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ADZ ACZ Inc. <br />Engineering and Environmental Services <br />1475 Pine Grove Road, Suite 205 <br />• P.O. Box 774018 <br />Steamboat Springs, Colorado 80477 <br />303-879-6260 <br />October 1, 1990 <br />Mr. Brent Anderson <br />Parcel, Mauro, Hultin & Spaanstra, P.C. <br />I801 California Street, Suite 3600 <br />Denver, Colorado 80202 <br />Re: Rockcastle Coal Company Pit 4 Haul Road Stability <br />Dear Brent: <br />On Tuesday, September 11, 1990, Jerry Nettleton and I performed a field <br />inspection of the Rockcastle site. Included in this inspection was a <br />relatively detailed look at slide area identified as No. 3 on the map <br />titled "Grassy Gap Mine, Unstable Slope Segments", (Map No. 1, October, <br />1985). The purpose of the site visit was to review the existing condition <br />of the slide and develop conceptual plans for any necessary stabilization. <br />• The slide is on the nose of a ridge where the haul road turns around the <br />ridge. Maps indicate that original undisturbed topography in this area <br />ranged from 25% to 38% slopes. Examination of materials on the site <br />indicate a thin topsoil layer (approximately 1 foot thick) underlain by <br />unconsolidated native materials. <br />The slide extends for 300-400 feet along the road around the nose of the <br />ridge. The slide extends in excess of 100 feet above the road in some <br />areas. Scarps appear at the head of the slide, some with displacements of <br />2 to 3 feet. In other areas, scarps appear en echelon with each scarp <br />having a smaller displacement. <br />The ground surface in the slide area has several features indicative of <br />previous movement. There is a general bulge in the slope just above the <br />nose of the ridge. In another spot, a large aspen tree is laid over <br />indicating that the slip zone is between the ground surface and deep roots <br />of the tree. <br />I have been informed by Rockcastle personnel that these slides took place <br />following the winters of 1983-'84 and 1984-'85. These winters were the <br />years in which the "El Nino" current caused changes in normal weather <br />patterns and greatly increased precipitation throughout portions of <br />Colorado. This would indicate that the slides are related to saturation <br />of ground surface and associated increases in pore pressures. Examination <br />of geologic maps available in the permit document shows that the slide <br />area is stratigraphically and topographically below the coal seam. Spoil <br />springs are unlikely to form in this area making surface runoff the most <br />• tikeiy source of water. <br />