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STATE OF COLORADO <br /> MINED LAND RECLAMATION DIVISION of Coro <br /> Department of Natural Resources <br /> 1313 Sherman St., Room 215 "eVM ms 10 <br /> Denver,CO 80203 *# ryo <br /> 303 866-3567 �s�s <br /> FAX 303 832-8106 <br /> Roy Romer, <br /> Governor <br /> Fred R.Banta, <br /> DATE• June 12, 1990 Division Director <br /> TO: Dan Mathews <br /> FROM: Jim Pendleton <br /> RE: National)(-rng Coal ermit Revision PR-02 - Supplemental Responses <br /> (Permit No: C-81-035) <br /> I have reviewed the permit application amendments proposed within National <br /> King Coal 's supplemental responses to our earlier adequacy comments. I have <br /> specifically reviewed the topics of storage and final placement of coal <br /> refuse, and surface subsidence. I believe additional amendments will be <br /> necessary before we can approve the National King Coal application, <br /> Storage of Waste Materials <br /> Coal waste from the mine is temporarily stored in an approved storage pile <br /> within the surface facilities area. Under the regulation in affect at that <br /> time this material was defined as "underground coal development waste". Under <br /> the regulations now in effect, the material is defined as "coal refuse" . <br /> A simplistic stability analysis was performed as a portion of the original <br /> permanent program permit application. The waste is compacted in 2 foot lifts, <br /> an underdrain will be installed beneath the pile, and the drainage is <br /> controlled. In my opinion this storage pile, with the addition of the "french <br /> drains" proposed to be installed within this revision application, is <br /> geotechnically acceptable. <br /> Final disposition of Waste <br /> As a portion of final reclamation of the surface facilities area, the operator <br /> proposes to excavate and redeposit the coal refuse against the high wall of <br /> the surface facilities bench. The operator proposes to construct a permanent <br /> sideslope coal mine waste bank structure against the highwall , complete with <br /> blanket drain, and placed in compacted 2 foot lifts. The final facial slopes <br /> will not exceed 2.5:1 (horizontal to vertical ) slope gradients, which do <br /> conform with our Rule 4.10 requirements. The operator also proposes to conduct <br /> test plot studies to determine what thickness of best available material is <br /> necessary to assure revegetation success. <br /> In my opinion, the operator must amend this portion of the application to <br /> include an analytical determination of the static slope safety factor of the <br /> coal refuse disposal pile. I assume that many of the necessary material <br />