A conceptual model for correcting groundwater 14C age

Abstract

Determining groundwater age is critical for understanding hydrogeological systems and groundwater renewability. The 14C with a half time of 5730 years is an important tracer to determine groundwater age ranging typically from 1000 years to 40,000 years. The use of 14C age relies on the dissolved inorganic carbon of groundwater. The correction of the 14C age of groundwater remains largely uncertain due to complex sources of dissolved inorganic carbon. This study provides a novel conceptual model to correct groundwater 14C age by determining a virtual initial 14C content (A0). This method has avoided large uncertainties of parameters used in conventional methods, such as the δ13C values of soil CO2 and (continental) carbonates. The uncertainty of the method is relatively small. A case study from the Xifeng loess tableland in the NW China showed that the initial 14C content was estimated to be 46.1 ± 1 percent Modern Carbon through determining the groundwater age around the water table using soil water percolation velocity, resulting in the uncertainty within 200 years, smaller than 500–2000 years using conventional methods. This study would help determine groundwater age and understand hydrogeological conditions.