2020-03-30_HYDROLOGY - M1981021 - Laserfiche WebLink

Home Browse Search

SUNDAY MINE COMPLEX-HYDROGEOLOGIC REPORT The conceptual regional head sources are the Dolores River, or perhaps the highlands of exposed Salt Wash further west. Given these sources, the anticipated static potential head may range from 5,500 to 5,600 ft amsl at the SMC. If left unchecked, water will continue to flood the workings until the static potentiometric surface is attained (a true static condition may not exist). CDM and Denison (2012) reported that the Sunday Mine had not been pumped from 1991 through 2009 and estimated that mine inflow during the period (18 years) was 55.4 million gallons, which they equated to a rate of approximately 5.8 gallons per minute (gpm). At the West Sunday Mine, dewatering was restarted in early 2008 and continued through most of 2009 at an estimated rate of 400 gallons per day. Dewatering occurred through use of the water for drilling and dust suppression, removal of water to the atmosphere via the ventilations circuits, and pumping water from active mine areas to inactive mine areas and/or underground sumps. Prior to this dewatering period, the water level in the West Sunday Mine was approximately 5,438 ft amsl; the dewatering reduced the water level in the mine to approximately 5,424 ft amsl (CDM and Denison, 2012). On the basis of measurements conducted by WWL in 2019, it is estimated that between 2009 and 2019, approximately 12.9 million gallons have flowed into the Sunday Mine and 8.4 million gallons have flooded the West Sunday Mine. Estimated inflow rates are 2.3 gpm for the Sunday Mine and 1.5 gpm for the West Sunday Mine. A vent shaft water level taken on February 18, 2020 at S-8 (Table 8-1) indicates that water levels in the mine workings are still rising as of this date. The calculated average head increase is approximately 0.7 ft per month. If the mine continues to flood to an elevation of 5,550 ft amsl, approximately 90 million gallons of groundwater will occupy the mine workings, but saturation of the surrounding unsaturated rock will take decades. Assuming an overall porosity of 20%, one cubic foot of water equals five cubic of saturated aquitard material. The displacement of groundwater from the aquitard to the mine workings area may result in a small reduction of the overall potentiometric head for the SMC area. If the Dolores River is hydraulically connected to the Salt Wash Top Rim Sandstone then the river may recharge water to the aquitard, thereby allowing for the potentiometric head to recover. The impact of past dewatering at the SMC to the potentiometric head in the Salt Wash is unknown, as no formal means of measurement were undertaken by mine operators or others. Similar to a pumped well, the influx of groundwater to the mine workings may cause a local depression in the potentiometric surface. Such a depression has not been measured and would Western Water& Land, Inc. 43