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4 Introduction <br />1 0 , Sediment Pond 002, also known as the Wedge Impoundment was established in 1976. <br />The pond is located in the Little Grassy Creek drainage, which is tributary to <br />Grassy Creek. The contributing watershed is approximately 2,977 acres (PM -1: <br />2701 acres & PM -15: 276 acres), of which approximately 1,524 acres were <br />disturbed by mining activities, and which have since been reclaimed and <br />revegetated. The reclaimed areas that drain to Pond 002 include the 'pre-law" <br />mining area, as well as most Wedge and Wolf Creek mining areas that were mined <br />between 1980 and 1996. This pond is located in the NE /4, Section 34, Township <br />6 North, Range 87 West (see Exhibit 13 -2A, Permanent Postmining Features). <br />Pond 002 is an incised impoundment without an embankment (see Exhibit 7 -8, <br />wadge Impoundment 002 and Cross - Section). It was created by leaving the _ Pit <br />highwall open and letting the pit fill with water. The pond is approximately <br />60 feet deep at its deepest point. The spillway system is a single open <br />channel trapezoidal spillway with a bottom width of 7 -feet, a left side slope <br />of 2H:1V and a right side slope of 1H:1V. The channel is well vegetated, with <br />additional protection provided by riprap. The spillway is located at the 100 <br />percent sediment storage level. <br />The Colorado Mine Land Reclamation Division, in its Proposed Decision and <br />Findings Document, dated December 31, 1986, indicated that Pond 002 was an <br />approved permanent impoundment. <br />Design Analysis <br />Seneca Coal Company evaluated the pond design in 1986 as part of Permit <br />Revision No. 1. The evaluation was completed to demonstrate that the pond <br />contained sufficient storage capacity, detention time and efficiency to satisfy <br />the regulations of the Colorado Mined Land Reclamation Board Rule 4.05.6. The <br />design evaluation is presented in Appendix 7 -6a. The certified as- built' <br />drawing is presented on Exhibit 7 -8; the spillway design is presented on <br />Exhibit 7 -9. <br />Pond 002 was constructed to meet the following specifications: <br />1) Provide adequate capacity to treat runoff to the pond from a 10 -year, 24- <br />hour storm event to assure compliance with receiving water quality <br />standards in accordance with Rule 4.05.6(3)(a). <br />2) utilize a single open- channel spillway system configured as required by <br />Rule 4.05.9(2)(a)(i) <br />3) Provide a spillway system than safely passes runoff from the 25 -year, 24- <br />hour storm event in accordance with Rule 4.05.9(2)(c)(ii). <br />Revised 04/05 <br />TR -37 <br />