ESI, now part of Stantec, was commissioned by several water companies to review trends of increasing nitrate concentrations in a large number of boreholes which abstract groundwater from the Permo-Triassic Sandstone.
Concentrations of nitrate in groundwater have increased significantly over the last few decades, largely in response to increased application of nitrate to land. Initially water companies were able to avoid additional treatment costs by blending this groundwater with water from lower nitrate sources. However, as trends have continued to rise, options for blending have reduced. Meanwhile, the Water Framework Directive puts an onus on water companies and regulators to work together to solve water quality issues at source rather than continuing to rely on ‘end of pipe’ solutions. Both of these factors require an improved understanding of current and future predicted trends in water.
In AMP6 ESI carried out a review of Severn Trent Water Limited (STWL) public water supply groundwater resources to identify trends in water quality which could lead to the need for additional blending or treatment. The primary concern was nitrate, for which 260 sources were evaluated; an additional 25 sources were evaluated for other water quality trends including pesticides, solvents, MTBE, cadmium, chloride and sulphate. This work provided an update to previous work by ESI in AMP5 and patterns observed within the nitrate trends were compared to those in previous work.
ESI subsequently developed a better technique for forecasting future trends in nitrate concentrations based on land use and historic loadings. This gave significantly different results from the previous simple extrapolation and was a crucial tool for helping STWL to prioritise sites for catchment management measures.
ESI has again recently updated all this work for AMP6 which showed that the observed trends have matched the AMP5 predictions well. This means that we have a very good appreciation of regional patterns of nitrate trends in the Permo- Triassic sandstone and will be able to identify anomalous results quickly and efficiently in AMP7.
This tool was then linked to GIS (using regional groundwater model outputs to identify groundwater catchments) and used to identify the most effective areas for catchment interventions and the likely timescales of responses.
The results of the modelling were discussed with both the Environment Agency and the water company and decisions on whether to proceed with catchment management were agreed for each source.
ESI, now part of Stantec, carried out similar nitrate trending work for four other water companies and the nitrate trending tool has now been used on over 100 sources.