THE CHALLENGE:
Comprehensive soil & groundwater remediation works were required to enable redevelopment of the 0.3Ha site to 21nr affordable residential houses / apartments. Localised areas of gross hydrocarbon contamination were present together with a smear zone and significant dissolved TPH in groundwater across the majority of the site. Geotechnically poor ground conditions also presented a significant challenge.
Consultants initially advising the prospective Affordable Housing provider concluded the only option to remediate the site was to carry out wholescale excavation and disposal of contaminated soils to below the water table, rendering the scheme economically non-viable. Soilfix therefore proposed a more practical sustainable and cost-effective remediation solution to mitigate risks to controlled waters using predominantly in-situ based methods.
OUR SOLUTION:
Soilfix carried out the following remediation and enabling works to the satisfaction of the Environment Agency, fully in accordance with CL:AIRE Code of Practice:
- Removal of surface hard standing and controlled grubbing out of in-ground obstructions following site turnover—processing hardcore to 6F2 specification;
- Decommissioning and removal of underground fuel storage tank & infrastructure;
- Targeted excavation and on-site bioremediation of hydrocarbon impacted soils;
- Backfilling and re-engineering geotechnically poor soils using lime/cement stabilisation techniques, with a working platform for future piling operations constructed;
- Installation of groundwater recovery sumps using rotary drilling techniques, and groundwater injection ‘pre-wells’ using more rapid sonic drilling techniques;
- Injection of a chemical oxidant (Regenox PetrocleanzeTM) over 3 campaigns to promote surfactant flushing of residual free-phase hydrocarbon contamination and betterment of residual dissolved phase concentrations to meet the objectives agreed with the EA (no measurable NAPL and >70% betterment of recorded TPH in groundwater during post-completion monitoring); and,
- Periodic pumping and off-site disposal of groundwater / product from remediation wells.
Soilfix successfully achieved all contract requirements on programme and to budget despite extremely poor ground conditions and widespread TPH contamination. Out of 2,750m3 materials generated, 100% materials recovery was achieved during the project. The required betterment of dissolved TPH concentrations was comfortably met during post-completion monitoring, with an overall reduction of 85% achieved.
