A30 Road Runoff Study

Study of diffuse inputs of road-derived contaminants

Upper areas of the River Teign catchment are classified as having moderate overall status under the Water Framework Directive with Fingle Brook shown to be failing to achieve good status for fish (specifically Brown Trout). It is suspected that diffuse inputs of road-derived contaminants could be impacting upon the system. As part of the Dart and Teign River Improvement Project, Westcountry Rivers Trust (WRT) headed a research programme, alongside staff of the Plymouth University Catchment and River Science research group to address these key knowledge gaps. Four research packages were undertaken:

Diatom & walkover survey
Monitoring water & sediment chemistry in the main river channel
Assessing water chemistry against environmental quality standards (EQS)
High spatial resolution monitoring of water chemistry to identify key contaminant pathways

Diatom samples suggested that sites were not heavily impacted by nutrients from sewage treatment works or agricultural sources.

The WRT walkover survey did not detect factors likely to specifically impact upon brown trout, further emphasising the need for chemical data.

Elevated concentrations of road-related metals such as lead and zinc were found in water and sediment. Storm sampling using automatic water samplers and conductivity monitoring showed an early flush of solutes in the main channel below road drains.
Concentrations of zinc were above EQS (biotic ligand model-derived) potentially owing to road drainage inputs and drainage from an historic mine site.

4.Detailed spatial sampling showed elevated dissolved concentrations of metals below road drainage inputs, particularly lead, with values above EQS. It is possible that the legacy of sediment-bound lead in the channel bed is a source of lead to the water column under certain environmental conditions.

WRT is instigating remedial works to focus upon a drainage attenuation pond and flow regulation in the existing drainage gullies. Mitigation will also be considered for the historic mine site given its potential for longer-term, chronic metal inputs.