2020-12-22_REVISION - M1977300 (6)

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ti 4) The operator estimates the Black Forest Mine to have a capacity of approximately 15,000 CY. It is the Division's understanding the majority of this capacity may need to be utilized in order to complete the alluvial excavation project as planned. Therefore,the Division requires additional information on the placement of this material into the mine, particularly how far the operator expects to place the backfill material up to the mine opening gates. Please describe the anticipated interface between the edge of the backfilled contaminated alluvial materials inside the mine and the gated mine openings. Does the operator propose backfilling the mine up to the gates,or will there be some space left between the toe of the backfill and the gates? If so,please provide the estimated buffer distance proposed. The Division is particularly interested in the anticipated interface between the contaminated alluvial materials placed inside the mine and the proposed backfill materials to be placed against the gates of the mine openings. The Division believes these interfaces as well as the proposed backfill plan would be best depicted in a conceptual diagram. Please provide a conceptual cross-section showing the anticipated outer edge of backfilled materials inside the mine, the gated mine openings, and the proposed backfill plan for the mine openings(from mine opening gate to toe of backfill).Please ensure the backfill plan shown on this cross-section portrays the proposed types of material (e.g., Rock, Common Fill, Plant Growth Medium) and approximate placement depths of this material. 5) Please make the following revisions to the Water Quality Monitoring Plan provided in Section E.6: a) On page 13, the operator states "Water quality samples are collected quarterly from thirteen surface water sample locations and sixteen groundwater sample locations". However, according to the approved permit, there are fifteen groundwater sample locations, including wells MW-00, MW-0, MW-6, MW-7, MW-12, MW-13, MW-14, MW-15, MW-16, MW-17, MW-18, MW-19, MW-20, Raw Feed/Mine Refill, and collected sump water from Sump#1 (Master Sump). Please correct this statement accordingly. b) In Table E-3 —Groundwater Sample Locations, all sumps (including Sumps 1, 4, 5, 8, 9, and 10) are said to be "Discontinued". Additionally, under the Sumps sampling location(in the last row), it states "Combined pumpback water from sumps". However, according to the approved permit, Sump 1 has not been discontinued and is designated as the "Master Sump", from which, water is collected (inside the water treatment plant) for water quality analysis. Please correct this table accordingly. c) The Figure E-3 — Groundwater Monitoring Locations map is not the most recent version of this map from the approved permit (see enclosed Groundwater Monitoring Locations map provided with the 2nd Quarter 2020 Sampling Results on October 16,2020). It should be noted,there is one error on the enclosed map which should be corrected for future submittals — the surface water monitoring location "SW-BPL" is erroneously included and should be removed. Please revise Figure E-3 accordingly. Exhibit F—Reclamation Plan May (Rule 6.4.6): 6) The revised F-1 —Reclamation Plan Map does not show less of the property boundary(not a required feature) and more of the affected land boundary, as recommended by the Division in its preliminary adequacy review letter. This makes it difficult to assess the expected physical appearance of the