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owner requires greater confidence in the potential effectiveness of the repair/stabilization measures <br />discussed below,further investigation,landslide characterization,analysis and design will be needed. <br />The following areas were identified as appropriate for repairs: <br />Oil Well Access Road Slide" This is a fairly small slump in the Pond 6 area above an existing county <br />road that leads to an oil well. The toe of the slide has encroached into the ditch above the road, disrupting <br />surface drainage and causing water to accumulate in the ditch. The current plan consists of regrading the <br />slide and reopening the ditch,installing a trench or V-shaped drain through the horizontal midpoint of the <br />slide mass,and embedding large boulders along or near the base of the slide mass,above the ditch,to act <br />as a toe buttress or retaining wall. <br />Pump House Slide" The mine operator is planning to reclaim several switchbacks above the Pond 6 <br />slide area. The"Pump House Slide"has a narrower shape and more of a mudflow morphology than other <br />landslides in the area. Rough grading to create surface drainages in the toe area had been performed just <br />before our visit. Reestablishing vegetation and improving surface drainage above the slide area to reduce <br />infiltration are appropriate strategies to help stabilize this area. <br />Pit Ramp Slide" This area contains mapped mud flow and landslide deposits and unstable slopes <br />Madole,Colton, and Miller),and has been the site of ongoing slope failure and repairs over the last <br />approximately 8 years. The scarp and toe features have recurred at least three times in virtually the same <br />location within several years after repairs have been made. The head scarp appears to correspond to a cut <br />excavated into the original slope to create a haul road. When the haul road was reclaimed,a fill prism <br />was placed within the road cut. It appears that this fill prism,soil and topsoil placed on the slope below <br />the original road,and possibly some of the shallow in situ soil and/or rock are unstable. Erosion gullies <br />have developed across the surface of the slide in several areas. Although the slide has been regraded <br />several times,it appears that the underlying failure surface continues to be weakened by perched water <br />shallow subsurface water from surface infiltration). <br />The repair plan that we discussed in the field consists of excavating two trench drains(either lined or <br />filled with rock),regrading the toe bulge,gently knocking down the vertical head scarp,seeding,and <br />weed control. One trench drain is planned along existing erosion gullies near the horizontal midpoint of <br />the slide mass, and another in the wet area near the western toe bulge above the road ditch. The trenches <br />should extend through the slide mass and into the original road surface at the head scarp area,and will <br />become shallower as they approach the ditch. We discussed angling the drains 300-45°laterally as they <br />descend the slope in an effort to capture more surface water. If the drains are angled,fully penetrate the <br />slide mass(extending below the failure surface),and are filled with hard,angular rock,they should act as <br />shear keys and increase the overall strength of the slide mass,thereby reducing,but not eliminating,the <br />risk of future movement. <br />Numerous slides surrounding Ponds 16 and 16A. Ponds 16 and 16A are located at the base of a <br />mapped,pre-mining mudflow that encompasses the area surrounding drainage PM-2A. NWCC <br />investigated the Pond 16 slides and presented recommendations in a"Site Observations and Slope <br />Stabilization Recommendations,Pond 016 Area Slides"report,dated October 28,2010. An approved <br />repair plan,TR-73,is in place for this area. The plan includes stabilizing the slides and slumps through <br />improved surface and subsurface drainage. Pond 16A will be backfilled and the Road J/K curve will be <br />relocated toward the west,over the backfilled area;underdrains will be installed from a cluster of <br />abandoned artesian wells and the Pond 16 slide to new surface drainage PM-2; and the area below the <br />shrub plot will be excavated to intercept shallow subsurface flow currently emanating from the area <br />surrounding the distinctive spoil spring cavity. Excavations to intercept subsurface flow along the base of