ARCHIVED REPORTS_1994_1 - Laserfiche WebLink

Home Browse Search

The downdrains will be constructed of 12-inch corrugated steel pipe that will cross under the maintenance road and down the exterior of the landfill. The downdrains have already been constructed and will be adjusted to final grades as final cover is built. The downdrains will extend to the toe of the exterior slope and discharge to the open drainage channel surrounding the perimeter of the landfill. A 5-foot width of riprap erosion protection will be placed across the width of the drainage channel at each downdrain junction. Drainage channels around the primary and secondary sites will convey all storm water runoff to the southwest corner of the primary site, at which point a culvert will carry the water over the EBMUD aqueducts to the storm water detention basin. Water collected in the storm water detention basin is automatically pumped into South Paddy Creek just south of the basin. Flood studies have not yet been completed for South Paddy Creek in the area of the landfill, so Flood Insurance Maps are not available at this time. However, if South Paddy Creek floods, the detention basin is capable of storing combined flood waters from the 100 year event for both the landfill and South Paddy Creek. Additional information_concerning the drainage system is contained _.. in Appendix D of this report. 12 . SLOPE PROTECTION AND EROSION CONTROL Erosion will be controlled mainly by vegetating and keeping all slopes at or under a ratio of 1.75: 1. The steepest slopes will be located around the perimeter of. the landfilled areas. The other final cover slopes will be constructed at 3-6% to prevent drainage slope reversal from landfill settlement and to minimize overland flow velocity. The entire final site face will be vegetated with Bromme grass to provide a low maintenance form of erosion control. The species of Bromme grass called Brommus Mollis will be used. It is a self- growing, self-seeding species that will consistently produce forage and seed even under adverse soil and weather conditions. The grass will be fertilized annually as needed, but will not require irrigation. Silt fencing may be constructed along steeper toe slopes parallel to the drainage ditches to prevent soil from being washed into the drainage ditches. Annual soil loss is predicted below using the Universal Soil Loss Equation (Figure 3) . 10