Modelling of groundwater flow conditions at the contaminated site of a former dry-cleaning facility

Abstract

The thesis aims to investigate the hydrogeological conditions at the site of a former dry-cleaning facility where contamination of chlorinated ethenes (PCE and TCE) has been documented. This is done through the development of a steady-state numerical groundwater flow model in the widely used software Visual MODFLOW Flex. As an initial step of the modelling process, a conceptual site model was developed and presented. The site model includes two adjacent tunnels situated in the shallow bedrock, for which the impact on the local groundwater system is unknown. Using the calibrated model, a sensitivity analysis was performed, identifying crucial hydraulic parameters and boundary conditions which could be subject to further investigation to minimize model uncertainties regarding the calculated groundwater inflow to the nearby tunnels and the travel time of particles situated at the former dry cleaner’s location within the hydrogeologic system. The model suggests that the two tunnels have a significant impact on the hydrogeological system to the west of the former dry-cleaner. The site of the former building is located at a groundwater divide, and the developed numerical model was not able to reproduce groundwater heads both west and south-east of the former dry-cleaner. The groundwater levels south-east of the former dry-cleaning facility are found to be governed by unknown hydraulic conditions, which were not identified and included in the conceptual model. The performed sensitivity analysis indicates that the boundary conditions of recharge and drain leakance of the tunnels need to be investigated further to reduce uncertainties of the model. The developed model suggests that the tunnels, primarily the sewage tunnel, act as a contaminant pathway of chlorinated ethenes present in groundwater flowing from the contaminated site.