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<br />~.~~rF ., = -~~.~-~° :-:::, ~.~,._~. IIIIIIIIIIIIIIIIIII <br />~.... ,.. " .: iiF `.~- .?4L ..°.FS'JU?.Cc'.5 999 <br />H arras U Snerm.a n. E•e~:~~:va 0:!eetor <br /> <br />423 Cen,enn~ai B~,~c;c a, 73'.3 Sharman Street <br />Denver, ColoraCO 3:,23 Tei. (303) 839-367 <br />David C. Shelton <br />Director <br />July 23, 1980 <br />~ -.. _ <br />TD; Tim Nerron / ~ ~ _ <br />FROM: Jim Pendleton (~~ --.~-- <br />RE: Geotechnical Aspects o~he "Plan for Disposal of Refuse from <br />the Northern ply-{F~am) Coal Mine" <br />I have reviewed Northern Coal Company's application for a development <br />waste disposal pile. I forward the following comments regarding that <br />application for your consideration. <br />Classification of the Fill <br />The application designates the refuse fill as a "durable rock fill°_ <br />The OSM interprets the durable rock Fill regulations to mean the fiZ1 <br />material must contain at least 80~ by 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 slake durability and slake index tests required in section 30 CFR <br />7IS.I5(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 ill Coal Mine is <br />located, this problem is characteristic. <br />With the recognition of this problem, it is prudent to review this <br />application with the concern for the implications of potential deviation <br />of fill properties from those an_*icipated by examination of overburden <br />waste samples. In this particular case the implications concern material <br />placement and compaction. The application states on page I3-15 and on <br />(cont'd) <br />