Containment of any material produced during mining begins with a geomembrane. Geomembranes are flexible barriers made from synthetic materials like polymers. They’re designed to be low in permeability, which prevents liquids like water and leachate from traveling through them and into the surrounding environment. Surface mines that produce large volumes of overburden require extensive containment to keep the material and its leachate under control. While berms and embankments are usually necessary to keep liquids from escaping over the surface, they won’t suffice on their own. Flexible liners are essential to keep seepage from becoming a problem. Explore how liners work for overburden containment and get key advice on how to select a material for handling this challenging material.
Concrete or Asphalt Only Works for Stability
There is a common misconception in many industries that concrete or asphalt coatings are the most durable and secure containment barriers available. While these rigid surface coatings are often recommended for giving stability and structure to a containment area for a material like overburden, they don’t actually do the work of containment. This is especially true for leachates and other liquids that soak through the heaped material. Concrete and asphalt are both porous materials that allow accumulated liquids to slowly seep through the surface over time. Seepage is also a problem if a heap is left unlined. Without a liner, even the driest materials slowly contaminate the soil under and around them due to the slow effect of leaching. Even if concrete or asphalt is recommended for the containment design, it should always be paired with a compatible geomembrane liner to control the liquid that gets through it.
Liners That Can Bear the Weight
The weight of the rocky overburden material is one of the things that makes it particularly challenging to store. Most liners used for liquid containment are designed to only hold up the weight of water. While sand-based overburden can start out seeming lightweight enough when it’s first piled up in the heap, it becomes heavier over time as rainfall infiltrates the pile. Even covering the material will not completely solve the problem of the overburden heap growing heavier over time. If a weak liner material is selected, it is inevitable that it will tear. Trying to remove the huge volume of material from the storage pad just to repair or replace the liner is usually more expensive than just remediating the area after the operation shuts down. To save money in the long run either way, it’s best to choose a liner that’s designed for handling the highest possible weight loads. Reinforced liners, in particular, are a good choice not only for the weight but for the abrasiveness of the material.
Chemical Considerations
Overburden is not primarily a chemical-rich mixture. This makes it somewhat easier to store and handle than other by-products of mining like tailings or processing runoff. However, many overburden mixtures from coal mining and oil sand facilities tend to be high in oil content. The bitumen mixed into the sand and rock can easily react with any liner installed below it, especially as rainfall leaches the oil out and causes it to settle directly against the material. Choosing a liner that is petroleum-compatible is therefore essential in these cases. Even heavy metals and salts in overburden from ore mining can shorten liner lifespan, so check on compatibility with each geomembrane you consider for the job.
Primary vs Secondary Containment
It’s important to understand the differences between primary and secondary containment when shopping for any kind of liner material. Primary containment is also considered storage because it’s the space designed to hold the raw overburden. These spaces need liners to ensure that runoff doesn’t escape the pad or basin set aside for containing it. However, they won’t fulfill secondary containment requirements set by local or state regulations. Secondary containment refers to the extra measures taken to control any liquids that escape from the primary storage area. A single layer of liner will allow runoff to escape directly into the soil if it leaks, while putting in another layer of liner creates a secondary containment barrier. Check for relevant regulations and laws to determine if secondary regulation is recommended or required for overburden in your particular district.
Which Liner Material is Right?
- PVC: Polyvinyl chloride is one of the most commonly used materials for pond liners and other geomembranes. While it can be found in some commercial products, it’s not recommended in general for mining applications. This includes use as a liner for overburden containment areas. First, PVC has very little stretch and tends to rip or tear easily when the wrong forces are applied. Due to the high weight of large overburden piles, it’s a poor choice for dealing with the constant addition of new material. Also, PVC is not good at dealing with extreme temperatures without becoming brittle. Many oil sands are located in areas where bitter cold can threaten the durability of most materials. Finally, PVC is too sensitive to UV damage for exposed installation, which is preferred for storage pads at most mining sites.
- EDPM: Also known as ethylene propylene diene monomer rubber, was originally introduced as a form of roll roofing for commercial applications. As one of the first flexible geomembranes that were highly impermeable, it was quickly applied to many other uses. Yet, as with many materials, it’s best left to its original purpose now that better alternatives are available. It’s simply too thick and inflexible for most commercial installations, including as a barrier or liner for overburden containment. It’s also prone to degradation if exposed to UV light and isn’t the most resistant to chemical damage from petroleum products either. It should be avoided for mining applications in general.
- HDPE: High density polyethylene has the durability and stiffness to stand up to the abrasive overburden material, but it is still far from the best choice for containing it. It has some chemical resistance, but not as much as overburden storage demands. It’s also too inflexible for lining the sides of basins that lack a subtle slope. Due to its stiffness, small folds can turn into a crack due to the compounding effect of the weight of the heap pushing down on it. In general, HDPE is not quite as good a liner material for overburden containment as RPE.
- LDPE: Low density polyethylene is also a less than ideal choice for lining overburden pads. First, oils and petroleum products are particularly damaging to this material, even at average temperatures. Add in extreme hot or cold and the damage is practically guaranteed to shorten the lifespan of the liner. It also lacks some of the UV resistance that HDPE has, making it a less than ideal choice for exposed installation. As a more flexible material, it doesn’t have the tear and stretch resistance needed for storing large piles of heavy materials. Finally, it’s not puncture resistant enough in most cases.
- RPE: Reinforced polyethylene combines both LDPE and HDPE materials to create a highly flexible yet tear resistant material that can withstand both chemical and UV exposure. The reinforced design is key to increasing the tear and puncture resistance enough to withstand the harsh conditions of an overburden pile. This material can also be factory fabricated in large custom sizes to reduce or even eliminate the need for sealing seams on-site. This reduces the chances of leaks while simplifying installation, making it easier to get onto to hard work of surface mining. For overburden storage and containment, RPE is the best choice.
There are a lot of options out there for commercial lining products, but BTL Liners is the right place to turn. We have the heavy duty RPE liners you need for storing mining by-products like overburden, tailings, and more. Don’t let valuable ore go to waste or risk fines for environmental damage when our affordable and reliable liner products can help you achieve perfect containment right from the start.
