Landfills must be capped and closed when they’ve reached capacity and can no longer accept more waste. Depending on the risk of the material contained within, this process can extend to installing multiple layers of impermeable liners and dozens of feet of compacted soil. Most municipal waste streams only need moderate capping and covering, yet, using the right permanent cover materials is still essential for leachate control. However, these materials are different in many ways from those used as short-term rain covers between daily uses. Even temporary covers, used to close a cell for a few months, will have different requirements than those for permanent covering. Find out how to select materials for both purposes with these tips.
Volume of Water Control
The sheer volume of water that must be shed or collected by the rain cover is far greater for the permanent cover than for a temporary one. Most covers are designed only the shed water to surrounding trenches or ditches, but some capture the runoff itself due to a concave design. Either way, permanently installed cover materials have to withstand millions of gallons of runoff sliding over them. Comparatively, temporary rain covers have relatively limited exposure. Yet, this is usually balanced out by the extra wear and tear on the temporary rain covers since they’re removed and replaced regularly. Either way, the cover must be strong enough to shed water continuously without becoming worn or letting it seep through.
Permanent covers require careful application, but the material is only stretched out over the surface once. Heavy equipment and manual labor are usually combined to complete the job since some wrinkles and creases are best removed by hand for the smoothest possible fit. However, temporary covers may be extended by hand or by machine depending on the size of the cell. Most facilities using flexible geomembranes on a daily basis invest in specialty equipment to both extend and retract the material over the surface. This kind of equipment is completely unnecessary for permanent covers since they’re only installed once rather than at the end of each working day.
Due to the need for flexibility and fast installation to reduce labor costs, temporary rain covers for landfills tend to be much thinner than those used for permanent capping. This reduces labor and equipment costs for handling the material and makes it easier to get a smooth fit. However, it also runs the risk of making the material too weak to handle the wear and tear of daily handling. Reinforced materials are a good choice for both types of covers. A reinforced material is less likely to tear or crack when handled daily as a temporary cover, and it’s also better at withstanding the weight of soil cover for permanent capping.
Temporary rain covers have the greatest need for tear resistance since it’s handled on a daily basis. Material that is too stiff is likely to crack when being folded up or spread out during the daily cover routine. On the opposite end, stiffness can be helpful when installing the final permanent cover since it helps the material lay flat with minimal wrinkles. Reinforced materials offer the best of both worlds by being tear and wrinkle resistant without being too stiff. Good tear resistance is still a good idea for permanent covers as well, since the material is likely to press up against uneven and sharp edges from the final layer of compacted trash.
Anchoring and Cover
Permanent rain covers are generally just one part of the total cover system when closing out a landfill cell. The geomembrane is surrounded by layers of geotextiles and anywhere from one to a dozen feet of soil. The soil helps hold down the cover material and protect it from UV exposure. Temporary rain covers may be stretched out over a six-inch soil cap, but it’s usually used alone. This means that the same equipment used to automatically cover the ground often serves as the anchoring system to hold it in place. Without powered arms or pipes to spread the cover, you will need sandbags or some other kind of anchor to hold it down.
Finally, temporary rain covers tend to receive a lot more UV exposure than permanent ones due to the difference in uses. Permanent covers are almost always topped with a thick layer of soil and turf to give the closed facility a natural appearance and to help prevent water from even seeping down to the geomembrane. This protects the material from UV exposure for years as long as the soil stays in place. Alternatively, temporary covers are the last material spread over the top of a cell for the day, leaving them exposed until they’re removed again. This means the material must be highly UV resistant, so it doesn’t break down from the combination of sun exposure and constant handling.
Both types of raincovers work well together. By using temporary rain covers on a regular basis, the leachate system is protected and more likely to work as designed. Then, when the permanent rain cover is added, it’ll be able to continue protecting the system from excess storm water. Find the RPE materials you need for both types of rain cover here at BTL Liners.