THE CHALLENGE:
This 0.7Ha former gasworks and gasholder station was proposed for redevelopment into 81 residential apartments close to the River Arun. Site investigations had identified contamination including coal tar residues, spent oxide and asbestos cement fragments. A further challenge was presented by groundwater below the site being tidally influenced and underlying chalk deposits designated a Principal Aquifer. The site had previously been remediated to an ‘Open Storage’ standard, however further remediation was required to render the site suitable to for residential end-use.
Additionally, significant variations in site formation level were required to create an upper pile platform adjacent to an undercroft parking ‘flood storage’ zone with underlying stormwater attenuation to be constructed. This created a significant challenge for materials management due to a calculated net surplus, and the client’s preference to not remove any hazardous classified soils during ongoing construction.
OUR SOLUTION:
Soilfix implemented remediation and development platform preparation scheme in full compliance with CL:AIRE Code of Practice and Waste Duty of Care, to the satisfaction of the retained environmental consultant (RSK), the EA and Local Authority. Works included:
- Careful site strip to recover Type 1 aggregates previously placed across the site, followed by a site-wide turnover to identify remnant obstructions and contaminated materials;
- Controlled excavation and breakout of 3nr gasholder bases plus a tar liquor tank, removing remnant pipework and other gasworks infrastructure;
- Significant temporary works design and implementation to facilitate the above works;
- Targeted excavation of soils previously subjected to stabilisation/solidification treatment and additional identified areas of gross hydrocarbon / tar impacted soils;
- Tanker recovery of hydrocarbon impacted shallow groundwater to facilitate deep excavation and promote betterment—removed to off-site permitted treatment facility;
- Supplementary stabilisation/solidification treatment on all coal-tar impacted soils to meet leachate criteria agreed with the EA, strategically backfilling in areas not to be disturbed during future works;
- Screening/sorting of excavated Made Ground to segregate oversize for recycling with broken out obstructions;
- Construction of split level ’hybrid’ pile platforms with access ramp for the pile rig comprising 2x layers cement stabilised soil, geo-grid reinforcement and protective crushed aggregate running layer. Completed and validated to a Temporary Works Design completed to FPS requirements; and,
- Off-site disposal of gross tar impacted materials, surplus non-hazardous and inert classified soils.
Soilfix successfully achieved all contracted remediation and enabling works objectives to facilitate the client’s construction programme, despite significant excavation and processing requirements (8,000m3) on a small, logistically challenging site. Stringent environmental monitoring & controls (in particular odours) and proactive communication with adjacent site residents was required to mitigate significant complaints.
