When it comes to engineering, what happens below the surface is as important as what’s built on top. Every site has a unique history and set of properties which will determine the design of the proposed structure, the materials used and even the programme sequence. This history can become especially complex when working on brownfield sites or in urban or industrial areas. The presence of previous structures and proximity to industrial activity increases the risk of contaminated ground which must be assessed and dealt with before construction can continue.
Contaminated ground isn’t just about extreme examples involving radioactive waste. Soil is contaminated if it contains a higher concentration of pollutants than occur naturally and could cause significant harm to people, property or protected species or significant pollution of surface waters or groundwater. These pollutants include heavy metals (like arsenic, cadmium and lead), oils and tars, solvents, gases and asbestos. If allowed to remain in high concentrations these materials pose a danger to human health and the surrounding environment.
Ascertaining whether a site is contaminated or not is often a condition in acquiring planning permission. The levels of acceptable pollutant concentration will depend on the intended use of the land and whether it is destined for residential or commercial use. If the levels of pollutant are deemed too high then developers will need to ‘clean up’ the soil before they begin work. This is done via excavation and removal of contaminated soil, soil treatment (including bioremediation, chemical oxidation and soil ‘washing’) or limiting the spread of contamination if treatment costs are unrealistically high or create further risks.
Contaminated land is an added complication for any project but – if well managed – it doesn’t need to be an issue. Our project at Gransden Avenue in Hackney, London was located on the site of a former street which was demolished due to heavy bomb damage and had subsequently been used for as a garage and workshop. As we identified this early, through our historical search, the presence of contaminants didn’t derail the programme. We implemented a remediation strategy which involved removing the contaminated soil so construction could continue and future occupants would be free from danger.
Our team also faced contaminated soil on our Stirling Estates project in Newbury, Berkshire. The two phase residential development was located on a site with historic contamination issues and we were called upon to value engineer the scheme and resolve crucial pre-commencement conditions. Following our thorough site investigation we found that large-scale excavation and removal of contaminated soil would be greatly disruptive to the local environment and add significantly to project costs. We therefore worked to minimise soil excavation by reviewing the levels on the site and implementing a raft solution. Removing the need for piling eliminated the potential for pollutants find a route to lower strata and potential aquifers.
Understanding a site’s context is crucial to a successful project both for cost effectiveness and safety. A site investigation is an essential first step so that the plot’s individual characteristics may be identified and the design and construction programme can be properly adapted. Armed with this knowledge and the right industry expertise, there’s no challenge that can’t be overcome.