The utility company was fined £540,000 and ordered to pay costs of more than £142,000 and a £170 victim surcharge, totalling almost £700,000.
Durham Crown Court heard on Monday that on 22 May 2017, a blockage in a combined sewer caused sewage to pour out of a manhole cover and discharge into the watercourse that runs through Heads Hope Dene, south of Durham city.
It is thought that the pollution incident took place over two to three days, but the court heard it was impossible to quantify how much sewage entered the water course.
The Environment Agency said that the ecology and habitat of the watercourse was damaged for 2km and caused a “detrimental impact on water quality” for 4km.
Northumbrian Water self-reported the incident to the Environment Agency. It was originally due to stand trial this week, but reportedly changed its plea to guilty ahead of its court date.
According to the Northern Echo, Judge James Adkin said the company was aware of serious tree root ingress following checks on 3 April, 2017, and while there was little time for immediate significant work, the company made only "a makeshift response to an active pollution threat”, using chicken wire and bales near the manhole to hold back sewage debris. Judge Adkin described this as proving “totally inadequate” when the pollution incident took place.
Commenting on the fine, Rachael Caldwell, environment manager for the Environment Agency in the north east said: “Our officers have worked tirelessly to bring this case to court and we’re pleased with the result, which demonstrates our commitment to holding water companies accountable.”
She added that water companies “have a legal duty to avoid pollution and must act quickly to reduce any damage that happens as a result of their activities”.
Northumbrian Water wastewater director Richard Warneford said that the company fully accepted the fine handed to them.
“This pollution incident at Head Hope Dene was something that we quickly identified and dealt with....We would like to reassure our customers that since this incident in 2017, we have made many changes and improvements to how we reduce pollution risk on our wastewater network”, he said.
“However, we will continue to strive to do even better and are currently investing £5m on upgrades to the sewer network in the area around Heads Hope Dene, to protect the environment and future proof our assets.”
He added that over the last three years the Environment Agency had awarded Northumbrian Water the highest level of four stars in environmental performance assessments.