Groundwater chemistry for East Anglia Chalk
Description
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.
Files
Steps to reproduce
The data have been harvested from research reports cited in the data, public water supply operators, and the English Environment Agency. Research reports contain the results of single samples, considered to be the best sample available under the conditions, but varying from a continuously pumping public supply borehole to a depth sample from an un-pumped but open borehole. The samples were collected 30-40 years ago and many of the boreholes are now unavailable. Analysis was mainly by water undertaker laboratories. Samples from current public water supply operators: Anglian Water Services (January 2017 – May 2019), Essex and Suffolk Water (2018), and Affinity Water (January 2010 – April 2019). The data used are averages. Environment Agency data are collected as part of routine aquifer monitoring and cover various time frames. Where multiple results are present for a site, the data have been averaged. All results reported as below detection have been saved as a result at the detection limit. The data have been anonymised for data protection and national security reasons. An effort will be made to deposit a key to data owners, see the referencing paper.