Conditioned backward probability modeling to identify sources of groundwater contaminants subject to sorption and decay

摘要

If contamination is observed in an aquifer, a backward probability model can be used to obtain information about the former position of the observed contamination. A backward location probability density function (PDF) describes the possible former positions of the observed contaminant particle at a specified time in the past. If the source release time is known or can be estimated, the backward location PDF can be used to identify possible source locations. For sorbing solutes, the location PDF depends on the phase (aqueous or sorbed) of the observed contamination and on the phase of the contamination at the source. These PDFs are related to adjoint states of aqueous and sorbed phase concentrations. The adjoint states, however, do not take into account the measured concentrations. Neupauer and Lin (2006) presented an approach for conditioning backward location PDFs on measured concentrations of non-reactive solutes. In this paper, we present a related conditioning method to identify the location of an instantaneous point source of a solute that exhibits first-order decay and linear equilibrium or non-equilibrium sorption. We derive the conditioning equations and present an illustrative example to demonstrate important features of the technique. Finally, we illustrate the use of the conditioned location PDF to identify possible sources of contamination by using data from a trichloroethylene plume at the Massachusetts Military Reservation.