Using groundwater geochemistry and environmental isotopes to assess the correction of 14C ages in a silicate-dominated aquifer system

The use of C-14 to constrain groundwater residence times requires careful correction of C-14 activities (a C-14) and an assessment of the degree of inter-aquifer mixing In groundwater of the Campaspe Valley in the Southern Murray Basin, Australia, delta C-13 values of dissolved inorganic carbon (DIC) range from -18 parts per thousand, to +2 parts per thousand, Using these delta C-13 values to correct C-14 ages assuming that dissolution Of or exchange with matrix calcite had occurred implies that locally >90 of the DIC is derived from carbonates In turn, this Suggests that low-salinity groundwater in the deeper confined Calivil-Renmark Formation up to 50-60 km from the basin margins in the Campaspe Valley has a component of modern recharge, which would require that widespread leakage from the overlying Shepparton Formation had occurred