Designing Water Balance Covers for Sustainable Waste Containment : Transitioning State of the Art to State of the Practice

This paper describes key steps in the design process for water balance covers using a case history at a municipal solid waste landfill in Missoula, Montana, USA as an example. The intent is to illustrate how state-of-the-art concepts can be applied in the state-of-the-practice. The process begins by understanding the design objective (including regulatory requirements) and investigating lines of evidence indicating that a water balance cover is likely to function satisfactorily at the design location. Data from two other instrumented water balance covers in the region are used to evaluate efficacy along with historical meteorological data and information contained in a prior unsuccessful submittal for a water balance cover at the Missoula landfill. Site characterization is conducted to define properties of the soil resources and vegetation at the site for preliminary cover sizing and numerical modeling of the water balance. A numerical model is used with various design metrological conditions as input to evaluate whether the cover will meet the design goal under realistic conditions. The final design consists of a monolithic cover comprised of a 1.22-m storage layer overlain by a 0.15-m topsoil layer. A field test with a fully instrumented lysimeter was constructed and monitored to confirm that the cover performs as anticipated in the design.