Flooding and Underground Storage Systems

Posted on February 15, 2017


In June of 2013 some southern Alberta communities experienced extreme flooding.  In High River a number of service stations in their downtown were completely under water.  We seem to be living in a period of extreme weather conditions.  The Government of Canada has instituted a program to support the future resilience of Canada’s infrastructure to the effects of climate change.  The objective of this program is to consider extreme weather when technical standards and regulations are prepared.  In the future our technical systems may be more prepared for extreme weather conditions but it’s important to be able to respond to a flooding condition that may be just a week of heavy rain away from becoming a problem today.  Oil companies, petroleum contractors and regulators learned a great deal from the High River flood but we can benefit from more extreme incidents elsewhere.  The best response to the flooding of underground petroleum systems came from the State of Louisiana after Hurricane Katrina in 2005.  The recommendations that came from their experience have been used to educate Alberta tank owners and operators in case we see a repeat of the flooding of 2013.  The focus of this guide is to return flooded facilities to operation while ensuring protection of human health and the environment.  Thank you to Louisiana’s Department of Environmental Quality for sharing their recommendations.

What Happens when Tank Systems are Flooded?

Damage that occurs to underground storage tank (UST) systems generally result from the buoying up of tanks which are partially full or empty, water entering the tanks and displacing product, failure of underground piping from groundwater pressure or debris and damage to electrical systems from extended contact with water.  Tanks that are weighted down with fuel or anchored by other means and have tight fill caps should sustain little impact, even after being submerged for days.  If tanks ‘float’, the entire system will have to be replaced.  There will very likely be a loss of petroleum when tanks lift and piping breaks so an expensive remediation can be expected.

UST System Evaluation:

Flooded UST facilities must be evaluated to determine the necessary steps to be able to put these systems back into service.  No equipment should be turned on prior to examination.  Check all electrical panels and make sure they are clean and dry.  All equipment related to electric power service should be inspected and any necessary repairs should be made prior to power restoration.  This includes all fuelling systems, leak detection devices and corrosion protection (impressed current) equipment.  The electrical system should be checked for continuity and shorts (pumps, turbines, dispensers, ATG consoles, emergency shutoff, panel box, etc.).  Specifically, all electrical junction boxes and dispenser heads should be opened, inspected and dried, if necessary.  Conduits should be inspected for the presence of water, insulation damage, shorts or opens.  Conduits exhibiting water should be dried or vacuumed as appropriate and all defective wiring should be replaced.  To apply electrical power to a UST system before conducting basic examination could be extremely dangerous.  Submerged pumps and dispensers should not be operated if there is the possibility of water entering the system as pumping water may damage hydraulic components.

To Place Tanks Back into Service:

1.      Dip tanks using water-finding paste or read ATG systems to determine if water has entered the tank.

2.      Flooded or water impacted tanks and all lines may need to be drained of water and dirt/mud or pumped dry and cleaned as conditions warrant.

3.      Interstitial spaces of tanks and lines of double-walled systems, if flood-impacted, will need to be drained and flushed where possible.  Blockage of interstitial spaces will render leak detection useless.  Tanks with brine or vacuum interstitial sensors may be returned to service if brine or vacuum levels are normal. 

4.      All facility sumps, pans, and spill buckets need to be pumped dry and cleaned.  Replace sump lid gaskets if needed.  If sump lids are missing, replace with new water-tight lids.  Replace sumps and spill buckets that fail to prevent water intrusion after initial cleaning and drying.

5.      Check tank bottoms for water and debris. 

6.      Check deflection of fibreglass tanks.  If deflection is greater than manufacturer’s specification (general guideline is 2%) call the manufacturer for instructions.

7.      If tanks shifted and problems are found, repair or replace them according to the Fire Code, manufacturer’s instructions and appropriate industry standards.

8.      Check vents for movement, cracking, blockage and proper operations.

9.      Check dispenser filters and submersible check-valve screens for plugging with dirt or mud.

10.   Flush dispensers and UST system if necessary.

11.   Check critical safety devices (e.g., emergency power-off controls, line leak detectors, shear valves, stop switches, isolation relays on dispensers, etc.)   Shear valves may be salvaged if they can be cleaned and lubricated with corrosion prevention material. 

12.   Sump sensors may need to be replaced after emergency conditions cease.

13.   In-tank pumps, ATG probes, overfill devices, automatic line leak detectors, fill and vapour dust caps, etc., should be assessed.  Assess their condition after cleaning and replace as necessary.

14.   ATG consoles and associated electronics that are not submerged should have a programming and operability check performed by a qualified technician.

15.   If an impressed current corrosion protection system is used a NACE certified inspector should evaluate the system to ensure it is still protecting steel tanks and/or piping.

16.   Check accessible fittings, valves and miscellaneous piping for damage and corrosion.  Clean and replace as necessary.

17.   Submerged dispensers will have to be assessed including hanging hardware.  Suction pump motors may have to be replaced.

18.   Document all inspection, assessment and repair activities at each UST facility.

Upon Resumption of Service:

 Depending on the amount of fuel that may have escaped during the flood, certain leak detection methods may no longer be viable.  Daily inventory control may be the short-term leak detection method by necessity.  Daily checks for water with water-finding paste should be done for several days until it has been determined that the system is tight.  Take tanks out of service and remove product if the water test indicates the ingress of water.  A precision test should be conducted of flooded tanks, lines and interstitial spaces.  Assess interstitial spaces for blockages, especially if used for leak detection.  Decisions regarding replacement of tanks and lines should be made based on outcome of these tests.  Any water or dirt collected during cleaning procedures that may have come in contact with fuel will have to be disposed of appropriately.  Check with Alberta Environment for disposal options.