Buncefield blast leaked "large amounts of contaminant"
The Buncefield oil depot explosion had leaked "large amounts" of fuels and polluted firewater into the ground, with the full effects on drinking water resources likely to remain unknown for years, the second official report into the accident found.
But fuel and chemically contaminated water used to put out the fire may also seriously pollute the chalk aquifer underlying the Hertfordshire site, which supplies groundwater for the region, the report said.
"During the incident ... fire water and fuels flowed through the site drainage and along the roads within the site perimeter", the report states. A 10 by 20 metre pool of contaminated water had formed in Cherry Tree Lane within the site, and was only cleaned up in January this year. Road drains connected to the chalk aquifer are one potential route for contaminated liquids to reach groundwater 45 metres below ground level.
So far, only low-level water contamination has been found. But because water may take years to drain though the ground, the effects of the blast may only be experienced years down the line.
"It is important to emphasise that if contamination of the aquifer took place, it would take months or years to materialise," said Taf Powell, in charge of the investigation into the causes and aftermath of the inferno.
Operators of large fuel depots like Buncefield, which serve as centres for the distribution of petrol, diesel and aviation fuel, must report to the EA on the provisions they have in place to contain fuel if it escapes from tanks and pipes holding it.
The Buncefield Investigation Board had found that the bunds - or walls designed to hold in escaped fuel - had been damaged and ceased to be impermeable.
The second progress report focused on the environmental impacts of the incident, rather than the investigation into how the fuel escaped, and why it vaporised so rapidly. A full report into the causes of the accident should be published within a month, Taf Powell said.
A copy of the Second Progress Report can be accessed here.