『Abstract
The Swanscombe area of Kent, SE England represents a typical
example of a heavily quarried Chalk area currently undergoing
re-development. Because the Chalk is also an important aquifer,
a good understanding of groundwater movement is required if environmental
impacts are to be minimised and the water resource maximised.
In particular, the nature of the relationship between the River
Darent and groundwater in the Swanascombe Chalk Block requires
better characterisation. Here, ‘environmental tracers’ in the
form of ambient concentrations of stable isotopes, chlorofluorocarbons
(CFCs), sulphur hexafluoride (SF6) and tritium
(3H) are used to investigate this and other aspects
of groundwater movement in the vicinity of the quarries. Stable
isotopic contrasts indicate little evidence for widespread river
infiltration to the regional Chalk aquifer, although stable isotope
and 3H data suggest the 20-35％ of the abstraction by
river-valley public water supply boreholes may be derived from
the river. The CFCs, while present at above-modern concentrations
in almost all groundwaters, can be used as tracers., indicating
basically S-N flowpaths in the area south of the quarries, though
sub-karstic conduits associated with areas of Palaeogene cover
add a level of uncertainty at the local scale. Simple piston flow
residence times based on SF6 range from 1
to 17 a, but the data are probably better interpreted in terms
of mixing between varying amounts of modern recharge derived from
the south and deeper stored groundwater. The information gained
from environmental tracers can therefore contribute to effective
resource management.』
1. Introduction
2. Background
2.1. The Swanscombe Chalk Block
2.2. Environmental tracers
2.2.1. Stable isotopes
2.2.2. Trace gases
2.2.3. Tritium
3. Sample collection and analysis
4. Results
4.1. Sites in the Darent Valley
4.2. Sites in the Eastern Quarry and adjacent area
5. Discussion
5.1. Isotopic variations in the River Darent
5.2. The relationship between the River Darent and groundwater
in the quarried area
5.3. Groundwater flow in the area south of the Eastern Quarry
6. Conclusions
Acknowledgments
References