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-~ .. <br />Dennis Burns <br />-2- <br /> <br />May 26, 1988 <br />the maximum discharge was 15 gallons per minute. During the spring melt <br />following the construction of the system, flows in excess of 45 gallons a <br />minute were observed. These construction and operating challenges resulted in <br />the development of non-freezing water conveyance systems, wetland design <br />principles which allow for wide variance in discharge rates, static limestone <br />barrier designs which are not subject to coating by iron oxides or gypsum, and <br />pretreatment schemes to prevent accelerated iron buildup in the constructed <br />wetland. <br />The value of the passive mine drainage treatment system at the Thompson No. 2 <br />Coal Mine has been fully realized. Its main purpose was as a heuristic device <br />to further refine passive treatment design and construction principals. The <br />Inactive Mine Reclamation Program plans to remove the system when weather <br />conditions permit in late spring or early summer, 1988. Our reclamation plan <br />involves collecting the mine drainage within the portal in an oversized PYC <br />pipe designed to convey the mine drainage under the county road. The pipe <br />will discharge into an open channel constructed on the slope leading down to <br />the creek. This drainage corridor is currently employed by the PMDT system. <br />The channel will be designed with a large safety factor to provide long term <br />stability and erosion resistance. The sides of this channel will be bermed in <br />order to divert away water from the surrounding permit area and prevent it <br />from comingling with the mine drainage. The berm will be sized properly to <br />divert the agreed upon design event (e.g. 25-year-storm-event). The <br />• reclamation project will be coordinated with the WQCD. <br />I understand that you are involved in discussions with the Candy Thompson in <br />our Coal program regarding this project. If I can be of assistance in <br />providing further information please do not hesitate to ask. I look forward <br />to working with you as we undertake this hydrologic design and reclamation <br />process. I appreciate your help and cooperation. <br />/bdc <br />cc Bob Liddle, MLRD <br />cc Bob Shuckle, WQCD <br />4950E <br /> <br />