2021-09-03_PERMIT FILE - C1981019A (8)

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RULE 2 PERMITS Well DH -76- (Map 11B), is an encased well (except for surface casing), with the top of the sandstone at approximately 6,100 ft amsl and the water level of approximately 7,175 ft amsl. This is based on available data. The water level from this well was not used in the construction of the Trout Creek Sandstone potentiometric surface map since it is an uncased hole and construction details are not available. The Trout Creek Sandstone projected potentiometric surface shows a gradient to the north-northeast based on the three monitoring wells. Due to lack of Trout Creek Sandstone water level data in the Collom pit area, the potentiometric contours can not be projected to the pit area. However, comparison of the 2015 water level data with that obtained in 1996-7 (the last time the water levels in these wells were monitored for a water level) show no significant change in levels over the 19 year difference in collecting water levels. Discharge from the bedrock units occurs primarily to the valley -fill aquifers where the steeply -dipping north limb of the Collom Syncline is dissected by streams and along the northern portions of the stream channels. Numerous small springs and seeps present in and along the sides of the stream valleys crossing the area are indications of groundwater discharge from the bedrock units, but the discharge rates are small and the springs and seeps do not comprise a significant source of discharge from the bedrock units. The valley -fill aquifers lose water to evapotranspiration, primarily during the spring through early fall growing season, and discharge from the valley -fill aquifers also supports stream baseflow. At the northern, down gradient boundary of the Collom permit expansion area, because the bedrock aquifers do not continue north past the north limb of the syncline, nearly all groundwater outflows from the permit expansion area occurs through the valley -fill aquifers. The elevation of the valley floors where they cross the northern limb of the syncline is about 6,500 ft amsl. Groundwater Quantity — WMC (2006) estimated of groundwater flux through the general area from Good Spring Creek on the east to Morgan/Straight Gulch on the west in conjunction with development of a regional hydrogeologic model. The calculations used water -balance methods based on average hydraulic conductivities, saturated thicknesses and aquifer widths for both bedrock and valley -fill aquifers. The methods are described in detail in WMC's 2006 report Collom Pit Hydrogeologic Model, included as Exhibit 7, Item 22. The results were broken down by drainage and included recharge, loss to evapotranspiration, groundwater outflow as stream base flow, and groundwater outflow through the valley fill at the north boundary of the area. The flux estimates are summarized in Table 2.04.7-43. For the Collom Gulch and Jubb Creek drainages, which encompass the Collom permit expansion area, the total flux of groundwater through the valley fill and bedrock units above the KM layer was estimated to be about 31,000 cubic feet per day (ft3/day). About 65 percent of the outflow of groundwater at the northern boundary of the Collom permit expansion area was through the valley -fill aquifers, and the remaining 35 percent was outflow as stream baseflow. The groundwater flux through the Collom Gulch and Jubb Creek drainages comprises about 11 percent of the total groundwater flux through the area included in the calculations. The bulk of the flow (about 86 percent) occurs in the Morgan/Straight Gulch, Wilson Creek and Good Springs Creek drainages. Groundwater Quality — Baseline monitoring was conducted in 1996-1997 of the bedrock and valley -fill aquifers and during 2004-2006 of the valley -fill and bedrock aquifers in the Collom permit revision area. The data are summarized in Tables 2.04.7-41 and 2.04.7-42. The Colorado Mined Land Reclamation Division's (CMLRD) Guidelines for the Collection of Baseline Water Quality and Overburden Geochemistry Data were utilized during the baseline monitoring, and the sampling plan was reviewed and approved by the CMLRD prior to completion of the baseline monitoring program. Water quality sampling and laboratory analyses were conducted in accordance with Rule 2.03.3(4). The depth to water in each of Collom — Rule 2, Page 26 Revision Date: 4/7/17 Revision No.: RN -07