Choosing the Right Secondary Containment System: An In-Depth Evaluation of Your Options for Safe Storage

On January 9, 2014, a chemical spill fouled the water supply for thousands of West Virginians in the U.S. A hazardous chemical used for washing coal called 4-methylcyclohexane methanol, or “crude MCHM,” leaked from an industrial facility into the Elk River near Charleston, West Virginia. The incident could have been prevented if a proper secondary containment system had been in place.

Secondary containment is an important safeguard that helps plant operators mitigate the risks associated with chemical spills. The system consists of a primary container, which is surrounded by a secondary container or wall. Between the two is an interstitial space. If the primary container fails and a chemical leaks out of the primary tank, the secondary system prevents the chemical from spilling out beyond the unit.

In the event of a leak or failure of the primary storage vessel, secondary containment systems can prevent costly damage to equipment and physical risk to employees and nearby residents.

In this article, we’ll walk you through the different secondary containment systems available, and help you understand which one is the best choice for your containment needs.

Industries That Rely on Secondary Containment

Secondary containment is an essential system for any company that needs to contain harmful chemicals or corrosive liquids. Here is a sampling of the most common industries that use secondary containment systems.

Municipal Water and Wastewater Treatment Plants

Most of the chemicals used in water treatment pose risks of contamination or harm to humans in the event of leaks or spills. Secondary containment is a must.

Chemicals such as sodium hypochlorite, citric acid, and sodium hydroxide are commonly used to clean and flush the membrane materials used in filtration. Sodium hypochlorite is a bleach commonly used to disinfect water. Often, hydrofluorosilic acid (fluoride) is also added to municipal water treatment. 

While we treat our water with small amounts of fluoride in some geographical areas, hydrofluorosilic acid is extremely dangerous if not stored properly. To balance pH levels, a strong acid such as sulfuric acid, or a base chemical such as sodium hydroxide, may be added to the water. 

All of these chemicals must be stored on-site at a treatment plant.

Chemical Manufacturing and Supply Facilities

Chemical manufacturers and chemical supply facilities rely on secondary containment units to safely store the hazardous liquids they use. These facilities frequently store aggressively corrosive compounds, and they must take great precaution to ensure the proper safeguards are in place in the event of storage spill or failure.

Industrial Facilities

Three of the most challenging industries for storing chemicals are areas we’ve serviced for over 30 years. The plating, mining, and high-tech industries use aggressive chemicals, and they require chemical storage solutions that can handle highly corrosive compounds.

Plating

The plating industry needs to safely store harsh chemicals used in many different plating processes, including:

• Zinc Sulfate
• Potassium Chloride
• Boric Acid
• Sodium Hydroxide
• Sodium Carbonate
• Sulfuric Acid
• Potassium Hydroxide

Mining

When mining companies leach copper from oxide ore, they often use concentrated sulfuric acid. This highly exothermic acid presents serious storage challenges, because it’s an extremely heavy chemical that will test the mechanical integrity of any tank system.

High-Tech Industry

In the high-tech industry, chemicals vary from manufacturer to manufacturer—and in many cases they’re proprietary. Many of the solutions are high-purity or ultra-high-purity chemicals that are used for applications like circuit board manufacturing.

De-icing

Manufacturers of de-icing fluids can use several harmful chemicals, including brine, magnesium chloride, propylene glycol, and ethylene glycol. Whichever chemical is used during the de- icing process, it is important to store it safely so that it is properly contained according to environmental regulations.

These and other industries rely on their secondary containment systems to protect their workers, the environment, and their investments. But many businesses make uninformed decisions about what kind of containment system is the best option, and they create more work for themselves—and lose more revenue—as a result.

Types of Secondary Containment Systems

Concrete secondary containment systems are the most well-known option, but there are other types of containment systems that may be a smarter choice for your company. Here’s an introduction to three basic types of secondary containment units available to your business.

Concrete Containment

Concrete containment structures are the traditional solution for secondary containment systems. Generally speaking, they consist of a poured concrete foundation that is combined with vertical concrete walls. These walls are usually reinforced with rebar. After the concrete is poured, its interior must be coated with a substance that prevents spilled chemicals from eating away at the concrete. Neglecting to protect the walls can cause serious damage to the containment structure.

The containment area is open, allowing rainwater and debris to collect in the overspill space. Often, the containment walls are only a few feet high—workers can potentially come in contact with a leaked chemical. These concrete systems can be very expensive as well.

Polyethylene Containment Basin

To reduce the costs associated with concrete containment, you may want to consider a polyethylene containment basin. In this solution, a polyethylene tank is placed inside of a polyethylene open-top tank. The open-top tank eliminates many of the primary costs and maintenance costs that come with concrete units. They can also be stored indoors to prevent contamination from rainwater and debris.

However, the basin solution has its disadvantages as well: workers can still be exposed to spilled chemicals, and not every facility has the space to house the units indoors.This means spilled chemicals must be disposed of and replaced.

Crosslinked Polyethylene Double Wall Tank System

A crosslinked polyethylene (XLPE) double wall tank system is a “tank-within-a-tank” that keeps contaminants from entering the interstitial area. These tanks provide enclosed secondary containment to prevent damage to equipment or property, lost chemicals, and injured employees in the event of a spill.

Poly Processing’s innovative XLPE double wall storage and containment system provides customers with an investment that delivers peace of mind and environmental care. The high-density XLPE SAFE-Tank containment system alleviates the need to build large, high-maintenance concrete containment areas.

In the event of a spill, the tank system’s all-in-one design features a protected containment area that safely isolates reactive chemicals, protects employees from harm, and protects you from environmental remediation—all within the footprint of a standard vertical tank.

The SAFE-Tank Double Wall Tank System:

• Eliminates the expense and maintenance of secondary concrete containment.
• Minimizes the system’s footprint by providing secondary containment in a more compact way.
• Provides a minimum of 110% secondary containment. The double-wall system uses equalization to provide a minimum of 110% of the working volume of the primary tank.
• Is constructed with high-density XLPE. XLPE is specifically engineered to accommodate the demands of the harshest chemical storage.
• Eliminates potential exposure and dangerous chemical reactions, such as sulfuric acid to water.
• Is excellent for outside storage. Any debris or rainwater that could enter the secondary containment vessel is eliminated therefore not contaminating the chemical being stored.

If your primary tank develops a leak, the liquid is captured by the outer sealed secondary tank and the system essentially becomes a single-wall tank until it can be repaired. This allows you to continue using the chemical within the primary tank until the tank system can be emptied, inspected, and repaired if necessary.

Poly Processing’s double-wall XLPE SAFE-Tanks are ideal for almost all chemicals including chemicals that have dangerous exothermic reactions to water that could occur in a traditional containment that will capture rain or wash water.

Which Containment Solution Do You Need?

Each secondary containment system has its advantages and disadvantages. Whichever option you choose, it’s important to make the right choice for your operation’s needs. Selecting the wrong system results in unplanned expenses, more maintenance, or more operational frustrations.

Cost

There are several components of a chemical storage system with secondary containment. You must consider costs of the primary tank, the secondary tank, any coating on the containment structure, maintenance costs, fittings and accessories, and the potential cost of purchasing new chemicals in the event of a spill. Altogether, the SAFE-Tank system can be up to 90% more cost effective than traditional concrete containment structures.

The SAFE-Tank itself costs much less than a primary tank with a concrete system, and it is maintenance-free. Once you’ve made the purchase, and installed it, you’re done. There are no additional man-hour costs or maintenance investments to drain your bottom line.

On the other hand, there are several costs involved with concrete containment structures. Concrete can cost up to $12 per gallon or more, depending on the type of coating that is used. Because a secondary containment tank must be able to hold 110% to 120% of the primary tank, the secondary containment for a 1000-gallon tank could cost upwards of $12,000 or more. That doesn’t include the cost of the primary tank.

See a comparison of your upfront costs when installing a 6150 gallon 1.9 SPG Polyethylene tank with various containment options.

While an open-top tank system is less expensive than concrete, you could expect a total loss of the chemical. As with concrete systems, the entire chemical supply can become contaminated by rainwater or debris in the event of a chemical spill or leak.

Properly disposing of leaked or contaminated chemicals can involve renting a tanker truck, which can range from $5,000 to $10,000 or more. In addition to this cost, replacing the chemicals can cost from $1 to $10 per gallon or more. But the XLPE double wall tank’s enclosed system allows leaked chemicals to be fully used which eliminates unplanned costly expenses.

Space

The XLPE double wall tank system reduces the footprint of your containment system by taking up less space around the primary tank. Since it’s built from high-density cross- linked polyethylene that can hold the chemical, there is no need to designate a large area for a concrete containment structure. Only one tank pad is needed. And since any spills are self-contained, you can store acids and bases right next to each other.

Safety

The XLPE double wall tank system completely encased sidewalls provide superior safety protection. Not only is a spilled chemical protected from rainwater and debris, but workers are protected from splashing and spurting if the leak occurs.

You don’t have to worry about leak detector false positives due to environmental moisture— rainwater can’t enter the interstitial space to trip the detectors.

Need a Certified Tank?

Poly Processing’s SAFE-Tank systems can be designed to meet NSF/ANSI/CAN 61. Poly Processing is the first and only company with a complete chemical tank system certified to NSF/ANSI/CAN 61. As a tank manufacturer in the chemical storage tank industry, Poly Processing holds this stringent chemical certification and can design and build a certified tank system to meet your specific applications.

Components of the XLPE Double Wall Tank System

XLPE Tank Itself

A XLPE double wall tank system is made of the same high-density cross-linked polyethylene (XLPE) resins that the top rotationally molded chemical storage tanks are made of. These rotationally molded tanks provide added security and support for chemical storage that many have come to expect from Poly Processing.

A Bellows Transition Fitting

The XLPE tank is double walled, but we know that at the fitting, especially the drain or pump outlet on the lower third sidewall of the tank, is the most common place for a chemical leak to occur. Since the tank wall must be cut—and thus compromised—in order to install a fitting, that connection is more susceptible to pressure, vibration, installation, operating, or maintenance errors. It becomes a more vulnerable issue than the rotomolded cross-linked wall itself.

To minimize this threat, Poly Processing offers the Bellows Transition Fitting, with a flexible expansion joint that protects one tank wall from the other against hinge and flex lock. A fitting is attached to the inner tank, while a flexible expansion joint allows the inner tank to expand and contract. The piping is fully contained by this fitting, so there is no hinge point, and the fitting fully contains any leaks that occur.

The Bellows Transition Fitting solves the problems presented by any sleeve-fitting system available. When storing chemicals, you can never be too careful. These systems can be double wall piped from the tank to wherever you want the pipe to terminate using a true double wall transition fitting.

Fittings and Accessories

Selecting the proper tank fittings—and location for the fittings—is an important matter. You need the right fittings for your application, and it’s not always easy to understand which ones are the best choice for your needs.

It’s also critical to place the fitting in the best location on the tank. On the top of the  double wall tank system, you can add almost any kind of fitting and accessory needed.  However, because of the interstitial space, the transition fitting should be used on the sidewall of most XLPE double wall tank systems.

Learn more about the benefits of a SAFE-Tank and double-wall piping in our guide.