Title page for ETD etd-06242011-155219


Document Type Master's Dissertation
Author Van Wyk, Yazeed
Email yvanwyk@geoscience.org.za
URN etd-06242011-155219
Document Title Transport mechanisms of uranium and thorium in fractured rock aquifers
Degree MSc
Department Geology
Supervisor
Advisor Name Title
Mr M A Dippenaar Co-Supervisor
Prof J L Van Rooy Co-Supervisor
Prof K T Witthueser Supervisor
Keywords
  • Beaufort West
  • hydrogeology
  • fractured rock aquifer
  • radioactivity
  • transport mechanisms
  • tracer test
  • pumping test
  • flow conceptualisation
Date 2011-04-05
Availability unrestricted
Abstract
The Karoo has been receiving considerable attention since the early 1970s when uranium mining was at its peak, with numerous research studies being instigated to look at all aspects of uranium mining. It has recently been observed that there seems to be resurgence in uranium exploration in and around the town of Beaufort West. A study on the transport mechanisms of uranium and thorium in fractured-rock aquifers, initiated in the hope of understanding the actual processes controlling radionuclide mobilisation, is reported here.

Hydrochemical investigations of the various boreholes were sampled for water quality in June, 2009. The hydrochemical description is typical of shallow fresh groundwater, changing composition to a more sulphate hydrochemical facies along the flow path. While the geochemistry of groundwater in the study area seems to have minimal effects on uranium concentrations, the low levels of uranium in boreholes sampled suggest the importance of hydrological and lithological variability on the measured concentrations. Nevertheless, the uranium concentration is within the recommended levels as specified in the US-EPA, WHO and SA water quality guidelines and thus poses no immediate threat to the general public. Analysis of pumping and tracer tests, reveals that the fractured-rock aquifer can be highly transmissive and that transport can take place via multiple flow paths having different hydraulic properties. Tracer diffusing into stagnant water zones within fracture asperities and the rock matrix are seen as an important retardation mechanism, that has implications for remediation should the aquifer be contaminated by radionuclides. In terms of conceptualising flow at a local scale, aperture sizes ranging from (563-828m) along with high flow velocities (1.90E-03m/s), points to the importance of bedding-plane fractures as conduits of groundwater flow. The groundwater flow has been influenced by dolerite dykes creating compartments isolated from each other, suggesting a highly complex aquifer system. Based on the conceptual model, it is shown that these structures can create unique, site specific flow conditions.

The integration of all available data into the conceptual model provides an effective research tool that can be built upon as a basis for further research.

2010, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria.

Please cite as follows:

Van Wyk, Y 2010, Transport mechanisms of uranium and thorium in fractured rock aquifers, MSc dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-06242011-155219/ >

E11/426/gm

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