An introduction to Groundwater in Crystalline Bedrock David Banks & Nick Robins Norges geologiske undersøkelse © 2002 Norges geologiske undersøkelse Published by Norges geologiske undersøkelse (Geological Survey of Norway) N-7491 Trondheim Norway All rights reserved ISBN 82 7386 100 1 Editor: Rolv Dahl Design and print: Grytting AS Recommended bibliographical reference for this volume: Banks, D. and Robins, N. (2002): An introduction to Groundwater in Crystalline bedrock Norges geologiske undersøkelse, 64pp ISBN 82 7386 100 1 PAGE 1 An introduction to Groundwater in Crystalline Bedrock David Banks1,Nick Robins2 1 Geological Survey of Norway,N7491 Trondheim,Norway (Current address:Holymoor Consultancy,86 Holymoor Road,Holymoorside,Chesterfield,Derbyshire,S42 7DX,United Kingdom). 2 British Geological Survey,Maclean Building,Crowmarsh Gifford,Wallingford,Oxfordshire,OX10 8BB,United Kingdom. PAGE 2 David Banks Having been employed Prologue with the Thames Water Authority, the National Rivers Authority and the "Therefore a miner, since we think he ought to be a good and serious University of Sheffield in man, should not make use of an enchanted twig, because if he is prudent the UK,David Banks worked and skilled in the natural signs, he understands that a forked twig is of no for six years with the Section for Geochemistry use to him.....So if Nature or Chance should indicate a locality suitable for and Hydrogeology at NGU. mining, the miner should dig his trenches there; if no vein appears, he In 1998,he returned to Chesterfield in England,where must dig numerous trenches until he discovers an outcrop of a vein." he runs his own international "Holymoor Consultancy" business, through which he has gained hydro- Agricola (1556). De Re Metallica. geological experience from regions as diverse as the Bolivian A ltiplano,Afghanistan and South Yorkshire. Nick Robins Dr Nick Robins works with the British Geological Survey at Wallingford in Oxfordshire. He has extensive experience overseas on hard rock hydro- geology and has also been responsible for promoting interest in groundwater throughout Scotland and Northern Ireland. Other interests include groundwater in Chalk, in Quaternary deposits, mine water arisings and island hydrogeology, as well as groundwater manage- ment. PAGE 3 Contents Contents...........................................................................................................................................3 Introduction.....................................................................................................................................5 1.What is Groundwater in Crystalline Bedrock?................................................................................7 2.How to Get Groundwater out of the Ground..................................................................................8 3.Well Drilling in Bedrock.Bingo,Poker or Chess ? ..........................................................................12 4.Where Should I Drill My Borehole?..............................................................................................15 5.Fracture Zones ..........................................................................................................................17 6.Superficial Deposits...................................................................................................................20 7.Fracture Mapping......................................................................................................................21 8.Geophysics................................................................................................................................23 9.Stress........................................................................................................................................26 10.Borehole Orientation.................................................................................................................27 11.Drilling .....................................................................................................................................28 12.Borehole Yield Stimulation ........................................................................................................31 13.Test Pumping ............................................................................................................................33 14.Water Quality............................................................................................................................38 15.Water Treatment .......................................................................................................................43 16.Vulnerability and Source Protection ...........................................................................................44 17.Maintenance & Rehabilitation ...................................................................................................47 18.Ground Source Heat...................................................................................................................49 19.Conclusion ................................................................................................................................52 20.References ................................................................................................................................53 21.Glossary....................................................................................................................................61 PAGE 4 Cover photos: 1. Shedding light on rock and water.Corbiere Lighthouse,Jersey,Channel Islands. Photo by Joe Bates. 2. Geologist Helge Skarphagen examines springs from gneisses exposed in a road cutting near Herefoss,southern Norway.Note that groundwater tends to emerge along the boundaries of pegmatites (light rocks).Photo by David Banks.See Figures 25a,b for locations of sites mentioned in the text. 3. Winter drilling,near Glasgow,Scotland.Photo by Nick Robins. PAGE 5 Introduction his small book has a big Smedley 1994, Blackie et al. 1998). A ambition. It aims to present number of small British communities Tpractical information and a little are almost entirely dependent on philosophy to those involved in locating bedrock groundwater, such as several groundwater resources in areas of the islands of Scilly (Banks et al. underlain by crystalline bedrock, that is 1998e), and such groundwater provides to say: an attractive alternative resource for other communities with a currently • Private groundwater users, potential unsatisfactory water supply (Ellingsen well owners and water bottlers & Banks 1993). • Local authorities • Water companies and local water Bedrock aquifers are also exploited supply undertakings widely in tropical climes; in much of •Drillers Africa and India, for example. There, • and Consultants however, the hydrogeological conditions are very different. The rocks Each of these users will inevitably have are deeply weathered and rainfall different requirements and this volume recharge may be scarce. We will thus may be considered to be a "maximum largely, though not exclusively, restrict version", hoping to provide something ourselves to consideration of bedrock for everyone. We have consciously aquifers in the glaciated terrain of mixed practical advice with some Norway and the northern U.K., where hydrogeological theory. Pick and rock outcrops are relatively fresh and choose the parts that you find useful. where the quantity of precipitation is We have also provided a comprehensive depressingly abundant. reference list for those of you who wish to delve further into the subject. We Groundwater in bedrock is a difficult aim to try to communicate resource to understand and pin down. Scandinavian findings (often largely It is very difficult to predict the yield or published in Nordic languages) to an water quality of a new borehole with international audience. A Norwegian any degree of certainty. It is, however, version of this book will be published possible to quantify the chances of later. being successful. We will attempt to guide you through the maze of Almost all of Norway (Figure 25b) is fractures and uncertainties comprising underlain by some type of crystalline a bedrock aquifer in such a way as to bedrock, and groundwater from such allow you to make an informed choice rocks is an important drinking water about its potential as a water resource. resource in rural areas, with over 100,000 bedrock wells thought to exist in a country with a population of somewhat over 4 million! In the United Kingdom, crystalline bedrock groundwater is probably an underused resource. Such rocks underlie much of the U.K.'s "Celtic Fringe" - Cornwall, Wales, Scotland and parts of Northern Ireland (see Figure 25a: Robins 1990, 1996a,b, Robins and Misstear 2000), as well as the Channel Islands (Robins & PAGE 6 PAGE 7 1.What is Groundwater in Crystalline Bedrock? There are, of course, two parts to this system is very sensitive to the fracture question: aperture and degree of fracture connectivity, it is very difficult to 1.1 What is Groundwater? predict the yield of a well or borehole in Groundwater is simply water that crystalline bedrock. To be successful, we occurs in the ground; in the pore spaces need to understand, as Agricola between mineral grains or in cracks and recommended in 1556 (see Prologue) fractures in the rock mass. It is usually both Nature (in the guise of geology) formed by rain water or snow melt- and the element of Chance. water that seeps down through the soil and into