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Groundwater in the Celtic regions

N. S. ROBINS 1 & B. D. R. MISSTEAR 2

1British Geological Survey, Maclean Building, Wallingford, Oxjordshire OXIO 8BB, UK 2 Department of Civil, Structural & Environmental Engineering, University of Dublin, Trinity College, Dublin 2,

Abstract: The Celtic regions of Britain and Ireland have a complex and diverse geology which supports a range of regionally and locally important bedrock aquifers and uncon- solidated Quaternary aquifers. In bedrock, aquifer units are often small and groundwater flow paths short and largely reliant on fracture flow. Groundwater has fulfilled an important social role throughout history, and is now enjoying renewed interest. Groundwater quality is generally favourable and suitable for drinking with minimal treatment. However, many wells are vulnerable to microbiological and chemical pollutants from point sources such as farmyards and septic tank systems, and nitrate concentrations from diffuse agricultural sources are causing concern in certain areas. Contamination by rising minewaters in abandoned coalfields and in the vicinity of abandoned metal mines is also a problem in some of the Celtic lands.

At the close of the Hallstatt period the soils. Land use includes grassland characteristic occupied much of central and western Europe, of much of lowland Ireland, upland pastoral and Britain and Ireland were home to the , farming typical of much of central Wales and the Picts and the Britons. Nowadays, the land of arable cultivation in eastern . Forestry the Britons is divided between England and is also extensive. Many lowland coastal areas Wales, and the Celtic regions are considered support the highest population density as well as principally as Wales, south-west England (the traditional heavy industry, manufacturing and Cornish peninsula), , Scotland and service industry, and mining has left its impact Ireland. Celtic regions have become those areas over the Midland Valley of Scotland, South farthest from continental Europe and the English Wales, south-west England and parts of central capital. History has repeatedly demonstrated and eastern Ireland. that the people of the Celtic regions share an Up and until now the main focus in hydro- independence of outlook which in Britain has geology has been groundwater development recently been reflected in political devolution. and resources evaluation. These activities pre- But as well as similarities in the aspirations, occupied hydrogeologists throughout the 1980s history and culture of the different Celtic peoples, and early 1990s, but since then the empha- there is a common thread through many of the sis has moved towards environmental aspects hydrogeological and associated environmental of groundwater. Of particular importance are issues affecting the Celtic regions. groundwater protection against pollution and The Celtic regions enjoy a maritime temperate the interrelationship between groundwater and climate with orographic rainfall over upland or surface water, especially in sensitive wetland hilly terrain on the western margins. Apart from habitats. these characteristic upland areas there are a A number of specific technical issues are number of broad tracts of lowland. The geology pertinent to the Celtic regions. These include: of these lands is diverse and complex, with ages and lithologies ranging from Precambrian gran- (a) recharge is difficult to quantify, more so ite and metasediments, through Palaeozoic lime- where Quaternary deposits are present; stone, Permo-Triassic sandstone and Cretaceous (b) the hydrogeological characteristics of gla- Chalk, to Palaeogene volcanic rocks (Fig. 1). cial tills require detailed research, especially Drift geology includes a widespread blanket the role of bypass flow; mantle of till as well as a range of coarser (c) hydrogeological processes in peat are little granular Quaternary deposits. Above this the understood (e.g. 14% of Scotland is cov- variety of soil types include peat, gley and sandy ered by I na or more thickness of peat);

From: ROBINS, N. S. 8,: MISSTEAR, B. D. R. (eds) Groundwater in the Celtic Regions: Studies in Hard Rock and QuaternaJT Hydrogeology. Geological Society, , Special Publications, 182, 5-17. 1-86239-077-0/00/$15.00 @ The Geological Society of London 2000. Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

6 N. S. ROBINS & B. D. R. MISSTEAR

• ...... : -.. -~. :.- -..-.

0 100 k,m ': ..::2.:.'.:i"..: ,... :."~ i , p ~,-:.'.-.-" .- :" .....' . "':i

z¢

...:...-....

~i~ '

Cretaceous and Palaeogene

Permian and Triassic

Devonian and Carboniferous

~ Ordovician and older strata; Igneous rocks

Fig. 1. Broad geological/hydrogeological groups in the Celtic regions.

(d) fracture flow of groundwater predomi- (f) minewater discharges in the shallow and nates, and is difficult to replicate by mod- surface environment require evaluation and elling; remediation; (e) karst hydrogeology involves complex inter- (g) valley bottom hydrology/hydrogeology is actions with surface water, and requires poorly understood, particularly in upland intensive study; catchments; Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

GROUNDWATER IN THE CELTIC REGIONS 7

(h) local groundwater quality is often affected by point sources of pollution such as septic ~i~ i~ ~iiiiii~i)~ ~ ~ ~i I~ ~: ~ tank systems, and diffuse pollution from agriculture is also a threat to water quality in particular regions; (i) development of brownfield sites and con- taminated land has implications for groundwater quality.

Groundwater and people Groundwater fulfils an important role through- out the Celtic lands in satisfying demand for water, both on a local and a national level. Groundwater is not generally considered as the mainstay of bulk public supplies in many areas, although its contribution to public supply is significant (Table 1). Exploitation for generally small volume private consumption, principally for domestic or farm use, is also very impor- tant, and larger volume uses for irrigation and industry are also surprisingly widespread. There are a number of reasons why ground- water supply is important even in areas facing the prevailing moisture-laden westerly winds, and blessed with abundant surface water resources. The reasons for this include: (a) the consistent and generally favourable quality of groundwater; (b) ready access to groundwater, at least in Fig. 2. Exploratory drilling for public water supply small volumes; on Arran. (c) economics of development and supply; (d) mainly licence-exempt development. and space for surface water gathering make These factors conspire to increase the impor- groundwater a preferred option (Fig. 2). Perhaps tance of groundwater for rural and island the greatest advantage of groundwater is that it is community supplies. Many peat-coloured village available at many, diverse locations, and it does supplies in upland regions, and other surface not need long and expensive pipe runs connect- water supplies of variable quality and associated ing source and consumer. treatment difficulties, are being replaced by small Poor aquifer characteristics in many areas, groundwater schemes targeted at village level. especially in the older bedrock formations, mean Groundwater is also valuable for island commu- that groundwater supplies are often relatively nity supply where insufficient catchment area small by comparison to groundwater schemes in

Table 1. Estimates of groundwater in supply

Groundwater as Volume of Estimated number Volume of water in a % of total groundwater in of private sources private supply public supply public supply (M1 d -1) (Mld -1)

Scotland 5 l 10 20 000 110 N Ireland 10 77 1 500 31 Ireland 15 270 > 100 000 80 Wales 8 250 5 000 95 Northumbria 10 110 3 000 30 Cornwall 3 12 10 000 62 Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

8 N. S. ROBINS & B. D. R. MISSTEAR the Sherwood Sandstone and Chalk aquifers of This burgeoning industry plays on the image central and southern England. However, there of green and pleasant lands to sell untreated are a very large number of wells in the Celtic bottled groundwater at prices that currently lands. Although it is not possible to give an exceed those of petrol, volume for volume. How- exact number, one estimate is that there are ever, not all bottlers are situated in such pris- more than 200 000 wells in Ireland alone (Wright tine environments as consumers might imagine. 1999). In addition to wells, groundwater supplies Some draw from shallow alluvial sources at risk are obtained from springs, infiltration galleries to pollution by local farming activity, whilst and Ranney wells (Jones & Singleton this others draw from sandstone aquifers adjacent volume). Some of the springs have very large to rivers of periodically indifferent quality and flows e.g. the Schwyll spring in South Wales has of undefined hydraulic connectivity with the an average flow of 3901s -1 (Hobbs this volume) groundwater. and the Pouladower spring in County Clare in western Ireland has mean flows of between 115 and 720 ls -1 (Deakin this volume). Groundwater and the environment The traditional social importance of ground- water sources is illustrated by the naming of Groundwater is a key to many environmental certain springs and wells after saints. This issues in the Celtic regions. Its role in maintain- practice conferred some measure of protection ing low surface water flow is as fundamental to on the source from elements of evil, and the the maintenance of wetland areas, including water could be drunk for cures and grace. groundwater fed peatlands, as it is to the main- Although pilgrimages to Holy wells are less tenance of the integrity of stream flow (Soulsby common nowadays, many wells are still visited, et al. this volume). It also plays a part in especially on the Saints' day. Selected Clootie moderating acid surface water environments, wells (Devil or Witch) in the Black Isle of as baseflow is commonly alkaline even in areas northern Scotland are annually bedecked with a apparently devoid of calcite, so that otherwise variety of torn coloured rags (clooties) to attract acid upland streams may temporally become a cure from disease. Elsewhere, Holy wells- alkaline. there are believed to be about 3000 in Ireland Groundwater, although seemingly innocent, is alone (Logan 1980) - are adorned with plaques not all good news. Acid and iron-rich mine- bearing the scriptures and may be blessed waters accumulate in abandoned mineworkings periodically by the priest. and rebound to contaminate the shallow envir- Nowadays, groundwater also contributes to onment and ultimately surface waters (Younger bulk public supply. In Ireland about 15% of the & La Pierre this volume). Contamination from water supplied by local authorities comes from point sources such as landfill, industry or septic groundwater, and groundwater accounts for tank systems coupled with diffuse pollution from about 25% of all water supplies in the country. agricultural and other activities requires careful In some counties the proportion of total water management of groundwater resources (Lewis supply from groundwater is much greater, e.g. et al. this volume; Misstear & Daly this volume). Roscommon 86%, Offaly 56% and Laois 52% Source protection can be undertaken in many (Department of the Environment and Local fractured hard rock aquifers according to the Government et al. 1999). There are also impor- prevailing groundwater setting rather than by tant wellfields for public supply in the Lagan means of detailed data gathering and analytical Valley in , in , modelling (Robins 1999). In addition, manage- Morayshire and Fife in Scotland, and in alluvial ment activities need to be supported by enabling valley fill material in west Wales. legislation in order that resource derogation is Groundwater has fostered a number of high minimized (Fox this volume). profile industries. The major brewing centres all at one time relied on groundwater for make-up water, the mineralization of the water offsetting Groundwater occurrence the need to add brewing salts and providing each centre with a unique product flavour. Distil- Classes of aquifer leries, both in Scotland and Ireland, rely heavily on groundwater and jealously guard the chem- Three classes of aquifer occur within the Celtic istry of their many spring and borehole sources regions (Table 2). The first incorporates bedrock from competitors. Nowadays, Celtic ground- aquifers of regional importance such as the water is also packaged and sold neat, not only sandstone basins of North Wales, south-west through the home market but also worldwide. Scotland and Northern Ireland; the limestone Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

GROUNDWATER IN THE CELTIC REGIONS 9

Table 2. Hydraulic characteristics of the three aqu~,r classes in the Celtic regions Class Geology Location Properties Transmissivity Storativity Borehole yield (m2d -1) (Is -1 )

Regionally Permian and Generally in Anisotropic, 100 to 4000 0.01-0.20 5 to 40 important Triassic basins; lowland fracture bedrock some Devonian areas; Karst flow sandstones; limestone in dominant, Carboniferous Ireland & regional and Limestone; South local flow some volcanics Wales paths Locally Precambrian and Widespread, Anisotropic, 20 to 100 <0.05 1 to 5 important Lower in lowland secondary bedrock Palaeozoic; and upland porosity some Upper areas; dominant, Palaeozoic; Lough local flow some volcanics Neagh basin paths Superficial Alluvium; Widespread, Primary 50 to 5000 Variable 3 to 40 granular best porosity glacial developed in only, deposits; raised valley potential is beach; and bottoms limited by wind-blown and coastal geometry sand areas

aquifers of Ireland; and the Devonian and these aquifers, and this reflects the small stor- Carboniferous aquifers of South Wales and the ativity of a fracture that is locally remote from Midland Valley of Scotland (Fig. 1). The second the 'water table'. Groundwater flow paths may class comprises the bedrock aquifers of local be several kilometres in length, and may pass importance, which are widespread, and include across a number of surface water catchments Lower Palaeozoic and Precambrian strata as between principal recharge area and discharge well as volcanic aquifers, and some Devonian area. The majority of the groundwater transport and Carboniferous rocks. The aquifers that is shallow except where deeper intergranular occur within the Quaternary and younger super- porosity and dilated fractures are present as, for ficial strata form the third class. These are also example, in parts of the Permo-Triassic sand- widely distributed, and in some areas can form stones in Scotland and Northern Ireland. Good aquifers of regional importance (e.g. the Cur- data on aquifer properties, such as transmissiv- ragh glacial gravel aquifer in eastern Ireland). ity and specific yield, are relatively scarce in the The regionally important bedrock aquifers are Celtic regions, and aquifer performance is often typically characterized by secondary permeabil- expressed in terms of potential well yield and/or ity of considerably greater magnitude than the specific capacity (Wright this volume). Sustain- available intergranular permeability. The aqui- able borehole yields are typically in the range fers may be anisotropic with the prevailing 5 to 201s -a, but yields up to 401s 1 have been geological structure influencing the preferred obtained in some areas. horizontal flow paths, and with vertical perme- Locally important bedrock aquifers generally ability controlled by bedding and the availability have little intergranular permeability except in of vertical joints. The degree of preferential isolated horizons, so that nearly all groundwater flow varies from the weakly fractured Devonian storage and transport takes place within avail- aeolian sandstones of the Midland Valley of able secondary porosity. Enhanced storage may Scotland (Gaus & 6 Dochartaigh this volume) be available if the bedrock aquifer is in hydrau- to the conduit flow dominated karstic limestones lic contact with saturated granular superficial of Ireland (Coxon & Drew this volume) and deposits. These aquifers are strongly aniso- South Wales (Hobbs this volume). Although tropic and may react to pumping as if they these aquifers are generally unconfined they may were confined, for the reason given above. Bore- locally be confined by till, especially in low-lying hole yields are typically in the range 1 to 51 s 1 areas. Whether physically confined or not, a although some higher yielding sources, notably confined response is not uncommon on pumping spring flows, have been recorded. Groundwater Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

10 N. S. ROBINS & B. D. R. MISSTEAR flowpaths are generally short and usually corre- stone aquifers that issue via sand and gravel spond to groundwater catchment scale (Robins horizons (Daly 1995). et al. this volume). There are few non-aquifers although many Groundwater in unconsolidated superficial unweathered rocks have low permeabilities. A deposits offers intergranular porosity for storage non-aquifer comprises massive rock with no and transport of groundwater. The geometry of transmissive discontinuities and such conditions the deposit may constrain the storage potential do not generally exist in the relatively shallow unless the aquifer is in hydraulic contact with a weathered zone other than on a limited scale. nearby stream or river. Different lithologies may Most of the geological formations in the Celtic be interbedded within one deposit and horizon- regions are capable of providing at least a small tal permeability may exceed vertical permeabil- water supply, and so cannot be regarded as non- ity with, for example, a gravel layer offering aquifers. greater potential than a silty sand. Peat and clay layers may act as local aquicludes within super- ficial sequences. Sustainable yields from these Role of secondary permeability deposits are variable, but range up to 401s 1 in selected locations which have both enhanced Deformation and weathering of consolidated storage from a surface water body and suit- rock creates fractures that promote ingress of ably high transmissivity (Hiscock & Paci this groundwater and further potential for weath- volume). In this respect, two major bankside ering. The blocks of unweathered material may wellfield schemes have been developed in allu- break down to form a granular weathering prod- vial gravels in Scotland in recent years (Jones uct, and subsequently a clay grade material. In & Singleton this volume). Thin aquifers are northern Britain these products have been self-limiting wherever the pumping drawdown removed or reworked by glacial action, but the from a groundwater source reduces the effective underlying fractured bedrock remains in place. aquifer thickness, and hence also transmissivity, The fractures provide secondary porosity which leading to declining yields. As well as forming enables groundwater transport in rocks with aquifers in their own right, permeable superficial little if any primary or intergranular porosity deposits are often significant in terms of the (Fig. 3). This is illustrated by comparing lab- additional storage they provide for underlying oratory determined permeability and porosity bedrock aquifers. They may also act as path- values with hydraulic conductivity and storativ- ways for groundwater discharge. For example, ity derived from field testing in Permian and there are many springs in ireland fed by lime- Triassic aquifers (Table 3). The field conductivity

Fig. 3. Open fracture in Devonian sandstone from Morayshire. Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

GROUNDWATER IN THE CELTIC REGIONS l l

Table 3. Aquifer evaluation data for boreholes in the Permian and Triassic aquifers in south-west Scotland and Northern Ireland

Area Yield Hydraulic Laboratory Storativity Laboratory (1 s- 1) conductivity permeability porosity (md 1) (md-1)

South-west Scotland Dumfries 53 1 0.001 0.01 0.15 Dumfries 17 5 0.1 Dumfries 8 20 0.01 0.19 Mauchline 41 7 0.000 [ Mauchline 19 9 1 0.01 0.26 Mauchline 46 10 1 0.01 0.27 Thornhill 24 3 1 Northern Ireland Lagan Valley 12 0.3 0.001 to 0.01 - 0.15 to 0.27 Haw Hill 20 3 0.1

values are between 3 and 1 000 times greater ments in , as part of the UK radio- than the laboratory derived values for perme- active waste research programme, demonstrated ability, depending on the degree of fracturing in that groundwater transport readily takes place the vicinity of the test borehole, whilst storativity to considerable depths even though the inter- often indicates an elastic, rather than an uncon- granular porosity of these rocks is less than 0.01 fined, response to pumping (Lovelock 1977; (Mather 1997). Packer testing of exploratory Robins 1990). boreholes demonstrated that the hydraulic con- Hydraulic enhancement of secondary perme- ductivity of these strata ranges from 0.1 md 1 ability is common to all fractured aquifers and down to very low, at depths from just beneath it is critical to the occurrence of groundwater the water table to about 150m. Values fall in many of the Celtic regions. There are a num- rapidly at greater depths. Hydrochemical evi- ber of special cases in Ireland. One is the dence demonstrated both shallow and relatively widespread karstification in the Carboniferous short groundwater flowpaths which are up to Limestone and the Ulster White Limestone, 2km in length, and longer groundwater flow- whereby fracturing has developed through solu- paths with older water circulating to depths tion and attrition into extensive cavern and con- of over 200 m along a lateral distance of up to duit systems (Barnes this volume; Coxon & 5km (Kay et al. 1983). Total infiltration to the Drew this volume; Deakin this volume). These groundwater system was estimated with the aid act as preferred pathways for rapid groundwater of thermal imaging of springs and seepages to be transport, often between sink-holes and emer- about 100 mm a 1 (Brereton & Lee 1987). gences. A second case is the important influence Similar flow path systems have been identi- dolomitization has had on secondary perme- fied in other basement rock types. The majority ability in carbonate aquifers, especially in the of shallow flow takes place in the upper 25m south Midlands (Daly 1995). Another special of saturated aquifer over catchment-scale flow case is the Palaeogene Antrim Plateau Basalt paths. which contains relatively conductive fossil soil Deep, but small volume, groundwater cir- horizons, or 'boles', which developed between culation has been identified at a number of lava flows, and combined with a sub-vertical saline discharges at former spa sites in Silurian conjugate fracture system provide an otherwise and Ordovician rocks. These include Melrose, weakly permeable volcanic rock with significant Moffat and Hartfell in the Southern Uplands of potential for groundwater transport and sto- Scotland, and the small discharges in mid-Wales: rage. On a smaller scale the Durness Limestone 0.11s -1 at Llandrindod, and only 0.051s -1 at and the Loch Tay Limestone in Scotland also Builth Wells (Edmunds et al. 1998). In Ireland show karst features. the former spa at Mallow is one of a group Little quantitative analysis of the role of of warm water discharges in Munster indica- fracture flow has been carried out in basement tive of deep circulation in Carboniferous strata. rocks. However, investigation into the Strath A similar group occurs in Leinster to the west Halladale Granite and Precambrian metasedi- of Dublin (Burdon et al. 1983). Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

12 N. S. ROBINS & B. D. R. MISSTEAR

Significance of till and lateral rather than longitudinal flow in the upper Lagan Valley. With the exception of south-west England, the Similar analyses are now available for most of Celtic regions were covered by ice through much the significant bedrock aquifers in the Celtic of the Quaternary Period. Glacial deposits of lands. For example, owing to extensive structural all kinds are, therefore, characteristic of many deformation, the main Palaeozoic bedrock aqui- areas. These include permeable deposits such fers in the Irish Republic form relatively small as outwash fans, eskers and kames, lacustrine discrete aquifer units, frequently with complex deposits and associated alluvial terrace material, boundaries. Faults may occur at separations of as well as low permeability lodgement till. The 0.5 to 1 km and have a major impact on the flow extent of these deposits is such that 90% of regime in these aquifers (Daly 1995). Ground- the land area of Ireland is covered by drift. water flow paths are constrained by the geometry Much of this is till or ground moraine, which of the aquifer unit and the head differences across is an irregular layer of variable lithology, typic- it. A detailed study of the groundwater flow ally containing poorly sorted silt- or sand-grade system of the Castlecomer Plateau showed that material in a matrix of clay, with cobbles and the Wesphalian sandstone aquifer system is boulders and occasional sand and gravel hor- divided by faulting into three main blocks, with izons. Till may vary in thickness up to 100m but little or no hydraulic connection between them is generally less than 20 m thick. (Misstear et al. 1980). The overall hydraulic conductivity of till is Groundwater flowpaths in granular drift generally low and it will not readily conduct deposits are also limited by the geometry of infiltrating water. It therefore has a significant the aquifer. In valleys, where these deposits are role as an inhibitor to recharge as well as a most common, hydraulic contact with surface protective shield to bedrock aquifers otherwise waters may induce local flow systems between vulnerable to surface pollution. The integrity of gaining and losing reaches of a river. Where the deposit is usually unknown and small scale there is significant baseflow, the dominant variations in lithology and the presence of groundwater flow direction may be laterally fractures or deep root zones offer the potential towards the river rather than longitudinally for rapid by-pass transport to the base of the down the length of the valley. till. As a general rule, till reduces the recharge potential to an underlying aquifer by about 30%, but actual determination of recharge is difficult to determine and expensive to attain. In Karst addition, available drift mapping is inadequate About 50% of the Irish Republic is underlain by even for zoning areas of greater and lesser Lower Carboniferous Limestone (Coxon & recharge potential although modern mapping Drew this volume), which forms the most techniques, such as drift domain mapping, are important aquifer in the country. Carboniferous beginning to address this difficulty (McMillan Limestone is also an aquifer of regional sig- et al. 2000). nificance in South Wales (Hobbs this volume). The degree and extent of karstification is varied. In areas with well developed karst, groundwater Groundwater flowpaths flow occurs via large conduits- with recorded flow rates of up to 200mh 1, comparable to The first attempt at delineating groundwater surface water velocities (Drew & Daly 1993)- flowpaths in a Celtic aquifer was made by and via a diffuse network of smaller fractures, in Hartley (1935) in an analysis of the hydraulics which flow rates are much lower. of the Triassic aquifer in the Lagan and Dun- The uneven distribution of permeability is donald valleys of Northern Ireland. This sur- reflected by small numbers of high yielding wells prisingly robust analysis has stood the test of in areas otherwise characterized by low yield- time and Hartley's piezometric contour map ing wells. Drew and Daly (1993) analysed the and groundwater flow paths are reproduced in performance characteristics of 225 wells in lime- the marginalia of the Hydrogeological Map of stone aquifers in the west of Ireland, and some Northern Ireland (BGS 1994). The map shows of the results are reproduced in Table 4. Yields a groundwater flow system with recharge areas vary from zero up to 761s 1, with a relatively in the higher ground with least cover of till, low median value of 1.21s -1. More recently, and discharge areas in the lower parts of the as part of a national study of well yields and valleys towards the coast. It clearly defines the specific capacities, Wright (this volume) found groundwater divide in the Dundonald Valley, that wells in the Lower Carboniferous Limestone Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

GROUNDWATER IN THE CELTIC REGIONS 13

Table 4. Summary oj'perJbrmance characteristics of 225 Carboniferous Limestone wells in the west of Ireland (after Drew & Daly 1993)

Variable Maximum Minimum Mean Median Standard deviation

Depth (m) 177 3 57 53 27 Yield (1 s -1) 76 0 2.4 1.2 6 Specific capacity (1 s 1 m) 7.6 0 0.8 0.2 1.4 aquifers in the west of Ireland covered ahnost the (Daly 1993), and there is an estimated surplus of whole range of yields. resource over abstractions equivalent to 50 mm A key feature of karst hydrogeology is the of rainfall over the area of the whole country close interrelationship between groundwater (Wright et al. 1982). and surface water. This is especially the case The main mechanisms for recharge are: in lowland areas, since surface water drainage (a) direct recharge from rainfall infiltrating is rare in upland karst (Coxon & Drew this through outcrop, soil and drift; volume). Groundwater and surface water catch- (b) secondary recharge from losing streams, ments rarely coincide, and it is difficult to define additional runoff from nearby low perme- an exact zone of contribution to a well or spring ability areas and, in karst, via swallow holes. (Deakin this volume; Hobbs this volume). This has implications for groundwater protection and Several of the mechanisms may be important for managing turloughs, the temporary ground- in any one area. The large Schwyll spring near water-fed lakes that are sites of ecological Bridgend in South Wales is recharged from importance (Coxon & Drew this volume). The infiltrating rainfall over the limestone aquifer combination of rapid conduit flow, low stor- outcrop, from stream sinks and by influent ativity and close relationship with surface water sections of river (Hobbs this volume). Quantifi- means that karst areas can be prone to extreme cation of recharge is usually by relatively simple flooding events. In the Gort area in County methods such as soil moisture balance and Galway, major flooding problems occurred in analysis of baseflow. More sophisticated ana- response to heavy winter rainfall in both 1990 lyses are rare owing to a lack of knowledge on and 1995 (Drew & Daly 1993; Coxon & Drew recharge processes such as infiltration rates in this volume). Conversely, spring flows and bore- low permeability tills. hole water levels in karst aquifers may decline In the Dumfries basin in Scotland recharge is rapidly during prolonged periods of drought. estimated to be 436 mm a -1 or about 31% of the mean annual rainfall (Gaus & 6 Dochartaigh this volume). In Fife, on the east side of Scotland, Recharge, throughput and baseflow recharge is only between 115 and 145 mm a -t but this represents between 18 and 28% of the long In contrast to south-east Britain and continental term rainfall. Similarly in west Wales, potential Europe, the Celtic regions possess a relatively infiltration of 535 mm a -1 represents 38% of the humid temperate climate. Rainfall increases long term rainfall (Robins et al. this volume). from east to west, and with elevation. In Ireland, The groundwater contribution to rivers as mean annual precipitation varies from about baseflow is often significant. Analysis of river 700ram around Dublin to over 2000mm in flow data from 1972 to 1981 in the mainly upland areas in the west and south-west (Collins Carboniferous Limestone Nore River Basin in & Cummins 1996), where soil is retained at field southern Ireland indicated the groundwater com- moisture capacity for a large part of the year. ponent to be 50% of the total flow, equivalent Potential recharge- i.e. the excess moisture to 26% of the total rainfall (Daly, E. 1994). after evaporation is deducted from precipita- tion - varies from 400 to 1000ram (Daly 1995). Despite the relatively high potential recharge, Groundwater quality actual recharge is often much less because of low aquifer storativity. Evidence of 'rejected Most of the aquifers in the Celtic lands are recharge' includes high level springs, flooding unconfined, with shallow flow systems, and so the and water logging of land. In Ireland, annual groundwaters are generally well-oxygenated and groundwater abstractions are estimated at only weakly mineralized, with calcium and bicarbo- about 3% of the estimated annual recharge nate forming the main ionic components (Daly Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

14 N. S. ROBINS & B. D. R. MISSTEAR

1989; Robins in press). More mineralized ground- waters, depleted in oxygen, occur in deeper aquifer systems such as Devonian sandstones in Scotland and Westphalian sandstones in Ireland. A high degree of mineralization, dominated by sodium and chloride ions, is found locally in coastal aquifers including the Carboniferous Limestone of south Galway, the Permo-Triassic sandstone near Belfast and the sandstone aqui- fers of East Lothian. The hydrochemistry of the recharge water is strongly influenced by the mineral composition of the drift deposits (Robins et al. this volume). Natural groundwater quality problems are usually associated with excessive hardness in carbonate and some drift aquifers, where con- centrations are often in the range 200-400 mg 1 1 CaCO3 (Daly, D. 1994). Elevated iron and man- ganese concentrations are present in ground- waters in igneous and other basement rocks, muddy limestones, sandstones, peat and allu- vial gravels (Jones & Singleton this volume; Robins et al. this volume). Manganese, in par- ticular, can be a problem for water supply, as the maximum admissible concentration in drinking water (MAC) is only 0.05mg1-1. There are a large number of anthropogenic impacts on groundwater quality. Pressures from Fig. 4. A typical farmyard well-head in the north point sources of pollution include farmyards, of Ireland. sheep dips, septic tank systems, solid waste dis- posal, industry and mining. Diffuse pollution sources from agriculture include the application from diffuse pollution by inorganic and organic of inorganic fertilizers and landspreading of fertilizers. In Scotland, high nitrate levels are organic wastes. Diffuse pollution sources asso- found widely in areas of intensive cultivation or ciated with infrastructure developments such as grassland in Fife and the Southern Uplands roads and housing are a growing concern. (Robins in press). In Ireland, groundwater con- Many of the small private well abstractions tamination by nitrate is generally only wide- are affected by local point source contaminants, spread in the intensive arable areas in the east especially microbiological. The problems are and south, including the alluvial aquifer of the often compounded by a combination of factors: Barrow valley (Daly, D. 1994). A national sur- poor well construction, especially the absence of vey of groundwater quality in Ireland between a proper sanitary seal to the upper casing; high 1995 and 1997 identified nitrate at above the aquifer vulnerability; the predominance of frac- MAC of 50mgl 1 NO3 at only 2.5% of the sites ture flow of groundwater; the presence of a sampled, and concluded that nitrate pollution nearby contamination source such as a septic was generally a localized problem (Environmen- tank system, itself often badly constructed; and a tal Protection Agency 1999). low well abstraction rate and hence low poten- Another agricultural contaminant, phos- tial for dilution (Fig. 4). Microbiological con- phorus, has received much less attention than tamination is usually detected by the presence nitrate. This is mainly because phosphorus levels of faecal bacteria. However, there is growing in groundwater are generally quite low compared concern that other microbiological pollutants to the MAC of 2.2mg1-1 P. However, phos- such as viruses and protozoa (including cryptos- phorus can give rise to eutrophication problems poridium) could be present in wells that are in lakes and rivers at concentrations of as little as susceptible to pollution from livestock activities. 20 and 30 lag 1-1 , respectively. Hence phosphorus Chemical contaminants associated with point at these low levels in groundwater may be of sources in rural areas include chloride, sodium, concern where the groundwater is discharging potassium, iron, manganese, ammonia and into a sensitive surface water body. In a recent nitrate. High nitrate concentrations also result study of phosphorus in groundwater in the west Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

GROUNDWATER IN THE CELTIC REGIONS 15 of Ireland (counties Limerick, Mayo and Clare), legislative drivers intended to regulate anthro- 38% of groundwater samples collected in the pogenic activities as part of the resource man- summer of 1998 had phosphorus concentrations agement process, environmental influences such above 30 pgl 1 (Kilroy et al. 1999). The authors as climate change, and changing patterns of go on to highlight that more research is needed demand, and of supply to meet demand. into the means by which phosphorus reaches Legislative influences are ongoing. The main surface waters. changes over the next few years will stein from Trace organics occur in groundwater through- the proposed European Water Framework out the Celtic regions as a response to human Directive, which requires integrated manage- activities. The most prevalent compounds are ment of both groundwater and surface water to petroleum hydrocarbons, chlorinated solvents be carried out within the geographical unit of and pesticides. The risks posed to the aquatic the river basin. This will not be easy in the Celtic environment by the disposal of spent sheep dip regions where aquifer units tend to be small and is a particular Celtic concern. Sheep dip insecti- compartmentalized, and consideration of indi- cides have traditionally been of the organo- vidual catchments within each river basin unit phosphate type, but are now being increasingly will be required to enable resource manage- replaced by synthetic pyrethroids which are ment. Implementation of the Water Framework neither toxic to sheep or humans. Whereas bio- Directive will also involve the introduction of degradation of organophosphates can produce abstraction licensing in Ireland, Northern Ire- yet more toxic products, the effect of sunlight land and Scotland. and hydrolysis on the synthetic pyrethroids The implications of climate change include reduces their harmful potential. increased annual rainfall over much of the Celtic Elevated metal concentrations occur in regions with a small increase also in potential groundwaters and surface waters in former evapotranspiration (Hulme & Jenkins 1998). mining districts. Important historical mining This may influence the hydrology of wetland activities included: tin in Cornwall; copper in areas if the elevation of the water table changes, Ireland, Wales and Cornwall; and coal in South a particularly critical issue in the many coastal Wales, Northumbria and Scotland. Whereas wetland and duneland areas of eastern Scotland modern mining developments such as the new (Malcolm & Soulsby this volume). The implica- lead/zinc mines at Galmoy and Lisheen in tions of rising sea level and increased river base Ireland are subject to strict environmental con- levels, particularly in lowland areas, are also trols, the abandonment of old metalliferous and significant. coal mines has led to serious pollution problems. Changing patterns of demand and supply Perhaps the best known case occurred in Corn- have had a profound influence on ground- wall in 1992, when a large discharge of acid mine water abstraction in the past, and continue drainage fl-om the former Wheal Jane tin mine to do so. The decline of water intensive industry contaminated the River Carnon, resulting in in the 1960s and 1970s reduced groundwater concentrations of cadmium and zinc in the river consumption in the Lagan Valley of North- of up to 600gg1-1 and 450mgl -l, respectively ern Ireland, the lower Clyde area of the (National Rivers Authority 1994). At the Avoca Midland Valley of Scotland, and the indust- copper mines in County Wicklow, which were rial areas of South Wales. More recently, finally closed in 1982, mine drainage with a pH of increased costs of public supply have created about 3.5 is discharging to the surface rendering renewed interest in groundwater supplies for the Avoca river effectively biologically dead for a industry, and extensive development pro- reach of several kilometres (Wright et al, 1999). grammes have been carried out with varying In Wales, over 50 km of rivers are adversely degrees of success. affected by discharges from abandoned coal Alternative sources for public supply in rural mines (National Rivers Authority 1994), and and island areas have also seen an upturn in there are reported to be more than 80 adits from interest in groundwater by many water under- coal and oil shale mines in the Midland Valley of takers. Welsh Water is actively developing bulk Scotland that are releasing polluted mine water supplies from valley bottom Quaternary fill to surface water sources. material in west Wales, so that the area south of Aberystwyth, for example, is largely ground- water dependent (Hiscock & Paci this volume). Influences of change However, the Water Service in Northern Ireland has pursued a policy of discarding smaller Change is currently being effected from a sources and this has reduced its dependence on number of different directions. These include groundwater. Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

16 N. S. ROBINS & B. D. R. MISSTEAR

Conclusions COXON, C. & DREW, D. 2000. Interdependence of groundwater and surface water in lowland areas Groundwater occurrence and its role within of western Ireland: management issues arising from the environment have a distinct character in the water and contaminant transfers. This volume. Celtic regions. Hydrogeological processes are DALY, D. 1993. Groundwater resources in Ireland. In: dominated by small aquifer units, short and MOLLAN, C. (ed.) Water of Life. Royal Dublin shallow groundwater flow paths, fracture flow in Society Seminar Proceedings, Number 5. --1994. Chemical pollutants in groundwater: a re- otherwise poorly permeable strata, and complex view of the situation in Ireland. In: Chemicals- interrelationships between bedrock and drift A Cause for Concern? Cork 3-4 November 1994, groundwater and surface water. Prevailing Sherkin Island Marine Station. westerly air streams ensure that soils are kept DALY, E. 1989. Natural chemistry of groundwater. at field moisture capacity for much of the year, In: Proceedings of the 9th Annual Groundwater although infiltration is inhibited by a widespread Seminar, International Association of Hydrogeolo- blanket cover of till. gists (Irish Group), Portlaoise, 25-26 April 1989. The social and historical importance of 1994. Groundwater resources of the Nore River groundwater can be traced from the Celtic Basin. Geological Survey of Ireland Report RS94/1. peoples, through medieval times to the present ---1995. The principal characteristics of the flow day. Abundant surface water resources have not regime in Irish aquifers. In: Proceedings of the prevented the use and development of ground- 15th Annual Groundwater Seminar, International water owing to its wide geographical availability, Association of Hydrogeologists (Irish Group), low cost of development and its generally favour- Portlaoise, 25-26 April 1995. able and constant quality. Renewed interest in DEAKIN, J. 2000. Groundwater protection zone delin- groundwater for both public and private supply eation at a large karst spring in western Ireland. has greatly increased the number of sources and This volume. the volume of groundwater in supply in recent DEPARTMENT OF THE ENVIRONMENT AND LOCAL GOVERNMENT, ENVIRONMENTAL PROTECTION years. Other influences include changing legisla- AGENCY & GEOLOGICAL SURVEY OF IRELAND. tive requirements for the management and pro- 1999. A scheme for the protection of groundwater. tection of groundwater and the possible impact Geological Survey of Ireland, Dublin. from climate change. DREW, D. & DALY, D. 1993. Groundwater andkarstifica- tion in mid-Galway, south Mayo and north Clare. A number of the papers in this volume derive either Geological Survey of Ireland Report RS 93]3. from presentations at a joint meeting of the Geological EDMUNDS, W. M., ROBINS, N. S. & SHAND, P. 1998. Society Hydrogeological Group and the Scottish The saline waters of Llandrindod and Builth, Hydrological Group of the Institution of Civil Central Wales. Journal of the Geological Society, Engineers, which was held at Glasgow in March London, 155, 627-637. 1999, or from the annual meeting of the International ENVIRONMENTAL PROTECTION AGENCY. 1999. Water Association of Hydrogeologists Irish Group, held at quality in Ireland 1995-1997. Environmental Portlaoise in April 1999. Protection Agency, . Fox, i. A. 2000. Groundwater protection in Scotland. This volume. GAUS, I. & O DOCHARTAIGH, B. t~. 2000. Conceptual References modelling of data-scarce aquifers in Scotland: the sandstone aquifers of Fife and Dumfries. This BARNES, S. 2000. Groundwater resources and vul- volume. nerability in the Cretaceous Chalk of Northern HARTLEY, J. J. 1935. The underground water re- Ireland. This volume. sources of Northern Ireland. The Institution o[ BGS. 1994. Hydrogeological Map of Northern Ire- Civil Engineers, Belfast and District Association land, 1:250000 scale. British Geological Survey, Pamphlet. Nottingham. HISCOCK, K. & PACl, A, 2000. Groundwater resources BRERETON, N. R. & LEE, M. K. 1987. Fluid flow in in the Quaternary deposits and Lower Palaeozoic crystalline rocks: relationships between ground- bedrock of the Rheidol catchment, west Wales. water spring alignments and other surface linea- This volume. tions at Altnabreac, . Journal of HO~BS, S. 2000. Influent rivers - a pollution threat to Geophysical Research, 92, 7797-7806. Schwyll Spring, South Wales? This volume. BURDON, D. J., BURNS, D. J. & PEEL, S. 1983. HULME, M. & JENKINS, G. 1998. Climate change Geothermal energy investigations in Ireland. scenarios for the United Kingdom: UKCIP. Tech- Proceedings of the Third International Seminar nical Report 1. UK Climate Impacts Programme, on the Results of EC Geothermal Energy Research, Oxford. Munich 1983, 350 360. JONES, C. & SINGLETON, A. 2000. Public water supplies COLLINS, J. F. & CUMMINS,T. (eds) 1996. Agroclimatic from alluvial and glacial deposits in northern atlas Of Ireland. AGMET, Dublin. Scotland. This volume. Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021

GROUNDWATER IN THE CELTIC REGIONS 17

KAY, R. L. F., ANDREWS, J. H., BATH, A. H. & IVANO- NATIONAL RIVERS AUTHORITY. 1994. Abandoned VITCH, M. 1983. Groundwater flow profile and mines and the water environment. National Rivers residence times in crystalline rocks at Altnabreac, Authority, Bristol. Caithness, UK. Isotope Hydrology, 231 248. ROBINS, N. S. 1990. Hydrogeology of Scotland. KILROY, G., COXON, C., ALLOTT, N. & RYBACZUK, R. HMSO, London. 1999. The contribution of groundwater phos- 1999. Groundwater occurrence in the Lower phorus to surface water eutrophication. In: Palaeozoic and Precambrian rocks of the UK: Proceedings of the 19th Annual Groundwater implications for source protection. Water and Seminar, International Association of Hydrogeol- Environment Management, 13, 447-453. ogists (Irish Group), Portlaoise, 20-21 April 1999. in press. Groundwater quality in Scotland: major LEWIS, M. A., LILLY, A. & BELL, J. 2000. Ground- ion chemistry of the key groundwater bodies. water vulnerability mapping in Scotland: mod- Hydrology and Earth System Sciences (in press). ifications to classifications used in England and --, SHAND, P. & MERRIN, P. D. 2000. Shallow Wales. This volume. groundwater in drift and Lower Palaeozoic bed- LOGAN, P. 1980. The holy wells of Ireland. Colin rock: the Afon Teifi valley in west Wales. This Smythe, Buckinghamshire. volume. LOVELOCK, P. E. R. 1977. Aquifer properties of SOULSBY, C., MALCOLM, R. & MALCOLM, I. 2000. Permo-Triassic sandstones in the United King- Groundwater in headwaters: hydrological and dom. Bulletin of the Geological Survey of Great ecological significance. This volume. Britain No 56. WRIGHT, G. 1999. How many wells are there in MALCOM, R. & SOULSBY, C. 2000. Modelling the Ireland? The GSI Groundwater Newsletter, 35. potential impact of climate change on a shallow 2000. QSC graphs an aid to classification of coastal aquifer in northern Scotland. This volume. data-poor aquifers in Ireland. This volume. MATHER, J. D. 1997. The history of research into --, ALDWELL, C. R., DALY, D. & DALY, E. 1982. radioactive waste disposal in the UK and the Groundwater resources of the . selection of a site for detailed investigation. Vol. 6 in the European Community Atlas of Environmental Poli 0, & Practice, 6, 167-177. Groundwater Resources, SDG, Hanover. MCMILLAN, A. A., HEATHCOTE, J. A., KLINCK, B. A., --, MISSTEAR, B. D. R., GALLAGHER, V., O'SuIL- SHEPLEY, M. G., JACKSON, C. P. & DEGNAN, P. J. LEABHAIN, D. & O'CONNOR, P. 1999. Avoca 2000. Hydrogeological characterisation of the mines: uncontrolled acid mine drainage in Ire- onshore Quaternary sediments at Sellafield using land. In: Proceedings of the International Con- the concept of domains. Quarterly Journal of gress of the International Mine Water Association Engineering Geology and HydrogeoIogy, 33(4). 'Mine, Water and Environment ./'or the 21st Cen- MISSTEAR, B. D. R., DALY, E. P. D., DALY, D. & tury: Mine/Quarry Waste Disposal and Closure', LLOYD, J. W. 1980. The groundwater resources q[ Sevilla, Spain, 13-17 September 1999. the Castlecomer Plateau. Geological Survey of YOUNGER, P. L. & LAPLERRE, A. B. 2000. 'Uisge Ireland Report RS 80/3. M6inne': mine water hydrogeology in the Celtic MISSTEAR, B. D. R. & DALY, D. 2000. Groundwater lands, from Kernow (Cornwall, UK) to Ceap protection in a Celtic region: the Irish example. Breattain (Cape Breton, Canada). This volume. This volume.