OPTIMAL MANAGEMENT OF THE SUBSURFACE ENVIRONMENT / L'aménagement optimal de l'environnement souterrain

Abstract

A mathematical model for the optimal, conjunctive management of a groundwater basin's quality and quantity resources is presented. The quality resource, the assimilative waste capacity, is the ability of the aquifer to degrade certain non-conservative constituents through the actions of molecular diffusion, hydrodynamic dispersion, adsorption, biochemical reactions and convective mass transport. The model is applicable to saturated, isothermal, porous media. The Galerkin method is used to express the spatial and temporal variations in hydraulic head and constituent concentrations as a function of possible recharge, pumping, and treatment decisions. The Galerkin procedure ensures that the constraint equations actually model the response characteristics (flow and mass transport) of the groundwater basin. In each planning period, the groundwater basin is required to meet an exogenous water demand while maintaining adequate water quality levels throughout the aquifer. The model, structured as a mathematical program, minimizes the sum of waste water treatment and pumping and recharge costs. The results indicate (1) the feasibility of conjunctive management of an aquifer's quality and quantity resources, and (2) that the assimilative waste capacity can function as a form of secondary or advanced waste water treatment.