Sustainable drainage system cleans up stretch of M56

A sustainable drainage system, which can protect water from toxic metals, has been installed on a busy stretch of the M56 motorway.

The SDS Aqua-Xchange system, which has been developed by SDS, turns roadside filter drains into treatment devices.

Contractors BDB Special Projects installed the new granular treatment system into an existing filter drain along the M56 to prevent pollution of a vulnerable Cheshire stream, which receives runoff from a 1 kilometre stretch of the motorway via a single outfall.

It could now be installed into many hundreds of kilometres of existing filter drains that flank motorways and trunk roads across the country.

Highways England has identified 2,500 high-risk pollution locations as part of its ongoing Priority Outfall Programme and is looking for practical and affordable treatment solutions.  

As part of the continuous improvement programme for the Highways England Area 10, a study was completed of the Mag Brook outfall, a small tributary that runs through farmland to the south of Lymm.

Water from Mag Brook flows via another stream, Bradley Brook, into a small lake known as Lymm Dam, a popular local beauty spot and nature reserve. 

“The risk assessment revealed the stream was vulnerable to pollution because of the high traffic volumes travelling to and from Manchester and the airport,” said SDS market development manager and water quality specialist, Jo Bradley.

“There was very little water flow in the brook to dilute the runoff from the motorway. It confirmed a treatment scheme was needed to clean the water significantly, reducing both the soluble copper and zinc levels to bring them within permitted levels.

“There was no space to build SuDS ponds or other vegetative features behind the carriageway to treat the metals, or to install a manufactured stormwater filter to capture the pollutants.  So, it would have been extremely problematic to mitigate the pollution risk otherwise.  Using SDS Aqua-Xchange also meant less excavation and less disruption. There will also be no need for maintenance during the 12 to 15 years design life.”

Ben Dobson, director of BDB added: “We were able to complete the works during ten overnight closures, with minimal disruption to the travelling public. 

“Through our experience in filter drain refurbishment works, we understand that detailed planning of the logistics is key to successful and safe delivery. By making a few small changes, introducing Aqua-Xchange into the process became seamless, leading to efficient outputs not dissimilar to traditional filter drain replacement methods.”