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A. Surface Water <br />March 24, 1988, Walden Coal Company submitted a permit revision application for an <br />alternative sediment control to remove the four sediment ponds at the site and replace <br />them with treatment facilities consisting of terrace benches constructed at two hundred <br />(200) foot intervals. <br />Walden Coal Company proposed in early 1988 to limit slope length and utilize terraces as <br />"treatment facilities" at the newly reclaimed mine. Walden Coal Company's proposal <br />was accompanied by a SEDCAD' (Sediment, Erosion, Discharge by Computer Aided <br />Design) computer tun which predicted that settleable solids value off the site would not <br />exceed the NPDES effluent limitation of 0.5 ml/1. The following discussion is broken <br />into three parts: the regulatory perspective on this issue, a brief description of the Bourg <br />Mine property, and a chronology of the work done and assumptions made to justify this <br />proposal. <br />The two regulations which speak directly to this proposal are found in Rule 4.05.2. Rule <br />4.05.2(1) states: "All surface drainage from the disturbed area shall be passed through a <br />sedimentation pond, a series of sedimentation ponds or a treatment facility before leaving <br />the permit area." Division regulations had no specific definition of a treatment facility. <br />(Rule changes proposed in 1987 specifically defined treatment facilities). The Colorado <br />Attorney General's office recommended that terraces could be alternative treatment <br />technologies falling under the treatment facility category. With that legal interpretation, <br />Walden Coal Company set out to satisfy Rule 4.05.2(7) with site specific empirical data <br />and the modeling of a 10 yeaz -24 hour storm event. <br />Rule 4.05.2(7) states: "Dischagge of water from areas disturbed by surface coal mining <br />and reclamation operations shall be made in compliance with all applicable Federal and <br />State Water quality standazds" Walden Coal Company's effluent standards for sediment <br />generation aze regulated by N.P.D.E.S. Permit No. CO-0036854. This permit utilizes the <br />total suspended solids parameter during periods of no precipitation. The permit utilizes <br />the total settleable solids parameter during precipitation events. Walden Coal Company <br />submitted a SEDCAD' run which predicted that the settleable solids concentration <br />generated by the 10 yeaz - 24 hour event would be 0.15 ml/1, significantly less than the <br />effluent standard of 0.5 m]/l. <br />The Bourg Mine is located on 160 acres in North Park, Colorado. The property slopes <br />gently (7.5%) to the north-northeast into Mann Draw, an ephemeral tributary of the <br />Canadian River. All disturbed areas have been backfilled, graded, topsoiled, seeded and <br />mulched. The Fluetsch - Tiagos soil series originally covered much of the site. It is <br />classified by the Soil Conservation Service as a sandy loam series with a moderately low <br />runoff potential (H=B) and a moderate soil erodibility factor (K=0.32). <br />Bourg Strip Mine. C-81-021 l7 August 4, 1998 <br />