Water & Wastewater Treatment

WWT September 2017

Water & Wastewater Treatment Magazine

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Page 27 of 43

28 | SEPTEMBER 2017 | WWT | www.wwtonline.co.uk Q: How eff ective is regulation? A: There is a patchwork of regulations covering the devolved regions of the UK, which is enforced to a lesser, or greater, degree. Scotland is the most advanced, and successful, in applying Sustainable Drainage Systems (SuDS) under the Water Environment (Controlled Activities) Regulations (2011). SuDS are common on runoff outfalls and there is an extensive network of fi lter drains across the road network. In England and Wales, the Environmental Permitting Regulations (2016) give the regulators powers to require highways authorities to apply for a permit where there is a risk of water or groundwater pollution. In practice, the regulators mostly rely on voluntary improvements and, while it's encouraging that treatment schemes are being introduced on the highest risk outfalls without permits, such interventions are limited and Q: What is the extent of the water pollution? A: A key challenge is that the data used to show levels of current pollution is limited and there is little evidence of its cumulative eff ects. For example, in England the EA does not routinely monitor for benzo[a] pyrene in the water environment. However, the Highways Agency Water Risk Assessment Tool (HAWRAT) was developed as a model to remove the need for expensive and time-consuming monitoring and to indicate a risk of failure of water quality thresholds. HAWRAT concludes that more than 2500 outfalls in England pose a very high or high risk of pollution. Assuming the outputs from the model are reliable, the risk of water pollution is very real and extensive. Q: Who is responsible? A: Ownership of highway outfalls in the UK is spread across Highways England, Transport Scotland, the Welsh Government, Transport Northern Ireland, local highways authorities, private land owners and Water and Sewerage Companies (WASCs). In urban areas, runoff from local authority roads frequently ends up in a surface water sewer owned by the WASC. Vehicle manufacturers, road users and governments all have a responsibility to take steps to reduce the pollution being generated in the fi rst place. The introduction of hybrid and electric vehicles, for example, will reduce the levels of pollution from hydrocarbons. The Knowledge Getting to Grips with... highway pollution inconsistent and no monitoring is taking place to see if they are adequate. Q: What treatment so- lutions are available? A: When people think of SuDS, they tend to think of vegetative, above-ground features. However, a well- designed SuDS scheme for highway runoff will include a selection of SuDS devices which encompass a toolbox of above and below-ground components, engineered to meet the water volumes, fl ows and level of pollution appropriate to the site. SuDS designs should consider vegetative devices initially because of the advantages to biodiversity. Features like fi lter drains, ponds, swales and detention basins can sometimes be eff ective in slowing fl ows and capturing pollutants individually but, in other cases, a management train of SuDS components may be needed. For example, where the highway runoff is grossly polluted, or where space is at a premium, manufactured devices, such as vortex separators, address high concentrations of gross pollution including litter, debris and high sediment loads. They can facilitate the use of vegetative devices and protect their effi cient operation. For example, installing an SDS Aqua-Swirl prevents ponds from fi lling with contaminated sediment and protects sediment forebays at the inlet from clogging. Q: How much mainte- nance is required? A: Insuffi cient maintenance can be the 'Achilles heel' of SuDS and it is essential that every device, whether vegetative or manufactured, is maintained and operated properly, or it will quickly become ineff ective. Manufactured devices off er the advantage of predictable maintenance regimes as well as measured and proven performance. Under fi eld test conditions completed in 2012, the SDS Aqua-Swirl achieved 80% removal of total suspended solids, where a large unit was installed to allow for infrequent, large storm events. When smaller units are installed to treat more frequent, smaller rainfall events, removal effi ciencies of 50% total suspended solids are achieved and off er a signifi cant improvement in runoff quality. On more challenging sites, or where space is at a premium, a hydrodynamic vortex separation and fi ltration system, such as the SDS Aqua-Filter, can be installed to reduce the copper and zinc pollutant load. Q: What happens next? A: While Westminster has been preoccupied with legislating for SuDS in new development through planning, more stringent regulation and penalties are routinely applied to control water quality discharges by WaSCs from wastewater treatment. As we move towards developing a new legal framework and a 25- year plan for the environment post-Brexit, improved monitoring and control of highways must be a priority. About the author: Before joining SDS, Jo Bradley worked for much of her 25-year career at the Environment Agency, identifying and preventing pollution in highway run-off . Motorway outfalls mean that highway run-off can o en be a point source, rather than a diff use, pollution problem The SDS Aqua-Filter. Manufactured devices can play a key part in the SuDS toolbox

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