Using innovating treatment products for transport infrastructure project
BDB Special Projects installed SDS Aqua-Xchange™ granular treatment media into an existing filter drain along the M56 to prevent pollution of a vulnerable stream, which receives run-off from a 1km stretch of the motorway via a single outfall. Aqua-Xchange™ is designed to capture and retain copper and zinc, poisonous metals released through the abrasion of tyres and brake pads, which dissolve in surface water during heavy rain.
Balfour Beatty Mott MacDonald (BBMM) project investigation
BDB Special Projects installed SDS Aqua-Xchange™ granular treatment media into an existing filter drain along the M56 to prevent pollution of a vulnerable stream, which receives run-off from a 1km stretch of the motorway via a single outfall. Aqua-Xchange™ is designed to capture and retain copper and zinc, poisonous metals released through the abrasion of tyres and brake pads, which dissolve in surface water during heavy rain.
As part of their Highways England Area 10 maintenance contract, designers from the Balfour Beatty Mott MacDonald (BBMM) Joint Venture first investigated the potential of Aqua-Xchange™ to deal with pollution entering Mag Brook, a small stream that runs through farmland near Lymm in Cheshire. Their risk assessment revealed the need to reduce the soluble zinc content in the run-off by a minimum of 7% and the soluble copper by 52%. Water from Mag Brook flows via another stream, Bradley Brook, into a small lake known as Lymm Dam, a local nature reserve; Mag Brook is a small tributary with limited water flow to dilute the run-off from the motorway.
The filter drains that line the sides of the carriageways are stone-filled trenches that provide a highly-effective and sustainable way of capturing the suspended solids in the run-off; they are, however, not capable of capturing soluble pollutants.
THE RESULT
BBMM’s risk assessment showed that Mag Brook was vulnerable to pollution because of the high traffic volumes travelling to and from Manchester and the airport. With 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, it would have been extremely problematic to mitigate the pollution risk otherwise.
Using SDS Aqua-Xchange™ has also meant less excavation and less disruption, and there will be no need for maintenance during the 15-year design life.
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