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Memo to Joe Dudaeh <br />Trapper Landslide - Hydro-Geo Report <br />page 2 <br />(3) "During recontouring of the slide area a bulldozer should be <br />used to decrease the permeability of the top layer of the <br />spoils. Several runs by the bulldozer on top of the reclaimed <br />surface should be sufficient to substantially reduce the <br />infiltration potential." <br />The Division will need additional detail before it can render an <br />opinion regarding these specific recommendations. <br />(1) A simple smoothing of the existing extensional graben trench <br />surrounding the landslide block will not be acceptable to the <br />Division. Care will be necessary to prevent this trench shape <br />from acting as an infiltration gallery, which would contribute <br />moisture to the basal plane of the failed spoil block. <br />However, the operator should also avoid reloading the failed <br />mass. A specific regrading scheme should be proposed. The <br />lower portions of the extensional zone on each side of the <br />landslide mass might be convenient locations for the placement <br />of trenched gravel drains to express any infiltrating water. <br />(2) Particular attention should be paid to a toe ditch to convey <br />any water effluent from the failed mass. <br />(3) Is it the intention of this recommendation to recompact the <br />entire upper horizon of the failed spoil block, or merely the <br />regraded areas? Care will have to be taken to remove and <br />replace topsoil. Otherwise overcompaction of topsoil will <br />retard revegetation. Further, over compaction of earthen <br />materials may only result in a transient benefit. If these <br />soils exhibit any swelling potential, exposure to moisture <br />will cause them to swell, lowering their density and <br />increasing their permeability. Swell/consolidation tests <br />should be performed to determine the equilibrium density of <br />these materials under field conditions. <br />(4) Saturation of the failed spoil mass might also be prevented by <br />enhancing drainage of the landslide mass. The installation of <br />a toe drain and axial trenched (french) gravel drains might <br />help to avoid resaturation of the mass. In the event that <br />regrading and recompaction do not prevent infiltration, drains <br />will intercept and depress the saturated surface. <br />The Division should review and approve the specific proposed <br />remedial actions as a portion of the Technical Revision required as <br />a portion of the abatement of NOV 95-17. The application should <br />include a work plan and schedule for completion of the remedial <br />actions. <br />