Leachate is a liquid that forms as water passes through toxic land surfaces, picking up contaminants from waste materials, and entering into the underlying soil and potentially the water table. Landfill leachate is the most common occurrence, as landfills are the most numerous toxic sites across the country, but the same phenomenon can occur in dairy farms, chemical plants, hydrocarbon sites, and other waste-producing areas.
Landfill leachate typically contains dissolved organic compounds, suspended solids, acids, toxic metals and disease-causing microorganisms. Rainwater percolating through the landfill waste is the most prevalent cause of leachate, but moisture can also be contained in the waste itself, or be produced during the decomposition process.
Variable factors that can determine the impact of the landfill leachate will include the age of the landfill and the types of waste being deposited, as well as local conditions such as the general pH that indicates excess alkalinity or acidity, the ambient temperature, and of course the amount of new water entering the landfill.
Landfill leachate is an obvious environmental concern since it can so easily seep through soil and contaminate groundwater and nearby water sources. Sometimes containing hazardous and toxic substances that can spread disease, leachate is considered a hazardous material by environmental agencies, and regulation exists to prevent its occurrence.
Management and Treatment
Modern sanitary landfills are designed to prevent leachate contamination using impermeable bottom liners, leachate collection systems and by treating collected leachate before releasing it. Common treatment methods include biological treatments using a bioreactor – a system or device that provides optimal conditions for biological reactions from microorganisms, enzymes and the like. Additionally, chemistry can come to aid of biology with various physicochemical approaches such as advanced oxidation, adsorption and membrane filtration.
Testing is usually required to detect leachate contamination in water sources. Immediate clues beforehand can include odors or vapors from water faucets and local reports of deteriorated quality. Residents are especially vigilant for these indicators of course with the presence of a nearby waste disposal site.
Proper management and monitoring of landfill leachate is crucial for protecting public health and the environment. Even after landfills close, leachate can continue to be produced for many years and this threat requires ongoing management.
Several measures can be taken to prevent leachate contamination from landfills, from the design of the site and the operational practices, to regular inspection, testing and treatment. Regulatory compliance from good-actor operators is also a key factor here.
Site Design
Using impermeable geomembrane landfill liners at the bottom of landfills are the most effective means to prevent leachate from seeping into soil and groundwater. Landfill daily cover is important also, using similar synthetic liner materials, both to keep dust and particulates from entering the air, and, most importantly in the case of leachate, to keep rainwater off the waste materials.
Stormwater collection systems around the landfill site will prevent ground flooding, and leachate collection systems will channel and remove leachate from the landfill before it can contaminate surrounding areas. Landfill cell design creates cells that isolate active waste management, and each cell will embody all the features mentioned here.
Landfill Operation
A landfill is continuously being groomed by earth moving equipment, to segregate and consolidate the waste materials. Best practices here include intelligent grading to establish landfill plateaus and slopes to maximize rainwater runoff toward perimeter stormwater ditches. This can be extended into a landscape of swales and berms, as well as temporary drainage features to divert runoff away from waste areas.
The goal of the well managed landfill is to minimize the exposed waste at any time, limiting the size of the active disposal area through consolidation, and covering the waste promptly. Temporary top covers of geomembrane tarps are also spread over inactive areas that will not receive waste for extended periods.
Maintenance and Monitoring
Regular inspection of liners, collection systems and covers are important to identify and repair any damage. Vigilance at the intake end of the operation is important also, for proper waste acceptance that excludes hazardous and difficult materials from the landfill.
Water quality testing is a crucial part of good landfill operation, with groundwater and surface water monitoring programs to detect potential any contamination as early as possible. Treatment of collected leachate treatment can be handled on-site or by transporting it to appropriate treatment facilities. A landfill is necessarily a regulated site. Local, state and federal guidelines for landfill design, operation and monitoring exist to protect the environment and the people and animals living in it. Following the guidelines will greatly reduce the risk of harm to us all from leachate contamination.
