Use of numerical modelling when designing a full-scale field test of landfill top covers

Abstract

Landfill closures typically include cover systems with a low-permeable barrier to limit the flow of water to and from the waste to minimize contamination of the surrounding environment. Commonly the lowpermeable barrier in the top cover consists of compacted clays and/or geomembranes. An ongoing fullscale pilot test in southern Norway examines the performance of landfill low-permeable barriers, sometimes called sealing layers, constructed of two different recycled clayey soils compared to a traditionally used dry crust clay. Four test cells have been constructed with a top cover consisting of a coarse protection layer overlying a sealing layer. A lysimeter lies at the base to collect and measure the water which percolates through the entire top cover. By modelling the seepage through a simplification of the pilot test top cover, this paper investigates how 2D numerical hydrogeological modelling may be used to inform the design and/or construction of top cover pilot tests in temperate climates. It assesses the effect of sealing layer inclination, thickness and saturated hydraulic conductivity, as well as how detailed, as-built cross-section models compare to simple column models. Saturated hydraulic conductivity was found to be the most important feature when varied within a realistic range. Further, it asserts that 2D modelling may provide an efficient way to assess the consequences of deviations from designed geometry. Simple column models were found to be as suitable for this as more detailed crosssection models.

Use of numerical modelling when designing a full-scale field test of landfill top covers