Groundwater chemistry for East Anglia Chalk

The data were collected as part of programme to manage Chalk groundwater resources in a sustainable way. The data are mainly the results from pumped samples of open boreholes used for public, industrial and private supply, collected over a timespan of 40 years, and cover ~900 sites. Measured results are ‘major ions’ + Sr and F and the equilibrium PCO2 value has been computed. The results comprise both fresh and brackish water.
The fresh waters have been classified on the basis of a subset of the analytical data, and these classes have been assigned to larger groups that are chemically and geologically coherent. Nitrate-containing waters have evolved under closed system conditions where the Chalk crops out or is covered by sands, and under open-system conditions where the cover is the Lowestoft Till Formation (Group A). Nitrate depleted waters may also have been recharged under open or closed-system conditions (Group B). Nitrate reduction may be ongoing. Some low-nitrate waters show the effects of pyrite oxidation in the Lowestoft Formation, and some show the results of ion exchange in the overlying Thanet Formation.
Sr and F-enriched brackish waters have been identified as resulting from a marine incursion at c. 2Ma, depositing the Crag Group sands (Group C). There are also effects from historic saline intrusion from the North Sea (Group D).
The distribution of chemical groups is considered to be consistent with the distribution of recharge to the Chalk aquifer used by the current calibrated groundwater model used for water resource management.
Updated 24 April 2025