URGENT: contaminated land investigation and remidiation
The aim of the Natural Environment Research Council's URGENT programme is one of managing the interactions between natural processes and the effects of past, present and future human activities. Mike Welch, national facilitator for the programme and a consultant to the Chemical Industries Association, highlights URGENT activities in the field of contaminated land.
As an example, the potential for rising groundwater under Wolverhampton to mobilise contaminants, including toxic heavy metals that could pollute surface waters and the local aquifer is being investigated by the University of Sheffield, the British Geological Survey and the Macaulay Land Use Research Institute. Researchers are using groundwater and geochemical modelling to predict the effect of groundwater composition on mobilisation and as a means of assessing the impact on groundwater quality of land remediation strategies and different abstraction regimes. Work between Imperial College and the University of Nottingham, involving brownfield sites in Nottingham as well as Wolverhampton, aims to provide assistance to local authorities in the interpretation of urban geochemical maps and to provide a decision support system for the risk assessment of metal contaminated soils. A key issue is the extent to which contaminants are bioavailable and therefore a risk to human health or the local ecosystem. A new model has been developed to predict metal up-take by vegetable plants and a hazard quotient used to give a measure of risk to potentially exposed populations consuming locally grown vegetables. A battery of new chemical and biochemical analytical tools has been developed in the course of these studies.
A joint project between the University of Edinburgh and the Macaulay Land Use Research Institute has developed a model to predict the behaviour of chromium at sites where chromite ore processing residues were deposited some 30 years ago, and to simulate potential remediation treatments. Using sophisticated analytical tools, the mechanism for the continual release of Cr(VI) from these sites has been identified, and it has been shown that common remediation techniques, such as the addition of ferrous sulphate to reduce Cr(VI) to the less harmful Cr(III) can greatly increase the release of Cr(VI) via ion exchange with sulphate. The work demonstrates that direct transfer of remediation techniques from one situation to another needs to be very carefully considered, and the final version of the model will enable users to understand better the issues at particular sites and to simulate potential remediation treatments.
A project at the British Geological Survey with potentially very wide application involves the development of non-intrusive techniques capable of providing 3D views of underground structures, including waste deposits. Using electrical resistivity measurements, high-resolution 3D images can be created that enable complex underground features to be visualised more precisely than is possible with conventional methods. Large volumes of ground can be scanned down to tens of metres, and it can be used where there are buildings or roads. The technique has already been used to view old waste depositories and landfills where it shows the distribution of leachate and any points of leakage. Amongst other applications it can be used to identify pockets of non-aqueous liquids, leakages from underground transport systems, and potential physical hazards, such as incipient landslips, subsidence, etc. Currently the technique is being developed to provide a continuous record over time of changing conditions within landfills, with data fed by telemetry to a remote monitoring point.
Remediation of degraded land by natural processes can take many years unless contaminated soil is moved off-site or chemicals are used to encourage growth, which may not be sustainable over time. Attempts to establish vegetation, such as trees, which promote soil formation at a rapid rate and, in conjunction with micro-organisms, help to reduce contaminants, tend to have limited success. A team led by the University of York, however, has completed a project that has identified fungi that are adapted to growing in contaminated soils with high levels of organic contaminants and which can form a symbiotic relationship that helps the tree to acquire important nutrients and protects it against disease.
Several projects in the programme are investigating ways of assessing the quality
of groundwater and the potential for using groundwater that is rising under
cities, such as Birmingham and Nottingham, to reduce the demands on other aquifers.
Direct Toxicity Assessment has been shown by the Royal Holloway University to
be a viable method of rating the quality of groundwater, and Research at Birmingham,
Sheffield and Surrey Universities is leading to the development of models that
can be used to show the likely impact of abstracting urban groundwater based
on activities in the area including actual or potential inputs and other local