Improved regional groundwater flow modelling using geochemical and isotopic constraints

Previous groundwater flow modelling of the Triassic Sherwood sandstone aquifer in Northern Ireland by Yang et al. (2000) highlighted uncertainties in the conceptual hydrogeological. model. Geochemical and isotopic sampling of groundwater was undertaken in the study area to better refine this conceptual model. Subsequent geochemical modelling provided useful insights into the recharge mechanisms occurring in the region. This work describes new flow modelling combining the findings from the previous flow modelling studies and geochemical/isotopic investigations. This incorporated alterations to the conceptual model and the use of 'soft data' to constrain a least-squares inverse modelling process. The new inverse modelling provided improved output from previous work. Recharge to the Lagan Valley was modelled as similar to 43,000 m(3)/d with groundwater flow velocities in the range 15 to 75 m/yr. Good correlation between MODPATH particle tracking travel times and geochemical residence times was achieved. This work highlights the importance of combining numerical flow modelling with geochemical/isotopic analysis in hydrogeology