Progress Report on NCASI Landfill Cover Research, 1990 Environmental Conference Proceedings

The first two years’ progress on the field study portion of an NCASI/USEPA project in-vestigating the use of pulp and paper mill sludge as barrier material in covers for municipal, industrial, and hazardous waste is described. For this study four landfill cover simulators have been constructed. Two covers contain clay as the barrier material, one contains a paper mill primary sludge, and one contains a paper mill combined sludge. Each test cell is approximately 15.25 m (50 feet) square and 1.85 m (6 feet) deep. At the cell top is a 0.15 m (0.5 foot) layer of topsoil with vegetation. Below this is a 0.46 m (1.5 foot) layer of silty sand. Below this is the 0.61 m (2 foot) barrier layer.Below the barrier is a 0.61 m (2 foot) layer of compacted clean sand. At the bottom of each simulator is a 30 mil pvc flexible membrane liner (FML). A perforated pvc pipe collection system embedded in a pea gravel envelope lies on the perimeter of the surface. It directs surface runoff to a collection basin. Another collection system lies at the bottom of the cell. It directs seepage trapped by the bottom FML to another collection basin.

The combined sludge cell has produced less seepage and more runoff than the clay cell throughout the study. The primary sludge cell initially generated more seepage and runoff than the clay cell, but the cumulative volumes of seepage and runoff are now greater for the clay. After approximately six months of operation the primary sludge exhibited a large decrease in hydraulic conductivity. After approximately ten months of operation, and following a severe summer drought, the clay exhibited an eighteen-fold increase in hydraulic conductivity not demonstrated by either sludge. Since fall 1988, all the hydraulic conductivities have been fairly constant with the paper mill sludges exhibiting slightly lower values than the clay.