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In any event, the ECOSA underdrain system is designed to conduct water in excess of that <br /> which will seep through the foundation clay till from areas underlain by Precambrian rock <br /> to areas underlain by diatremal rock. <br /> It appears that the underdrain system may not be a long-term(or short-term) solution to <br /> preventing impacted groundwater from leaving the diatreme infiltration zone. Are you <br /> working on an alternative long-term solution to this problem? <br /> RESPONSE:No. See response to 3.6.6 above. Newmont considers that the existing <br /> mitigation for toe seepage at ECOSA is working so no further alternative long term <br /> solution is required. As noted above, Newmont personnel will continue to monitor the toe <br /> of ECOSA as part of its regular inspection procedures. <br /> 3.6.7 Formation of Pit Lakes in Worked Out Surface Mines <br /> • Page 19: The text states that the lowest planned mine floor elevation is 9,200 ft amsl <br /> (North Cresson [Globe Hill]), which is 1,000 feet above the water table in this location in <br /> CPC 14-3 (8,285 ft amsl). Accordingly, no pit lake can form,no impact will occur,and no <br /> mitigation will be required."Although the North Cresson Mine is located mostly within <br /> the northern eruptive center of the diatreme, its southern portion(Schist Island) is located <br /> in the low-permeability Precambrian rock curtain that separates the north eruptive center <br /> from the western and eastern eruptive centers. Is it possible that the Precambrian rock <br /> curtain could work to trap water infiltrated into the northern eruptive center area at <br /> least temporarily, resulting in some pit inflow? <br /> RESPONSE: The Precambrian rock curtain does not currently retain water in the <br /> northern eruptive center to an elevation in excess of 8,200 ft amsl(Plate S). There is no <br /> reason to expect any surface mine to retain water, other than temporarily during heavy <br /> precipitation, and no influent water has been observed in WHEX since mining of the <br /> (saturated)surface clay-till during mine stripping. <br /> 3.7 Conclusion <br /> • Page 19: Under Item#2(b),the text states"while it is not expected that there will be any <br /> environmentally significant impacts(from temporary flow from toe of ECOSA during <br /> periods of high infiltration), it is proposed that toe seepage be diverted to runoff control <br /> ponds or collected for use in the mining process." Please provide more detail on the <br /> surface water structures to be constructed for this purpose, including their design <br /> and location(s).The locations of these structures should be shown on a map of the <br /> ECOSA area with sufficient detail. <br /> RESPONSE.All structures are currently in position. For details see Amendment I1, <br /> Appendix 10: Design Report for Storm Water Management-Amendment No. 11, Steffens <br /> and Associates, December 2015. The water structures for this purpose are shown in <br /> Drawing#CCVSAII-11. <br /> • Page 19: Under Item#2(c),the text states"upon reclamation of the project,the valley <br /> leach facilities will be punctured and any seepage through the spent ore will be directed to <br /> the diatreme. This will result in an increase of the flow to the diatreme of 119 gpm over <br /> the pre-mining flow."Is the pre-mining flow considered to be 7,000 gpm (as listed <br /> under 3.4 Ground Water,Item#3 on Page 7),or an average of 1,691 gpm (as listed <br /> for the time period of 1992-2002 in the small table shown on <br /> page 8)? <br /> RESPONSE. The latter. The 7,000 gpm figure relates to the transient flow from the <br /> Carlton Tunnel in 1941 during draindown of the diatreme immediately following <br /> Page 10 of 28 <br />