2019-12-13_REVISION - M1980244 (55)

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STORMWATER MANAGEMENT PLAN VICTORNEWMONT CRIPPLE CREEK AND GOLD MINING COMPANY • EMP-016, -017, and -019 (Figure 11): These ponds comprise a stormwater runoff control system of sediment ponds that collects runoff from the Wild Horse Extension ("WHEX") Mine, East Cresson Overburden Storage Area (ECOSA) and surrounding roads, soil stockpiles, and associated disturbance. This system is designed to capture stormwater runoff and is managed to promote exfiltration from the ponds and to facilitate infiltration into the shallow ground water regime. EMP- 017 is the terminal pond that is designed to collect and store excess flow from the other ponds. EMP-019 is temporary and will be mined through in the future; overflows from EMP-019 currently (January 2019) report to the WHEX pit. • EMP-020 (Figure 11): A stormwater runoff pond below the south portion of East Cresson Overburden Storage Area (ECOSA). The EMP-020 stormwater basin is physically lower, and the interim terrain is higher than EMP-017, thus requiring a separate and independent pond The pond collects stormwater from the face of the ECOSA, pre-operation stripping, and haul roads. • The east inlet channel to EMP-020 has been recently (December 2017) redesigned to improve stormwater conveyance to EMP-020 and reduce the potential for stormwater to overwhelm the channel • The EMP-020 spillway is has been evaluated (2018) and will be redesigned if necessary. • EMP-021 (Figure 9): A stormwater runoff pond that was constructed in early 2015 located on the west flank of the North Cresson Mine in the general area of Schist Island. The pond is also located above Poverty Gulch and the headwaters of Cripple Creek. It will collect stormwater from temporary access roads, areas being stripped and prepared for mining, from haul roads during mining of Schist Island and subsequent backfill of the mine. • EMP-022 (Figure 9): EMP-022, also known as Conley Sediment Trap and the Chicago Tunnel Bypass detention pond, is a stormwater detention pond located below the Chicago Tunnel bypass system that collects stormwater flows from within Poverty Gulch,the historic Chicago Tunnel mining area, and from the North Cresson Mine area, roads and undisturbed slopes. This pond has been evaluated in 2018 and improvements are planned for 2019 4.3.3.1 Desiqn Criteria for EMPs The downstream EMP's are the primary structural control measure used to manage stormwater discharge from each of the stormwater management areas and basins. The Site EMPs are designed according to the following criteria: EMPs are detention pond systems consisting of one or more detention basins or structures designed to contain at least twice the volume of runoff resulting from a 10-year, 24-hour precipitation event Pond