Design and Performance Features of a Zone of Saturation Landfill, 1996 Environmental Conference Proceedings

Thilmany Pulp and Paper Company, Division of International Paper, has permitted, constructed, and put into operation an expansion to its existing industrial landfill. The landfill is a clay-lined monofill designed to accommodate approximately 100,000 cubic yards of solid waste annually. Construction and operation permits were obtained for a landfill that extends up to 30 feet below the natural groundwater table or zone of saturation. The geological setting and proximity to the existing landfill were conducive to expansion of a landfill designed with inward hydraulic gradients. The geology of the area consisted of approximately 100 feet of glacial lake clays and glacial clay till above the dolomitic bedrock. Piezometers indicated that the seasonal groundwater table was only 1.5 to 3 meters below the existing ground surface.

To accommodate these geologic conditions and the proposed landfill configuration, a slope stability and dewatering analysis were performed. This indicated that an underdrain system should be placed below the clay liner to relieve uplift pressures that may develop before the filling of the landfill commences. A groundwater flow net was developed using a numerical model which indicated that an inward gradient potential existed for the clay-lined facility. The modeling was used to develop a monitoring program and to estimate groundwater yield into the leachate collection system. As part of the permit approval, pneumatic piezometers were constructed above and below the liner to verify that an inward gradient existed at the landfill after construction and during operations. Performance readings of these piezometer over three years are presented along with construction details and groundwater monitoring results.