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<br />Memo to Christine Johnston <br />MCC 3rd Quarter 1995 Compaction Reporting <br />page 3 <br />the constituency of "durable rock". A "durable rock fill" is <br />defined as consisting of at least 80 percent, by volume, durable <br />non-acid- and non-toxic-forming rock (e.g., sandstone, or <br />limestone) that does not slake in water and will not degrade to <br />soil material". The largely non-durable nature of the sedimentary <br />rock associated with Colorado coal measures makes the occurrence of <br />a "durable rock" coal mine waste extremely unlikely, but not <br />impossible. <br />If MCC desires to complete a determination of whether its lower <br />refuse pile represents a "durable rock fill", I suggest it proceed <br />as follows. Representative samples of the waste should be <br />collected from the pile. These samples should be composited to <br />create a material believed to be representative of the waste's <br />constituency. This composite material should then be tested for <br />slake durability. If in excess of 60% of the overall bulk sample <br />survives the slake durability test, then I would agree that the <br />waste represents durable rock and that the coal mine waste pile is <br />a "durable rock fill". <br />If MCC succeeds in demonstrating that it's lower refuse pile <br />constitutes a "durable rock fill", and it met the additional <br />conditions of sections 4.09.4(3) through (6), it could then propose <br />an alternative method of disposal of it's coal mine refuse by <br />gravity placement in single or multiple lifts. It is not <br />appropriate to perform field density determinations on "durable <br />rock", therefore the field density determination and reporting <br />problems would be muted. However, MCC would then risk violation if <br />the character of its refuse were to change to non-durable due to <br />stratigraphic or processing changes. <br />As an alternative I suggested to Ms. Welt that MCC might consider <br />specifying a method for validating its field density <br />determinations, as I mentioned above. In this manner the <br />compaction testing implications and occurrence of coarse durable <br />cobbles is recognized. However, MCC can demonstrate compliance <br />with compaction requirements by the preponderance of "validated" <br />tests. Of course, MCC may exercise either of these or any hybrid <br />approach to resolving these problems at its discretion. <br />cc: David Berry <br />Susan McCannon <br />Doc: M:\MIN\JAP\MTGICOM2.WP5 <br />JP/JP <br />