For most farms, custom containment basins will work best for protecting practically any kind of storage unit. From above-ground tanks to concrete silos and bunkers, flexible liners known as geomembranes, create an impermeable barrier that stops the loss of valuable fertilizer. Pre-made containment solutions for fertilizer usually cost more and perform poorer than custom designs involving raised barriers and lined surfaces. Make sure your fertilizer containment efforts pay off with these design considerations, including how to match the right liner to the project.
Dikes and Drainage Basins
Dikes are similar to dams in the fact that they’re raised areas placed around the edges of a containment area to hold in rising levels of liquid. This liquid can be a manure slurry, chemical fertilizer solutions, or powders and granules that act almost like liquids. Curbs are smaller versions of dikes, used when only a few inches of a raised edge is needed for containment. Dikes for fertilizer containment are generally made from pre-cast or poured-in-place concrete, but they can also be formed with earth. Both concrete and earthen dikes should be covered with an impermeable liner to keep them from seeping or leaking over time. Solid fertilizers don’t always require a curb according to regulations, but they’re still more easily managed with some kind of lip between the containment area and the rest of the ground.
When combined with a liner over the ground below the tank or tote, dikes work together to form a larger drainage basin. These basins typically feature drains so that spilled fertilizer is easily removed from the basin and relocated. Don’t overlook the difficulties of pumping out a thick manure sludge or slurry when planning your containment basin.
Even when building or re-purposing an entire building to keep fertilizer dry and cool, it is important to add secondary containment to the flooring to ensure spills don’t make it out of the doors or under the walls. When installing a flexible liner either over or under a concrete slab, consider running it up the walls a foot or more to create a tight seal around the edges of the building. Large scale leaks are easily contained with a little extra consideration to the floor covers and their design. Curbs along the edges of the walls are another good containment feature, but they won’t replace floor covers and liners on their own.
Drainage for Rainwater
Outdoor fertilizer tanks are constantly being washed by rainwater, resulting in potential runoff that should be collected in the secondary containment basin below them. Yet, this also means that rainwater can gather in the containment system and overfill it, causing overflows that wash fertilizer out where it’s not needed. Work drains into your design so that won’t rainwater runoff and rinsate won’t escape into the surrounding environment. All drains in secondary containment systems should connect to closed storage units, to ensure runoff isn’t lost until it can be properly processed.
Choosing the Right Containment Liners
Fertilizer containment can be trickier than other forms of secondary containment because of the chemical composition of the fertilizers. Most farmers also store a wide range of potentially incompatible chemicals, meaning that any lined facilities must be covered with a material with diverse chemical resistances. The right geomembrane or flexible liner will provide years of reliable spill containment with little maintenance and few repairs. Here are your most common options for materials and how they stack up for this use.
Polyvinyl Chloride (PVC)
Flexible membranes are popular because they move independently of the primary container and offer high tear and rip resistance. PVC is one of the most widely used materials for geomembranes manufactured for fertilizer containment. This is primarily due to its flexibility, allowing it to fit tightly into sharp cornered catch basins or when used to line an existing tank. However, PVC has less chemical and UV resistance than many forms of polyethylene that are available for geomembrane use. When used alone, PVC is stronger than some forms of polyethylene, but reinforced and high-density polyethylene is stronger yet than the PVC. For challenging installations where durability and chemical resistance is key, reinforced polyethylene (RPE) is a far better choice for most projects than the common PVC. PVC does offer more fire resistance than other membrane materials, but since liners are typically buried away from the fertilizer material itself, this isn’t much of an active benefit in these installations.
Polyethylene is a large category of thermoplastics that includes many specific formulas and blends. One liner made from PE may be a great choice for fertilizer use while another similar looking product would rapidly fail. For fertilizer containment, look for reinforced polyethylene (RPE) made with a combination of both low density (LDPE) and high density (HDPE) polymers. As their name suggests, the differing densities of these formulas allow them to offer either higher strength or greater flexibility. When you bring them both together, you get a flexible, yet strong liner, that has superior chemical and UV damage resistance.
Polyurethane (PU) liners are the third most popular product you’ll find recommended for fertilizer containment. They’re allowed for this purpose by most state regulations. Many farmers are familiar with sheets of polyurethane used to line grain elevator equipment like hoppers. Unfortunately, most PU formulas lack good chemical resistance and they’re prone to wear and tear from friction over time. This is especially true in areas where abrasive dry fertilizers are poured or loaded directly over an exposed liner surface. Stick with polyethylene, preferably an RPE product, for more reliable performance from your secondary containment system.
Bentonite Clay (BC)
Bentonite clay is a natural product used for sealing ponds and drainage ditches when polymer liners aren’t desired. Some state regulations allow for its use for sealing in large in-ground drainage basins. A layer of compacted clay may be better than nothing, but it doesn’t offer the impermeability to truly control spills and leaks. It’s also very hard to clean up fertilizer resting against a clay covered surface without damaging the clay itself and potentially causing a leak. Don’t assume this method of sealing is less expensive than installing a real liner either. Since you’ll need multiple inches of clay over the surface and special blends designed to use dry rather than underwater, the cost of installing and maintaining a layer of BC may well outweigh the costs of a better RPE liner.
Asphalt and Concrete
Even with flexible liners in place, most drainage basins end up needing a layer of asphalt or concrete for stability and to form the raised curbs or dikes around the edges. Don’t assume that these materials alone can also act as the containment barrier. Asphalt and concrete need sealing to remain impermeable like a geomembrane, and this sealant must be reapplied every few years. When flexible liners are installed under or above these reinforcement layers, there’s little to no need to seal the concrete and asphalt just for liquid containment.
Still need help deciding on the right liner for your fertilizer containment project? Contact our team here at BTL Liners. We’re happy to help you find the right material for your particular storage needs and your state’s regulations. No matter what kind of liquid or dry fertilizer you’re storing, we have a liner to match.