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TABLE 2 <br />Soil Strength Parameters Used for the Slope Stability Analysis <br />Soil Type Moist <br />Unit Wt <br />(pcfl Saturated <br />Unit Wt <br />(pcfl Cohesion <br />Intercept <br />(pefl Angle oP <br />Internal <br />Friction <br />(degrees) <br />Coal Refuse 80 90 288 30 <br />Colluvium 124.1 135 432 25.4 <br />Weathered Sandstone 150 150 500 30 <br />Shale 125 125 500 45 <br />Competent Coal Seam 150 150 500 30 <br />Mined Coal Seam 90 90 10 30 <br />Competent Sandstone 150 150 5000 30 <br />The phreatic water surface has been conservatively established at a 50 <br />feet depth below the upper refuse site, and comes to the surface along the slope <br />below the bench in the vicinity of the WEM main portals. Below the portals <br />the phreatic surface remains within 10 feet of the surface. <br />The site is located in an area of minor seismic activity. According to <br />published data, the entire azea of Colorado is in seismic risk Zone 1. Previous <br />earthquake activity records indicate most earthquakes of magnitude 5 or <br />greater occur at a distance greater than 100 miles from the mine site. Section <br />4.09.1 of the Regulations of the Colorado IVTined Land Reclamation Boazd for <br />Coal Mining states that excess spoil shall be placed to ensure a .long-term <br />10 <br />