Abstract This paper reviews the Environment Agency chalk groundwater level monitoring network. The network has evolved over many years to enable management of the resource and to assess the impact of abstractions on the environment. The paper considers the strengths and weaknesses of the network, the use and accessibility of the data and how the network supports, and works with, the Environment Agency's regional groundwater models. It concludes with the suggestion that the network is suffering from a degree of lack of maintenance and that there is a disparity between the ambitions of the modelling programme with its Modflow6-driven shift to multi-layer conceptualization and a largely open-hole, single-layer monitoring installation.

Abstract In Groundwater-Dependent Terrestrial Ecosystems (GWDTEs), atmospheric nitrogen (N) inputs have often been studied in isolation from terrestrial groundwater and surface water inputs. We describe for the first time the development and application of a combined atmospheric and terrestrial N source apportionment methodology, able to identify contributing catchment and N loadings to GWDTEs. We combined all N inputs using a site-specific conceptual model supported by 12 months’ monitoring for a Chalk-fed GWDTE at Newbald Becksies, East Yorkshire. We discuss implications for effective catchment management, wetland protection and development of a source apportionment methodology. Potential sources of nitrate include: atmospheric deposition, mineralization, leaching from agricultural soils, manure heaps, septic tanks, sewer and mains water leakage. Atmospheric deposition was calculated from measurements of ammonia and nitrogen dioxide concentrations together with rainfall inputs of ammonium and nitrate. Quantification of agricultural sources used the FarmScoper modelling tool to estimate nitrate leaching in the groundwater catchment. Comparison between modelled nitrate concentrations in leachate (15–17 mg N l −1 ) and observed groundwater nitrate concentrations (12.3–19.8 mg N l −1 ) are good. The majority of nitrate is leached from arable land. FarmScoper allows mitigation scenarios to be tested, supporting measures to reduce nitrate within a groundwater catchment.

Abstract This paper explains the background and development of the Environment Agency National Groundwater Modelling System (NGMS) to integrate recharge functionality with the existing groundwater modelling (Modflow functionality). The Environment Agency groundwater models were originally developed primarily as a tool for making high-level strategic decisions but their use for short-term extreme event scenarios, such as drought or flood, has been relatively limited. This functionality has been constrained by the format of the rainfall/recharge input datasets. Undertaking scenario runs based on change in climate and weather has only been possible by direct manual alteration of those input datasets, which is not always practical on a day-to-day basis. Full implementation of recharge models into NGMS changes this, allowing the recharge models to be run in the NGMS environment and output to be generated. The fusion aspect of the process involves that output being processed in such a way that it can be used by NGMS as input into a Modflow scenario run. This process is explained using the example of a recent drought scenario in the Wessex Basin groundwater model.