2011/06/15 Council Agenda Packet

ATTACHMENT B Repairs to Landfill Eastern Slope The City will excavate soft and or eroded soils on the Eastern and Northern slopes from the rivulets and from the soft areas below the standing water, at locations to be determined by the field engineer that will eliminate existing soft areas and erosion features while armoring the slope against future erosion. The areas will be repaired by replacing the excavated soil with a combination of geosynthetic filter fabric and 2 to 4 inch Quarry Spalls. The filter fabric would be placed at the base of each excavation and the Quarry Spalls would be placed and compacted over the fabric to return the slope to its original configuration. The filter fabric will keep the underlying soils from migrating into the Quarry Spalls during high flow events and the Quarry Spalls would provide armored spillway down the slope at location that we know already experience concentrated flows. 3. The approximate locations rivulets and soft areas to be reconstructed are indicated in Figures 1 and 2 of the HWA February 15, 2011 Recommendation letter. It should be noted that these areas are approximate and that their location, lateral extent, and depth of excavation will be determined by the engineer in the field during reconstruction. 4. The geosynthetic filter fabric should consist of a 4 oz per cubic yard needle punched non -woven geotextile such as a Mirafi MiraGreen D4 or equivalent. The filter fabric should be placed on a benched slope surface, as indicated in Figure 3, and the Quary Spalls should be compacted firmly into the fabric to reduce the potential for the fabric to slide down the slope. Under no circumstances should the filter fabric be placed on a smooth 2H to 1V slope. 5. The City will complete minor re -grading of the top of slope at the two locations where standing water exists. Preventing future standing water at the top of the slope will prevent future softening of the underlying soil. If re -grading requires substantial removal of cement treated soil to facilitate drainage, the removed material should be replaced with the same Quarry Spalls material used on the slope. 6. Excavation work should be completed in such away as to limit disturbance to slope areas and associated vegetation not be reconstructed. 7. Material that has accumulated at the base of the slope, as a result of the above described erosion, should be re -graded or removed in such a way as to provide a surface conducive to uniform flow away from the base of slope. 8. All disturbed areas around and adjacent to the work being performed will be hydroseeded in the Spring and Summer following the work. IWA