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  • by Karma Loveday

Unmonitored and largely uncontrolled road run-off is poisoning rivers, report finds

A toxic cocktail of pollutants is running off our roads and into rivers from hundreds of thousands of highway outfalls – yet this is unmonitored and largely uncontrolled. That’s according to research from Stormwater Shepherds and CIWEM.


A report, Highway runoff and the water environment, analysed samples from nine locations (three motorway outfalls and six local highway outfalls) and found discharges to be multiple times (between 20 and 730 times) above the Environmental Quality Standards (EQSs) for several polyaromatic hydrocarbons (PAHs). It said PAHs have been shown to be carcinogenic and hormone disrupting to aquatic life. The pollution comes from tyre particles, fuel spills and other vehicle fluids, road surface fragments, sediment and herbicides.


National Highways has a statutory duty to control pollution from its network, via the Environmental Permitting Regulations. But according to Stormwater Shepherds and CIWEM: “Highway outfalls are not permitted, due to a voluntary agreement between the Environment Agency and National Highways.”


They explained National Highways uses a risk assessment tool to ascertain the highest risk outfalls from its road network that require remediation (Highways England Water Risk Assessment Tool – HEWRAT). “But there are questions over the efficacy of HEWRAT. The samples unveiled in the report with the highest concentrations of PAHs are in fact from an M6 outfall classified as ‘low risk’ by the tool. Stormwater Shepherds and CIWEM are concerned that there is currently no robust process to systematically prioritise remediation of harmful highway runoff.”


The key recommendations of the report were: 

  • The Department for Transport must turn its attention to issues that are of increasing importance to the public, such as managing the considerable environmental impact of roads.

  • There must be far greater emphasis on the control of pollutants at their source, including enforcing legislation to control use of PAHs in the manufacture of tyres, and ensuring new Euro 7 Emissions Standards on tyre abrasion limits are properly adopted by manufactures when they come into force in 2025.

  • All new road schemes should include good drainage design, and crucially provision for effective monitoring, operating and maintenance of drainage and treatment schemes.

  • The HEWRAT model should be reviewed and its outputs compared with the risk assessments undertaken by the Environment Agency. 

  • A catchment-based approach to assessing risk of harm from highway outfalls should be adopted, so that the most polluting outfall sources can be prioritised for remedial action and the most cost-effective solutions developed.

  • The introduction of extended producer responsibility levies on products such as tyres, fuel oils and brake pads should be introduced. This could provide the Department for Transport with greater budget to allow National Highways to install remediation schemes at high risk outfalls.

  • Alternatively, or in addition, the introduction of a Stormwater Utility Levy should be considered (as used in Germany). Under this mechanism each household pays a monthly fee into a central or regional fund to pay for better management of surface water. This could be set up to give local authorities the power to prioritise and address polluting outfalls within their area, as well as delivering against wider government policy objectives, for example, storm overflows and surface water flooding.

  • The Environment Agency should seriously consider issuing permits for high-risk outfalls from the road network. This would enable them to control the pollution by dictating the level of treatment that is required to protect the receiving watercourse and requiring that treatment devices be maintained and operated properly. It would also generate an income to allow the Agency to resource the control of the outfalls.


Jo Bradley from Stormwater Shepherds UK said: “The samples of highway runoff that we have taken over the last 18 months have revealed levels of toxic substances, called PAHs, up to 700 times higher than the legal standard. This is important because the standards are set to protect the organisms that live in our rivers and streams from the acute toxic effects of the chemicals. These effects include changes in behaviour so the organisms cannot feed properly; changes to their reproductive success; mutations and, sometimes, death.


“The fact that this highway runoff pollutes our rivers with these toxic compounds means that the Environment Agency should control the discharges using the permitting regime, but they don’t. It means that they should measure the extent of this pollution, but they don’t. They allow National Highways and other highway authorities to decide for themselves whether or not their runoff is causing pollution and whether or not they need to do anything about it. 


“This isn’t good enough. These discharges are poisoning our rivers and the life within them. It is time that they were properly monitored and controlled. We know how to treat highway runoff. We just need to get on with it.”

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