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Pond 009 Postmining SEDCAD Modeling <br />This sediment control plan update addresses the current conditions of the watershed tributary to <br />Pond 009 to reflect the fact that the entire tributary area is now reclaimed and has a maturing <br />vegetative cover in place. The system collects all runoff from the 30.24 acres into a below grade <br />sediment control pond excavated near the north boundary of this area. This area is currently <br />draining to Pond 009 via several ditches described in more detail below and a culvert system <br />under 2700 Road, with some area directly tributary to the sediment pond. <br />The area that drains to Pond 009 includes 28.06 acres of reclaimed lands with more than 3 years <br />growth, 0.52 acres of undisturbed land, and 1.66 acres of paved road (2700 Road). <br />The design considerations used for this evaluation are described in the following paragraphs. <br />The watershed boundaries, associated drainage areas, and runoff curve numbers are shown on <br />Map 1 Postmining Drainage Analysis, Pond 009 Area, hereafter referred to simply as "Map 1 ". <br />Hydrologic Methodology <br />The SCS Curve Number method has been used to determine runoff volumes and runoff flow <br />rates. The runoff curve number is a factor relating the amount of rainfall to the amount of runoff <br />for a given area. The best reference for application of this method to coal mine applications is <br />Barfield, Warner, & Haan (198 1) in "Applied Hydrology and Sedimentology for Disturbed <br />Areas", Oklahoma Technical Press, Stillwater, OK. Tables are included in this reference, as <br />well as several widely accepted NRCS (formerly SCS) publications, present the appropriate CN's <br />(curve numbers) for specific land uses and conditions. <br />Although the volume of runoff can be calculated manually using the SCS Curve Number <br />method, for this evaluation the SEDCAD computer model, developed and marketed by Civil <br />Software Design, was used to make the runoff calculations. In addition to its wide acceptance <br />for use in coal mine permitting work, it also provides a consistent tabular output of all design <br />assumptions and all calculated results. <br />Location Specific Hydrologic Parameters <br />The 10 year, 24 hour precipitation event for sediment control analysis for this location has been <br />identified as 2.0 inches. The 25 year, 24 hour precipitation event used for spillway evaluation <br />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) -IA. <br />Attachment 2.05.3(3)-30 Revision Date: 3/14/2016 <br />Page 2 Revision No.: TR -70 <br />