New report unveils new data showing extremely high levels of toxic chemicals in highway discharges

The jointly-commissioned report by Stormwater Shepherds and CIWEM shows that pollution comes from tyre particles, fuel spills and other vehicle fluids, road surface fragments, sediment and herbicides. These contain heavy metals and toxic chemicals such as polyaromatic hydrocarbons (PAHs) which have shown to be carcinogenic and hormone disrupting to aquatic life.

There are likely 100s of thousands, if not millions, of highway outfalls across the country discharging this toxic mix into the water environment. Yet these outfalls are unmonitored and largely uncontrolled, despite the control of pollution from National Highways’ road network being a statutory duty.

The lack of routine monitoring of these outfalls by the Environment Agency, National Highways and local highway authorities means that their impact on aquatic ecosystems and human health is not well understood.

With sewage dominating political and media attention, this pollution has been flying under the radar.

Other polluting discharges to water must be controlled under the Environmental Permitting Regulations subject to a sequence of tests being met. Yet highway outfalls are not permitted, due to a voluntary agreement between the Environment Agency and National Highways.

Samples analysed by this research from nine locations (three motorway outfalls and six local highway outfalls in north west England) show that the discharges concerned are multiple times above the Environmental Quality Standards (EQSs) for several PAHs – at one site between 20 and 730 times greater. Moreover, sampling from the River Lostock at Cuerden Valley Park demonstrates a motorway outfall causing PAH levels above EQSs in the river itself. Assessment undertaken against the Environment Agency’s environmental permitting guidance indicates that this type of outfall should be considered permittable.

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 report calls for HEWRAT to be reviewed and its results compared with the risk assessments undertaken by the Environment Agency.

The report calls for the government to take seriously its statutory duty to control pollution from the strategic road network. The Department for Transport should include an ambitious settlement for environmental protection in National Highways’ next road budget, and increase the emphasis on the control of pollution at source. The report also asks that the Environment Agency seriously consider the use of its environmental permitting powers to better control highway pollution.

Read more about the samples analysed, the solutions available to control highway pollution and recommendations for government in our new report here.

CIWEM’s policy team worked with Stormwater Shepherds and members of our Urban Drainage Group to collect the case study sample data found in this in-depth report, alongside subsequent recommendations for implementing solutions.

We are grateful for the generous funding by the Rees Jeffreys Road Fund to enable this work.