Conference Abstracts

Abstract

Currently limited progress is made in South Africa (and Africa) on the protection of groundwater quality. To achieve the objective of water for growth and development and to provide socio- economic and environmental benefits of communities using groundwater, significant aquifers and well-fields must be adequately protected. Groundwater protection zoning is seen as an important step in this regard. Till today, only one case study of groundwater protection zoning exists in Africa. Protection zone delineation can be done using published reports and database data. However, due to the complexity of the fractured rock at the research site, more data are required. This data can be collected by conducting a hydro census and through aquifer tests. An inventory of the activities that can potentially impact water quality was done and aquifer characteristics such as transmissivity and hydraulic conductivity were determined through various types of aquifer testing. Fracture positions were identified using fluid-logging and fracture flow rates were also measured using fluid-logging data. A conceptual model and basic 3D numerical model were created to try to understand groundwater movement at the research site. The improved information will be used to build a more detailed numerical model and implement a trustworthy groundwater protection plan, using protection zoning. The expected results will have applicability to groundwater management in general. The protection plan developed during this project can be used as case study to update and improve policy implementation.

Abstract

Groundwater  is  a  reliable  freshwater  resource.  Its  location   underground  prevents  it  from evaporative  forces.  Thus  it  serves  as  storage  of  most  of  the  world’s  liquid  fresh  water.  Being enclosed in the ground it is not also easily contaminated. Since groundwater can be used wherever it exists without costly treatments, there is over-dependence on the resource. Though in the past it was mainly used by rural dwellers for domestic water supply, presently, due to effects of climate change on surface water resources, pressures of population growth leading to expansion of towns and cities, groundwater is also supplied for agriculture and industrial purposes. But, the resulting effect from these additional users is the vulnerability of groundwater resources to reduction and pollution. Its importance in sustaining livelihood and development has been highly credited and its management  is  looked  upon  as  a  prerogative.  To  enhance  groundwater  management  in  the Sandveld, a qualitative content analysis approach was used to evaluate six factors considered to be highly needed in groundwater management. This background was used to find out how institutional arrangement in South Africa facilitates or constraints groundwater management in the Sandveld, a highly groundwater dependent area in the West Coast of the Western Cape. The results showed that all  six  factors  are  present,  but  three  facilitate  groundwater  management  while  three  others constrain management. The community involvement which ranked first, is deficient. Thus, institutional weaknesses that need to be strengthened have been identified.

Abstract

Acid-mine drainage (AMD) has received considerable media coverage in South Africa as of late. This have caused a considerable increase in researches, most of them with emphasis on decanting of contaminated water from the old gold mines in Witwatersrand basins and fewer on mine residue contamination from coal and gold mines in the Mpumalanga Province. The paper outlines results of ground geophysical surveys that were carried out along the perimeter of two mine residual deposits (dumps) in the Barberton Greenstone Belt, Mpumalanga Province. The aim of the study was to generate a  3D geoelectric model of the subsurface showing possible acid-mine drainage contaminant pathways. Two geophysical methods, namely Frequency Domain Electromagnetic Profiling (FDEM) and Electrical Resistivity Tomography (ERT) were applied in order to investigate the variation of electrical conductivity in the subsurface. The ERT method was done over frequency domain electromagnetics anomalies.

FDEM electrical conductivity values ranging between 40 mS/m to 60 mS/m were considered as anomalous in that geological terrain. These areas were then surveyed by the ERT method to check the depth extent of these FDEM anomalies. On the resistivity section, between station 40 m and 80 m of Dump 1 – ERT1, a discontinuity in the bedrock was identified. The area could act as a pathway for contaminants to flow from the dump to groundwater. The FDEM survey identified an area with high conductivity values to the north of Dump 1. The ERT results also showed a shallow plume at 30 m depth which is consistent on two parallel sections on Dump 1. The area could be a possible AMD pathway of a mine dump residue to a Komati tributary on the north. The bedrock is generally characterised by high resistivity values; a break in the bedrock exists on this high resistivity zone on ERT 6. This break could be a fault zone which can act as possible pathway of (AMD) from a mine dump residue to a shallow aquifer.

Potential contaminant recharge pathways were delineated using geophysical, electrical and electromagnetic methods. Potential groundwater recharge pathways and sub-vertical low resistivity zones with values <100Ohm.m   were   delineated   using   the   ERT   method.   Investigation   of   contaminant   plume   migration   is recommended over the anomalies that were generated from geophysics data in the Barberton areas. New technologies (artificial neural networks (ANN), fuzzy logic, etc.) combined with laboratory studies is recommended for development of a software platform that accepts 3D geoelectric data (present study), constrained with geology, geochemistry (soil and water), hydrology and hydrogeology data.

Abstract

After drilling technology improvements in South Africa in the early 1900s, several deep (>300 m) exploratory drilling programmes were conducted to explore for pressurised groundwater resources. The results were not significant, except for the Cretaceous Uitenhage Artesian Basin and recent investigations in folded Table Mountain Group Aquifer systems. Large sedimentary units in Southern Africa do have the structural geometry to drive regional artesian systems; however, diverse climate and aquifer hydraulic limitations counteract these conditions to such a level that sustainable basin- like  deep  flow mechanisms  are  probably  non-existing,  except where enhanced  by  deep mining activities.

On the contrary, several deep drilling projects in South Africa, Botswana and Namibia have undoubtedly  proven  the  existence  of  pressurised  groundwater  strikes  below  300 m  (northern Kalahari)  to  as  deep  as  3 000 m  (western  Karoo  Basin).  Given  the  regional  hydrogeological characteristics of these systems, the availability of sufficient recharge zones required to drive sustainable artesian flow or semiartesian conditions becomes a challenge. The existence of isolated pressurised compartments as a result of the lithostatic pressurisation in the deeper sections of many of the sedimentary successions may prove to be a more realistic explanation for these pressurised water strikes observed during deep drilling operations in Southern Africa.

Abstract

Abstract

Abstract

Artesian boreholes are a common feature worldwide in confined aquifers. However, the hydraulic testing of these boreholes and estimation of aquifer properties from such tests still pose a challenge for hydrogeologists. Common hydraulic tests, such as step-drawdown or constant discharge rate tests  require  a  static water  level  at the  start  of  the  test,  and  the measurement of  drawdown (increasing over time) and abstraction rate (fixed for a period of time). Usually, when undertaking a pumping test in an artesian borehole, the drawdown is measured from ground level, and the drop in hydraulic head between static pressure and ground level is often ignored. This also implies that the starting time of the test is not at the static water level. A constant head test, set at ground level, is the other option. However, the decrease in flow rate is not only dependent on the hydraulic properties of the aquifer, but also masked by pipe hydraulic effects within the well. This kind of test would also limit the available drawdown to be utilised for the test. 

Hence,  it was  required  to  develop a method for undertaking hydraulic tests in  strong artesian boreholes allowing for the drawdown to fluctuate between above and below ground and avoiding the pitfalls described above. The solution is a specially designed and constructed well-head for the installation of the pump and monitoring equipment prior to the hydraulic test. The standard tests are slightly modified and will only be carried out after sealing the well-head and reaching static hydraulic pressure. 

The recommended well-head construction and subsequent hydraulic tests were carried out at a strong artesian borehole in the Blossoms Well-field, south of Oudtshoorn in the Western Cape of South Africa.

Abstract

The  possible  future  exploitation  of  methane  in  the  Karoo  has  stimulated  work  from  various disciplines to examine its occurrence, exploitability and exploitation risks. Groundwater issues are vital in this context because of its possible use during exploration and exploitation, and more important, to understand the risks of its pollution during and after all these activities. This paper presents the experiences of the authors to document the presence of methane in the Karoo based on data from boreholes, springs, tunneling and deep drilling. There have been frequent anecdotal reports of explosive gas in boreholes, both dry and wet, in the Karoo. In some cases the gas is identified as methane. Thermal spring waters in the Karoo invariably contain some amounts of methane. Methane pockets have been found in the Karoo during tunneling projects and in some deep Soekor boreholes. A groundwater study in the vicinity of the Gariep Dam indicated substantial quantities of methane in warm groundwater and an association with helium. The isotope concentrations of carbon and hydrogen in methane characterise the methane-forming processes. Such analyses in samples from the central Karoo basin are consistent with that of thermogenic gas found  elsewhere  in  the  world.  Towards  the  edges  of  the  basin,  lower  13C-values  indicate  that methane  there  is  produced  by  microbial  processes  at  shallower  depths.  The  presence  of thermogenic methane together with helium on the surface is likely to give clues to pathways from depth.

Abstract

POSTER Lake Kosi Bay is an estuary-linked lake system composed of four interconnected lakes, namely Makhawulani , Mpungwini , Nhlange , Amanzamnyama and interconnecting channels, which drains via a sandy opening to the Indian ocean and three extensive areas of swamps (Wright 2002 ). The Kosi Bay lake system is considered as the most pristine lake system on the South African coast and has been used as a recreational fishing destination since 1950 (James et al. 2001). The lakes are separated from the ocean by a strip of forested sand dunes (South African Wetlands Conservation Programme 1999;  Wright  2002).  Groundwater  utilisation  in  the  area  ranges from  extraction  of seasonal groundwater from shallow, hand-dug wells to drilling of boreholes for family or communal use and development of groundwater well-fields for agricultural projects (Botha et al. 2012). The exact amount of abstraction of the groundwater is unknown. 

The  Kosi  Bay  system  is  situated  on  the  northern  KwaZulu-Natal  coast,  2.9 km  south  of  the Mozambique international boarder. According to a Statistics South Africa survey (2007), the approximate  population  is  163 694.  The  Kosi  system  falls  under  the  UMkhanyakude  District Municipality, which covers more than 128 818 km2. The travelling distance from north of Durban is 470 km and coordinates of the Kosi Bay system are 2650S-2711S, 3238E- 3253 (Write et al. 1997). The catchment has an area of about 304 km2. The Kosi Bay system is principally clean, white sands, particularly in the northern most reaches where tidal influences are most marked and the system experiences a seasonal inflow of fresh water into its heard (Andeas Holbach 2012).

Abstract

The subject mine has a policy of avoiding groundwater inflow into the underground workings due to the impact on the mine operations. It has already implemented a significant mitigation measure by excluding shallow mining and a large pillar under the river that is present in the mining area. To assess the potential for groundwater inflows into the underground mine workings as a result of a planned expansion project, Environmental Resources Management (ERM) undertook numerical groundwater modelling based on a detailed geological investigation to define the proposed mining area into high, medium and low mining risk areas with respect to potential groundwater inflow. The conceptual definitions of the mining risk areas are: 

High Risk – general groundwater seepage and inflow expected in the face and roof of the mining unit from numerous joints and fractures which is regarded as serious enough to permanently halt mining operations. 

Medium Risk – possibility of limited point source groundwater inflow in the face and roof of the mining unit from sporadic selective joints and fractures. Not expected to halt mining operations. 

Low Risk – no significant groundwater risk to mining operations expected.

The areas identified as being potentially at risk from groundwater inflow were determined using a combination of geological mapping, ground geophysics and percussion drilling that was incorporated into a numerical hydrogeological model. The study undertaken by ERM enabled the mine to incorporate the identified mining risk zones into the early stages of the mine planning, and allowed for a significant reduction in the size of the safety pillar under the river.

Abstract

Flowing fluid electrical conductivity (FFEC) profiling provides a simple and inexpensive way to characterise a borehole with regards to the vertical location of transmissive zones, the hydraulic properties  of  the  various  transmissive  zones  and  the  intra-well  flow  conditions  which  may  be present in the well under ambient conditions. The method essentially involves analysing the time evolution of fluid electrical conductivities in a borehole under pumped and ambient conditions using a down-hole conductivity/temperature data logger. The premise of the method is that the borehole column of water has its electrical conductivity altered by adding saline water into the borehole. This results in a contrast in electrical conductivity (EC) between the water in the borehole and the water in the adjacent formation. At depths where transmissive zones are present, decreases in EC values in the FFEC profile will be observed where formation water with a lower EC (relative to the borehole water column) enters into the well, whilst pumping at low abstraction rates (between 500 ml and 1 liter per minute). By altering the EC of the well-borewater and maintaining a constant pumping rate,  the  sequence  of  FFEC  profiles  depicts  the  dynamic  flow  and  transport  response which  is dependent upon the hydraulic properties of the formation. In this paper the authors present several examples where FFEC profiling has been used to identify transmissive zones in boreholes where no information existed with regards to the vertical distribution of transmissive zones. Furthermore, the authors present case studies where FFEC profiling has been employed as an alternative technology to more conventional hydraulic profiling techniques. This includes a comparative technology case study where down-hole impeller flow meter technology was employed in addition to FFEC profiling and a multi-rate FFEC profile test which was used to determine discrete fracture transmissivity values in a borehole where packer testing equipment could not be installed. Within the context of groundwater contamination investigations, the method holds several attractions as it generates minimal waste water to be managed and disposed of, is inexpensive and can be completed within a relatively short time period.

Abstract

Determining   impacts   associated   with   the   production   of   shale   gas   in   the   semi-arid   Karoo   on groundwater is vital to people living in the Karoo. On the one hand shale gas can be a game-changer for energy supply, but on the other it may have a devastating effect on the environment. Knowing the potential  impacts  of  shale  gas  mining  beforehand,  the  government  can  set  appropriate  regulatory protocols  and  tools  in  place  to mitigate  potential  risks.  This paper  describes research  done  on  the potential impact that hydraulic fracturing could have on groundwater in the Karoo. A wild card that only exists in the Karoo Basin of South Africa is the numerous dolerite intrusions. These dolerite structures are associated with relative high-yielding boreholes because of the fractured contact aureole that exist between solid dolerite and the adjacent Karoo sediments. Compromised cement annuli of gas wells are the  major  preferential  flow  paths along which  methane  and fracking fluid  can escape  into shallow, freshwater aquifers. This study focused solely on the impact of compromised cement annuli of gas wells. The Karoo Basin is under artesian conditions which imply that any pollutant will always try to migrate upwards in the Karoo. The hot-water springs in the Karoo indicate that upward velocities of water are relatively high (the spring water take only days to travel from deep down to the surface). The cubic law was  used  to  estimate  potential  upward  leakage  rates  from  gas  wells  (during  production,  but  after cessation thereof as well, when pressures will rebuild  because  of  artesian  behaviour  of  the  Karoo formations).  Potential  leakage  rates  along  faulty annuli of a well can vary between a value close to zero to two liters per second in the case of an aperture of 0,5 mm. These leakage rates were used as input to a 2D numerical groundwater flow and mass transport model. The 2D model was run for 30 years and the movement of pollution from the gas wells on the pad simulated. The model indicates that an area of 300 ha could be contaminated over a period of 30 years in a downstream groundwater flow direction.  If  an  abstraction  borehole  drilled  along  a  fault  zone  or  a  dyke,  intersecting  the  fracked reservoir, is introduced into the model, results predict that the pollutant will reach the borehole in less than two months if the borehole is situated six kilometres from the well-pad. The total impact that fracking will have on the groundwater in the Karoo, is a function of the total area that will be fracked.

The outcomes of this research clearly show that fracking in South Africa cannot be done in the same way than  it  is  currently  done  worldwide.  A  rule  that  will  force  gas  companies  to  disclose  fracking  fluid contents is non-negotiable. Companies should also be required to measure pressures in the fracked gas reservoir after closure. An additional requirement to enforce sealing of the entire fracked reservoir with a very dense material like bentonite or a mud with a very high density to capture the fracking fluids deep down in the gas reservoir should not be negotiable.

Abstract

The Karoo Supergroup has a hydrogeological regime which is largely controlled by Jurassic dolerite dyke and sill complexes. The study area is located in the north-eastern interior of the Eastern Cape Province,  close  to  the  Lesotho  border.  The  sedimentary  rocks  of  the  upper  Karoo  constitute fractured and intergranular aquifers, due to relatively hydro-conductive lithologies. The main groundwater production targets  within  the  upper-Karoo  are  related  to  dolerite  intrusions  that have  a  number  of  characteristics that influence groundwater storage and dynamics. Magnetic, electromagnetic and electrical resistivity geophysical techniques are used to determine the different physical  characteristics  of  the  dolerite  intrusions,  such  as  size,  orientation  and  the  level  of weathering. Trends in the data collected from a large-scale development programme can provide evidence that intrusion characteristics also play a role in determining the hydrogeological characteristics of the area. Interpreted geophysical borehole drilling, aquifer  testing  and  water chemistry  data  can  be  used  to  indicate  hydrogeological  differences  between dolerite intrusion types. Observed trends could be used for more accurate future well-field target areas and development.

Abstract

The so-called apparent increase of transmisivity (T) or hydraulic conductivity (K) with scale is an artifact and does not exist in the field. The reason for the apparent increase of T with scale is due to the use of the “not applicable” random log Gaussian stochastic models that are used by geohydrologists. In the petroleum field, where deterministic methods are applied, the apparent increase of T with aquifer volume does not occur. Groundwater practitioners have to change their view and use models that do not show this effect.

Abstract

In  South  Africa  salinisation  of  water  resources  by  dissolved  sulphates  resulting  from  acid  rock drainage (ARD) and metal leaching (ML) from surface coal mine spoils has a significant effect on water supply in the Gauteng Province. Predictions of mine water quality is required to select cost- effective rehabilitation and remediation measures to reduce future ARD and ML risks and to limit long-term  impacts.  A  load  balance  model  was  developed  in  Microsoft  Excel  to  simulated contaminant loads in a completely backfilled opencast mine in the Karoo Basin of South Africa after closure. The model calculated the balance between contaminant load into the pit water system from mainly pyrite oxidation processes in the spoils and load removed through decanting. Groundwater flow modelling data and simulated spoils seepage qualities for the mine site were used as input in the contaminant load calculations. The model predicted that the amount of contaminants added to the pit from spoils decrease considerably from the time of closure over a period of approximately 100 years. Thereafter the contaminant load decrease is gradual. This is due to a decrease in the volume of unsaturated spoils, as spoils at the bottom become permanently inundated as the pit fills up, thus limiting oxygen diffusion and oxidation. Cumulatively, the contaminant load gradually increases  in  the  backfilled  pit  until  the  onset  of  subsurface  and  surface  decant,  when  the contaminant load declines. This is due to removal of contaminants from the mine water system via decanting. Approximately 200 years after mine closure, 86% of the spoils are inundated. The model predicted that the quality of decanting water improves with time due to a decrease in load from spoils, removal of contaminants through decanting water and dilution effects of relatively clean groundwater inflows. Mass loads were used as input into the numerical groundwater model for the contaminant mass transport simulations to predict the migration of contaminant plumes with time. The geochemical model results assisted in developing conceptual water and waste management strategies for the opencast mine during operational and closure phase.

Abstract

POSTER Water is an invaluable resource without which life would cease to exist. Supply in South Africa has become limited due to increases in demand brought upon by population growth, urbanisation and industrialisation. In Southern Africa, water systems are considerably degraded by mining, industry, urbanisation and agricultural activity and a large amount of the fresh surface water has already been utilised. The stresses on this resource will unlikely make the current usage sustainable in years to come. In order to provide for basic needs for the future, groundwater as a resource will have to play a major role. It is for this reason that groundwater integrity needs to be preserved. 

Hydrocarbon contamination is a huge threat to groundwater as it contains toxic substances that are insoluble in water. These toxins are carcinogenic and mutagenic, and have a major impact on human health and ecosystem stability. When spilled, hydrocarbons will move downward through the unsaturated zone under the influence of gravity and capillary forces, trapping small amounts in the pore spaces. Accumulation will result in added weight along the water table, forcing the entire surface to be displaced downward. Some of the components can dissolve in the groundwater and move as a plume of contaminated water by diffusion and advection within the saturated zone. The transport of contaminants from petroleum hydrocarbon spills needs to be described in terms of a multiphase flow system in the unsaturated zone, taking into account contaminant movement in each of the three phases: air, water and free light non-aqueous phase liquid. Petroleum hydrocarbon behaviour in the subsurface is additionally complicated by the presence of multiple compounds, each with different properties. The net result is that some hydrocarbon fractions are transported faster than others and a contamination plume of varying intensity may spread over a large area.

The aim of this study is to develop a methodology to map and simulate the movement of groundwater that has been contaminated by hydrocarbons and to determine the fate of the water quality through decomposition. Associated remediation options will be determined thereafter.

Abstract

Open pit mining operations are located in various, usually complex, geological settings and equally variable climatic regions from arid to extremely high rainfall. Many Southern African open pit mines occur in competent and un-weathered rock masses, and groundwater flow is therefore structurally controlled. Assessing and reducing pit slope pore pressure should be incorporated into pit slope design. Site hydrogeological investigations followed by numerical groundwater modelling is completed to produce predicted pore pressure distributions over the life of a mine and to assess the potential effect of dewatering actions on slope stability. Investigations were completed for two Southern African pits and simulated pore pressure distributions were used in slope stability analysis. In the first case, the simulated slopes are shown to be free draining, and the designed pit slopes are predicted to remain safe and remain so even with the built-up of pore pressure. In the second instance, pore pressure reduction through an aggressive horizontal drill holes programme is demonstrated to improve probability of failure. This has demonstrated the need for collaboration between geotechnical and hydrogeological investigations to improve slope design, reduce likelihood of pit wall failures and reduce mining cost through excavating steeper depressurised slopes.

Abstract

Quantification of hydrological processes is required for many projects related to potential groundwater recharge. Thus, investigation on various hydrogeologic conditions is paramount. Changes of climate can affect the hydrological cycle by altering groundwater recharge. As a result, an understanding of the hydrological conditions is essential to make sensible predictions of the possible groundwater recharge. Thus WetSpass, which yields spatially varying groundwater recharge using hydrological inputs, can be used together with a geographical information system to quantify the environmentally acceptable flow regime of the catchment area. This paper presents an overview on the use of WetSpass in combination with GIS on quantification of groundwater potential which will assist to sustainable groundwater development in the catchment area. Previous applications are presented.

Abstract

PMWIN5.3 has been one of the most commonly used software for groundwater modelling because of its free source and the adoption of the popular core program MODFLOW. However, the fixed formats required for data input and lack of GIS data support have posted big challenges for groundwater modellers who are dealing with large areas with complicated hydrogeological conditions. In South Africa, most geological and hydrogeological data have been captured and stored in GIS format during various national research projects such as WR2005, NGA, etc. Therefore, a proper linkage between PMWIN and ArcGIS is expected to do the pre-processing for modelling in PMWIN. Visual Basic for Application (VBA) embedded in ArcGIS 9.3 was used to develop the linkage. Based on the conceptualisation of the study area, the model dimension, discretisation and many value-setting processes can be easily carried out in ArcGIS other than directly in PMWIN. Then the grid specification file and other input files can be exported as the PMWIN-compatible files. The functions on the modification of model geometrics have also been integrated with the toolbar. The linkage can be used with a higher version of PMWIN or ArcGIS. It has been applied to several gold fields in the Witwatersrand gold basin to simulate the groundwater flow and mass transportation for various conditions and scenarios. One of the applications will be presented in this paper. It has been proven that the linkage is efficient and easy to use.

Abstract

South Africa has an energy crisis. The country requires 53 Gigawatt of new capacity by 2030. The exploitation  of  unconventional  gas  is  a  potential  game-changer  to  meet  South  Africa’s  current energy deficit to fuel economic growth and development. Water management, both in terms of abstraction and disposal, has emerged as a critical issue in the development of unconventional gas reservoirs. This presentation focuses on a high-level, qualitative analysis of the groundwater-related institutional and governance challenges associated with unconventional gas exploration and production. The findings represent a synthesis of information sourced from regulatory and legislative documents as well as international experience. The analysis maps the current groundwater institutional and governance landscape in South Africa and lessons learned from other regimes such as the United Kingdom and United States of America. Good governance entails ensuring that there is compliance with policy and legislation, effective decision-making, appropriately allocated accountability, transparency and that stakeholder interests are considered and balanced. This forms the basis of a preliminary gap analysis.

Abstract

POSTER One of the critical elements of water resource management is the dynamic exchange between groundwater and surface water. Quantifying this exchange strongly relies on an adequate characterisation of the lithological architecture of the involved aquifer system. In the past, this characterisation often relied on lithological data obtained through invasive methods. However, given the spatial heterogeneity of the subsurface, these methods do not provide the density of sampling required for an accurate ‘‘image’’ of the large‐scale architecture of the aquifer system, leading to large uncertainties in the variations and continuities of subsurface structure. These uncertainties inevitably lead to inaccuracies in the conceptual geohydrological model, thereby diminishing the prospects of an accurate assessment of the groundwater–surface water interaction. In order to limit the uncertainties, the results of electrical resistivity tomography (ERT) surveys conducted on a  site  near  the  Krugersdrift  Dam in the Free State Province of South Africa  were used to make inferences   regarding  the   prevailing  geohydrological  conditions.  The   resistivity  models   were compared to borehole logs from existing boreholes to produce a refined model of the subsurface architecture related to groundwater–surface water interactions.

Abstract

After a period of heavy rainfall in 2006, pit water from a rehabilitated opencast coal mine in the Mpumalanga Province started decanting, causing impacts on the adjacent agricultural land and river system. Various actions have since been taken to manage the pit water, including construction of contour berms to prevent clean water entering the ramps, construction of levees and dam walls to increase the decant level, irrigation of mine water on the rehabilitated areas of the pits, disposal of pit water in nearby pans, recirculation of pit water by means of pumping between the various voids, controlled release of pit water to the river system, and construction of a pipeline to pump pit water to a nearby colliery where there is a demand for process water. For the purpose of mine closure, a water management plan was required for which an estimate of the water make of the colliery was needed. The water make was estimated by using measured quantities (rainfall data, pumping rates, dam water levels) and estimated quantities (evaporation from open water bodies), while making a number of simplifying assumptions. This approach revealed that the conventional method of estimating the water make as a percentage of rainfall recharged through the spoils, significantly underestimates the volumes of water that need to be dealt with at the colliery. Large volumes of groundwater appear to be entering the pits along preferential pathways connected to recharge zones at higher elevations, contributing to the water make of the colliery.

Abstract

This paper has been based on a study conducted at the Nyalazi plantation in KwaZulu-Natal, South Africa. The study was conducted in order to determine the impacts of the different timber species planted on the groundwater levels associated with the site area. Commercial timber plantations are widespread  throughout  the  country  and  form  an  essential  component  of  the  South  African economy. The site is located 200 km north of the port of Durban and approximately 20 km north of the town of St Lucia in the KwaZulu-Natal Province. The study area, the Nyalazi plantation, is located on the western shores of Lake St Lucia, situated on a peninsula between the Nyalazi River, west of the site and Lake St Lucia to the east. The two main tree species which are located in the Nyalazi plantation are Pinus elliottii and Eucalyptus grandis Camaldulensis. The geological units which influence the hydrogeological regime of the site area include the recent deposits of cover sands and the Port Durnford Formation. These geological successions are the most influential on the groundwater environment as these are the units closest to the surface. The study area is located on the Maputuland coastal plain, also referred to as the Zululand coastal plain, which is classified as a primary aquifer and is the largest of its kind in South Africa. High recharge is experienced within the upper formations of the coastal plain which are unconfined aquifers (Mkhwanazi, 2010). This aquifer consists of unconsolidated clays and sands, which may be defined as an alluvial or primary aquifer (Rawlins & Kelbe, 1991). The monitoring network was initiated by SAFCOL (South African Forest Company, Ltd) in 1995, now known as SiyaQubeka. In total 21 monitoring points were installed, which  includes  piezometers  and  deeper  boreholes.  The  trends  of  the  groundwater  level  data collected over the 17-year period was analysed. Limited historical information was available for the Pinus elliottii plantation; however, based on the data it was evident that the mature pine plantations had minor effects on the groundwater environment of the study area. Conversely, the Eucalyptus species indicated a significant impact with the lowering of the groundwater table between 10 and 16 m over a period of 13 years within the plantation area, which equates to an average decline of one metre per year.

Abstract

The monitoring of groundwater to detect changes resulting from anthropogenic activities requires an understanding of the particular aquifer system, release mechanisms and migration pathways which form the basis of a conceptual hydrogeological model. This conceptual hydrogeological model illustrates the connections between sources, pathways and receptors. The objective of a monitoring programme implemented in the context of shale gas exploration activities in the Karoo would be the detailed monitoring of groundwater quality for the protection of groundwater users. This objective requires a defensible baseline dataset so that changes in water quality can be investigated.  In selecting parameters to monitor, cognisance must be taken of parameters which occur in multiple sources, those naturally present in the shallow potable aquifer, potential tracers representing the deeper groundwater and additives arising from the exploration activities. Sodium, potassium and chloride  are  all  likely  to  be  present  in  both  deep  and  shallow  groundwater  and  are  potential additives. Given the expected higher salinity of deep connate groundwater, the use of aggregate parameters such as electrical conductivity might be of particular importance. Lithium, fluoride, strontium and uranium, while constituents of both the shallow and deep groundwater, are likely to be present at higher concentrations in the deeper groundwater, and could be indicators of deeper groundwater.  Geochemical  analysis  of  cores  may  provide  initial  clues  as  to  such  indicator parameters. Methane, which is known to occur in some existing Karoo boreholes, is potentially one of the more mobile tracers which could indicate migration from potential future production zones to shallow aquifers. The viability of using methane and other dissolved gasses (for example ethane) as indicators would require the use of stable isotope analyses to elucidate the origin of the gases.

Abstract

The increase in awareness of environmental issues and the desire for a cleaner environment by the public has caused mining companies to place greater emphasis on the continuous rehabilitation of harmful effects caused by mining operations. Ongoing rehabilitation is also a requirement of the government departments involved in mining in South Africa. The biggest concern for the relevant government departments is the possible uncontrolled pollution of water resources in the vicinity of mines, after they have closed. In  the  compilation  of  this  paper,  the  unique  nature  of  the  South  African  situation  has  been considered – this refers to a legally acceptable approach towards current legislation and policies. This study leads to the construction of a logical approach towards mine closure, specifically to understand issues around costs and financial liability. The final product of this approach should ultimately give more clarity on: 

the principles followed to identify objectives for mine closure and groundwater assessment;

key steps to follow when assessing site hydrogeology and to determine related impacts, risks, closure costs and liabilities; and an overview of methods that could be used for the mitigation of polluted aquifers and a brief site-specific application.

Abstract

POSTER Electrical Resistivity Tomography (ERT) surveys were conducted in the Kruger National park (KNP) as part of a recent Water Research Commission project (titled: Surface water, groundwater and vadose zone interactions in selected pristine catchments in the Kruger National Park). The surveys were carried out in a pristine ephemeral third-order supersite catchment, namely the southern granite (Stevenson Hamilton). This supersite is representative of the southern granite region of KNP as it covers part of the dominant geology, rainfall gradient and dominant land system.

Electrical   resistivity   profiling   provided   valuable   data   on   the   subsurface  geological   material distribution and results depended on soil/rock properties, water content and salinity. The purpose of electrical surveys was to characterise the hydrogeological components of weathering and depth to water level using the subsurface resistivity distribution. The ground resistivity is related to various geological parameters such as the mineral and fluid content, porosity and degree of water saturation in the rock.

Based on the initial ERT survey interpretations, boreholes were drilled providing actual subsurface results in the form of borehole drilling logs, water levels, hydraulic data and in situ groundwater quality  parameters.  Integrating  the  ERT  survey  data  with  the  results  from  the  intrusive  survey enabled an updated conceptualisation of groundwater flow characteristics and distribution across the southern granite supersite.

Abstract

The Department of Water Affairs (DWA), Chief Directorate: Resource Directed Measures has developed guidelines over the past decade  in order  to  facilitate  proper implementation of the Groundwater   Resource   Directed   Measures   (GRDM)   (also   known   as   determination   of   the groundwater component of the Reserve). An intrinsic component of the GRDM is delineation of Integrated Units of Analysis (IUAs) from which the allocatable groundwater and surface water components are calculated, which essentially drives the allocation of water use licenses. Delineation typically follows a three-tiered approach, namely primary, secondary and tertiary level. Primary delineation is based on quaternary boundaries (considered to be the basic building block of the IUA); secondary follows geological, hydrogeological and hydrological boundaries, groundwater abstraction zones and baseflow contribution; and tertiary is dependent on management criteria. How then, do we undertake this challenging task of delineating IUAs to a level where it can be better managed and monitored? Complexities arise when hydrogeological data are scarce, hydrological and hydrogeological systems are not in sync, aquifers extend across a quaternary, water management area, provincial and administrative boundaries, surface water and groundwater interactions are not well understood, and legislation on protection of water resources differs greatly from one country to the next. Having undertaken delineation of IUAs in the Waterval Catchment (Upper Vaal WMA), Olifants WMA and Mvoti to Umzimkhulu WMA with the available datasets, the key criteria for the respective  WMAs  have  ultimately  been  management  class,  significant  aquifers,  groundwater– surface water interaction and groundwater stressed areas, and secondary catchment boundaries, followed by other hydrogeological, geological and management considerations.

Abstract

Industrial  facilities  and  mining  activities  represent  a  potential  contamination  hazard  to  down gradient surface water and groundwater environments. The assessment of the risks posed by such contaminant sources should facilitate regulators to determine set compliance limits. These limits should, however, take in consideration the heterogeneous nature of fractured rock aquifers. This paper will focus on the limitations or technical feasibility of applying single groundwater quality compliance limits for fractured rock aquifers. It will also aim to describe how groundwater contamination limits could be determined in a more feasible manner.

Abstract

Groundwater boreholes are a key element of many mining projects, as part of dewatering and water supply  systems,  and  must  achieve  high  levels  of  operational  efficiency  and  service  availability. Outside of the mining industry, planned borefield maintenance programmes have become a key part of professional well-field management, with proven benefits in terms of operational cost savings and continuity of pumping. However, the benefits of proactive planned maintenance of groundwater boreholes on mine sites have only recently been widely recognised. Potential operational problems are described, including water quality issues which can result in mineral contamination leading to deposits and scale build-up which can clog screens and pumps, reduce water flow and yield, and eventually cause pump breakdowns and mine stoppages. Best practice methodologies to remove or minimise the contamination are described and the benefits of implementing a planned maintenance programme are discussed. Case studies are described from two significant mines in Australia, where boreholes suffered from mineral contamination, including calcium carbonate and iron bacteria contamination. Both mines suffered  from  increased  pump  breakdowns,  groundwater  yields  consistently  below  target  and serious cost overruns. Borehole rehabilitation treatment plans were implemented to resolve the immediate contamination problems followed by an ongoing maintenance programme to prevent or minimise their reoccurrence. Treatment programmes included a downhole camera survey, use of a bespoke software program to review the results of the survey and the available water quality data, and a purpose built rehabilitation rig that included the use of specialist chemical treatments to remove and control the existing encrustation and clogging deposits.

Abstract

The deterioration of wetlands due to human activity has been a problem for many years. Under the old Water Act 36 of 1956 no provision of water was made for managing the environment. This idea was only introduced in the 1970s and focussed mainly on maintaining the floodplains and estuaries in the Kruger National Park, with small amounts being allocated to drinking water for wildlife. This was followed by the Conservation of Agricultural Resources Act, 43 of 1983, the first legislation under which wetlands could be protected, and which today still provides an important legal platform for the protection of wetlands, through integrated conservation of the soil, water resource and vegetation. South Africa became a signatory to the Ramsar Convention in 1975, but until the late 1990s not much was done to enforce wetland conservation. With the introduction of the National Water Act, 36 of 1998, and the National Environmental Management Act, 107 of 1998, South African legislation  became  the  first  to  balance  human,  environmental  and  economic  interests,  for  the purpose of sustainable development. As part of this review I refer to case studies in Gauteng and discuss some of the challenges we still face.

Abstract

Groundwater is not often regarded as ecosystems and especially fractured aquifer systems are seen as organism free. Conventional tests show very little to no presence of micro-organisms in groundwater. However, these micro-organisms are ubiquitous and can be detected by using sophisticated methods. In this specific case study where petroleum hydrocarbon  contamination exists in a fractured rock aquifer, the presence of micro-organisms has been for years inferred by means of monitoring for secondary lines of evidence that prove attenuation of the contaminants, not only by means of dilution, adsorption or diffusion into the matrix, but through metabolism. The sampling evidence is clear that the preferential sequence of metabolism is taking place whereby electron acceptors are reduced as predicted for such biodegradation. Specifically sulphate is consumed and mostly manganese is reduced, with some iron reduction also being observed. Monitoring has shown that  groundwater recharge bringing in  new  nutrients effected increased biodegradation. In order to definitively identify the contribution made by micro-organisms, DNA testing was performed. The results support the secondary lines of evidence. Outside of the contaminated zone very low population numbers of organisms were detected in the groundwater. Inside the contaminated zone elevated population numbers were observed indicating that active biodegradation is taking place. Furthermore, the edges of the plume, where contaminant levels are mostly below detection, contained a more diverse population of micro-organisms than the central area. Conditions on the edge of the plume probably represent an ideal nutrient environment for the organisms as opposed to the high concentration source, which might be toxic to some organisms. Better understanding of the bio-dynamics of this fractured aquifer presents a unique opportunity to better manage and enhance the remediation of the contaminants. Possible strategies include the addition of nutrients when necessary and the cultivation of the naturally occurring organisms to augment the population. The data shows that aquifers are ecosystems even in fractured environments.

Abstract

When the South African Government in 1998 re-demarcated its 283 municipalities in such a manner that they now completely cover the country in a “wall-to-wall” manner (Section 21), their main focus was on facilitation of effective and sustainable developmental municipal management; in other words, the improvement of basic municipal services such as formalised municipal basic services (for example, safe potable water, effective refuse removal and environmental health) to all the residents of the new geographical areas consisting of millions of citizens who previously might have been neglected. Unfortunately, it seems like topographical, physical and environmental characteristics of all the resulting municipal areas have been negated in this important demarcation process. Fuggle and Rabie (2005:315) are of the opinion that this can lead to ineffective, inefficient and non- economical municipal management of basic services.

By means of a literature review as well as the use and study of geographical tools such as maps, ortho-photos and information data bases, and field visits, the bare essential geographical and geo- hydrological aspects of importance for the municipal service providers and managers in the Lindley area have been identified. From this research and various other obvious reasons (for example, deteriorating physical environment due to pollution, sub-standard storm water and sewage management, and migration [informal settlements] and increasing sophisticated needs of municipal residents), the presenters of this paper want to state  that the quest for improved cooperative governance in the developing South Africa, and especially in the case of the Lindley town’s geographical area of responsibility, must be facilitated according to the DWA identified surface water catchment regions.

In conclusion, the presenters will recommend adherence to the following requirements as essential:

•  An  environmental,  holistical  and  integrated  management  (IWRM)  approach  by  all  the involved and committed role-players, researchers and stakeholders must be adopted in the whole Vals River catchment.
• Effective co-operative governance must be facilitated and maintained.
• Basic hydrological, geo-hydrological and engineering geology knowledge and skills must be identified,  obtained,  modified  into  layman  language  and  incorporated  in  the  afore- mentioned approaches.

Abstract

The colliery is situated in the Vereeniging–Sasolburg Coalfield, immediately southwest of Sasolburg in the Republic of South Africa. The stratigraphy of this coal field is typical of the coal-bearing strata of the Karoo Sequence. The succession consists of pre-Karoo rocks (dolomites of the Chuniespoort Group of the Transvaal Sequence) overlain by the Dwyka Formation, followed by the Ecca Group sediments, of which the Vryheid Formation is the coal-bearing horizon. Mainly the lava of the Ventersdorp and Hekpoort Groups underlie the coal. The Karoo Formation is present over the whole area and consists mainly of sandstone, shale and coal of varying thickness.

The underground mine was flooded after mining was ceased at the colliery in 2004. The colliery is in the fortunate position that it has a very complete and concise monitoring programme in place and over 200 boreholes were drilled in and around the mine throughout the life of the mine. To stabilise mine workings located beneath main roads in the area, an ashfilling project was undertaken by the colliery since 1999. A key issue is if the mine will eventually decant, and what the quality of the water will be. This is important for the future planning of the company, as this will determine if a water treatment plant is necessary, and what the specifications for such a plant will be, if needed. Therefore it was decided to do a down-the-hole chemical profile of each available and accessible borehole with a multi- parameter probe with the aim of observing any visible stratification. Ninety-four boreholes were accessible and chemical profiles were created of them.

From the data collected a three-dimensional image was created from the electrical conductivity values at different depths to see if any stratification was visible in the shallow aquifer.  The ash-filling operations disturbed the normal aquifer conditions, and this created different pressures than normally expected at a deeper underground  colliery.  From  the  three-dimensional  image  created  it  was  observed  that  no stratification was visible in the shallow aquifer, which lead to the conclusion that in the event that if decant should occur, the water quality of the decanting water will still be of very good quality unless external factors such as ash-filling activities are introduced. It is not often that it is possible to create chemical profiles of such a large number of boreholes for a single colliery and as a result a very complete and informative three-dimensional electrical conductivity image was created. This image is very helpful in aiding the decision-making process in the future management of the colliery and eventually obtaining a closure certificate, and also to determine whether ash-filling is a viable option in discarding the ash.

Abstract

This study, near Thyspunt between St. Francis and Oyster Bay in the Eastern Cape Province of South Africa, focused on identification and quantification of surface water–groundwater links between the mobile Oyster Bay dune field and the coast. The specific objective was to establish the extent to which important wetlands such as the Langefonteinvlei and the numerous coastal seeps along the coast are directly or indirectly dependent on groundwater as their main water source. A further objective was to establish the extent to which any of the coastal seeps derive their water from the Langefonteinvlei, and are thus interdependent on the integrity of this system. The study also investigated the contribution of the Algoa and Table Mountain Group aquifers to these wetlands. The   monitoring   network   established   as   part   of   this   study   focused   on   unpacking   the interrelationships between surface and groundwater flows, aquifer hydrochemistry and wetland function, as related to the Langefonteinvlei and the coastal seeps in particular. Results indicate that the Langefonteinvlei is fed by groundwater flowing from the mobile Oyster Bay dune field in the north and the water divide in the northeast, which emerges at the foot of the high dune in the north and northeast of the wetland. However, the majority of the vlei area is ‘perched’ above the local water table on a layer of organic-rich sediment. The coastal springs located southwest and west of the Langefonteinvlei are not fed by water from the Langefonteinvlei. They emerge near the coast, where the bedrock lies close to the surface, and are fed by groundwater draining directly from the Algoa and Table Mountain Group aquifers to the Indian Ocean.

Abstract

The concept of the ‘Groundwater Reserve’ is enshrined in the National Water Act that stipulates that a classification of all significant water resources must be undertaken and the Reserve requirements be determined and gazetted. The Reserve covers two different aspects, the Ecological Reserve to protect the water dependent ecosystems and the Basic Human Needs (BHN) Reserve to ensure that all people who depend on that water resource have sufficient water for their livelihood. The approach for determining and implementing the Reserve that was developed for surface water resources was adopted for groundwater resources as provided for in the Groundwater Resource Directed  Measures  (GRDM)  Manual,  inter  alia.  However,  there  is  no  separate  ‘Groundwater Reserve’, but rather a groundwater component of, or contribution to, the ecological Reserve and BHN. Hence, the implementation of this methodology often results in undesirable outcomes and is one of the inhibiting factors for sustainable groundwater development, as some of the aspects and methods are not applicable to groundwater and not appropriate for implementation. The current separation of the ‘Groundwater Reserve’ determination process from the ecological Reserve determination emphasises this pitfall of the process and methodology. This paper provides a critical review of the current concept of the ‘Groundwater Reserve’ and its implementation based on several case studies. It concludes  with recommended changes to the standard methodology and a possible way forward for developing an appropriate methodology for addressing and protecting the groundwater contribution to both the ecological and BHN Reserve.

Abstract

The article presents the application of a water balance model as a preliminary tool for investigating groundwater–surface water (GW–SW) interactions along an alluvial channel aquifer located in a semi-arid climate in the central province of South Africa. The model is developed based on the conservation of mass; solute and stable isotopic mixing of the model components. Discharge measurements were made for the river segment inflow and outflow components using stream velocity-area technique. The Darcy equation was used to calculate the groundwater discharge from the alluvial channel aquifer into the river segment. Electrical conductivity (EC) and δ2H isotope were measured for the inflow and outflow components of the model as indicators of solute and stable isotopic ratios. Measurements were conducted during a low river flow once-off period in October 2011, thus offering a great opportunity to assess GW–SW exchanges when other potential contributors can be regarded as negligible. The model net balance shows that the river interval is effectively losing water. The mass and solute balance approach provided close to a unique solution of the rate of water loss from the model. The model outcome provides a platform from which to develop appropriate plans for detailed field GW–SW interaction investigations to identify the mechanism through which the river is losing water.

Abstract

Evidence suggests that physical availability of groundwater may be only one of many factors in determining whether groundwater-based rural water supply schemes in South Africa are reliable or "sustainable". Other factors include budgetary constraints, community preferences, policy decisions, operation and maintenance procedures, and the availability of skilled staff. These factors and others combine to create "complex problems" around the issue of rural water supplies that require a multidisciplinary approach if they are to be effectively resolved. This work is an on-going part of Water Research Commission Project K5/2158, “Favourable Zone Identification for Groundwater Development: Options Analysis for Local Municipalities”, due to be completed in March 2014.

Abstract

National legislation is the outcome of processes, locally, provincial and nationally. Certain aspects of water management have first been the product of legal initiatives of the South African government, seeking  to  address  local  problems.  As  a  result,  the  National  Water  Act,  36  of  1998,  was promulgated. The Act is in line with the Constitution of the Republic of South Africa, 108 of 1996, which embrace human rights. The Water Services Act, 108 of 1997, regulates the accessibility of water and sanitation by domestic users. Groundwater, in many parts of South Africa, provides the sole  and/or  partial  water  supply  for  meeting  basic  human  needs.  With  an  increase  in  the dependency on groundwater usage, the need to properly and effectively protect, use, develop, conserve,  manage  and  control  groundwater  resources  has  become  a  national  priority  by  the custodian of all water resources: the National Department of Water Affairs. The question arises whether  or  not  the  current  groundwater  allocation  decision-making tools  are  enough  to  make informed  decisions  regarding  the  final  approval,  or  not,  of  groundwater  use  licenses,  and whether  a  proper  framework  that  includes  guidelines  together  with  licensing  conditions  are available  for  decision- making   in   complex  groundwater   scenario   situations   as   part   of   the groundwater license decision process. The current research contributes to answering this question and finding solutions in order to improve and make the groundwater use authorisation process more  effective.  The  groundwater  situation  will  be  discussed  on  a  comparative  basis  from international case studies regarding water legislation and groundwater resource management tools. A full evaluation and analysis of groundwater use authorisation process and decision-making tools on  regional and  national level  in  South  Africa will be done  and a Framework and tool for the evaluation, decision-making and determination of authorisation conditions of groundwater use authorisations, which includes existing lawful water use, general authorisations, and groundwater use licensing, will be developed. Scenarios and case studies are currently implemented.

Abstract

Limestones  and  dolomites  form  an  important  aquifer  system  in  Zambia.  The  municipal  water supplies for Lusaka and several population centres on the Copperbelt all depend on the carbonates for a substantial proportion of their water supply. Currently 155,912 ha of land are irrigated in Zambia, which is about 30 percent of the economical irrigation potential. Development of large scale irrigation schemes from carbonate rock aquifers proves to be a viable groundwater resource in Zambia.

The Katanga carbonate rock aquifers are considered to have good groundwater potential, with high yielding anomalies of up to 60l/s common in certain areas of the country. A phased approach was adopted  to   characterise   the   Katanga   Carbonates   by  means  of  quantifying   the  volume  of groundwater available for abstraction within the geological boundaries. The first phases included geophysical surveys (mainly electrical resistivity and magnetic methods), exploration drilling and aquifer   testing.   Later   phases   included   the   drilling   of   production   boreholes   and   wellfield development. 

Lessons learned during the exploration included the identification of high yielding drilling targets and the role of anomaly frequency in target selection. Further development of the Katanga aquifers for production provided challenges regarding production borehole construction and design. The feasibility of the optimum  design of  production  boreholes versus  the  initial capital  cost of the development of these carbonates proved to be an important consideration in this regard.

Abstract

The 11 coal-bearing zones currently being mined at Exarro's Grootegeluk mine, discard intraburden onto discard dumps. During mining operations the open pit will be backfilled with plant discards, overburden and interburden on completion of mining. The plant waste will be covered with overburden  and  topsoil.  Intraburden  spoils  consist  of  sandstone,  mudstone  and  shale  rich  in minerals such as pyrite and siderite. These intraburden spoils thus have the capacity to generate acid when exposed to the appropriate conditions. The oxidation of iron sulphides (Pyrite (FeS2)), present within the discard dumps and stockpiles, can influence the hydrochemistry by generating acid-mine drainage, while siderite (FeCO3) can have a basic effect to the immediate surroundings. Acid-base- accounting done on samples gathered from different boreholes in the Waterberg coalfield helped to determine lithological units that can generate acid, with specific regard to the interburden removed and placed on the discard dumps, the interburden used in the pit as backfill, and the acid generation possibility from coal seams in stock piles. This indicated the zones that are more prone to acid- and base-producing potentials. Mineralogical investigations with X-ray diffraction and X-ray fluorescence gave a better record of minerals and elements present in trace amounts within interburden zones that could also have additional problems during storage and use. The areas that possess the highest risk regarding acid generation are the zones enriched in pyrite, as well as the coal seams from stock piles. The management plan for the acid generating spoils of the area has two possibilities: Firstly where acid producing potentials are higher, spoils should not be used where it will be exposed to oxygen and water for long periods of time, as the amount of acid generated cannot be controlled. A second option would entail the immediate compaction and flooding of the mined area so that the amount of acid produced would be controlled and limited.

Abstract

Zachariashoek  catchment  was  one  of  the  study  areas  looking  into  the  hydrological characteristics  of winter rainfall catchments in the Western Cape. Nearly thirty years of historical data are available for the Zachariashoek area. This data include rainfall, gauge plate readings for the weirs, and water levels for the boreholes in the area. Numerous articles and reports had been written  about  the  research  done  in  the  area,  concentrating  mostly  on  the  effects  of  fire  on streamflow and vegetation. This article will look at patterns that can be observed from the data record and correlate the different data sets for the Zachariashoek sub‐catchment. It will use the data from the two weirs, three rain gauges and at least three of the boreholes that was drilled in this sub‐catchment.  The information gained from this comparison can then be used to evaluate possible future hydrological patterns and the interaction between the various components of the hydrological system.

Abstract

Zimbabwe occupies a tectonically stable plateau underlain by ancient Precambrian crystalline basement rocks. These  form a central craton bounded by east-west trending mobile belts; the Zambezi mobile belt to the north and the Limpopo mobile belt to the south. Zimbabwe receives generally low and variable quantities of seasonal rainfall within a semi-arid to savannah type climate characterised by moderate to high temperatures. Evaporation commonly exceeds rainfall so that recharge to the thin near surface aquifers is generally low and in some years non-existent. The groundwater resources of the weathered and fractured basement aquifers that underlie more than 60% of the country are of limited potential, typically sufficient to supply the needs of small villages and cattle ranches. However, within the central plateau area of the African to Post-African erosion surfaces, the weathered and fractured basement may exceed 60 m in thickness. The thickness of this zone diminishes towards the main valley systems where subsequent cycles of erosion have stripped the weathered zone away, leaving only a shallow surface fractured zone that may only be 20-30 m thick. Groundwater resources have been developed extensively in Zimbabwe since the 1920s. During 1991/92 drought abstraction from urban boreholes within the southern Harare area caused yield decline and ultimate failure of numerous boreholes. It is now time to question the long-term viability of groundwater development within the basement aquifers in Zimbabwe given the uncertainty in groundwater resources, the complexities of the climate–groundwater interactions and the projected demands of a growing rural population.

Abstract

This paper was presented at the GWD Central Branch Symposium, Potchefstroom in 2012

Numerical modelling of hydrogeological systems has progressed significantly with the evolution of technology and the development of a greater understanding of hydrogeology and the underlying mathematical principles. Hydrogeological modelling software can now include complex geological layers and models as well as allow the pinching out of geological features and layers. The effects of a complex geology on the hydraulic parameters determined by numerical modelling is investigated by means of the DHI-WASY FEFLOW and Aranz Geo Leapfrog modelling software packages.

The Campus Test Site (CTS) at the University of the Free State in Bloemfontein, South Africa was selected as the locale to be modelled. Being one of the most studied aquifers in the world, the CTS has had multiple research projects performed on it and as a result ample information is available to construct a hydrogeological model with a high complexity. The CTS consists primarily of stacked fluvial channel deposits of the Lower Beaufort Group, with the main waterstrike located on a bedding-plane fracture in the main sandstone aquifer.

The investigation was performed by creating three distinct hydrogeological models of the CTS, the first consists entirely of simplified geological strata modelled in FEFLOW by means of average layer thicknessand does not include the pinching out of any geological layers. The second model was created to be acopy of the first, however the bedding-plane fracture can pinch out where it is known to not occur. The third and final model consisted of a complex geological model created in Leapfrog Geo which was subsequently exported to FEFLOW for hydrogeological modelling.

Abstract

The Namibian uranium province, located in the Namib Desert, derives its name from the local presence of almost ten uranium tenements. The mines conduct monitoring of natural radionuclide concentrations of Ra226, Ra228, Pb210, U234, U238, Th232 and Po210 in local aquifers. This data is useful in mine rehabilitation and developing closure criteria, as only radiation doses additional to natural doses are usually considered ‘controllable’ for radiation protection purposes. An accredited laboratory analyzed the baseline data collected through quarterly groundwater sampling with submersible pumps. The uranium deposits are hosted in Damara age granites or as secondary mineralization in Tertiary calcareous paleochannels. The analysis of the long-term baseline data provides the background radionuclide concentrations of three aquifer types in the province, i.e., the Quaternary saturated alluvium of the Khan and Swakop ephemeral Rivers, the Tertiary paleochannel sediments, and Proterozoic basement aquifers. The ephemeral rivers are important because they supply groundwater downstream of the mines for agricultural use. The analysis demonstrated that the alluvial aquifers have the lowest natural radionuclide content, with the U234 concentrations ranging between 0.03 and 3.4 Bq/l, while paleochannel and basement aquifers show intermittent U234 concentrations ranging between 0.25 and 5.1 Bq/l. The groundwater in the immediate ore zones shows the highest U234 concentrations, ranging between 44.8 and 86.3 Bq/l, exceedingly higher than the WHO standards of 1 Bq/l. This study illuminates that radioactivity is a natural phenomenon and that groundwater baseline data is paramount to groundwater protection.

Abstract

For the Department of Water and Sanitation (DWS) to better leverage the wealth of information being collected by various “silo” operational source water information systems, a high-priority initiative was launched to establish a National Integrated Water Information System (NIWIS), which currently consists of over 40 web-accessible dashboards including groundwater related dashboards mostly accessible to the public. Dispersed and disintegrated data and information stored in different sources and formats would hinder decision support in the water sector and deter improvement in service delivery by the DWS. The DWS undertook an extensive and rigorous business requirements analysis exercise within the DWS to ensure that the proposed system does not become a white elephant and facilitate the prioritization of system deliverables. A prototype (waterfall) approach was adopted to develop the NIWIS to ensure the development was still within the suggested business requirements. NIWIS has enabled mostly DWS managers to establish one trusted source of decision-making information for timeous, effective and efficient responses to service delivery. The number of NIWIS dashboards continues to grow as improved data-related business processes are adopted. The unavailability of reliable data from DWS data sources and the exclusion of business requirements from organizations external to DWS were identified as the main challenges to NIWIS disseminating comprehensive, credible information. Therefore, this paper aims to provide some details of the geohydrological information that NIWIS provides and seek feedback from this International Hydrogeologists community for further development of NIWIS.