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CYCC - .Sediment Yield Demonstration Eckman Park Area 41 • 1.0 INTRODUCTION Colorado Yampa Coal Company (CYCC) is in the process of requesting a Phase Iii bond release for Area 41 (238.41 acres). This area is covered under Colorado Yampa Coal Company (CYCC) -Mine 1, Mine 2, and Eckman Park Permit No. C-81-07I and is located approximately 20 miles southwest of Steamboat Springs, Colorado. CYCC has developed the following sedimentology demonstration in support of this application. According to Division of Minerals and Geology (DMG) Regulation 3.03.1(3)(b), no more than 60 percent of the bond can be released until the applicant demonstrates that existing conditions will result in equivalent or lesser sediment contributions to surface runoff when compared with predisturbance conditions or undisturbed areas. The following information is provided to meet the requirements of the specified demonstration. The post-mining land use for Eckman Park has been defined as pastureland. Slopes average approximately 12% across the reclaimed area. The maximum slope, approximately 49%, in this reclaimed azea is located on the overburden stockpile #2. The approved reference area is the pastureland reference site located just west of Pond A in Eckman Par1c. The topography in the Pasture Reference Area varies significantly from the reclaimed areas in Eckman Park in that a much gentler slope prevails. The average slope measured on the Pastureland Reference Area is approximately 2.1%, while the average slope of the reclaimed areas is approximately 12%. Due to the significant topographic difference between the reference area and the reclaimed area, it is inappropriate to develop a direct sediment yield comparison between the areas to satisfy DMG Regulation 3.03.L(3)(b). In the alternative, CYCC will utilize a • model to compare the runoff from Blocks East and West to adjacent undisturbed pasturelands. A SEDCAD+ model has been developed by CYCC to demonstrate that runoff from the reclaimed area results in equivalent or lesser sediment contributions to surface runoff when compared to adjacent undisturbed conditions. SEDCAD + is a computer software program developed to assist in the evaluation of stornwater runoff, erosion, and sediment control management techniques. The 1998 Area 41 vegetation survey conducted by CYCC and available soils information from the existing permit document were utilized as input to the SEDCAD+ program. To develop a comparative model for unmined adjacent areas, CYCC utilized vegetation information derived from the 1998 Eckman Park Reference Area vegetation survey conducted coincident with the Area 41 survey. This reference area has been established as being representative of the vegetation found in adjacent, unmined lands. OI/ The reclaimed area and associated reference area boundaries do not coincide with watershed boundaries; therefore, representative portions of the areas are modeled on a small scale tt~th model inputr selected as appropriate to ^ distinguish those characteristics unique to the reclaimed area. Grading practices which enhance surface 111~"AJ roughness, reduce the length of overland flow, and increase infiltration are the primary modeled attributes which strengthen the reclaimed areas ability to reduce suspended solids concentrations. To model areas with similar topography and soil apes. CYCC combined the vegetation survey information for the Pastureland Reference Area with information on the topography and soil types determined for Eckman Pazk. The so es and topo ttnd-in Ec k are similar to the soils and topography found in adjacent unmined ar Thc Reference Arca soil hpe an vegetation data were modeled with the topography of the • reclaimed areas small watershed for comparison with the reclaimed areas. By modeling comparable adjacent areas in this manner, the sediment }field demonstration provides a reasonable companson of the success of the rcvegctatton efforts and their effectr on surface runoff and sediment loads. • i rn~enrimmnrnul4YAm`hunJrcl!v.a41 d.x