County Clare Groundwater Protection Scheme County Clare Groundwater Protection Scheme Main Report Clare County Council Geological Survey of Ireland New Road Beggars Bush Ennis Haddington Road Dublin 4 March 2000 ii County Clare Groundwater Protection Scheme Authors Jenny Deakin, Groundwater Section, Geological Survey of Ireland Donal Daly, Groundwater Section, Geological Survey of Ireland Subsoils mapped by: Oscar Bloetjes, Quaternary Section, Geological Survey of Ireland and Department of Geography, University of Amsterdam in collaboration with: Clare County Council iii County Clare Groundwater Protection Scheme Table of Contents 1 Introduction ...................................................................................................................................... 1 1.1 Groundwater Protection – A Priority Issue for Local Authorities..............................................1 1.2 Groundwater – A Resource at Risk............................................................................................1 1.3 Groundwater Protection Through Land-Use Planning: A Means of Preventing Contamination2 1.4 ‘Groundwater Protection Schemes’ – A National Methodology for Groundwater Pollution Prevention...........................................................................................................................................2 1.5 Objectives of the County Clare Groundwater Protection Scheme .............................................4 1.6 Scope of County Clare Groundwater Protection Scheme ..........................................................4 1.7 Clare County Development Plan................................................................................................5 1.8 Structure of Report .....................................................................................................................5 1.9 Acknowledgements ....................................................................................................................5 2 Bedrock Geology .............................................................................................................................. 9 2.1 Introduction ................................................................................................................................9 2.2 Ordovican Rocks ......................................................................................................................11 2.3 Silurian Rocks ..........................................................................................................................11 2.4 Old Red Sandstones..................................................................................................................11 2.5 Lower Carboniferous Rocks.....................................................................................................11 2.6 Namurian (Upper Carboniferous) Rocks..................................................................................14 2.7 Structural History .....................................................................................................................14 3 Subsoils Geology............................................................................................................................. 17 3.1 Introduction ..............................................................................................................................17 3.2 Data Availability ......................................................................................................................17 3.3 Subsoil Types ...........................................................................................................................18 3.3.1 Till................................................................................................................................... 18 3.3.2 Sand/Gravel ................................................................................................................... 19 3.3.3 Till with Gravel.............................................................................................................. 20 3.3.4 Alluvial Deposits............................................................................................................ 20 3.3.5 Peat ................................................................................................................................. 20 3.3.6 Lake Sediments.............................................................................................................. 20 3.3.7 Marine Deposits............................................................................................................. 21 3.3.8 Estuarine Deposits......................................................................................................... 21 3.4 Subsoil Thicknesses .................................................................................................................21 4 Hydrogeology And Aquifer Classification ................................................................................... 23 4.1 Introduction ..............................................................................................................................23 4.2 Data Availability ......................................................................................................................23 4.3 Rainfall and Evapotranspiration...............................................................................................23 4.4 Groundwater Usage..................................................................................................................24 4.5 Aquifer Classification...............................................................................................................24 4.5.1 Aquifer Categories ........................................................................................................ 24 4.5.2 Bedrock Aquifers........................................................................................................... 26 4.5.3 Sand/Gravel Aquifers.................................................................................................... 26 4.5.4 Karstification ................................................................................................................. 26 iv County Clare Groundwater Protection Scheme 4.5.5 Dolomitisation................................................................................................................ 27 4.5.6 Use of Well Yields in Defining Aquifers ...................................................................... 27 4.6 Ordovician Rocks.....................................................................................................................30 4.7 Silurian Rocks ..........................................................................................................................30 4.8 Old Red Sandstone (Ors)..........................................................................................................31 4.9 Lower Limestone Shales (Lls)..................................................................................................32 4.10 Ballysteen Limestone (Ba) ...................................................................................................32 4.11 Waulsortian Limestone (Wa) ...............................................................................................33 4.12 Cregmahon Limestone (Tucm), Ballycar Limestone (Bc) And Lough Gur Limestone (Lr)34 4.13 Finlough Limestone (Fl), Parsonage Limestone (Pa), ‘Mudbank Limestone’ (‘Mk’) .........35 4.14 Tubber Limestone (Tu), Burren Limestone (Bu), Slievenaglasha Limestone (Sl)...............35 4.14.1 Epikarst Flow............................................................................................................. 36 4.14.2 Discrete Conduit Flow Systems................................................................................ 36 4.14.3 Dispersed Fissure/Joint Slow Flow System ............................................................. 37 4.14.4 Surface Water/Groundwater Interaction................................................................ 37 4.14.5 Degree of Karstification............................................................................................ 38 4.15 Visean Limestones (Vis) ......................................................................................................39 4.16 Volcaniclastic Rocks (V)......................................................................................................39 4.17 Clare Shales (Cs) ..................................................................................................................39 4.18 Ross Sandstone (Rs), Gull Island Formation (Gi), Tullig Sandstone (Ts), Central Clare Group (Ccg)......................................................................................................................................40 4.19 Sand/Gravel Aquifers...........................................................................................................41 4.20 Summary Of Aquifer Categories..........................................................................................41 5 Groundwater Vulnerability........................................................................................................... 43 5.1 Introduction ..............................................................................................................................43 5.2 Sources Of Data........................................................................................................................43