Evidence of CFC degradation in groundwater under pyrite-oxidizing conditions

Sebol, Lesley A.; Robertson, W. D.; Busenberg, Eurybiades; Plummer, L. Niel; Ryan, M. Cathryn; Schiff, Sherry L.

doi:10.1016/j.jhydrol.2007.08.009

Cited by 46 publications

(35 citation statements)

References 29 publications

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“…This tends to affect CFC-11 and CFC-113 more rapidly than CFC-12, as reported in a number of studies (e.g. Khalil & Rasmussen, 1989b;Oster et al, 1996;Hinsby et al, 2007;Sebol et al, 2007;Horneman et al, 2008). Fig.…”

Section: Microbial Breakdownmentioning

confidence: 53%

The practicalities of using CFCs and SF6 for groundwater dating and tracing

Darling

Gooddy

MacDonald

et al. 2012

Applied Geochemistry

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Knowledge of groundwater residence time is important in understanding key issues in the evolution of water quality, whether this occurs due to water-rock interaction or simply by mixing or contamination. The build-up in the atmosphere of the trace gases chlorofluorocarbons (CFCs) and sulphur hexafluoride (SF 6 ) from the middle of the last century offers a convenient way of dating waters up to ~60 yrs old. The gases are well-mixed in the atmosphere so their input functions are not area-specific as is the case with tritium. While any one of these trace gases can in principle provide a groundwater age, when two or more are measured on water samples the potential exists to distinguish between different modes of flow including piston flow, exponential flow and simple end-member mixing. As with all groundwater dating methods, caveats apply. Factors such as recharge temperature and elevation must be reasonably well-constrained. Primarily for SF 6 , the phenomenon of 'excess air' also requires consideration. Primarily for the CFCs, local sources of contamination need to be considered, as do redox conditions. For both SF 6 and the CFCs, the nature and thickness of the unsaturated zone need to be factored into residence time calculations. However, as an inexpensive dating method, the trace gases can be applied to a wide range of groundwater problems where traditional age indicators might once have been used more sparingly. Examples include tracing flowlines, detecting small modern inputs in 'old' waters, and pollution risk assessment. In the future, with the main CFCs are already declining in the atmosphere, new anthropogenic trace gases are likely to take their place.

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Section: Microbial Breakdownmentioning

confidence: 53%

The practicalities of using CFCs and SF6 for groundwater dating and tracing

Darling

Gooddy

MacDonald

et al. 2012

Applied Geochemistry

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“…Gas stripping also causes CFC depletion in groundwater. Gases such as carbon dioxide, nitrogen, hydrogen sulfide, and methane are known to form through microbial degradation and denitrification processes , and CFC compounds may be partitioned into the gas phase (Sebol et al, 2007). Indeed, gas bubbles were observed in the groundwater from a few wells when the samples were collected.…”

Section: Cfc Depletion Mechanisms Interpreted From the Hydrogeochemicmentioning

confidence: 99%

“…CFCs in groundwater are now used regularly as transient tracers, and many successful applications of CFCs as transient tracers have been reported (e.g., Katz et al, 1995;Plummer et al, 1998a;Szabo et al, 1996). The conservativeness of CFCs is usually assumed in such applications (Happell et al, 2003), but the depletion of CFCs has been found in various environments, including aquifers (Cook et al, 1995;Happell et al, 2003;Hinsby et al, 2007;Horneman et al, 2008;Oster et al, 1996;Plummer et al, 1998aPlummer et al, , 1998bSebol et al, 2007), surface water (Happell et al, 2003;Oster et al, 1996), and marine water (Shapiro et al, 1997). Cook et al (1995) showed that the groundwater recharge rate estimated using CFC-113 (90 mm y À1 ) was smaller than the rate estimated using a 3 H bomb pulse (150 mm y À1 ) or CFC-12 (130 mm y À1 ) because of the sorption of CFC-113 to materials in the aquifer.…”

Section: Introductionmentioning

confidence: 99%

“…Assuming that transport occurred through turbulent vertical mixing and assuming first-order degradation kinetics for the CFCs, the estimated degradation rates ranged between 0.01 and 0.03 y À1 for CFC-12 and between 6 and 9 y À1 for CFC-11. Sebol et al (2007) found that were completely degraded at a depth at which reduced sulfur (originating from pyrite) was oxidized by nitrate ions and dissolved oxygen. The estimated first-order degradation rates from that study were 0.3 y À1 for CFC-12, 0.7 y À1 for CFC-11, and 1.6 y À1 for CFC-113.…”

Section: Introductionmentioning

confidence: 99%

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Multiple tracer study in Horonobe, northern Hokkaido, Japan: 2. Depletion of chlorofluorocarbons (CFCs) estimated using 3 H/ 3 He index and lumped parameter models

Kashiwaya

Hasegawa

Nakata

et al. 2015

Journal of Hydrology

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“…Simple binary 336 groundwater age mixing can often be detected by plotting SF 6 versus CFC 337 (chlorofluorocarbon) concentrations. However, owing to the reducing conditions in most of 338 the groundwaters, CFC analyses were not undertaken because of probable degradation effects 339 (Sebol et al 2007). 340…”

mentioning

confidence: 99%

Understanding the hydrochemical evolution of a coastal dune system in SW England using a multiple tracer technique

Allen

Darling

Williams

et al. 2014

Applied Geochemistry

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An improved knowledge of the hydrology of coastal dune systems is desirable for 1 successful management of their diverse ecology under a changing climate. As a near-pristine 2 coastal dune spit system, Braunton Burrows (SW England) is an ideal location for the study 3 of the natural processes governing recharge to the dune groundwater system and the 4 evolution of its water quality. Whereas previous investigations have tended to focus on inter-5 dune slacks, this study has also given attention to infiltration through the high dunes. Cores 6 were taken through dunes and the resulting sand samples processed to provide information on 7 grain size distribution and porewater chemistry. Groundwater samples were obtained from 8 beneath dunes and slacks. A variety of geochemical techniques were applied including 9 hydrochemistry, stable isotopes and residence time indicators. The unsaturated zone profiles 10 indicate the existence of piston flow recharge with an infiltration rate of 0.75-1 m/yr, 11 although faster rates probably also occur locally. Groundwater beneath the high dunes gave 12 ages in the range 13-16 yr, compared to the dune slack groundwater ages of 5-7 yr, and an 13 age of 22 yr for groundwater from the underlying mudstone aquifer. The chemistry of waters 14 in both unsaturated and saturated zones is dominated by Ca and HCO 3 , supplemented by 15 variable amounts of other ions derived from marine aerosols and limited reaction with sand 16 grains and their coatings. The main chemical evolution of the porewaters occurs rapidly 17 through the mobilisation of surface salt crusts and dissolution of shell carbonate. This 18 situation changes little in the underlying groundwater, though an evolution towards reducing 19 conditions increases the concentrations of redox-sensitive species such as Fe and Mn. The 20 rapid chemical evolution of the infiltrating water means that its composition will respond 21 quickly to changes in the supply of shell material and/or marine salts, which are possible 22 consequences of climate change. However, the residence time measurements suggest the 23 dune aquifer has a relatively long turnover time which will to some extent buffer such 24 changes. The results of the present study should be transferable to natural dune systems in 25 similar coastal situations. 26

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Evidence of CFC degradation in groundwater under pyrite-oxidizing conditions

Cited by 46 publications

References 29 publications

The practicalities of using CFCs and SF6 for groundwater dating and tracing

The practicalities of using CFCs and SF6 for groundwater dating and tracing

Multiple tracer study in Horonobe, northern Hokkaido, Japan: 2. Depletion of chlorofluorocarbons (CFCs) estimated using 3 H/ 3 He index and lumped parameter models

Understanding the hydrochemical evolution of a coastal dune system in SW England using a multiple tracer technique

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