THE CHALLENGE:
A 21-acre portion of a wider, large redevelopment site comprised extensive concrete racetracks, car storage yard and 30,000m3 of surrounding soil ‘viewing bunds’. Site investigations identified significant deleterious materials (including spent tyres) within the cohesive soil bunds, areas of hydrocarbon, widespread asbestos containing materials (ACM’s) and localised Japanese Knotweed (JK) stands. There was also a high risk of buried tyres impeding development, and the site was situated directly adjacent to ancient woodland (with protected dormice and badger setts) that required careful consideration and sequencing of mitigation measures, working alongside CALA’s retained ecologists.
OUR SOLUTION:
Soilfix provided CALA with early contractor involvement (ECI) support pre / post land acquisition to develop a sustainable and cost-effective site preparation and remediation scheme that retained as much material on-site as practicable – significant off-site disposal costs would have rendered the development commercially non-viable. Through advanced planning of materials management, working in conjunction with CALA’s engineering consultants, Soilfix developed a strategy for re-using processed bund material that could not be accommodated across the development area. The optimal and most sustainable solution, agreed with regulators, was to construct a large Noise Attenuation Mound (NAM) along the busy A27 highway situated to the immediate north of the development.
Site remediation and enabling earthworks, carried out under a Materials Management Plan developed in full accordance with CL:AIRE Code of Practice, comprised:
- Targeted excavation and ex-situ bioremediation of hydrocarbon hotspots;
- Targeted excavation, hand-picking and encapsulation of JK impacted soils within a root barrier cell—warranted with a 10yr insurance-backed guarantee;
- Site-wide turnover to a depth of 2m below existing ground level, with any obstructions encountered removed (including extensive buried tyre pits);
- Segregated tyres (over 1,000m3) pre-processed to remove excess soil for removal off-site by CALA’s waste contractor;
- Further modular processing of segregated mid-range aggregates using a covered picking station to remove plastics and cement-bound ACM’s using certified asbestos operatives— over 2 tonnes of ACM bagged for hazardous waste removal;
- Processing of >10,000 tonnes site-won aggregate to a 6F2 specification for re-use by CALA;
- Gross ACM impacted soils segregated and removed off-site as hazardous waste;
- Earthworks to create a large noise attenuation mound (NAM) along the A27 highway using site-won screened fill, capped with site-won topsoil stripped from the field;
- Soil stabilisation for geotechnical improvement along proposed road corridors; and,
- Site-wide regrade using GPS enabled plant to development platform levels.
In spite of two periods of exceptionally inclement (wet) weather, all works were completed on programme and under budget with zero lost time accidents. Out of a total 60,000m3 of materials arising from surface hardstands, bund processing and reduced level excavation, only 1,500m3 of unsuitable materials (segregated tyres, general waste, timber, metal & asbestos containing materials) were removed off-site, resulting in >97% materials re-use, fully in accordance with CL:AIRE DoWCoP.
