Leachate management is potentially the most significant, long-term, recurring cost for landfill care. In temperate regions, it can account for up to 20 to 30 percent of operations budgets. What’s more, leachate management and monitoring could extend for decades after a landfill has been decommissioned.
The basic rule in managing leachate is that it must never be permitted to escape the landfill system. Any escape risks both an environmental disaster and the health of human populations. For that reason, a leachate drainage system is a required and highly legislated element in every modern municipal solid waste landfill.
Landfill cells are lined on the sides and bottom with impermeable geomembranes, often underlaid with a thick compressed clay liner for additional stability. Above that layer is an array of moisture detectors, designed to detect leaks and raise the alarm before any leachate hits the last defense. Another impermeable liner isolates the landfill mass above the leak detection system, and it’s on top of this primary liner that leachate collects and is pumped away. Typically, the leachate is allowed to flow into perforated pipes which are installed on a slight slope, directing leachate to an area where it is pumped up to the surface and piped into a leachate pond, which itself must be lined with multiple layers and a leak detection system.
Liners for Leachate Management
Since leachate must be so carefully controlled, any location where it is produced, where it flows, and where it is collected, must be lined with a chemically resistant impermeable liner. Additionally, a secondary liner with a leak detection system must be employed. The extremely toxic nature of leachate demands a durable, long-lasting liner that will not degrade and weaken, even in the presence of a wide variety of chemicals. BTL Liners’ ArmorPro line offers durable options that perform in even the most challenging environment.
In some landfills, the collected leachate might be removed altogether and treated until it’s deemed safe and clean for release into the environment. A more recent practice is to recirculate the leachate through the decaying waste by pumping it back to the top and allowing it to percolate again. The additional moisture provided by recirculating leachate promotes faster and more complete decomposition of organic components. We’ll discuss this practice in an upcoming article on bioreactor landfills.
The Groundwater Monitoring Stations
Groundwater monitoring stations are employed to test water in the environment near the landfill for leachate chemicals that may have escaped the landfill’s lined enclosures. If leachate chemicals are detected downstream in underground water tables or aquifers, operators are alerted to identify and repair any leak or malfunction that has led to the contamination.
Typically, wells are drilled both uphill from the landfill and downhill. The uphill station gives a baseline reading on water quality before it passes the landfill. If samples from the downhill well show contamination or any other impact to the groundwater, action can be taken to locate and fix the source of any leaks or other issues.
Using Leachate
Traditional municipal landfills take a decidedly unfriendly position against leachate and have operated for decades on the principle that no moisture shall be allowed to remain within the landfill, lest it leach through the waste pile and create…toxicity! In these landfills, heroic efforts are made to prevent any precipitation from infiltrating, and every drop of naturally occurring leachate is collected, pumped out, and disposed of. This is a reliable way to ensure that no leachate ever escapes into the environment, but natural microbial breakdown of organic material (old cabbages to last year’s newspapers) can’t take place without at least some moisture. Kept dry as the proverbial mummy, this style of landfill tended to preserve readily compostable materials in a pristine state for 50 years or more. It’s not surprising this moisture -free approach is called a “dry tomb.”
On the other end of the spectrum, some landfills incorporate a bioreactor system into their waste management strategy. When both liquid and air are introduced to layers of mixed waste, natural microbial action is increased, which accelerates the breakdown of organic compounds,
Speedier waste processing leads to reduced production of greenhouse gases, which in turn reduces the years that must be devoted to monitoring for leachate and gas production. In turn, this hastens the time when the former landfill can be opened for new use as anything from a wildlife park to a solar farm to a parking lot.
