Stable-isotope and groundwater chemistry analyses on samples from about 40 boreholes in the Lorraine region (eastern France) are used to evaluate the paleohydrological regime of the Lower Triassic sandstone aquifer in the study of the mechanisms of the general water dynamics of the aquifer at present. In this sandstone aquifer, the estimation of the 14C activity, A 14, in the total dissolved carbon (TDC) to 100% of modern carbon is justified by the absence of carbonates in the reservoir and by the 13C contents in the TDC. A significant relation could be determined between the 14C activity in the TDC and 13C: A 14 = −7.7 δ 13 −59.6%. This gradual enrichment of the TDC with 13C results from the escape of the dissolved CO 2. The meaning of the radiometric age is discussed as a function of piston and exponential-type flows. The study of the stable isotopes 18O and 2H revealed two water families. The most recent waters have δ 18O-values higher by 1‰ than the more than 10 4 yr. old waters. This 1‰ discontinuity corresponds to the improvement of weather conditions during the Holocene, which amounts to 2.5°C. The isochrons of the aquifer reveal the existence of hydrogeological sections bounded by faults where the rates of circulation are different.