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3.0 Design Details <br />Segments A and B will consist of 18" perforated pipe buried along the toe of the mining <br />highwall. This pipe will be surrounded by durable rock as shown in Detail A of Map <br />2.05.3(3) -21. It will run into a nexus point of all three segments where the spoil water will <br />enter into a solid pipe. Rock used to surround the perforated pipe in each segment of the <br />trench drain has been selected to ensure stability of the installation based on <br />engineering experience. <br />Segment C consists of two parts: a rock drain extending southeast, and the solid pipe <br />running northwest to Pond 013. The rock drain portion will consist of an 18" perforated <br />pipe surrounded by durable rock as shown in Detail B of Map 2.05.3(3) -21. At the <br />segment nexus, the SE Rock Drain, Segment A, and Segment B will converge and drain <br />into the 18" solid pipe that then conveys the spoil water to Pond 013. The solid pipe will <br />be buried beneath at least three feet of material as it passes under the Prime Farmland <br />area. Most of the perforated pipe sections of the trench drain will be under significantly <br />more cover, but will also have a minimum of three feet of cover in all areas. <br />According to Section 2.05.6(3) — Protection of the Hydrologic Balance, the realistic flow <br />anticipated for the spoil spring is 0.68 cfs (-305 gpm). Currently the spoil water is <br />running at approximately 250 gpm. Pond 013 is designed to hold 9 ac -ft of water, <br />according to the as -built (Attachment 2.05.3(3) -18). The anticipated spoil spring flow of <br />0.68 cfs translates into 0.07 ac -ft of needed storage, according to SEDCAD. The <br />anticipated runoff feeding into Pond 013 is 5.89 ac -ft. Therefore Pond 013 is more than <br />capable of handling the spoil water inflow as well as over 3.0 ac -ft of sediment <br />(5.89 +3 +0.07 < 9.0 ac -ft). <br />The SEDCAD report showing the above analyses is attached. The currently approved <br />drainage area of 82.9 acres and the approved curve number of 86 are used for the <br />general stormwater inputs of Pond 013. The area is from the approved Map 2.05.3(3) -1- <br />2, and the curve number is that used for poor quality pasture land. <br />March 2014 (TR 63) Attachment 2.05.3(3) -25 -4 <br />