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• Replacement of Piezometers and Inclinometers. As part of [he ongoing monitoring program, work will <br />be performed [o replace piezometers and inclinometers which have been damaged by landslide movement, <br />thus allowing continued monitoring of landslide behavior. <br />Horizontal Trenches Above Material Storage Bench. Within the area of the secondary slides, <br />additional work will focus on enhancing drainage of water from these slopes through the use of horizontal <br />dewatering trenches. Probable construction is in the summer of 1999. Additional horizontal dewatering <br />trenches could also be used to increase capture of water in the landslide. The trenches will be similar in <br />design to those already constructed on the main landslide. Figure H2 shows a preliminary layout of the <br />proposed plan. <br />Reconstruction of Upper Clearwater DiversioB Ditch and Fregc6 Drains. French drains, located on <br />the upper slope above the landslide, intercept both groundwater and surface water. The drains are aligned <br />perpendicular to the slope, acting as infiltration galleries to saturate the head of the landslide. The drains <br />will be removed or capped to prevent surface water infiltration and new ditches/drains will be constructed <br />• to redirect surface and groundwater flows away from the landslide. Probable construction is during the <br />Fall of 1999. Figure H2 shows a preliminary layout of the proposed plan. <br />Surface Water Ditches. A routine maintenance plan is th place to repair ditches (especially in the spring) <br />to prevent infiltration of surface water. Long-term reclatnation will remove the ditches to prevent <br />concentrated flow. <br />Portal Retaining Structures. Further studies have found that repair of the portal retaining wall is not <br />essential for stabilization of the landslide. More likely, future removal of a portion of this wall and re- <br />grading of the portal bench will be performed to improve mining operations. The benefit of this re-grading <br />will be to close tension cracks at the head of the slide, thereby preventing infiltration of surface water. <br />Sanitary Sewer Line. The plant sanitary sewer line remains the only utility still buried below grade. The <br />line is located between the administration building and wastewater treatment plant at the lower toe of the <br />slide. The line will be inspected and any leaks will be repaired to prevent infiltration into the slide. <br />• Barr Engineering Company July 37, 1999 <br />PCDOCS1209220/CAK 13 Appendix H <br />1999 Addendum to <br />1997199 landslide Corrective Measures Report <br />