Integrating geophysical and hydrochemical borehole-log measurements to characterize the Chalk aquifer, Berkshire, United Kingdom |
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Authors: | Marc Schürch David Buckley |
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Institution: | (1) British Geological Survey, Maclean Building, Crowmarsh Gifford, Wallingford, OX10 8BB, UK,;(2) Federal Office for Water and Geology, Swiss Geological Survey, 3003 Bern-Ittigen, Switzerland, |
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Abstract: | Geophysical and hydrochemical borehole-logging techniques were integrated to characterize hydraulic and hydrogeochemical properties
of the Chalk aquifer at boreholes in Berkshire, UK. The down-hole measurements were made to locate fissures in the chalk,
their spatial extent between boreholes, and to determine the groundwater chemical quality of the water-bearing layers. The
geophysical borehole logging methods used were caliper, focused resistivity, induction resistivity, gamma ray, fluid temperature,
fluid electrical conductivity, impeller and heat-pulse flowmeter, together with borehole wall optical-imaging. A multiparameter
data transmitter was used to measure groundwater temperature, electrical conductivity, dissolved oxygen, pH, and redox potential
of the borehole fluid down-hole. High permeability developed at the Chalk Rock by groundwater circulation provides the major
flow horizon at the Banterwick Barn study site and represents a conduit system that serves as an effective local hydraulic
connection between the boreholes. The Chalk Rock includes several lithified solution-ridden layers, hardgrounds, which imply
a gap in sedimentation possibly representing an unconformity. Lower groundwater temperature, high dissolved-oxygen content,
and flowmeter evidence of preferential groundwater flow in the Chalk Rock indicated rapid groundwater circulation along this
horizon. By repeating the logging at different times of the year under changing hydraulic conditions, other water-inflow horizons
within the Chalk aquifer were recognized.
Electronic Publication |
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Keywords: | Borehole logging Chalk Fractured rock Hydraulic properties of aquifers United Kingdom |
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