Halon-1301 – further evidence of its performance as an age tracer in New Zealand groundwater

Abstract. We recently discovered a new groundwater age tracer, Halon-1301, which can be used to date groundwater recharged after the 1970s. In a previous study, we showed that Halon-1301 reliably inferred groundwater age at the majority of groundwater sites studied. At those sites, ages inferred from Halon-1301 agreed with those inferred from SF6 and tritium, two reliable widely applied groundwater age tracers. A few samples, however, showed reduced concentrations of Halon-1301, preventing meaningful age interpretation from its concentration. These reduced concentrations were likely a result of degradation or retardation of Halon-1301 in the aquifer. However, we could not provide full evidence for this due to the limited number of groundwater samples analysed (18 in total). In this study, we assess the potential of Halon-1301 as a groundwater age tracer for a larger dataset of groundwater samples under specific groundwater conditions, including highly anoxic young groundwater which can significantly degrade Halon-1301, to gain more information on the magnitude of occurrence and the causes of reduced Halon-1301 concentrations. In this study, we analysed 302 groundwater samples for Halon-1301, SF6, tritium and the CFCs CFC-11, CFC-12 and CFC-113. Comparison of age information inferred from the concentrations of these tracers allows assessment of the performance of Halon-1301 compared to other well established and widely used age tracers. The samples are taken from different groundwater environments in New Zealand and include anoxic and oxic waters with mean residence times ranging from < 2 years to over 150 years (tritium-free). The majority of assessed samples have reduced or elevated concentrations of CFCs, which makes it impossible to infer a reliable age using the CFCs for these samples. Halon-1301, however, reliably infers ages for CFC-contaminated waters. Three other groundwater samples were found to have elevated SF6 concentrations (contaminated). Again, at these SF6-contaminated sites, ages inferred from Halon-1301 agree with ages inferred from tritium. A few samples (14 sites) exhibit reduced concentrations of Halon-1301, which result in elevated inferred Halon-1301 ages in comparison to those inferred from SF6, tritium and/or CFC-113. Assessment of the groundwater environment at these sites gives further insight into the potential causes of Halon-1301 reduction in groundwater. Overall, Halon-1301 gives age information that matches ages inferred from SF6 and/or tritium for the majority (97 %) of the assessed groundwater sites. These findings suggest that Halon-1301 is a reasonably reliable groundwater age tracer, and is in particular significantly more reliable than the CFCs, which may have contamination and degradation problems. Halon-1301 thus has potential to become a useful groundwater age tracer where SF6 and the CFCs are compromised, and where additional independent tracers are needed to constrain complex mixing models.

Download Full-text

Renewed thinking on groundwater age

10.5194/egusphere-egu21-3479 ◽

2021 ◽

Author(s):

Grant Ferguson ◽

Mark Cuthbert ◽

Kevin Befus ◽

Tom Gleeson ◽

Chandler Noyes ◽

...

Keyword(s):

Environmental Flows ◽

Numerical Models ◽

Groundwater Age ◽

Holistic Approach ◽

Water Levels ◽

Residence Times ◽

Groundwater Sustainability ◽

Long Time ◽

Mean Residence Times ◽

Recharge Rates

<p>Groundwater age and mean residence times have been invoked as measures of groundwater sustainability, with the idea that old or "fossil" groundwater is non-renewable. This idea appears to come from the link between groundwater age and background recharge rates, which are also of questionable use in assessing the sustainability of groundwater withdrawals. The use of groundwater age to assess renewability is further complicated by its relationship with flow system geometry. Young groundwaters near recharge areas are not inherently more renewable than older groundwaters down gradient. Similarly, there is no reason to preferentially use groundwater from smaller aquifers, which will have smaller mean residence times than larger aquifers for the same recharge rate. In some cases, groundwater ages may provide some information where groundwater recharge rates were much higher in the past and systems are no longer being recharged. However, there are few examples where the relationship between depletion and changes in recharge over long time periods has been rigorously explored. Groundwater age measurements can provide insights into the functioning of groundwater flow systems and calibration targets for numerical models and we advocate for their continued use, but they are not a metric of sustainable development. Simple metrics to assess groundwater sustainability remain elusive and a more holistic approach is warranted to maintain water levels and environmental flows.</p>

Download Full-text

Assessment of Halon-1301 as a groundwater age tracer

Hydrology and Earth System Sciences ◽

10.5194/hess-19-2775-2015 ◽

2015 ◽

Vol 19 (6) ◽

pp. 2775-2789 ◽

Cited By ~ 5

Author(s):

M. Beyer ◽

R. van der Raaij ◽

U. Morgenstern ◽

B. Jackson

Keyword(s):

Groundwater Age ◽

Groundwater Resources ◽

Water Soluble ◽

Elevated Concentration ◽

Environmental Tracers ◽

Halon 1301 ◽

Gaseous Substance ◽

Groundwater Samples ◽

Groundwater Dating ◽

Age Estimates

Abstract. Groundwater dating is an important tool to assess groundwater resources in regards to their dynamics, i.e. direction and timescale of groundwater flow and recharge, contamination risks and manage remediation. To infer groundwater age information, a combination of different environmental tracers, such as tritium and SF6, are commonly used. However, ambiguous age interpretations are often faced, due to a limited set of available tracers and their individual restricted application ranges. For more robust groundwater dating multiple tracers need to be applied complementarily (or other characterisation methods need to be used to complement tracer information). It is important that additional, groundwater age tracers are found to ensure robust groundwater dating in future. We have recently suggested that Halon-1301, a water soluble and entirely anthropogenic gaseous substance, may be a promising candidate, but its behaviour in water and suitability as a groundwater age tracer had not yet been assessed in detail. In this study, we determined Halon-1301 and inferred age information in 17 New Zealand groundwater samples and various modern (river) water samples. The samples were simultaneously analysed for Halon-1301 and SF6, which allowed for identification of issues such as contamination of the water with modern air during sampling. All analysed groundwater sites had also been previously dated with tritium, CFC-12, CFC-11 and SF6, and exhibited mean residence times ranging from modern (close to 0 years) to over 100 years. The investigated groundwater samples ranged from oxic to highly anoxic. All samples with available CFC data were degraded and/or contaminated in one or both of CFC-11 and CFC-12. This allowed us to make a first attempt of assessing the conservativeness of Halon-1301 in water, in terms of presence of local sources and its sensitivity towards degradation, which could affect the suitability of Halon-1301 as groundwater age tracer. Overall we found Halon-1301 reliably inferred the mean residence time of groundwater recharged between 1980 and 2014. Where direct age comparison could be made 71% of mean age estimates for the studied groundwater sites were in agreement with ages inferred from tritium and SF6 (within an uncertainty of 1 standard deviation). The remaining (anoxic) sites showed reduced concentrations of Halon-1301 along with even further reduced concentrations of CFCs. The reason(s) for this need to be further assessed, but are likely to be caused by sorption or degradation of the compounds. Despite some groundwater samples showing evidence of contamination from industrial or agricultural sources (inferred by elevated CFC concentrations), no sample showed a significantly elevated concentration of Halon-1301, which suggests no local anthropogenic or geologic sources of Halon-1301 contamination.

Download Full-text

Using a Soil Chronosequence to Identify Soil Fractions for Understanding and Modeling Soil Carbon Dynamics in New Zealand

Radiocarbon ◽

10.1017/s0033822200042946 ◽

2007 ◽

Vol 49 (2) ◽

pp. 1093-1102 ◽

Cited By ~ 14

Author(s):

Christine A Prior ◽

W Troy Baisden ◽

Frank Bruhn ◽

Jason C Neff

Keyword(s):

New Zealand ◽

Residence Times ◽

Turnover Rates ◽

Mineral Association ◽

Soil Carbon Dynamics ◽

Soil Chronosequence ◽

Grazed Pasture ◽

Mean Residence Times ◽

Initial Results ◽

Pool Sizes

We are developing practical methodologies to characterize pool sizes and residence times for fractions of soil organic matter (SOM) using radiocarbon, with a particular focus on SOM in New Zealand pasture soils that responds to global change on decadal timescales. As single mean residence times for the entire SOM pool can be misleading or uninterpretable, we focus on the use of samples collected about 7 and 40 yr after the bomb14C spike to separate SOM into at least 2 pools. These results from a box model methodology yield sensible estimates of the proportion of “passive” SOM, and the residence time of the dominant pool with approximately decadal residence times. These results are supported by chemical analysis. Approximately 45-yr residence times of light-fraction SOM in a relatively infertile soil contrast with ∼16-yr residence times in a more fertile soil, and correspond to large differences in the proportion of lignin- and polysaccharide-derived SOM in these soils measured using pyrolysis-GC/MS. To achieve greater detail and assess the degree to which “active” SOM with annual turnover rates may bias results from the simple model, we use density as a means of isolating SOM with different degrees of mineral association. Initial results from grazed pasture soils sampled in 2003–4 emphasize that isolating non-mineral-associated light fractions can improve understanding, but may be less important than identifying fractions associated with unique mineralogy. In this soil, a fraction with density ≥2.55 g/mL shows much larger proportions of passive SOM than other fractions.

Download Full-text

Assessment of Halon-1301 as a groundwater age tracer

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-12-1397-2015 ◽

2015 ◽

Vol 12 (1) ◽

pp. 1397-1436

Author(s):

M. Beyer ◽

R. van der Raaij ◽

U. Morgenstern ◽

B. Jackson

Keyword(s):

Groundwater Age ◽

Groundwater Resources ◽

Water Soluble ◽

Elevated Concentration ◽

Environmental Tracers ◽

Halon 1301 ◽

Gaseous Substance ◽

Groundwater Samples ◽

Groundwater Dating ◽

Age Estimates

Abstract. Groundwater dating is an important tool to assess groundwater resources in regards to their dynamics, i.e. direction and time scale of groundwater flow and recharge, to assess contamination risks and manage remediation. To infer groundwater age information, a combination of different environmental tracers, such as tritium and SF6, are commonly used. However, ambiguous age interpretations are often faced, due to a limited set of available tracers and their individual restricted application ranges. For more robust groundwater dating multiple tracers need to be applied complementarily and it is vital that additional, groundwater age tracers are found to ensure robust groundwater dating in future. We recently suggested that Halon-1301, a water soluble and entirely anthropogenic gaseous substance, may be a promising candidate, but its behaviour in water and suitability as a groundwater age tracer had not yet been assessed in detail. In this study, we determine Halon-1301 and infer age information in 17 New Zealand groundwaters and various modern (river) water samples. The samples are simultaneously analysed for Halon-1301 and SF6, which allows identification of issues such as contamination of the water with modern air during sampling. Water at all analysed groundwater sites have also been previously dated with tritium, CFC-12, CFC-11 and SF6, and exhibit mean residence times ranging from modern (close to 0 years) to over 100 years. The investigated groundwater ranged from oxic to highly anoxic, and some showed evidence of CFC contamination or degradation. This allowed us to make a first attempt of assessing the conservativeness of Halon-1301 in water, in terms of presence of local sources and its sensitivity towards degradation etc., which could affect the suitability of Halon-1301 as groundwater age tracer. Overall we found Halon-1301 reliably inferred the mean residence time of groundwater recharged between 1980 and 2014. Where direct age comparison could be made 71% of mean age estimates for the studied groundwater sites were in agreement with ages inferred from tritium and SF6 (within ± 2 years). The remaining (anoxic) sites showed reduced concentrations of Halon-1301 along with even further reduced concentrations of CFCs. The reason(s) for this need to be further assessed, but are likely to be caused by sorption or degradation of the compounds. Despite some groundwater samples showing evidence of contamination from industrial or agricultural sources via elevated CFC concentrations, no sample indicated significantly elevated concentration of Halon-1301, which may indicate a lack of local anthropogenic or geologic sources of Halon-1301 contamination.

Download Full-text

Seasonal recharge and mean residence times of soil and epikarst water in a small karst catchment of southwest China

Scientific Reports ◽

10.1038/srep10215 ◽

2015 ◽

Vol 5 (1) ◽

Cited By ~ 31

Author(s):

Ke Hu ◽

Hongsong Chen ◽

Yunpeng Nie ◽

Kelin Wang

Keyword(s):

Southwest China ◽

Residence Times ◽

Mean Residence Times ◽

Karst Catchment

Download Full-text

The use of tritium in groundwater to determine fluid mean residence times of Valles caldera hydrothermal fluids, New Mexico, USA

Journal of Volcanology and Geothermal Research ◽

10.1016/0377-0273(94)00102-m ◽

1995 ◽

Vol 67 (1-3) ◽

pp. 187-205 ◽

Cited By ~ 17

Author(s):

Lisa Shevenell ◽

Fraser Goff

Keyword(s):

New Mexico ◽

Hydrothermal Fluids ◽

Residence Times ◽

Valles Caldera ◽

Mean Residence Times

Download Full-text

Calibration of a transient transport model to tritium data in streams and simulation of groundwater ages in the western Lake Taupo catchment, New Zealand

Hydrology and Earth System Sciences ◽

10.5194/hess-17-1217-2013 ◽

2013 ◽

Vol 17 (3) ◽

pp. 1217-1227 ◽

Cited By ~ 32

Author(s):

M. A. Gusyev ◽

M. Toews ◽

U. Morgenstern ◽

M. Stewart ◽

P. White ◽

...

Keyword(s):

New Zealand ◽

Transport Model ◽

Groundwater Age ◽

Uniform Grid ◽

Groundwater System ◽

Small Surface ◽

Streams And Rivers ◽

Groundwater Levels ◽

Transient Transport ◽

Western Lake

Abstract. Here we present a general approach of calibrating transient transport models to tritium concentrations in river waters developed for the MT3DMS/MODFLOW model of the western Lake Taupo catchment, New Zealand. Tritium has a known pulse-shaped input to groundwater systems due to the bomb tritium in the early 1960s and, with its radioactive half-life of 12.32 yr, allows for the determination of the groundwater age. In the transport model, the tritium input (measured in rainfall) passes through the groundwater system, and the simulated tritium concentrations are matched to the measured tritium concentrations in the river and stream outlets for the Waihaha, Whanganui, Whareroa, Kuratau and Omori catchments from 2000–2007. For the Kuratau River, tritium was also measured between 1960 and 1970, which allowed us to fine-tune the transport model for the simulated bomb-peak tritium concentrations. In order to incorporate small surface water features in detail, an 80 m uniform grid cell size was selected in the steady-state MODFLOW model for the model area of 1072 km2. The groundwater flow model was first calibrated to groundwater levels and stream baseflow observations. Then, the transient tritium transport MT3DMS model was matched to the measured tritium concentrations in streams and rivers, which are the natural discharge of the groundwater system. The tritium concentrations in the rivers and streams correspond to the residence time of the water in the groundwater system (groundwater age) and mixing of water with different age. The transport model output showed a good agreement with the measured tritium values. Finally, the tritium-calibrated MT3DMS model is applied to simulate groundwater ages, which are used to obtain groundwater age distributions with mean residence times (MRTs) in streams and rivers for the five catchments. The effect of regional and local hydrogeology on the simulated groundwater ages is investigated by demonstrating groundwater ages at five model cross-sections to better understand MRTs simulated with tritium-calibrated MT3DMS and lumped parameter models.

Download Full-text