Boring Waste Management Story at Europes Largest Construction Project - Crossrail

Some 6 million tonne of tunneling waste, known as spoil, from Europe’s largest construction project currently taking place under the streets of London. In order that this material can be recycled to create an RSPB bird sanctuary it must be carefully assessed for contaminants. The Crossrail project is creating 42km of new East/West underground tunnels and nine new stations – the London’s first completely new underground line in three decades. As a by-product of the construction work, approximately 6 million tonnes of spoil will be created. However, this will not go to waste however, with approximately two million tonnes being recycled for use at Wallasea Island, creating a new RSPB bird sanctuary. The additional spoil being used for land restoration. However, inspection, testing and compliance firm ESG, explained that prior to placement of the waste, it must be chemically characterised for typical ‘brownfield’ contaminants and more specialist compounds derived from the injection of grout and polymers used when tunnelling. According to the company this assessment is key to ensuring the material does not fail the relevant chemical criteria set by the site’s environmental permit. In order to assess whether the spoil is fit for purpose, ESG is analysing numerous samples collected from the construction of Crossrail. Boring story In order to construct the new tunnels, drilling with Tunnel Boring Machines (TBMs) started in November 2012 and is expected to complete in March 2015. Operated by Joint Ventures, each TBM weighs nearly 1000 tonnes, is 7m in diameter and 150m long. Following the injection of polymers to condition the ground, each TBM can tunnel at 8-10 cm/min, through the London Clay Formation, Lambeth Group and Thanet Sand stratigraphic groups. Keeping it clean According to, a key concern for Crossrail is making sure that it remains compliant with the Water Framework Directive which aims to monitor, measure and set benchmarks for the ecological and chemical status of ground and surface waters. As such, for this project, the main uncertainties came from the potential risk to the aquatic environment. If it was assessed that the polymers were considered to cause harm, Crossrail faced three possible outcomes, each with a significant cost attached: Change the polymer, delaying the TBM start date, at a cost of approximately £250,000 per day Design a bund and cell within the facility to accept the material, at a cost of tens of thousands of pounds, requiring a requisite major change to a facilities permit – again delaying the TBM start date Prevent the tunnelled waste from being deposited in an area in close proximity to controlled waters, resulting in logistical issues. This would have resulted in the highest costs, running into >£1M’s including TBM delays. To determine whether any of these would be necessary, ESG was brought on board to contribute to the assessment of the potential eco-toxic risks of the tunnel spoil. To do this, ESG explained that its Environmental Chemistry team at worked closely with the two major contractors - Joint Ventures, constructing the running tunnels and stations, and Atkins Limited, a design, engineering and project management consultancy, to analyse the tunnel spoil. Sidestepping secrecy Due to the Intellectual Property rights of the polymer manufacturers, ESG (along with the Joint Ventures and Atkins) was not party to the chemical makeup of each type of polymer, which it said significantly increased the difficulty in determining their potential environment impacts. Instead, the company created a methodology for analysis using a careful evaluation of polymer chemistry, utilising techniques such as ICP-OES (Inductively Coupled Plasma – Optical Emission Spectroscopy) and GC-FID (Gas Chromatography – Flame Ionisation Detector). According to ESG, this process allowed it to determine the concentrations of polymer within the excavated soil following biodegradation, and also the potential for it leaching into the surrounding environment. As part of the determination of the soil’s fitness for purpose for the Wallasea nature reserve, ESG is also testing for five key contaminants: asbestos, cyanide, aromatic hydrocarbons, arsenic, and cadmium. If present, the contaminants could cause issues for the local eco-system, such as toxicity, carcinogenicity, polluting the water or stunting plant growth. ESG said that these tests are routine and ongoing for the tunnel spoil at the Western (C300), Eastern (C305), Thames Tunnels (C310), Bond Street (C411, C412), Paddington (C405) and Docklands Transfer Station (C807) sites. “This is a project made more complex by the secrecy which has to surround the polymers we use to prepare the soil for drilling,” commented Jonathan Evans, principal consultant at Atkins. “Yet the expertise of the Environmental Chemistry team at ESG has enabled an alternative method of testing for polymer detection.” Amy Parekh-Pross, technical marketing manager in ESG’s Laboratories and Analytical Services Division added: “Our tests enabled Atkins to make a technically robust and meaningful assessment of the impact that the polymer may have on the aquatic environment.” “This meant that the client (Crossrail) and the Environment Agency had sufficient data and information to agree the deposition of the material with the confidence that there would be negligible (if any) impact to aquatic life,” she added. 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