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• Bob Liddle <br />G]aste Material and Spoil <br />-2- June 30, 1981 <br />The application has several deficiencies in regard to the disposition of <br />underground waste materials and overburden spoils. The application should <br />specifically discuss the underground waste material placement and compaction <br />specifications to be utilized. Plans and cross-sections of the backfilled <br />pit to receive waste material should be included within the application. <br />The applicant presents the opinion that the permanent overburden spoil pile <br />located in Section 24 predates the permanent regulatory programs inception <br />and is, therefore exempt. If the applicant does not redisturb that pile, <br />as the application proposes, I agree. The applicant should topsoil and re- <br />vegetate that pile as soon as possible in a timely manner. <br />The application also states the applicant's opinion that the regulatory <br />requirements of Rule 4.09 do not apply to temporary spoil piles, two of <br />which are contained within the application. The Division disagrees with this <br />opinion. The application should be amended to include discriptions of the <br />construction specifications as utilized during material placement within the <br />two piles, as well as cross-sections and plans for these temporary piles <br />located within Section 12. The applicant should conform with the requirements <br />of Rule 4.09. Division policy has been to consider variance from the required <br />long-term static safety factor requirements, if the applicant is not intending to <br />• redisturb the piles. If continued disturbance is proposed, the Division will <br />investigate the possibility of achieving conformance by selective placement <br />of additional material to reconfigure the slopes of the existing temporary <br />piles. Periodic inspections in keeping with Rule 4.09 will also be required <br />to assure maintenance of a safe condition during the piles life span. <br />Subsidence <br />The subsidence evaluation within the application has several major deficiencies <br />which must be eliminated by the applicant. First, the applicant's subsidence <br />prediction (exhibit 15) projects subsidence based upon extrapolation from <br />empirical graphs contained within a publication by Syd Peng. The applicant <br />utilizes this graphical information to project subsidence beneath "area A" <br />equivalent to 7X of the extracted seam thickness. "Area A" contains Foidel <br />and Middle Creeks. This presentation is inadequate. The applicant should <br />amend the application to include pillar stability ground control calculations, <br />which are described at length in the same publication by Syd Peng ("Coal Mine <br />Ground Control", 1978), from which the graphical techniques were excerpted. <br />Rny one of the normally acceptable techniques for roof stability calculation <br />may be applied to the task by the applicant. <br />Secondly, the applicant describes the existence of an approximately 200 ft. <br />wide fault zone, which constitutes the eastern boundary of the Middle Creek <br />underground mine plan. Faults comrtnnly influence the character of ground <br />subsidence above underground workings. A homogeneity assumptions implicit <br />in the normal graphical and mathematical subsidence projection techniques <br />. often do not apply in faulted situations. Subsidence can occur along existing <br />shear plains within the faulted zone, increasing the possiblity of discrete <br />