A regional flux-based risk assessment approach for multiple contaminated sites on groundwater bodies

In the context of the Water Framework Directive (EP and CEU, 2000), management plans have to be set up to monitor and to maintain water quality in groundwater bodies in the EU. In heavily industrialized and urbanized areas, the cumulative effect of multiple contaminant sources is likely and has to be evaluated. In order to propose adequate measures, the calculated risk should be based on criteria reflecting the risk of groundwater quality deterioration, in a cumulative manner and at the scale of the entire groundwater body. An integrated GIS- and flux-based risk assessment approach for groundwater bodies is described, with a regional scale indicator for evaluating the quality status of the groundwater body. It is based on the SEQ-ESO currently used in the Walloon Region of Belgium which defines, for different water uses and for a detailed list of groundwater contaminants, a set of threshold values reflecting the levels of water quality and degradation with respect to each contaminant. The methodology is illustrated with first results at a regional scale on a groundwater body-scale application to a contaminated alluvial aquifer which has been classified to be at risk of not reaching a good quality status by 2015. These first results show that contaminants resulting from old industrial activities in that area are likely to contribute significantly to the degradation of groundwater quality. However, further investigations are required on the evaluation of the actual polluting pressures before any definitive conclusion be established.     

Evaluating the risks of methyl tertiary butyl ether (MTBE) pollution of urban groundwater

MTBE, a fuel oxygenate added to gasoline in parts of the USA, appears to have imposed significant adverse impacts on groundwater. In the UK, the impacts of MTBE are not well known in part because insufficient data has been presented to allow an accurate assessment. With the recognition of urban groundwater as a potentially valuable resource due to the growing pressure on rural groundwater, there is need for pollution risks to urban groundwater to be evaluated for contaminants such as MTBE. This paper presents the application of a risk-based water management tool called Borehole Optimisation System (BOS) in the evaluation of the risk of MTBE to urban groundwater at city scale using Nottingham city as our case study. The risk model was validated by comparison of its predictions with observations of MTBE detections for about 1100 boreholes in England and Wales. The output of the risk analysis was the production of a map showing the predicted MTBE concentration at all locations in the city. The results indicate that MTBE does not currently pose a major risk to urban groundwater although there may be a potential risk to groundwater in the southern part of the city where most industries are concentrated.