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Groundwater Well Installation Work Plan Sharpe Army Depot Lathrop, California Ahtna Environmental, Inc. 6 Active monitoring by an onsite Qualified Biologist will be required during well installation activities if any active burrows are found at the site or within a 100-meter buffer, or if burrowing owls are observed at the site during the survey. Biological surveys and monitoring is not required for well installation outside of the Sharpe boundaries. 3.1.5 Support Facilities Support facilities include lockable containers, portable containment tanks, and bins with lids. Lockable support facilities will be secured when project personnel are not onsite. An equipment decontamination pad will be located in the Ahtna Environmental, Inc. site trailer parking lot, south of Building 404 (Figure 2). Decontamination water will be collected in portable tanks for subsequent disposal. It is anticipated most of the support facilities will be located at EWNC7 and at the Central Area Groundwater Treatment Plant (GWTP). Sanitation facilities will be located at the onsite Ahtna field trailer. 3.1.6 Security Field activities will be performed within and outside the Sharpe installation boundaries. Access will be limited to project personnel, subcontractor personnel, and authorized visitors. 3.2 Well Installation Activities Groundwater extraction and monitoring wells will be installed using a truck-mounted mud rotary drill rig operated by a State of California-licensed driller. The proposed well locations are included in Figures 8, 9, 10, and 12. Figures 2-5 show the hydrogeologic cross-section with the proposed wells in relation nearby wells and groundwater plumes. Proposed well construction specifications (Table 1) are based on local geology and hydrogeology, groundwater contaminant concentrations and trends, construction specifications and production rates of nearby existing wells, and professional judgement. Wells will be set at the following depths: • EWNC7 will be set in the C Zone at approximately 145 ft bgs (Figure 13) • Three monitoring wells (MW543B, MW544B, and MW545B) will be set in the B Zone at approximately 70 ft bgs (Figure 14) • Two monitoring wells (MW546C and MW547C) will be set in the C Zone at 85 ft bgs (Figure 14) • EWA1R will be set in the A Zone at approximately 45 ft bgs (Figure 15) The borehole diameter will be 16-inch nominal for extraction wells and 8-inch nominal for monitoring wells. Well installation will be completed under the supervision of the Project Geologist, who will be responsible for oversight of borehole logging, well installation, and development activities. General procedures for borehole drilling and logging include: • The well location will be verified and determined to be safe from underground utilities and aboveground hazards during construction operations. • Drilling equipment will be staged at each location to avoid disturbing the normal flow of traffic, using safety delineators as needed. Drilling equipment will be set up in a centrally-located staging area at the Ahtna office trailer.