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1 <br /> <br /> <br /> <br /> <br /> <br />1 <br /> <br />1 <br />1 <br /> <br />lJ <br /> <br />MEMORANDUM <br />TO: Kathy Welt <br />Mountain Coal Company <br />FROM: Wright Water Engineers, Inc. <br />David M. Jubenvil e, P.E. and John W. Rold, C.P.G. <br />DATE: June l 1, 1998 <br />__ z_ <br />III IIIII~~IIIIII III <br />RE: Technical Discussion of the Geology and Geotechnical Aspects of the <br />Beaz No. 3 Landslide with Representatives of CDMG on June 3, 1998 <br />John Rold and I met with Dr. James Pendleton and Mr. David Berry of the Colorado Division <br />of Minerals and Geology (CDMG) on June 3, 1998. The purpose of the meeting was to shaze <br />new data developed by Mountain Coal Company on the geology and geotechnical <br />engineering aspects of the slide. Attached is a list of exhibits which were used to aid in the <br />presentation of the key points discussed below. <br />The discussion began with a review of the history of the slide. We presented a series of <br />photographs taken between 1984 and 1998 which show the progression of downslope <br />movement in the azea. The key point was that the slide movement started yeazs ago, as <br />indicated by aerial photography back to 1984 taken by the CDMG. As the slide has <br />progressed, it has developed an increasingly chaotic surface drainage pattern that increased <br />the amount of surface water infiltration into the slide mass. <br />A key to the recent reactivation of the slide mass appeazs to be heavy precipitation which <br />occurred in 1997. Our original submission to CDMG had provided only anecdotal evidence <br />to support this conclusion and Dr. Pendleton had requested that we provide more specific <br />information. We presented a figure which shows remarkable agreement between <br />precipitation ai Paonia and the reactivation of slide movement during 1997. <br />Several photographs taken between November 1997 and May 1998 by John Rold were used <br />to show the progression of the slide and the nature of the failure surface between the bedrock <br />and the colluvium. The key points made included John Rold's observation of a low strength <br />soil (mud) at the bedrock colluvial contact and that the slide appeazed to have initiated above <br />the level of the C-Seam on the hillside. This latter observation seems to eliminate <br />groundwater from the historic mining as a trigger mechanism for slide movement. <br />The warm air exiting a crack east of the slide was discussed. The wazm air appeazs to be the <br />cause of the wet soils observed by Dr. Pendleton and Bruce Stover during their site visit <br />eazlier this yeaz. No wet ground was noted during Mr. Rold's visit in May at the same <br />location. Therefore, it appears the warm air was causing snowmelt which, in tum, saturated <br />the soils in the immediate area. <br />U <br />Z <br />N <br />W <br />W <br />_Z <br />Z <br />W <br />W <br />a <br />3 <br />H <br />S <br />(~ <br /> <br />.: <br />