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Site Assessment Report *,,w N„ Former Texaco Service Station Chevron Site ID 309075 March 18, 2010 3.2 GROUNDWATER MONITORING WELL INSTALLATION Upon completion of the soil borings, the monitoring wells were constructed using 2 inch OD schedule 80 poly vinyl chloride (PVC) casing with a 15 foot screen interval (MW-6) and a 10 foot screen interval (MW-6D) of 0.010 inch slotted PVC well screen. A 2/12 sand filter pack was placed around the well screen from the bottom of the borehole to approximately two feet above the screen interval. Approximately two feet of TR30 bentonite chips were placed on top of the filter pack. The remainder of the borehole annulus was grouted with tremie piping to approximately 1 foot bgs. Traffic-rated 8 inch (MW-6)and 12 inch (MW-6D) diameter flush mounted well boxes were installed in concrete. Well construction details are summarized in Table 2. Detailed boring logs with well construction details are included as Attachment C. 3.2.1 Shallow Water-Bearing Zone The shallow water-bearing zone was encountered at approximately 55 feet bgs and MW-6 was screened at a depth interval of approximately 55 to 70 feet bgs. As detailed in ARCADIS' Downgradient Well Installation Approval Request letter, dated January 5, 2010, the SJCEHD approved installing the screen interval at a depth of 55 to 70 feet bgs rather than the proposed 65 to 75 feet bgs. 3.2.2 Deep Water-Bearing Zone The deep water-bearing zone was encountered at approximately 110 feet bgs and MW-6D was screened at a depth interval of approximately 109 to 119 feet bgs. The exposed screen interval is approximately 109 to 115.6 feet bgs due to grout entering the PVC screen. ARCADIS believes that the well is still viable for groundwater sampling of the 109-115 foot water bearing zone. For further details regarding MW-6D screen interval, please reference ARCADIS' Downgradient Well Installation Approval Request letter, dated January 5, 2010. .r To minimize the potential for cross contamination between the shallow and deep water-bearing zones, MW-6D was double-cased with steel conductor casing as detailed in Section 3.1. 3.2.3 Groundwater Monitoring Well Development and Sampling On November 17, 2009, the newly installed groundwater monitoring wells were developed by Cascade and sampled by ARCADIS. Groundwater samples were collected in accordance with California Environmental Protection Agency (CaIEPA) procedures outlined in Representative. Sampling of Groundwater for Hazardous Substances (CaIEPA, 1995). Monitoring well development field data sheets are included as Attachment F. .r .r \\CA5FP\Data\Aproject\ENV\CHEVRON\309075\6 Deliverables\Reports\DG Wells Assessment\Assessment Report_4741010950.doc 4 V