Paper presented in ModelCare Conf. 2005 Influence of Continuous Pumping on Detection of Contaminant Plumes Under Conditions of Uncertainty

The focus of groundwater investigation has traditionally been on quantification of this resource, but increasing detections of contaminants during the last decades have shifted this focus towards assessment and protection of groundwater quality. Landfills are one of the major contamination sources that influence the groundwater quality. Therefore detection and characterization of the contaminant are crucial prerequisites of a monitoring network at a landfill sites. However the efficiency of such a network highly depends on the uncertainties due to subsurface heterogeneity and the nature of the landfill itself. The particular intention of this study is to investigate whether continuous pumping from the monitoring wells will improve the efficiency of the widely applied common practice that fulfils the minimum regulatory requirement, namely a monitoring network system of three downgradient wells. A hypothetical problem is presented where Monte Carlo framework is used to incorporate uncertainties due to subsurface heterogeneity and the leak location. Hydraulic conductivity and leak location are considered as random variables with prescribed probability density functions. A finite difference groundwater model coupled with a random walk particle-tracking model simulates a contaminant plume released from the landfill for each Monte Carlo realization. The efficiency the three well monitoring network has been compared for monitoring with and without pumping from the monitoring wells. It has been observed that the efficiency of monitoring network increases considerably by pumping from the monitoring wells. Furthermore, the analyses show that the pumping rate has a great influence on detection probability. The detection probability increases as the pumping rate increases.