Recovering the pollutant release history in aquifers with non uniform flow field, Abstract H13D-1355

The great interest in environmental issues has led to an attention to the quality of groundwater. Scientific efforts in groundwater flow studies have primarily focused on the flow and transport behavior and on the identification of the corresponding parameters. Since ’90 increasing attention has been paid to the problem of recovering the release history of a pollutant because the knowledge of the pollution injection function gives information about the future pollution spread and allows a better planning of remediation action (Liu and Ball, 1999, Snodgrass and Kitanidis, 1997, Skaggs and Kabala, 1994, Butera and Tanda, 2003). Moreover, from a legal and regulatory point of view, it is also important to determine the release time period and the highest values of concentration released; in fact, an available release history can be a useful tool for sharing the costs of remediation of a polluted area among the actors. Some approaches developed in the literature to the inverse problem solution (geostatistical approach (Snodgrass and Kitanidis, 1997), Tikhonov regularization method (Skaggs and Kabala, 1994)) require the computation of the function that describes the effect, in time at a certain location of the aquifer, due to an impulsive release of pollutant at the source. This function, named transfer or Kernel function can be analy1itically determined if the problem has a simple geometry and regular boundary conditions. In many cases the characteristic of the groundwater flow field do not allow for the analytical transfer function formulation; this is the case, for instance, of non uniform in the mean flow due to complicated boundary conditions, existence of pumping wells, high heterogeneity of the aquifer (Sudicky, 1986) etc.. With the available procedures the technician has to reduce the real problem to a very simplified scheme to which the analytical transfer function can be applied. As a consequence a rough approximation in the results can be expected. In this work, a numerical procedure useful to determine the transfer function in cases without analytical solution is developed. It is based on the analogy with the techniques for identification of the Instantaneous Unit Hydrograph used by the surface Hydrologists in determining the flood response of a basin to a rain event.