Influence of landfills on ground-water quality

This paper identifies existing and potential sources of ground water contamination assignable to landfills, discusses factors affecting site selection and qualification, and addresses general procedures for monitoring active and inactive landfills. Waste materials are gradually removed in percolating waters. The thickness and character of unconsolidated deposits beneath a landfill influence the time of waste transport and degree of modification before leachate reaches the water table. For bedrock, both lithology and structure may influence travel time and chemical change of the leachate. Most soils and sediments are chemically active toward dissimilar fluids. Thus, the vadose zone acts as a buffer between landfills and ground water. Chemical activity occurs at surfaces of clay mineral, hydrous oxide and carbonate mineral particles. Silicates are less reactive. Microbial activity may involve indigenous or transported cells. The cation exchange capacity of natural particulates immobilizes some of the leached cations. Solution concentration, pH, and percolation rate affect these reactions. Leachate reaching the water table tends to maintain its chemical integrity with dilution occurring mainly where it contacts the ground water. The leachate moves in the direction of ground water flow as a plume whose shape is determined by the flow characteristics of the aquifer. The velocity tendsmore » to be greater at shallow depths. Attenuation of concentration is caused by chemical or biochemical reactions which remove constituents from solution; by dilution; and by adsorption or filtration. The dominating influences of geology, ground water hydrology, surface water hydrology, and climate must be considered in site evaluation. Monitoring of both active and inactive landfills is essential to detect their impacts upon ground water resources. 13 references.« less