Abstract Contaminant mass flow rates originating from a contaminant source zone provide a basis for quantifying the environmental impact and may thus play an important role in assessing natural attenuation as a remedial or management option for contaminated aquifer cleanup. A reliable quantification of the contaminant mass flow rate is thus sought. The integral groundwater investigation method provides a possibility for estimating mass flow rates by using long-term pumping tests. This work focuses on the performance and reliability of this method in heterogeneous aquifers and under "realistic" conditions, representative of a typical site investigation. The Virtual Aquifer method is used for study. The results show that the method is mainly influenced by the hydraulic flow regime near the control plane, where uncertainty in hydraulic conductivity or estimated hydraulic gradient may severely influence the mass flow rate obtained. Determination of the average concentration along the control plane is much less uncertain.

Keywords integral groundwater investigation method; mass flow rates; monitoring strategy; uncertainty assessment