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Bureau of Land Management Environmental Assessment <br /> Royal Gorge Field Office DOI-BLM-CO-F020-2020-0036 EA <br /> Since obsidian does not allow timely infiltration of impounded storm/meltwater,periodic <br /> dewatering of the impounded water from the quarry floor would be necessary if water ponds <br /> longer than 72 hours. All pumped water would be routed to the sediment ponds below the <br /> proposed mine site. Due to the lithologic characteristics of the obsidian, and suspended fines <br /> being minimal, the pumped water would not contain any residual sediment from the quarried <br /> material. <br /> Depth to Groundwater <br /> According to the Colorado Division of Water Resources (CDWR), depth to static groundwater <br /> level within the proposed expansion boundary is estimated between 80 and 275 feet, with the <br /> lower levels found within a clay rich rhyolite and higher levels within a decomposed granite. The <br /> obsidian deposit occurs approximately between the rhyolitic and granitic formations; therefore, <br /> the maximum mining depth of 120 feet could potentially expose groundwater; however,this is <br /> strongly dependent on the thickness of the overburden and dip angle of the obsidian deposit. A <br /> groundwater contour map was constructed by BLM using known CDWR well log data to <br /> illustrate the approximate depth to groundwater(Figure 5). Groundwater depth throughout the <br /> surrounding area was determined to range from 23 to 700 feet with elevation approximately <br /> between 7800 and 8200 feet. This range is strongly dependent upon the topographic relief and <br /> the formation type the reservoir is sourced. The lowest groundwater depths were recorded from <br /> water wells either near surficial ephemeral drainages or lower elevated areas. <br /> The operator has mined in the existing quarry since the 1980s and has conducted exploration <br /> drilling beyond 100 feet within the proposed expansion footprint and has never encountered <br /> groundwater. The present pit floor elevation is 8,020 feet. Three test holes were recently drilled <br /> on private land to an additional 85 feet(bottom elevation of 7,935 feet) from the current quarry <br /> floor and the holes were concluded to be dry. If the Black Obsidian Quarry were to encounter <br /> groundwater at any point during the expansion process,the operator would comply with all <br /> CDWR regulations(e.g., obtaining a Substitute Water Supply Plan(SWSP))to account for all <br /> evaporation loss for storm/meltwater retained longer than 72 hours). <br /> Structures <br /> Any necessary structures,processing facilities,mining related equipment and material storage <br /> areas would be located on private lands on either the new pad at the base of the quarry or the <br /> proposed processing area(Figure 3). All potential structures could include storage buildings, a <br /> generator station, fuel tanks, sanitary facilities, scale house, scale,processing facility,petroleum, <br /> oil, and lubricants (POLs) and hazardous storage(e.g., batteries, cleaners, explosives, etc.)and <br /> smoking area. The operator may add a temporary modular office/dry room or install a metal <br /> building on the pad to conduct daily business. All permits, easements and management plans <br /> would be obtained and followed prior to construction of any structures. A pre-existing 4-strand <br /> barbed-wire fence surrounds the active mine boundary with a locked pipe-gate located at the <br /> mine entrance. This fence would be extended to include all future mining related disturbance. <br /> 11 <br />