Question: I store bulk oil at my facility in round 500- and 1,000-gallon rectangular tanks. Is it better to have spill containment for each tank or tanks combined? How do you determine required spill containment dimensions in height and size?
Answer: The most common way to get spill containment in this situation is to have one large containment area that surrounds all of the tanks, as long as the liquids stored in each of the tanks are compatible with each other. There are several advantages to creating one containment area versus several smaller areas, including:
- Easier maintenance: Fewer walls/berms/gates/valves to maintain
- Easier access to the area: No need to open multiple gates or maneuver through a maze of separate containment areas
- Easier to inspect: The walls won’t need to be as high as if you created individual containment areas
Keep in mind that if there ever is a spill, the overall area that needs to be cleaned up will most likely be larger than if you have multiple secondary containment areas. But if you regularly perform preventative maintenance and have a security plan to prevent vandalism, the chance for a spill should be pretty small.
You’ll need the following information to calculate the size of the containment area:
- The number of tanks that you will be containing and the volume that each tank is capable of holding (even if you only usually store 100 gallons in a 1,500-gallon tank, the tank is capable of holding 1,500 gallons and should be counted as a 1,500-gallon tank).
- The minimum length and width of the area around all of the tanks in feet. If you were going to make a square or rectangle around the entire area, how long and wide would it be?
- The volume that will be displaced by each tank in the containment area.
- For a rectangular tank: Volume = Length x Width x Height
- For a cylindrical tank: Volume = π r²h were “r” is the radius and “h” is height
Note: When putting in a height measurement, use the expected height of the containment sump’s sidewalls, not the overall height of the tank.
Next, add up the total volume of all the tanks that you want to contain and multiply that number by 0.10. Compare this number with the volume of the largest tank and whichever number is greater is the number of gallons that you will need to contain. Add any volume the tanks themselves displace to this number.
Keep in mind that you do not need to be able to contain the total volume of all of the containers collectively. You only need to contain 10 percent of the total volume or 100 percent of the largest container, whichever is greater. But, if your containment area is outdoors, you’ll also need to allow some additional capacity for rain or snow run-on that may accumulate in the area. Some states also have regulations requiring 100 percent or even 150 percent containment. It’s best to verify state requirements before any construction.
Here’s the standard equation for calculating volume:
Volume = Length x Width x Height
Rearrange the equation to get the height of your sidewalls:
Height = Length x Width x Volume
Note: Any number less than 1 is a fraction of 1 foot.
Before constructing your spill containment area, consider whether you will need an impervious base and how you will remove rainwater or snowmelt from the area.