2018-11-26_GENERAL DOCUMENTS - C1980004

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and silt fencing demonstrated to be sufficient to ensure that runoff from the 10 year, 24-hour storm event will meet the settleable solids discharge limit of 0.5 ml/l (Appendix pages M-2 through M- 4xxiii). The silt fences were approved within TR -11 to replace total containment sumps that had previously provided sediment control for the small areas. The silt fencing was installed in 2002. Mine water collected underground in sumps is authorized within the NPDES permit to be pumped to the surface and directly discharged through a pipe to the McClane Drainage without being routed through a sedimentation pond. Mine water discharges have been necessary on occasion, and the discharges have been in compliance with applicable discharge permit effluent limits. Drainage and sediment control measures are addressed in Section 2.4.4 of the application text, as well as various exhibits and appendices referenced in the text. The following finding is made pursuant to the three small area exemptions referenced above. 1. The Division proposes to grant small area exemptions (SAE's) from use of sediment ponds for the office facility area (SAE -1, .78 acres), the topsoil stockpile (SAE -2, .39 acres), and the construction dirt stockpile (SAE -3, .30 acres) due to the limited size of the areas and due to the fact that the operator has demonstrated that ponds and treatment facilities are not necessary for the drainage to meet the effluent limitations of Rule 4.05.2 and applicable State and Federal water quality standards for receiving streams, and also due to the fact that no mixing of surface drainage with a discharge from underground workings will occur (4.05.2(3)(b)(i). B. Diversions, Conveyance of Overland Flow, and Stream Channel Diversions The segment of McClane Canyon affected by mine surface facilities extends approximately 3000 feet from a box canyon at its upper end to its junction with East Salt Creek. Five tributary drainages come together at the upper end of the canyon to form the main ephemeral drainage. The mine portal facilities are situated at this location, and four of the five tributary drainages have been diverted via culverts beneath the mine bench. The culverts are adequately sized for the design event and have functioned well for over 25 years, with the exception of a couple occasions when they were overwhelmed by 100 year magnitude cloud burst type storm events in late summer. One ephemeral drainage on the south side of the portal bench is ditched around the shop building at the base of the cut slope, and is directed to the sedimentation pond. A temporary diversion ditch to the south of the sediment pond routes flow from three small ephemeral drainages around the pond, sediment drying area, topsoil stockpile and construction material stockpile. Berms in the office facilities area divert overland flow around the site. An additional diversion of the McClane Canyon stream channel occurred when the access/haul road was constructed in the spring of 1977. The point of diversion was between the riprap storage area and the office area, where the road was constructed across the channel. Due to the placement of road fill in the original channel, the flow in McClane drainage was diverted for many years. The diversion channel flowed generally straight west to East Salt Creek. Lower segments of the diversion channel developed into a steep sided gully, deeply incised into the colluvial/alluvial deposits, as is typical of ephemeral stream channels in the region. In 2006, Haul Road Culvert "P" was installed as approved by TR -14, which re -connected the upper segment of McClane Creek with its original lower segment. Upon final reclamation, all temporary diversion ditches, berms and culverts will be removed, and ephemeral drainages will be reconstructed in their approximate original locations. Fill embankments in locations where the haul road crosses McClane Creek will be removed and the approximate original channel configurations will be restored.