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srnrp or r_oi or+n r~o ~~~~ ~~,, ui, u ~ ~,,. <br />nF%Ai.^,S f1 <br />DEPARTMENT OF NATURAL RESOURCES ~~({~---"-~~41, <br />Harms D. Snerman. Executive Director Il ll~~~~ti~'~~~ <br />~r~l~~» i~:~~» NH.cLi~lf~:,~rluy <br />423 Centennial Building, 1373 Sherman Street ~ _ _ <br />Denver, Colorado 80203 Tel. (303) 839-3567 ~ ~+.nor <br />.A7J~. <br />David C. Shelton <br />Director <br />July 23, 1980 <br />TO: Jim Herron /. ~ - <br />FROM: Jim Pendleton ~~_,,~ <br />RE: Geotechnical Aspects o~he "Plan for Disposal of Refuse from <br />the Northern N~~(FF-~am) Coal Mine" <br />I have rev.ewed Northern Coal Company's application Fora developmert <br />-- waste disposal pile. I forward thB following comments regarding that <br />application for your consideration. <br />Classification of the Fi11 <br />The application designates the refuse fill as a "durable rock fi1Z". <br />She OSM interprets the durable rock fill regulations to mean the fill <br />material must contain at least 80a b_y volume of non-slaking rocks (sand- <br />stone, limestone or other rocks) that will not pass through a 1/4" <br />sieve. In addition, the material placed in the fill must be able to <br />meet the slakes durabiZ.ity and slake +:ndex tests required in section 30 CFR <br />715.15(d), 816.74 and 817.74. (Reference: Federal Register, volume 45, <br />No. 75, page 26000, Wednesday, April 16, 1980) <br />Problems have arisen in some fills previously approved by other states <br />because approval of durable rock character was based upon testing of <br />overburden core samples. Later when the fill was under construction, <br />fill properties varied from those originally determined from the core <br />samples, due to factors such as processing, transport and deposition of <br />fill materials. In coal-bearing stratigraphic sections, such as the <br />Mesa Verde group formations in which the Northern bl Coal Mine is <br />located, this problem is characteristic. <br />With the recognition of this problem, it is prudent to review t/ri.s <br />application with the concern for the implications of potential deviation <br />of fill properties from those anticipated by examination of overburden <br />waste samples. In this particular case the .implications concern material <br />placement and compaction. The application states on page 13-15 and on <br />(cont'd) <br />