CORONA – Confidence in forecasting of natural attenuation as a risk-based groundwater remediation strategy

There are hundreds of thousands of sites in Europe where groundwater is polluted, often by manufactured organic chemicals. Unfortunately the pollutants are technically difficult to remove and so the cost of engineered clean up can be high, often higher than the value of the land. A risk-based approach to managing groundwater pollution is becoming widely accepted in Europe because it targets resources to those sites where human health or the environment are at significant risk of harm. Risk assessment enables us to take account of the natural processes, collectively known as natural attenuation, which reduce the concentrations of pollutants. Biodegradation, in which native bacteria consume the pollutants as food, is usually the most important attenuation process. A good understanding of the transport and fate of pollutants is required to make predictions of future behaviour and generate confidence in risk assessment. The outcomes of the CORONA project will increase confidence in assessment and forecasting of natural attenuation through the following: 1. We have strengthened the scientific understanding of natural attenuation by studying a range of real polluted sites, using field investigations, laboratory studies and computer simulation. All of the sites had complex pollution problems, with mixtures of pollutants, poorly known histories and a variety of groundwater flow conditions. We were able to go beyond the usual qualitative assessment, and provide quantitative descriptions of the transport and fate of the pollutants. As these descriptions are published in the scientific literature they will enable practitioners to translate our findings to other difficult sites. 2. We have provided robust engineering tools for the assessment and quantification of natural attenuation, and made these publicly available. One tool is a numerical model which can be tailored to suit the chemistry, geology and history of particular sites. A second tool is a simple spreadsheet-based method of predicting the length of pollution plumes, using a minimum of expensive data. It is based on a new conceptual model of how plumes behave, and includes a new mathematical solution. These are supported by guidance documents which explain how quantitative assessment of natural attenuation can be carried out. 3. We have promoted the use of these tools in the end-user community of contaminated site owners, regulators and their advisors through a website and a series of short courses. Further courses will be held after the end of the project, and the engineering tools and guidance documents will remain available through the project website. In addition to these scientific and technical outcomes, the project has initiated new research collaborations in Europe and beyond, and contributed to the training of 10 new research scientists to PhD level. Overall, CORONA will make a significant improvement in the economy and environment of the European Union.