The Challenge
The 8Ha Tipner East site has had a long history of reclamation and industrial land-use on the banks of Tipner Lakes, a RAMSAR protected SSSI and has remained undevelopable for a significant period of time. Comprehensive soil and groundwater remediation was required to address gross contamination was required to render the site ‘suitable for use’ and facilitate ongoing safe construction. Phase 1 Remediation was completed for the private landowner (TRC), as a precursor to Phase 2 Remediation & Enabling Works carried out on behalf of PMC Construction acting for Vivid Housing Association.
Our Solution
Soilfix designed and implemented the following Phase 1 remediation works over a 28 week period, fully in accordance with CL:ARE Code of Practice:
- Installation of a 325m long cement bentonite cutoff barrier to 7.0mbgl in advance of main remediation works phase—full CQA testing carried out;
- Installation of 250m of sheet piled retainment to facilitate deep excavations;
- Breakout and processing of over 7,500m3 slabs & sub-structures across the site to facilitate future construction;
- Excavation, pre-processing and ex-situ bioremediation of 26,000m3 hydrocarbon / tar impacted soils from across the site to depths up to 6.0mbgl. On-site feasibility trials carried out to optimise the soil treatment approach;
- Modular processing of an additional 60,000m3 geotechnically poor fill materials segregated during site regrade, remedial excavations, obstructions removal and clean corridors construction;
- Lime/cement stabilisation/solidification of 80,000m3 soils (processed and/or bio-treated) to mitigate residual risks to controlled waters – this included formation of substantial low-permeability barriers around large portions of the site boundary (tied in to the slurry cutoff barrier);
- Exposure and breakout / removal of over 20nr submerged barges forming part of the RAMSAR protected foreshore – often in tidal conditions;
- Comprehensive groundwater pumping & treatment on-site prior to discharge to foul sewer – over 20 million litres of water treated;
- Targeted excavation, hand-picking and on-site encapsulation of Japanese Knotweed infested soils with a full Insurance-backed Guarantee;
- Excavation of made ground and backfilling with 20,000m3 of clean inert material to form clean service corridors across main spine roads;
- Formation of hybrid pile platforms along the entire foreshore (to be sheet piled) and for the development blocks across the site;
- Implementing various temporary environmental protection works to protect key receptors (in particular Tipner Lakes) between remediation phases; and,
- Comprehensive environmental monitoring & controls, in particular focus on VOC / odour emissions due to the presence of gross contamination by coal-tars, cresols and phenols.
Soilfix successfully completed both phases of remediation with zero lost time accidents and all Remediation Strategy objectives completed to the satisfaction of Portsmouth City Council and the Environment Agency.
