Containment for wastewater, especially hazardous materials, goes beyond just holding it in a simple tank or lined pond. These features may function as a form of primary containment, but it doesn’t make up for the use of secondary containment measures. Many regulations will state exactly how many redundant layers of containment you’ll need based on the risks of a leak or release. A mining process pond or salt evaporation flat is more likely to need secondary containment than a storm runoff zone for a small neighborhood. Compare the various levels of containment to ensure you’re adding the right protections to your designs.
The main vessel for holding or storing the wastewater is the primary level of containment. Depending on the amount and type of wastewater, these primary methods might include:
- Pre-formed or custom fabricated tanks, including concrete cisterns cast on site
- In-ground ponds lined with geomembranes and/or concrete
- Trenches, troughs, canals, and channels that direct water to larger holding tanks and ponds
- Barrels and drums for very small amounts of wastewater or hazardous liquids in need of careful handling.
For low risk wastewater, primary containment is likely the only level of protection needed. This risk is determined by both the total volume of stored water and its chemical composition. Even relatively clean water needs secondary containment if there’s enough of it to create a flood or damage risk. Don’t forget about proximity to sensitive equipment, which deserves extra containment measures to prevent damage.
Secondary containment refers to any backup method of protection designed to control wastewater loss if the primary method fails. This includes small tubs and pads set under drums, and extends all the way to layers of geomembranes stretched under multiple acres of soil. Secondary containment methods are often combined into multiple backup systems. If one layer of liner doesn’t stop a spill, a second and third layer greatly increases the chances of keeping it under control. Portable containment tools are often referred to as secondary measures, but they don’t qualify under most regulations unless permanently installed.
Holding Tanks and Ponds
While holding tanks and ponds may serve as primary containment only, they can still be integrated directly with the secondary containment equipment. For example, lined in-ground ponds may feature a two-layer liner system with leak detection sensors installed between the two levels. The first layer may serve as the primary containment method, but it’s the second layer that truly protects the system. A leak that makes it through one layer will trip the sensors and receive attention before any wastewater gets through the secondary containment barrier. Tanks are harder than ponds to combine with their secondary systems, but it’s still possible to find double-walled designs that keep both levels of containment within the same compact footprint.
Designing a primary containment vessel to process wastewater into a safer liquid doesn’t eliminate the need for secondary containment. In fact, process and treatment ponds especially need secondary containment, since the water is often blended with chemical additives at this point. If evaporation is involved, the increasing concentration of chemicals and contaminants also increases the risk for damage as time goes by. Secondary containment provides peace of mind against the risks of processing waste on-site rather than shipping it to a remote facility.
Stormwater Catchment Systems
It’s a common misconception that storm water catchment systems can’t integrate secondary containment features. It’s also untrue that these containment measures are unnecessary for storm water. In most developed areas, the wastewater running off of paved surfaces like roads, is high enough in chemicals to require backup containment measures. Widespread use of geomembranes and reinforced polyethylene (RPE) liners is the best way to back up a concrete catchment system that is likely to develop dozens of tiny leaks as it ages.
Check on both the primary and secondary containment requirements for your local area before planning out a wastewater system. Confusing the requirements for the two will result in a costly system that doesn’t perform as expected.