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Pond 013 <br /> Sediment Control Plan <br /> This sediment control plan addresses the condition of the watershed tributary to Pond 013 which <br /> is assumed to be completely backfilled to the postmining topographic surface but only recently <br /> reclaimed and retopsoiled. As such the entire area will be in a "topsoiled and seeded" condition, <br /> which would be the worst case for a large volume of runoff to Pond 013 The system collects all <br /> runoff from the 66.96 acres into Pond 013 near the northwest corner of this area. <br /> Except for a small (0.76) acre band of undisturbed land immediately adjacent to the C9 Ditch, <br /> and another 1.14 acre undisturbed area immediately south of the pond, the entire watershed is <br /> represented as "Topsoiled and Seeded" land. <br /> In addition to the rainfall runoff inflow from the above described areas, there may also be inflow <br /> collected from the trench drain in the reclaimed area as well as inflow from various other sources <br /> such as Tuttle Draw and CCC irrigation ditch as described in detail later in this summary. <br /> The design considerations used for this evaluation are described in the following paragraphs. The <br /> watershed boundaries, associated drainage areas, and runoff curve numbers are shown on Map <br /> 2.05.3(3)-32. <br /> Hydrologic Methodology <br /> The SCS method has been used to determine runoff volumes and runoff flow rates. The runoff is <br /> a factor relating the amount of rainfall to the amount of runoff for a given area. The best <br /> reference for application of this method to coal mine applications is Barfield, Warner, & Haan <br /> (1981) in "Applied Hydrology and Sedimentology for Disturbed Areas", Oklahoma Technical <br /> Press, Stillwater, OK. Tables are included in this reference, as well as several widely accepted <br /> NRCS (formerly SCS) publications, present the appropriate CN's (s) for specific land uses and <br /> conditions. <br /> Although the volume of runoff can be calculated manually using the SCS method, for this <br /> evaluation the SEDCAD computer model, developed and marketed by Civil Software Design, <br /> was used to make the runoff calculations. In addition to its wide acceptance for use in coal mine <br /> permitting work, it also provides a consistent tabular output of all design assumptions and all <br /> calculated results. <br /> Location Specific Hydrologic Parameters <br /> The 10 year, 24 hour precipitation event for permitting efforts for this location has been <br /> identified as 2.0 inches. The 25 year, 24 hour precipitation event produces 2.4 inches of rain. <br /> Site Specific Hydrologic Parameters <br /> Curve numbers were designated on a land use basis as determined from field observations and <br /> are presented on Table 2.05.3(3)-1 in Section 2.05.3(3). <br /> Attachment 2.05.3(3)-32 Revision Date: 3/30/20 <br /> Page 1 Revision No.: TR-99 <br />