OR/16/036 Foreword

Stuart, M E, Wang, L, Ascott, M, Ward, R S, Lewis, M A, and Hart, A J. 2016. Modelling the groundwater nitrate legacy. British Geological Survey Internal Report, OR/16/036.

This report is a deliverable of a project jointly funded by the British Geological Survey (BGS) and Defra through the Environment Agency to consider the potential for incorporating the unsaturated zone travel time in the nitrate risk model that is used as part of the nitrate vulnerable zones (NVZs) groundwater designation process. NVZs are delineated by the Environment Agency in support of Defra’s implementation of the Nitrate Regulations which in turn stem from the European Nitrates Directive (91/676/EEC). A further consideration has been how the model may provide additional evidence to support the implementation of the European Water Framework Directive (2000/60/EC) (WFD) and in particular the starting point for trend reversal and justification for alternative (environmental) objectives.

This report presents the results of the further development of a national scale model of unsaturated zone movement of pollutants, in this case nitrate (the ‘Nitrate Time Bomb’ model). This includes improved process representation in the model, better input data and also an evaluation of its performance at different scales through comparison with results of independent discrete modelling studies. The model improvements are shown to significantly improve its performance and the case studies demonstrate the value of its application to support future designation (and performance) of NVZs and achieving/managing environmental objectives under the WFD.