Analytical and numerical modelling for conceptual site model refinement: A case study

Contaminated fractured bedrock site management benefits from a phased field investigation approach supported by groundwater modelling to continually enhance the conceptual site model (CSM). This study discusses learnings from a multi-year phased investigation at a site in Central Alberta, Canada. The site is underlain by fractured bedrock contaminated with salinity and hydrocarbons. The impacts have been contained by intercepting and pumping groundwater for 18 years. Groundwater modelling was used to refine field investigation targets and to test elements of the CSM. An equivalent porous medium (EPM) modelling approach successfully reproduced the flow field, but not the solute transport behaviour. A detailed discrete fracture network (DFN) model was able to closely reproduce both groundwater flow and solute transport behaviour at the site. An analytical solution was also developed based on mass recovery data and concentration rebound behaviour and was used to estimate initial conditions for the DFN model. The analytical solution was also successfully used as a screening tool to determine the effectiveness of remediation by pumping. The phased approach has led to an effective CSM and remedial action plan, and the simple analytical model has aptly supported the more detailed site and numerical investigations.