Westhorp & Associates was also selected by Miami-Dade County for the design of the base liner and drainage system for Cell 5 as well as the construction oversight at the South Dade Landfill (SDLF). The SDLF is a 320-acre Class I municipal solid waste facility which is owned and operated by the County. It is located in the southeastern portion of Miami-Dade County, adjacent to the South District Wastewater Treatment Plant, the Blackpoint Marina, and Biscayne Bay. The base liner system for the 50-acre cell consists of multiple layers including a geosynthetic protective layer, a leachate collection system, a leachate detection system, a composite secondary liner, and a soil layer.
Construction was broken down in phases, the first two phases began in September 2011 and included subbase grading and the import of cover material to prevent vegetative growth. The first step was to classify and sort an on-site soil stockpile based on its usability. The usable soils which were suitable for use as subbase were spread across Cell 5 and placed according to the slopes required per the design drawings. All soils were shaped and compacted to the requirements of the technical specifications. Additionally, one foot of limerock cover was placed across Cell 5 and compacted to prevent vegetation from overgrowing which was an often documented issue.
The final phase of construction, tentatively scheduled to begin in 2014, will include the placement and compaction of additional fill material to achieve the required grades prior to the installation of the geosynthetic materials and drainage system. A certified geosynthetic installer will then be charged with placing the multi-layered liner and drainage system which will be tied into the adjacent landfill cell. The liner installation will undergo rigorous testing to ensure that the runoff from the waste is contained within the landfill and will not impact the soils and water below. To protect the liner from damage, two feet of sand will be placed across the entire area prior to filling with waste.