The highest radiocarbon ages resulted higher than those obtained with the hydraulic method, probably because depth and confinement of A2 CAS may generate lower K values.
The hydraulic method suggests ages in the order of 3000 years (between 1500 and 7000 years) for the A1 CAS system and in the order of 4000 years (between 2000 and 9000 years) for deeper systems (A2a and A2b CASs).
Moreover, the hydraulic method only takes into account the advection process, whereas the age is affected by hydrodynamic dispersion then, the methods may produce similar results but never the same.
The isotopic ages were checked with the hydraulic method estimation based on the groundwater flow velocity (using Darcy Law) and on the distance to the recharge perimountain area (Kazemi et al. 2006).
Field estimations of soil water fluxes by 'classical' hydraulic methods are often difficult to obtain.
Typical vertical hydraulic conductivity (KZ) values in argillaceous materials estimated using hydraulic methods are 10−12 10−9 m s−1.
These analyses further demonstrate that recovery of LNAPL by hydraulic methods is often ineffective at reducing risk.
Younger ages estimated for groundwater in C13 well (A2a CAS) and C15 well (A2b CAS), even lower than those estimated with hydraulic methods, would be related to groundwater mixtures with the overlying systems, which confirms the interpretation from stable isotopes.
Methods applied to the whole aquitard thickness (some field hydraulic methods, regional groundwater flow modelling, aquitard porewater and aquifer chemistry) consistently result in lower KZ values, most probably indicating the presence of very low KZ layers within the aquitard, likely to be missed while using field hydraulic methods that test only a section of the entire thickness.
Hydraulic methods, namely laboratory, field and regional groundwater flow modelling, are used to estimate hydraulic conductivity (K), whereas chemical methods, namely aquitard porewater and aquifer groundwater chemistry, are used to estimate either leakage rates or porewater velocity (V).
This can include, for example, hydrological techniques (e.g. spring hydrographs, rainwater gauges), hydraulic methods (e.g. piezometric maps, hydraulic tests) and the application of natural (e.g. hydrochemistry, D-/O-isotopy) or artificial tracers (e.g. fluorescent dyes) (Goldscheider and Drew 2007).
