Using environmental tracers to assess the extent of river–groundwater interaction in a quarried area of the English Chalk

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 Swanscombe Chalk Block requires better characterisation. Here, 'environmental tracers' in the form of ambient concentrations of stable isotopes, CFCs (chlorofluorocarbons), SF 6 (sulphur hexafluoride) and tritium ( 3 H) 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 tritium data suggest that 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 SF 6 range from 1 to 17 years, 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.

Groundwater connectivity of a sheared gneiss aquifer in the Cauvery River basin, India

“…Montzka et al 2018), or could be due to diffuse, low level contamination of the subsurface from anthropogenic waste such as refrigerants (e.g. Darling et al 2010). Together, these results show that the residence time tracers are not suitable for quantitative estimates of groundwater mean residence time, but instead can be used in a qualitative tracer of modern recharge within the groundwater system.…”

Non-stationary nonparametric inference of river-to-groundwater travel-time distributions

“…Besides concentrations of dissolved gases, such as radon (e.g., Hoehn and von Gunten, 1989), noble gases (e.g., Stute et al, 1997;Massmann et al, 2008), and chlorofluorocarbons (e.g., Beyerle et al, 1999;Darling et al, 2010), time series of naturally fluctuating properties, such as water isotopes (e.g., Stichler et al, 1986;Hunt et al, 2005), temperature (e.g., Anderson, 2005), and specific electric conductivity (e.g., Cox et al, 2007;Cirpka et al, 2007) can be used to infer riverto-groundwater travel times. Specific advantages of using time series of physical properties are their low cost of detection and their continuous quality, which can be recorded over years.…”

Development of a methodology for the application of synthetic DNA in stream tracer injection experiments

“…[3] A multitracer approach can overcome the problem of lack of spatial coverage. According to Gourcy and Brenot [2011], new environmental tracers such as Sr, B, and SO4 isotopes, as well as chlorofluorocarbons (CFCs) and SF6 [e.g., Vengosh et al, 2002;N egrel and Pauwels, 2004;N egrel and Petelet-Giraud, 2005;Gooddy et al, 2006] have been successfully applied in multitracer approaches, and also for an improved understanding of the interaction between groundwater and surface water [Oxtobee and Novakowski, 2002;Lamontagne et al, 2005;Darling et al, 2010]. In addition, Haggerty et al [2009] used the reactive tracer resazurin to assess hyporheic exchange within river systems.…”