THE CHALLENGE:
This split level 0.7Ha former gasworks and gasholder station was proposed for redevelopment into 111 luxury residential apartments next to Oxted Rail Station. Site investigations had identified contamination including hydrocarbons, spent oxide and foul lime. Further challenges included the requirement to remove 3nr gasholder walls / bases to a depth of up to 7.0mbgl depth in close proximity to a live railway embankment, artesian groundwater conditions , a small, logistically challenging site footprint adjacent to residential / commercial premises and a 12m fall in ground elevation across the entire site.
OUR SOLUTION:
Soilfix implemented remediation and development platform preparation scheme in full compliance with CL:AIRE Code of Practice (DoWCoP) and waste Duty of Care, to the satisfaction of the clients environmental consultants (WSP Group), the Environment Agency and Local Authority. Works included:
- Controlled breakout of a 30m diameter reinforced concrete gasholder tank & base to 7.0mbgl and two other historical gasholder bases in a complex location adjacent to an embankment owned by Network Rail —wholescale removal required due to logistical constraints;
- Significant temporary works design and implementation to facilitate the above works – this included facilitating sheet piling to form the basement walls combined with temporary slope retainment;
- Decommissioning and removal of remnant gasworks infrastructure;
- Targeted remedial excavation of grossly hydrocarbon / tar contaminated soils, subsequently disposed off-site to a permitted hazardous waste treatment facility;
- Careful segregation / disposal of material impacted with spent oxide and foul lime;
- Controlled excavation to development platform levels, segregating contaminated from inert materials, including a basement to the lower block. Significant de-watering and treatment required to facilitate deeper excavation during basement excavation and ongoing piling works;
- Stabilisation treatment of site won material to provide a more sustainable working platform solution across the site to enable both sheet-piling and CFA piling. This was combined with traditional crushed concrete platforms and use of geo-grids;
- Off-site disposal of surplus segregated, pre-treated materials arising from reduced level excavation as non-hazardous and inert waste, fully in accordance with Duty of Care; and,
- Attendances to all piling operations, including disposal of CFA pile arisings off-site.
Soilfix successfully achieved all contracted remediation and enabling works objectives despite poorer ground conditions than anticipated, significant unforeseen groundwater ingress and overlapping with piling operations on a logistically challenging site.
Minimal complaints were received by local residents during the works – even during removal of the tar tank and odorous gasworks contamination where potential for fugitive odours/vapours was significant greater.
