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1~': ':e Savage • -1- • January 7, 1982 <br />74i ni mum overburden thickness - 40 ft. <br />Maximum overbut~icn thickness - 180 ft. <br />Average overburden thickness - 110 ft. <br />Average coal thickness - 13 ft. <br />:,verage excavated depth - 110 ft. + 13 ft. = 123 ft. <br />Total excavated overburden volume = 48,571,447 BCY <br />Average pit depth _ 3 <br />x Average overburden thickness - 54,311,709 yd <br />Total excavated overburden/34 months <br />Total pit volume = 19,168,838 yd3/y r. <br />Rnnual utility waste volume = l60 acre-feet <br />= 258,133 yd3, compacted in-place <br />This Haste quantity represents: <br />258,133 yd3/y r, x 100 = 1.350 of the extracted overburden volume <br />19,169,000 ud3/ur. <br />Utility ash and sump sludge will be generated by the power plant at a <br />rate equivalent to 1.35'a of the total pit volume excavated during the <br />same time period. Unfortunately, all of the mined areas are not usable <br />for ash and sludge ~.'aste disposal. llor does ash disposal for pit <br />excavation generally occur at a steady rate, as evidenced by the applicant's <br />pit overburden extraction data. Because the applicant projects an over- <br />burden overall swell factor of 1.17 and commits to a limit of 1.20 (page <br />3-49) for overburden swell plus utility waste introduction, it will be <br />important to carefully plan the disposal of tl~e ash and sump sludge <br />wastes. <br />The applicant's available residual volume for ~.'aste disposal amounts to <br />3%0 of the excavated pit volume: <br />Flinimum pit depth - 53 ft, x .03 = I.6 ft. <br />Fla xi mum pit depth -193 ft. x .03 = 5.8 ft. <br />Average pit depth -123 ft. x .03 = 3.7 ft. <br />On page 4.28, the applicant discusses a scenario of 25 ft, of waste material <br />placement, which would require 190 acres of mined area for total disposal. <br />Obviously, such a Large thickness e•ould exceed the al1o:.~able waste volume. <br />As I discussed in my earlier memo to you of ~~'ovenber 11, 1981, in order <br />for us to find that the applicant is in conformance with the backfill <br />and grading and approximate original contour post-mining topography <br />requirements of oui permanent regulatory program, the applicant should <br />clarify the rates and locations proposed for ash and sump sludge risposal. <br />This will provide guidance to the operator in achieving an acceptable <br />reclamation configuration and provide a regulatory cornnarison for judging <br />compliance in the Future. The applicant should amend the post-mining contour <br />map to reflect the addition of utility wastes to the pit backfill. <br />/mt <br />cc: rli-Y-smvvt~ <br />Dave Shelton <br />