ENFORCE20007 - Laserfiche WebLink

Home Browse Search

Mr. Steve Shuey May 12, 1993 Page 2 groundwater would be anticipated to be moving in an easterly direction roughly parallel with the cut boundary. Had subsurface flora contributions played a dominant role in producing the slope failure it is likely that failures would have occurred along the western edge of the portal cut as well where groundwater would be anticipated to be moving in an easterly direction roughly perpendicular to the cut boundary. As no signs of slope instability are noted in this area, groundwater contributions are thought to have played a relatively insignificant role. The potential for surface runoff to have contributed to the slope instability does exist as a small portion of the portal cut perimeter in the area of the slope failure appears to be subject to potential surface runoff from a limited area above the portal cut. However, given the steep face of the portal cut (approximately 1.5 horizontal to 1.0 vertical) , surface runoff reaching the slope would be expected to travel downslope quickly with little opportunity for significant infiltration to occur. No signs of slope instability nor evidence of surface runoff had been noted in this area during the previous six years of the cut slope existence. The area of slope failure occurs on a northern aspect subject to snag acclumilation during the winter months. Immediately following the slope failure, approximately twelve (12) inches of acc~miulated snow was observed on the area encon~assed by and immediately adjacent to the slide. The primary cause of the slide is believed to be the slag, sustained, and prolonged melting of this snowpack which had accimnilated directly on the slope and provided consistent moisture contributions at a rate conducive to infiltration resulting in the subsequent slope failure. Several general recoimnendations are detailed in the Lambert. report with regard to repair of the cut slope failure and prevention of future slide occurrences. COVCC will develop detailed plans >n consultation with the Division which specify a particular stabilization plan and will incorporate the mitigation plan into the permit as required by the Division. The plan will generally entail the following: 1.) Salvage and store additional topsoil as required by regulation from all areas proposed for further disturbance and from areas immediately adjacent to the existing slide area. 2.) Construct a surface water diversion ditch above that portion of the portal cut slope subject to potential surface water runoff. 3.) Remove the slide debris in the existing bench drain ditch and recontour the ditch to reestablish rapid runoff of surface water. 4.) Recompact or remove loose or disturbed soils on the slope face to promote rapid runoff of surface water.