When we think about solid waste, we don’t really think about water being a consideration. Afterall, that’s what wastewater management is for. Surely a dump exposed to the sun would be dry and dusty, right? Landfills, however, contain a surprising amount of moisture. As organic materials break down and rainfall makes its way into and through the waste, a toxic mixture of heavy metals, microorganisms, and chemicals is formed. This liquid is called leachate and is a major concern for anyone looking to manage a landfill.
Leachate is the mixture of all the moisture and liquid that seeps through the landfill or is created by decomposing matter. This mixture can contain dissolved organic compounds, heavy metals, pathogens, and dangerous chemicals. If allowed to enter the environment, these can accumulate within the ecosystem itself, passing along the food chain. If these toxins make their way to humans, they can cause serious harm, like cancer, disease, or birth defects. However, leachate isn’t all bad news. This highly concentrated liquid can feed bacteria and decomposing microbes within the waste if it’s reapplied to the landfill, speeding up the decomposition process.
Proper leachate management includes prevention, collection methods, and systems for removal. Leachate is often collected by wells at the bottom of a landfill and pumped back up to the top of the landfill, or to a leachate pond. The nature of leachate means everything used to store or transport leachate will need to be watertight, durable, and chemical-resistant. Both natural and synthetic liners are employed within a solid waste landfill. Durability and resistance are paramount in a long-term sanitary landfill that may be in active use for up to half a century.
Liners within a sanitary landfill must be:
- Highly flexible
- High tensile strength
- Durable
- Resistant to abrasion and punctures
- Highly chemically resistant
- Able to withstand temperature variations
- Resistant to UV degradation
The bottom layer of a sanitary landfill is the last defense in preventing liquids from passing from the landfill into the surrounding soil. This layer is often made up of compacted clay. To ensure impermeability, engineers will usually cover this base with additional layer(s) of high-density plastic or geosynthetic material.
Clay Liners
Clay liners, most often made of bentonite clay, are convenient for their relatively small environmental impact and low initial cost. However, puddled clay is easily spread too thin during the application, resulting in a less than watertight seal. The sensitivity of this step makes clay liners practically as tricky to install as their geomembrane alternatives. Clay also allows the permeation of chemicals and nutrients between water and the underlying soil. A soft clay liner is also easily disturbed by wildlife or erosion. Damage is tough to identify and locate, and frequently complete reinstallation of another lining solution is necessary.
PVC Liners (Polyvinyl Chloride)
These are very common in small backyard pond projects due to their affordability and ease to purchase and set up. Conventional PVC isn't as durable as other liners and usually has a lifespan of only ten years. PVC also lacks the U.V. protection found in newer liner technology, meaning they need to be buried to avoid brittleness and damage from sun and movement. Tears are common throughout installation and use, and frequent disturbance for maintenance only contributes to the problem.
EPDM Liners (Ethylene Propylene Diene Monomer)
This is a popular kind of synthetic rubber liner. This is more durable than PVC and is accordingly thicker and heavier. This more robust liner is still somewhat flexible, but its weight and general unwieldiness complicate shipping and installation. EPDM liners are sealed using adhesive tape, and any mistakes during installation will significantly impact the liner's permeability. EPDM is less sensitive to U.V. damage than PVC but still needs protection from long-term sunlight and decay. Leaks are easier to locate and repair in EPDM liners than the above. However, the rubber is susceptible to punctures from wildlife or damage during installation.
HDPE Liners (High-Density Polyethylene)
These geomembranes are increasingly popular options as they become cheaper and more available. These are thick and stiffer than PVC or EPDM liners and are incredibly resistant to U.V. degradation and tearing. Despite their durability, HDPE liners are lighter than their EPDM cousins. However, the material's stiffness means that any folds or creases are permanent -- these liners would require professional installation. Their seams are heat-welded, leaving their watertight seal virtually permanent. Holes and damage are patchable, saving you the cost and trouble of choosing and installing an entirely new solution. HDPE liners are also chemical-resistant, protecting the surrounding soil and local watershed. (In situations where RPE liners involve unavailable expense, HDPE is a worthy alternative).
RPE Liners (reinforced polyethylene)
RPE liners are on the frontlines of geotextile technology today. These are lightweight, durable, and UV-resistant. RPE liners are welded using the same heat technology as HDPE liners, reducing the frequency and severity of damage from installation or wear-and-tear. They are also built to be chemical-resistant, preventing seepage from chemical-rich irrigation water into groundwater aquifers beneath the soil. RPE is also built to avoid the leaching of internal chemicals, essential for water used on crops. BTL has manufactured RPE liner panels in immense sizes beyond 150,000 sq ft. The lightweight flexibility of RPE liners means that even the largest panels can be factory-welded to be delivered installation-ready. RPE is also simpler to install, meaning that in all but the largest projects, manual installation is possible. BTL and our team of experts installed an RPE liner in a 40-acre irrigation reservoir manually in only four days.
Concrete Liners
Frequently, waste ponds are built using precast or poured concrete. Concrete is porous, and capillary action will quickly pull water through the material towards the earth below. Sealants will protect the concrete from permeation for some time but aren't permanent. A geomembrane liner serving as an underlayment between the concrete and the soil will be a waterproof layer. This will keep any water from soaking into the ground when it makes its way through cracks or pores. Additionally, this will protect the concrete from underground movement (like traffic or minor tremors).
