Leachate Leachate is produced as water percolates through solid waste, extracting soluble chemicals and products of degradation. Composition depends upon the nature of the waste, rate of water flow, landfill design, operation and age. The two most significant components of leachate are organic chemicals and heavy metals. They are also present as organic chemicals discarded in the waste, eg benzene, toluene, ethers, dioxins, halogenated aliphatics, alcohols, phenols, pesticides, PCBs and organophosphates. Heavy metals, such as mercury, chromium, nickel, lead, cadmium, copper and zinc, are often found in landfill leachate.
Discharges depend mainly on the acidity and the rates of flow of leachate.
Many heavy metals come from the non-regulated hazardous waste fractions from households and businesses. In previous studies, mercury has been linked to paints, thermostats and containers from dental and medical clinics. Chromium and barium have also been shown to come from old paint containers. No engineering design can guarantee total containment, even with the most highly engineered sites some migration of leachate to contaminate groundwater supplies may occur. In recent years, regulators have demanded quality control systems and the use of environ- mental impact and risk analysis techniques.