Joint investigation helps to track down drainage issues in Llangollen
Llangollen is a much-loved town on the banks of the River Dee, and we know how important it is to protect the river for the people, wildlife and businesses that rely on it.
As a Senior Environment Officer with Natural Resources Wales, part of my role is to respond to reports of pollution and work with partners to find the source. We’ve recently been working closely with Dŵr Cymru Welsh Water (DCWW) in Llangollen to track down possible misconnections to the drainage system, following reports of fungus growth and a strong foul smell near a surface water outfall that flows into the River Dee.
Early checks and CCTV surveys
Initial checks showed that while there is a combined sewer overflow (CSO) on the surface water line, it hadn’t discharged since 24 January 2025. Rain gauges in the area recorded heavy rainfall that day, so the CSO has reacted to this and operated as designed.
Since then, DCWW has helped us move things forward by carrying out a CCTV survey of the drainage network. This flagged a few areas of concern where connections from properties might be going to the wrong place – potentially straight into the river.
Tracing the source
Our joint team has been dye testing toilets and sinks to see where they’re draining to. This involves putting dye into the system and tracking it through inspection chambers. So far, we’ve tested four properties – six toilets in total. Three of those properties (five toilets) are correctly connected to the foul sewer network.
One toilet couldn’t be traced to either the foul system or the surface water outfall. The CCTV footage shows that water may be pooling in a section of the culvert, which could mean it’s just taking longer to move through the system. We’re following this up with the property owner to find out more.
We also identified two sinks that appear to be misconnected. There’s more work to do on this drainage line to check for any further issues.
A team effort to protect the Dee
This is still a live investigation, but working with DCWW has helped us move more quickly. Sharing knowledge and resources makes it much easier to rule connections in or out.
We’ve also had fantastic cooperation from local businesses and property owners, which has been a big help. By working together, we’re getting closer to understanding what’s happening in Llangollen and how best to protect the River Dee from potential pollution.
Know your drains
The connections identified in Llangollen appear to be historic, having been in place for many years. The misconnections have continued throughout the years unknown to the property owners and occupiers. Do you know where the drains from your property go to? Here is some guidance: