Retrofit of an Unlined Landfill with a Composite Liner-Design and Construction Experience, 1996 Environmental Conference Proceedings

After constructing and initiating fill operations in a 45 acre landfill phase, it was decided to install a highly-effective liner system in half the site. Waste materials were excavated and placed in the remaining half, leaving 22 acres to be lined. Approximately 4 of the 22 acres were originally constructed with 2:l slopes, with slope lengths up to 90 feet. The site had been excavated to the maximum depth possible to maintain the regulatory separation between waste and ground water. The liner retrofit had to be accomplished with a minimum of excavation to maintain the ground water separation, and with a minimum of fill to preserve waste disposal airspace. Liner system options to meet a performance standard of less than 25 gallons of infiltration per acre per day were examined using the HELP model. In addition to the infiltration performance standard, liner system options were evaluated on the basis of cost, volume of landfill airspace required, and availability of construction materials. Twenty-one options were modeled, including 12 with the slopes unlined. It was determined that infiltration from the landfill could not be kept to less than an average of 25 gallons per acre per day unless the bottom and the slopes were lined with a synthetic composite liner system. Natural clay liners could not meet the performance criteria. A liner system consisting of prepared subgrade, geosynthetic composite liner (GCL), high-density polyethylene (HDPE) liner and an aggregate drainage layer was selected. The design for the system was approved by the Alabama Department of Environmental Management without modification. Special geotechnical design features and construction techniques were required to install the liner system on the slopes. The first 4 cells, including half of the slope area, were constructed during the fall of 1995.