2021-12-29_PERMIT FILE - M2021009 (9)

Home Browse Search

stormwater control structures/features (e.g., ditches, sumps, culverts, sediment ponds) are shown on the appropriate Exhibit C figures. The revised Exhibits C and G figures note the location design of the stormwater berms that will be used onsite. Additionally, prior to starting site disturbing activities, a site wide SWMP will be implemented to ensure stormwater is handled appropriately. This SWMP will be periodically updated to ensure stormwater compliance throughout every phase of mining. Additionally, all SWMP related questions will be handled by CDPHE as part of the CDPS. 52. On page G-3, the application states "after allowing sufficient time for sediment settling, clean, sediment-free water will be allowed to flow into and through a gated arrangement to control flow"and "this arrangement will be an elevated culvert that moves water from the processing area sump and under the CCP and WRL to the toe of the dump". Please provide a design drawings) for this proposed stormwater structure. At what point during the mining operation will this structure be constructed? How will water discharging from this structure east of Central City Parkway be managed? How will the structure be maintained during operations? Will this structure be necessary throughout all mining phases to manage surface water west of the parkway? Will this structure be reclaimed? If so, please be sure to address reclamation of this stormwater structure in Exhibit E and in the bond estimate provided in Exhibit L. See the revised Exhibit C and G figures showing the stormwater drainage arrangement via the underpass to the WRL. All stormwater structures will be constructed, altered as needed, and maintained over the course of mining regardless of phase. Exhibit C maps detail the final stormwater arrangement for each phase which are effectively the same as each lift is mined down to create the final 8050' phase 1 pad. Stormwater structures such as ditches, sumps, and berms will be maintained and moved, as needed, throughout the life of the mine and may require reclamation. Where applicable, stormwater structures are considered and detailed in the phase 1 bond calculation as shown in Exhibit L of the revised narrative. 53. This exhibit mentions constructing sumps in the quarry areas to collect stormwater, and states the location of these sumps may change as new mining phases are opened up. Please describe how water from these sumps will be managed in the event the water does not fully infiltrate or evaporate within 72 hours, as required by the Division of Water Resources. Will this water be pumped out and discharged to North Clear Creek under a CDPHE discharge permit? If so, how will this be accomplished? While all stormwater collected within relocated sumps throughout the mine's life is expected to infiltrate within 72 hours, any standing water that remains will be pumped and sent through the Central City Parkway underpass constructed during opening and phase 1 and continue the path detailed in Division question #12 above. 54. On Pages G-3 and G-4, the application states "sediment ponds will not be installed at the WRL toe". Please clarify whether any diversion ditches will be constructed around the edges of the waste rock landforms to convey stormwater around these features, and if so, to which location(s) will this water report? Please describe how water conveyed around the two waste rock landforms, water retained on each lift, and water draining from the base of these features will be managed. Lastly, does the applicant anticipate a CDPHE discharge permit will be required for any discharge to North Clear Creek from the waste rock landforms? December 2021 18 Lewicki&Associates