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2025-04-11_REVISION - M1988112 (2)
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2025-04-11_REVISION - M1988112 (2)
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Last modified
4/14/2025 8:52:02 AM
Creation date
4/14/2025 8:31:15 AM
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Template:
DRMS Permit Index
Permit No
M1988112
IBM Index Class Name
Revision
Doc Date
4/11/2025
Doc Name Note
Appendix D Thru Attachment E Binder 2 of 2
Doc Name
Request For Amendment To Permit
From
Battle Mountain Resources, Inc.
To
DRMS
Type & Sequence
AM4
Email Name
LJW
THM
EL1
Media Type
D
Archive
No
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Newmont Corporation <br /> July 23, 2020 <br /> Page 6 <br /> 3.5 Partial Cutoff Wall <br /> A partial cutoff wall that extends along the eastern and southern portion of the West Pit was <br /> simulated using the MODFLOW-2005 hydraulic flow barrier package. The assumptions in <br /> simulating this feature are: 1) there are no flaws in the construction of the cutoff wall; 2) the <br /> hydraulic conductivity of the cutoff wall and the cutoff wall thickness as entered as model input <br /> are consistent; 3) the height of the cutoff extends the full saturated thickness of the aquifer layer. <br /> Model simulations show the amount of alluvial groundwater flow into the West Pit is reduced with <br /> the partial cutoff wall because the groundwater is diverted around the partial cutoff wall (Figure <br /> 9). However,there is approximately 30 gpm to 37 gpm of groundwater flow into the West Pit from <br /> the North Pit area and the Precambrian unit. The models simulate groundwater flow out of the <br /> West Pit between 29 to 38 gpm primarily from seepage through the cutoff wall over time. <br /> Groundwater flowlines show the 29 to 38 gpm leaving the West Pit migrates to the alluvium and <br /> subsequently discharges to Rito Seco(Figure 9).A smaller portion is captured by alluvial pumping <br /> wells M32 and M33. <br /> The low-hydraulic conductivity of the cutoff wall also results in the cutoff wall acting as a dam to <br /> groundwater flow for water that would naturally flow from upgradient areas, moves through the <br /> West Pit, and eventually towards the alluvial aquifer (Figure 9). Simulated groundwater levels <br /> therefore increase in the West Pit. These increased groundwater levels may result in water levels <br /> rising above the ground surface. That water will find the path of least resistance and flow towards <br /> lower lying areas, in this case, the Rito Seco alluvium. With inflows from the North Pit area and <br /> the Precambrian unit accumulating in the West Pit and ultimately discharging without treatment <br /> due to no water level controls inside the pit, this option doesn't appear feasible. <br /> 3.6 Full Cutoff Wall <br /> The simulated full cutoff wall extends the partial cutoff wall to the west side of the North Pit above <br /> the estimated location of the Green Clay deposit.The Green Clay is simulated with a low hydraulic <br /> conductivity value relative to other geologic units represented in the model and is, therefore, is <br /> generally an effective barrier to groundwater flow. In this simulation, there are two cutoff walls <br /> but no water level control through the pumping of BF5. <br /> With a longer extent of the cutoff wall in two locations, simulated groundwater levels increase on <br /> the upgradient side of the cutoff walls because the presence of the extended low hydraulic <br /> conductivity cutoff wall results in an increase in groundwater levels. These conditions are similar <br /> to the groundwater levels with the partial cutoff wall shown in Figure 9. The increase in <br /> groundwater levels changes the gradient of flow from the West Pit towards the alluvium to the <br /> sourth east resulting in alluvial groundwater seeping through the cutoff wall over time. The <br /> estimated outflow in the models through the cutoff wall and towards the alluvium is estimated to <br />
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