The United States has experienced a number of record breaking floods in the past few decades. From Hurricane Katrina in 2005 to Hurricane Sandy in 2012 to Hurricane Harvey just two weeks ago, the 100-year and 50-year storms are hitting harder and faster than anyone could anticipate. These types of superstorms are incredibly destructive, with people loosing homes, properties, businesses, and even lives.
With many of these storms hitting areas that were previously considered safe from flooding, homeowners and businessowners who have underground storage tanks (USTs) aren't necessarily making sure their tanks are as flood-proof as they could be. In 2010, the US Environmental Protection Agency (EPA) created a document outlining what tank owners need to know about flooding. Below is an outline of what can happen, how to prevent it, and what to do before and after a flood to keep your system safe.
Impacts of Flooding on Tanks
There are 4 key impacts that flooding can have on storage tanks:
When floodwaters come in and saturate the soils, the tank becomes surrounded by significantly less dense material that its used to. When this happens, buoyant forces come into play. Similar to submerging a rubber duckie under water, the less dense material (whether air or oil) wants to pull the vessel to the surface. While some USTs are equipped with straps or collars to prevent shifting, not all are. If the UST is unanchored, it could lift out of the ground and float, resulting in a rupture or separation of the connecting pipes, releasing product into the environment.
• Erosion and Scour
Its no surprise that floodwaters move quickly. When the swift waters of a flood encounter the soil and backfill around the tank, it can begin eroding the material from the area. If enough erosion occurs, the tank will eventually be unearthed and exposed to the surface conditions. Exposing the tank to surface stresses from flood water pressure or floating debris makes it even more vulnerable to being undermined or even collapsing. As a result of erosion and scour, underground piping can also shift and become detached from the UST, releasing product into the environment.
• Product Displacement
During a flood, water or other debris can enter an UST through openings such as fill pipes, vent pipes, gaskets, loose fittings, covers, sumps, and damaged tank walls. As water and debris settle on the bottom of the UST, product will rise and float on top until it eventually exits the tank through openings, resulting in a product release.
• Electrical System Damage
Extended contact with floodwaters may cause damage to electrical equipment associated with many commercial and residential UST systems (such as automatic tank gauging systems, panel boxes, emergency shutoff switches, submersible turbine pumps, dispensers, motors, cathodic protection, etc.).
So, what can be done to limit/ prevent the damaging impacts that we listed above? If you know your tank is in an area prone to flooding and want a bit more security, you have a few options:
• Increase the burial depth and/or amount of pavement above the UST. The extra weight of the backfill and pavement may be enough to keep the tank from floating. The burial depth should not exceed the manufacturer’s recommendation.
• Anchor the UST to counteract the buoyancy force exerted by saturated soil during a flood to prevent flotation by:
Owners and operators may also want to consider taking the following precautionary actions:
• Equip fuel lines below the flood elevation level with automatic shut-off valves. This will help prevent loss of fuel in case of line breaks or disconnects from the UST.
• Add an extension to the vent pipe if it appears the tank may be submerged in deep flood waters. If water enters the vent pipe, it will settle at the bottom of the tank, pushing product out.
What to do before the flood?
If you know there is a flood warning in effect, you should consider a few precautions to prevent both UST system displacement and water from entering your system.
• Turn off all electricity to the UST system including power to dispensers, pumps, turbines, automatic tank gauging (ATG) consoles, lighting, and any other system components.
• Take product inventory and water level reading of all USTs to help account for possible product loss.
• Fill the tank to weigh down the tank so it will not float out of the ground. NOTE: At first glance it may make sense to fill your tank with water to prevent buoyancy. DON'T! Any water that winds up in your tank will be considered petroleum contaminated water and will have to be pumped out and disposed of, which will just be one more costly expense.
• Secure all openings on top of the tank and make sure fill caps are in good condition and fastened securely in place and locked. If fill caps are not tightened, tanks will fill with water and release product. Empty or near-empty tanks may float up, destroying overlying concrete/asphalt and distribution lines, which can also release product.
• Make sure the seal on spill bucket plungers are operational so water cannot enter the tank.
• Close the shear valve on pressurized piping to prevent releases from product dispenser lines.
• Temporarily cap off the vent pipes to prevent water from entering the tank and displacing product.
• Place a dumpster, sand bags, or large containers full of sand or rock over the tank to reduce the chance of a tank floating out of the ground.
What to do after the flood?
So the floodwaters have subsided and the storm has passed.
Depending on the site-specific situation, owners and operators may want to take the following actions to check on their system, but only after the water has receded and local officials allow for re-entry:
• Make sure the power is off to any UST-related equipment (such as power to the dispensers, pumps, release detection equipment, and other devices).
• Determine if product leaked from the UST.
• Determine if water or debris entered the UST.
• After inspecting the electrical system, return power to the UST system.
• Check release detection system for proper operation. Perform release detection again, as soon as possible after the flood.
• Check all equipment including pumps, shear valves, fill pipes, and vent lines for proper operation.
• Clean and empty spill buckets and sumps, including those under the dispensers and above the tanks. Inspect the piping and fittings for damage and possible leaks.
• Perform an UST system tightness test to ensure integrity prior to adding product.
• Test spill buckets and sumps to ensure they are tight.
• Test cathodic protection to ensure it is operating properly.
Floods are extremely destructive and dangerous natural disasters. If you have any questions in regards to flood preparation, or need assistance with your UST system after a flood, reach out to your local tank management companies.
And, should a flood event occur within the Hudson Valley, Optima will be here with our 24-hour emergency response and experienced service and compliance technicians.
Neighbors watch out for each other.
USEPA Underground Storage Tank Flood Guide: https://www.epa.gov/sites/production/files/2014-03/documents/ustfloodguide.pdf