Laserfiche WebLink
compromised the slope stability analysis that had been performed for the gob pile. <br />The slope stability analysis of the gob pile was based on the material properties <br />and a Standard Proctor compaction test of coal waste only. This is stated on pages <br />20 and 21 of Volume IV of the permit application. The Division believes that an <br />additional material properties test, or tests, including a sieve analysis, and another <br />Standazd Proctor test, or tests, should be run on the actual amended gob pile <br />material being placed. Whether or not one or several test samples are taken for <br />analyses depends on whether the material in the gob pile is homogeneous or <br />stratified. In this way, a comparison can be made between the properties of the <br />coal waste material and the properties of the composite material. With this <br />comparison, it can be determined whether or not additional laboratory tests and an <br />accompanying slope stability analysis need be completed. Please comment. <br />3. The Division is concerned that, if subsoil is being used to mix with overly wet coal <br />mine waste material, there might not be enough subsoil stockpiled at the coverfill <br />stockpile to use as cover over the gob pile when the pile is reclaimed. Please <br />comment. <br />Second, the operator also stated during the February inspection that there had not been a <br />compaction test perfotined at the gob pile, although one was being planned soon. It had <br />been observed during the February inspection that a considerable amount of coal waste <br />material had already been placed at the gob pile. The gob pile was about 20 feet high at <br />the outslope crest. <br />4. The Division is concerned that no compaction tests have been performed to date at <br />the gob pile. It is the Division's opinion that compaction testing should be <br />performed at least quarterly, possibly on each two foot lift, and especially in the <br />very eazly stage of the gob pile's development. In that way, the geotechnical <br />engineer would be able to determine whether or not the gob pile construction was <br />proper, so that any remediation work, if needed, would not be costly and difficult. <br />Please comment on why no compaction testing at the gob pile has been done to <br />date, considering how much material has already been placed there. Also, please <br />comment on how the operator is confident [hat the compaction at the gob pile has <br />occurred according to design. <br />Finally, during the inspection, the operator stated that the fitter fabric that had been placed <br />around the underdrain had been opened up before the underdrain had been covered with <br />coal waste. It was observed during the February inspection that no filter fabric was on top <br />of the exposed portion of the underdrain. This is in accordance with the underdrain <br />2 <br />