ARCHIVED REPORTS_1996_1 - Laserfiche WebLink

Home Browse Search

Page 1-27 SECTION 1 -LANDFILL EXPANSION ISSUES monitored for leachate seepage. The perimeter surface water ditch system is shown on the Final Grading Plan (Drawing Pl) and on the Phase Development Plans (See Drawings P3 and P4). Silt fences will be used as required in active and intermediate landfill closure areas to help control soil erosion. 1.6.6 Final Closure Surface Water Run-off Control The layout of the surface water system for final site closure is shown on the Final Grading Plan (see Drawing Pl). As shown on that drawing, the landfill closure uses a network of interception ditches on the slope to collect surface water sheet flow. Interception ditches will have a suitable ditch lining for the design velocities. Most of these interception ditches terminate at catch basins. Culverts from the catch basins convey the storm water to the perimeter ditch system, which in turn conveys the storm water to the detention facility. Culvert outlets will include outlet control structures designed to protect the perimeter ditch lining. The sizing for the surface water conveyance system is preliminary and based on a 100-year, 24-hour storm. Sizing calculations for the conveyance system are included in Appendix D. Final design criteria may result in changes in the sizing and arrangement of the conveyance system. At this conceptual design phase, the final cover system design has only a soil cover layer over the geomembrane. Landfill closure systems sometimes employ a drainage layer between the geomembrane and the soil cover layer. If the final closure design utilizes a drainage layer, then drainage piping should be included within the drain layer for efficient removal of water from that drain layer. These drainage pipes would outlet to the interception and perimeter ditches. 1.6.7 Landfill Surface Water Detention Facility All the landfill surface water is routed to a single detention facility located in the southwest comer of the site. The surface water detention facility would be designed and constructed to meet the requirements of the San Joaquin County design standards. Sizing of the facility is based on a 100-year, 24-hour storm incident on the entire full closure area of both the existing and expansion areas as shown on the Site Plan. The detention pond would be excavated below the current existing grade; discharge to Little Johns Creek would be achieved by pumping. As required in the ISSJC, the pump facility would be capable of emptying the detention basis with 48 hours. The detention basin facility would be fenced to prevent unauthorized access. Preliminary design calculations are included in Appendix D. At this preliminary conceptual design phase, all collected surface water is drained via one system to a surface water detention facility located at the southwest comer of the site. An alternative approach that could be explored at the time of design is to collect and treat the surface water in two systems. A western system would drain approximately half of the site to a downsized surface water facility as indicated on the drawings. An eastern system would drain the other half of the site to another surface water facility that could be located in the northeast comer of the site, i.e., in the wildlife preserve and in between the landfill mass and the flood plain containment dike. Some advantages might accrue to this split, such as an enhancement of the wildlife preserve and City c'.Stockton R.W.Beck and Associate 1811.002