The company appeared at Durham Crown Court for sentence on Wednesday, 6 October, after pleading guilty at a previous hearing on Monday (4 October) to discharging sewage effluent into the watercourse that runs through Heads Hope Dene near Castle Eden.
They were fined £540,000 and ordered to pay costs of more than £142,000 and a £170 victim surcharge.
The court heard 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.
Northumbrian Water self-reported the incident to the Environment Agency and an agency officer attended to investigate. Water sample results indicated raw sewage had entered the Dene.
The impact is visible in the watercourse
Impact on water quality for 4km
Surveys later found the ecology and habitat of the watercourse was damaged for 2km, with river sample results indicating a detrimental impact on water quality for 4km.
Northumbrian Water began immediate work to clear the blockage that day as well as remedial work to make improvements. A longer term solution to re-route the sewer out of the Dene is underway.
Rachael Caldwell, Environment Manager for the Environment Agency in the North East, said:
We take our responsibility to protect the environment very seriously. 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. The regulations are clear and are enforced robustly.
In this case raw sewage poured out of a manhole cover and into the Dene, which had a negative impact along 4km of the watercourse. 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.
Since 2015 the Environment Agency has brought 46 prosecutions against water companies, securing fines of over £131million. This enforcement action and the pressure it has put on water companies has led to £30billion of investment by the water industry.
To report a pollution incident contact the Environment Agency's 24-hour Incident Hotline on 0800 807060
