Water quality impacts and palaeohydrogeology in the Yorkshire Chalk aquifer, UK

A large hydrochemical data-set for the East Yorkshire Chalk aquifer has bee n assessed, Controls on the distribution of water qualities reflect: water- rock interactions (affecting especially the carbonate system and associated geochemistry); effects of land-use change (especially where the aquifer is unconfined); saline intrusion and aquifer refreshening (including ion exch ange effects); and overexploitation (in the semi-confined and confined zone s of the aquifer). Both Sr and I prove useful indicators of groundwater esi dence times, and I/Cl ratios characterize two sources of saline waters. The hydrochemical evidence clearly reveals the importance both of recent manag ement decisions and palaeohydrogeology in determining the evolution and dis tribution of groundwater salinity within the artesian and confined zones of the aquifer. Waters encountered in the aquifer are identified as complex ( and potentially dynamic) mixtures between recent recharge waters, modern se awater, and ancient seawater which entered the aquifer many millennia ago.