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w <br /> —:i ■ .. <br /> M;J <br /> From Science to Solutions <br /> August 15, 2007 <br /> Mr. Mark Clardy <br /> Regional Water Quality Control Board 6f, S/735 <br /> 11020 Sun Center Drive#200 <br /> Rancho Cordova, California 95670 <br /> Subject: Soil-Vapor Sampling and Analysis Work Plan <br /> Former Shell Central Valley Crude Oil Pipelines <br /> Machado Property(Neighborhood B)Parcel 209-060-08 <br /> Mountain House Parkway at Grant Line Road <br /> Mountain House, San Joaquin County,California <br /> Dear Mr. Clardy: <br /> This letter has been prepared by Science Applications International Corporation(SAIC)on behalf of <br /> Shell Oil Products US(Shell)regarding the Machado Property of Neighborhood B in Mountain House, <br /> California(the site). Presented herein is a work plan to collect and analyze soil-vapor samples along a <br /> portion of the former Shell Central Valley Crude Pipelines, in order to evaluate potential risk to indoor air <br /> following construction at the site. <br /> SITE BACKGROUND <br /> The pipelines are located in the western portion of the Central Valley,just west of the Tracy city limits <br /> (see Figure 1). The site consists of an approximately 3,000 foot-long section of the former Shell pipelines <br /> located west of Mountain House Parkway and south of Grant Line Road. Shell operated two 8 inch- <br /> diameter pipelines that ran in a northwest-southeast direction through farmed property. The area has also <br /> been used for dairy operations, but is apparently scheduled for residential and commercial development. <br /> The site is located in the Central Valley at the eastern edge of the Coast Ranges. The site slopes <br /> topographically downward to the northeast. Based on surface topography,groundwater flow is <br /> anticipated to be toward the northeast. Soils underlying the site consist of sands, silts, and clays, <br /> deposited as alluvial fans. Depth to groundwater at the site is approximately 20 to 30 feet below ground <br /> surface(bgs). <br /> Site investigations completed to date indicate that petroleum hydrocarbons were present at shallow depths <br /> (approximately 5 feet bgs),extending down to groundwater in some areas. Shell is currently performing <br /> remediation at the site in accordance with a work plan dated April 3,2006. In that work plan, Shell <br /> committed to perform a soil-vapor study,the plan for which is presented herein. <br /> Based on initial site investigation data,soil concentrations of total petroleum hydrocarbons in the diesel <br /> and crude oil ranges(TPHd and TPHc,respectively)along the pipeline alignment ranged from non- <br /> Science Applications International Corporation <br /> 1000 Broadway I Suite#675/Oakland,CA 94607/tel: (510)433-0835/fax: (510)446-7919 1 saic.com <br />