Leachate is a fancy name for liquid waste. While this thick runoff liquid is similar to many other byproducts from commercial and industrial processes, it’s also unique in some ways. For example, it’s one of the only runoff liquids that is produced primarily, but also in the greatest volume after the active use of the site ends. Understanding where leachate comes from, and how to control the amount produced, is essential to planning an affordable collection system. Without correct estimation of all the various sources of leachate, it’s far too easy to undersize a leachate pond and leave it overflowing at a key time.
Slow Leaching Through the Waste
Most leachate is created as rainfall soaks through the accumulated trash. In early landfills before the modern sanitary design, leachate hit the surface of the ground after running through the uncompacted trash relatively quickly. In modern landfills, compaction between daily loads and the use of thick layers of soil cover help slow the leaching effect. However, this also gives the water more time to dissolve chemicals and pick up particulate along the way. The majority of leachate volume comes from this downward trickling effect, but the waste liquid also mingles with the rest of the sources along the way, until it reaches the very bottom layer of the landfill.
Leachate vs Clean Runoff
It’s important not to confuse or mix leachate from a landfill with the clean runoff that is often captured over or around it. Active landfills should direct as much clean rainwater as possible away from the open working cells to minimize leachate volume. Clean runoff water is often safe enough to release directly into the environment, or a nearby body of water, as long as it’s handled correctly and isolated by liners from leachate and trash. Clean runoff can only be created with the use of impermeable liner and cover materials. A properly covered, closed landfill should produce more clean runoff than dirty leachate water; reducing the volume needed for permanent storage ponds.
What’s in Leachate Liquid?
Leachate liquid is a complex mixture, that varies between landfills, depending on what’s stored within. In addition to what’s allowed and forbidden in the individual cells, various factors like the local population and their trash habits factor into the final leachate formula. Some of the compounds and chemicals commonly found in leachate include:
- Dissolved organic materials from broken down yard waste, food, and more
- Inorganic macro components like microfibers, bits of plastic, and degraded styrofoam
- High levels of heavy metals, which are some of the most hazardous ingredients in leachate
- Xenobiotic organic compounds, a complex range of hazardous chemicals that can persist in soil and water for years.
Leachate can be many times more concentrated than sewage fluid and other liquid wastes. It must be handled with care and contained at all times to ensure there’s as little environmental impact as possible.
Condensates from Landfill Gas Production
Landfills aren’t just covered and controlled to keep leachate in. They also produce a large volume of various mixed gases, the majority of which is methane. Landfill gas (LFG) can be captured and claimed as a valuable source of power and heat with relatively little treatment and separation. However, the covers used to trap and accumulate these gases also create condensation that is rich in contaminants. Condensation left behind during landfill gas production is hazardous just like leachate, so it’s often mixed in with it for long-term storage and treatment. Condensate from gas production has similar reactivity issues as other leachates, so similar liners should work well for containing them.
Containing Contaminated Ground Water
The final source of leachate in most landfill systems today is contaminated ground water. Where liners have failed or trash was introduced into the environment without appropriate preparations, effected groundwater must be contained until it’s either treated or removed for permanent disposal in a facility that handles liquids. This includes groundwater contaminated by leachate or by other spills of concentrated fluids transferred or stored at the facility. Leaving compromised groundwater underground can result in drinking water supply issues or long-term soil contamination in a larger area.
Environmental Risks of Leachate Seepage
The heavy metals and chemicals mixed into leachate are damaging to the sensitive ecosystems of soil and water around the landfill. Everything from bacterial die-offs to fish kills is possible if leachate is allowed to escape into the surrounding area. Even evaporation can cause risks if the fumes generated are too rich in flammable gases. That’s why some leachate ponds require covers and must be treated as landfill gas generating fixtures rather than just basic storage basins. Don’t let slow seepage through permeable liner materials, like compacted clay, risk damage to the environment that will result in costly remediation fees later.
Regardless of its specific composition, landfill leachate is a concentrated mixture high in many risky compounds and chemicals. It must be handled carefully and stored securely to meet all current state and federal guidelines. Turn to a reliable source of impermeable geomembranes like BTL Liners to get all the essential materials for both lining and covering landfill leachate systems.
