The average atmospheric concentrations in the northern hemisphere can be seen in the figure below.
Each of the isotopes has specific time periods in which they were introduced in industrial applications and subsequent introduction into the atmosphere.
Nitrate-nitrogen is an indicator of water quality impacts from surface activities such as septic effluent and fertilizer application.
All the water samples obtained and analyzed had concentrations well below the drinking water standards of 10 milligrams per liter.
The concentrations of these chemicals in the atmosphere have generally increased over time and will be reflected in the water concentration.
When the water from precipitation or seepage from lakes and rivers recharges the aquifer and is no longer in contact with the atmosphere, the concentrations of CFCs and SF6 in ground water will no longer change and reflect the time of recharge.
Water has the chemical composition of HO concentration ratios that will plot on a single line called the global meteoric water line (GMWL).
The plotted location of the ratios will change position on the line dependent on various factors such the seasons and distance from the ocean.
In addition, there has been an improved awareness of the interconnection of surface water and ground water along with water quality and water quantity issues.Both the CFCs and SF6 can be used for dating relatively young water generally less than 50 years.Age dating of the RPA ground water using chlorofluorocarbons (CFC-11, CFC-12, CFC-113) along with SF6 showed mixed results.The chlorofluorocarbons indicated either very high concentrations indicating an external source (other than the atmosphere) or very low concentrations most likely reflecting chemical changes that take place when water is recharged through the thick unsaturated zone or from the peripheral lakes.There are a number of external sources that could be the cause of the elevated CFCs in the aquifer.