Flooding is unpredictable and can be caused by many different types of natural processes, including but not limited to: heavy rains, hurricanes, and earthquakes. The failure of manmade structures such as levees or dams can also lead to flooding. During floods, underground storage tank (UST) systems can be compromised, and recognizing what to do in case of severe weather is imperative for all owner/operators of USTs.
USTs become potentially harmful to the environment if they are fully submerged or displaced by flood waters. After being exposed to flood waters, USTs may become buoyant or uprooted from their intended positioning. During floods, the product within the USTs may be displaced and then released into the environment. If USTs become buoyant they can also cause soil erosion and scour, along with affecting the electrical system associated with the UST equipment. As a result, USTs may be damaged and release regulated substances into the environment. The release of these regulated substances causes the surrounding soil, groundwater, and surface water to be contaminated. Flooding is unpredictable and unavoidable, thus the safest option for UST owners is to prepare their tanks for a potential natural disaster in order to minimize the possible damage.
If USTs are not properly anchored when they become buoyant, there is a possibility that they will rise out of the ground and float, causing pipes to rupture or separate. After the pipes are compromised, they can unfortunately release regulated substances into the environment.
Product displacement is a process that can occur during a flood. It is possible for water and other debris to affect USTs by entering the system through various openings. As these foreign substances settle in the UST, the original product held by the UST rises to the top and escapes through openings, releasing regulated product in the environment.
If flood waters are rapidly moving, soil erosion and scour are likely to take place. Soil erosion is the result of the soil encasing the UST becoming displaced and carried by wind or water. Scour results from rapidly-flowing water, which causes the soil cover and supporting backfill material surrounding the USTs to be removed. If exposed to these stressors, the USTs are more susceptible to collapsing. Erosion and scour can also force the underground piping to shift and detach, letting product in the environment. Electrical equipment such as panel boxes, emergency shutoff switches, motors, and dispensers can be damaged if they are in contact with floodwaters for extended periods of time.
Before a flood, securing all openings in the USTs will ensure that water will not enter the tank and product will not escape. If there is a possibility that a tank is submerged in flood waters, an extension to the existing vent pipe is beneficial to avoid water entering the vent pipe, subsequently pushing the regulated product in the tank out into the environment. In order to protect USTs from buoyancy, burying the tank deeper and/or increasing the volume of pavement above the UST. When floods are expected in the near future, placing a dumpster or large quantities of sand or rock will increase protection against the tank floating. Properly anchored USTs can also offset the force of buoyancy from saturated soil. Automatic shut-off valves avoid the loss of regulated product when a pipe or line disconnects from the UST.
For more information, you can find the EPA’s guide to UST in severe weather here.