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Newmont Goldcorp ■ <br /> VLF/OSA Closure Stormwater Analysis <br /> NewFields Project No.475.0106.035 <br /> November 8,2019 <br /> 3.1. East Cresson Overburden Storage Area <br /> Runoff from ECOSA is divided into nine watersheds and eight diversion channels. Three of the <br /> channels, which convey runoff from the Northeastl, Northeast2, East1, and East2 watersheds, <br /> will discharge to Grassy Creek on the east. Runoff from the Northeastl will discharge into ECOSA <br /> Channel 1A whose centerline is aligned with the existing EMP-17a channel and has a peak flow <br /> of 377 cfs. Runoff from the Northeast2 watershed will discharge into ECOSA Channel 1B and has <br /> a peak flow of 550 cfs. Runoff from the East1 and East2 watersheds will discharge into ECOSA <br /> Channel 2 and has a peak flow of 332 cfs. <br /> The Northl watershed will convey runoff to the north via ECOSA Channel 7 into the WHEX pit. <br /> The channel for this watershed will have a peak flow of 108 cfs. <br /> The two watersheds, West1 and West2, will discharge into the SGOSA North and South diversion <br /> channels. The ECOSA Channel 5 will convey stormwater from West1, which will discharge into <br /> the SGOSA Channel 2. The ECOSA Channel 6 will convey stormwater from West2 and discharge <br /> into SGOSA Channel 1. The peak flows for ECOSA Channel 5 and 6 are 135 cfs and 65 cfs, <br /> respectively. <br /> At the south end of the facility, the Southwest and South watersheds will discharge into ESOCA <br /> Channels 4 and 3 respectively, which will eventually convey water to the Cresson Pit. The ECOSA <br /> Channel 4, from the Southwest watershed, will have a peak flow of 200 cfs. The ECOSA Channel <br /> 3, from the South watershed, will have a peak flow of 81 cfs. The proposed stormwater plan can <br /> be seen on Figure 2. <br /> 3.2. Wild Horse Extension Pit Backfill <br /> The majority of runoff from the WHEX Pit Backfill will flow to the west into the WHEX pit. A small <br /> portion of the facility on the eastern side will report to the WHEX Channel and flow to a pond at <br /> the toe of the stacking surface. The peak flow for this portion of the facility will be 41.6 cfs. The <br /> proposed stormwater plan can be seen on Figure 3. <br /> 3.3. Squaw Gulch Overburden Storage Area <br /> The SGOSA closure consists of three main watersheds, Northl, Stack North and Southl, and has <br /> two channels, SGOSA Channel 1 and 2. SGOSA Channel 1 will convey stormwater runoff from <br /> watersheds Northl and Stack North. Additionally, this channel will convey flow from the ECOSA <br /> Channel 6. This channel has a peak flow of 462 cfs. <br /> Page 5 <br />