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007 WEST DITCH <br />The topography of the land at New Horizon Mine slopes gently to the southwest at <br />approximately 3%. To provide vehicle access to the mine area and to control surface <br />water runoff, a perimeter road and embankment will be constructed along the proposed <br />new permit boundary . This road will run along the west and south sides of the property <br />and will tie into 007 Pond embankment. A flat bottom ditch with cross sectional area <br />equal to a 10 feet wide trapezoidal ditch with 2:1 side slopes and energy dissipaters <br />will be constructed on the up dip toe of this perimeter road. This ditch will be know as <br />the 007 West Ditch and will collect and transfer all water from the proposed permit area <br />to 007 Pond for treatment, see Exhibit 2.05.3-1. <br />There are two natural occurring drainage channels that 007 East Ditch must traverse to <br />arrive at 007 Pond. The drainage channels will be blocked by the perimeter road <br />mentioned above. The roadway will be constructed in compacted lifts and will be of <br />sufficient height to contain the water in 007 East Ditch and of sufficient height to allow <br />• water to rise to a height in the natural drainage channels to continue its flows south <br />and easterly toward 007 Pond . Both diversion structures will store less than 20.0 Acre- <br />feet and will not be utilized at this time for water quality treatment purposes but rather <br />to just divert water runoff to 007 Pond. WFC understands that some benefits exist <br />from this ponding action to allow sediment to settle out before discharging to Calamity <br />Draw. WFC has elected at this time to design 007 Pond to handle the entire duties of <br />water quality and water retention time. 007 Pond will continue to be the designated <br />NPDES discharge point . <br />The two perimeter road diversion structures ,now known as 007 Diversion Structure 1 <br />& #2 will have two designed outlet structures as required by DMG. There will be a <br />primary and emergency spillway structure that will be of sufficient size to handle either <br />the 10yr-24hr or 25yr-24hr event. Atypical cross section can be seen in Exhibit 2.05.3- <br />9. The computer program SEDCAD + was used to model the area for surface water <br />runoff and sediment deposition. A 10yr-24hr and 25yr-24hr precipitation event was <br />calculated and can be seen in this attachment. <br />l~ <br />LI <br />(REVISED 72100) Attachment 2.05.3(3)-2-1 <br />