2019-06-28_REVISION - M1977004 (9)

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Homestake Mining Company May 10,2019 Regular(112d)Operation Reclamation Permit Application Package 4.3.1. Regulatory Context One of the primary regulatory drivers at present involves the quality of water discharging from the Mine as surface water, with dissolved uranium presenting the greatest challenge for future compliance. As described previously in Section 3.3.1, surface water exits the permitted boundary at the SW-33 outfall,flowing first into Indian Creek and then into Marshall Creek, exhibiting dilution along this path (HMC, 2017). Each of these stream segments have different water quality classification, with correspondingly different water quality compliance standards applied to them. HMC is working with the CWQCD of the Colorado Department of Public Health and the Environment (CDPHE) on these water quality standards and the concentrations of uranium leaving the site. Importantly, uncertainty in the final water quality regulatory compliance limits on these stream segments, and hence uncertainty in the level of uranium load reduction ultimately required, still exists as of preparation of this amended reclamation plan. Upper Gunnison Segment 21 (Reg. 35, COGUUG21; Figure 1) includes the mainstem of Marshall Creek down to its confluence with Tomichi Creek, as well as all tributaries and wetlands with the exception of Indian Creek and its tributaries, designated as Segment 20. Segment 21 currently carries the water supply use designation, with the "basin-basic" standard for uranium of 16.8-30 µg/L limit as established in Regulation 35. However, a temporary modification to the uranium standard on Marshall Creek was adopted in 2017, with the uranium standard temporarily set to "current condition" until December 31, 2022, allowing time for pursuance of BMPs for load reduction at the Mine. In contrast, Segment 20 (Indian Creek) is not a water supply use-designated stream. A draft discharge permit was issued for Segment 20 in 2014; however, this permit has not yet been adopted, and responses to HMC comments on the draft permit have not yet been received from the CWQCD. In the meantime, HMC remains in compliance with the uranium discharge requirements established under the older permit (with uranium concentrations based on cold water aquatic standards), but is actively working to define the LPL for uranium at the site, as per agreements with Water Quality Control Commission (WQCC). The LPL corresponds to the lowest practical level achievable discharge concentration that would result following the implementation of BMPs for uranium load reduction acknowledging the difficulty in building and maintaining year- round active water treatment given the elevation, limited winter access, and lack of power at the Mine. It is currently unknown whether the LPL, when defined, will be a set of narrative conditions/activities to be implemented or whether it will be a numeric standard. If the LPL is determined as a BMP based or narrative standard, HMC will be able to implement the needed actions and continue to demonstrate that the BMPs will meet the standard. If the LPL is determined to be a numeric value, HMC may need to implement the appropriate actions, take time to monitor the results, and then determine if any additional steps are needed. As such, a numeric definition will take significantly more time to develop than the narrative or BMP based approach. EXHIBIT E-RULE 6.4.5(AMENDED RECLAMATION PLAN) Page 57 HOMESTAKE MINING COMPANY