Conference Abstracts

All Abstracts were presented at the Groundwater Conferences

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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

A coal mine in South Africa had reached decant levels after mine flooding, where suspected mine water was discharging on the ground surface. Initial investigations had indicted a low-risk of decant, but when ash-backfilling was performed in the defunct underground mine, decant occurred. Ash-backfilling was immediately suspended as it was thought to have over-pressurised the system and caused decant. Contrariwise, a number of years later decant was still occurring even though ash-backfilling had been terminated. An investigation was launched to determine whether it was the ash-backfilling which had solely caused decant, or if additional contributing factors existed. Understanding the mine water decant is further complicated by the presence of underlying dolomites which when intersected during mining produced significant inflows into the underground mine workings. Furthermore, substantial subsidence has taken place over the underground mine area. These factors combined with the inherent difficulty of understanding unseen groundwater, produced a proverbial 1000-piece puzzle. Numerical groundwater modelling was a natural choice for evaluating the complex system of inter-related processes. A pre-mining model simulated the water table at the ground surface near the currently decanting area, suggesting this area was naturally susceptible for seepage conditions. The formation of a pathway from the mine to the ground surface combined with the natural susceptibility of the system may have resulted in the mine water decant. This hypothesis advocates that mine water was going to decant in this area, regardless of ash backfilling. The numerical groundwater flow model builds a case for this hypothesis from 1) the simulated upward flow in the pre-mining model and 2) the groundwater level is simulated above the surface near the currently decanting area. A mining model was then utilised to run four scenarios, investigating the flux from the dolomites, subsidence, ash-backfilling and a fault within the opencast mine. The ash-backfilling scenario model results led to the formation of the hypothesis that completing the ash-backfilling could potentially reduce the current decant volumes, which is seemingly counterintuitive. The numerical model suggested that the current ash-backfill areas reduce the groundwater velocity and could potentially reduce the decant volumes; in spite of its initial contribution to the mine water decant which is attributed to incorrect water abstraction methods. In conclusion, the application of numerical models to improve the understanding of complex systems is essential, because the result of interactions within a complex system are not intuitive and in many cases require mathematical simulation to be fully understood.

Abstract

The importance of groundwater in South Africa has become evident over the past decades, especially as pressure on surface water resources intensifies in response to increasing water supply demands. Research has significantly progressed on the shallow groundwater resources conventionally used for water supply, and leading on from this deeper groundwater resources have become a focus point as a future water source. This focus on deep aquifers is driven by new developments, such as shale gas development, injection of brines into deep aquifers, carbon sequestration and geothermal energy. The understanding of deep groundwater in South Africa is often limited due to insufficient data at these depths. To develop a body of knowledge on deep geohydrology in South Africa, an investigation on the currently available information was launched to assess potential deep groundwater resources. The investigation formed part of the larger WRC Project K5/2434 (Characterisation and Protection of Potential Deep Aquifers in South Africa). The geology of South Africa was reviewed from a deep groundwater perspective to provide an initial analysis of potential deep groundwater aquifers. The main potential deep aquifers were identified for further investigation using a ranking system, where Rank 1 shows a positive indication, Rank 2 shows some indication, Rank 3 shows a neutral indication, and Rank 4 shows a negative indication for deep groundwater systems. The Rank 1 geological groups include (in no particular order): the Limpopo Belt, Witwatersrand Supergroup, Transvaal Supergroup, Waterberg and Soutpansberg Groups, Natal Group, Cape Supergroup, Karoo Supergroup. In a number of the identified potential deep aquifers, the indicator for deep groundwater flow systems was the presence of thermal springs. Additionally, deep groundwater occurs below the traditionally exploited weathered zone, and the importance of fractured aquifers becomes paramount in the investigation of potential deep aquifers. In conclusion, three main components were considered for the investigation of potential deep aquifers systems, 1) geological groups; 2) thermal springs and 3) depth of fractures. These three components should be used holistically going forward to best characterise the potential deep aquifers of South Africa.

Abstract

Soil and water pollution are major environmental problem facing many coastal regions of the world due to high population, urbanisation and industrialisation. The hydrofacies and water quality of the coastal plain-sand of part of Eastern Niger-Delta, Nigeria, was investigated in this study. Hydrogeological investigations show that the aquifers in the area are largely unconfined sands with intercalations of gravels, clay and shale which are discontinuous and, however, form semi-confined aquifers  in  some  locations.  Pumping  test  results  show  that  the  transmissivity  ranged  between 152.0 m2/day  and  2 835.0 m2/day  with  an  average  value  of  1 026.0 m2/day,  while  the  specific capacity varied between 828.0 m3/day and 15 314.0 m3/day with a mean value of 6 258.0 m3/day. Well-discharge  ranged  between  1 624.0 m3/day  and  7 216.0 m3/day  with  an  average  value  of 3 218.0 m3/day, while hydraulic conductivity varied between 3.2 m/day and 478.4 m/d with a mean value of 98.6 m/day. These findings indicate that the aquifer in the area is porous, permeable and prolific. The observed wide ranges and high standard deviations and mean in the geochemical data are evidence that there are substantial differences in the quality/composition of the groundwater within the study area. The plot of the major cations and anions on Piper, Durov, and Scholler diagrams indicated six hydrochemical facies in the area: Na-Cl, Ca-Mg-HCO3, Na-Ca-SO4, Ca-Mg-Cl, Na-Fe-Cl and Na-Fe-Cl-NO3. Heavy metal enrichment index revealed 12 elements in the decreasing order of: Fe > Ni > Cu > Zn > Mn > Cd > V > Co > Pb > Cr > As > Hg. The study identified salt intrusion, high iron content, acid-rain, hydrocarbon pollution, use of agrochemicals, industrial effluents and poor sanitation as contributors to the soil and water deterioration in the area. Saltwater–freshwater interface occurs between 5 m to 185 m, while iron-rich water is found between 20 m to 175 m. The first two factors are natural phenomenon due to the proximity of the aquifer to the ocean and probably downward leaching of marcasite contained in the overlying lithology into the shallow water table, while the last four factors are results of various anthropogenic activities domiciled in the area. The DRASTICA model, a modification of the DRASTIC model, was developed and used in the construction of the aquifer vulnerability map of the area. Modern sanitary landfill that ensures adequate protection for the soil and groundwater was designed and recommended to replace the existing  open-dumpsites.  Owing  to  the  monumental  and  devastating  effects  of  hydrocarbon pollution in the area, the need to eradicate gas-flaring and minimise oil spills in the area was advocated. Bioremediation and phytoremediation techniques were recommended to be applied in the clean-up of soils and water contaminated with hydrocarbon in the area.

 

Abstract

The CSIR has embarked on a study to investigate the potential for additional water in the West Coast, Western Cape through the application of Managed Aquifer Recharge (MAR). The benefits of MAR is that it may generate additional water supplies from sources that may otherwise be wasted with the recharged water stored in the aquifer to meet water supply in times of high demand. Determining recharge is the most important aspect of hydrological system. However, the accurate estimation of recharge remains one of the biggest challenges for groundwater investigators. Numerous studies have been conducted using geochemical methods to estimate and distinguish sources of recharge in different groundwater units of unconfined and confined aquifers internationally. The application of geochemical methods to produce accurate conceptual model describing natural recharge in aquifer units of Lower Berg River Region has not been widely published. The Lower Berg River catchment, consisting of 4 primary aquifer units (Adamboerskraal, Langebaan Road, Elandsfontein and Grootwater) will be used to demonstrate the applicability of such methods. The aim of the study is to estimate recharge in the lower berg river catchment, and develop a conceptual natural recharge model that will improve understanding of the aquifer system and be an indicator for water availability in the Lower Berg River Catchment. The objectives in developing the conceptual model includes establish groundwater recharge sources, groundwater flow paths, recharge mechanism and potential mixing of groundwater by using environmental isotopes; and obtain a reliable estimation of its recharge amount using the Chloride Mass Balance. As this study is still in progress, this publication will focus on reviewing literature and the outcomes envisioned from the project as to provide a complete understanding of the complex geology. This will lead to a better understanding of the functioning of natural recharge of the aquifer units in the Lower Berg River Catchment.

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 thgeneration 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

Records review and field based methods were used to collect and interpret groundwater level and hydro- chemical data to characterise groundwater occurrence and flow system in the Heuningnes catchment, Western Cape Province of South Africa. Our research outcome indicates that the study area has alluvial and fractured rock aquifers. The groundwater system has a rainfall driven recharge mechanisms resulting in freshwater in higher altitudes situated in the northern and western parts of the catchment. Highly saline waters are found in low-lying areas. Few samples showing high salinity water exhibit a signature of seawater although in many instances the groundwater chemistry is by and large governed by the geological formation. Groundwater potentiometric surface map shows that the general groundwater flow direction is southwards. In relation to the surface water bodies, groundwater mainly flows towards the Nuwejaars River especially in the northern and north-west part of the study area resulting in fresh water in this part of the river. As this is an ongoing study, these preliminary findings provide the required insight for further analysis and investigation. Future work will involve carrying out aquifer hydraulic tests and collection of water samples for analysis of major ions and stable isotopes. Further discussion will wait for the validation of these results to inform a meaningful implication of such findings.

Abstract

The effluent at the eMalahleni water reclamation plant is being processed through reverse osmosis which improves the quality of the mine water to potable standards. Brine ponds are generally used for inland brine disposal and this option has been selected for the eMalahleni plant. Limited capacity to store the brines requires enhanced evaporation rates and increased efficiency of the ponds. This study aims to establish the physical behaviour of the brine from the eMalahleni plant in an artificial evaporation environment. This includes the actual brine and synthetic salts based on the major components.

An experimental unit was designed to accommodate and manipulate the parameters that affect the evaporation rate of brines and distilled water under certain scenarios. Two containers, the one filled with 0.5M of NaCl and the other with distilled water were subjected to the same environmental conditions in each experimental cycle. Each container had an area of a 0.25 m² and was fitted with identical sensors and datalogger to record the parameter changes. The energy input was provided by infra-red lights and wind-aided electrical fans. This equipment used in these experiments was to simulate actual physical environmental conditions. 

The rate of evaporation was expected to be a function of humidity, wind, radiation, salinity and temperature. The experiments showed the type of salt and thermo-stratification of the pond to be significant contributors to the evaporation rate. The results also showed that the NaCl solution absorbed more heat than the water system. The difference in evaporation observed was ascribed to a difference in the heat transfer rate, which resulted in a higher temperature overall in the brine container than in the water container under similar applied conditions. This effect remained despite the introduction of 2 m/s wind flow over the tanks as an additional parameter. The wind factor seemed to delay evaporation due to its chilling effect upon the upper layers of the ponds, initially hindering the effective transfer of radiative heat into the ponds.

 

Abstract

The 2011 Olifants River Water Supply Scheme (ORWSS) Reconciliation Strategy recommended that the Malmani Subgroup dolomites along the Limpopo-Mpumalanga escarpment be investigated as a potential groundwater resource for input into the ORWSS. The Department of Water and Sanitation - Directorate: Water Resource Planning Systems (DWS D: WRPS) in turn initiated a 2-year project that began in mid- 2016 to develop a feasibility plan for the groundwater resource development of the Malmani Subgroup dolomites within the ORWSS, with the main aims of the project being: 1) to secure groundwater as a long- term option to augment the water supply to the ORWSS by optimising surface water-groundwater conjunctive use; and 2) to determine the artificial recharge potential of the dolomitic (and/or other) aquifers within the ORWSS. The ~2000 m thick, Late Archaean (~2.6-2.5 billion year old) Malmani Subgroup is comprised of stromatolite-bearing dolomites and limestones (i.e. chemical sediments including chert, with some local clastic shale and quartzite), and forms part of the Chuniespoort Group (lower Transvaal Supergroup) with the overlying banded ironstones of the Penge Formation, and mudstones, dolomites and limestones of the Duitschland Formation. The Malmani Subgroup dolomites (and Transvaal Supergroup as a whole) have undergone deformation, fracturing/faulting and dyke intrusion by a range of tectonic events (including the Bushveld Complex intrusion and slumping, Vredefort meteorite impact, “Transvaalide fold-and-thrust belt”, Pan African Orogeny, Gondwana breakup and current East African Rift development), which have resulted in the development of a high yielding (>10 l/s sustainable yields and transmissivities of ~500-2500 m2 /day per borehole in the vicinity of large regional faults/fractures or dolerite intrusions) fractured dolomitic karst aquifer. Quaternary alluvial deposits (of up to 30-40 m thickness) also occur within valleys incised into the Malmani Subgroup at Fertilis (Mohlapitse River), Penge (Olifants River and associated tributaries), Ga-Maditsi (Steelpoort River), and along the Ohrigstad, Blyde and Treur River valleys. Groundwater quality within the Malmani Subgroup dolomitic aquifers in the ORWSS area is generally good (EC of <70 mS/m), however poorer water quality can be present (e.g. elevated EC, nitrates and trace metals) as a result of contamination from human settlements, agricultural irrigation, mining, and recharge from contaminated surface water e.g. the Olifants and Steelpoort Rivers. Current work completed/being undertaken as part of the project includes: identification of two preliminary regional hydrogeological targets and twelve related wellfield target zones (WFTZ); hydrocensus of selected DWS NGA and GRIP boreholes within these two preliminary targets; re-testing of selected high yielding GRIP boreholes at constant discharge rates of 20-25 l/s, and re-analysis of existing GRIP Malmani Subgroup data; macrochemical and dissolved trace metal analysis of groundwater chemistry from tested and drilled boreholes; development of a regional groundwater balance model to determine the groundwater potential per WFTZ; surface-groundwater interaction and artificial recharge assessments (the latter focusing on alluvial deposits overlying the Malmani Subgroup dolomites); identification of potential wellfield sites within the WFTZs based on structural analysis, measured aquifer parameters, groundwater potential and geophysics; numerical groundwater modelling; and drilling/testing of exploration/monitoring boreholes within selected wellfield sites.

Abstract

Governing groundwater in a way that does not deplete the source of water, nor cause any form of degradation is a global challenge. In South Africa, scholarship shows an extensive history of groundwater governance doctrines. Yet, the country’s groundwater remained a poorly governed resource. A recent regulatory regime change culminated in the National Water Act 36 of 1998 (NWA), which was specifically promulgated to ‘provide for fundamental reform of the law relating to water resources’. While the NWA provided an ideal opportunity for the judicious governance of South Africa’s groundwater, groundwater governance remain problematic. The regulatory focus is still very much on surface water. In fact, up to date, no regulations have been made to specifically protect vulnerable aquifers, or aquifers on which communities depend as a source of water supply, or aquifers that supports large scale agriculture. This paper sets out to achieve three objectives: to assess South Africa’s existing regulatory approach to the protection of groundwater; to identify gaps in the regulatory framework; and to explore regulatory opportunities to strengthen groundwater governance. The discussion follows a focussed approach, and hinges on the case of the dolomitic aquifer of Delmas. The Delmas case study is expected to show why policy makers and planners need to be more concerned about groundwater. It will also introduce, explain and propose an established international or foreign legal measure that may be incorporated to strengthen the regulatory status of the Delmas aquifer. The paper concludes with recommendations for strengthening South Africa’s groundwater regulation.