2024-05-17_REVISION - M1977493 (4)

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production related processes. This consumptive use is estimated monthly for water rights accounting that is reported to the State. Using this historic data,the average annual consumptive use at the site from 2014 to 2022 is about 2,310 acre-feet(approximately 1,430 gpm average annual rate). Adding this volume to the treated effluent provides an estimate of the current process water inflow of 11,651 acre-feet(approximately 7,220 gpm average annual rate). This volume will be used to estimate the future closure water treatment requirement. G-3.4.2 Estimated Closure Water Treatment Requirement The closure scenario process water area that will contribute water to the water treatment system is approximately 1,850 acres, as shown on Figure G-4. This area is about 32 percent of the current operating process water area. As shown on Figures G-5 to G-9, it is expected that there will be water pools at the reclaimed site. The total surface area of these pools within the closure process water area is estimated to be about 210 acres. Using an evaporation rate of 1.21 acre-feet per year(from the water rights accounting) the future consumptive use of water due to evaporation is about 254 acre-feet per year(approximately 160 gpm average annual rate). The procedure used to estimate the closure water treatment requirement is to evaluate the individual process water sources in the current scenario and make assumptions to estimate the flow from those sources at closure after final reclamation is complete. The following is a summary of the assumptions and resulting flow volume: A. Open Pit Basin: As shown on Figure G-4, the open pit basin will remain part of the process water area after final reclamation. The open pit area is currently dewatered using the 5-Shaft Pump Station. Flow meter records indicate that the total flow from this area has averaged about 1,973 acre-feet per year over the last 9 years(approximately 1,220 gpm average annual rate). It is assumed that the future process water volume from the pit basin will be similar with a range of about 1,500 to 2,500 acre-feet (930 to 1,550 gpm). B. 5 Dam Seepage: Runoff and seepage from 5 Dam currently reports to Mayflower Pump Station. Historic meter records indicate that the average annual flow from 5 Dam has been about 2,127 acre-feet over the last 9 years (approximately 1,320 gpm average annual rate). This volume is expected to increase somewhat between now and the time 5 Dam reaches the ultimate height due to increased hydraulic head. However, it is also expected to decrease somewhat after final reclamation due to a smaller water pool. It is assumed that these effects approximately offset and the process water volume with be similar to the existing volume (2,127 acre-feet per year) with a range of about 1,600 to 2,700 acre-feet (1,000 to 1,670 gpm). C. 1 Dam Seepage: Runoff and seepage from 1 Dam currently reports to Warren's Pump Station. Historic meter records indicate that the average annual flow from 1 Dam has been about 1,453 acre-feet over the last 9 years. This volume is expected to decrease after final reclamation due to the dry cover configuration but will not be completely eliminated. It is estimated that the future process water volume from this source will be approximately one-half the current volume, or about 727 acre-feet per year (approximately 450 gpm average annual rate), with a range of about 500 to 1,000 acre-feet (310 to 620 gpm). D. Storke Area: Runoff and seepage from the former Storke Camp area reports to the Storke Wastewater Pump Station. Historic meter records indicate that the average annual flow from the Storke area has been about 99 acre-feet over the last 9 years (approximately 60 gpm average annual rate). This volume is expected to decrease after final reclamation because of the tributary area being reduced from 71 acres to 30 acres (43 percent of current), as shown on Figure G-5. It is assumed that the runoff and seepage from this area will also decrease by 43 percent to about 43 acre-feet per year, with a range of about 20 to 60 acre-feet (10 to 40 gpm). E. Mill (Camp) Area: As shown on Figure G-5, structures and paving in the mill area will be demolished and removed and the area will be graded and capped as necessary. Runoff and seepage from the mill area is expected to continue to contribute process water flow after final reclamation,similar to the reclaimed Storke area. It is assumed that the mill area process water volume will be similar to the current volume from the Storke area, 100 acre-feet per year Exhibit G G-15 May 2024