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RULE 2 PERMITS <br />The direct surface runoff from 8% of the drainage area of Collom Creek above the confluence with Little <br />Collom Gulch will be intercepted by the pit. The direct surface runoff from 8% of the drainage area <br />which is associated with the temporary spoil pile will be routed to the Sidehill Pond and West Pond <br />sediment ponds. It will either be stored for on-site use or discharged using CPHDE criteria to Collom <br />Creek downstream of the Collom Pit. Therefore, the reduction of the amount of direct surface runoff in <br />Collom Creek caused by the mine is probably less than 16% and more likely in the range of 8 to 16%. <br />As described in Section 2.04.7 (2) the upper reach of Collom Creek is generally intermittent with <br />measured base flow in the range of 0.004 cfs and periods when the stream goes dry. The lower reach of <br />Collom Creek generally has perennial flow that is maintained during the summer and fall by discharge of <br />groundwater from the valley fill. Most of the groundwater recharge to the valley fill comes from the flow <br />in the upstream reach of Collom Creek during the spring runoff season, which will not be affected by the <br />mine. Therefore, the impacts of the mine on stream base flow are expected to be insignificant. <br />Flow in springs SPRC-02, V27, V28 and SPRC-04 may be reduced by mine dewatering operations as <br />described above. These springs make up less than 5 % of the measured surface flows in Collom Creek so <br />the potential impact of reduced flows on Collom Creek is not considered significant. <br />There may be periodic releases of water from the Section 25 pond located in the Collom Creek watershed <br />at the toe of the spoil pile. This water will be released to Collom Creek via a surface channel and will <br />either infiltrate into the valley fill or contribute to surface flows in Collom Creek, depending on the time <br />of year. <br />There are no plans to release any flows from the dewatering well system to Collom Creek. <br />Potential Impacts to Groundwater <br />Drilling of exploration and monitoring wells by Colowyo and other parties in the Collom pit area as <br />discussed in Section 2.04.7 identified very limited perched water in the shallow coal beds and interburden <br />and saturated conditions in the lower third of the sequence to be mined. There are no continuous non -coal <br />aquifers in the saturated section of the pit to be mined. <br />This subsection provides a discussion of the following potential impacts to groundwater: <br />• Changes in groundwater levels during mining <br />• Potential interactions with springs and seeps <br />• Potential interactions with valley fill aquifers and streams <br />• Effect on existing groundwater users in the area <br />• Effect on the Trout Creek Sandstone aquifer <br />• Effect of mining on the groundwater flow system <br />• Re -saturation of the pit backfill during the post -mining period <br />Figures 2.05.6-1 and 2.05.6-2 in Volume 15 show a plan view and typical cross section A -A of the <br />Collom pit and its location with respect to the upper section of Wilson Creek. On the cross section, the <br />pre -mining topography is shown as well as the KM layer and top of Trout Creek sandstone and their <br />outcropping in Wilson Creek. The southern limit of the cross section is near the location of several <br />beneficial use wells located in Wilson Creek. (This can be seen by reviewing Map 11C with Figure <br />2.05.6-1). <br />Collom — Rule 2, Page 115 Revision Date: 12/30/16 <br />Revision No.: TR -108 <br />