Chemicals that leaked into the groundwater during the Buncefield inferno are still being extracted, a decade after the disaster.
Work continues to protect rivers and drinking water under the watchful eye of the Environment Agency.
During the firefighting battle, 50million litres of water was sprayed on to the fire but only 33million litres were successfully contained within the site.
The water was kept onsite and moved by tanker to two nearby sewage works for storage until it was treated using reverse osmosis and activated carbon to remove the hydrocarbons and other toxins.
During the blaze firewater and firefighting foam containing the toxic man-made chemical PFOS, which escaped the depot’s concrete bunds, flooded Cherry Tree Lane and Hogg End Lane percolating into the ground.
Since then the boreholes, some reaching 40 metres underground, have been closely monitored and water has been extracted from the ground several times and cleaned of toxins before being put back.
Alex Chown, area environment manager for the Environment Agency, said: “In terms of how long it will continue for, that is quite difficult to say. It will continue until we are satisfied.
“When something is underground it can be out of sight out of mind, that is not the case here because we have still got lots of boreholes compiling data.
“The end goal would be that we can say that it is remediated fully.
“I think it is very, very challenging to bring back a site to as if there was never the incident beforehand.”
There were concerns about what impact the pollution would have on the River Red in Redbourn and the River Ver, which continues to be monitored.
Alex said: “Groundwater, particularly in this part of the world, is a major resource here for drinking water and also for the basis of chalk streams.
“It is a commodity that is extremely precious to man and the ecology. When you have contamination of groundwater, it is very challenging to clean it up. It is very difficult to go back to zero.
“The reality is once it is damaged, it is very difficult to restore.”
Monitoring and treatment of groundwater around the Buncefield site is being monitored by the companies in charge of the depot at the time of the disaster, while the Environment Agency acts as a watchdog.
Since the disaster a series of industry-wide safeguards have been introduced to better product the environment from such pollution.
Alex said: “10 years on, industry and the workforce have worked closely with regulators to implement these changes.
“The industry continues to be committed to working with us to improve.”