2022-07-19_REVISION - M1987026 (31)

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Bureau of Land Management Environmental Assessment Royal Gorge Field Office DOI-BLM-CO-F020-2020-0036 EA Since obsidian does not allow timely infiltration of impounded storm/meltwater,periodic dewatering of the impounded water from the quarry floor would be necessary if water ponds longer than 72 hours. All pumped water would be routed to the sediment ponds below the proposed mine site. Due to the lithologic characteristics of the obsidian, and suspended fines being minimal,the pumped water would not contain any residual sediment from the quarried material. Depth to Groundwater According to the Colorado Division of Water Resources(CDWR), depth to static groundwater level within the proposed expansion boundary is estimated between 80 and 275 feet, with the lower levels found within a clay rich rhyolite and higher levels within a decomposed granite. The obsidian deposit occurs approximately between the rhyolitic and granitic formations;therefore, the maximum mining depth of 120 feet could potentially expose groundwater;however,this is strongly dependent on the thickness of the overburden and dip angle of the obsidian deposit. A groundwater contour map was constructed by BLM using known CDWR well log data to illustrate the approximate depth to groundwater(Figure 5). Groundwater depth throughout the surrounding area was determined to range from 23 to 700 feet with elevation approximately between 7800 and 8200 feet. This range is strongly dependent upon the topographic relief and the formation type the reservoir is sourced. The lowest groundwater depths were recorded from water wells either near surficial ephemeral drainages or lower elevated areas. The operator has mined in the existing quarry since the 1980s and has conducted exploration drilling beyond 100 feet within the proposed expansion footprint and has never encountered groundwater. The present pit floor elevation is 8,020 feet. Three test holes were recently drilled on private land to an additional 85 feet(bottom elevation of 7,935 feet)from the current quarry floor and the holes were concluded to be dry. If the Black Obsidian Quarry were to encounter groundwater at any point during the expansion process,the operator would comply with all CDWR regulations(e.g., obtaining a Substitute Water Supply Plan(SWSP))to account for all evaporation loss for storm/meltwater retained longer than 72 hours). Structures Any necessary structures,processing facilities,mining related equipment and material storage areas would be located on private lands on either the new pad at the base of the quarry or the proposed processing area(Figure 3). All potential structures could include storage buildings,a generator station, fuel tanks, sanitary facilities, scale house, scale,processing facility, petroleum, oil, and lubricants (POLs) and hazardous storage (e.g.,batteries, cleaners, explosives, etc.) and smoking area. The operator may add a temporary modular office/dry room or install a metal building on the pad to conduct daily business. All permits,easements and management plans would be obtained and followed prior to construction of any structures. A pre-existing 4-strand barbed-wire fence surrounds the active mine boundary with a locked pipe-gate located at the mine entrance. This fence would be extended to include all future mining related disturbance.