Implications of flow patterns in the sandstone aquifer beneath the mature conurbation of Nottingham (UK) for source protection

Abstract

The protection of groundwater sources in urban areas is difficult due to uncertainties in hydrogeology, future changes in pumping, and complexities of land use. This paper presents an improved understanding of the hydrogeology of the Permo–Triassic Sherwood Sandstone aquifer underNottingham, and considers protection policies for this example of a highly developed groundwater system. Groundwater flow models were constructed for the pre-industrial period (before 1850) and for the 1980 s, and confirmed the existing conceptual model of the hydrogeology. In the early period, spring flows were much more significant than they are now, while abstractions through wells account for virtually all the discharge in the recent period. In recent decades, abstraction has fallen, but there has been a significant reduction in recharge from mains leakage so that there has been no overall rise in groundwater levels. Particle tracking revealed that during recent times the regional aquifer has behaved as a series of local flow cells rather than a regional whole due to the numerous abstractions. Wells in the unconfined aquifer capture most of the urban (and potentiallypolluted) recharge with travel-times up to 200 years. Confined wells with travel-times over 10 4 years, will abstract pre-industrial waters for years to come, and are likely to be protected by natural attenuation of pollutants. Deterministic source protection zones will not be fully protective of public and industrial water supplies, due to the likely changes in pumping regimes in future and the resourcing implications of attempting to control polluting activities over the whole city. A risk-based approach to managing urban groundwater may be more practical and useful. It could predict the risks to existing water supplies, and help in the selection of low risk locations for new wells.