Jo Bradley investigates how road runoff pollution is damaging the quality of England's waters and endangering both the aquatic environment and human health.
When it rains heavily and persistently on busy urban highways, the surface water runoff will often contain toxic pollutants that are poisonous to aquatic life and dangerous to human health. If they are not removed, sediments and microplastics originating from tyre erosion, exhaust emissions and fuel spills can then settle in rivers and streams.
The fact that this happens should come as no surprise to any environmental professional. The Environment Agency (EA) has warned that 86% of England's water bodies still fail to meet the 'good' status required by the European Water Framework Directive, with urban and transport runoff accounting for 13% of the problem.
The pollutants of most concern for the aquatic environment, and also for human health, are metals, particularly copper and zinc, and a spectrum of chemicals known as polyaromatic hydrocarbons (PAHs), including benzo[a]pyrene.
These have been shown to reduce species numbers of both macroinvertebrates and diatoms in rivers and streams, reducing the amount of food available to fish and other aquatic species.
Our failing water environment
The load of sediment produced by tyre abrasion alone in the UK has been estimated at 63,000 tonnes. The pollution is most threatening at high-risk locations on motorways and trunk roads, especially near vulnerable ditches and tributaries. Even in rural locations, where there is little other pollution and the flows in the streams are low, the risk of highway pollution can be significant.
There are an estimated 1 million discharges of road runoff via drainage outfalls across the UK, and more than 2,500 of the 25,000 outfalls operated by Highways England (HE) pose a 'very high' or 'high' risk of pollution, according to the HAWRAT assessment tool.
It would be easy to assume that runoff pollution is mostly a diffuse problem and that it is difficult to quantify, regulate and control. In fact, it is completely possible to monitor, identify and control all of these point-source discharges into the environment using a range of well-proven techniques and technologies.
Sustainable drainage systems
A management train, ideally using Sustainable Drainage Systems (SuDS) devices, is usually engineered to work together to remove sediments and treat pollutants. The design choices range from simple gravel filter strips, to vegetative features like ponds and swales, and manufactured devices capable of delivering measured and repeatable performance.
Where the runoff is grossly polluted, hydrodynamic vortex separators are increasingly being deployed to remove sediments, and sometimes to protect the efficient operation of vegetative features. On challenging sites, perhaps where the receiving environment is particularly sensitive, more sophisticated stormwater filtration devices can deliver reliable removal of suspended solids and soluble pollutants together.
Most recently, engineered filter media have been developed to capture and retain heavy metals, particularly copper and zinc. This mix of innovative granular materials works via the processes of adsorption and ionic exchange to form unbreakable bonds with the heavy metals, including copper and zinc, capturing and retaining them even in major storms.
However, to treat the pollution, you must first know where to find it. The problem is, we simply do not understand enough about highway runoff pollution because there is hardly any routine monitoring and consequently very little enforcement. The data is limited, and the EA does not routinely monitor copper, zinc and benzo[a]pyrene across the water environment in England, so elevated levels are not always recorded.
Benzo[a]pyrene is carcinogenic, mutagenic, toxic for reproduction, bioaccumulative and persists in the environment for a long time. The EU classes it as a 'Substance of Very High Concern' under REACH, and as a Priority Hazardous Substance under the Environmental Quality Standards Directive4. Yet, across England & Wales, the water quality monitoring programme does not look for Priority Hazardous Substances downstream of major road runoff discharges.
The good news...
There has been some welcome progress in surface water flood risk protection and management in the UK. HE and other authorities are beginning to voluntarily install treatment devices on the highest risk outfalls in England and Wales, even in the absence of permits. Scotland is generally much more successful at controlling water quality than the other UK regions.
It's also true that the EA has been working hard to counter pollution from all sources - and not just from transport and highways. Its annual report: “Regulating for People, Environment and Growth Report“5, published in October 2018, told a rare good news story for the environment in an otherwise sorry collection of gloomy headlines about climate change and air quality.
The number of serious pollution incidents (categories 1 and 2) in 2017 has reduced by 18% from 2016 to 419.
However, where the EA has been able to identify the source of the pollution incidents, 44% were from unregulated industries. There were 68 (16%) significant pollution incidents that came from 'unknown' sources.
Of course, we can't assume that the 'unknown' sources in this particular report are from highways. However, the report aptly demonstrates that the problem with regulation is you end up looking for pollution in the places where you are most likely to find it.
The EA's very nature is focussed on regulated industries and the monitoring programme is designed around controlling known or permitted discharges to measure their impact. The system is not set up to look, in any detail, for other discharges that are not, or perhaps should be, regulated.
A level playing field?
The EA recorded 52 serious pollution incidents from water companies during 2017, yet all the while, there could be an uncontrolled highway outfall upstream of a sewage treatment works, releasing sediment and toxic chemicals into the same water body.
Of course, there will never be enough resources to control every discharge, or to prevent every illegal pollution incident. There must always be priorities and choices, alongside appropriate regulatory controls.
However, there are many more highway discharges that could be easily measured and then routinely controlled. Depending on your point of view, the impact and extent of highway runoff pollution remains, at best, overlooked and misunderstood; or, at worst, shamefully neglected.
It seems the authorities believe it is just too difficult, or too costly, to face up to the full risks of this toxic and bioaccumulative scourge on our water environment.
Jo Bradley is market development manager at SDS Limited
References
Environment Agency: State of the Environment: water quality, 19 February 2018 Jan Kole, Löhr, Van Belleghem & Ragas: Wear & tear of tyres: A stealthy source of microplas-tics in the environment. Int. Journal of Environmental Research & Public Health. 2017 Oct; 14 (10): 1265 The Design Manual for Roads and Bridges (2009) HD 45/09 Road Drainage and the Water Environment for information about the HAWRAT model. http://www.standardsforhighways.co.uk/ha/standards/dmrb/vol11/section3/hd4509.pdf. The HAWRAT model can be downloaded with permission of Highways England.
European Parliament and Council; Environmental Quality Standards Directive 2008/105/EC.
Environment Agency: Regulating for people, the environment and growth, October 2018
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