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Monitoring Well Destruction and Soil and Groundwater Investigation Report US Can—Welty Road September 24,2009 2.4 REGIONAL HYDROGEOLOGY The site is located near the western margin of the Central Valley. Underlying this area are interbedded clay, silt, sand, and gravel Quaternary alluvial deposits from the Coast Ranges to the west. The soils encountered in this area appear to consist of predominantly fine-grained material such as silts and clays, with lesser amounts of coarser-grained material such as sands and gravels. The topography in the area is relatively flat and at approximately 105 feet above mean sea level. The depth to groundwater generally ranges from approximately 31 feet to 37 feet below ground surface (bgs). Historical data for the site indicates that the groundwater flow direction is inferred to be to the east at 0.001 feet per foot. Regional groundwater flow-direction information and local topography on the relevant United States Geological Survey (USGS) topographic map indicates that groundwater flow in the vicinity of the site is to the east (California Department of Water Resources [DWR], 2003; USGS, 1980). 2.5 PREVIOUS ENVIRONMENTAL ACTIVITIES The site emerged after several non-HPP related environmental investigations were performed in 1995 and 1996 at the Hunter Container property located at 35275 Welty Road. In the process of investigating a former burn pit and a release from a condensate outlet, petroleum hydrocarbons were encountered in soil and groundwater on the Hunter Container property in the vicinity of the former HPP pipelines. As a result, in 1997 Chevron Pipeline Company(CPL) initiated investigation of the former HPP pipelines in the area near the Hunter Container property. This HPP investigation area is known as the US Can-Welty Road site, which is the subject of this report. A summary of site investigation activities and results are included in Appendix B. Based on the results of previous investigations and the recommendations presented in SAIC's 2007 work plan and 2008 addendum, the RWQCB concurred that wells MW-3 through MW-5 could be destroyed if TPH quantified as diesel (TPHd) did not exceed the WQO during the January 2008 sampling event, and that additional lateral delineation of affected soil and groundwater was necessary (RWQCB, 2007a and 2008b). Well MW-3 indicated a TPHd concentration in excess of the WQO during the January 2008 groundwater monitoring event; therefore, this well was not destroyed. 3. SCOPE OF WORK SAIC implemented the recommendations presented in the work plan and addendum as described in sections 3.1 through 3.4. 3.1 PERMITTING,ACCESS,AND SITE SAFETY To maintain regulatory and legal compliance, protect the health of all involved persons, and prevent accidents: • CEMC secured site access agreements with UPRR and private property owners on whose parcels the scope of work was to be conducted. • SAIC completed strategic-planning and project-setup activities, including preparing the site-specific Health and Safety Plan(HASP) and Journey Management Plan(JMP). The HASP was kept on site, reviewed daily with all on-site personnel, and was available for review during investigation activities. The JMP was made available to all personnel and subcontractors prior to mobilization. 3 from Science to Solutions