The Challenge
The 1.6Ha site presented contaminative issues associated with varying former land uses including coal tar contamination below the former gas works area and asbestos in soils across wider areas. These required addressing to meet the Planning Conditions for the redevelopment. Geotechnically poor soils & peat also underlay much of the site and required re-engineering to facilitate the proposed development. Raising of finished levels above the flood plain created a significant material shortfall—this required on-site materials management for re-use to be optimised, as well as suitable clean fill requiring importation as a Direct Transfer under CL:AIRE Code of Practice.
Our Solution
Soilfix designed and implemented the following remediation scheme to satisfy planning requirements as well as addressing the issues of poor ground conditions and material shortfall:
- Supplementary pre-start site investigation to delineate contamination hotspots and areas of peat / soft clay;
- Controlled strip and modification of topsoil to improve its physical/chemical quality for re-use;
- Breakout of surface slabs & sub-structures, including removal of a former gasholder base;
- Targeted excavation of hydrocarbon / coal tar hotspots and effective segregation of grossly contaminated soils to minimise off-site disposal. Gross tar impacted soils were removed from site, with suitable soils cement stabilised for reuse at appropriate locations;
- Excavation and processing of Made Ground soils from the scrapyard area to remove deleterious materials, ACMs and oversize aggregates;
- Targeted excavation / segregation of peat and soft clays below road corridors and replacement with lime/cement stabilised fill for robust settlement management;
- Injection of oxygen release compounds into the base of removed contamination hotspots to achieve betterment of residual organic contaminants in groundwater; and,
- Importation of clean fill & construction of ‘hybrid’ piling platforms across proposed residential plots.
Soilfix successfully achieved the objectives of the remediation scheme to the satisfaction of the Local Authority, enabling Hill to commence construction works on programme. This was in spite of unforeseen delays experienced due to ecological constraints (nesting birds).
