Jo Bradley, Market Development Manager, SDS Ltd and formerly Water Quality Advisor and Highway Outfall Project Manager with the Environment Agency, looks at the challenges posed by urban and highway runoff which are contributing significantly to UK water quality failures.
Jo Bradley: Our water environment may be cleaner than it has been for decades, but the health of our rivers and streams still falls woefully short of acceptable standards. Only 14% of England’s water bodies reached “good” ecological status, according to the latest State of the Environment update from the Environment Agency EA).
Pollution from agricultural runoff, CSOs, urban and highway runoff are all contributing significantly to water quality failures, the report says.However, efforts to identify, understand, and eliminate the sources of contamination are vastly inconsistent.
To stop pollution, you have to start by looking in the right places for it. So, it should be a matter of huge concern, especially when it comes to urban and transport runoff (13% of the total according to the EA), that hazardous and often highly toxic pollutants are frequently overlooked, inconsistently monitored and poorly controlled in water bodies across the UK.
Of course, there are never going to be sufficient resources to look everywhere for every kind of pollution; there have to be priorities. But not looking for pollution, in places where you might reasonably expect to find it, is wholly unacceptable – especially when the regulatory powers, professional knowledge and technologies already exist to prevent it.
Changing environmental regulatory landscape is unprecedented opportunity
We are approaching a ‘once-in-a-generation’ moment to get a stronger grip on environmental pollution. A new environmental watchdog post-Brexit, the Government’s first Environment Bill for more than 20 years, an ambitious and committed 25 Year Environment Plan, the Environment Agency’s own Strategic Monitoring Review – all could present unprecedented opportunities to overhaul the way we identify the pollutants of most concern, find and track them in the environment and take action to prevent further contamination.
So why does urban runoff persist as an almost forgotten polluter? There is no such escape for water companies, who are under increasing regulatory pressure to invest £billions in monitoring and treatment. They are already routinely controlled and face hefty penalties for breaches. Yet, just upstream of the wastewater treatment works, there could easily be an uncontrolled highway outfall releasing sediment and toxic chemicals into the same water body.
Pollutants of Concern
During peak and prolonged rainfall, rainwater washes pollutants from road surfaces into the drainage network and into receiving rivers and streams. The pollutants are primarily the result of tyre erosion, dust from brake and clutch pads, engine wear, exhaust emissions, oil and fuel leakages.
Of most concern for the aquatic environment, and for human health, are metals, particularly copper and zinc, and polyaromatic hydrocarbons (PAHs), including benzo[a]pyrene. Pervasive pollution from microplastics as a result of tyre abrasion is also a potentially major source of pollution. The metals and hydrocarbons bind to the sediment and microplastics and some metals also dissolve in the surface water. They can persist in the environment for many years.
Unfortunately, the current evidence data for runoff pollution is limited. The EA does not routinely monitor for copper, zinc and benzo[a]pyrene across the water environment in England, so elevated levels are not always recorded. Very little is yet understood about the pathways of microplastics and long-term effects of build-up and wash out in the water environment and onward into the sea.
A significant proportion of water bodies are classed by the EA as ‘Do Not Require Assessment’ (DNRA) and are given ‘good’ Water Framework Directive chemical status, even though they are not monitored at all.
However, it is likely that many failures in macro-invertebrate populations in urban rivers are, at least, partly a result of the load of toxic pollution from road runoff, but, as it is not monitored, it is impossible to accurately quantify this concern. At high-risk locations on motorways and trunk roads, the nature of the pollutants is most threatening, but in rural locations, where there is little other pollution and the flows in the streams are low, this pollution is still important.
We do know that there are more than 1 million discharges of highway runoff across the UK and, according to Highways England (HE) assessment tool (HAWRAT), more than 2500 outfalls in England pose a ‘very high’ or ‘high’ risk of pollution2.
By using HE drainage design guidelines, we can estimate that 7000 tonnes of contaminated sediment and microplastics are being washed off England’s motorways alone every year.
Monitoring and data
The EA’s State of the Nation report, referred to earlier, acknowledges that a lack of long-term data on chemical substance failures is a key challenge. Astoundingly, it also fails to call out one single action to tackle pollution from urban and transport runoff, whilst specifically highlighting actions for agricultural and sewage treatment sources.
The design criteria for highway drainage in England are based on a five-year collaborative research study by Highways Agency (now Highways England) and the EA and carried out by WRc plc from December 1997. The study showed that some discharge levels were above European Environmental Quality Standards (EQSs) at that time. Since then, laboratory technology has advanced so that pollutant levels can be measured more accurately. In 2008 the EQSs were revised and a target of 20 years was set to eliminate pollution of 33 priority substances, of which 11 are classed priority hazardous substances.So, if current EQSs were applied to the data now, there would be even more failures.
A study in Preston conducted in 2014 by the University of Salford , also found that samples of road runoff exceeded the EQS for 13 determinands and the EQS for five PAHs, including benzo[a]pyrene, were grossly exceeded.
The European Union has classified benzo[a]pyrene as a ‘Substance of Very High Concern’because of its carcinogenic and mutagenic properties and its toxicity to reproduction. Yet across England & Wales the water quality monitoring programme does not look for Priority Hazardous Substances downstream of major road runoff discharges.
Regulation and treatment
Across the devolved governments of the UK, the regulatory frameworks already exist to control discharges, but particularly in England, these powers are not being enforced, especially on motorways and trunk roads where many discharges are to vulnerable ditches and tributaries. The Environmental Permitting (England and Wales) Regulations 2016 are not being used consistently to control highway outfalls.
There has been welcome progress in surface water flood risk protection and management in the UK and Highways England 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 much more successful at controlling water quality than the other UK regions, and has a more straightforward regulatory system which simply states that highway discharges must be drained by a SuDS system that prevents pollution.
However, many more point-source discharges could be easily measured and then routinely controlled with straightforward treatment measures. There’s no doubt that both the knowledge and the treatment technologies exist to treat road runoff, ideally using Sustainable Drainage Systems (SuDS). Both vegetative and manufactured devices have their place in drainage designs to encourage biodiversity and ensure repeatable, maintainable treatment efficiency. A management train of devices works in series to manage the pollutants effectively and to keep persistent bioaccumulative chemicals out of the environment.The devices are often included together to maximise the treatment capability.
Where the runoff is grossly polluted, manufactured devices address high concentrations of pollution and can be deployed to protect the efficient operation of vegetative features. For example, they can prevent ponds from siltingup with contaminated sediment, and therefore increase the length of time between costly maintenance interventions.
A hydrodynamic vortex separator such as the SDS Aqua-Swirl™ can remove gross pollution where high pollutant loads are expected. For even more challenging sites, the SDS Aqua-FilterTMcombines the vortex separation with filtration of stormwater to deliver reliable removal of suspended solids and soluble pollutants together.
New sustainable drainage material offers simple, cost-effective and versatile method of removing toxic heavy metals pollution from highways
A new sustainable drainage material that offers a simple, cost-effective and versatile method of removing toxic heavy metals pollution from highways has been developed by SDS. Aqua-XchangeTM is a flexible and highly-efficient granular material that captures copper and zinc in surface water runoff from motorways, trunk roads and other high-traffic areas.
SDS Aqua-XchangeTM has been proven in independent testing to achieve 99% removal of dissolved copper and zinc, toxic metals identified by Highways England as ‘priority pollutants’ and subject to strict regulatory controls.
SDS worked with scientists at the University of Chester to perfect SDS Aqua-Xchange. A unique combination of naturally-occurring materials, it uses 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 heavy storms.
There has never been a better time to review the monitoring of water bodies and to take rapid action to implement more robust control and enforcement. Many will be point-source impacts that are relatively easily isolated and controlled.
The methods of controlling runoff pollution using SuDS and stormwater treatment devices are well proven and well understood and the technologies and techniques for monitoring, including real-time digital control, are advancing all the time.
There is still a great deal more we need to understand about the locations and threats of toxic pollutants in the water environment, as well as their pathways and their potential effects.Urban runoff pollution should no longer be the ‘elephant in the room’.
To heal our rivers, we have to start by looking in the right places. Otherwise, we are guilty of failing to recognise an environmental disaster because it is potentially too difficult, or too costly, to tackle.