Water, in general, is a tricky thing to handle at a waste facility. Most municipal waste facilities known as landfills accept only dry waste products, but there’s still quite a bit of water in most “dry” waste streams. Even if there’s only a little moisture in the trash as it enters the landfill, the decomposition process often creates water as organic material breaks down. This is especially true for general purpose municipal dumps that accept food and yard waste. On top of the water that is generated from within the trash itself, there is also the issue of rainfall. Every droplet of water that splashes down onto an open landfill cell will slowly trickle through the trash, transforming into a concentrated liquid waste known as leachate. Managing leachate means managing storm water too, since it’s the primary contributor to the volume of waste liquid produced by a landfill cell.
What is Leachate?
Leachate is defined generally as any liquid that percolates through permeable materials and picks up dissolved compounds along the way. In terms of waste management, leachate is the liquid that seeps through compacted trash and other solid waste products. It’s a little different from slurries or liquid waste like sewage, but shares many of the same hazards and handling challenges. Leachate is usually a combination of both internally and externally generated water. This includes moisture released from rotting food and other organic waste and storm water that finds its way into the mound. Unlike many other types of liquid waste, leachate is generated unevenly over the lifespan of a landfill and can unexpectedly increase many years after a cell is capped and covered.
How is It Different from Storm Water?
Storm water that runs over open surfaces, like parking lots and roofs picks up a lot of contamination, so it’s often treated as a waste water in its own right. However, proper design and rain cover use at a landfill can keep storm water runoff far cleaner than that. This means that storm water handled correctly at a landfill is usually safe for direct discharge into the surrounding environment. If the storm water only makes contact with a stable cover material, then it’s unlikely to pick up anything of consequence to the environment while running off into nearby collection areas. However, storm water that enters the system, even partially, becomes leachate. Keeping storm water and leachate separate requires the use of temporary and permanent rain covers that are as impermeable as possible. Yet, since they have to fit tightly over an uneven surface of compacted trash, they must also be flexible and tear-resistant as well.
Why Keep Them Separated?
Even though every modern sanitary landfill features some kind of leachate collection system, it’s not a good idea to simply let rainwater percolate freely through the cell and collect in it. Each system is designed only to handle a specific amount of water and no more. Overfilling the system with too much storm water leads to rapid flushing that increases the number of contaminants and solids mixed into the water. It also threatens to destabilize the compacted trash layers and floods surrounding areas to potentially cause environmental damage. By minimizing the amount of rainwater allowed to enter the leachate system, landfill operators can leave as much space as possible for the moisture generated internally that is unavoidable.
How Leachate Escapes into the Environment
Once leachate is produced through percolation, it slowly trickles down until it hits a surface it can’t seep through. Since water can seep through most materials, even solid rock when given enough time, leachate eventually travels wide and far if it’s not contained. Wastewater produced decades ago can continue seeping out of a landfill that’s missing a liner, resulting in long-term contamination that is difficult to stop and remediate. Leachate can also evaporate into the air and create gas issues, so covers for landfill cells often play a dual role in containing odors and emissions as well.
The Results of Leachate Loss
Leachate isn’t just any old wastewater either. The slow percolation process causes a lot of complex contamination to occur and each landfill has a different composition due to variations in the waste stream. When leachate escapes the containment system and enters the environment, it can cause:
- Irritation to the respiratory and gastrointestinal systems of animals and humans if consumed due to drinking water contamination
- Infections due to bacteria like E. coli that flourish in the leachate
- Heavy metal contamination of surrounding soil that lasts for decades
- High levels of nutrients like nitrogen that cause algae blooms in open waterways that kill off fish and other water life.
Estimating Leachate Volume
One of the biggest challenges of managing landfill leachate, especially over the long term, is estimating the volume correctly. Many landfills have overflowed or developed serious anaerobic conditions under the surface due to underestimation. Part of the issue is that leachate doesn’t develop evenly over the lifespan of the landfill. Leachate is usually relatively low during the active use of a cell, especially if an appropriate rain cover is used. It begins to increase in volume from the first year after capping and peaks shortly after, depending on the size and volume of the individual cell. Careful estimation requires checking historical rainfall levels and testing the trash composition to measure how much organic material is included to produce leachate.
While leachate may be challenging to manage, it’s a task worth the effort. The best results come from combining durable liners at the bottom of the landfill cell with impermeable and flexible covers over the top. Use both temporary and permanent rain covers to keep leachate levels under control and separate out storm water before it can enter the system. BTL Liners provides both liner and rain cover materials for landfills and other industries.
