Sustainable development is a key element of CTRL. Bruno Guillaume looks at some of the regeneration challenges on Section 2.
Stratford Contamination of the Stratford railway lands is the result of more than 150 years of railway yards, including a small gas works, a power station, metal workings, foundries, coal stores and oil stores.
Principles of sustainable development are being applied to construction of the massive box for Stratford international station which involves raising the surrounding area by about 7m over 50ha of contaminated land using material excavated from the box and the tunnels east and west of it.
Desk studies identified potentially contaminating land uses over the entire site. Geology comprises made ground, alluvium and terrace gravels (the upper aquifer), the Lambeth Group (a non-aquifer), and Thanet Sand and Upper Chalk (the lower aquifer).
Ground investigations revealed the made ground typically comprised black ash, sand and clinker contaminated by heavy metals and occasionally by hydrocarbons. Two major 'hot spots' of significant hydrocarbon contamination were identified in an area formerly used for the gasworks and an area used for refuelling operations.
Monitoring of groundwater quality by RLE, carried out for both aquifers, confirmed that the upper aquifer was contaminated with polyaromatic hydrocarbons and diesel range organic compounds associated with the gasworks and the refuelling area.
However, monitoring showed the heavy metal concentrations in both aquifers were below the levels specified for drinking water.
RLE carried out a risk assessment in accordance with statutory guidance, which confirmed the need to treat hydrocarbon contamination affecting groundwater quality. However, heavy metal contamination appeared to be of low solubility and mobility and therefore did not affect groundwater.
It was clear that by placing 7m of spoil over most of the site - using 'acceptable' spoil from the box and tunnels - the risk of contaminants adversely affecting humans at the new ground level would be removed, because the pathway between hazards and receptors would be removed.
Remedial objectives for hydrocarbon contamination were derived using Environment Agency guidance to protect groundwater resources. Remedial works are being undertaken by Skanska Construction using exsitu treatment involving bioremediation of the soils in a 'biopile' and the removal of free hydrocarbons floating on groundwater.
More than 400,000 litres of free hydrocarbons - mostly weathered diesel - have been pumped out of the ground from drainage trenches. Around 20,000m 3of soil has been excavated and transported to the biopile, ready for treatment. The biopile will be operated by remediation contractor Biogénie under contract to Skanska. It is anticipated that 65,000m 3of soil will need to be treated, and that this will take four months. Treated soil will then be incorporated into the land raise.
Remedial works are not only being scrutinised by the EA, but also by the local authority, the London Borough of Newham - which is exercising its new obligations under Part IIA of the Environment Protection Act - and future developers of the site.
London and Continental Railways will work with developers Stanhope and Chelsfield to develop the lands once the land raise has been completed. Regular meetings are held by RLE with all parties.
By retaining soils on site and treating contamination with bioremediation, the best environmental solution will be attained.
Site redevelopment will bring social and economic benefits to the Stratford area and a sustainability 'win-win'.
Ebbsfleet and Swanscombe Both Contracts 320 (Thames Tunnel) and C342 (Ebbsfleet civil works) are affected by landfill sites. The southern portal of the Thames Tunnel lies within the boundary of a landfill site, albeit outside the zones where waste has been deposited. In the Ebbsfleet valley, the route crosses the tip of two landfill sites which have taken domestic and industrial waste.
Landfill sites are regulated by the EA and hence close cooperation is required by RLE and its contractors with the agency to ensure that there is no compromise of liabilities associated with waste management.
Both the Swanscombe Marshes Landfill on C320 and the Northfleet Landfill on C342 are owned by Blue Circle Industries (BCI) with which Union Railways and RLE have been in talks since early on in the project.
The Swanscombe Marshes Landfill is licensed to receive cement kiln dust and inert industrial waste from the Northfleet cement works. It is divided into three sections and the third of these, where waste has not been deposited, is the site of the Thames Tunnel southern portal and approach structures.
RLE and contractor, HochtiefMurphy JV, prepared a working plan in consultation with BCI for approval by the EA. This identified all work intended under the contract and presented a risk assessment of this work to enable the environmental liabilities associated with the CTRL contract to be differentiated from those associated with the landfill.
The Northfleet Landfill took domestic waste and has recently been re-opened to receive non-special waste of contaminated soil. The CTRL alignment crosses the tip of the landfill and negotiations were undertaken by RLE with both BCI and its landfill operator, Jayflex, to relocate the waste - about 60,000m 3- within the landfill. Consent was required from both the EA and Kent County Council: the Agency had to approve the working plan and the local authority had to modify the planning conditions before waste could be moved.
The relocation of waste within the Northfleet Landfill clearly presents an environmental benefit from reduced lorry movements, but it has also saved the project about £1.3M for Landfill Tax.
Bruno Guillaume RLE lead contaminated land specialist