1997-11-13_REVISION - M1977493 (50)

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Eagle Park Reservoir Final Analytical Summary October 29, 1997 Slope Stability Topics 1. The Lower North Interceptor has been obliterated and graded to slopes that approach 4:1 (h:v). 2. The Division requested that slopes in the east end of the reservoir be incorporated into a wetland development plan. CIVIC believes that the incorporation of a wetland development plan to the east end is outside of the context of the currently approved Reclamation Plan for the Climax Mine. In view of the disturbance that would be caused to slopes at the east end of the reservoir, an engineered and constructed terracing does not appear warranted. Minor vegetative improvements appear plausible above the reservoir high water mark including the area located along the lower access road to the south of the reservoir. This area is targeted for vegetative reclamation activities in 1998. CIVIC is willing to discuss, with the Division, additional reclamation opportunities above the reservoir high water mark as part of the continuing reclamation program for the Climax Mine. At this time, CIVIC does not feel these discussions limit concurrence by the Division that Eagle Park Reservoir is a completed water development. In addition, given water quality in the reservoir, improvements to vegetative buffers at the reservoir fringe would provide, at best, very limited and immeasurable water quality benefit. CIVIC has evaluated the east end of the reservoir within the context of slope stability (see item 3 below) and determined that slope instability is unlikely along the eastern reservoir fringe. 3. A letter report by Woodward Clyde Consultants (WCC) is provided as an assessment of • deep-seated slope stability on the south end of the reservoir. The report states that the south slope of the reservoir is likely to remain stable when the reservoir is filled. An area of weakness was identified on the southeast shore of the reservoir in a location where shores presently approach 3:1 above and below the high water mark. A recommendation by WCC to monitor the slopes has been accepted by CIVIC. Three monuments are in place, initial monitoring is complete, and monitoring will occur in the spring during reservoir fill. CIVIC will inform the Division if future work on this area is planned following spring monitoring. ' The area of shallow landsliding on the steep south slope of the reservoir may continue. The Division, however, has requested that CIVIC provide a summary of vegetative techniques to stabilize the slope. The Division inspection on May 19, 1997 noted that water diversion on the road above the slope would allow removal of lubrication to the thin veneer of soil covering the steep slopes. CIVIC has graded the road to remove surface waters east and west of the slope in question. A vegetative improvement to the soil veneer will be implemented in 1998 using the following techniques: • CIVIC has, on the Climax Mine property, a stand of asexual western wheatgrass. Western wheatgrass is a rhizomateous species capable of forming a mat-like vegetation cover with deep rooted growth. The plant is also capable of rapid growth. CIVIC intends to transplant and plug this plant in 1-2 foot spacing along the slope where the veneer is subject to slippage. • Wolfe's current (Ribes wolfit) is a shrub that grows along the south slope of Eagle Park. The plant is prostrate and prone to vegetative reproduction as evidenced by rooting that occurs where stems contact soil. A collection of seed was made this year and plants are currently under propagation at a local nursery. Given that an adequate number of plants can be propagated, CIVIC will plant the slope on a spacing of 4-5 feet.