Composition and variability of leachate from recent and aged areas within a municipal landfill

Abstract

A leachate study was conducted at a large, operating, regional municipal solid waste (MSW) landfill near Seattle, Washington, to examine differences in composition and emission rates between old and new areas of the fill. The landfill began operation in 1966, was receiving approximately 2000 tpd of MSW and had 30 × 106 m3 (∼12 × 106 tonnes) waste in place at the time of this study. The two areas studied had average ages of 3.7 and 16 years, and contained 5.7 × 106 and 2.04 × 106 tonnes of MSW, respectively. Variations in flow rate, total dissolved solids (TDS), chemical oxygen demand (COD), total organic carbon (TOC), Fe, and Mn were monitored over a 3‐month period in the winter and spring of 1992. Increases in flow driven by precipitation caused gradually increasing leachate mass emissions from the aged fill. The rate of mass emission increase with increasing flow from the new fill was more than three times higher than that from the old fill. Leachate flow through the old fill appeared more channelized, resulting in diluting effects with increasing percolation. In leachate from the new fill concentrations were essentially independent of flow. Overall, mass emissions per unit waste mass in place decreased with increasing waste age for TDS and Mn, indicating that these components were leachable independent of degradation processes. Mass emissions per unit waste mass in place increased with increasing waste age for COD, TOC, and Fe, which typify components that increase in availability for leaching with increasing age and progressing stage of decomposition.