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Geosynte& C011SUltaluS LWD-6. Downward vertical gradients are observed both north and east of the Site and increase toward the water supply wells as a result of the pumping from the transmissive zone overlying the Corcoran Clay. Due to pumping, groundwater elevations are also highly dynamic and range from approximately 25 to 50 feet bgs in the vicinity of the proposed new groundwater extraction wells east of Howland Road. Historical groundwater monitoring data and preliminary results from the ongoing supplemental characterization as shown on Figure 3 suggest that sulfolane in the eastern portion of the Site has migrated vertically downward to the well-graded sand and gravel layer overlying the Corcoran Clay, and then laterally outward from the Site through this transmissive layer. 3, EXTRACTION WELL DESIGN M Selection of Well Locations Based on the conceptual site model the PW30 (EW-18A/B) and PWOI (EW-19) locations were identified as areas where additional pumping may be needed to contain sulfolane (Figure 2). Three new groundwater extraction wells are proposed to be installed, as follows: • Two new groundwater extraction wells on the north side of groundwater monitoring well PW30 in the transmissive sand zones between approximately 70 to 95 feet bgs (EW-18A) and 110 to 185 feet bgs (EW-18B)to remove sulfolane mass and prevent continued downward vertical and horizontal migration of sulfolane east of Howland Road (Figure 2). • One new groundwater extraction well will be installed next to PWOI (EW-19) in the deep transmissive sand zone above the Corcoran Clay from approximately 185 to 270 feet bgs to reduce the off-site migration of sulfolane in the deep transmissive sand layer between the Site and the supply wells(Figure 2). The extraction well locations were selected to account for logistical considerations. The wells are proposed to be installed on the Simplot property adjacent to existing monitoring wells PWOI and PW30. Groundwater extracted from EW-18A/B and EW-19 will be conveyed via a pipeline to the treatment plant located west of Howland Road (Figure 2). Details on the wellhead design, pipeline design, pumps and upgrades to the GETS will be provided in a separate engineering design report. 3.2 Depth and Screen Intervals The proposed EW-18A, EW-18B, and EW-19 well construction designs, including depths and screen intervals, are based on geologic logs from adjacent wells and borings, the conceptual site model, and geologic layering observed during the recent field investigation. The coarser grained sand and gravel transmissive zones with sulfolane concentrations greater than 500 µg/L were targeted for the extraction well screens. Figure 3 shows the proposed extraction well locations projected onto a preliminary cross section from the supplemental Site characterization. Appendix A includes the PW01, PW30, and PW43 (Site Characterization Location 3) geologic logs. Extraction Well Installation Work Plan 2 November 30,2018