Anew and efficient method for the synthesis of novel 3-acetylcoumarins oxadiazoles derivatives Molecules. Application of Exp-function method for nonlinear evolution equations with variable coefficients Physics Letters A. New traveling wave solutions for nonlinear evolution equations Physics Letters A. Energy, 14 Energy, 15 An operational approach to the classical slowing-down problem. Kerntechnik 55
The practicalities of using CFCs and SF6 for groundwater dating and tracing
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Morris Abstract 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 SF6 from the middle of the last century offers a convenient way of dating waters up to similar to 60 a old.
The gases are well-mixed in the atmosphere so their input functions are not area-specific as is the case with H 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 SF6, 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 SF6 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 already declining in the atmosphere, new anthropogenic trace gases are likely to take their place.
Atmospheric SF6 near a large urban area
Hydrogeology ; aquifers ; hydrochemistry ; isotopes ; hydrodynamics ; numerical modelling International Conferences – J. Insight into groundwater flow within a crystalline aquifer. Le Coustumer, Et M.
Data on concentrations of environmental tracers, such as chlorofluorocarbons CFCs and sulfur hexafluoride SF6. Tracing and Dating Young Ground Water. New York City Webcams. The ages of the young-water fractions in the Upper Floridan aquifer were mapped throughout the Valdosta area. Radio City Dating is the fun and easy way to meet people just like you.
The AMS lab has dated thousands of C14 sf6 groundwater dating since its inception. The gas samples are heat-sealed in borosilicate glass ampoules with a torch.
Special Issue “Environmental Tracers”
Local emissions of SF6 are of interest for studying their impact on the use of SF6 as a groundwater-dating tool near source regions as well as for investigating the spatial distributions of inert gaseous compounds spreading from urban or industrial centers. A precondition for the use of SF6 in such studies is the capability to document the temporal and spatial evolution of SF6 in and around source regions with sufficient resolution.
The data show that, below about 2 m depth, the vadose zone integrates atmospheric SF6 mixing ratios over time scales greater than 1 month.
References References Aeschbach-Hertig, W. Interpretation of dissolved atmospheric noble gases in natural waters. Determining soil hydrologic characteristics on a remote forest watershed by continuous monitoring of soil-water pressures, rainfall and runoff. Irrigation and Drainage Paper Food and Agriculture Organization of the United Nations. A standardized system for evaluating ground water pollution potential using hydrogeologic settings. On the treatment of evapotranspiration, soil moisture accounting, and aquifer recharge in monthly water balance models.
Flow and storage in groundwater systems.
Using CFCs and SF6 for groundwater dating : a SWOT analysis
A dedicated, GC-based analytical system is presented which allows detection of four anthropogenic trace gases SF6, SF5 CF3, CFC and Halon in a single water sample, with detection limits and measurement uncertainties sufficiently low to employ them as quantitative indicators of groundwater age. The gases dissolved in water are extracted in the field using the method based on a dynamic head-space concept.
In the laboratory, the investigated gases are cryogenically enriched, separated and measured using an electron capture detector. The investigated tracers were measured in several production wells located in the recharge area of an intensively exploited aquifer in southern Poland. While the piston-flow ages of groundwater in the investigated wells revealed internal consistency, they appeared to be generally smaller than the ages derived from time series of tritium content in those wells, interpreted by lumped-parameter models.
This information is useful for evaluating groundwater sustainability and vulnerability by identifying groundwater provenance and information for water budgets. Gibsons, British Columbia is a growing coastal community relying on groundwater to supply drinking water to two thirds of its 4, residents. The Town of Gibsons is proud of its untreated groundwater resource and proactive about keeping it protected and sustainable for future generations.
Samples of noble gases, tritium, and stable isotopes of oxygen and hydrogen were collected from the aquifer. Tracer results improved the site conceptual model by identifying a previously unknown contribution of mountain block recharge MBR and by providing recharge elevation estimates using noble gas thermometry. The updated conceptual model including the mountain block was integrated into a regional three-dimensional numerical groundwater flow model calibrated to both hydraulic heads and to recharge elevation, a non-traditional approach to model calibration.
This is the first study to use recharge elevation as a calibration target, which proved to be imperative for constraining bedrock geometry and minimizing model non-uniqueness.
Environmental tracers and groundwater dating
Studying imprints of climatic and environmental change in a regional aquifer system in an arid part of India using noble gases and other environmental tracers Funded by DFG Project summary Temperatures estimated using dissolved noble gases in groundwater have played a major role in determining continental climate during the last glacial maximum, particularly for the tropics.
Such tropical paleotemperature records are available from South America, Africa, and the Arabian Peninsula, but not from Asia. A major goal of the proposed study of an aquifer system in the North Gujarat – Cambay NGC region in a semi-arid part of western India is therefore to provide high-quality paleotemperature information from an area that has not been well studied so far.
Recent research has shown that noble gas temperatures NGTs in semi-arid tropical regions may in part reflect the influence of changing humidity and vegetation conditions on soil temperature, and the “excess air” component in groundwater may be a potential indicator of past changes of humidity.
These openings occur in very irregular fashion and make prediction of aquifer properties very difficult. Reliable tools for resource evaluation in fractured rock aquifers are nevertheless needed for efficient management of these resources. The Water Research Commission identified hard rock or fractured rock aquifers as a theme of groundwater research requiring a high priority in terms of funding.
These gases are chemically stable, safe and have convenient boiling points resulting in widespread use in society. Used CFC gas accumulates in the atmosphere where it poses a serious hazard to’ stratospheric ozone. The known growth rates of CFCs in the atmosphere over the last fifty years, the rapid mixing in the world’s atmosphere, their solubility in water and their good chemical stability have enabled this hazard to become a useful tool for hydrologists.
This phenomenon is used to trace water movement in the oceans, in surface water and in groundwater and will likely remain useful for a few decades in the near future.