There was little information on natural groundwater chemistry in Scotland before the Baseline Scotland project. Existing data was mainly old, of variable quality, limited (often to a few major ions only), and skewed to areas of groundwater contamination, particularly related to mining.
At the start of the Baseline project, previous studies of groundwater chemistry and available groundwater chemistry data in Scotland were reviewed by BGS (MacDonald and Ó Dochartaigh, 2005).
Fewer than 500 good quality major ion analyses were identified, biased towards the more productive Scottish aquifers, in particular the Devonian aquifers of Fife, Strathmore and Morayshire, and the Dumfries Permian aquifer.
The pre-Baseline groundwater chemistry data were subject to a thorough quality assurance assessment. Poor quality data were removed, and the remaining data divided into logical divisions, based on concentration categories, to help make interepretation more robust.
Main limitations of the data:
Major ion data were used to characterise Scottish groundwaters.
Groundwaters from the Permian sedimentary aquifers in Scotland have well defined chemistry and the least variation in concentrations of major ions of all Scottish groundwaters. Groundwater is typically of Ca-Mg-HCO3 type with a narrow range in the Mg/Ca ratio, and near-neutral pH.
The most highly mineralised groundwater in Scotland is found in Carboniferous aquifers. There is a marked bimodal distribution for Cl and Na which may indicate mixing with formation water. SO4 concentrations are considerably higher than for other aquifers, which may reflect the oxidisation of sulphide minerals within mudstones and the legacy of coal mining.
Devonian groundwaters tend to be of Ca-HCO3 to Ca-Mg-HCO3 type and show a wider range in Mg/Ca ratio than for Permian groundwaters, but similar HCO3 concentrations (median Devonian HCO3 178 mg/l, median Permian HCO3 157 mg/l). The median pH of Devonian groundwaters is 7.5.
The available data for superficial deposits, Precambrian and Silurian/Ordovician aquifers indicate a similar variability of major ion chemistry. This may reflect the short residence time of much of the water, and the high proportion of samples from springs and shallow wells. The waters are typically weakly mineralised, with pH less than 7.
Groundwaters in volcanic aquifers are generally of Ca-HCO3 type, and similar to the sandstone aquifers, with the exception of K which varies considerably across the volcanic aquifers. A small proportion of samples have elevated Cl, Na, SO4 and Ca concentrations.
There are insufficient reliable data to identify clear trends in the concentration of trace elements in Scottish groundwater. However, some potential trends can be highlighted:
More detail on the data summarised above is given in the report:
MacDonald A M and Ó Dochartaigh B É. 2005. Baseline Scotland: an overview of available groundwater chemistry data. British Geological Survey Commissioned Report CR/05/239N. British Geological Survey.
Another report output from the Baseline Scotland project provides an estimate of the potential distribution of trace elements in Scottish groundwater from proxy geological and geochemical information:
MacDonald A M, Fordyce F M, Shand P and Ó Dochartaigh B É. 2005. Using geological and geochemical information to estimate the potential distribution of trace elements in Scottish groundwater. British Geological Survey Commissioned Report CR/05/238N. British Geological Survey.