Laserfiche WebLink
Rock Tunnel[sl Sediment Control <br />Three sediment ponds in series having a total storage capacity of 11.1 <br />acre -feet have been constructed to control runoff from the disturbed area <br />at the Rock Tunnel. All sediment accumulated over a three year period <br />can be stored in the upper two ponds. The total runoff volume from a <br />10 -year, 24 -hour precipitation event can be stored in the lower two ponds, <br />assuming the upper pond is full of sediment. <br />All three ponds are equipped with 36 -inch CMP emergency spillways <br />which will pass the 25 -year, 24 -hour peak flow. The lower two ponds are <br />equipped with 6 -inch, CMP gated dewatering pipes. The middle pond has <br />the dewatering device located above the maximum sediment storage level. <br />The dewatering device on the lower pond is located 2.5 feet above the <br />bottom of the pond. The 2.5 feet of storage is for sediment in excess of <br />three years accumulation or for sediment which is not settled out in the <br />upper two ponds. Even with this amount of additional dead storage, the <br />sediment ponds are capable of containing the runoff from a 10 -year, <br />24 -hour precipitation event, as designed. <br />A major concern and point of MLRD regulation is the level of total dissolved <br />solids (TDS) and total suspended solids (TSS) discharged from this series of ponds. <br />This is clear from the MLRD permit rationale: <br />Probable Hydrologic Consequences - Surface Water <br />The Coal Basin mine plan is designed to minimize the impacts on the <br />surface water hydrology of the area. Mid- Continent has designed and <br />constructed water control structures and closed water use systems to <br />mitigate adverse impacts on the hydrologic balance. For more information <br />on the drainage control plan, see Appendix II -B -7 in Volume 3 of the <br />application and Section V of this document. <br />The hydrologic consequences of mining in Coal Basin are expected to be <br />minimal. The applicant's statement of probable hydrologic consequences <br />on page 22.1 of Chapter W, Volume 7, predicted no affect on the quantity <br />and quality of surface water other than increased sediment loading, but <br />provided no supporting discussion. Therefore, the following is the <br />26 This is clear from the language of the statute. A permit application must contain <br />a "determination of the probable hydrologic consequences of the surface coal mining and <br />reclamation operations, both on and off the mine site, with respect to the hydrologic regime <br />and the quantity and quality of water in surface and ground systems, including the dissolved <br />and suspended solids under seasonal flow conditions[.]" 14 COLO. REV. STAT. § 34-33- 110(2)(1) <br />(1984 Repl. Vol.); Brief Appendix, Appendix -10. <br />Mid - Continent Answer Brief <br />- 30 - Appeal No. 93 CA 297 <br />