Tailings are a potentially hazardous material, depending on the exact content of the material and what was being mined during its production. With the potential for long-term environmental damage if not stored properly, containment goes beyond the basic level of keeping it in one place. Everything from the amount of wind and rain the site receives, to the stability of the underlying soil, plays a role in the containment of tailings. This attempt to control and prevent environmental damage can be split into two major stages: primary and secondary containment. Primary containment is the first stage in managing mining by-products and waste, but it’s not enough for hazardous and potentially hazardous materials like tailings. Secondary containment may also be necessary to ensure that the worst impacts can’t spread far if there is a leak, loss, or collapse.
Primary vs Secondary Containment
Primary containment is better referred to as storage because it’s only intended to keep the materials in one place. These measures may include impermeable liners to stop seepage and other migration of hazardous liquids, or it may not. It is important to verify exactly what level of protection and control is offered by any specific system or storage design before assuming it will offer sufficient containment. Primary containment for tailings should always include liners, even if the material will be stored dry, since rainfall that turns into leachate has the potential to carry contaminants far from the pile or pit. If secondary containment is required beyond this level of protection, another layer of liner is usually used. This creates a space for capturing moisture that leaks through the first layer of liner, allowing for the detection of leaks before any liquid actually escapes the system.
Single- and Double-Layer Liner Systems
Single layer systems may serve as primary containment, but they can’t serve as secondary containment. Only a double layer liner system will qualify. However, double liners are not the only option for secondary containment of tailings. Some systems involve buried wells or sensors that aren’t installed above a second liner layer, while others rely on concrete or asphalt above a liner to form a dual layer system. For an embankment system, built where it is likely leachate will escape from the bottom of the dam or dike, secondary containment may be installed around the base of these structures instead. If dual liner systems are preferred for secondary containment of tailings, BTL Liners has the products to install both layers without compatibility or durability issues.
Secondary Containment for Tanks, Processing Ponds, and More
Tanks and ponds are generally used for processing the raw mined material before it’s separated into tailings for storage. These features also need secondary containment to ensure that any leaks or discharges that occur during transfer can’t affect the surrounding environment. These lined and reinforced areas are usually connected to the containment for tailings and other storage areas if they are located near each other, otherwise they need to be free-standing. If tanks or other above-ground units are used for temporarily holding or processing tailings, they must be surrounded by lined drainage areas as well for proper containment.
Containment for Dams and Embankments
Dams and raised embankments, like dikes, are also prone to leaking due to the amount of moisture that accumulates against them; especially at the base. Even with proper lining on the interior surfaces of these structures, some amount of moisture can escape over time due to capillary action and pore pressure. Putting in secondary containment for the base of the dam or embankment is usually the best way to control this eventual loss. This can be as simple as a lined trench that connects to a larger collection system or as complex as sealed drains that send the runoff directly back into the mine for recycling. This type of secondary containment is also generally used for water that flows over the surface of the dam or overflows from the impoundment.
Who Regulates Containment for Tailings?
Tailings were once completely unregulated because the risks of the material were not as well understood. Even as late as the 1960s, some states in the US and provinces in Canada did not specifically regulate how these materials were handled or disposed of. Today almost all developed countries have moderate to stringent requirements on tailings disposal. In the US, the Environmental Protection Agency (EPA) sets tailings storage regulations on the federal level. Each state also sets its own limitations and requirements on the process. In some states, individual regions can set up their own water protection agencies or other natural resource divisions that regulate mining and similar activities. Even the county may have regulations set on a street by street basis through codes or by-laws. It’s important to thoroughly research the applicable regulations at every level instead of just designing containment by federal or state laws alone.
Most tailings impoundments will need some kind of secondary containment, even if only a single layer of liner is sufficient for primary containment. Installing leak detection and control at the base of dams and embankments is the key to catching problems long before they can destabilize larger parts of the storage structures. Choose BTL Liners as your partner for lining and containment on both the primary and secondary level. Our industrial grade liners are capable of handling even the roughest tailings materials since they’re reinforced and made from chemical resistant polyethylene.
