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Thermal groundwater movement and radionuclide transport in SW England

Published online by Cambridge University Press:  05 July 2018

E. M. Durrance  and
M. J. Heath
E. M. Durrance
Affiliation:
Department of Geology, University of Exeter, Devon, UK
M. J. Heath
Affiliation:
Department of Geology, University of Exeter, Devon, UK
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Abstract

Heat flow in SW England is well above average for the UK as a whole, but northwards towards Bath and Bristol the values decrease rapidly. However, hot springs occur both in the Bath-Bristol area and in mines in Cornwall. The development of hydrothermal circulation systems is thus not controlled entirely by geothermal gradient: the presence of a suitable fracture permeability is the main requirement. The thermal ‘head’ produced, which nevertheless depends upon the temperature and volume of water in the system, theoretically can exceed local topographic heads even in areas of low geothermal gradient.

Thermal groundwaters usually carry above average quantities of radioelements in solution because of the long residence times involved. 222Rn values are often particularly high. High concentrations of 222Rn in surface waters arise from the discharge of groundwater. The results of a survey of 222Rn in streams in SW England have established areas of high values which are interpreted as rising limbs of convection cells with dimensions in the order of 5–10 km.

In SE Devon γ-ray spectrometry of soils shows two E.-W. belts of high activity. The northern is coincident with the faulted southern margin of the Crediton Trough, while the southern is coincident with the westerly extension of the Abbotsbury fault system. Groundwater movement along deep-seated fracture systems is considered to be the explanation of these features. The horizontal scale of the area involved suggests that a thermal rather than local topographic head is the driving force. Groundwater circulation within fractures, driven by a thermal head, may therefore occur even in areas of low geothermal gradient and should be considered when selecting waste disposal sites.

Keywords

radionuclide transportgroundwatersSW Englandradon
Type
Research Article
Information
Mineralogical Magazine , Volume 49 , Issue 351 , April 1985 , pp. 289 - 299
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1985

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