Progress needs to be made in obtaining representative samples.
Concentrations of He and Ne in excess of solubility equilibrium indicate that the dissolved gases are not fractionated.
The resulting residence-time distribution, or age, of groundwater sampled at a given well is a key property that reflects not only local conditions but in fact global information about the subsurface materials along the historical flow path of the water (Marçais et al., in review; Mc Callum et al., 2014).
With the governing equation of groundwater age distributions (Ginn, 1999) we have begun using isotopic data (Massoudieh and Ginn, 2011) in combination with high-resolution three-dimensional regional groundwater modeling to assess the way that moments of age – e.g., mean and variance – varies with space, and how this reflects sustainability of water resources (Woolfenden and Ginn, 2009; Ginn et al., 2009).
Geochemistry has contributed significantly to the understanding of ground-water systems over the last 50 years.
Historic advances include development of the hydrochemical facies concept, application of equilibrium theory, investigation of redox processes, and radiocarbon dating.