[en] Detectable concentrations of chlorofluorocarbons (CFC's) were observed in ground water and unsaturated-zone air at the Idaho National Engineering Laboratory (INEL) and vicinity. The recharge ages of waters were determined to be from 4 to more than 50 years on the basis of CFC concentrations and other environmental data; most ground waters have ages of 14 to 30 years. These results indicate that young ground water was added at various locations to the older regional ground water (greater than 50 years) within and outside the INEL boundaries. The wells drilled into the Snake River Plain aquifer at INEL sampled mainly this local recharge. The Big Lost River, Birch Creek, the Little Lost River, and the Mud Lake-Terreton area appear to be major sources of recharge of the Snake River Plain aquifer at INEL. An average recharge temperature of 9.7±1.3 degrees C (degrees Celsius) was calculated from dissolved nitrogen and argon concentrations in the ground waters, a temperature that is similar to the mean annual soil temperature of 9 degrees C measured at INEL. This similarity indicates that the aquifer was recharged at INEL and not at higher elevations that would have cooler soil temperatures than INEL. Soil-gas concentrations at Test Area North (TAN) are explained by diffusion theory

[en] This guidebook brings together the results of some of these studies, as they apply to the groundwater environment, and summarizes the principles of CFC dating, with special emphasis on applications and limitations of the methods. Methods of sample collection and analysis are also presented, along with new software to aid in the interpretation of measured groundwater concentrations of CFCs. Often the application of multiple environmental tracers to a particular hydrological system enhances the level of understanding that can be gained. Applications of CFCs in groundwater studies will complement and enhance uses of other atmospheric environmental tracers in the hydrological sciences, including uses of tritium and tritium/helium-3 and sulphur hexafluoride. In the southern hemisphere and in low latitude/equatorial regions, the CFCs are particularly promising additional tools for groundwater dating because of very low tritium levels prevailing there and the associated problems for tritium dating. In addition, those regions were not affected so much by local industrial CFC emissions, as was the case for decades in western Europe and in the USA. However, the potential of applications for CFCs as groundwater tracers in low latitude regions has not yet been fully explored

[en] CFCs were predominantly consumed and released by industrialized nations between the latitudes of 30 deg. N and 70 deg. N (Hartley et al., 1996); therefore, the troposphere mixing ratios in the northern hemisphere historically have been higher than those of the southern hemisphere. However, with the phasing out of CFC production by the developed countries (Montreal Protocol on Substances that Deplete the Ozone Layer), the interhemispheric differences in the mixing ratios have appreciably decreased. Near urban areas, some CFC mixing ratios are often raised relative to background air composition. If these differences are neglected, then the calculated age of the water from these urban or densely populated sites will appear contaminated or younger than the actual recharge age of the groundwater

[en] Sulphur hexafluoride is a colourless, odourless, non-flammable, nontoxic, stable gas with excellent electrical insulating and arc-quenching properties, and is mainly used as an electrical insulator in high voltage switches and transformers. Industrial production of SF₆ began in 1953 with the introduction of gas-filled electrical switches and production has increased from nearly zero in 1953 to 85,700 t of SF₆ in 1995. SF₆ has received significant recent interest because of its high greenhouse warming potential which is estimated to be 23 900 times that of CO₂ (Climate Change 1995) and is the second highest value measured. SF₆ was one of the six gases covered by the Kyoto Global Warming Protocol Agreement of 1997

[en] Seventy new measurements (Srsub(T)-Psub(CO₂)) of the solubility of strontianite were used to evaluate the equilibrium constant for the reaction SrCO₃(cr) = Sr²⁺(aq) + CO₃^2-(aq) between 2 and 91 deg C. An expression is given for the temperature dependence of the equilibrium constant. The log K of strontianite, the Gibbs energy, enthalpy and entropy of the reaction at 25 deg C are given. The equilibrium constants are consistent with an aqueous model that includes the ion pairs SrHCO₃⁺(aq) and SrCO₃⁰(aq) which were evaluated by potentiometric methods between 5 and 80 deg C. Expressions are also given for the equilibrium constant for the association reaction Sr²⁺(aq) + HCO₃^-(aq) = SrHCO₃⁺(aq), and for the association reaction Sr²⁺(aq) + CO₃^2-(aq) = SrCO₃⁰(aq). The results lead to reliable calculation of the aqueous speciation and solubility of strontianite in the system SrCO₃-CO₂-H₂O from 0 to more than 90 deg C. Literature data on the solubility of strontianite have been evaluated and compared with these results. Our new data for strontianite have been used in an evaluation of the thermodynamic properties of Sr²⁺(aq), SrCO₃(cr) and related compounds. Values are recommended for the standard enthalpy Gibbs energy and entropy,respectively, of Sr²⁺(aq). (U.K.)

[en] Chemical analysis of surface snows and dated ice core samples from Dye 3, Greenland, suggests that the ammonium cation is a major constituent in all samples and that the annual ammonium levels present in the south Greenland samples have varied from 3.3 to 26.3 μg/kg between the seventeenth century and the present time. The annual range of 1974--1975 surface samples was between 3.8 and 8.8 μg/kg, while the mean was 5.7 +- 1.8 μ/kg. The recent large-scale uses of fixed nitrogen fertilizers and industrial pollution have apparently not affected the levels of ammonia reaching southern Greenland. The sodium and chloride present are predominantly derived from ocean spray, while more than 90% of the calcium is of continental origin. The levels of these three elements have not apparently been affected by human activity since the industrial revolution. Sulfate levels have increased dramatically since the industrial revolution, suggesting that sulfate of anthropogenic origin is the most important source of sulfate in modern snows from southern Greenland. The amount of the sulfuric acid neutralized by the ammonium cations was approximately 100% in the seventeenth and eighteenth centuries, dropping to approximately 20% in the 1974--1975 samples. These figures imply that there has been in increase in the acidity of precipitation in southern Greenland since the end of the eighteenth ce

[en] This chapter summarizes selected data for CFCs and other environmental tracers in water samples from a variety of hydrogeological environments. Some of the examples are taken from case studies discussed in other chapters. Examples are included that have apparently reliable age estimates, as well as samples that have been affected by one or more processes that limit age interpretation

[en] Groundwater dating with CFCs refers to the process of estimating the historical date at which a parcel of water was recharged to a groundwater system. Several assumptions are necessary in assigning an apparent age based on CFCs. It is first necessary to collect and analyse a water sample for CFCs that is representative of the aquifer at a given location. It is then assumed that the water sample was in solubility equilibrium with the unsaturated zone air at the time of recharge. All gas solubilities are functions of temperature, pressure and dissolved solute content. Therefore, it is necessary to estimate the temperature and pressure during recharge. In some cases, recharge temperature can be estimated from shallow groundwater temperatures, but recharge temperatures are more precisely estimated from measurements of other dissolved gases, such as nitrogen and argon. In groundwater dating with CFCs, it is further assumed that the local historical CFC composition of air is known and that the composition of unsaturated zone air closely follows that of the atmosphere. The recharge date is then determined by comparing the calculated partial pressures of CFCs in solubility equilibrium with the water sample with historical CFC concentrations in local air. One criterion for rejection of apparent CFC ages is that calculated CFC concentrations in air are greater than that possible for water in solubility equilibrium with air at the time of the peak in atmospheric concentration

No abstract available

[en] Water that is pumped from a well or discharges from a spring is a mixture of the waters from all the flow lines reaching the discharge point. If the age distribution of waters reaching the point of discharge is narrow, the apparent CFC age can be reasonably representative of the travel time from the point of recharge through the aquifer. Thus, water samples from wells open to relatively narrow intervals of an aquifer, or water discharging from a spring in a predominantly conduit flow system will tend to have apparent ages that are less affected by mixing than those samples from wells with large open intervals, or springs discharging from diffuse flow systems. Mixtures of groundwater can also be produced by the sampling process, such as in water pumped from fractured rock aquifers