Laserfiche WebLink
..: ':e Savage -2- January 7, 1982 <br />Fiinimum overLur~icn thickness - 40 ft. <br />F.'axinium overbur~lc•n tl~icl:ness - 160 ft. <br />Average overburden thie.tness - 110 ft. <br />Average coal thickness - 13 ft. <br />.average excavated depth - 110 ft. + 13 ft. = 123 ft. <br />Total excavated overburden volume = 48,571,447 BCY <br />x Average pit depth = 54,311,709 yd3 <br />Average overburden thickness Total excavated overburden/34 months <br />Total pit volume = 19,168,838 yd3/y r. <br />Annual utility ~.~aste volume = 160 acre-feet <br />= 258,133 yd3, compacted in-place <br />This ti•aste quantity represents: <br />258,133 yd3/y r. <br />19,169,000 yd3/ur. x 100 = I.35e of the extracted overburden volume <br />Utility ash and sump sludge will be generated by the power plant at a <br />rate equivalent to Z.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. l;or 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 Zimit of 1.20 (page <br />3-491 for overburden s::e11 plus utility waste introduction, it will be <br />important to carefully plan the disposal of t7~e ash and sump sludge <br />wastes. <br />The applicant's available residual volume for ~.~aste disposal amounts to <br />3q 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 tl~ickn~ss would exceed the alio~~able waste volume. <br />As I discussed in my earlier momo to you of ~`'ovenber 11, 1981, in order <br />for us to find that the aonlicant is in conformance with the backfill <br />and grading and approximate original contour post-mining topography <br />requirements of our nerm~nent regulatory program, the applicant should <br />clarify the rates and Locations proposed for ash and sump sludge disposal. <br />This will provide aiiidance to the operator in achieving an acceptable <br />reclamation configuration and provide a regulatory comparison For judging <br />compliance in the future. The applicant should ar..end the post-mining contour <br />map to reflect the addition of utility c.~astes to the pit backfill. <br />/mt <br />Dave Shelton <br />