TESTING AND EVALUATION OF ARTESIAN AQUIFERS IN TABLE MOUNTAIN GROUP AQUIFERS Dissertation submitted to the University of the Western Cape in the fulfilment of the degree of Doctor of Philosophy by XIAOBIN SUN Department of Earth Sciences Faculty of Natural Sciences, University of the Western Cape Supervisor Professor YONGXIN XU August 2014 Cape Town, South Africa i DECLEARATION I declare that TESTING AND EVALUATION OF ARTESIAN AQUIFERS IN TABLE MOUNTAIN GROUP AQUIFERS is my own work, and that has not been submitted for any degree or examination in any other university, and that all the sources I have used or quoted have been indicated and acknowledged by complete references. Full name: Xiaobin Sun Date: July 2014 Signed…………….…. ii ABSTRACT Testing and evaluation of artesian aquifers in Table Mountain Group Aquifers Xiaobin Sun PhD Thesis Department of Earth Sciences University of the Western Cape, South Africa Keywords: Fractured rock aquifer, hydraulic properties, hydraulic test device, hydraulic testing, conceptual model, groundwater storage capacity, analytical solution, reciprocal rate derivative, artesian aquifer, Table Mountain Group, free-flowing The Table Mountain Group (TMG) Aquifer is a huge aquifer system which may provide large bulk water supplies for local municipalities and irrigation water for agriculture in the Western Cape and Eastern Cape Provinces in South Africa. In many locations, water pressure in an aquifer may force groundwater out of ground surface so that the borehole drilled into the aquifer would produce overflow without a pump. Appropriate testing and evaluation of such artesian aquifers is very critical for sound evaluation and sustainable utilization of groundwater resources in the TMG area. However, study on this aspect of hydrogeology in TMG is limited. Although the flow and storage of TMG aquifer was conceptualised in previous studies, no specific study on artesian aquifer in TMG was made available. There are dozens of flowing artesian boreholes in TMG in which the pressure heads in the boreholes are above ground surface locally. A common approach to estimate hydraulic properties of the aquifers underneath is to make use of free-flowing and recovery tests conducted on a flowing artesian borehole. However, such testing approach was seldom carried out in TMG due to lack of an appropriate device readily available for data collection. A special hydraulic test device was developed for data collection in this context. The test device was successfully tested at a flowing artesian borehole in TMG. The device can not only be used to measure simultaneous flow rate and pressure head at the test borehole, but also be portable and flexible for capturing the data during aquifer tests in similar conditions like artesian holes in Karoo, dolomite or other sites in which pressure head is above ground surface. i The straight-line method proposed by Jacob-Lohman is often adopted for data interpretation. However, the approach may not be able to analyse the test data from flowing artesian holes in TMG. The reason is that the TMG aquifers are often bounded by impermeable faults or folds at local or intermediate scale, which implies that some assumptions of infinite aquifer required for the straight-line method cannot be fulfilled. Boundary conditions based on the Jacob-Lohman method need to be considered during the simulation. In addition, the diagnostic plot analysis method using reciprocal rate derivative is adapted to cross-check the results from the straight-line method. The approach could help identify the flow regimes and discern the boundary conditions, of which results further provide useful information to conceptualize the aquifer and facilitate an appropriate analytical method to evaluate the aquifer properties. Two case studies in TMG were selected to evaluate the hydraulic properties of artesian aquifers using the above methods. The transmissivities of the artesian aquifer in TMG range from 0.6 to 46.7 m2/d based on calculations with recovery test data. Storativities range from 10-4 to 10-3 derived from free-flowing test data analysis. For the aquifer at each specific site, the transmissivity value of the artesian aquifer in Rawsonville is estimated to be 7.5–23 m2/d, with storativity value ranging from 2.0×10-4 to 5.5×10-4. The transmissivity value of the artesian aquifer in Oudtshoorn is approximately 37 m2/d, with S value of 1.16×10-3. The simulation results by straight-line and diagnostic plot analysis methods, not only imply the existence of negative skin zone in the vicinity of the test boreholes, but also highlight the fact that the TMG aquifers are often bounded by impermeable faults or folds at local or intermediate scale. With the storativity values of artesian aquifers derived from data interpretation, total groundwater storage capacity of aquifers at two case studies was calculated. The figures will provide valuable information for decision-makers to plan and develop sustainable groundwater utilization of artesian aquifers in local or intermediate scales. With the hydraulic test device readily available for data collection, more aquifer tests can be carried out in other overflow artesian boreholes in TMG. It becomes feasible to determine the hydraulic properties of artesian aquifers for the entire TMG. Thereof quantification of groundwater resources of artesian aquifers in TMG at a mega-scale becomes achievable. This would also contribute towards global research initiative for quantification of groundwater resources at a mega-scale. ii ACKNOWLEDGEMENTS This thesis would not have been possible without the assistance and cooperation of many individuals and institutions. I would like to acknowledge my debt and wish to record my sincere thanks to the following: . My supervisor Professor Yongxin Xu from Department of Earth Sciences at University of the Western Cape (UWC) for his continuous support of my study and research, for his patience, motivation, enthusiasm, and immense knowledge. His guidance helped me in all the time of research and writing of this thesis. I could not have imagined having a better supervisor and mentor for my PhD study. Water Research Commission for funding the project. The De Vlaamse Interuniversitaire Raad (VLIR) for providing author the scholarship. Mr. Rodney Bishop from City of Cape Town and Mr. Mike Smart of DWA for facilitating data collection for artesian boreholes in TMG. The Oudtshoorn Municipality of the Western Cape Province for granting the author permission to access free-flowing test data collected by the UMVOTO Africa. The staff and postgraduate students of the Department of Earth Sciences at UWC for their constructive roles; especially the ones in Groundwater Group who helped me complete the field work, namely, Messrs Liang Xiao, Shamiel David, Michel Fabrice Menie Ondo, Shuaib Dustay and Thokozani Kanyerere. Mrs. Caroline Barnard and Mrs. Mandy Naidoo for all their hard work and patience for assisting me to complete this thesis. Special thanks to my dear friends for their valuable friendship and supports near and far. I am deeply grateful for the supports from friends: Iris, Lucy, Tommy, Jonathan, Xiao Liang, Zhou Yi, Shen Di, Shibin and Dai Zhaoxin etc. Last but not least, special acknowledgements to my beloved parents. I would have not completed my PhD study without their love, wholehearted encouragement and support. iii ABBREVIATIONS BH borehole ch collar height DN diameter nominal DPFM Differential Pressure Flow Meter DWA Department of Water Affairs GAB great Artesian Basin GH report geohydrology report at the DWA GIS Geological Information System GRA II Groundwater Resource Assessment Phase II GW groundwater IARF Infinite Acting Radial Flow L length Ma million years mamsl meters above mean sea level magl meters above ground level mbch meters below collar height mbgl meters below ground level NGDB National Groundwater Database PRF Pressure Release Flowing Test RSA Republic of South Africa SUP Sustainable Utilizable Potential TMG Table Mountain Group UAB Uitenhage Artesian Basin UFM Ultrasonic Flow Meter iv UWC University of the Western Cape VBA Visual Basic for Applications WL Water level WMA Water Management Area WRC Water Research Commission v NOTATIONS A The size of confined aquifer Acrop The area of TMG outcrop B Leakage factor D Diameter of pipe or the thickness of confined aquifer D’ Saturated thickness of the aquitard h Artesian head of artisan aquifer above ground surface hmin The lowest water level during hydrogeological year hmax The lowest water level during hydrogeological year K Hydraulic conductivity K’ Hydraulic conductivity of the aquitard for vertical flow kPa Kilopascal L Length of pipe m The reciprocal rate derivative n Porosity Pa Pascal Q Flow rate ri The distance between the image borehole and barrier rw/rew Effective radius of test borehole s Drawdown s’ Residual drawdown S Storativity S’ Storativity during recovery Ss Specific storage Sw Constant drawdown Sy Specific yield t Time since the start of free-flowing test vi t’ Time since cessation of free-flowing test T Transmissivity V Total groundwater in storage Va Adjustable storage V0 The maximum volume of groundwater released from artesian aquifer Vp Available pressurized storage of artesian aquifer W(u,rew/B) Hantush’s borehole function for leaky aquifer vii Contents ABSTRACT .............................................................................................................................. I ACKNOWLEDGEMENTS .................................................................................................