An investigation by the Environment Agency found that the company had breached its environmental permit when contaminated water was washed down highway drains and into the River Don.
It submitted an Enforcement Undertaking to the Environment Agency, which has now been accepted.
An Enforcement Undertaking is a voluntary offer made by companies and individuals to make amends for their offending, and usually includes a donation to a wildlife charity to carry out environmental improvements in the local area.
Costain Limited had an environmental permit which allowed it to discharge water treated by a sediment treatment facility into the River Don during work to the A19 at Testos roundabout.
On 6 December 2019, whilst works were being carried out, an Environment Agency officer in the area reported a plume of sediment in the river.
Following a dry spell of weather, Costain had decided to jet wash and sweep the road surface to remove a build up of mud.
But the road sweeper was not powerful enough to suck up all of the dirty water and instead the contaminated water ran directly into highway drains, bypassing the company’s sediment treatment measures, and into the River Don.
The silt in the water was vastly in excess of what the permit allowed, and it caused discolouration for at least 500 metres.
After the incident the company introduced a new monitoring and maintenance regime as well as training for site staff, and no further incidents occurred. There was no long-term ecological impact on the river.
Tyne Rivers Trust will use the donation on projects that will improve water quality in the River Don catchment.