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SCORIA STORAGE AREA SAE AND ASC'S <br />Twentyttule Coal Company (TCC) is requesting approval of a Small Area Exemption (SAE) for the Scoria Storage <br />Area located at the Foidel Creek Mine az shown on Map 24, Surface Facilities. Drainage and sediment control for <br />the Scoria Storage Area is provided by site grading, which results in some level of internal containment for the <br />storage area, and a site drainage system consisting of the following Alternative Sediment Control (ASCj meaztues: <br />• Grading, which directs anysignificant drainage to the south and east <br />• Bemis along the western and southern margins of the area, to contain the nuroff from a 10-year, 24-hour <br />storm event <br />• Two v-shaped drainage collection ditches, Ditches SPA 1 and SPA 2, which intercept any runoff and route <br />it to a sedimem trap (Scoria Area Sump) <br />• A sediment collection sump <br />• Ditch SPA 3, a trapezoidal graveled and vegetated ditch which transfers water from the sediment trap to the <br />old Foidel Creek channel <br />• A segment of the okl Foidel Creek channel (abandoned oxbow) which connects to the active Foidel Creek <br />channel and serves az a natural vegetative fiber <br />As a relatively sma[I area (approximately 0.87 acres), and given the effectiveness of the ASC measures identified <br />above in controlling both drainage and sediment from this area, the additional disturbance required to construct a <br />sediment pond or route drainage from this area to an existing sediment pond is not justified Off-site sediment <br />contributions can be effectively controlled through the proposed ASC measures, consistent with applicable <br />provisions of Rule 4.052(3)(6). There will be no discharge or mixing of site surface drainage with mine water. <br />Based on the accompanying SEDCAD4 modeling for this area, the peak flow and runoff for the Scoria Storage Area <br />discharge (Ditch SPA 3) are 0.55 cfs and 0.07 af, respectively. The estimate peak settleable solids concentration for <br />the discharge is 0.00 ml/L The natural vegetative fiber is not considered in the modeling results and would provide <br />an added measure of protection relative to effective control of off-site sediment discharge. <br />The drainage configuration for the Scoria Storage Area is shown by the accompanying Figure 1. Drainage design <br />documentation is provided by the accompanying SEDCAD4 computer modeling summaries. Designs for the <br />referenced ditches are snmmnri~rd by Table 1, Qtarmel Design Schedule for Scoria Pile Area and Trud}~s Comer. <br />Assumptions: <br />1) The Scoria Storage Area location and configuration and layout of <br />shown on Figure 1. <br />2) Hydrology and sedimentology inputs to the SEDCAD4 model <br />previouslysubmittedand approved drainage designs. <br />Design Parameters: <br />WatershedArea - 0.87 acres <br />10-yEar, 24hour storm - 1.8 inches (NRCS Type Il) <br />C[~l- 89/100 (graveledarea/disturbed) <br />ASC drainage control measures are az <br />are consistent with those utilized for <br />All other design parameters are az shown on the accompanying SEDCAD4 modeling summaries. <br />Design Results: <br />Peak flow- 0.55 cfs <br />~ Runoff Volume - 0.07 of <br />Settleable Solids Concentration - 0.00 ml/1 <br />