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The settlement agreement required a monitoring program to evaluate the effectiveness of the overall project. Monitoring stations were installed throughout the landslide, mainly along the west perimeter of the slide (figure 6). These stations allow measurements of the subsurface ground water collected by the Eljen drains, the surface water being diverted off the landslide by the lined ditches, and the total flow in the various channels, which eventually feed into McClain Creek.

Figure 6. Monitoring station to measure ground water and
surface water flows drained from the middle site.

Brief Construction Summary

Prior to startup, all construction materials had been procured by the Forest Service and delivered by helicopter to various sites throughout the slide. Materials delivered onsite included Eljen drains, ADS piping and fittings, and several rolls of HDPE liner. The contractor's fuel for the spider hoe was also delivered by helicopter in three 55-gallon drums.

Work was started on the lowest Eljen drain (between the upper and lower roads). This location was the steepest section of the slide in terrain and would have been difficult to excavate under adverse weather conditions. Trenching operations were relatively straightforward for this drain because the ground conditions were dry throughout the length of the trench.

The Eljen drain panels were installed on the uphill side of the trench, then backfilled on the downhill side, in accordance with the manufacturer's specifications (figure 2). After backfilling, the spider hoe excavator was used to shape the surface drainage ditch, and a 6-foot wide HDPE liner was installed over the shaped lined ditch. Finally, the excavator was used to place rock and excavated material to key in the sides of the ditch liner.

Upper Site

The upper site is located at the top of the slide within the vicinity of the headscarp (figure 1). Excavating a trench, through the pressure ridge, between the two monitoring stations for the 8-inch outlet pipe was the first stage. More than 200 feet of 8-inch-diameter solid ADS pipe was installed, then trenching proceeded up the hill for the four 4-inch diameter collector pipes. This piping drains the existing Womack structures and all Eljen drains at the upper site (figure 4).

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