A study on new approaches for delineating groundwater protection zones in fractured-rock aquifers
Delineation of groundwater protection zones in fractured-rock aquifers usually involves the equivalent porous media (EPM) assumption, although research studies have proved that, often, such an assumption is inadequate. This thesis is concerned with the study of flow and transport models that, while preserving the main hydrodynamic features of fractured rocks, are still practical enough to be applied to low-budget studies such as the delineation of groundwater protection zones. Methodologies are developed for three different types of fractured-rock aquifers. The first group comprises composite aquifer systems, a single linear structure in an otherwise homogeneous aquifer. The transport model adopted is based on advection and the procedure for delineation of protection zones involves the derivation of advective velocity and stream function equations. The stream function facilitates visualisation of the capture zones, while isochrones are delineated through particle tracking. Dual and multiple-porosity aquifers, the second group, are dealt with analytically. The well- known flow and transport features of dual-porosity media are used to develop a method that takes into account the influence of matrix diffusion on the shape and size of protection zones. The methodology returns probability related protection zones that, when compared with single- porosity models, show that matrix diffusion has a dramatic effect on protection zones size. Additionally, a new multiple-porosity model is developed, that simulates the hydraulic behaviour of hierarchical fracture systems. Analytical solutions are presented for 2-D flow and 1-D transport. The third group comprises fracture network aquifers. The work conducted involves the implementation of practical tools for simulating solute transport in fracture networks, which are then used to delineate probabilistic protection zones. A first approach applies the Statistical Continuum Method, a hybrid tool that combines the use of Discrete Fracture Networks and Continuum Models. A second method relies on a Continuous Time Random Walk (CTRW). Analytical solutions for modelling solute transport in fracture networks according to a CTRW are found and combined with MODFLOW to simulate solute transport in catchment-scale domains. Additionally, the following are discussed: methodologies for assessing protection zones in fractured-rocks delineated using EPM approaches ways for implementing a 3-D CTRW and the two issues of probability versus concentration and of forward versus reverse particle tracking, when simulating solute transport in fractured-rock aquifers.