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HomeMy WebLinkAbout1.02 Grading And Drainage North Hangs Mine February 2023 21 Grading and Drainage Plan The North Hangs Mine affected area is located adjacent to the Colorado River. The disturbance area of the site will be at least 100 feet from the Colorado River, southwest of the river. Groundwater is roughly four feet below the natural grade and is the alluvial aquifer of the Colorado River. The 100-YR FEMA floodplain encompasses the entire mining area. There is no mapped floodway within the property. Temporary stormwater control berms, topsoil, and overburden stockpiles will exist during mining, but will be removed for reclamation. Exhibit G of the CDRMS application in Appendix 4 contains all hydrologic calculations. Maps showing the applicable information required by the Garfield Land Use and Development Code for Grading and Drainage Plans are listed in Table 4. Table 4. Grading, Drainage, and Hydrology Maps Grading Plan Maps Drainage & Hydrology Plan Maps C-2 Mining Plan G-1 Hydrology Map C-3 Cross Sections G-2 Ditch Reroute C-4 Cross Sections F-1 Reclamation Plan All slopes greater than 20% are identified on the Grading Plan maps listed above. 1. Construction Schedule The schedule of steps to bring the North Hangs Mine online are outlined below in Table 5. For the purpose of this land use application, construction is considered to cover the startup period of mining operations only. Table 5. North Hangs Startup Construction Schedule Days Activity 0-5 Stake and mark all boundaries 5-35 Strip initial topsoil from processing area and build berms. Install temporary erosion control measures around berms. Seed all long term berms and stockpiles. 35-60 Install permanent site access. Install temporary erosion control measures along perimeter. 60-100 Vegetation development on all applicable areas. 100-105 Removal of temporary erosion control measures as vegetated areas reach 80% cover. 2. Permanent Stabilization Permanent stabilization will be accomplished early in the operation life on long term berms or stockpiles via vegetation with the seed mix within Exhibit E of the CDRMS application in Appendix 4. The processing area and active mining pits will maintain internal drainage using slopes and stormwater berms until they are reclaimed. All portions of the site will be reclaimed North Hangs Mine February 2023 22 according to Exhibit E of the CDRMS application in Appendix 4, including vegetation measures identified therein. 3. Erosion and Sediment Control Measures - Estimate Cost Temporary soil erosion control measures include the construction, maintenance, and removal of stormwater berms. Temporary seeding of stormwater berms. Temporary seeding of stockpiles as needed. Occasional watering for dust suppression as needed. Erosion control measures can be seen on Map G-1, which is attached to this application. The total cost of these measures is estimated to be $ 25,000. 4. Neighboring Areas Neighboring areas of the North Hangs Mine are shown in Figure 6. N. Zoning for neighboring parcels is shown, with the North Hangs property highlighted in red. All surrounding zoning is Rural. Figure 6. North Hangs and Neighboring Areas N Irrigated Pasture Rangeland and Irrigated Pasture Rangeland (CPW) Active Mine North Hangs Mine February 2023 23 5. Stormwater Management Plan A stormwater management plan has been developed for North Hangs, in accordance with CDPHE guidance for such plans. The SWMP has not been submitted to CDPHE as no discharge permit has been applied for yet. Upon approval of this land use change permit, permits such as the CDPHE discharge permit will secured in advance of operations. A copy of the proposed SWMP can be found in Appendix 6.