Recovering the release history of a groundwater contaminant using a non-linear least-squares method

A non-linear least-squares (NLS) method is used without regularization to r ecover the release history of a groundwater contaminant plume from its curr ent measured spatial distribution. The flow system is assumed to be one-dim ensional, with the plume originating from a known single site. The solution is found to be very sensitive to noise and to the extent to which the plum e is dissipated. Although the NLS method is extremely sensitive to measurem ent errors for the gradual release scenario, it can resolve the release his tories for catastrophic release scenarios reasonably well, even in the pres ence of moderate measurement errors. A number of synthetic numerical exampl es are analysed. We find that for catastrophic contaminant releases the NLS method may be an alternative to the Tikhonov regularization approach. Copy right (C) 2000 John Wiley & Sons, Ltd.