The lined and capped design of a modern landfill cell may make it seem like the perfect way to contain solid waste, regardless of its composition or age. However, there a few invisible challenges that can make it harder than it appears to keep everything contained. Gas is generated almost constantly by landfill cells, especially after they are capped and closed. Even if the methane and other gases can’t be seen by the naked eye, most of them can be smelled. Gas production is a problem unique to capped landfill cells since open dumps release vapors to the air, but it can also become a boon to the company running the facility if it’s handled correctly.
Generous Gas Production
Altogether, municipal solid waste landfills produce over 15% of the methane gas emissions in the U.S. That makes the industry the third-largest producer of the gas. Combined with CO2 production, the emissions produced by U.S. landfills are equivalent to the energy needed for 11 million homes. Unlike the CO2 however, methane is valuable as a fuel that can generate heat and energy on its own. There’s little standardization of gas production between landfill cells, so each unit can generate between thousands and hundreds of thousands of cubic feet of methane gas per year. All that pressure definitely strains landfill cell covers, making it essential to choose a reinforced material.
Odor Complaints
Landfills are often located near residential and commercial areas to make it convenient to transport municipal waste to the facility. Yet, this also increases the pressure to control gas production and direct it away from nearby buildings. This is more than just a concern about unpleasant odors. Letting residents inhale high concentrations of methane, ammonia, and other gases can also cause health issues over long periods of time. Properly designed landfill cell caps help trap these gases, so they’re easily directed wherever it’s best to release or use them. Impermeable liners are sometimes used for landfill capping because a dry climate doesn’t necessitate the use of a more impermeable material. In these cases, odor issues often develop over time as waste settles and anaerobic conditions set in. Using an impermeable cover material is often recommended even where it’s not required specifically for gas control.
The Value of Capturing Methane
The methane and other gases produced by the breakdown of trapped waste products aren’t just a potential problem. It can also become a source of profit or direct supply of power if it’s captured, refined, and stored as landfill gas (LFG) or renewable natural gas (RNG). These gases can be used for power generation, direct heating and cooking purposes, or for other less common uses like cooling. With rising costs for extracting natural gas from underground deposits that will eventually run dry, landfill gas refinement will grow in value in coming years. Setting up new landfill cells with methane capture in mind, is a great way to increase its value to the community long as it is closed to accepting new waste streams.
Physical and Chemical Stress
Most of the focus on pairing cap and cover materials with landfill cells is on physical wear from gas. The accumulation of these gases does put a lot of stress and strain on the material, making a reinforced cover a good idea. Chemical stress can also be an issue with certain cover materials, especially in designs where gas is directly exposed to the cap. Some gases can condense into petroleum-based compounds that may react with certain polymers. A non-reactive material, like reinforced polyethylene (RPE), is a good choice for resisting both physical and chemical stress.
Changing Conditions and Varying Volumes
Another challenge of trying to contain and channel methane and other gases is the changing proportions and volumes of gas produced. A landfill cell might produce a lot of CO2 for one month and then transition into more methane production later. The gases produced between cells can vary, even if they’re side by side, if they contain drastically different types of waste. Some of the changing conditions that affect the type and amount of gas produced include:
- Ambient temperature, which can differ deep underground from the layers closest to the surface
- Moisture content, both from the mix of waste packed in the cell and from rainwater allowed to seep in
- Aging of the waste, which peaks with maximum gas production around 5 to 7 years after the waste is capped
- The amount of oxygen mixed in with the waste, a gas that is easily reduced from the start with intensive compaction and daily capping efforts.
Gas Production Under the Liner
A few simple mistakes commonly made during landfill cell construction can also result in issues with gas production under the liner, not just the cap. Vegetation left or buried under the clay base of the landfill cell will break down over time, releasing gas just like the waste contained inside the cell. Clearing and removing the soil, rather than grinding or burying plant waste, is essential to preparing the new cell for the liner material. A rising liner, inflated by underground gas, can tear and release liquid into the ground below. So, soil preparation is also essential to gas control in a less direct way.
Don’t let methane and other gases interfere with the capping process to close out the landfill. Durable cover materials that can stretch and expand under the pressure of the gas without tearing are the key to long-term protection. While there are many materials that can handle small volumes of gas production, only a tough material like reinforced polyethylene (RPE) will work for landfills maximized for harvesting and reusing the gas. Find the RPE covers and liners you need here at BTL Liners.
