Robinson, Judith Nicola; (2003) Delineation of groundwater protection zones for fractured aquifers in the UK. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Groundwater protection zones (GPZs) are defined as part of the policy for the protection of groundwater for England, Wales, Scotland and Ireland. GPZs are delineated by the relevant UK regulatory authority for boreholes and springs on the basis of horizontal flow time and distance from the source. The zones are usually determined through reverse particle tracking using 'porous media' numerical models. There are two principal drawbacks with the existing methodology: a) the majority of the major and minor aquifers of the UK are fractured to a certain degree, but are being represented by porous media models, and b) the regulatory authority's existing protection zone methodology only has a limited uncertainty analysis associated with it. This thesis aims to provide alternatives to the sole use of porous media models in fractured rock scenarios to delineate protection zones, as well as a more robust uncertainty analysis. Having conducted an extensive appraisal of protection zone methodologies world-wide it was found that no country reviewed had an adequate policy for delineating protection zones in fractured rock. Therefore any methodology developed for the UK must be from first principles. Possible modelling approaches were then explored, together with potential methods of providing a rigorous uncertainty analysis, leading to probabilistic protection zones. Since fracture models were found to require large amounts of data, standard and alternative methods of obtaining fracture data were investigated. The characteristics of anisotropic kinematic porosity in fractured rock were also examined. From a series of stochastic fracture modelling studies in 2-D, it was considered necessary to develop a methodology in 3-D. A pilot study was conducted to test a proposed 3-D methodology. Although the confidence in the probabilistic protection zones produced was much greater than in the porous media zones, successful calibration of stochastic fracture models was discovered to be a significant issue.

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