It’s easy to assume that all gas issues in a landfill cell are handled by the cover and that the liner only manages leachate and other liquids. However, this is a misconception because even the impermeable liner at the bottom of a cell plays a role in ensuring a steady supply of landfill gas (LFG). By ignoring the importance of the liner or choosing the wrong material, it’s all too easy to compromise the entire landfill cell and cause more issues than just sluggish gas production. Start the entire gas control and collection system off right with proper liner selection for all of the following reasons and more.
Rising Groundwater Levels
First, if not properly lined, there is always the risk of rising groundwater filling the landfill cell from the bottom up during heavy rainfall events. Liners are often thought of as only controlling leachate from the inside of the cell and keeping it from escaping. Yet, they’re just as important for keeping rising water from entering the cell as well. Rising water can not only cause leachate to escape the containment system, it can also interfere with gas production by clogging up the wells and trenches used for accumulation. When these areas are filled with water rather than drained properly through the leachate system, it’s impossible for gas to exit the system or pass through the mass of trash. Maintaining only the expected level of leachate is essential and only an impermeable liner like a geomembrane can ensure this.
Gas Penetration Through Soil
Leachate and other liquids aren’t the only concern for seepage in a landfill cell. Heavier gases also settle to the bottom of the cell, which means most of them can also seep through the soil over time if it’s left unlined. The losses of valuable gases into the surrounding soil is more than just a waste of potential income. It’s also an environmental hazard that can take thousands of dollars to remediate. If the gas doesn’t become trapped in the soil, it’ll eventually reach the surface again and escape into the atmosphere. Durable liners at the bottom of landfill cells and pits are essential for keeping gas right where it’s needed until the collection system can direct it to wellheads and storage tanks.
Controlling Compaction
Liners can play an essential role in maintaining the correct arrangement of a pile, so it doesn’t slump or become more compacted than expected. Compaction on a daily basis is an essential practice for preventing trash loss and wasted space, but it must be limited so that air and gas still flow easily through the finished pile. If a cell is compacted more in some areas than others, pressure can build up and threaten the stability of the entire stack. Liners, especially on the sides of valley-style landfill cells, support the layers of trash so they remain stable for a decade or more until the gas collection process ends.
Removing Intermediate Liners
If a landfill cell has intermediate liners installed, that are made from impermeable membranes, it may or may not affect the gas collection process later. Removing the impermeable liners as new layers are added may help with gas movement through the entire mass of trash. It’s much harder to remove these liners after the entire landfill cell has been compacted and capped. Vertical wells are often the only option for gas collection in these landfills since the boring process can easily penetrate multiple layers of the liner. If a cell is being planned for LFG production from the beginning, avoiding intermediate liners is likely a good choice from the start.
Limiting Chemical Reactions
In some cases, it may be necessary to leave intermediate lift liners in place and not remove them or penetrate them with vertical wells. These separations are recommended when incompatible types of waste, especially chemicals that react badly when combined, could produce unwanted gases. Most modern municipal waste landfills don’t suffer from this problem because of careful management of the incoming waste stream for proper mixing. Hazardous waste landfills are much more likely to experience this problem, making it more complex to harvest LFG from these sites than other facilities. However, a complex liner system that separates various waste types can allow for gas harvesting from nearly any type of landfill cell.
BTL Liners doesn’t just fabricate the covers needed for capping a complete gas collection system at any landfill. We also produce durable RPE liners that are ideal for handling the demands of the gas-generating landfill cell. Choose our team to support you through the process of landfill design and installation with our decades of industry experience.
