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Wattenberg Mine, Exhibit G—Water Information May 2023 4.0 HISTORIC AND FUTURE GROUNDWATER LEVELS Appendix G presents hydrographs for the nine on-site monitoring wells. Labeled, dashed lines are included to indicate mine dewatering in 2006 and the completion of the Pond 3 slurry wall in 2013. Wells MW-2 and MW-3 experienced noticeable groundwater elevations declines during dewatering which both recovered quickly due to the high transmissivity of the area. Many of the monitoring wells show a rise in groundwater elevations following 2013. Upgradient wells such as MW-7 and MW-8 exhibit gradually climbing water levels, while MW-2 and MW-5 show quick water level increases at the end of 2013 followed by plateauing values. Figure G-3 shows that MW-2 and MW-5 are immediately upgradient of the Pond 3 slurry wall. In the absence of other information, the water level increases at MW-2 and MW-5 could be interpreted as groundwater mounding due to the slurry wall. However, due to the major flooding of the area in September 2013 and the gradual water elevation increase at upgradient wells MW-7 and MW-8, the late 2013 water level increase at MW-2 and MW-5 does not conclusively point to a notable groundwater mound. These wells show relatively consistent groundwater elevations since the installation of the slurry wall, although with the general water level increases across the rest of the site this could indicate some form of minor groundwater shadow. Due to the high transmissivity of the area, and based on the hydrographs is Appendix G, it is anticipated that implementing the remaining mining activities and associated dewatering, the Struck Pond slurry wall installation, and the reclamation work will have minimal impact on local groundwater elevations. Nevertheless, it is important to recognize that the Struck Pond may create a partial barrier to groundwater flow due to its positioning between locations that currently have slurry walls, namely Pond 3 and the Parker-Dersham Pond. Due to the unique positioning, the hydraulic impacts from the Struck Pond both during dewatering and potentially after the slurry wall is installed may be greater than without the two other structures in place. The perimeter drain around the slurry wall is expected to minimize these potential effects. Structures and wells (not including monitoring wells, Figure G-6 and Table 1) located within '/z mile downgradient of the Struck Pond include: • Stillwater Ski Lake • Huett Seep/Ditch • Well 10—permit number 21385- • Well 80—permit number 191-WCB • Well 231 —permit number 6291-R • Well 272—permit number 49717-F Wells 10 and 272 are not screened in the shallow alluvial aquifer and would therefore be unaffected by dewatering or the slurry wall. Wells (not including monitoring wells) located within '/z mile upgradient and cross gradient from the Struck Pond which could be affected by dewatering include: • Well 36—permit number 138214--A • Well 138—permit number 132424--A • Well 166—permit number 130499--A • Well 171 —permit number 138214- • Well 173—permit number 19893- • Well 223—permit number 202399- • Well 295—permit number 48617-F • Well 387—permit number 6647-F • Well 392—permit number 213-WCB • Well 438—permit number 158810--A Wells 166, 295, and 438 are not screened in the shallow aquifer and would therefore be unaffected by dewatering or the slurry wall. OTETRA TECH Page 4 1 8