Defusing the nitrate timebomb

Defusing the nitrate timebomb

Led by: Portsmouth Water

Partners: Wood Group UK Limited, Southern Water Services, Anglian Water Services, Wessex Water, South East Water, Affinity, Environment Agency for England

Nitrate pollution has long been a threat to Chalk drinking water and dependent environments in Southern England. To reduce nitrate in drinking water requires expensive treatment or changes in farming practice. Water companies work with farmers to reduce nitrate inputs, but lack detailed knowledge of where to focus efforts for efficient, rapid results. The project will develop modelling software that can predict concentrations throughout the Chalk so that land use options can be tested to select those that deliver efficient nitrate reduction. This will reduce treatment costs and energy consumption and help to protect habitats and biodiversity.

Defusing the nitrate timebomb A 4R Nitrate tool was developed in 2023 and tested against a simple trial catchment, but this revealed an issue with the underlying MODFLOW software contaminant transport model. There is also an issue with the 4R nitrate model related to run-off from impermeable areas and movement of nitrate in this water. We should be able to fix the later in-house. Unfortunately, lack of modelling resource has also meant that we have not been able to fix either, although we are working hard to complete. Scenario testing will follow, and we are running a short online workshop with project stakeholders to develop and agree these scenarios prior to modelling. The Test and Itchen MODFLOW6 and 4R models have been agreed for use to test the approach with the EA and the main water company sponsors. To calibrate the model we have put together a calibration dataset with timeseries and spatial time slice maps of observed nitrate concentrations in groundwater and surface water across the model area. Porewater profile data has also been collected to calibrate 4R nitrate.

“This funding will allow us to develop tools to predict nitrate concentrations in our catchments and to test catchment management scenarios which means that we can better target our nitrate reduction efforts and further reduce the need for expensive treatment of nitrate for drinking water “- Simon Deacon, Catchment and Environment Manager Portsmouth Water

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Update from the project (October 2024)

Since July 2024 we have overcome modelling issues (Task 2) and then encountered a few more which we are working hard to resolve. We may have to cut down the size of the modelled area to ensure we can produce calibrated outputs on which to test scenarios. In July we ran a short online workshop to get feedback on the types of scenarios (Task 3) we would run in the final model and to help us design how the outputs will be  visualized. We are looking forward to completing the model build, running scenarios and planning the final presentations in a stakeholder workshop in December (Task 4).