For all the benefits they may deliver to a business, there comes a point in the life of an underground storage tank (UST) where it has outlived its usefulness and has to be decommissioned. It may be that the site is no longer fit for its original purpose and is now to be redeveloped. However, of most concern is the possibility that any remaining product or vapour in a tank or system could leak and pollute or contaminate surrounding land and groundwater, creating risks to people, property and the environment.
Removing a UST, rather than the cheaper option of leaving it in place, is the safest and most environmentally-sound practice, points out DP Fuel Tank Services, a leading operator that specialises in oil and fuel tank removal.
Decommissioning includes a range of activities: from completely closing off and removing a UST facility, to replacing individual tanks or lengths of pipework. Making sure this is carried out in a safe and secure way is paramount and a requirement of the EWC waste code (www.is.gd/wumazo). Where waste that contains a persistent organic pollutant (POP) is being disposed of, there are additional guidelines (www.is.gd/avikub).
“So, removing a tank is clearly more than a matter of undoing a few rusty bolts and lifting it on to the back of a lorry,” points out DP Fuel Tank Services’ managing director Nigel Plumb. “We have to clean it thoroughly first, so that it can be transported safely and recycled, in accordance with the regulations. But there’s a whole process that comes before that where we need to understand the history of the project and the client’s end goal. First, we have to establish the status of the tank or tanks. Are they live – that is, is there fuel inside them still – or already infilled? If there is residual fuel or contaminated water that has to be removed, and the tank infilled with a lean-mix cement slurry or foam as a void filler, which will also ensure that no fuel vapour remains behind.”
FOAM VERSUS WATER
Injecting USTs with foam is cheaper than filling them with water and subsequent water disposal by tanker, states Plumb. “For the past two decades, we have been using Nitro-foam, which we have since developed and improved with our own self-contained inerter. This keeps the foam consistent, regardless of local mixing water quality. The nitrogen-filled bubbles force out fuel vapour and then dissolve away to virtually nothing. It also saves time, with only one operation, instead of two, and avoids delays while waiting for tankers.”
It isn’t just about the USTs, though. Establishing the condition of the existing pipework is also essential. “Pipework will drop from the top of the tank to the floor, so fuel may be sealed in and not open to the environment or potential ignition sources, with the potential for a thermal atmosphere where the fuel ignites. So, all of the tanks and any associated pipework have to be degassed before the excavation can go ahead.”
Once this has been completed, the tank can usually be excavated in one piece by a hydraulic breaker – attached to earthmoving machinery, pictured above – and taken away to be cut up at a safe location. “Occasionally, a section of the tank will be left in the ground where part of the UST is providing support – for a party wall, for example – but that is rare.”
Once the job has been completed, how does the client know the waste has been disposed of in an environmentally responsible manner? “We work with companies that remove the waste to an approved treatment plant under the EWC Waste Code,” he explains. “An audit trail is created for that waste, which we pass on to the client, which includes a consignment note” (see also www.is.gd/senecu). These notes are obligatory for all movements of hazardous waste, confirms the Environment Agency (EA).
Such are the responsibilities of the contractor undertaking the safe removal of a UST; what about an owner’s obligations? According to the EA, these are the type of measures that need to be followed: “You should immediately decommission any USTs that you’re no longer using. Decommissioning includes both closing and removing a UST system (the tank and any equipment connected to it) as a whole, and replacing individual tanks or lengths of pipe.
“You can decommission a UST either permanently or temporarily. If you only temporarily decommission a UST, you must make sure that it doesn’t cause pollution and you have plans to permanently decommission it as soon as possible. As part of the decommissioning process, you should:
Carry out a full environmental risk assessmentSample any surrounding soil and groundwater (you should do this before, during and after decommissioning) - the results from this will be important in your risk assessmentRemove any residual product from the tank and pipes (called ‘bottoming’)Get rid of any explosive vapours from the tank and pipes to make them safe, before removing them from the groundRemove and then clean tanks, pipes, dispensers and separators.“You should consult the Blue Book [www.is.gd/ivubox] for further technical guidance on decommissioning tanks [including health and safety issues],” adds the EA. “To avoid pollution, you should remove tanks and associated pipework that you’re unlikely to use again. If you leave tanks in place, there’s a risk that some product remains in the tanks that you won’t be monitoring or maintaining.”
It also advises that you should review your plans to decommission the UST if you can’t make sure of the following:
Your methods don’t lead to a loss of fuel to the ground either accidentally or on purposeYou don’t leave any equipment undergroundYou don’t leave any product underground (for example, in tanks, pipes or drains)You dispose of contaminated tanks and pipework lawfullyYou comply with relevant waste management requirements [www.is.gd/arayux] by using registered waste carriers and any permits that you may need for waste treatment or storage.
POLLUTION RISKS
“Equally important is to make sure any drainage systems that remain active after decommissioning [a UST] do not provide a channel for pollutants to reach groundwater or other surface waters, for example, rivers, streams, lakes or wetlands.”
This is a timely reminder concerning wider environmental responsibilities, it should be said, especially in the wake of data released earlier this year by the EA, showing water companies discharged raw sewage into English rivers 372,533 times last year.