2018-03-09_PERMIT FILE - M2017049 (29)

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� 1n ' o Transit Mix Concrete Co. slope is maintained while the stockpile is constructed, and then the stockpile is regraded to 3H:1V for reclamation. The stockpile design includes benching to minimize the regrading volumes. The only additional work will be the drainage channel and placing material in the pit area between F2 and the highwall. Therefore, volumes and costs have not been provided as this work is to be completed during Phase III. Exhibit D has been revised to more clearly discuss the stockpile slope gradients and grading. 124) On page 5 of the Waste Stockpile Stability Analyses, the Applicant states that seeps are known to be present in the vicinity downstream of stockpile TSI, but they are located below the toe of the stockpile near the creek. However, information provided in Exhibit G shows an upward vertical hydraulic gradient component at groundwater monitoring wells GW-1, GW-3, and GW-4, indicating areas of potential groundwater discharge to Little Turkey Creek surface water flow or to ground surface within the Little Turkey Creek valley in the form of seeps. Monitoring wells GW-3 and GW-4 are located upgradient from stockpile TS1. This is particularly well shown in Figure 3-2 —Potentiometric Elevations for Groundwater in the Hydrogeology and Impact Analysis by Hydro-Logic Solutions, Inc., where locations of the monitoring wells are plotted along with mine features. Figure 3-2 shows GW-3 (7,072 feet potentiometric elevation) located within the F2 backfill area, approximately 375 feet from the northern quarry edge. Figure 3-2 shows GW-4 (7,024 feet potentiometric elevation) located within the plant area, approximately 300-375 feet from the northern quarry edge. This means that potential seeps are present upgradient from the proposed TS 1 stockpile. Please provide clarification on these seep areas, including any potential impacts they might have on stability of stockpiles/backfill areas. Additionally, because the plant area is to be mined down to an elevation of approximately 6,950 feet, which is well below the potentiometric elevation of GW-4, please discuss whether the Applicant anticipates this having any effects on plant operations. Response: No seeps have been identified upgradient from the locations presented on the various maps in Exhibit C and G, and seepage into the stockpile is not expected. Regardless, seepage is not expected to have an adverse impact on stockpile stability. The Waste Stockpile Stability Analyses specifies that the fines material is considered to be a well-drained material that will sufficiently convey any seepage waters to Little Turkey Creek without the phreatic surface rising beyond the contact between bedrock and the fines material. Seepage is also not expected to have any impact plant operations. The groundwater assessment demonstrates that seepage flows during Phases I and II of mining are less than 5 gallons per minute. These flows will be diverted into Little Turkey Creek through the stormwater management system without impacting 125) In the Waste Stockpile Stability Analyses, Figures G1.1 through G2.2 for Section G (across F2 backfill area) do not appear to correlate with the G-G' section line shown in Figure 1 — General Arrangement with Section Lines, particularly at the G' end of the sections. The G end (left side) of the sections appear to line up with the G-G' section line shown on Figure 1, as they start at about the elevation of the pit floor, 6,950 feet. However, the elevations of the ground surface at the G' end (right side) of the sections is not consistent with the Hitch Rack Ranch Quarry(M-2017-049) Response to Comments—March 9,2018