Inverse problem of water flow and multicomponent reactive solute transport: Application to the delta aquitard in Spain.

A mathematical and numerical methodology for solving the inverse problem of water flow, heat transport and multicomponent reactive solute transport in variably saturated media has been developed. The inverse problem is solved by minimizing a generalized least-squares criterion with a Gauss-Newton-Levenberg-Marquardt method. Statistical measures of goodness-of-fit as well as confidence intervals are computed. All these features are incorporated in INVERSE-CORE2D, a general code which solves both the for-ward and inverse problems. The forward model is based on CORE2D (Samper et al, 2000) a code which can handle: 1) 2-D confined or unconfined, saturated or unsaturated steady or transient groundwater flow with general boundary conditions, 2) Transient heat transport, 3) Chemical reactions including acid-base, redox, aqueous complexation, surface sorption, cation exchange, mineral. dissolution-precipitation, and gas dissolution. INVERSE-CORE2D has been verified with synthetic data and applied to a field case study dealing with salt water leaching with fresh water at the Llobregat Delta Aquitard (Spain).