Page 265 - Hydrogeology Principles and Practice

HYDC06 12/5/05 5:34 PM Page 248

248 Chapter Six

between fissured zones revealed it to be composed
predominantly of freshwater. Analysis of seasonal
changes in the fluid log profiles showed that the salin-
ity increases in response to the natural depletion of
groundwater storage in the Chalk during the summer
and can respond rapidly to changes in abstraction
rates from wells located as much as 6 km inland
(Headworth & Fox 1986).
Groundwater management to limit saline water
intrusion in the Brighton Chalk Block is based on
abstracting from pumping stations located around
the margins of the aquifer in order to intercept
outflows from the aquifer, while at the same time
reducing abstractions from inland pumping stations
in order to conserve aquifer storage. In addition,
aquifer losses to the sea in winter are reduced as far as
possible to assist inland storage levels to recover to
be able to support increased output in summer. In
drought years, following winters with below-average
recharge, coastal outflows from the aquifer decline,
and inland storage levels, increased as a result of the
Fig. 6.28 Fluid electrical conductivity logs recorded by downhole
geophysical borehole logging at a site on the Brighton sea front, operating policy, allow greater use to be made of
Sussex, illustrating the inland penetration of saline water along inland pumping stations so as to meet high summer
discrete horizontal fissures in the Chalk aquifer. After Headworth demand for water in the coastal resorts (Headworth
and Fox (1986).
& Fox 1986; Miles 1993).
extraction barrier created by a continuous pumping
trough with a line of wells adjacent to the sea; (iv) an 6.5 FURTHER READING
injection barrier to maintain a pressure ridge along Appelo, C.A.J. & Postma, D. (1994) Geochemistry, Ground-
the coast by a line of recharge wells injected with high water and Pollution. A.A. Balkema, Rotterdam.
Bitton, G. & Gerba, C.P. (eds) (1984) Groundwater Pollution
quality imported water; and (v) an impermeable sub-
Microbiology. John Wiley, New York.
surface barrier constructed parallel to the coast and
Domenico, P.A. & Schwartz, F.W. (1998) Physical and
through the vertical extent of the aquifer.
Chemical Hydrogeology, 2nd edn. John Wiley, New York.
An example of the first of the above methods is Fetter, C.W. (1999) Contaminant Hydrogeology, 2nd edn.
practised in the Brighton Chalk Block on the Sus- Prentice-Hall, New Jersey.
sex coast of southern England. For fissured aquifers Freeze, R.A. & Cherry, J.A. (1979) Groundwater. Prentice-
such as the Chalk, there is no simple saline interface Hall, Englewood Cliffs, New Jersey.
and over-abstraction can induce seawater to invade Hemond, H.F. & Fechner, E.J. (1994) Chemical Fate and
the aquifer along discrete fissure zones, often for Transport in the Environment. Academic Press, San Diego.
discernable distances (Fig. 6.26c). This complex form Pankow, J.F. & Cherry, J.A. (eds) (1996) Dense Chlorinated
of intrusion is illustrated by the downhole fluid elec- Solvents and other DNAPLs in Groundwater: history, behav-
ior, and remediation. Waterloo Press, Portland, Oregon.
trical conductivity logs for a coastal borehole at
Todd, D.K. (1980) Groundwater Hydrology, 2nd edn. John
Brighton (Fig. 6.28). The geophysical borehole logs
Wiley, New York.
reveal freshwater moving seawards and saltwater
Williams, P.T. (1998) Waste Treatment and Disposal. John
moving inland along discrete horizontal fissures Wiley, Chichester.
extending to 100 m below sea level. Below a depth of Younger, P.L., Banwart, S.A. & Hedin, R.S. (2002) Mine
about 130 m the fluid logs indicate the existence of a water: hydrology, pollution, remediation. Kluwer Academic
saline water zone. Analysis of porewater in the Chalk Publishers, Dordrecht.