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C-1982-057 TR-73 Engineering-Geotech PAR 24-Mar-2011 Page 2 of 5 • Between Jun-2009 and Jul -2010, the downward displacement at the head scarp increased from just I to 2 feet to 5 to 8 feet. • One test hole (TH- 11) drilled in Jun-2009, and 3 more (TH-12, -13, and -14) in Jul- 2010. • Four test pits (16A -1 thru 16A-4) dug in Jun-2010. Recommended stabilization efforts are described beginning on NWCC page 5. • Fill Pond 016A, creating a buttress at the toe of the landslide, using Pond 016 slide material • Construct a drainage channel/interceptor ditch (PM-2) across upper portion of failed area a. Prior to backfilling Pond 016A, the pond must first be dewatered, and all saturated soils must be removed (NWCC text says "stabilized", but no details are provided) from pond bottom and in-slopes b. Standard Proctor curves must be developed for any materials used backfill Pond 016A. The use of curves developed previously for other SCC projects is not acceptable. Given the high clay content of the native materials, and the proposed relocation of Road J/K across the Pond 016A fill, compaction should be a minimum of 95% Maximum Dry Density (NWCC recommends 90%), with a moisture content between 0 and 4% above Optimum Moisture Content (NWCC recommends OMC +/-4%). It is critical that Pond 0 1 6A be backfilled and compacted sufficient to prevent, to the extent possible, the infiltration of additional moisture into the fill. Lift thicknesses of 12" to IS" proposed by NWCC may be too great to achieve the desired densities. d. The fifth full paragraph on NWCC page 5 indicates that channel PM-2 should be excavated into "competent bedrock materials". Test Holes 12 and 13, which are near to the proposed realignment of PM-2, are logged on NWCC Figure #2. In these holes, weathered claystone was encountered at —10 feet beneath the surface, and claystone bedrock was present at 13 to 17 feet below the ground level. Shrub Plot Landslide Site observations and subsurface investigations described beginning on NWCC page 3 In 2010, slope failure had increased in length to WSW; height and location of head scarp remained constant; a new tension crack was observed upslope of head scarp Four test pits (SP -1 thru 4) excavated in Sep-2008; Test Holes 15 and 16 drilled in Jul- 2010. Groundwater was encountered only in SP -1 and TH- 16.