Cleaner run-off water from highway construction projects

| Water Management

Siltbuster system for treating construction water run-off

Road constructors are meeting Environment Agency water run-off cleanliness criteria using surface water decontamination technology.

Siltbuster is helping to prevent water pollution on highway construction projects across the UK. Currently used on five dual carriageway sites in Aberdeen, Cambridgeshire, Cornwall, Manchester and South Wales, the company’s technology is aiding contractors by decontaminating surface water run-off, meaning it can be safely discharged into local watercourses.

In the case of the 10km Manchester Airport Relief Road where soil stripping has exposed areas of clay, periods of heavy rain resulted in run-off collecting slow settling solids. Within a week of being contacted by Morgan Sindall, the main contractor for the project, Siltbuster had installed the first of ten portable lamella clarifiers at the site, treating up to 200 cubic meters of the contaminated water per hour.

Chemical coagulation

The clarifiers used a chemical dosing system to coagulate the solids, making them large enough to be separated and remove leaving the water clean enough to meet the Environment Agency’s strict discharge standards. Bringing further environmental benefit to the project, the resulting sludge was moved to storage lagoons where it was left to dry out before being used in the restoration and landscaping of the site.

Dr Richard Coulton, CEO of Siltbuster Group, comments: “We initially installed one system onsite but, having seen first-hand how well the technology works, our client quickly requested nine more. The clarifiers were strategically placed along the site at points where significant volumes of surface water were collecting or where streams ran close to the works, enabling us to ensure that no contaminated water entered the local watercourses.”

Cleaner run-off in Bodmin

In Cornwall, where a 2.8 mile stretch of the A30 near Bodmin has been widened, Siltbuster was called in to help with two large attenuation lagoons that were capturing surface run-off. The lagoons contained very slow settling solids, with little to no settlement being observed over an extended period of time. To enable the most accurate diagnosis, samples were taken from the water and analysed at Siltbuster’s laboratory enabling experts to develop a bespoke treatment system.

As a result, Siltbuster deployed two 3-stage 4-40m3/hr chemical treatment systems. Using its unique water treatment systems, which have been on site for over 12 months, Siltbuster has been able to increase the particle settling rate and clean the water via gravity separation techniques.

The discharge criteria Siltbuster had to achieve was a Total Suspended Solids (TSS) content of less than 30mg/l and a pH level of between 6 and 9 – both of which have been met. In fact, thanks to Siltbuster’s monitoring system, the feed pump will switch off if the discharge waters exceed the predetermined discharge criteria. In total, the flow treated onsite to date is 55,000m3.

Maintaining pH levels

One challenge experienced onsite was keeping the pH level within the permitted range as local lime stabilisation works made the pH of the incoming waters increase to 11-12. As a result, Siltbuster had to introduce a CO2 dosing stage into its system, which was set-up and fully functional within two working days. The CO2 was used to reduce the pH to neutral prior to the water’s discharge from the site.

Dr Richard Coulton, continues: “Both these projects differed in their initial brief, but had similar overall objectives – to decontaminate water and ensure that discharge standards were met. As with any project, we analysed the problems and created bespoke solutions, ensuring that the water was cleaned to the highest standards. Whether it is removing clay particles or balancing the pH levels of water discharge, our goal is always the same – make the water free from pollutants and safe for its release back into the local area.”

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