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RESPONSE: Section 3 was created by NewFields to evaluate the stability of the western aspect slopes of ECOSA and thus along the eastern aspect slopes the section line is not in exact alignment with the steepest portions of the slope. Therefore there appears to be a more shallow slope angle than the true 2.5H.•I V slope. 44. Appendix 7, Table 2—Runoff Coefficients • This table indicates 100 percent runoff from precipitation for areas that are actively being leached or lined, but with no ore covering the liner. This is a very reasonable assumption,but it is unclear where runoff peak flows are directed such that they are controlled and contained within the VLF. Please explain how the runoff from the 100- year, 24-hour precipitation event is controlled and contained within the VLF. RESPONSE: For modeling purposes, the entire runoff volume from the 100 year, 24- hour event was assumed to be conveyed to the PSSA. This volume of water is considered in the model in two different ways. First, monthly precipitation is modeled stochastically. While peak mean monthly precipitation on the site is on the order of 4 inches (see Attachment H, Table 1),peak modeled monthly precipitation is on the order of 10 inches (see Attachment H, Figure 2). This extra amount of monthly precipitation accounts for larger individual events that could occur. Secondly the model explicitly incorporates the volume for the 100 year storm plus draindown for a power outage. The volume from this storm and draindown are added to the PSSA volumes predicted from the stochastic monthly results. This is a conservative approach as it adds the storm and draindown to the monthly results which, as discussed above, already include extreme wet months. Using Squaw Gulch as an example, Figures 8 and 9 in Attachment 11 show the total volume in the PSSA as well as the remaining freeboard for the combined stochastic results plus the 100 year storm and draindown. The model demonstrates that at any given time throughout the simulation, the PSSA is capable of containing all inflows from the range of anticipated operating volume plus the 100 year runoff, while still maintaining a water surface elevation below the maximum 80%operating level. 45. Appendix 7, PSSA Capacity and Pumping Rates • The first paragraph states"Minimum operating volumes were not provided for PSSA 5 of the Arequa Gulch site or for the Squaw Valley PSSA". Why were these values not provided? RESPONSE: Updated minimum operating volumes were provided to ERC for all PSSAs, including the two mentioned in Comment 445, and the water balance report has been updated to reflect the new results (Attachment H). The minimum operating volumes for PSSAs 1, 2, 4, and 5 at the Arequa Gulch sites are 2,790,000 gallons, 1,414,000 gallons, 768,000 gallons, and 12,232,000 gallons, respectively. The minimum operating volume for the Squaw Gulch PSSA is 9 78,000 gallons. 46. Appendix 7, PSSA Capacity and Pumping Rates. • The last paragraph states "As a criterion for evaluating adequacy of storage in each facility, five feet of freeboard was required to be maintained in each PSSA". Does this five feet of freeboard correspond to the maximum 80 percent operating level in the PSSA's? If not, what is the purpose of the five feet of freeboard? RESPONSE: The five feet of freeboard described in the report is in reference to the total capacity of each PSSA. Based on the simulation results and the 80%operating levels provided by Newmont, the model demonstrates that during all times of operation, the water surface elevations in all of the PSSAs are well below the 80%operating levels, even when considering runoff from the 100 year, 24-hour event. This information has been added to the water balance report(Attachment 11). Page 21 of 30