Characterizing a heterogeneous hydrogeological system using groundwater flow and geochemical modelling

Characterization of heterogeneous hydrogeological systems plays an important role in groundwater protection and remediation of contaminated sites. However, sparse field observations and/or lack of relevant in situ test results hinder regional characterization process. In such cases, advanced modelling techniques can improve characterization of such complex hydrogeological systems. A sequential approach using groundwater flow modelling with nonlinear inverse calibration, advective transport and geochemical modelling and isotope study to characterize heterogeneous systems has been developed in this case study. It was used to better understand the regional hydrogeology and groundwater system of the Triassic Sherwood Sandstone aquifer underlying the Belfast area, Northern Ireland. Based on the inversely calibrated flow model and advective transport modelling by particle tracking, geochemical interpretation of groundwater quality data and isotopic and geochemical inverse modelling at well-distributed spatial locations in the sandstone were carried out to verify the flow pathways and residence times and to identify the geochemical evolution in this heterogeneous hydrogeological system. These approaches provide multiple lines of evidence for characterization of the heterogeneous aquifer system. The flowpaths and residence times from the flow and advective transport modelling agreed well with the geochemical modelling and isotopic radiocarbon dating. This demonstrates the importance of incorporating both flow and geochemical analysis techniques in a hydrogeological study