Northampton is within one of four major growth areas identified in the Government’s 2003 “Sustainable Communities Plan”. The two former landfill sites of Sixfields and Harvey Reeves Road had been identified as key areas for redevelopment. Remediation of the sites was necessary to protect the local surface waters and groundwater from the impact of landfill leachate.
The site is essentially a combination of two former landfill sites located to the west of Northampton city centre.
Halcrow carried out comprehensive site investigations on both sites and identified serious groundwater contamination which was considered to be a significant risk to controlled waters (in particular the River Nene which is in close proximity to the landfill sites.
Groundwater contamination was considered to be the largest challenge facing the development of the Sixfields and Harvey Reeves Road sites. The site contamination was very diverse in nature reflecting the historical landfilling activities – the contaminants of concern included ammoniacal nitrogen, arsenic, iron, manganese, nickel, total petroleum and polyaromatic hydrocarbons.
Removal of the source contamination was considered to be impractical and prohibitively expensive. A pump and treat system was also considered – this would have necessitated sealing off the sites with a low permeability barrier in order to ensure that water ingress was prevented – this option was also considered to be impracticable and would have adversely affected the natural groundwater regime in the area.
The preferred remediation solution was the installation of reactive barrier systems designed to intercept groundwater contamination migrating from the site in the direction of the River Nene. The barrier system for each landfill site was designed to have a minimal impact on the natural groundwater regime.
The barrier systems comprised of permeable reactive barrier [active] sections to intercept groundwater and low permeability [passive] sections to channel groundwater in the direction of the permeable reactive sections.