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Tracer tests and the structure of permeability in the Corallian limestone aquifer of northern England, UK |
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| Authors: | Aidan Foley Gerd Cachandt Janine Franklin Fergus Willmore Tim Atkinson |
| Institution: | 1. Environmental Geology and Geotechnical Consultants Ltd, 75 Rockdove Avenue, Hulme, Manchester, England, M15 5EH, UK 2. Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT, UK 3. Arup, Admiral House, Rose Wharf, 78 East Street, Leeds, LS9 8EE, UK 4. Yorkshire Water Services Ltd. Western House, Western Way, Bradford, BD6 2LZ, UK 5. School of Environmental Sciences, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK |
| Abstract: | The Corallian limestone of northern England (UK) is widely exploited for water supplies and exhibits the karstic phenomena of sinking rivers, conduit development and groundwater velocities of several kilometres per day. To test a number of model-derived source protection zones and elucidate contaminant transport mechanisms in the aquifer, three tracer tests were conducted from a set of swallow-holes draining the River Derwent toward public water supply wells in the eastern part of the aquifer. Tracers used included: Enterobacter cloacae (bacteriophage), Photine C (optical brightener), sodium fluorescein (fluorescent dye) and sulphur hexafluoride (dissolved gas), the varying properties of which make them suitable analogues for different types of potential contaminant. Observed tracer transport times and arrival patterns indicate that tracer transport occurs through karstic channels embedded in a network of primary fissures which exert control over tracer concentrations once initial tracer plumes have passed. A dipole flow system is observed between the swallow-holes and the closest abstraction well, whilst previously modelled source protection zones do not accurately reflect either groundwater velocity or those areas of the aquifer supplying the wells. These findings imply that managing such aquifers for potential contamination should rely upon empirical tracer evidence for source-protection zone modelling. |
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