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EXHIBIT 7, ITEM 23, PART C <br />SEDIMENT PONDS AND ASSOCIATED MODELING DURING MINING <br />This section describes the system of sediment ponds needed to control runoff from the out of pit <br />temporary spoil pile. Map 29C describes the location and dimensions of the spoil pile. Over a <br />period of several years, the maximum configuration of the temporary spoil pile will be achieved. <br />The runoff from a portion of the haul road and the mine facilities are also included in the <br />sediment control system. Mine Facility Areas are shown in more detail on Map 22B. <br />The sediment control plan consists of two separate systems, one for the west side and one for the <br />east side, as shown on Exh. 7-23, Figures Cl, C2 (west side), and C3, and C4 (east side). <br />Separate SEDCAD models were prepared for each system. Hydrologic and sedimentology input <br />parameter used in the SEDCAD models are the values described in the Introductory Text of <br />Volume 2D in the document entitled "Methodologies and Assumptions for Sedimentation Pond Design <br />Evaluations". <br />Based on recommendations provided in a February, 2015 telephone conversation with Dr. <br />Richard Warner of the University of Kentucky Biosystems and Agricultural Engineering <br />Department, and a coauthor of the SEDCAD Design Manual and User's Guide, the "Cover <br />Factor" appropriate for loose dumped spoil is between 0.40 and 0.45. The higher value was <br />conservatively selected for use in this analysis. When advised that we are using curve number of <br />74 for runoff from loose dumped spoils, as per the approved Introductory Text of Volume 2D, <br />Dr. Warner pointed out that a value of 74 is probably an overly conservative number, and a value <br />on the order of 65 would be more appropriate based on his experience and measurements made <br />over the years at numerous coal mines. A curve number of 74 was nevertheless used for spoil <br />piles in the SEDCAD modeling included in this submittal. <br />Selection of SEDCAD input parameters L and S which are needed for sediment generation in the <br />sedimentation evaluation analysis are selected on a case basis for each subwatershed. The <br />MUSLE (Modified Soil Loss Equation) is used to estimate sediment generation at the source. <br />Selection of the parameters R, K, LS C and P is described in the literature. LS is derived via an <br />equation that includes a "length" parameter "L", and a "slope" parameter "S". However, LS is <br />not the simple product of those two terms. Both "L" and "S" are based on the topography of the <br />subwatershed in question with certain limitations provided in the literature as well as SEDCAD <br />users' training courses. First a representative slope is determined from the topography, and this <br />sets the parameter "S". The "length" parameter "L" is more complicated as it represents the <br />longest slope that water will have to flow before encountering a concentration point, such as a <br />rivulet of a distinct slope change. SEDCAD instructors advise that regardless of the topography, <br />"L" can ever practicably exceed about 200 feet. <br />The selection of "L" and "S" for input into the SEDCAD model for the near repose angle slopes <br />of a benched spoil pile is also complex. The values of 145 feet for "L" and 31% for "S" were <br />selected for the dumped spoil pile lifts to approximate the combined LS factor that would apply <br />to a compound slope, in this case a concave slope with a very steep (repose angle) upper part and <br />a very flat lower part (bench). SEDCAD cannot handle a compound slope directly, but a method <br />to do so is described in Chapter 5 of "Hydrology and Sedimentology for Disturbed Areas" by <br />Barfield, Warner and Haan, 1981. The method uses the original 1965 Wischmeier and Smith <br />Exh. 7-23C-1 Revision Date: 11/09/15 <br />Revision No.: PR -04 <br />