Debate | Tackling pollution from road runoff

The environmental movement which developed in the late 20th century secured a widespread understanding of pollution, such as the impact of greenhouse gas emissions on the climate. It has also ensured pollution is a consistent item on the political agenda.

Air pollution from transport is fairly easily linked to impacts on human health as can be seen in the connection between nitrous oxide emissions from car exhausts and exacerbated asthma in children.

What is less well understood is the impact of road runoff on water quality, soil health, food chains and human health.

Keyline Civils Specialist, part of the Travis Perkins group, recently organised a round table discussion about the impact of road runoff on water quality. The discussion was chaired by NCE editor Gavin Pearson.

Impact on water quality

When vehicles are driven, they undergo wear and tear. Solid parts like tyres and brake pads shed tiny particles into the environment. In addition, liquids like fuel, oil and screen wash fall onto highways and into drainage systems.

A significant proportion of these pollutants will exit highways via less managed pathways like gulleys, and some will enter fully managed drainage systems which could feature hard engineering solutions such as oil and water separators and drainage ponds. From these drainage routes, the road runoff pollutants end up in the wider water catchment.

This process has significant failings that contribute to waterway contamination, a major issue in the UK. Keyline technical director George Woollard says: “Only 14% of rivers meet ‘good’ ecological status in the UK.”

The government says a river has good ecological status when there is only a ‘slight change from natural state as a result of human impact’. Woollard continues: “There are in excess of probably 1M outfalls across the whole country. The Strategic Road Network (SRN) alone has 18,000 deemed to be at risk of discharging potentially contaminated runoff, and the SRN represents just 3% of the total road network.

“What this highlights is an ever-increasing issue, as we see the increase in vehicular traffic. This is probably going to get worse with brake wear when comes to the heavier electric cars.”

Much of this is unnoticed pollution. Acute pollution events that hit suddenly and significantly are often visible and their impact is more easily monitored. They sometimes discolour waterways and provoke a demand for remedial action.

Chronic pollution can be much more gradual and difficult to track. The impacts are poorly understood but pollutants that are consistently entering catchments can build up in groundwater and estuaries where they can enter the food chain via invertebrates, amphibians and birds.

Middlesex University Urban Pollution Research Centre professor of environmental science Lian Lundy says: “There’s a range of peer-reviewed studies that show impacts downstream of road runoff.

“[That includes] the pollution tolerance of different species, degradation of water quality, sediment quality and the potential impacts on groundwater.”

Stormwater Shepherds, a not for profit organisation working to improve water quality, monitors pollutants in English waterways. Its operations director Jo Bradley adds: “We definitely find these pollutants in estuaries and shellfisheries, so they’re getting there.”

John Bryden is head of improving rivers for Thames21, a charity which describes itself as the voice for London’s waterways. He proposes a monitoring system as a response to the lack of chronic pollution data.

“It’s relatively easy to retrofit a long term monitoring device that will give you a sensible continuous flow rate related to rainfall prediction, so you can understand those [longer term] trends,” he says.

The existing data used to help engineers decide on appropriate drainage infrastructure to manage runoff is potentially inaccurate and out of date, according to Woollard.

At the round table he said: “I’m sure some of you will be sitting here thinking: ‘how can [the data] possibly be completely accurate if the calculations aren’t correct?’ The rainfall data isn’t necessarily up to date, I think it’s 2014 data that they’re showing in some of these frameworks.”

Tackling pollution

Hard engineering solutions for strategic roads drainage only became the norm relatively recently. Nature-based solutions, including sustainable drainage systems (SuDs), are also coming through as a mainstream solution, but often only on newer roads and in a piecemeal way.

Wavin assistant design engineer Mark Henly said more consistent implementation of hard and soft engineering solutions “would need to come from the very top” of client and contractor organisations.

Referring to value engineering, he warns that too often “the first thing to go will be anything that costs a lot of money” such as hydrodynamic separators, which use cyclonic separation to control water pollution.

Henly and Bradley agreed that it sometimes results in monitoring and maintenance systems being stripped out from original designs to save money in the short term.

Fractured responsibilities for water management cause significant issues relating to water quality. Many stakeholders and landowners affect and are affected by water management. At the same time, while National Highways’ SRN is a major source of pollution, most roads are maintained by local authorities.

Adding to this complexity, water companies and highways authorities sometimes share combined sewer overflows, which mean there is a shared responsibility for managing the pollutants flowing through drainage.

One proposed solution is a wider uptake of existing catchment partnerships between public authorities, private enterprise, academia and non-governmental organisations.

Meanwhile differing funding arrangements for the policing of water companies versus National Highways and local roads authorities pose another challenge.

The Environment Agency’s pollution assessments for water companies are funded by licenses – in turn funded by the water companies themselves. However, there is no such arrangement for roads.

For now, the best way to remove this discrepancy remains unclear.

What is clear, however, is that focus on the urgency of reducing pollution from roads is on the rise. 

At the debate

This report is based on a round table held in February. The discussion was organised by Keyline. Contributing to the conversation were:

Olivier Bouzigues technical product manager storm water control, Aco

Jo Bradley UK director of operations, Stormwater Shepherds

Daniel Brockley senior policy officer, Department for Environment, Food & Rural Affairs

John Bryden head of improving rivers, Thames21

James Hale smart wastewater director, Environmental Monitoring Solutions

Mark Henly assistant design engineer, Wavin

Neil Hoskins head of highways and coastal, Southend on Sea City Council

Dan Ingram sales director, Prosolve

Craig Lashford deputy head of surface water management, Jacobs

Lian Lundy professor of environmental science, Middlesex University London

Gavin Pearson editor, NCE

Joe Pecorelli conservation programme manager, Zoological Society of London

Alasdair Reisner chief executive, Civil Engineering Contractors Association

Mark Shearer business development director, Polypipe Civils and Green Urbanisation

Serena Solanki national engineering manager, Keyline Civils Specialist

Ian Titherington senior advisor – sustainable drainage, Welsh Government

James Vance group head of environment, Travis Perkins

George Woollard technical director, Keyline Civils Specialist

• Published in association with Keyline Civils Specialist

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