The inversion method of pumped concentration can be used as an alternative or complementary method to the conventional methods for groundwater pollution evaluation and quantification. This method is useful even when the monitoring wells are few and also when the contamination source is unknown. In a homogeneous-isotropic case, with radially dominated groundwater flow field, this method of inversion can be performed analytically. However, in many cases, the real aquifer systems are heterogeneous. A novel volume-based inverse model (VINMOD) is developed for numerical inversion of pumped concentration under heterogeneous conditions. VINMOD helps us to determine the mean concentration and mass flow rate of an “undisturbed” contaminant plume at a predefined imaginary control plane (ICP). Model verification and preliminary tests are presented using a hypothetical single-layer aquifer. It is noticed that VINMOD is highly sensitive to the groundwater flow velocity and the well capture zone geometry, which in fact influences the determination of total mass flow rate of a pollutant in the groundwater.