Groundwater flow and transport in deep crystalline rock is an important area of research. This is partly due to its relevance for constructing a long term repository for storing radioactive spent nuclear fuel in deep bedrock. Understanding the behavior of flow and transport processes in deep crystalline rock is crucial in developing a sustainable solution to this problem. This study aims to increase the understanding of how channel network models (CNM) can be applied to represent groundwater flow and solute transport in sparsely fractured crystalline rock under site specific conditions. A main objective was to determine how to incorporate structural and hydrogeological site characterization data in the construction of the CNMs. In addition to this, the associated key parameters of the CNMs were investigated to gain further understanding of model site application. To that end, a scripting approach with the python scripting library Pychan3d was used to create alternative channel network representations of a field site. A conceptual discrete fracture network (DFN) model was constructed using field site data obtained from a structural model of the fractures present at the site of the Tracer Retention Understanding Experiments (TRUE) - Block Scale at the Äspö Hard Rock Laboratory (HRL). This conceptual model was used as a base for constructing two different alternatives, denoted respectively as sparse and dense, of a CNM. The sparse CNM consisted of a limited amount of channels for each fracture, while the dense CNM acted as a DFN proxy, taking the full extent of the fracture areas into account and creating a dense, large network of flow channels for each fracture. In order to verify the performance of the generated CNMs, a reproduction of tracer tests performed at the same specific field site was attempted using a particle tracking technique. In addition to this, long term predictions of solute transport without the interference of the pumps used during the tracer tests were done in order to estimate transport time distributions. Pychan3d and the scripting approach was successfully used to create CNMs respecting specific conditions from the TRUE-Block Scale site. The sparse CNM was found to give very adequate flow and transport responses in most cases and to be relatively easier to calibrate than its dense counterpart. The long term transport predictions at the site according to the models seem to follow a channelized pattern, with only a few select paths for transport. The difficulties encountered in matching the dense CNM with the tracer tests most likely stem from difficulties in flow calibration, as well as certain key parameters being assigned too generically.

Seawater-fresh groundwater natural equilibrium conditions in the aquifers of the Sel&ccedil / uk sub-basin may be disturbed by the discharge occurred during the past 30 years in order to supply water for irrigation and domestic purpose usage. Two dimensional density dependent cross sectional saturated flow and solute transport simulations were carried out to determine whether seawater intrusion has occurred in the Sel&ccedil / uk sub-basin due to the imposed discharge or the determined salt-water in the western section of the aquifers represents natural interface equilibrium conditions. The numerical simulation model was calibrated using field measurements. The results of the simulations suggest that the seawater intrusion has occurred in the study area since the pumping activity increased in the region. Five scenarios were simulated for future predictions: (1) Present recharge and discharge conditions are maintained, (2) Discharge increases at a rate of the municipality need as a result of increasing population, (3) Discharge decreases by 12% from the present value, (4) Discharge decreases by 25% from the present value, and (5) No discharge occurs or recharge amount equals to the present discharge amount condition supplied to the aquifer. These scenario results suggest that seawater intrusion in the Sel&ccedil / uk sub-basin would progress in the following years unless proper management measures are taken into consideration. KEYWORDS: seawater intrusion, density dependent groundwater flow, solute transport, contamination, Sel&ccedil / uk sub-basin.

Masters of Science / The thesis investigates the potential of the Rietfontein and Spitskop aquifer to meet a demand of 1000 m3/d (12 Lis) as an alternative water resource for the Rietfontein and Spitskop Community. Increasing demand for clean and hygienic drinking water puts more pressure on one of our most valuable resources and supplying all communities with surface water is an extremely difficult and costly task in rural areas like Rietfontein and Spitskop in South Africa. Therefore it is necessary that interim water supplies be found from local aquifers and be utilized to address water supply challenges. Groundwater may serve as a short-term and an interim water supply which may be useful during future dry periods. Abstraction of groundwater is sensitive to recharge. Due to semi-arid conditions in Rietfontein and Spitskop area, there is high rainfall variation and disparity each year. During the research, hydrocensus was carried out. Water samples for chemistry analysis were taken. Literature review and pumping test data was utilized from the previous studies done by different consultants (Botha, 2000, Vivier and Pretorius, 2003). A numerical groundwater flow model for the local aquifers in the area and surroundings was constructed focusing on recharge and abstraction scenarios for the water supply from the local aquifers. For Rietfontein and Spitskop area, the mean annual precipitation (MAP) is 617mm/year. To be assured and rational in determining aquifers ability to meet the required demand a recharge with ninety-five (95th ) percentile was recommended, which estimates the MAP of 308mm/year which is 50% lower than the average MAP of 617mm/year. For a period of ninety six (96) years, the data indicates a severe drought occurred four (4) times where the rainfall was even lower than 95th percentile level of assurance of recharge estimated. This gives a comprehensible indication that average mean is not ideal or steadfast stature when building a water supply numerical groundwater flow modelling. These aquifers can only be exploited and managed if a reliable method can be obtained to estimate their long-term sustainable potential, since the sustainable potential of these aquifers to supply the communities is dependent upon the recharge from rainfall. The results from a numerical groundwater flow model indicated that a combined potential from the local aquifer from eighteen (18) boreholes is sufficient to meet the required demand and a total of 2600m3 Id can potentially be abstracted from the aquifer. With ninety-five (95th ) percentile recharge rate of 308mm/year a numerical groundwater flow model shows that the rate of abstraction is 80% far less than recharge, which gives high level of assurance in terms of local aquifer water supply demand. The abstraction of the boreholes confirmed by a numerical groundwater flow model shows the least impact on the surrounding aquifer for an extended period of time. In the event of drought, the boreholes will see a decline in water level after two (2) months of pumping local aquifer. The water level will decline steadily from two (2) months to two (2) years with a change in water levels of up to 40m. The impact of the drought is minimal compared to recharge rate, which verifies less depletion of the aquifer. The local aquifer shows the potential of 3MLld can be supplied to the communities with an assurance level of 95th percentile of rainfall. Reliable quantification of groundwater recharge rate remains the main challenges the hydrologist experienced and further research is essential for improvement of groundwater management for the area concerned.