2019-12-13_REVISION - M1980244 (55)

Home Browse Search

Newmont Goldcorp . VLF/OSA Closure Stormwater Analysis ■ NewFields Project No.475.0106.035 November 8,2019 The SGOSA Channel 2 conveys runoff form the Southl watershed and flow from the ECOSA Channel 5. This channel will have a peak flow of 199 cfs and will discharge into the East Cresson Pit. The proposed stormwater plan can be seen on Figure 4. 3.4. Valley Leach Facility 2 Runoff from VLF2, also known as Squaw Gulch Valley Leach Facility (SGVLF), was divided into fourteen watersheds and five different diversion channels. Watersheds 3a, 4a, 5a, 6a and 7a flow into down drains down the outside of the facility and discharge directly out of the facility area. Watershed 1 contributes to VLF2 Channel 5 and eventually merges with SGOSA Channel 2 to discharge into the Cresson pit. The VLF2 Channel 5 has a peak flow of 206 cfs. The VLF2 Channel 4 conveys flow from watersheds 2, 3b and 3c.At approximately STA 41+00 and STA 48+00, flow from VLF1 channels 4 and 3 also merge into VLF2 Channel 4. The peak flow in VLF2 Channel 4 is 879 cfs. The VLF2 Channel 3 conveys flow from watershed 4b and its peak flow is 26 cfs. VLF2 Channels 3 and 4 merge with the down drain from watersheds 3a and 4a and discharges under Highway 67 to Squaw Gulch. This design does not include the required structures in order to convey this flow under Highway 67. Given the high value, it is anticipated that a substantial outlet structure will be required to divert the flow under the road. The VLF2 Channel 2 conveys flow from watershed 5b and has a peak flow of 17 cfs. The VLF2 Channel 1B conveys flow from watershed 6b and has a peak flow of 37 cfs. These two channels merge at an existing sediment pond. Reporting to this existing pond is also direct flow from the down drain between watersheds 6a and 5a. Watershed 8 contributes to VLF2 Channel 1A which has a peak flow of 139 cfs. This flow also reports to an existing sediment pond. Reporting to this pond is also direct flow from the down drain from watershed 7a. The proposed stormwater plan can be seen on Figure 5. 3.5. Valley Leach Facility 1 Runoff from VLF1, also known as Arequa Gulch Valley Leach Facility (AGVLF) is divided into six different diversion channels. Stormwater runoff from watersheds Northeast and East flow into channels VLF1 Channel 5 and 6 respectfully and discharge into the Cresson Pit. The peak flow reporting to VLF1 Channel 5 is 428 cfs and the peak flow reporting to VLF1 6 is 93 cfs. Channels VLF1 1 and 2 receive stormwater runoff from the Southeast and West watersheds and discharge into Arequa Gulch. The peak flow reporting to VLF1 Channel 1 is 324 cfs and the peak flow reporting to VLF1 2 is 357 cfs. Stormwater runoff from watersheds Northl and North 2 will report VLF1 Channel 4 and 3 merges into VLF2 Channel 4 and eventually discharge into Squaw Gulch. The peak flow reporting to VLF1 Page 6