Conference Abstracts

Abstract

Unconventional gas mining is a new and unprecedented activity in South Africa that may pose various risks to groundwater resources. According to legal experts, South Africa does not currently have the capacity to manage this activity effectively due to various lacunae that exist in the South African legislation. The possible impacts of unconventional gas mining on groundwater, as well as governance strategies that are used in countries where unconventional gas mining is performed; have been analysed and will be discussed. Based on possible impacts and strategies to manage and protect groundwater internationally, possible governance options for the management of South Africa’s groundwater resources are proposed

Abstract

The aim of this study was to determine the geohydrological status of the aquifer within the boundaries of the Vanrhynsdorp Water User Association with emphasis on the central catchment, E33F. This will assist the Department of Water Affairs with the introduction of compulsory groundwater-use licensing and empowerment of the Vanrhynsdorp Water User Association to manage the resource. In this study emphasis was given to the determination of the water balance and  groundwater  reserve  of  the  central  catchment  and  the  designing  of  a  representative groundwater monitoring network. A literature study of five projects conducted since 1978 was done. Comparisons were made between the data and results of these studies. All the historical data from these studies, as well as the data from the current monitoring programme up until December 2012, were put together and analysed. A conceptual model and groundwater reserve determination, as well as a representative monitoring network, were produced. The study showed a general decline in groundwater levels over a 34-year period. It also showed an increase in rainfall over the last 20 years. Based on the reserve determination and the declining groundwater level in spite of increased rainfall and thus recharge, it was concluded that over-abstraction of groundwater in the study area is taking place. It is recommended that compulsory licensing should be put in place as soon as possible and  that  no  additional  groundwater-use  licences  should  be  granted  in  the  study  area.  The installation  of  flow  meters  on  all  production  boreholes  should  be  stipulated  in  the  licensing condition. This will assist the monitoring and regulation of groundwater abstraction volumes.

Abstract

POSTER A quick analysis of spring water quality was conducted in four neighbouring villages, namely Vondo, Matondoni, Maranzhe and Murangoni in Thohoyandou town under the Thulamela Local Municipality (TLM) of the Vhembe District Municipality (VDM). For the purposes of this study these villages will be termed VMMM villages. A study on the spring water quality of VMMM villages was conducted by the CSIR to determine whether the natural quality state of the spring water used by the surrounding communities was suitable for drinking purposes without pre-treatment. From the four springs that were identified in the VMMM villages, namely Tshali (S1), Ramufhufhi (S2), Tshinwela (S3) and Tshivhase (S4), water samples were taken for the quality analyses in the laboratory. The results indicated that S2 and S4 had a high coliform count of 35 and 600 per 100 ml, respectively), that is above  10  counts  per  100 ml.  In  springs  S2  and  S4  the  total  coliform  count  also  displayed  the presence of E.coli (6 and 310 per millilitre, respectively)  – E.coli should not be detected at all according to SANS standard limits (2011). While all other parameters were within standard limits (SANS 241, 2011), it was also interesting to note that both S3 and S4 had a problem of high turbidity (1, 6 and 105 NTU, respectively) compared to 1 NTU which is the standard limit (SANS 241, 2011). These results showed that although these communities relied on groundwater in the form of springs for drinking purposes, unmonitored use of these resources may be a health hazard that has a potential to  result  in disease outbreak  and  unprecedented  deaths. While  groundwater through springs is considered natural, increased activity around the source due to human activity and interference by domestic animals, these sources may be rendered unsafe for drinking purposes without prior treatment. Therefore, there is need for local authorities to put measures in place to monitor water resources considered indigenous and traditional to the communities, especially in areas where these resources have become the main source of water supply for drinking purposes.

Abstract

Gold mining  activities over  the  past 60 years  in the Klerksdorp  goldfield produced  saline mine drainage that polluted water. Oxidation of sulphide material in tailings storage facilities, waste rock dumps and extraction plants is mobilised to produce saline mine drainage with sulphate, minor salts and  metals  that  seep  to  the  groundwater  and  ultimately  into  surface  water  resources.  Water regulation requires mines to prevent, minimise/reduce or eliminate pollution of water resources. The waste philosophy has matured from tolerate and transfer to treat and termination of pollution sources.  The  impact  of  the  pollution  was  determined  and  possible  technologies  to  treat  the impact   were   evaluated.   Source   controls   with   proper  water  management  by  storm  water management,  clean  dirty  water  separation,  lined  water  conveyance  structures  and  reduced deposition of water on waste facilities are crucial. The aquifer character determines the possible remediation technology. From the possible technologies phytoremediation, physical interception and  re-use  of  this  water  was  selected.  In  future  possible  treatment  of  the  water  would  be considered. This paper explain the strategy and report on the phased implementation of these plans and the expected results. The establishment of 500 ha of woodlands as phytoremediation, interception trenches of 1 000 m, 38 interception boreholes and infrastructure to re-use this water is planned. The total volume of 15 Ml/day would be abstracted for re-use from the boreholes and trenches. The woodlands can potentially attenuate and treat 5 Ml/day. The established woodlands of 150 ha prove to be successful to intercept diffused seepage over the area of establishment and reduce  the  water  level  and  base  flow.  The  two  production  interception  well- fields  that  are abstracting  50  and  30 l/s,  respectively  , indicate  a  water  level decline of between 2 to 14 m, with regional cones of depression of a few hundred meters to intercept groundwater flow up to a 20 m depth. Predictions from groundwater modelling indicate that these schemes can minimise pollution during the operational phase and protect downstream water resources. Predictions from modelling indicate that the pollution sources need to be removed to ensure long-term clean-up to return the land to safe use. The gold and uranium prize is securing the removal of the sources through  re-processing  of  the  tailings  and  waste  rock  dumps.  After  removal  of  the  sources  of pollution,  the  remediation  schemes  would  have  to  be  operated  for  20  years  to  return  the groundwater to an acceptable standard  of  stock  watering  and  industrial  water  use.  The  water quality is observed by a monitoring network of approximately 100 observation boreholes.

Abstract

The assessment and prediction of mine water rebound has become increasingly important for the gold mining industry in the Witwatersrand basin, South Africa. The cessation of dewatering lead to large volumes of contaminated surface discharges in the western parts of the basin. Towards the eastern extremity of the Witwatersrand basin the detached Evander Goldfield basin has been mined since the early 1950s at depths between 400 and 2000 metres below ground, while overlain by shallower coal mining operations. The hydrogeology of the Evander basin can be categorised by a shallow weathered-fractured rock aquifer comprising of the glacial and deltaic sediments of the Karoo Supergroup, while the deeper historically confined fractured bedrock aquifer consist predominantly of quartzite with subordinate lava, shale and conglomerate of the Witwatersrand Supergroup. The deep Witwatersrand aquifer has been actively been dewatered for the last 60 years with a peak rate of 60 Ml per day in the mid late 1960s. Modelling the impacts of mine dewatering and flooding on a regional scale as for the Evander basin entails challenges like the appropriate discretisation of mine voids and the accurate modelling of layered aquifer systems with different free groundwater surfaces on a regional scale. To predict the environmental impacts of both the historic and future deep mining operations, the detailed conceptual model of the aquifers systems and a 3-dimensional model of the mine voids were incorporated into a numerical groundwater model to simulate the dewatering and post-closure rebound of the water tables for the basin. The presented model could serve as an example for the successful modelling of mine dewatering and flooding scenarios for other parts of the Witwatersrand basin.

Abstract

The significance of a reliable groundwater resource assessment is of growing importance as water resources are stretched to accommodate the growing population. An essential component of a groundwater resource assessment is the quantification of surface water–groundwater interaction. The  insufficient  amount  of  data  in  South  Africa  and  the  apparent  lack  of  accuracy  of  current estimates of the groundwater component of baseflow lead to the investigation of a new method. This applicability of this new approach, the Mixing Cell Model (MCM), to quantify the groundwater contribution to baseflow is examined to assess whether the method would be of use in further groundwater resource assessments. The MCM simultaneously solves water and solute mass balance equations  to  determine  unknown  inflows  to  a  system,  in  this  application  the  groundwater component of baseflow. The incorporation of water quality data into the estimation of the surface water–groundwater  interaction  increases the  use of  available  data,  and  thus has  the  ability to increase the confidence in the estimation process. The mixing cell model is applied to datasets from the surface water–groundwater interaction test site developed by the University of the Free State, in addition to data collected along the middle Modder River during a fieldwork survey. The MCM is subsequently applied to a set of quaternary catchments in the Limpopo Province for which there are available calibrated estimates of the groundwater component of baseflow for the Sami and Hughes models. The MCM is further applied to the semi-arid quaternary catchment D73F to assess the applicability of the mathematically-based MCM in a flow system within a regionally-defined zero groundwater  baseflow  zone.  The  results  indicate  that  the  MCM  can  reliably  estimate  the groundwater component of baseflow to a river when sufficient data are available. Use of the MCM has  the  potential  to  evaluate  as  well  as  increase  the  confidence  of  currently  determined groundwater baseflow volumes in South Africa, which will in turn ensure the responsible and sustainable use of the countries water resources.

Abstract

Abstract

To date, South Africa has mined approximately 3.2 billion tons of coal from a number of different coal reserves located in various parts of the country. A large number of the mines have reached the end of their productive life, resulting in numerous mine closures. With closures, groundwater levels have rebounded, resulting in decant of mine water into the environment. This paper describes a case study of a closed underground coal mine, the rebound of water levels, the evolution of the groundwater quality and the impact it has had on the management of the potential decant.

On closure of the Ermelo Mines in 1992, initial water quality monitoring indicated that a water treatment plant would be required to treat the mine decant. However, as the groundwater levels in the mine rebounded, the water quality in the mine void evolved from sulphate type water to sodium type water. The evolution of the water quality can be attributed to sulphate reducing bacteria, vertical recharge from the hanging aquifer and stratification. Water level and quality monitoring have shown that the water in the old mine void will not decant to surface due to the depth of the mine void, hydrogeological conditions, a "hanging aquifer"  and the recharge mechanisms. As a result, no water treatment will be required and the mine will not impact on the surface water. The main applications from this paper are:

•  Design  of  a  correct  monitoring  procedure  to  allow  for  monitoring  of  water  quality stratification in rebounding mines.
•  Identifying the role of sulphate reducing bacteria in the evolution of groundwater quality in a methane rich coal mine void.
•  The role of a hanging aquifer in recharging of a coal mine void and resultant stratification. 
• Designing of a mine taking into consideration mine closure.

The main contribution of this paper is the use of hydrogeological information in design of a coal mine so as not to decant on closure.

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

An understanding of the movement of moisture fluxes in the unsaturated zone of waste disposal sites play a critical role in terms of potential groundwater contamination. Increasing attention is being given to the unsaturated or vadose zone where much of the subsurface contamination originates, passes through, or can be eliminated before it contaminates surface and subsurface water resources. As the transport of contaminants is closely linked with the water flux through the unsaturated zone,  any quantitative analysis of contaminant transport must first evaluate water fluxes into and through this region. Mathematical models have often been used as critical tools for the optimal quantification of site-specific subsurface water flow and solute transport processes so as to  enable  the  implementation of management practices that minimize  both surface water  and groundwater pollution. For instance, numerical models have been used in the simulation of water and solute movement in the subsurface for a variety of applications, including the characterisation of unsaturated zone solute transport in waste disposal sites and landfills. In this study, HYDRUS 2D numerical simulation was used to simulate water and salt movement in the unsaturated zone at a dry coal ash disposal site in Mpumalanga, South Africa. The main objective of this work was to determine the flux dynamics within the unsaturated zone of the coal ash medium, so as to develop a conceptual model  that  explains  solute  transport through  the unsaturated  zone  of the coal ash medium for a period of approximately 10 year intervals. Field experiments were carried out to determine the model input parameters and the initial conditions, through the determination of average moisture content, average bulk density and the saturated hydraulic conductivity of the medium. A two-dimensional finite-element mesh of 100 m × 45 m model was used to represent cross  section  of  the  ash  dump.  Two-dimensional  time  lapse  models  showing  the  migration  of moisture fluxes and salt plumes were produced for the coal ash medium. An explanation on the variation of moisture content and cumulative fluxes in the ash dump was done with reference to pre-existing ash dump data, as well as the soil physical characteristics of the ash medium.

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

Gold mining on the Witwatersrand has started in the late nineteenth century as sporadic open cast mining and ceased in the late twentieth century, leaving a complex network of haulages, tunnels and ultra-deep vertical shafts/sub-vertical shafts. At least three ore bodies (conglomeritic horizons) were mined down to a depth in excess of 3 000 m from surface. Three large mining basins resulted from the mining methodology applied, namely the Western, Central and Eastern (Rand) Basins.

In  the  early  days  of  mining  on  the  Witwatersrand  reefs,  gold  mine  companies  realised  that dewatering of their mine workings is required to secure mining operations at deeper levels and decades of pumping and treatment of pumped mine water followed. As the majority of deep gold mines on the Witwatersrand ceased operations since 1970, the deeper portions of the mine voids became flooded and led to a new era in the mining history in the Witwatersrand.

Rewatering of the mine voids is a combination between excessive surface water ingress generated by surface runoff, and to lesser degree recharge from an overlying fractured and weathered aquifer system (where developed). The flow regime in the mine voids from a scattering of ingress/direct recharge points and single discharge points are complex and is driven by shallow (<100 m) and probably deep (>1 000 m) man-made preferential pathways.

The high concentrations of iron sulphide minerals (pyrite. for example FeS2) content, three percent (by weight), of the mined reefs/backfilled stopes and surrounding waste rock piles/tailings dams mobilised significant levels of sulphates (SO4) and ferrous iron (Fe2+) producing an acidic mine-void water (<3 pH).

Monitoring of the rewatering mine void hydrological regime became necessary following the first acid-mine water decant from a borehole in the West Rand Basin, and the Department initiated a mine-void water table elevation trend and water quality monitoring programme. Results from this monitoring programme will be illustrated and discussed in this paper with some views on the future water quality and discharge scenarios.

Abstract

The mineral-rich basin of the West African region has vast reserves of gold, diamond as well as iron ore deposits. Throughout the regional geological setting characterised by structural variations and intrusive belts with metamorphic mineral-rich sequences covered by saprolite soils, one common chemical constituent remains a constant in the water reserves. Arsenic is in high concentrations throughout the region with chemical ranges commonly above the various country guidelines as well as international IFC and WHO standards. The aqueous chemical species is associated with arsenopyrite-rich mineralogy of the regional greenstone belts and highly weathered soils.

This conference presentation investigates the natural source of the arsenic through baseline data, as well as the effect of mining on the already high concentrations of arsenic in both the groundwater and surface water. Natural levels of various chemical species in the regional area are already high at baseline level. One of the main research questions is thus whether mining and other anthropogenic activities will have  an impact on the environment or will  the changes to concentrations be so insignificant to allow the ecosystems and water users to continue in their current ways without any effect. Various case studies in Burkina Faso, Liberia, Sierra Leone and other countries have been combined to investigate the arsenic-rich resources of the West African region through groundwater specialist investigative methods with emphasis on geochemical modelling of the fluid–rock and fluid–fluid interactions leading to the aqueous chemical conditions in the region.

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 Fountains East and Fountains West groundwater compartments (by means of the Upper and Lower Fountain springs) have been supplying the City of Pretoria with water since its founding in 1855. These adjacent compartments which are underlain by the Malmani dolomites of the Chuniespoort Group are separated by the Pretoria syenite dyke and are bounded to the north by the rocks of the Pretoria Group (Timeball Hill Formation). Inorganic chemistry data (2007-2012), as well as spring discharge volumes (2011-2012) for the Upper and Lower Fountain springs, supplied by the City of Tshwane Municipality, is being used to characterise the two compartments. This is done by means of piper diagrams, bar graphs and temporal plots. Interpretation of the combined chemical and discharge volume data as well as geotechnical and isotope data (in progress) will aid in understanding  the  karst  aquifer  and  the  controls  on  groundwater  system  within  and  possibly between these compartments.

Abstract

In this study, a petroleum hydrocarbon contamination assessment was conducted at a cluster of petroleum products storage and handling facilities located on the Southern African Indian Ocean coastal zone. The Port Development Company identified the need for the assessment of the soil and groundwater pollution status at the tank farms in order to develop a remediation and management plan to address hydrocarbon related soil and groundwater contamination. Previous work conducted at the site consisted of the drilling and sampling of a limited number of boreholes. The current investigation was triggered by the presence of a free-phase product in the coal-grading tippler pit located ~350 m down gradient and south-east and east of the tank farms, rendering the operation thereof  unsafe.  The  assessment  intended  identifying  the  source  of  product,  distribution  and mobility, the extent of the contamination, and the human health risks associated with the contamination. To achieve these, the investigation comprised site walkover and interviews, drilling of 76 hand auger and 101 direct push holes to facilitate vertical soil profile VOC screening and sampling  (soil  and  groundwater),  as  well  as  granulomeric  analysis  to  understand   grain   size distribution  within  the  soil  profile.  The  highest  concentrations  were  associated with the coarse sand layers with the highest permeability. Free-phase hydrocarbons product was found in holes adjacent to the pipeline responsible for the distribution of the product from the jetty to the different tanks farms. Of the 57 soil samples, 21 had high values of GRO and DRO, with 22 below Detection Limit and 14 can be described having traces of hydrocarbon. Both TAME and MTBE were detected in most of the water samples, including from wells located far down gradient. The groundwater sink, adjacent to the pipeline running from west to east, resulted in the limited lateral spread of MBTE in this area, with limited movement towards the sea. The depth of the soil contamination varies over the sites. Based on the site  assessment  results  it  was  concluded  that  most  of  the groundwater contamination, which is a mixture of different product types, is associated with the pipeline responsible for transporting product from the jetty to the different petroleum companies.

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

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

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 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

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

The thermal springs of Swaziland and adjacent KwaZulu-Natal have, over the years, attracted attention from hydrogeologists, hydrochemists and structural geologists. While some of the springs in Swaziland are well known amenities, others are less well-visited and some difficult to access. There are eleven warm springs in Swaziland, discharging between 1 and 10 l/s from Precambrian age rocks; all are situated at or near valley bottoms. The springs have surface discharge temperatures of between 25 and 52 oC and total dissolved solids concentrations of less than 400 mg/l. In all cases the water is meteoric in origin. Geothermometry indicates that maximum temperatures up to 100 oC are achieved during circulation. If the average geothermal gradient is about 20 oC/km as recorded in a deep mine at Barberton, then this would require circulation up to a depth of several kilometres. However, it is likely that circulation bottoms at about 1 km, as pressure of overburden inhibits dilation of fractures at such depths, and the excess temperature may derive from a locally enhanced geothermal gradient. The discharge water is young, with 14C ages of between 4 000 and 5 000 years.

Abstract

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 water quality in the crystalline rocks of the Johannesburg and its environs has been severely altered by the mining activity. Due to freshwater scarcity and dependency of the people on the groundwater, it is important to understand the extent of hydrogeochemical footprint in the area. The water quality characteristic has been thoroughly assessed in the crystalline aquifers based on the input from hydrogeochemical characteristics and environmental isotopes. The results show that the calculated dilution factor for acid-mine decant is in the range of 68% as a result of interaction with surrounding fresh water. The SO4/Cl ratio has a wide range of values that falls between 0 and 306.37, while that of Fe/Ca ratio falls between 0 and 5.59. High SO4/Cl values potentially indicate the interference of acid-mine decant with the groundwater system traced through sulphate concentration. Similarly, a high Fe/Ca ratio also indicates the impact of acid-mine decant on the groundwater system where iron is traced with respect to calcium concentration. In this regard the ratios above 0,25 (with the assumption of 1 to 4 natural abundance for Fe:Ca in water in the area) could potentially represent acid-mine decant source.The results confirm that most of the water- supply wells have heterogeneous chemistry with distinctive hydrogeochemical footprint represented by abnormally high Fe, SO4 and Si as a result of acid-mine decant.

Abstract

Unconventional gas mining is a new and unprecedented activity in South Africa that may pose various risks to groundwater resources. According to legal experts, South Africa does not currently have the capacity to manage this activity effectively due to various lacunae that exist in the South African legislation. The possible impacts of unconventional gas mining on groundwater, as well as governance strategies that are used in countries where unconventional gas mining is performed; have been analysed and will be discussed. Based on possible impacts and strategies to manage and protect groundwater internationally, possible governance options for the management of South Africa’s groundwater resources are proposed.

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

Lake  Sibayi  (a  topographically  closed  freshwater  lake)  and  coastal  aquifers  around  the  Lake  in eastern South Africa are important water resources and are used extensively for domestic water supplies. Both the Lake and groundwater support an important and ecologically sensitive wetland system   in   the   area.   Surface   and   subsurface   geological   information,   groundwater   head, hydrochemical and environmental isotope data were analysed to develop a conceptual model of aquifer–lake interaction for further three-dimensional numerical modelling. These local geologic, groundwater head distribution, lake level, hydrochemistry and environmental isotope data confirm a direct hydraulic link between groundwater and the Lake. In the western section of the catchment, groundwater flows to the lake where groundwater head is above Lake stage, whereas along the eastern section, the presence of mixing between Lake and groundwater isotopic compositions indicated that the Lake recharges the aquifer. Stable isotope signals further revealed the movement of lake water through and below the coastal dune cordon and eventually discharges into the Indian Ocean. Quantification of the 14-year monthly water balance for the Lake shows strong seasonal variations of the water balance components. Recent increase in rate of water abstraction from the lake combined with decreasing rainfall and rapidly increasing pine plantations may result in a decrease in lake level which would have dramatic negative effects on the neighboring ecosystem and a potential seawater invasion of the coastal aquifer.

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 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

South Africa currently ranks number nine in the world of the proved coal reserves that has been estimated to last for over 200 years. Coal constitutes about 77% of the primary energy needs in the country, with the Waterberg Coalfield estimated to host about 40% of the remaining South African coal resources. Coal deposits in the study area largely consist of shales, mudstones, siltstones and sandstones which host coal-containing clay minerals; quartz, carbonates, sulphides and the most abundant sulphide mineral is pyrite. Once mining begins, the sulphide minerals are exposed to surface which allows contact with atmospheric oxygen and water causes oxidation to take place, therefore causing acid-mine drainage (AMD). Acid-base accounting (ABA) was used to determine the balance between the acid-producing potential (AP) and acid-neutralising potential (NP). From the analysis the Net Neutralising Potential (NP-AP) was determined, which is one of the measurements used to classify a sample as potentially acid or non-acid-producing. Mineralogical analyses will be done by x-ray defraction (XRD) to define and quantify the mineralogy of the geological samples which can help in the management plan to minimise generation of acid. AMD does not only result in the  generation of acid, but as well as in decreased pH values and increased values of specific conductance, metals, acidity, sulphate, and dissolved and suspended solids. Inductively coupled plasma analysis was done to determine the release of the heavy metals which can be detrimental to the environment. Sample analysis was done on the interburden, overburden as well as the coal samples. From results obtained, over 35% to 50% of the samples have an excess of acid potential which classifies the samples as having a higher risk for acid generation. About 30% to 40% of the samples have a higher neutralising potential; the rest of the samples have a medium acid risk generation. The water demand will increase as developments continue in the  area, with inter- catchment transfers identified as the answer to fill the gap of water scarcity. Acid mine drainage poses a big threat on water resources, both groundwater and surface water nationally, which might be less of a problem in the Waterberg because of the cycle of low rainfall in the area, but the potential of AMD cannot be neglected.

Abstract

The pollution of water resources has become a growing concern worldwide. Industrial, agricultural and domestic activities play a pivotal role in water resources pollution. The challenge faced by pollution   monitoring   networks   is   to   understand   the   spatial   and   temporal   distribution   of contaminants. In hydrology, tracers have become a critical research tool to investigate surface water and groundwater transport dynamics. Synthetic DNA (deoxyribonucleic acid) tracers are being used in hydrological research to determine source areas, where uniquely labelled DNA from each source area  is  identified.  The main  objective  of the  study  was to  determine  the mass  balance of  the synthetic DNA tracer in surface water streams. Furthermore, to gain knowledge on DNA adsorption and decay and determine whether DNA behaves as conservative tracer in the surface water streams. Understanding the adsorption and decay characteristics of synthetic DNA tracers may promote its robustness in hydrological research. In this study, field injection experiments using synthetic DNA were  carried  out,  the  DNA  tracer  was  injected  together  with  sodium  chloride  (salt)  and deuterium as conservative reference tracers. The purpose was to compute DNA mass balance calculations with reference to the two conservative tracers. In this study two different DNA markers were used, namely T22 and T23. Additionally, with each injection experiment a field batch experiment was carried out to determine DNA loss characteristics on the field. From our study, the DNA loss between the injection point and the first measurement was greater than 90%. Therefore, it was important to conduct additional laboratory batch experiments to explain DNA loss characteristics. However, the issue of the initial DNA loss remained unresolved. Laboratory batch experiments results allow us to conclude the following: the type of material used, filtering, ion concentration and water composition reduced DNA concentration. Moreover, initial DNA losses occurred and not DNA decay. From our experiments we concluded that DNA can be used for long-term tracer experiments, subsequently, limiting synthetic DNA mass balance determination of synthetic DNA as it is a reactive. Overall, we can conclude that DNA does not behave as a conservative tracer.

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

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

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

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

This study examined the effective use of the hydrogeologic conceptual model (HCM) to implement the integrated water resource management (IWRM) approach. While research focuses on using hydrogeologic models  in  groundwater  for  planning,  few  studies  show  how  to  use  HCM  for  a successful IWRM approach, especially in  resource  poor  catchments.  This  is  largely  due  to  t he lack of adequate data to showcase such models. Despite the lack of numerical groundwater data, the HCM was used in this study and it provided the scientific and visual presentation of key issues for practical understanding by stakeholders. For the first time, HCM provided a  practical understanding of t he  groundwater system in the Limphasa River catchment. By using HCM and physical factors qualitatively, the study revealed that, apart from storage, abstraction mechanisms significantly contributes to regional initiatives of groundwater supply whose central objective is to utilise and manage such water sustainably. The model is based on the relationship between groundwater availability  and  its  related  hydrogeologic factors.  Findings suggest improvement  in quantifying the studied parameters through field experiments to provide a better estimation on storage and abstraction of groundwater in relation to impacts of a future changing climate. Since using HCM has shown practical usage, replicating it in catchments with similar physical and socioeconomic environments, would be desirable as refining the model progresses.

Abstract

The aim of this project was to establish a detailed geohydrological database and monitoring network for  the  karst  aquifer  within  the  boundaries  of  the  Vanrhynsdorp  Water  User  Association.  An adequate monitoring network is necessary for the Vanrhynsdorp Water User Association to implement sustainable water use management as well as for the Department Water Affairs to ensure its mandate as trustee of all water resources. Hydrocensus projects were conducted in phases as the project escalated from historic town supply during 1978 towards a catchment driven water user association after implementation of the new National Water Act in October 1998 (Act 36 of 1998). With the successive hydrocensuses conducted, the monitoring network also evolved in regard to area monitored, point locations, monitoring schedules and parameters measured. Hydrocensus data were captured on the National Groundwater Archive, time series data on the Hydstra database and chemical analysis on the Water Management System. Time series graphs were compiled to analyse the monitoring data and to create a conceptual model of the karst aquifer. The study showed a general decline in groundwater levels and quality in the study area. The conclusion is that the aquifer is over exploited. It is recommended that an extensive management plan is developed and implemented to ensure sustainable use of this sensitive water resource. The installation and monitoring of flow meters on all production boreholes should be seen as urgent and stipulated as such in licensing conditions. This will ensure the effective management and regulation of this valuable groundwater resource.

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

The Paleozoicage Natal Group Sandstone (NGS) that outcrops from Hlabisa (in the north) to Port Shepstone (in the south) and Greytown (west) to Stanger (east) in the Province of KwaZulu-Natal, South Africa, is investigated in terms of its hydrogeological characteristics. This sandstone group, which comprises a lower Durban and an upper Marrianhill Formations, is a secondary/fractured aquifer system that has variable but good productivity across its members. It is characterised by variable borehole blow yields ranging from 0.2 l/s to as high as 20 l/s, with more than 50% of the boreholes having blow yield > 3 l/s. Preliminary analysis of these boreholes yields indicates that higher yielding boreholes are associated with a network of intersecting fractures and faults, and are recommended targets for future water well-siting in the area. Groundwater in the NGS is of good quality in terms of major and trace element composition and it has a total dissolved solids (TDS) composition of <450 mg/l. It was observed that the specific electrical conductivity (EC), TDS and major ions composition of groundwater within the sandstone decrease from north to south, which appears to be controlled by the geochemical composition of the aquifer material and an increase in the rate of recharge. Depth to groundwater is also found to decrease southwards because of an increase in the rate of recharge. Groundwater hydrochemical facies are generally either Na-HCO3 or Na-HCO3–Cl, and environmental isotope data (2H, 18O, Tritium) indicates that the groundwater gets recharge from modern precipitation. Furthermore, the EC increases from inland to the coastal zone, indicating maritime influences and the general direction of groundwater flow is eastwards, to the Indian Ocean.

Abstract

Inadequate characterisation of petroleum release sites often leads to the design and implementation of inappropriate remedial systems, which do not achieve the required remedial objectives or are inefficient in addressing the identified risk drivers, running for lengthy periods of time with little benefit. It has been recognised that high resolution site characterisation can provide the necessary level of information to allow for appropriate solutions to be implemented. Although the initial cost of characterisation is higher, the long-term costs can be substantially reduced and the remedial benefits far greater. The authors will discuss a case study site in the Karoo, South Africa, where ERM has utilised their fractured rock toolbox approach to conduct high resolution characterisation of a petroleum release incident to inform the most practical and appropriate remedial approach. The incident occurred when a leak from a subsurface petrol line caused the release of approximately 9 000 litres of fuel into the fractured sedimentary bedrock formation beneath the site. Methods of characterisation included: 

Surface  geological  mapping  of  regionally  observed  geological  outcrops  to  determine  the structural orientation of the underlying bedding planes and jointing systems. 

A surface electrical resistivity geophysics assessment for interpretation of underlying geological and hydrogeological structures. 

Installation of groundwater monitoring wells to delineate the extent of contamination. 

Diamond core drilling to obtain rock cores from the formation for assessment of structural characteristics and the presence of hydrocarbons by means of black light fluorescence screening and hydrocarbon detection dyes. 

Down-borehole geophysical profiling to determine fracture location, fracture density, fracture dip and joint orientation. 

Down-borehole deployment of Flexible Underground Technologies (FLUTe®) liners to determine the precise vertical location of light non-aqueous phase liquid (LNAPL) bearing joint systems and fracture zones, and to assist in determining the vertical extent of transmissive fractures zones.

ERM used the information obtained from the characterisation to compile a remedial action plan to identify suitable remedial strategies for mitigating the effects of the contamination and to target optimal areas of the site for pilot testing of the selected remedial methods. Following successful trials of a variety of methods for LNAPL removal, ERM selected the most appropriate and efficient technique for full-scale implementation.

Abstract

The occurrence of groundwater around a mined-out open pit, connected to an active underground working is not completely understood, but it is fascinating. It has been established that gold mineralisation in study area was structurally controlled. The geomorphology of the local drainage system is highly controlled by the fold or fault architecture. Surface water flowed through, and eroded open fractures in exposed damaged zones (zone of subsidiary structures surrounding a fault). Previous  conceptual  hydrogeological models  of  groundwater  system  suggested  is  a  two-aquifer system, consisting of a fractured aquifer overlain by a weathered aquifer, where groundwater flow mimics surface topography. Based on recent drilling and reassessment of historic geological and hydrogeological data, the groundwater system around the mine could not only be described in terms of an elevation or stratigraphic units, as traditional aquifers are. The weight of the study was placed on accurately understanding the groundwater system in the deposit area by using structural hydrogeology as a best tool in the hydrogeological tool box. From a hydraulic head point of view, in addition to the weathered groundwater system, there are as many bedrock aquifers and aquitards as there are major structures in the pit area.

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

Vapour intrusion (VI) is the term used to define the encroachment of vapour phase contaminants from subsurface sources into structures such as buildings and basements. It is widely recognised that VI often forms the principal risk of exposure to receptors at petroleum release sites. Petroleum VI (PVI) generally occurs where a release of petroleum hydrocarbon product migrates from its source (for example, from a leaking underground storage tank) to the groundwater table at which point, given favourable conditions, the hydrocarbon plume may migrate laterally beneath an adjacent building or structure. Subsequent volatilisation of the petroleum product results in the upward diffusion of vapours towards the surface where the vapours may enter into the building or structure at concentrations which may be harmful to human health. The subject of PVI with regards to its fate and transport mechanisms, as well as associated mitigation measures, is rapidly gaining attention on a global scale, although to date this exposure pathway remains largely unassessed in South Africa, with no regulatory guidance currently available. In the late 1990s and early 2000s focus was placed on the development of VI screening criteria by which sites could be screened with respect to their hydrogeological conditions and contamination status so as to determine whether VI may be a potential exposure pathway of concern, with much of the early work being completed by the United States Environmental Protection Agency. For the past decade the majority of the available screening criteria  and  guidance  has  not,  or  has  only  partially  accounted  for  biodegradation  processes associated with VI, which has led to doubt over the application of such screening criteria in many cases. Furthermore, recent research conducted abroad has highlighted the importance of the role of oxygen in the vadose zone in the natural attenuation of petroleum hydrocarbon vapours as they diffuse through the soil profile. This research is pointing towards the notion that currently applied screening criteria may be overly conservative when applied to petroleum impacted sites, leading to many  unnecessary  PVI  investigations  being  conducted  to  the  disruption  of  occupants  of  the buildings, and at great cost. Over the last two years ERM has compiled a dataset of PVI results from numerous investigations it has conducted throughout Southern Africa and in this paper the authors present data that supports the growing global trend towards recognising the role that oxygen plays in attenuating petroleum hydrocarbon vapours in the vadose zone. The data also support the notion that confirmed cases of PVI into buildings have generally been found to be the exception to the rule and not the norm.

Abstract

A multi-data integration approach was used to assess groundwater potential in the Naledi Local Municipality located in the North West Province of South Africa. The geology comprised Archaean crystalline basement, carbonate rocks (dolomite and limestone) and windblown sand deposits of the Kalahari Group. The main objective of the study is to evaluate the groundwater resource potential using multi-data integration and environmental isotope approaches. Prior to data integration, weighting coefficients were computed using principal component analysis.

The results of integration of six layers revealed a number of groundwater potential zones. The most significant zone covers ~14% of the study area and is located within carbonate rocks in the southern part of the study area. The localisation of high groundwater potential within carbonate rocks is consistent with the results of principal component analysis that suggests that lithology significantly contributed to the total data variance corresponding to principal component 1. In other words, carbonate rocks consisting of dolomite and limestone largely account for groundwater occurrence in the southern part of the area. In addition, the relatively elevated isotopic signature of tritium (≥1.0 TU)  in  groundwater  samples  located  in  the  southern  part  of  the  area  suggests  a  groundwater recharge   zone.   Furthermore,   moderate-to-good   groundwater   potential   zones   within   the Ventersdorp lava coincide with maximum concentration of fractures, which is consistent with the results of statistical correlation between borehole yield and lineament density. The multi-data integration approach and statistical correlation used in the context of evaluating groundwater resource potential of the area provided a conceptual understanding of hydrogeological parameters that control the development of groundwater in crystalline and carbonate rocks. Such approach is crucial in light of the increasing demand for groundwater arising from municipal water supply and agricultural use. The two approaches are very effective and can be used as a sound scientific basis for understanding groundwater occurrence elsewhere in similar hydrogeological environments.

Abstract

POSTER The Evander Goldfield basin has been mined since the early 1950s at depths between 400 and 2 000 m below ground and is detached from the larger Witwatersrand basin. The assessment and prediction of mine water rebound has become increasingly important for the gold mining industry in the Witwatersrand basin as more mine shafts mothballs and dewatering ceases. The development of a  3-D  mine  void  model  is  crucial  in  predicting  the  rate  of  flooding  as  the  prediction  of  the groundwater rebound is primarily driven by the volumes of mine voids along with the amount of recharge. All available mine plan data for the Evander Gold Mine (EGM) were obtained digitally from Harmony Gold. However, the majority of the old mine workings (e.g. Leslie and Winkelhaak) were available  as  2-D  data  and  elevations  of  the  mine  developments  (stopes  and  drives)  had  to  be captured from hardcopy plans. Data from the more recent mining operations (e.g. Shaft 6), including updated survey and mine plan data, were directly used for the development of the 3-D void model. The calculated mine void volume, based on the EGM operations mine plan data, is approximately 80 518 045 m3. The mine void calculations were checked against the total tons of rock milled by the EGM operations since the late 1950s and was considered valid estimations of the EGM mine void volume. The validated EGM 3-D mine workings plan was subsequently used to determine the stage- volume relationships. The 3-D mine void model established, will then be incorporated into a regional numerical groundwater flow model to be calibrated against observed abstractions and water levels and utilised to predict future dewatering rates.

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.