Advancements in Landfill Capping with Paper Mill Sludge, 1999 Environmental Conference Proceedings

M. Taylor, C.J. Sprague, J. G. Kahle, C. Firman, D. Doyle--Since the early 1990s, a body of evidence has been growing which demonstrates the viability of using paper mill sludge to construct stable, low-permeability barrier layers for industrial landfills. Based on research by NCASI, full-scale closure projects have been designed and several have been constructed with satisfactory results.

This paper presents the details of recent experience at determining the critical geotechnical properties of individual paper mill sludges and the associated analytical tools necessary to develop an effective barrier system design. Although fiber sludge is soil-like, modified testing procedures were developed because of its unique behavior.

The fibrous nature of paper mill sludge gives it permeability, strength, and unit weight properties which must be quantified through carefully designed laboratory testing in which the moisture content and confining pressure reflects expected placement and as-built conditions. Side slope stability analyses must consider lateral seepage and benefit from using the “apparent” cohesion of the sludge, along with frictional properties, in determining resistance to downslope failure.

The testing and design strategy for a sludge barrier layer in a final cover system must address these unique conditions.