LABORATORY AND FIELD HYDRAULIC CONDUCTIVITY OF 3 COMPACTED PAPER-MILLSLUDGES

Hydraulic conductivities of three compacted paper mill sludges were me asured in various ways to assess their viability for use in barrier la yers in landfill final covers. Compaction tests showed that the sludge s have compaction curves similar to those for clays, albeit with lower maximum dry unit weights and higher optimum water contents. Hydraulic conductivities less than 1 x 10(-9) m/s can be attained for these slu dges at low effective stresses (<10 kPa) when compacted using standard Proctor energy if the molding water content is 50-100 percentage poin ts greater than optimum water content. The lowest hydraulic conductivi ties were obtained in this range. At higher effective stresses (>20 kP a), hydraulic conductivities less than 1 x 10(-9) m/s can be achieved at higher molding water contents. Field tests conducted on barrier lay ers constructed with two of the sludges showed that field hydraulic co nductivities can be obtained that are similar to those measured on lab oratory compacted specimens prepared at the same molding water content . Laboratory tests on large and small undisturbed specimens removed fr om the field showed that no scale dependence existed in the hydraulic conductivity of the field compacted sludge. Additional tests showed th at freezing increased the hydraulic conductivity of two of the sludges , regardless of whether the sludges were permeated between freeze-thaw cycles or only after the last thaw. In contrast, for the third sludge , increases in hydraulic conductivity only occurred if the sludge was not permeated between freeze-thaw cycles. Significant shrinkage and cr acking of the sludges occurred when they were dried, suggesting that b arrier layers constructed with sludge should not be permitted to desic cate. Long-term tests showed that the hydraulic conductivity remains s table or decreases slowly if permeation is continued over an extended period of time.