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1.0 Introduction <br />Sediment Pond 003, also known as the Northwest Impoundment, is located in the SE /4, SWA, <br />Section 27, Township 5 North, Range 87 West in the Grassy Creek drainage, which is tributary to the <br />Yampa River (see Map 2.05.3 M4, Drainage and Sediment Control Plan). The contributing <br />watershed is approximately 30.1 acres; 13.5 acres were previously disturbed by mining - related <br />activities associated with the closed Seneca II Mine — the shop /warehouse area drains to Pond 003. <br />There will be no expansion of the existing disturbance area within the Pond 003 watershed as a result <br />of the Peabody Sage Creek Mine activities. <br />Pond 003 is an earthen embankment; the pond configuration, embankment, principal spillway and <br />emergency spillway are pre- existing. The as -built configuration is shown on Map 2.05.3 -E2.B, <br />Sediment Pond 003 As- Built. The top width of the embankment is approximately 20 feet wide, with <br />upstream and downstream slopes of approximately 311:1 V, respectively. The principal spillway is an <br />18 -inch diameter straight CMP pipe capped with an end plate. A six -inch CMP pipe, with an invert <br />elevation at 6,577.10 feet, is fitted through the 18 -inch end plate. The emergency spillway is a <br />trapezoidal open channel with a bottom width of 10 -feet and 3H:1V side slopes. The invert elevation <br />of the emergency spillway channel is at 6,580.0 feet; the channel is well vegetated with additional <br />protection provided by rock riprap. <br />The original design, as -built plans and. modifications were prepared under the supervision of others. <br />Pond 003 was originally constructed by a precursor company to Seneca Coal Company, the operator <br />and permittee of the Seneca II Mine (Permit C -80 -003). Mr. Ronald J. Gerkhe, a Colorado registered <br />• professional engineer (P.E. No. 19959), experienced in the design and construction of earthen <br />structures certified the 1986 design and associated as -built plans. The 1986 design and as -built plans <br />are located in the Seneca II Mine permit in Appendix 7 -6b. The Seneca II Mine certified as -built <br />drawing is presented as Exhibit 7 -11, Northwest Impoundment #003. <br />The Colorado Division of Reclamation, Mining and Safety ( CDRMS) approved Pond 003 as a <br />permanent postmine structure as part of Technical Revision No. 42 (TR -42) for the Seneca II Mine <br />permit in a decision dated September 12, 2007. In discussions with CDRMS representatives on <br />March 9, 2009, Mr. Tom Kaldenbach of CDRMS agreed that submittal of the approved, permanent <br />postmine as -built configuration and accompanying report was all that is necessary for the Peabody <br />Sage Creek Mine permit application package (PAP). This determination is based on there being no <br />new disturbance in the contributing watershed during this mine permit term. <br />As noted above, the pond was originally constructed in 1979 by a precursor company to Seneca Coal <br />Company (SCC), the Seneca II Mine operator and permittee under Coal Mine Permit C -80 -003. <br />Following is a brief summary of the design and as -built documents from the Seneca II Mine permit <br />that have been inserted into the Peabody Sage Creek Mine PAP. <br />• The pond design was evaluated by SCC in 1986 as part of the first Seneca II Mine permit <br />term renewal (RN -01). The 1986 design evaluation demonstrated that the pond was <br />designed and constructed to meet the requirements of Rule 4.05.6. <br />• • SCC prepared an as -built report in 2005 as part of TR -37 which certified the pond met the <br />requirements of Rules 4.05.6(3)(a), 4.05.9(2)(b) and 4.05.9(2)(c)(ii). The 2005 as -built <br />report was certified by Mr. Robert Shevling, Colorado Professional Engineer No. 37382. <br />2.05.3 -E2.B1 11/09 <br />