2011-09-20_REVISION - M1981185 - Laserfiche WebLink

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AUGUST 8, 2011 MAY DAY MINE CLASS II - SUBMITTAL 2 REVIEW PAGE 5 OF 15 1. The new portion of the road is supported by an embankment that falls steeply toward wetlands to the east. The drainage and erosion control plans need to clearly demonstrate how the wetlands will be protected during both reconstruction of the new unpermitted portion of the access road and ongoing operation of the mine. 2. The road surface itself is sloped to the west so that stormwater drains to the east toward a rock outcrop and is collected in a bar ditch on the west side of the road. This bar ditch outfalls at the low point of the road. Details for the outfall are still needed, with sediment removal being of particular concern. 3. The 36 -inch drainage culvert crossing below the road outfalls directly into wetlands. Details are needed regarding how the inlet will be designed and managed to ensure no sediment enters the culvert and creates a point discharge to the wetlands. The potential for oil, fuel, and chemical spills is a concern on both the historic and the new portions of the access road. Detailed information regarding how this will be handled is needed. D. Water Supply As summarized above, water is needed at the site for employees (drinking), ore processing, drilling/extraction; sanitary uses, fire water storage, dust mitigation, and filling of augmentation ponds. The applicant proposes meeting drinking water needs for employees using bottled water and meeting other needs using two existing water rights. The applicant states their operation will require 40 gpm (58,000 gpd), and that 75% (30 gpm or 44,000 gpd) will be continuously recycled in the ore processing cycle. The ore processing operation involves submerging ore tailings in water and chemical to separate the mineral (gold and silver) from the ore tailings. Once the mineral concentrate is removed, the tailings are dewatered. The water removed from the tailings is routed to a recycled process water storage pond and reused in the subsequent mineral leaching cycles. The waste tailings retain approximately 25% of the water and are proposed to be buried in the excavated mine tunnels. The 30 gpm proposed to be continually recycled through the process water storage ponds will progressively accumulate chemicals. The water balance to be provided by the applicant needs to address how much fresh water (from surface or groundwater rights) is needed to replenish or dilute the recycled process water. It would be helpful to understand the rate and manner in which the process water will be disposed. Storage is proposed for both process water and augmentation. Augmentation water is distinct from process water in that it cannot contain chemicals as it will be released back to the stream to replace depletions caused by well pumping. The applicant's water balance needs to demonstrate how the augmentation ponds will be filled (weekly or monthly) for both average and dry years. It is assumed the augmentation ponds will be filled solely by fresh surface or groundwater. If they are filled with treated process water, however, implications of water treatment need to be addressed within the water balance. Specifically, what type of treatment is proposed and how much water will be lost in the process? The applicant has two water rights to supply the above needs - a surface water right (06CW91) and a groundwater right (80CW133). DOWR states that the surface right is junior and may be impacted by calls placed on the La Plata River. DOWR states the groundwater right does not have an associated permit and that obtaining the permit will require an augmentation plan. PLANNING DEPARTMENT • 970.382.6263. • 1060 E. 2ND ANTE. • DURANGO, COLORADO • 81301