2022-05-16_HYDROLOGY - M2018053 - Laserfiche WebLink

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Ms. Katie Todt January 10, 2022 Page 2 of 5 The operation will excavate and process a placer gold deposit. A schematic of the process is attached to illustrate the water uses. The gold bearing gravel is located approximately 20 feet above the existing clay layer. The overburden will be excavated and placed in previously mined areas for reclamation. Gold bearing gravel will be processed for the gold and the washed gravel will also be replaced into mined out excavations. The operation will mine all the way to the clay bed, and expose groundwater as the existing groundwater table is approximately three feet below the surface. The material is first processed on a large mesh screen, and the smaller materials will go to a hopper that feeds a trommel, where it will be washed. Finer materials containing gold will fall into the sluice box below the trommel, while the larger materials will be conveyed to a gravel heap for eventual disposition into mined out excavations. This SWSP is for operations associated with the southern processing area and wash plant. A maximum of two gold processing plants will be in operation at any given time. DEPLETIONS Depletions from the site consist of evaporative depletions of exposed groundwater, processing pond evaporation, first fill inflow, material processing and dust suppression. The Applicant has calculated the evaporation at the site to be 40 inches per year based on the evaporation atlases in NOAA Technical Report NWS 33. Therefore, the anticipated depletion calculations are: Plant Settling Ponds: 1.0 ac X (40"/ac/yr evap - 6.73" eff. ppt) = 2.80 AF Pump Pit Exposed GW: 0.2 ac X (40"/ac/yr evap - 6.73" eff. ppt) = 0.55 AF Dust Suppression: 30 ac disturbance X 0.15 AF/ac = 4.50 AF Grizzly overflow pile: 706 ft' X (40"/ac/yr evap - 6.73" eff. ppt) = 0.04 AF Trommel: 64 ft' X (40"/ac/yr evap - 6.73" eff. ppt) X (7 hrs/24 hrs) X 2.0 = 0.002 AF Trommel overflow pile: 706 ft' X (40"/ac/yr evap - 6.73" eff. ppt) = 0.04 AF Sluice: 160 ft2 X (40"/ac/yr evap - 6.73" eff. ppt) X (7hrs/24 hrs) X 2.0 = 0.006 AF First Fill Inflow: 0.2 ac X 17 ft depth X (1-0.3) = 2.38 AF TOTAL = 10.32 AF This mining operation has a mining permit (M-2018-053) approved by the Colorado Division of Reclamation, Mining, and Safety under the Hard Rock Mining Act (section 34-32). Mining operations that are permitted under the Hard Rock Mining Act, qualify under section 37-80-120(6) to offset gross evaporation losses by the amount of depletions that would have occurred due to pre-existing natural vegetative cover that has been eliminated. In this case, an offset of effective precipitation was applied to gross evaporation, resulting in a net evaporation amount of 33"/year that was used to calculate evaporative depletions to be replaced under this SWSP. Depletions resulting from evaporation of exposed groundwater may be reduced for ice covered periods. For the purposes of this SWSP, the Applicant shall replace the evaporation depletions from exposed groundwater any time the exposed groundwater is not completely covered by ice.