2017-03-23_PERMIT FILE - C1981019A

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RULE 2 PERMITS mining by the pit and the spoil pile. There may also be some discharge of perched groundwater from the upper bedrock units to the Little Collom Gulch valley fill that could be affected (e.g., springs SPRLC-01, SPRLC-02). The potential impacts on spring flow are discussed above and impacts to groundwater are discussed in a following section. There may be periodic releases of water from the Section 25 sediment pond located in Little Collom Gulch near the toe of the spoil pile. This water will be released to Little Collom Gulch and will either infiltrate into the valley fill or contribute to surface flows in Little Collom Gulch. It is possible that some surface flow may make it to Collom Creek during the higher flow periods. There are no plans to release any flows from the dewatering system to Little Collom Gulch. West Fork Jubb Creek The West Fork of Jubb Creek is an intermittent stream. It joins the East Fork of Jubb Creek to the northeast of the mine area to form Jubb Creek. The total drainage area of Jubb Creek above the USGS gaging station is about 7.53 square miles, including both the East and West Forks (WMC, 2005). The area of the West Fork of Jubb Creek within the pit footprint is about 0.21 square miles and no areas are within the spoil pile footprint. Thus, the mine disturbance affects is less than 3% of the total watershed area of Jubb Creek. As described in Section 2.04.7 (2), the West Fork of Jubb Creek produced flow from May through August with a peak flow of about 0.30 cfs in June. It remained dry during late summer, fall and winter. As described above, there is flowing well in the West Fork of Jubb Creek at the location mapped as spring V1. This well contributes water to a small stock pond. Water from the pond infiltrates into the stream valley fill deposits and contributes to shallow ground water flow. The lower portion of Jubb Creek below the confluence of the East and West Forks typically produces flow for much of the year except during the winter months. Based on USGS stream gaging data from 1976 to 1981 on the lower reach of Jubb Creek (WMC, 2005), the annual flow volume is highly variable, ranging from less than 2 to over 300 acre -ft per year with an average of 81 acre -ft per year. The direct surface runoff from about 3% of the drainage area of the Jubb Creek watershed will be intercepted by the excavation of the Collom Pit. This minor amount of disturbance is not expected to have a significant impact on the amount of direct surface runoff in Jubb Creek. Collom Creek Collom Creek is an intermittent stream in its upper reaches but generally has perennial flow in its lower reach. It has a drainage area of about 5.05 square miles above its confluence with Little Collom Gulch. The watershed area of Collom Creek within the pit footprint is about 0.41 square miles and the area within the spoil pile footprint is about 0.39 square miles for a total area of about 0.80 square miles. Thus, the mine disturbance is about 16% of the total watershed area above the Little Collom Gulch confluence. As described in Section 2.04.7 (2), the lower Collom Creek monitoring location had a maximum flow of about 3.5 cfs during the spring runoff period with a base flow of between 0.03 and 0.04 cfs during the summer and winter periods, respectively. Based on WMC (2005) the upper portion of Collom Creek flows during the spring runoff period and this streamflow contributes groundwater recharge to the valley fill along the stream channel. During the summer and winter base flow periods, the upper portion of the stream typically does not flow so stream base flow in the lower reach of Collom Creek is maintained by discharge of groundwater from the valley fill to the stream. Collom — Rule 2, Page 114 Revision Date: 1/6/17 Revision No.: TR -109