This selected site is located at former rail sidings containing contaminated soils. As such, a Polypipe Civils & Green Urbanisation [Polypipe CGU] Permavoid shallow depth solution was promoted by SEL to replace the compliant ‘big tank’ solution to provide water treatment, management and storage below the site’s car park, access road and service yard, while capturing and treating oils contained within the surface water run-off.
A Permavoid sub-base replacement system was selected to be installed within 500mm of finished ground level, ensuring excavation within the contaminated soils was significantly minimised and potentially expensive pumping equipment was not needed.
Permavoid cells lock together to form an interlocking raft of exceptional high compressive and tensile strength, allowing it to be used to support structural loads in heavily trafficked areas. Given the volume of contrete being produced and distributed at the Trackwork Moll site, and the level of traffic necessary in the supply chain of such a product, the Permavoid system made perfect sense for this project.
As well as storing the surface water run-off, the Permavoid system also provides an effective method of source control. The Polypipe CGU engineers recommended the use of Permavoid cells which contain an oil-treating geosynthetic layer that floats on water and is designed to intercept and treat potential residual oils that may be present within emulsified surface water.
A further pollution management measure was specified in the form of Permachannel. Designed to work in harmony with Permavoid systems, Permachannel acts as a separation device at source to prevent silt and oils from progressing beyond the Permachannel into the Permavoid storage system.