Remediation techniques
The site was acquired in July 2007 by the London Development Agency, and the ODA is completing the remediation of the site on their behalf. Since July 2007, over 215 buildings have been demolished, 90 per cent of the site has been cleared and over 1.3 million cubic metres of soil excavated. The site has historically been used for a range of uses including light retail and heavy industrial processes. The majority of the area being excavated consisted of made ground as a result of land reclamation of the old marshes in Victorian Times or early industrial revolution and land raising over the last 50 years.{mosimage}
The project aims to use sustainable treatment technologies, minimise disposal to landfill, recover materials for beneficial re-use within the project and to support legacy development. A co-ordinated parkwide approach has been adopted, allowing efficient logistics and flexibility, while supporting one of the most challenging construction programmes in the history of the United Kingdom.
As a result a range of treatment technologies are being utilised to successfully achieve these goals:
• Soil washing
• Chemical stabilisation
• Geotechnical stabilisation/solidification
• Bioremediation
• Complex sorting
• Simple/primary screening
• Crushing
• Invasive species treatment and on-site
burial
• Various groundwater approaches include
• In-situ pump and treat groundwater
• Hydraulic containment
• Chemical oxidation injection
• Chemical treatment by micro-organisms
The listed treatments required vary across the park on a site specific need and offer tailored solutions to the site specific requirements.{mosimage}
The Olympic Park Project is the first to design, procure and maintain a soil treatment centre (HUB) within the United Kingdom, dedicated to receiving and cleaning/recycling site derived materials from within the park’s multiple construction zones, for the sustainable reuse of engineering products and fill.
Materials are received from site demolition, site clearance, earthworks and remediation excavation works from within the multiple construction zones across the Olympic Park. Due to the sheer size of the park, Enabling Works Program has divided the site into two specified principal contractor areas (North and South) each with their dedicated treatment centre, but with the ability to share resources for both treatment and supply of suitable recycled materials/fill.
By bringing together specialist designers and contractors to undertake appropriate site risk assessments and soil reuse criteria, together with setting up and maintaining centralised treatment centres, the scheme has allowed for the maximum recycling of site derived soils and hard materials. Material recycling and reuse on the park, has so far exceeded best practice within remediation projects, achieving reuse targets in excess of 85 per cent of soils from excavations and more than 90 per cent reuse from demolition and site clearance hard materials.
Demolition materials in the form of brick and concrete are recycled to their maximum extent and value, using a combination of crushing and screening on the site, rendering the materials suitable as an engineering class of material/fill.{mosimage}
Site clearance materials in the form of soft landscape, topsoil and foliage, including invasive species, for hard landscape pavements (in concrete and blacktop) are processed on the site to maximize their reuse, or sent off site for recycling into new tarmacadam and compost/chippings.
Earthworks and soil remediation derived materials are both chemically and geotechnically assessed and classified, by the site specialist teams made up of consultants, project managers and specialist contractors. The teams have been so designed and procured to provide the most cost effective and sustainable expertise to optimise the treatment processes for the site-derived materials.
The team also provides the expertise to develop and blend the cleaned material’s outputs to generate engineering class material suitable for the follow-on construction.
Optimisation of the design through procurement and early specialist involvement
The treatment centre waste processing streams have been designed with close liaison, early involvement within the decision making process and interaction during procurement with the engaged specialist contractors.
The treatment centres were set up as a single soil washing plant in July 2007 and the main HUBs followed in January 2008, with soil washing and soil stabilisation equipment common to both sections of the site. One bioremediation bio-pile system was procured in the south of the site.
The material processes used within the soil treatment centres
All site-derived and excavated materials are firstly pre-screened to remove any biodegradable, oversized (<125mm should this be >125mm?) and metallic objects. All site-derived soils which have been classified with chemical exceedences are screened to less than 50mm, in order to allow for the screened soils to pass through secondary chemical treatment plants.
Five soil washing plants have been brought together on the park; this is the first time that so many processing plants have been brought together for a single scheme within the United Kingdom. The plants have been designed to treat around 1.5 million cubic meters of granular soils, using physico-chemical technology to remove a wide range of contaminants including organic such as TPH and PAH and inorganic such as heavy metals, arsenic and cyanides. So far over 500,000 cubic meters of site derived soils have been recycled through soil washing plants, with 180,000 cubic meters still to process from enabling works and around 200,000 cubic meters from the follow-on construction works.{mosimage}
Four output materials are produced from the soil washing plants - sands (>2mm, generally 40 per cent), gravel (<50mm, generally between 45 and 50 per cent), fine silts and clays as filter cake (waste, generally between 15 and 18 per cent) and fine/coarse organic matter and ashes/coke materials (waste, generally between 2 and 5 per cent). (Query – the composition of the output adds up to a minimum of 102%, max 113% - do you want to revise sand to ‘around 40 per cent?)
The design of the soil washing plants has been continuously under review, as the site-derived materials have varied from within the park enabling works. The plants have required high levels of technical support and backup laboratory trials from the specialist supporting teams to provide either advice and recommendations for site modifications within the plant equipment, or changes in water flush rates/volumes and modifications in the density separation additives used within the process.
The use of both external electromagnetic belts and magnetic drums are used to fine tune the output materials, in order to render them suitable for the variety of materials used as general fill, specific engineering class fill (CLASS 1a, 6F, 6N) and cover or break layer materials protective of the final intended land use.{mosimage}
Fine grained derived materials from the enabling works have been processed through one of the two ex-situ batch
pugmills, primarily for soil stabilisation of chemical contaminants using proprietary and specialised reagents to produce chemically stable constituents/materials.
The soil stabilisation equipment, is also available for soil for material strength enhancing using reagents and/or cement. Chemical soil stabilisation has to date processed 49,000 cubic meters of site derived soils, with around 10,000 cubic meters still to process from enabling works and 50,000 cubic meters from the followon construction works. Soil stabilisation of river silts and soft alluvium, for material strength enhancement is also being undertaken using in-situ techniques, with up to three specialist Wirgen machines. So far over 120,000 cubic meters of site derived soils
have been geotechnically stabilised, with around 20,000 cubic meters still to process.
Ground conditions within one construction zone within the north of the park, encountered an historical landfill, originating in Victorian times and active up until the 1960’s. Excavated materials required sorting on a complex level, prior to any main treatment of the soils to render them suitable for reuse as an engineered fill.
The complex sorting machinery was procured making careful consultation and use of the specialist contractor, who designed the combination of equipment uniquely for the site conditions. The equipment uses vibrating screens to separate the soil from the general landfill materials, before using belt electromagnets to remove materials and then pass them through a manual picking zone to undertake a final visual separation. The process has subsequently been refined and used for the manual abstraction of low grade exempt radiological wastes and asbestos materials.
One bioremediation system has been established in the south treatment centre to allow for the processing of soft alluvium or cohesive materials with principally hydrocarbon (organic) exceedence values in contamination. So far over 10,000 cubic meters of site derived soils have been bioremediated, with around 4,000 cubic meters still to process.
The works have also encountered invasive species in the form of Japanese Knotweed, Giant Hogweed, Himalayan Balsam and floating Penny Wort.
The works have undertaken a carefully designed sequence of treatments over the park, including spraying and controlled removal, together with excavation and burial within a root barrier containment system within the park. A specialist horticultural management contractor has been procured to recycle around 28,000 cubic meters of topsoil and sub-soils, also overseeing the design, burial and containment of 40,000 cubic meters of chemically contaminated excavation arisings, also containing Knotweed. Less than 3 per cent of soils infected by invasive species have been sent to appropriate licensed landfill.
Remediation processes for groundwater improvement
A number of groundwater improvement schemes are currently proposed within the park, to address local groundwater impacted with specific contaminants of concern. The methodologies adopted include containment by physical (below ground) structures and groundwater control by pumping; abstraction of light and dense free-phase hydrocarbons (NAPL); treatment of abstracted water by filtration, air stripping, granular activated carbon and micro-organisms; and injection of slow and quick release oxidising chemicals. In addition to these remedial treatments, locally deep basement construction is also requiring localised groundwater control by deep sumps and well-point systems.{mosimage}
Containment by installing a recirculating pump and reinjection system, has been designed to abstract shallow groundwater from the terrace gravels and treat the abstracted water for, principally, ammonia (seeding with Archaea microbes) and hydrocarbons (through skimming tanks and activated carbon filters), prior to around a third of the water being locally reinjected and the remainder disposed to combined sewer. The system will temporarily reverse the local existing groundwater gradient which flows towards the adjacent river courses. Physical containment in the form of both sheet and concrete pile walls are being used to control pathways and enhance groundwater treatment and improvement.{mosimage}
Both light and dense hydrocarbon skimming/abstraction systems are also being used for the abstraction of shallow and
deep groundwaters. In some instances the abstraction is combined with secondary injection of oxygen release compounds (ORC) in order to enhance natural attenuation of any residual contamination after primary treatment. A further scheme incorporating both passive collector drain and shallow in-ground physical barrier is also being considered, where perched water has been assessed to potentially impact upon the adjacent surface water course.
Summary
The combination of a range of treatment technologies has resulted in over 500,000 cubic metres of for processing in the last seven months, with around 300,000 cubic metres still to be processed in a sustainable and cost effective manner.
The stadium and aquatics sites have been delivered three months early and groundworks continue, leading to completion of platforms for the remaining venues. Bringing the design consultants, principal contractors, specialist treatment contractors and the regulators together from an early stage of the project, allows this prestigious project to fulfill the project objectives and goals.
The local community has been continuously engaged through a consultation, communication and engagement programme that has included meetings, workshops, drop-in sessions, educational activities for young people, newsletters and a dedicated website to inform of progress and to hear views and issues as they arise.
