Baseline groundwater chemistry : the Sherwood Sandstone of Devon and Somerset

This report describes the regional geochemistry of groundwater from the Sherwood Sandstone aquifer of Devon and Somerset. In order to assess the likely natural baseline chemistry of the groundwater in the area, information has been gathered from the strategic collection of 21 new groundwater samples, and from collation of existing groundwater, rainfall, mineralogical and geochemical data. The Sherwood Sandstone aquifer results from continental deposition during the early Triassic period. The deposition comprised thick clastic deposits in basins created during the late Permian. There are two distinct units: the Otter Sandstone Formation and the underlying Budleigh Salterton Pebble Beds Formation. These units form the most important aquifer in south-west England. The main chemical properties of the groundwater are determined by rainwater recharge reacting with the aquifer minerals. Of these minerals carbonates are the dominant influence on the water chemistry. While Ca is dominant in groundwaters from both aquifer units, the water types from the two units can be distinguished: the Otter Sandstone Formation aquifer has mainly Ca-HCO3 type waters, with some mixing towards Mg, and the groundwaters in the Budleigh Salterton Pebble Beds Formation aquifer are of Ca-HCO3 type to Na+K-Cl type. There is little variation in the major ion proportion of the groundwaters from the Otter Sandstone Formation, most likely as these represent groundwater in equilibrium with the minerals which give it this character. There is greater variation in the Budleigh Salterton Pebble Beds Formation groundwaters. Besides the difference in groundwater types, the groundwater from the Budleigh Salterton Pebble Beds Formation is more acidic, more oxic, has lower SEC values, and HCO3, Cr, U and Mg concentrations, and higher concentrations of Al, Be, Cd, Cr, Co, Tl and REE than the groundwater from the Otter Sandstone Formation. Human impacts on the water quality are evident. These are mainly visible in the presence of indicator contaminants, such as nitrate. The widespread presence and changes of nitrate concentrations over time indicate the extent to which the unconfined aquifer is influenced by modern farming practices or urban pollution. Concentrations of NO3-N exceeded the current drinking water limit of 11.3 mg L-1 in 25% of the sampled groundwaters, which probably reflects the intensification of agriculture in the study area over the last few decades. Indeed, the dominant land uses of the area are agriculture and grassland. However, recent legislation and the drive towards intelligent farming have meant that in some groundwaters the concentrations of nitrate are decreasing. While many of the groundwaters investigated in this study are of good inorganic quality there are some notable exceptions which contain elevated concentrations of Fe, SO4, Ni, Co and NO3. The distribution of the poor-quality is generally so sporadic that water quality would be difficult to predict prior to drilling a borehole. For many analytes, the 95th percentile of the distributions has been taken as a first approximation of an upper limit of baseline concentrations as this serves to eliminate the most extreme outlier concentrations that likely represent a distinct population

Arsenic in groundwater and the environment

Awareness of the problems associated with arsenic in drinking water and the environment has grown significantly over the last two decades or so and today an enormous literature exists documenting its occurrence, behaviour and impacts in many places across the globe. The mobilisation of arsenic in the environment occurs through a complex combination of natural biogeochemical reactions and human interactions. Most recognised problems are generated by mobilisation and transport under natural conditions, but mobilisation has also been caused, or exacerbated, by mining, fossil-fuel combustion and use of synthetic arsenical compounds (pesticides, herbicides, crop desiccants and arsenic-based additives in livestock feed). Arsenical pesticides and herbicides have been used much less over the last few decades, and more recent restrictions have been imposed on the use of arsenic in wood preservation (e.g. European Communities’ Directive 2003/2/EC), but the legacy of such sources may still pose a localised threat to the environment

Baseline Scotland : groundwater chemistry of the Carboniferous sedimentary aquifers of the Midland Valley

This report describes the baseline groundwater chemistry of the sedimentary aquifers of Carboniferous age in the Midland Valley of Scotland. Groundwater is an important resource in the Midland Valley, largely for agriculture, but also for industry – including food and drink processing and mineral water bottling, and for domestic use. A large but unquantified volume of groundwater is also still pumped from former mine workings, largely coal mines, in order to maintain water levels and for quality treatment. Analyses for 62 groundwater samples were interpreted for the purposes of this study. Of these, 36 samples were collected for the Baseline Scotland project between September and December 2008. These were augmented with a further 25 samples collected during separate BGS projects since 2001. The sites were chosen largely to be representative of groundwater in the area, and sources that were very poorly constructed were avoided. A small number of samples were deliberately targeted from mines, either from adits, shafts or boreholes. The data were classed in one of five different hydrogeological units (or aquifer groups): four chronostratigraphic groups, which in decreasing order of age are the Inverclyde, Strathclyde, Clackmannan and Coal Measures groups; and a fifth group incorporating waters sampled from mine discharges. An estimate of the baseline groundwater chemistry conditions in the four chronostratigraphic hydrogeological units is presented, based on a statistical summary of the chemical data, which represents values between the 10th and 90th A summary of the conclusions arising from this study follows. percentiles of the full dataset range. This statistical approach to estimating baseline compositions was complemented by selecting 11 analyses of groundwater from sources where there is little or no indication of direct contamination, including likely impact from mining. The chemistry of these samples represents the typical groundwater conditions in the four non-mine hydrogeological units in the sedimentary Carboniferous aquifers of the Midland Valley

Baseline groundwater chemistry: the Corallian of the Vale of Pickering, Yorkshire

This report describes the regional geochemistry of the groundwater from the Corallian aquifer in the Vale of Pickering, North Yorkshire. The study aims to assess the likely natural baseline chemistry of the groundwater. Data have been collected from strategic sampling of 24 groundwater sources, in conjunction with collation of existing groundwater, rainfall, and mineralogical data. The Corallian aquifer comprise Upper Jurassic shallow shelf marine sediments, with a variety of facies including muds to micritic limestone and oolites, to bioclastic limestones with interbeds of silts and sands. These strata represent an important groundwater source in north-east England. The main chemical properties of the groundwater are determined by the interaction of rainwater recharge reacting with the aquifer minerals. Within the Corallian aquifer, groundwater major ion composition is dominantly influenced by reaction with calcite, and little variation is seen within the major ion proportions. Human impacts on the water quality are clearly evident, mainly through the presence of NO3-N as an indicator contaminant. The widespread presence, commonly in excess of the drinking water limit and the increases over time suggest that the aquifer is heavily influenced by agricultural practices. Agricultural land dominates the area underlain by the unconfined aquifer. With the exception of NO3-N, the available data for groundwater within the Corallian aquifer of the Vale of Pickering indicate they are of good quality for the analytes tested, with few elevated concentrations of potentially harmful trace elements. For many analytes the 95th percentile serves as a first approximation of the upper limit of the baseline range of concentrations, as this serves to eliminate the most extreme outlier concentrations

Molybdenum distributions and variability in drinking water from England and Wales

An investigation has been carried out of molybdenum in drinking water from a selection of public supply sources and domestic taps across England and Wales. This was to assess concentrations in relation to the World Health Organization (WHO) health-based value for Mo in drinking water of 70 μg/l and the decision to remove the element from the list of formal guideline values. Samples of treated drinking water from 12 water supply works were monitored up to four times over an 18-month period, and 24 domestic taps were sampled from three of their supply areas. Significant (p  0.05) were detected. Tap water samples collected from three towns (North Wales, the English Midlands, and South East England) supplied uniquely by upland reservoir water, river water, and Chalk groundwater, respectively, also showed a remarkable uniformity in Mo concentrations at each location. Within each, the variability was very small between houses (old and new), between pre-flush and post-flush samples, and between the tap water and respective source water samples. The results indicate that water distribution pipework has a negligible effect on supplied tap water Mo concentrations. The findings contrast with those for Cu, Zn, Ni, Pb, and Cd, which showed significant differences (p < 0.05) in concentrations between pre-flush and post-flush tap water samples. In two pre-flush samples, concentrations of Ni or Pb were above drinking water limits, although in all cases, post-flush waters were compliant. The high concentrations, most likely derived from metal pipework in the domestic distribution system, accumulated during overnight stagnation. The concentrations of Mo observed in British drinking water, in all cases less than 2 μg/l, were more than an order of magnitude below the WHO health-based value and suggest that Mo is unlikely to pose a significant health or water supply problem in England and Wales

Iodine in drinking water from East African groundwater sources

Chronic deficiency has long been associated with development of iodine-deficiency disorders (IDDs). Drinking water, including groundwater, contributes to dietary iodine intake, and the prevalence of IDDs is widely reported. However, there are no minimum or maximum guideline concentrations for iodine in drinking water, and iodine is rarely analysed during traditional groundwater health studies. This study reviews the iodine content of drinking water sampled by the British Geological Survey, from groundwater sources in sixteen regions of Ethiopia, Uganda, Tanzania and Malawi. Preliminary results reveal that iodine concentration is associated with the amount of total dissolved solids, and shows the strongest relationship with sulphate, uranium, strontium, sodium and fluoride. Drinking water sourced from boreholes and hand dug wells are shown to have elevated iodine concentrations relative to local rainfall and spring sources. Work is ongoing to investigate the relationships between iodine and other solutes in the groundwater, and to build a database of groundwater in East Africa

Baseline groundwater chemistry in Scotland's aquifers

This report is an output from the Baseline Scotland project, which ran from 2005 to 2014. It provides a summary of data on the chemistry of groundwater from the eleven main bedrock aquifer groups in Scotland. Groundwater is an important natural resource for Scotland. It provides drinking water, supports agriculture, and is fundamental to the nation’s mineral water and whisky industries. Groundwater also plays a vital role in sustaining the flow of rivers and supporting many of Scotland’s fragile ecosystems. The naturally high quality of groundwater in Scotland is an important part of why it provides so many benefits. However, groundwater is not invulnerable, and it needs to be protected and managed to preserve it. This report presents a synthesis of the results of the Baseline Scotland project, which mapped the natural chemistry of groundwater in Scotland’s aquifers. The project ran from 2005 to 2014, funded mainly by the British Geological Survey with additional support from the Scottish Environment Protection Agency, and included ten regional surveys that covered much of Scotland. In this overview, the results of the surveys are combined to produce a summary of the baseline chemistry of groundwater in the eleven main bedrock aquifer groups of Scotland. These aquifer groups represent a range of hydrogeological environments with differing geological controls on both physical aquifer properties and natural groundwater chemistry. They were primarily divided according to rock type: sedimentary (indurated sedimentary or calcareous), metamorphic or igneous; and secondarily according to geological age. The aquifers are: Permo-Triassic; Carboniferous sedimentary rocks (not extensively mined for coal); Carboniferous sedimentary rocks (extensively mined for coal); Old Red Sandstone North; Old Red Sandstone South; Silurian- Ordovician; Precambrian North, Precambrian South; Igneous Volcanics; Igneous Intrusive rocks; and Highland Calcareous rocks. The chemistry of groundwater in Scotland’s bedrock aquifers is highly variable, reflecting a combination of lithology, mineral reactions, redox conditions, groundwater flow paths and residence times. Major ion water types include Ca-HCO 3 , Na-HCO 3 , Na-SO 4 and Na-Cl, with no single type dominating across Scotland. Total dissolved solid (TDS) concentrations in groundwater are typically between 54 and 520 mg/L (10–90th percentile; median 150 mg/L). Some of the highest values of TDS (up to 5000 mg/L) are seen in Carboniferous sedimentary aquifers in central Scotland, particularly where mining has occurred. Elevated TDS also affects some groundwaters in coastal areas. Mineralised springs (e.g. Na-Cl, Na-SO 4 types) occur rarely. Median pH values for each of the aquifers are near neutral, in the range 6.5 to 7.5 (overall median 7.2). However, acidic groundwater (pH<6) occurs in most of the aquifers, reflecting an absence of carbonate minerals and/or oxidation of pyrite and other metal sulphides. More strongly acidic conditions can give rise to the presence of dissolved Al, Fe, Mn and REE in some groundwaters. Oxic groundwater conditions dominate in most aquifers in Scotland, consistent with dominantly shallow groundwater flowlines in fractured bedrock. Local exceptions occur with mildly reducing zones in several aquifers, but the only regionally extensive reducing conditions are in the Old Red Sandstone North aquifer, particularly in Moray. Within the Carboniferous sedimentary aquifers, and in localised mineralised springs in the Ordovician–Silurian aquifer, conditions can be more strongly reducing, causing SO 4 and NH 4 reduction and even methanogenesis at some locations. The main impact of land use on groundwater chemistry is the common occurrence of high concentrations of NO3 in groundwater, which correlate reasonably well with the areal extent of agricultural land use. Occurrences of high P and K are also seen, but are more sporadic in distribution, reflecting the more complex transport properties of these elements in soils and aquifers. Not all the groundwaters sampled are used for drinking water, and it is not appropriate to assess the state of drinking water quality in Scotland on the basis of the data presented here. These data nonetheless show the typical chemical compositions of raw groundwaters from the sampled aquifers, and indicate the general state of groundwater quality and any potential problems that may be encountered within each aquifer. On this basis, the most frequent exceedances of drinking water limits in the groundwaters are for Fe and Mn (21% and 27% of samples respectively). These elements, together with NH 4 (6.7% exceedance), are largely naturally derived, linked to reducing aquifer conditions. Exceedances for NO 3 (11%) occur in oxic aquifer conditions, and are linked to pollutant inputs, particularly from agriculture. Exceedances for trace elements are less common but do occur locally. In this report the study methodology is described along with some of the main factors controlling groundwater chemistry. The inorganic chemistry of Scotland’s groundwater is then summarised and put in context, before the baseline chemistry for each aquifer is presented

Uranium in natural waters and the environment: distribution, speciation and impact

The concentrations of U in natural waters are usually low, being typically less than 4 μg/L in river water, around 3.3 μg/L in open seawater, and usually less than 5 μg/L in groundwater. Higher concentrations can occur in both surface water and groundwater and the range spans some six orders of magnitude, with extremes in the mg/L range. However, such extremes in surface water are rare and linked to localized mineralization or evaporation in alkaline lakes. High concentrations in groundwater, substantially above the WHO provisional guideline value for U in drinking water of 30 μg/L, are associated most strongly with (i) granitic and felsic volcanic aquifers, (ii) continental sandstone aquifers especially in alluvial plains and (iii) areas of U mineralization. High-U groundwater provinces are more common in arid and semi-arid terrains where evaporation is an additional factor involved in concentrating U and other solutes. Examples of granitic and felsic volcanic terrains with documented high U concentrations include several parts of peninsular India, eastern USA, Canada, South Korea, southern Finland, Norway, Switzerland and Burundi. Examples of continental sandstone aquifers include the alluvial plains of the Indo-Gangetic Basin of India and Pakistan, the Central Valley, High Plains, Carson Desert, Española Basin and Edwards-Trinity aquifers of the USA, Datong Basin, China, parts of Iraq and the loess of the Chaco-Pampean Plain, Argentina. Many of these plains host eroded deposits of granitic and felsic volcanic precursors which likely act as primary sources of U. Numerous examples exist of groundwater impacted by U mineralization, often accompanied by mining, including locations in USA, Australia, Brazil, Canada, Portugal, China, Egypt and Germany. These may host high to extreme concentrations of U but are typically of localized extent. The overarching mechanisms of U mobilization in water are now well-established and depend broadly on redox conditions, pH and solute chemistry, which are shaped by the geological conditions outlined above. Uranium is recognized to be mobile in its oxic, U(VI) state, at neutral to alkaline pH (7–9) and is aided by the formation of stable U–CO3(±Ca, Mg) complexes. In such oxic and alkaline conditions, U commonly covaries with other similarly controlled anions and oxyanions such as F, As, V and Mo. Uranium is also mobile at acidic pH (2–4), principally as the uranyl cation UO22+. Mobility in U mineralized areas may therefore occur in neutral to alkaline conditions or in conditions with acid drainage, depending on the local occurrence and capacity for pH buffering by carbonate minerals. In groundwater, mobilization has also been observed in mildly (Mn-) reducing conditions. Uranium is immobile in more strongly (Fe-, SO4-) reducing conditions as it is reduced to U(IV) and is either precipitated as a crystalline or ‘non-crystalline’ form of UO2 or is sorbed to mineral surfaces. A more detailed understanding of U chemistry in the natural environment is challenging because of the large number of complexes formed, the strong binding to oxides and humic substances and their interactions, including ternary oxide-humic-U interactions. Improved quantification of these interactions will require updating of the commonly-used speciation software and databases to include the most recent developments in surface complexation models. Also, given their important role in maintaining low U concentrations in many natural waters, the nature and solubility of the amorphous or non-crystalline forms of UO2 that result from microbial reduction of U(VI) need improved quantification. Even where high-U groundwater exists, percentage exceedances of the WHO guideline value are variable and often small. More rigorous testing programmes to establish usable sources are therefore warranted in such vulnerable aquifers. As drinking-water regulation for U is a relatively recent introduction in many countries (e.g. the European Union), testing is not yet routine or established and data are still relatively limited. Acquisition of more data will establish whether analogous aquifers elsewhere in the world have similar patterns of aqueous U distribution. In the high-U groundwater regions that have been recognized so far, the general absence of evidence for clinical health symptoms is a positive finding and tempers the scale of public health concern, though it also highlights a need for continued investigation

Baseline Scotland : groundwater chemistry of the Old Red Sandstone aquifers of the Moray Firth area

The groundwater chemistry of Old Red Sandstone aquifers in the Moray Firth area has been characterised based on new chemistry analyses generated during the Baseline Scotland project, combined with existing analyses from earlier projects. A total of 39 groundwater sample analyses were interpreted for the purposes of this study. Of these, 17 were collected in 2007 specifically for the Baseline Scotland project. These were augmented with a further 22 samples collected during separate BGS projects since 2001. The sites were chosen to be representative of groundwater in the area, and sources that were poorly constructed were avoided. A summary of the conclusions arising from this study follows. 1. Groundwater in the Old Red Sandstone aquifers of the Moray Firth is generally moderately mineralised, with a median SEC of 469 μS/cm (interquartile range 341–591 μS/cm). The pH is variable: median pH is slightly alkaline (7.31), but values range from 5.33 to 8.06. The major ion chemistry appears to be dominated by the dissolution of carbonate cements within the aquifer and overlying deposits, and the variable influence of seawater (either directly as saline intrusion or as aerosols). 2. The dominant cation is Ca, with a median concentration of 54.8 mg/L (interquartile range 42.5 – 74 mg/L). Mg and K concentrations are generally low (median 4.21 and 3.7 mg/L respectively). The median Na is 20.6 mg/L (interquartile range 12.6–28 mg/L); however, a few samples have been affected by proximity to the sea and have much higher concentrations, as illustrated by the 95th percentile (68 mg/L) and maximum concentration (153 mg/L). 3. The dominant anion is bicarbonate, with a median concentration of 183 mg/L (interquartile range 183–230 mg/L). Around one third of the samples are saturated with respect to calcite. Sulphate concentrations are generally low (median 14.6 mg/L, interquartile range 7.7–36.4 mg/L), although higher concentrations are encountered in samples affected by seawater, and/or possibly by gypsum bands within the aquifer. Chloride concentrations follow broadly the same distribution as Na and have a median of 38.8 mg/L and interquartile range of 19.5–49.5 mg/L; the same few samples show high Cl concentrations as do Na. 4. Concentrations of minor and trace elements in the groundwater are dominated by the redox conditions. Measured values of dissolved oxygen indicate a large range in redox conditions across the aquifer. Concentrations of DO close to 10 mg/L indicate fully oxic conditions. By contrast, groundwaters with DO concentrations <1 mg/L are indicative of sub-oxic or mildly reducing conditions, and appear to be prevalent in much of the Upper Old Red Sandstone outcrop, and parts of the Middle Old Red Sandstone. Reducing conditions may reflect the presence of low permeability layers (often marine in origin) within the thick superficial deposits overlying the Old Red Sandstone aquifer. The effect of reducing conditions is to increase concentrations of Fe and Mn, which show median concentrations of 38 and 43 μg/L respectively, and 75th percentile values of 354 and 227 μg/L respectively. 5. The majority of samples (21) were collected from the Upper Old Red Sandstone aquifer; 14 samples were collected from the Middle Old Red Sandstone and only 4 samples from the Lower Old Red Sandstone. The samples show broadly similar chemistry across the three aquifer units; however, there are several notable differences. Samples from the Upper Old Sandstone aquifer show very similar cation distribution, dominated by Ca, while the Lower and Middle Old Red Sandstone aquifers show a wider cation distribution and appear less affected by calcite dissolution. The pH of the Lower and Middle Old Red Sandstone aquifers is slightly lower (more acidic), generally less than 7.0. Groundwaters within the Upper Old Red Sandstone aquifer are generally more reducing, probably reflecting their location close to the coast and hence the influence of the sea and/or overlying marine superficial deposits. 6. Nitrate concentrations are variable across the aquifer units, although median concentrations are low (1.45 mg/L TON-N or less in each aquifer). The prevalence of low oxygen conditions in the sampled groundwaters has led to denitrification, which means the relationship between land use and nitrate concentrations is less obvious than for other parts of Scotland (MacDonald et al., 2005a). However, there is a clear relationship between nitrate concentrations and the Nitrate Vulnerable Zone (NVZ) that covers much of the study area, with the seven highest groundwater nitrate concentrations, ranging from 5.98 to 22.1 mg/L TON-N, all from samples taken within the NVZ. The highest median concentrations were from samples collected on land known to be used for dairy, pig or poultry farming. 7. Phosphorus concentrations in Moray Firth groundwaters range from less than detection limit up to 172 μg P/L, with an overall median of 36 μg P/L, which is in the eutrophic range for surface waters. Concentrations are generally low in the western part of the study area, and an observed relationship with the spatial pattern of F suggests that both elements may be in part derived from the dissolution of phosphate minerals, such as apatite, from the aquifer rocks. Concentrations in the eastern part of the study area are generally higher, usually in the mesotrophic or eutrophic range for surface waters. The higher values may be related to land use, with P inputs from agricultural activity. 8. An estimate of the baseline groundwater chemistry conditions in the Old Red Sandstone aquifers has been presented, based on a statistical summary of the chemical data. This represents data between the 10th and 90th percentiles, with the exception of NO3-N and P, where the influence of anthropogenic activity is likely to have distorted baseline conditions throughout much of the study area. This statistical approach to estimating baseline was complemented by selecting ten analyses of groundwater samples collected from high quality groundwater sources, which are unlikely to have been impacted by any agricultural contamination, and which represent the general the groundwater conditions in the Old Red Sandstone aquifers in the Moray Firth area

Baseline Scotland : the Lower Devonian aquifer of Strathmore

This report presents a summary of the groundwater chemistry of the Devonian sedimentary aquifer in Strathmore, eastern Scotland. The area covered by this study extends from Perth in the southwest to Stonehaven in the northeast. The survey forms part of the ongoing Baseline Scotland project. The Devonian sedimentary rocks of Strathmore form an important regional aquifer in an area of some of the most fertile agricultural land in Scotland, with a number of major urban settlements. The aquifer provides water for agriculture, industry, recreation and domestic use. The aquifer can be divided into six main geological units, largely sandstones but with significant conglomerates and, less commonly, mudstones. All of these units are classed as moderately or highly productive aquifers, but too few data are available to allow a detailed analysis of the hydrogeological variations between the formations. A total of 35 new groundwater samples were collected during this project, and the resulting chemistry data combined with data from 13 additional samples collected during a BGS sampling programme in 2001. The samples were analysed at BGS laboratories for a wide range of chemical constituents. The collection and interpretation of new groundwater chemistry data for the Strathmore area has led to the following conclusions. • The groundwaters of the Devonian aquifer in Strathmore are mainly weakly mineralised, with TDS concentrations mostly less than 400 mg l–1. Groundwaters have near-neutral to slightly alkaline pH values and are for the most part oxygenated, with detectable dissolved oxygen and high redox potentials. As a result, dissolved iron, manganese and ammonium (NH4-N) concentrations are usually low. Water from shallow boreholes and springs is often undersaturated with calcite, but in deeper boreholes, reaction with carbonate minerals in the aquifer is more usual and most of these are saturated with respect to calcite. • Nitrate concentrations are often high, with an interquartile range of 2.6 mg l–1 to 11.7 mg l–1 as NO3-N. Nearly one third of the samples exceeded the EC drinkingwater limit for nitrate of 11.4 mg l-1 as NO3-N. An anomalously high nitrate concentration of 81 mg l–1 as NO3-N was observed in one sample, and appears to result from direct downhole contamination by nitrogen fertiliser. Under the oxidising conditions, nitrate is a stable solute species across the aquifer and is found at depths in excess of 100 m. • Concentrations of phosphorous in groundwater across the aquifer are typically less than 0.1 mg l-1 (the 90th percentile), with a median of 0.03 mg l-1. Given the importance of P in controlling eutrophication in surface water, these concentrations in groundwater may be significant. • Increased salinity occurs in groundwater in some near-coastal boreholes, most likely as a result of mixing with seawater. • Most cationic trace elements have low concentrations, in accordance with the neutralpH groundwater conditions. Concentrations of arsenic are relatively high in some groundwaters (up to 8.8 μg l-1) though none exceeds the EC maximum permissible value for drinking water of 10 μg l-1. Concentrations of uranium reach up to 15.4 μg l–1, with the highest concentration just exceeding the WHO provisional guideline value for drinking water of 15 μg l–1. Two other exceedances above maximum permissible values for drinking were observed, for nitrite (highest concentration 0.194 mg l-1) and fluoride (highest concentration 3.7 mg l-1). The chemistry and residence time indicators (CFC and stable isotopes) indicate that the groundwaters are largely of young age, being mostly recharged within the last 40 years, with mixing throughout the top 100 m of the aqufier. The samples show little evidence of the presence of palaeowaters. The young age of the groundwaters means they are vulnerable to contamination. • A first estimate of the baseline groundwater chemistry conditions in the Strathmore Lower Devonian aquifer can be given by the statistical summary of the data collected in this study (with the exception of nitrogen (N) and phosphorous (P), where the influence of anthropogenic activity is likely to have affected concentrations across the aquifer). To compliment this approach, six good quality sites have been chosen which represent the majority of groundwaters found in Strathmore. • The most significant groundwater-quality problems identified by this survey are: o the widespread presence of elevated nitrate concentrations in groundwater, which is strongly linked to agricultural activity; o elevated phosphate concentrations which may affect the quality of surface water when discharged to rivers as baseflow. o the presence of saline water in some near-coastal boreholes, indicating localised saline intrusion. It is not clear to what degree the saline intrusion is natural and to what degree it has been enhanced by over-pumping