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The Guardian: Toxic legacy poses a giant problem

Officials ponder what to do with huge quantity of contaminated water
Ian Sample, science correspondent
Tuesday February 7, 2006
In a corner of Maple Cross sewage treatment works near Rickmansworth in Hertfordshire lies a 12m-litre problem that fails to go away. It is the forgotten legacy of the inferno at Buncefield oil depot in December – six giant settlement tanks full of spent firefighting foam, black water and a long list of toxic contamination.
It took 500 tankers five weeks to bring here the dirty mixture, known to environmental officers as “firewater”. During the 60-hour battle to contain the blaze, the foam and water used by 650 firefighters collected behind a protective bund, a wall designed to contain the spill if an oil tank on site ruptured its contents. For now, the firewater is safe, held in 20 metre-deep concrete tanks beyond the cesspools and pipes that criss-cross the 50-acre site.
“During the firefight we knew we needed to get it off site, because the bund was filling up like a bath with the taps full on,” said Colin Chiverton, who heads the team dealing with the foam for the Environment Agency. “But what to do with it next is uncharted territory.”
When the first tankers arrived at Maple Cross little was known about the firewater's toxicity. The blaze was so large that 16 forces from around the country were brought in to tackle it, bringing what foam they could lay their hands on. Scientists puzzling over what to do knew they were dealing with a host of toxic chemicals used to make the specialised oil fire foams. But also lurking in the liquid was a host of toxic substances released by the fire itself.
Scientists at the Environment Agency and Thames Water, which owns Maple Cross, sent samples of the firewater to labs in Cardiff, Leeds and Hampshire to look for more than 40 contaminants they feared might be there. Many tested positive. “We know enough to say we cannot allow this to get into the environment, either the ground or the water,” said Mr Chiverton.
Officials are most concerned about a toxic substance called PFOS or perfluorooctane sulphonate, a chemical used in some firefighting foams that does not break down in the environment. Instead, it accumulates in organisms and works its way up the food chain, where it can become a serious problem. Following an Environment Agency report on PFOS, the Department for Environment, Food and Rural Affairs (Defra) moved to phase it out, but so much foam was needed at Buncefield that fire brigades were forced to bring their old PFOS-containing stocks as well. The lab tests revealed other toxic substances too, including zinc, which is toxic to aquatic animals, and Pahs or polyaromatic hydrocarbons. Another substance, MTBE, was also picked up. Before the lab tests were complete it was clear that disposing of the firewater was going to be fraught with difficulty. Government officials were initially keen to see if it could be made safe by running it through the sewage treatment works, but the plan was quickly ruled out.
“If we try and pump it from the settlement tanks into the treatment works it will immediately foam up like bubble bath. Our pumps like pumping liquids and if they try to pump foam, they will destroy themselves,” said Dave Wiltshire of Thames Water. The problem became apparent when tankers arrived from Buncefield: as they released firewater into the tanks they brimmed with a head of foam one metre high.
Simply adding an antifoaming agent to flatten the froth is a non-starter. Antifoaming chemicals are made from oils, the one substance the foam is specifically designed to be resilient to. The lab results showed that even if the firewater could be safely pumped into the sewage treatment process, doing so could be catastrophic. The problem lies with what is called the chemical oxygen demand of the firewater – the amount of oxygen a substance consumes as it breaks down. Tests showed that the firewater was so full of organic chemicals that it would suck up nearly 500 times as much oxygen as the normal household effluent the treatment works is designed to handle. The vast tanks of bacteria used to digest waste into harmless byproducts would quickly suffocate and die through lack of oxygen.
“If the beds of bacteria go and die on us, we won't have a working treatment facility and that would be a major problem. We deal with waste from hundreds of thousands of homes from Hemel Hempstead to Watford and St Albans,” said Mr Wiltshire. “If you released this into a river, it would use up so much oxygen, it would knock it out. Nothing could cope with a shock like that, not even our treatment works.”
The biggest problem remains the PFOS. The huge tanks of bacteria at Maple Cross cannot break it down, so passing it through the treatment works will not remove it from the firewater. Since the treated sewage from Maple Cross runs into the River Colne, a tributary of the Thames which several water companies extract from downstream, it is a risk neither the Environment Agency or Thames Water will take.
Efforts are concentrating on ways of either extracting the PFOS from the firewater, or finding a more radical solution. One surefire way of disposing of PFOS is high temperature incineration, available at two sites in Britain, Ellesmere Port in Cheshire and Fawley in Hampshire. “The only problem is that water doesn't incinerate very well,” said Nick Cartwright of the Environment Agency.
For now, it is up to specialised consultants brought in by the oil companies based at Buncefield to work out what to do. The firms – Texaco, Total, Shell and BP – will foot the bill for disposing of the firewater, which is expected to run into many millions. “It's a case of polluter pays,” said Andy de Bell, another team member with Thames Water.
With luck, the consultants will come up with plans to deal with the Buncefield foam in the next few weeks, after which the combined forces of the Environment Agency, Thames Water, Defra, the Food Standards Agency, the Drinking Water Inspectorate and the Health and Safety Executive will be asked to agree on a way forward. It is likely the foam will be sat at Maple Cross for some time. “If there was a magic solution tomorrow, it would take around five weeks to tanker it off site, but in reality, we're probably looking at a few months before this is solved,” said Mr Wiltshire.
“We've done the difficult bit. We've got it here, we've contained it and it's not going anywhere until we're sure what the best option is. We're certainly not going to come this far and do something stupid with it now.”
PFOS Perfluorooctane sulphonate was used in older firefighting foams and is particularly effective against oil fires. It makes the foam spread out into a thin layer on top of the burning oil, smothering the flames. An Environment Agency risk assessment in 2004 recommended PFOS be phased out because of its toxicity. If released into watercourses it builds up in fish and organisms that feed on them. In 2001 3M, the major manufacturer of PFOs, voluntarily stopped production of the chemical.
Pahs Polyaromatic hydrocarbons. They are byproducts of the burning process and are also found in cigarette smoke and vehicle exhaust fumes. Many contain the toxic chemical benzene and most are carcinogenic to humans.
MTBE Methyl tertiary butyl ether is added to unleaded fuel to make it burn more efficiently and cut down on noxious emissions. It dissolves easily in water, so spillages can rapidly get into groundwater or watercourses. Very little is known about ingesting MTBE, but animals have developed cancers after inhaling large quantities. It makes water taste and smell awful at very low levels: at 20-40 parts per billion, contaminated water tastes similar to turpentine.

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