2013-10-30_REVISION - M1977310 (3)

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JD -6 Mine — Drainage Design Plan 1 1. INTRODUCTION 1.1 Purpose This Drainage Design Plan presents the design analysis for the stormwater drainage facilities at the JD -6 Mine, which is located in Montrose County, Colorado and owned by Cotter Corporation (N.S.L.) (Cotter). The plan addresses aspects of stormwater collection, conveyance, and retention design necessary to comply with the Colorado Division of Reclamation, Mining and Safety (DRMS) drainage criteria. 1.2 Overview - Runoff Areas and Routing The JD -6 Mine is located below the north - facing escarpment of Monogram Mesa. The underground mine is located on the Department of Energy (DOE) lease tract C -JD -6 (530 acres) as shown on Plate 1. The JD- 6 Mine is permitted for 6.24 acres of surface disturbance and the current affected area is 3.24 acres. Mining activities that have the potential to affect stormwater discharge at the JD -6 Mine include the following: • The waste rock storage pile (1.53 acres) • Access roads • Vent holes (2) These facilities occur in two main sub - basins, which are identified as B 1 and B2 on Plate 1. Sub -basin B 1 occupies 1,205.7 acres and is drained by an unnamed intermittent stream that flows east and northeast into the Paradox Basin (Plate 1). The two vent holes and associated access roads are located off county road EE16 in Sub -basin B1. The ground surrounding the vent holes is minimally graded to direct water away from the vent holes, and vegetation is well established. The vent holes would have minimal or no effect on stormwater quality. Sub -basin B2 occupies 296.1 acres and is drained by an unnamed intermittent stream that flows north into the Paradox Basin (Plate 1) and is tributary to East Paradox Creek. The stream is intermittent in its upper reaches and ephemeral on the floor of the Paradox Valley. Sub -basin B2 contains the mine facilities which are the area of primary focus for this Drainage Design Plan. Stormwater is managed to reduce the potential for runoff from upslope to contact disturbed ground in the mine facilities area, as described in detail in the following sections. Runoff from undisturbed surfaces, areas of minor disturbance, and areas not containing designated chemicals or potentially toxic or acid forming materials is considered "non- contact" stormwater because it has not had potential exposure to pollutants. Table 1. Major Sub -Basin Areas at th a JD -6 Mine Sub -Basin Area Area Description (ft ) (acres) B 1 52,519,930 1,205.7 Main sub -basin for lease area & underground workings B2 12,899,050 296.1 Main sub -basin containing waste rock pile, adit, mine facilities area 1.3 Adjacent and Ancillary Facilities The adjacent Mineral Joe claims (144 acres) are owned by Cotter and are permitted under a separate mining permit (M- 1977 -284) and stormwater permit (COR 040177). Due to its close proximity to the JD -6 Mine, some of the stormwater management performed at the Mineral Joe Mine site is beneficial to both properties. However, the two sites operate under separate mine reclamation permits and stormwater management plans. Specifically, the stormwater diversion structures which are associated with the JD -6 Mine are also beneficial in reducing run -on to the Mineral Joe Mine facilities, while the stormwater retention pond associated with the Mineral Joe Mine collects runoff from the JD -6 waste rock pile. 4148A.131028 Whetstone Associates