DEPARTMENT OF CIVIL ENGINEERING ENVIRONMENTAL GEOTECHNOLOGY 2011 Case study: Remediation of contaminated land at Greenwich Peninsula By Constantinos Tsiolis Christophoros Christoudias

Contents: INTRODUCTION DESCRIPTION OF CONTAMINATION AT GREENWICH PENINSULA REMEDIATION STRATEGY AND TECHNIQUES GREENWICH PENINSULA AFTER REMEDIATION CONCLUSIONS

INTRODUCTION Greenwich Peninsula UK Millennium Exhibition Site One of the largest gasworks in Europe 1970s Contamination had occurred principally relating to : gas production tar distillation benzol plant and a chemical works Figure 0 : Location of the site

CONTAMINANTS Soil : tars, polyaromatic hydrocarbons, volatile organics (from benzol production ,tar production and distillation) Groundwater : sulphur compounds, ammonia, contaminant from the River Thames aquifer Ground gas : cyanides and heavy metals (from gas purification)

REMEDIATION STRATEGY IN ACTION The most extensive and complex remediation works were undertaken in the area of both the former tar works and a benzol plant. Environment Agency was required to evaluate the relevant environmental hazards and risks Semi-quantitative site-specific risk assessments to develop a remediation strategy: Statutory Remediation 1995-1996 (British Gas) Redevelopment Remediation (English Partnerships)

Statutory Remediation Parts Remediation Technique 1) Statutory Remediation 1995-1996 (British Gas) Statutory Remediation Parts Description Remediation Technique Tar well removal In-situ Removal of the contents, structure, and residues from the main tar well Backfilled excavation based on DTP earthworks specification. (Fig 2) Soil Vapour Extraction (SVE ) In situ The area of volatile organic compounds (VOCs) directly associated with the former benzol plant. A dual-phase Soil Vapour Extraction (SVE) was designed. (Fig 3) Groundwater treatment Four sources of water were treated. Treatment plant processes : pH adjustment=>flocculation=>pressure sand filtration=>air stripping=>biological treatment=>settlement Materials recycling, reuse and soils washing Overall, about 245 000 m3 of natural and engineering materials (e.g. concrete foundations) were recycled for backfilling excavations. The sequence of operations was generally crushing, screening and washing 245000m3 of soil.

Figure 1 : Tar well before removal Figure 2 : Removing tar Figure 3 : Soil Vapour Extraction

2) Redevelopment Remediation (English Partnership EP) Soil contamination was not justified, engineering measures are needed to protect future uses and reduce risks : Construction of clay capping system (site user protection) Placement of surfacing capping layer Capillary break layer (control movements of contaminants) Clay backfill to service trenches (material protection) Figure 4 : Protecting land

Greenwich Peninsula today

CONCLUSIONS Millennium Exhibition Site was one of the largest gas works in Europe Tar works, chemical works and power stations Contaminants in: soil, groundwater and ground gas. The principal remediation works were carried out in two phases, statutory and redevelopment. Crucial risk assessments, experienced contractor team, adopting the most suitable remediation strategy were key aspects to the success.