Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021 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, Ireland 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 Celts 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 Gaels, farming typical of much of central Wales and the Picts and the Britons. Nowadays, the land of arable cultivation in eastern Scotland. 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), Northumbria, 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, London, 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