Contaminant transport of metal species in an urban environment

Numerical modeling of groundwater flow and mass transport was conducted to support a proposal to discontinue a groundwater extraction based remediation system at an industrial site. The extraction system had been in place for approximately 15 years to manage a metal plume in the groundwater. The main concern at the site is metal migrating and discharging into a nearby creek. Numerical modeling was conducted to predict the potential total metal mass flux to the creek if the current groundwater extraction system ceased operation. Simulations were extended two thousand years into the future to evaluate long term impacts. A modeling approach that considered model parameters and predictions as statistical distributions was used to quantify the uncertainty in model predictions and enable risk-based decisions. Approximately fifty alternative model parameter sets, all informed by calibration to observation data, were used to predict the mass flux to the creek for the next 2,000 years. The modeling results indicated the most likely maximum mass flux to the creek and the approximately arrival time. These model predictions provide estimates of total mass flux to the creek that could be used to assess the risk of negative consequences from terminating operation of the current groundwater extraction system.