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Final Compensatory Mitigation and Monitoring Plan—Version 2.0 <br />Climax Mine Overburden Storage Facility Expansion (SPK-2013-00045) <br />March 2017 Bikis Water Consultants, a division of SGM Page 17 <br />6.4 WATER SOURCES <br />Lake Irwin currently receives natural inflows from several drainages, seeps and springs at the <br />base of Sheep Mountain to the west of the site (Figure 4). These water sources sustain the <br />approximately 10-acre lake. The water availability study completed by Tetra Tech for the <br />mitigation site (Appendix C) indicates that the watershed tributary to the mitigation site yields <br />315 AF of flow per year, with most of this occurring during the growing season. Most of this <br />water comes from what is referred to as the Eastern Drainage #1 (See Figure 5a). To increase <br />the amount and reliability of this source, an existing diversion box and the conveyance to the <br />mitigation site will be replaced. With these improvements, the water supply available to the <br />mitigation site will be increased significantly and it is estimated that almost 300 AF can be <br />delivered during the growing season, on average. This equates to around 8 feet per acre and is <br />ample water to sustain the mitigation wetlands. <br />The proposed wetland outlet structure (Figure 5b) includes stop-logs and a gated outlet to allow <br />for adjustment of the water surface of the mitigation site, and return excess water to the Upper <br />Eagle River watershed. BWC-SGM has used a similar type of outlet structure successfully at <br />other wetland mitigation sites in Summit County and elsewhere. Based on past experience, <br />once the optimal water elevation for the mitigation site is determined, the outlet structure will be <br />set to maintain that water level. Although some minimal amount of maintenance and <br />adjustments may be needed during the first several years after mitigation site completion, it is <br />anticipated that no long-term maintenance will be required. <br />6.5 CONSTRUCTION TIMING AND SEQUENCING <br />Construction of wetlands at the mitigation site will be phased to correspond to the timing of <br />wetland impacts from expansion of the OSF as described in the Alternatives Analysis included in <br />the Section 404 permit application for the project. Ground disturbance and preparation for the <br />OSF expansion (reclamation soil salvage and construction of water controls) will occur over a <br />period of approximately five years in a sequential manner. Based on the plan for the OSF, <br />impacts will occur and therefore mitigation will be provided in three phases, as shown in Table 3. <br />Climax will construct each phase of mitigation so that it will be completed either prior to or <br />contemporaneous with McNulty phased disturbance. To facilitate construction, a small berm will <br />be constructed around each cell (phase) of the mitigation to allow for dewatering and water <br />management for the subsequent cells.