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3-1 3.0 CLOSURE PLAN 3.1 Introduction The Stage 1B partial final closure of the FL will be performed in accordance with the applicable regulatory standards included in 27 CCR, Chapters 3 and 4 and 40 CFR, Subpart F. The costs associated with the Stage 1B closure are described in Section 6.0 of this document. The improvements and systems required for the Stage 1B partial final closure include the final cover and final grading plan, supported by landfill settlement and slope stability analyses, drainage and erosion control systems, landfill gas control and monitoring systems, groundwater/surface water monitoring system, and decommissioning of environmental control systems, as necessary. A description of these closure improvements is presented in the following subsections. 3.2 Final Cover The purpose of a final cover is to provide long-term minimization of surface water intrusion, to isolate wastes from the ground surface, and to reduce the potential for odors and gas emissions. The cover also provides a base for vegetation, which will reduce drainage velocities and erosion. In addition, the final cover configuration is designed to accommodate settlement, subsidence and the effects of seismic events throughout the minimum 30-year post-closure maintenance period and beyond. 3.2.1 Final Cover Design 3.2.1.1 Regulatory Design Standards ® California Final Cover Prescriptive Design Standard The minimum final cover standards for the FL, as outlined in the closure and post-closure requirements for Class II landfills contained in 27 CCR, Section 21090 include: ♦ Foundation Layer: A minimum two-foot thick layer of soil placed immediately over the entire surface of the last lift of refuse. This layer shall have the appropriate engineering properties, so as to provide a relatively unyielding surface upon which to place and compact the low-hydraulic-conductivity layer. ♦ Low-Hydraulic-Conductivity Layer: A minimum one-foot thick layer of clean low- hydraulic-conductivity soil containing no waste or leachate placed over the foundation layer. The low-hydraulic-conductivity (or low through-flow rate) soils shall be placed on top of the foundation layer and compacted to attain a hydraulic conductivity, which is the lesser of either; — 1 x 10-6 cm/sec. — The hydraulic conductivity of any bottom liner system or underlying natural geologic materials. ♦ Erosion Resistant Layer: A minimum one-foot thick layer of soil containing no waste or leachate placed on top of all portions of the low-hydraulic conductivity layer. Vegetation root depths must not exceed the topsoil layer thickness. Vegetation is to be replanted, as needed, to provide effective erosion resistance. Forward Landfill Stage 1B Partial Final Closure/Post-Closure Maintenance Plan June 2011 SWT Engineering z:\projects\allied waste\forward\11-1014 partial fnl clsr pin\partial final closure plan document\text\sec 3.doc