitoring wells a <br /> groundwater monitoring program will be initiated. Soil and groundwater samples collected will <br /> be submitted for laboratory analysis of total petroleum hydrocarbons as diesel (TPHd) and <br /> TPHcr using EPA Method 8015M and benzene, toluene, ethylbenzene, and total xylenes <br /> (BTEX) using EPA Method 8020. <br /> California Environmental Protection Agency <br /> gip` Irecvc/cd <br />