Migration of Landfill Leachate Through Glacial Tills

Abstract

ABSTRACT To evaluate the potential of natural clay minerals for attenuating and preventing the pollution of water resources by landfill leachates, leachate was collected by anaerobic techniques from the 15‐year old Du Page County sanitary landfill near Chicago, Illinois, and was passed through 44 laboratory columns that contained various mixtures of calcium‐saturated clays and washed quartz sand. The columns were constructed to simulate slow, saturated, anaerobic flow, and manometers were placed at five locations in each column to measure any changes in hydraulic conductivity. Leachate was run through the columns for periods ranging from 6 to 10 months, during which time effluents were collected periodically and analyzed for 21 chemical constituents. The columns were then sectioned and the clays analyzed to determine the vertical distribution of the chemical constituents in each column. Sterilized landfill leachate was used in a duplicate set of columns to determine the effects of gross biological activity. Chloride and certain organic compounds were relatively unattenuated by passage through the clay columns; monovalent cations, such as Na, K, and NH 4 , were moderately attenuated; and heavy metals, such as Pb, Cd, and Zn, were attenuated by even small amounts of clay. Concentrations of Ca and Fe were much higher in the column effluents than they were in the original leachate. The increase in Ca in the column effluents was due to cation exchange with ions in the refuse leachate. The Fe increase probably resulted from reduction of the oxidized Fe on clay surfaces by anaerobic refuse leachate to more soluble reduced Fe. Both biologically active and sterilized leachate reduced the hydraulic conductivity of the clay‐mixture columns during the experiment. The active leachate reduced the hydraulic conductivity to a much greater degree than the sterile leachate. Results of the laboratory data were compared with field data from the Du Page County sanitary landfill and from other existing landfills where detailed data are available. The field data show a “hardness halo” corresponding to the Ca release in the columns. The relative attenuation rates of some of the ions were also confirmed by the field data. The change in hydraulic conductivity was not as clearly shown. Ion exchange capacity, hydraulic conductivity, and buffering capacity of the earth materials were all shown to be important in assessing the potential of landfills for water pollution.