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Scott Mansholt -2 - 13 April 2005 <br /> • ChevronTexaco <br /> Mountain House Site#6 <br /> a well survey will be conducted to obtain information of groundwater production wells used for <br /> municipal, domestic, agriculture, industrial, and/or other uses within 2,000 feet of the project. <br /> ChevronTexaco needs to complete characterization of the lateral and vertical extent of pollution in soil <br /> and groundwater in order to reduce/eliminate and/or identify potential risks to human health and the <br /> environment. Regional Board staff understands that portions of sites are in close proximity to the former <br /> OVP and are being considered for possible residential and/or commercial retail development. <br /> Based on our review, we have the following comments: <br /> • ChevronTexaco, SAIC, and Regional Board staff, to expedite the characterization process during <br /> the course of the investigation, will review the results of analysis and field observations to <br /> determine the need and/or location(s) for additional borings and corresponding sampling; and, <br /> • Elevated concentrations of TPHg were reported in groundwater, suggesting a leak from a refined <br /> product pipeline in close proximity to the OVP. The SAIC proposal includes analysis for BTEX, <br /> TPHg,THPd, and PAHs. However, the proposed analytes did not include testing for methyl <br /> tertiary butyl ether(MTBE). The delineation of MTBE in soil and groundwater should be <br /> included in the site characterization investigation. <br /> We concur with the 31 March 2005 workplan for the Mountain House Site#6 provided our comments <br /> outlined above are addressed. Please notify Regional Board staff 48 hours prior to initiating field <br /> drilling activities. <br /> If you have any questions or comments,please contact Dean Hubbard at(559) 445-5179. <br /> (' Qa,7 <br /> SHELTON R. GRAY C. DEAN HUBBARD <br /> Senior Engineering Geologist Engineering Geologist <br /> RG No. 6357 <br /> cc: Mike Infurna, San Joaquin County Public Health Services, Stockton <br /> Luis Mercado, SAIC, Sacramento <br />