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N. ■ am <br /> A=M0rXl`9 <br /> rrom Science to Solutions <br /> RPP-BTR MP#220.7/223.7 <br /> Mountain House Development Site#6 <br /> Plans <br /> Accession#06102.20090417.001 <br /> April 23, 2009 <br /> Mr. M. Scott Mansholt <br /> Chevron Environmental Management Company <br /> P.O. Box 6012 <br /> 6111 Bollinger Canyon Road <br /> San Ramon, California 94583 <br /> Subject: Addendum to the Soil and Groundwater Investigation Work Plan <br /> Mountain House Development Site#6 <br /> Mountain House, San Joaquin County, California <br /> Dear Mr. Mansholt: <br /> Science Applications International Corporation(SAIC)prepared this work plan addendum on <br /> behalf of Chevron Environmental Management Company (CEMC). SAIC's soil and <br /> groundwater investigation report(SGIR)1, submitted to the Regional Water Quality Control <br /> Board—Central Valley Region (RWQCB) in July 2008, included recommendations to further <br /> characterize the affected soil and groundwater at Mountain House Development Site #6 (see <br /> Figure 1). The RWQCB reviewed the SGIR in November 20082, and concurred with the <br /> proposed boring locations with the exception of location J. The RWQCB recommended that <br /> boring location J be moved 50 feet to the east-northeast, and that an additional boring (boring N; <br /> as shown on Figure 2) is necessary 50 feet to the east of original boring location J. SAIC also <br /> moved proposed boring locations D, G through I, and K through M to adjacent parcels <br /> (approximately 15 feet to the northeast of the originally proposed locations) due to site access <br /> issues. These repositioned borings will adequately accomplish the goals of the original boring <br /> locations as described in the 2008 SGIR. <br /> In accordance with the Consistent Technical Approach3, should SAIC encounter affected soils in <br /> a boring, contingency step-out borings may be advanced as part of the same field investigation <br /> effort to the extent allowed by current site access agreements. <br /> 1. SAIC,2008. Soil and Groundwater Investigation Report Mountain House Development Site#6,Mountain House,San <br /> Joaquin County, California. July. <br /> 2. RWQCB,2008. Review—Soil and Groundwater Investigation Report and Additional Investigation Work Plan,Mountain <br /> House Development Site#6,Mountain House,San Joaquin County. November 12. <br /> 3. Geomatrix Consultants,Inc.,2005. Technical Approach to Site Evaluation and Decision-Making,Historical Pipeline <br /> Portfolio, Central Valley Region. February. <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 />