This report forms a national overview of existing groundwater chemistry data for Scotland, carried
out to provide a foundation for the new project Baseline Scotland. This project is jointly funded by
the British Geological Survey (BGS) and the Scottish Environment Protection Agency (SEPA), and
aims to improve data availability and understanding of the chemistry of Scotland’s groundwater.
Understanding baseline groundwater chemistry is fundamental to helping to implement the Water
Framework Directive: it is difficult to determine whether groundwater is polluted unless the
baseline is known. Also, the presence or absence of various elements in water can occasionally
give rise to health concerns or make the water unacceptable for human use.
Chemistry data from Scottish groundwater samples collected prior to the start of the Baseline
Scotland project in June 2004 have been collated and described. Many of the data came from
previous BGS studies, but data were also available from Scottish Water, councils and SEPA. In
total, more than 800 groundwater chemistry analyses were identified.
The data are of variable quality and were subject to a thorough quality-assurance assessment. This
involved gathering additional information on sources, checking the units for consistency, removing
data from highly contaminated sites and calculating ionic balances. After this process the final
dataset was as follows:
• The dataset comprised 428 sites with full major ion chemistry with an error in ionic balance
of less than 10%;
• Of these 428 sites, 31 sites had a wellhead measurement of dissolved oxygen, and 103 had a
wellhead measurement of the redox potential;
• Information on trace elements was generally limited. Only iron and manganese had more
than 200 measurements across Scotland. For arsenic and fluoride (two trace elements
generally considered the greatest risk for health in groundwater) data are particularly
limited: 65 meaningful measurements for arsenic, and 149 for fluoride. The quality of the
data is also variable – samples from Scottish Water and SEPA are generally not filtered at
the sample site.
The dataset is highly skewed, with most good quality data being available for the Devonian aquifer
in Fife and parts of Morayshire, and the Permian aquifer in Dumfries. There are few data available
for Precambrian or Silurian/Ordovician rocks.
The major ion data were used to characterise Scottish groundwaters. Summary statistics have been
calculated and the data presented on box plots, cumulative frequency plots and tri-linear diagrams.
The data illustrate the variability of Scottish groundwater, reflecting the diverse geology and local
environmental conditions.
• The most highly mineralised groundwater is found within the Carboniferous rocks. There is
a marked bimodal distribution for chloride and sodium which may indicate mixing with
formation water. Sulphate concentrations are considerably higher than for other aquifers
which may reflect the oxidisation of sulphide minerals within mudstones and legacy of coal
mining.
• 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 of Ca-Mg-HCO3 type with a narrow range in Mg/Ca ratio,
and near-neutral pH. Most data are available for the Devonian aquifers in Scotland. Groundwaters tend to be of
Ca-HCO3 to Ca-Mg-HCO3
type and show a wider range in Mg/Ca ratio than for the Permian
rocks, but similar bicarbonate concentrations (median Devonian HCO3 178 mg/l, median
Permian HCO3 157 mg/l). Median pH from the Devonian groundwaters is 7.5.
• The available data for the superficial deposits, Precambrian rocks and Silurian/Ordovician
rocks indicate similar variability of major ion chemistry across the three hydrogeological
environments. 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 have typically low
mineralization and pH less than 7.
• Groundwaters in volcanic aquifers are generally of Ca-HCO3 type, and similar to the
sandstone aquifers, with the exception of potassium which varies considerably across the
volcanic aquifers. A small proportion of samples have chloride, sodium, sulphate and
calcium concentrations.
• Most of the small island sources have high chloride concentrations, probably as a result of
increased chloride concentrations in recharge. Other notable elevated chloride
concentrations are observed in the coastal areas of East Lothian, Arbroath, Morayshire and
northwest Fife The majority of inland sources have chloride concentrations less than
25 mg/l, and in upland areas concentrations are less than 10 mg/l.
• Nitrate data indicate a clear pattern across Scotland, with concentrations in excess of
25 mg/l as NO3 across the east and southwest. Concentrations over much of the rest of
Scotland are less than 10 mg/l as NO3. The elevated concentrations of nitrate largely
coincide with the agricultural areas of Scotland and are attributable to fertiliser applications
and the presence of intensive farming; this is consistent with other recent studies.
There are insufficient reliable data to identify clear trends in the concentration of trace elements in
Scottish groundwater. However, the following have been highlighted from the existing data.
• Iron and manganese concentrations greater than the EC maximum permissible value are
observed in all hydrogeological units in Scotland. Iron and manganese are ubiquitous in
rocks and the dominant controls on their presence in groundwater are the pH and redox
status.
• The limited data for aluminium indicate that concentrations approach or exceed the EC
maximum permissible value for drinking water in Precambrian and volcanic rocks and
granite. This is linked to the acidic conditions of groundwater in these environments.
• The available data indicate that natural chromium concentrations in Scottish groundwater
are typically well below the EC maximum permissible value, and usually below detection
limit. There are no data from the Glasgow area, where elevated chromium concentrations
may be expected due to widespread contamination from the chrome and steel industry.
• Fluoride concentrations greater than 0.5 mg/l have been measured in samples from the
Permo-Triassic sandstone in Morayshire and the Permo-Triassic sandstone in Mauchline,
southwest Scotland. There are several isolated samples scattered throughout Scotland with
fluoride concentrations greater than the EC maximum permissible value of 1.5 mg/l.
In conclusion, there is a lack of systematically collected groundwater quality data for Scotland.
Particularly lacking are data on trace elements and pH and redox status. The following
recommendations should be implemented to give a reliable national dataset.
1. New data are required that are collected in a consistent, reliable and systematic manner, and
analysed to a consistent degree of accuracy. There is not widespread coverage of groundwater chemistry data in Scotland. Certain
hydrogeological units have few reliable data and should be targeted for further sampling.
3. Wellhead measurements of redox potential and dissolved oxygen are required in order to
understand the groundwater geochemical processes and element distributions.
4. There is evidence that the sampled chemistry is affected by the type of water source (e.g.
well, borehole or spring). It is essential that comprehensive data are collected on each
sampled source.
5. Routine sampling for age dating would be helpful for understanding residence times of
groundwater and interpreting chemical variations – particularly nitrate data.
6. There are insufficient data on many trace elements in Scotland to characterise their
occurrence or understand their origin. Comprehensive analysis of groundwater chemistry,
including trace elements, should be carried out wherever possible
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