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Memo to Joe Dudash <br />Bowie #2 Mine -GOB Pile Density Study <br />page 2 <br />Mr. Stover states in his cover letter, "Considering the limitations in the sampling method <br />employed, the results of this investigation confirm the bottom twenty (20) feet of the gob pile <br />was compacted to achieve 90% of the maximum dry density." L~ my professional opinion, Mr. <br />Stover's conclusion is not supported by the study submitted in combination with his brief <br />statement. Rather. I conclude that several lifts of the lowermost twenty feet of [he GOB pile <br />were placed a[ substandard relative density. <br />My Observations <br />I consider several interpretations which might plausibly explain the observed results. I'm sure a <br />myriad of other also come to mind. <br />(1) The lowermost twenty Feet of GOB was inadequately compacted in the portions of the <br />pile nearest to the out slope. This is not uncommon because the waste lacks confinement <br />near the free face and is more difficult to compact. In addition, [he free face allows <br />enhanced evaporation which lowers the moisture content of the GOB rendering it more <br />difficult [o compact. Equipment operators tend to exert [he maximum traffic upon the <br />level portions of the pile, resulting in higher compaction in the body of the pile. <br />(2) Consolidation of the thicker portion of the pile, caused by significantly higher <br />superimposed GOB loading, has caused the material located towards the rear of the pile <br />to increase it's relative density since placement, whereas the lesser loading towards the <br />toe of [he pile has no[ had a similar effect. <br />(3) The character of [he GOB may have changed since the development of the portals and the <br />generation and placement of the first waste materials. The initial materials may have <br />been more variable in their composition, causing them [o be more difficult to compact <br />and to representatively test. <br />(4) Experience of the equipment operators with the specific compaction challenges <br />represented by the Bowie #2 GOB has increased through time, resulting in increased <br />success in compaction of the GOB. <br />I suspect that reality is some combination of the above scenarios, as well as additional influences <br />beyond my appreciation. <br />Recommendations on How to Proceed <br />The primary purpose for our concern is to ensure that the Bowie #2 Mine GOB pile is stable as <br />