Secondary containment is a principle line of defense that many facilities use to keep spills from tanks, containers and oil-filled equipment from entering the environment. Secondary containment is required for anyone storing hazardous waste onsite and it’s a key component of stormwater and Spill Prevention Control and Countermeasures (SPCC) plans.
Indoors, the formula for secondary containment is fairly simple. Figure out the volume of liquids that will be stored in the confined area and make it big and/or tall enough to contain 10 percent of that total volume or 100 percent of the largest container, whichever of those two numbers is greater.
Additionally, secondary containment sumps, the area where spilled liquids will collect, should be checked periodically to make sure that they are clean and in good condition. Any leaks and spills that are discovered must also be cleaned up promptly and completely.
Not all containers can be stored indoors though due to the requirements of certain regulations and best management practices. Storing containers outdoors in areas where rain and snow are common could lead to run-on entering your secondary containment systems.
Run-on is rain or snowmelt that accumulates in secondary containment sumps. If hazardous waste is being stored outside, the Environmental Protection Agency (EPA) says that run-on “must be prevented,” or there must be sufficient sump capacity to accommodate both run-on and the largest potential spill [40 CFR 264.175(b)(4)].
Sump capacity is the volume of liquid that a containment system will hold and can be calculated with the following equation: container length X width X height X 7.48. The answer will be the volume, in gallons, that the area will contain.
When calculating sump capacity, be sure to allow for any items such as drums, tanks, poles or anything else that will displace volume. If any such items will be present, subtract the volume that will be displaced from the overall sump capacity.
Roofs, tarps, canopies or other forms of covers can be used to prevent run-on. Depending on what is being stored and how often the item or area needs to be accessed, covers may be a viable option.
When they are not, the sump capacity needs to be increased to accommodate run-on. The volume that is needed can be calculated and figured into the design criteria for secondary containment structure. The two most prevalent methods for determining how much extra sump is needed are the 100-year storm and the 110 percent theories.
Preparing secondary containment areas with enough extra sump capacity to hold the rain or snowmelt for the largest 24-hour storm in the past 100 years is the required method of calculation for some state and local stormwater or other environmental management plans. The EPA has a national stormwater calculator that can be accessed to determine historic rainfalls throughout the country. The 110 percent approach uses the volume that is needed for secondary containment of the largest container (or 10 percent of the total volume stored, whichever is greater) and adds 10 percent to that figure.
No matter which method is used, rain or snowmelt that collects in secondary containment sumps needs to be removed in a timely manner and must be tested before being discharged to ensure that it does not contain trace chemicals or other pollutants that could harm the environment.
Storing containers, tanks and oil-filled equipment outdoors is sometimes an unavoidable reality. Providing adequately sized secondary containment systems and maintaining it helps to ensure that leaks, drips and spills will remain in check and not release to the environment.
You tell us: How does your company protect secondary containers from run-on?
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