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Response to DRMS Adequacy Review(2)—Cotter-9 Mine Reclamation Plan Amendment <br /> accounts for the reduction). The channel labeled "Existing Diversion Ditch" <br /> collects flows in the roadway at the corner, where it is shown to begin, and diverts <br /> them away from the road. This short channel was constructed previously and <br /> directs water south where it quickly becomes shallow, eventually"daylighting"to <br /> existing grade, allowing the flows to fan out and dissipate along the hillside. <br /> These flows do not impact the working portions of the mine and were therefore not <br /> considered for analysis. Upon further investigation, it was discovered that offsite <br /> basin 20B was originally thought to contribute to flows in the existing road ditch <br /> "4", but actually discharges to the south near the south side of the shop/dry <br /> building. Closer analysis of photos and site topography shows a natural swale <br /> existing south of the building created by the natural embankment along the east <br /> side of the roadway. This swale will intercept runoff from previously labeled offsite <br /> 20B (now labeled offsite 40)which has been deflected away from the shop area by <br /> the proposed diversion berm. Runoff will flow along the east side of the berm until <br /> going around the southeast corner of the shop/dry building where it will then be <br /> intercepted by the swale and directed south away from the roadway. A new basin <br /> 20B is shown on the revised drawings which encompasses the area from the top of <br /> the natural road embankment to the east side of the roadway. This basin, <br /> combined with 20A(the area immediately around the shop/dry building) is the total <br /> contributing area to the east side roadway ditch. New basin boundaries, labels and <br /> flow calculations are included in the attachments of this document. See <br /> Attachment 4 for the revised drawings and Attachment 2 for the new flow <br /> calculations. <br /> c. The new "existing" diversion ditch east of Offsite 20B is not analyzed for stability <br /> or capacity nor is the contributing subbasin drawn to consider it. Please <br /> reference Figure 2 (attached) to see the area (highlighted in magenta)DBMS <br /> deems necessary to address contributing runoff to this existing diversion ditch <br /> and ensure adequate design capacity and stability. Please revise the hydrology <br /> estimates and makes the necessary adjustments to the channel analyses for <br /> capacity and stability. <br /> Again,the "Existing Diversion Ditch"was constructed previously and collects <br /> flows from a relatively small area intercepted by the roadway above the portal. <br /> These offsite flows are diverted away from the active portions of the mine site and <br /> were therefore not considered for analysis. <br /> d. Subbasin IOA is not drawn to consider the proposed diversion channel O(ref. <br /> Sheet 3 label). Please reference Figure 2 (attached) to see the area (highlighted <br /> in green)DBMS deems necessary to address contributing runoff to this existing <br /> diversion ditch and ensure adequate design capacity and stability. <br /> 8 <br />