Conference Abstracts

Abstract

In this study the groundwater resource in the Tsineng area in the Northern Cape Province was assessed in terms of the volumes of water that may be sustainably removed from the aquifer system, and the quality of the available groundwater. A strong emphasis was placed on the use of airborne and ground geophysical techniques to gain a better understanding of the geological and geohydrological conditions in the study area. The airborne geophysical technique employed during the current investigation was the time-domain electromagnetic (TDEM) method employing the SkyTEM system, while the ground geophysical surveys consisted of gravity, magnetic, frequency-domain electromagnetic and electrical resistivity tomography surveys. The geophysical techniques were used to provide information on physical changes in the subsurface conditions that may be related to the presence of geological structures associated with potential groundwater resources.

The TDEM data revealed well-defined resistivity anomalies which correlated with two known prominent fault zones. Resistivity anomalies were also identified at the locations of mapped dolerite dykes known to intersect the study area. The ground geophysical investigations were conducted across preliminary targets defined from the airborne TDEM data and confirmed the presence of the identified structures. Based on the results of the geophysical investigations and the known geological conditions, drilling targets were selected at positions deemed promising for the installation of successful production boreholes. A total of 78 exploration boreholes were drilled of which 60 had water strikes. Forty of the boreholes had blow-yields in excess of 2 L/s, with a combined total blow-yield of 409 L/s. These boreholes were selected for hydraulic tests to assess the hydraulic parameters of the intersected aquifer systems. From the estimated hydraulic parameters the total sustainable yield from the boreholes was estimated at more than 7 500 m 3 /day.

Chemical analyses of water samples from the 40 high-yielding boreholes showed that the water in the study area is generally of very good quality, suitable for human consumption. The results of the current research demonstrate that the use of geophysical techniques could greatly contribute to an understanding of the geological and geohydrological conditions in a study area, which could in turn lead to a higher success rate during groundwater exploration programmes.

Abstract

The town of Loeriesfontein, situated in the northern Cape, is entirely groundwater dependent, and is currently facing a serious water shortage. Low rainfall and the lack of storm events have resulted in groundwater levels dropping drastically. The current supply boreholes have been over abstracted and cannot meet the required demand. Water levels are close to pump depth for some of the municipal boreholes, and yields are decreasing. The town at one stage was trucking in water in order to supply its residents. Additional supplies are therefore urgently required.

A number of measures were implemented to monitor and manage the current demand and the limited supply. Thereafter GEOSS investigated the occurrence of groundwater within a 20 km radius of Loeriesfontein, and found that dolerite represents the primary target formation for groundwater exploration. Groundwater occurrence is found at the lower dolerite contact with the host rock, or in fractures in the dolerite itself. Based on an extensive hydrocensus, geophysical surveys, drilling and yield testing, the Rheeboksfontein area was identified as a suitable water source. Initially water was being trucked into Loeriesfontein from Rheeboksfontein and later an innovative arrangement of solar driven borehole pumps and reservoir pumps resulted in water being transported much closer to Loeriesfontein, reducing the transportation distances and costs.

During this first Phase of exploration the projected supply still did not meet the water demand and water quality targets. A number of high yielding boreholes were drilled, however the water quality was such that it would have required treatment and disposal of brine in that area is problematic. The extent of the exploration was then increased to a distance of 40 km from Loeriesfontein. A detailed hydrocensus was completed, followed up with further geophysical surveys, drilling and yield testing. Successful boreholes were drilled and the required demand and water quality standards could just be met. This finding is being verified with numerical modelling.

A process is underway to develop a mini-wellfield and then the environmental processes are being followed so that a pipeline can be built delivering water directly into the reservoirs at Loeriesfontein. On-going monitoring and maintenance is crucial to the long-term success of the groundwater supply.

Abstract

The Heuningvlei pipeline scheme was built in the 1980s to supply water to rural communities in a low rainfall area (<300 mm/annum) – Northern Cape Province. In 2008, the Joe Morolong Local Municipality identified the need to refurbish and upgrade the pipeline scheme for socio-economic reasons. The safe yield and water quality information of existing sources supplying the scheme was unreliable. This was investigated by borehole test pumping and water quality sampling, which indicated reduced yields and deteriorating water quality since 1989.

Water demands, which includes supply to communities for domestic use, schools, clinics and stock watering in the Heuningvlei area, was estimated at 2 380 m3/day or 868 700 m3/annum. The potable groundwater  supply  recommended  from  11  existing  boreholes  is  316 937 m3/annum,  leaving  a deficit of 551 763 m3. The aquifers utilised for the existing water supply comprise fractured banded iron formations (BIF) and dolomite bedrock. Kalahari sedimentary and dolomite aquifers to the east of the pipeline scheme contain high saline water not suitable for domestic use.

No surface water sources exist in the area and the feasibility of the socio-economic development project depends on establishing local groundwater resources that would not impact on existing sources. A target area was identified which is approximately 10 km south from the pipeline. This area is covered by the thick Kalahari sediments (up to 130 m) underlain by dolomite bedrock with a potable groundwater balance of 2.3 million m3/a. Both the associated primary (Kalahari) and secondary (Dolomite) aquifers contain potable water. The target area was not investigated in the past due to perceived poor water quality (elevated salinity) conditions, very low (<10 %) borehole exploitability prospect and difficult drilling conditions.

The paper will discuss the importance of recharge estimate and understanding of flow regime at sub-catchment and local scale, use of an airborne magnetic survey in conjunction with ground geophysics, mapping of Kalahari sediment thickness, and successful drilling of exploration boreholes to exploit the deeper Kalahari sedimentary and dolomite bedrock aquifers. The successful development of localised potable water in a low rainfall area made it feasible to implement the Heuningvlei socio-economic development project.

Abstract

Hydrogeological mapping was first attempted in Kuruman River Catchment, Northern Cape Province, South Africa. The main geology underlying the area of study includes sediments of the Kalahari Group, limestone and dolomite of the Transvaal Supergroup, lavas of the Ventersdorp Supergroup, and Archaean granite and gneiss. The main objective of this study was to produce hydrogeological maps on a scale of 1/100 000. Demarcation of different aquifer types was done by analyzing factors that control groundwater occurrence. These factors include lithology, geological features such as fault and lineaments, groundwater levels, and groundwater chemistry. Four types of aquifers were identified: o - Intergranular aquifer, associated with alluvial and pluvial deposits. o - Intergranular and fractured aquifer, associated with weathered igneous and sedimentary rock. o - Fractured aquifer, dominated by basal formations. o - Karst aquifer, associated with the dolomitic formations. The groundwater quality in the four demarcated aquifers was assessed to determine the current groundwater status. Groundwater chemistry was measured by collecting groundwater samples from boreholes. Physical parameters such as pH, temperature and electrical conductivity were measured in-situ using an Aquameter instrument. The samples taken were analysed at MINTEK laboratory using Inductively Coupled Plasma Mass Spectrometry, Ion Chromatography, and Spectrophotometer for cations, anions and alkalinity respectively. The results obtained indicated sodium chloride water type in fractured aquifer, while calcium carbonate water type was identified in intergranular aquifer, karst aquifer, and intergranular and fractured aquifer. In conclusion, high concentration of Nitrate, Magnesium, and Calcium was seen in all the four aquifers. High concentration of nitrate is due to stock farming, whereas high concentration of Magnesium and Calcium is due to geology. Moreover, high concentration of mercury due to mining activities was picked in intergranular aquifers, karst aquifers, and intergranular and fractured aquifers.

Abstract

POSTER The areas studied in this paper are situated in semi-dry regions of Limpopo and Northern Cape Provinces of South Africa. Groundwater is the only dependable source of water for many local users and farming communities. The growing population is putting immense pressure in the current water resources, hence a need to find new groundwater resources. The areas are most dominated by fractured rock aquifers which accounts to over 90% of South African aquifers. Finding sustainable sources of groundwater in these regions is often a challenge due the complex nature of the fracturing network system of fractured aquifers. This study uses a supervised committee learning with artificial neutral network (SCLANN) model to improve the regional groundwater exploration in granitic basement terrains and valley controlled aquifers in metamorphic terrains of South Africa. The data used in the study was obtained from the national groundwater archive and interpretation of high resolution aeromagnetic data, ground surveys and remote sensing datasets. The artificial neural network (ANN), Fuzzy (F) and Neuro-fuzzy (NF) unsupervised models whose input were groundwater controlling parameters like regolith thickness, lithology, relief, faults, lineament density, lengths of lineaments was used. The results from the ANN, F and NF models were used as inputs to a nonlinear supervised SCLANN framework with the borehole yield as the training and validation outputs. Borehole yield was used as it is one of the measurable parameter that directly related to productivity of groundwater resources. The use of the unsupervised models improved the results significantly as the SCLANN model results as a combined advantage of the individual models to achieve the optimal high performance. The results show that the three models used to build a SCLANN model was able to improve the identification of potential groundwater targets at regional scales. This approach can be incorporated in regional groundwater exploration programs to improving drilling success rate on granitic basement and metamorphic terrains in South Africa. The results show that the SCLANN outperforms individual unsupervised models. However the SCLANN results for granitic basement terrains were far much better than the metamorphic terrains probably showing the limitation of the approach in metamorphic terrains.

Abstract

Wiegmans, FE

The increasing water demand for the Northern Cape Province resulted in the detailed assessment of the exploitation potential of three groundwater development target areas namely SD1, SD2 and SD4, largely underlain by karst aquifers. Since 2014 the implementation of the wellfields was delayed pending authorisation. The potential impact on the groundwater resources was raised by several stakeholders as part of the process, resulting in the re-assessment of the SD1 and SD2 wellfields. The model update considered crucial data retrieved from several groundwater level loggers from April 2014 to December 2019. As a precursor to the model update the Cumulative Rainfall Departure (CRD) curves for the relevant rainfall stations for the study areas was updated. While for most sites a good relationship between rainfall and groundwater fluctuations was observed. A poor response of groundwater levels in comparison to the observed CRD curve suggests abstractions more than the recharge of the aquifer. Metered groundwater use is for most parts not available but was estimated based on the hydrocensus data. Once the models demonstrated to reproduce past behaviour, they were used to forecast the future behaviour. More importantly was to assess whether the 2014 proposed abstraction rates still held true after the re-calibration of the model. Several simulations were carried out iteratively to identify the optimal pumping rates and the temporal variability of the withdrawal period considering the impact on the groundwater resource. Based on the results the 2014 proposed production rates were reduced from 751,608 m3/month to 597,432 m3/month representing a 2019 mitigated (optimised) proposed abstraction scenario. The case study is an excellent example of adaptive groundwater management informed by crucial datasets and scenario modelling.

Abstract

Multi-data integration approach was used to assess groundwater potential in an area consisting crystalline basement and carbonate rocks that are located in the North West Province of South Africa. The main objective of the study is to evaluate the groundwater resource potential of the region based on a thorough analysis of existing data combined with field observation. Integration of six thematic layers was supplemented by a statistical analysis of the relationship between lineaments density and borehole yield. Prior to data integration, weighting coefficients were computed using principal component analysis.
The resulting thematic layer derived from integration of the six layers revealed a number of groundwater potential zones. The most probable groundwater potential zones cover ~14% of the entire study area and located within carbonate rocks consisting limestone and dolomite. The presence of pre-existing structures together with younger and coarse sedimentary rocks deposited atop the carbonate rocks played a significant role in the development of high well fields in the southern part of the area. Moderate-to-high groundwater potential zones within Ventersdorp lava coincide with maximum concentrations of fractures. The results of statistical correlation suggest that 62% of high borehole yield within the Ventersdorp lave can be attributed to fracture density. In general, the present approach is very effective in delineating potential targets and can be used as a sound scientific basis for further detailed groundwater investigation.
KEY WORDS:- Multi-data, thematic layers, groundwater, carbonate rocks, structures

Abstract

Aurecon was appointed to conduct groundwater exploration for production well fields in the towns of Setlagole and Madibogo. These towns are located in an arid part of the North West province on the edge of the Kalahari. The landscape is flat and covered by aeolian sand underlain by basement granite of the Kraaipan Group Geology.
Historically groundwater exploration consisted of reconnaissance geophysical surveys followed by detail ground surveys. Where no potentially water bearing geological structures are shown on geological maps & aerial photos, the project area would be divided into a grid on which the ground geophysical survey would be done. This type of exploration is time consuming and expensive. In some cases the terrain or cultural noise prohibits the use of conventional geophysical methods, with only more expensive and time consuming methods being left as an option. This is where the high resolution airborne magnetic survey excels. The results obtained from this type of survey are of such nature that only a small amount of ground geophysics is necessary to locate drilling targets. This survey method is also cost effective allowing a larger area to be covered in a short amount of time as compared to conventional ground techniques.
This paper will discuss successes achieved using high resolution aeromagnetic surveys as the basis for groundwater exploration in traditionally low-yielding igneous geology.

Abstract

POSTER The poster presents the spatial-temporal assessment of groundwater-surfacewater (GW-SW) aspects in Skoonspruit River catchment, North West of South Africa. Despite the common use of quantitative methods to assess various aspects of GW-SW interaction, the use of qualitative methods remains poorly understood in assessing aspects of GW-SW interaction especially in the context of developing countries such as South Africa. While quantitative methods are envisaged to provide reliable and valid results,the use of qualitative methods are exploratory, site specific and more revealing to provide insights for more robust confirmatory methods. Such approach remains fundamental to comprehensive assessments that facilitate relevant generation of information to decision makers to enable them develop and improve interventions for the desired water utilization and management practice. However, the use of such qualitative methods in GW-SW interaction studies has not been applied, a situation which limit the basis for applying quantitative methods and that make quantitative methods not yield the desired results in most studies. The current study argues that the use of quantitative methods should be informed by the results from the qualitative methods and that the poor results from the GW-SW interaction studies is partly due to lack of implementing the qualitative methods prior to using the quantitative methods, especially in the context of developing countries such as South Africa. The current study established spatial variation in the water-type of the upper and lower catchment for both groundwater and surface water. Characterized water-type for several site specific reaches and determined the temporal trends for GW-SW interaction process in order to produce a comprehensive scenario for spatial-temporal pattern for GW-SW interaction in the Skoonspruit River catchment of North West to inform desired interventions for water use and management.
Key Words: Qualitative methods, Quantitative methods, Spatial-temporal assessment, GW-SW interaction, Water use and management, Skoonspruit River catchment, North West

Abstract

Environmental isotope and hydrochemical analyses were employed to improve existing understanding of groundwater flow dynamics in the defunct mine for assessing the source of water at a pumping shaft located near Stilfontein Town, Northwest Province, South Africa. Currently pumping is done using the shaft at an average rate of 37,000 m3 /day to prevent flooding of downstream mines. The current findings point out that the source of water at the shaft comes from a much narrow area than previously reported and that the contribution of seepage water from a nearby return water dam is significant enough to compensate groundwater flow from the upper dolomite aquifer and limit northerly expansion of the cone-of-depression. Hydrochemical data reveals that shaft-water at deeper levels (950 m bgl) exhibit evidence of mine seepage originating from the nearby tailings dam. The isotope data also show that up to 45% of water is recycled between shaft water and the surface water. Tritium values of the shaft-water samples are above 4 TU suggesting recent recharge is taking place at deeper levels through open fractures and mine underground haulages. The information from the hydrochemical and environmental isotope data was used to improve an earlier understanding that the source of water as coming dominantly from dolomite aquifer. Finally, the results highlight the relevance of coupling various methods to check the result of numerical modelling, and indeed the centralized pumping is key to controlling subsurface water flooding in downstream mines, a successful implementation of regional mine water management.

Abstract

The North West Province has produced a large portion of South Africa’s inland alluvial diamonds. Kimberlite intrusions are typically the parent source for the alluvial diamonds. Diamondiferous kimberlite intrusions were eroded over time by surface run-off and streams which transport the diamondiferous sediments downstream to depositional regimes. The diamondiferous alluvial deposits around Schweizer- Reneke were mostly deposited on magmatic rock of the Ventersdorp Supergroup. Formal alluvial mining in the area often requires a considerable amount of overburden material to be removed in order to access the coarser gravel beds which contain the economic grade diamonds. Diamond production from secondary sources in this region totalled approximately 14.4 million carats up to 1984, and small scale production persists today.

The case study focuses on the impacts of alluvial diamond mining operations on surface- and groundwater resources in the North West Province, South Africa. To recover diamonds from the sediments, the industry is currently focussing on using modern processing methods and a more clinical approach to increase the sustainability of mining, therefore minimizing the impact on the environment. Wastewater from the screening and the fines management phase is delivered to the primary water treatment phase where up to 70% of process water is recirculated to the processing plant, minimising the volumes of fresh water required. The settled sludge or waste is deposited on a tailings storage facility. Alluvial diamond mining operations, unlike many other industrial processes and types of mining, have a lower environmental hazardous risk associated with waste material, however, it is a possibility that leachate emanating from tailings often have a high salt content. The process raw water to these operations are supplied from both surface- and groundwater sources from the local area. Supplying processing raw water in a sustainable manner is often a challenge in drought stricken areas with limited surface flow and low aquifer potential.

Abstract

This paper follows on current research taking place in the Springbok Flats Basin focusing on Carbon Dioxide Geological Sequestration within coal seams. The research, commissioned by ESKOM, began in 2012 and has a primary aim of producing a hydrogeological risk assessment for carbon dioxide geological sequestration operations scheduled for national pilot testing within the basin. One of the fundamental tools used in the assessment has been finite element mesh modeling. A 3D finite element mesh model of the study area, that has 11307 nodes, has been generated using FEFLOW algorithms. Portions in the study area without linear and point physical features have been modeled with the Advancing Front Algorithm, while the Grid Builder Algorithm has been used to model portions with linear and point features. This paper has investigated the node angle accuracy and precision of the mesh model by generating a map of the maximum interior angle of triangles. Approximately 70 % of the triangles have equilateral angles, while the remainder triangles have obtuse angles. The majority of the equilateral triangles occur within the portions modeled with the Advancing Front Algorithm. Half of the obtuse triangles have been refined to equilateral triangles with the FEFLOW refinement tools while the other half has been refined manually with the node digitizing features. FEM models perform better with dense triangle matrices with equilateral angles, as they influence the accuracy of the FEM.

Abstract

This study was carried out in Lagos State, southwestern Nigeria. It is a coastal city that lies approximately between longitude 30 13’30”E and 30 17’15”E and between latitude 60 28’N to 6 0 42’N. The study assessed the groundwater pollution risk using geophysical methods and the concepts of Dar Zarrouk parameters as veritable tools. Resistivity measurement was taken at twelve (12) vertical electrical sounding (VES) stations and along eight (8) 2D resistivity profiles using the Schlumberger array and dipole-dipole array respectively. The VES data were processed using IP2Win computer iteration software. The geoelectric model from the interpretation revealed four/five geo-electric layers. These include: Top sandy layer with resistivity and thicknesses ranging from 2.29-1915 Ωm and from 0.46-4.55 m respectively. The second layer is mostly clay soil of varying degree of saturation which is obvious from its resistivity behavior. This layer has a minimum resistivity of 3.52 Ωm at VES1 and maximum resistivity of 20 Ωm at VES6. Also, the thickness of this layer varies from 1.85 m at VES9 to 7.32 m at VES6. The third/fouth layers delineated are clay and clayey sand/sandy clay. However, the highest thickness value of 43.1m for clay occurred at the third layer at VES10. The apparent resistivity of this layer varies from 1.61 Ωm to 265 Ωm and varies inversely with the clay content from 16.3 m to 33.3 m. Also the thickness of this layer varies from 4.8 m to 45.3 m. The 2D resistivity data (dipole-dipole) acquired along Oniru, Elegushi, and Adeniji were processed using RES2D. Along Oniru traverse 1, low resistivity zones diagnostic of contaminant plume was observe at distances between 12 m to 30 m and also, an isolated plume of contaminants deducible from low resistivity occur along traverse 3 at depth below 30 m. At Elegushi , vertically migrating plumes of contaminant indicated by low resistivity zones equally occur at distance between 320 m along traverse 1 and spread towards the centre from the western and eastern parts of the traverse respectively. Furthermore, pockets of contaminants are also observed all along the distance between traverse 2. However, at Adeniji, a plume was only observed at 384 m along the same traverse. The longitudinal conductance and the corresponding vulnerability of the lithologies delineated in the study area shows that the longitudinal conductance and protective capacity of clay is maximum at VES10 with a value of 26.7702 Ω-1 at a depth of 65.6 m. Therefore, the sand aquifer confined by clay is the least vulnerable in the study area. This is because the highly impervious clayey overburden, characterized by relatively high longitudinal conductance, offers protective shield to the underling aquifer. However, sand being the most vulnerable,has the least values of longitudinal conductance ranging from 0.6884 Ω-1 at VES11 to 0.0006 Ω-1 at VES2. The vulnerability sandy clay/clayed sand are of intermediate value and the risk improves/reduces with increasing clay content.

Abstract

The quality of groundwater is influenced by the chemistry of the rocks through which it migrates. The rock types in an area, particularly their weathered products and rainfall contribute greatly to the chemistry of groundwater. The present study examines the impact of bedrock on the chemistry of groundwater from shallow granite aquifers in Northern Nigeria. Groundwater samples from northeast (Hong), northwest (Zango) and Northcentral (Ogbomosho) were collected and analyzed for relevant water quality parameters. The concentration of fluoride (0.0-3.50) and some heavy metals such as iron (0.3-4.6), nickel (0.1-0.98), copper (0.0-.85), lead (0.001-0.4.0), Manganese (0.00-1.4) and arsenic (0.0-0.76) were slightly higher than their recommended maximum permissible limit in some locations and the observed anomalies can be attributed to geogenic influence as no visible industries are domiciled in these areas. Based on these signatures, the geochemical evolutions of groundwater from the three locations were quantitatively described by the interaction with rock-forming minerals released into the groundwater system through natural processes of weathering and dissolution in the flow-path. This is a testimony to the fact that groundwater can be grossly contaminated with critical elements by natural means. Analyses of rock samples from these locations revealed the presence of nacaphite, a fluoride rich mineral as well as arsenic, nickel, copper, lead and iron. The observed concentration ranges of fluoride and heavy metals are a reflection of the natural background concentration and a landmark in geochemical characterization of groundwater system in these areas. The enrichment trend is in the order of Zango > Hong > Ogbomosho. This implies that the granites in the area are composed of mineral containing these elements. Communities living in the granite/rhyolite dominated region where cases of fluorosis and heavy metal contamination have been observed should discontinue the use of groundwater from the area for domestic and drinking purposes. The Government should provide an alternative source of drinking water for the people.

Abstract

The manner in which municipal and industrial wastes generated are disposed in the urban areas in Nigeria is worrisome. The practice of dumping solid wastes in abandoned burrow-pits or valley and the discharge of liquid wastes directly on soils or surface water without any form of treatment has resulted in soil and water pollution. The continuous release of dangerous gases into the atmosphere by industries unabated has contributed to air pollution. These inadequate waste disposal techniques have created serious environmental and health challenges. Due to increasing population growth rate, urbanization, industrialization and economic growth, there has been a phenomenal increase in the volume of wastes generated daily and handling of these wastes have constituted an environmental problem. The need to manage these wastes in an environmentally-friendly manner that will guarantee safety of the soil and water resources lead to the present study. The newly designed waste management landfill incorporates advanced features such as complex multiple liner construction to facilitate organic decomposition and maintain structural integrity. The multiple protective layers and regular monitoring ensure that the waste management landfills exist in harmony with their surrounding environments and communities. These features that enhances maximum protection of soil and water from contamination by plume by decaying waste is lacking in the un-lined open waste dumps been practiced in the country. Pollution abatement, waste reduction, energy saving, health and economic benefits are some of the advantages of the newly designed sanitary landfill system.

Abstract

The Dahomey Basin is a transboundary sedimentary basin with its eastern half in south western Nigeria. The vulnerability assessment of the basin was carried out to ascertain the degree of the shallow unconfined aquifers sensitive to groundwater contamination through the investigations of the intrinsic properties of lithology over the unconfined aquifer systems. The basin is a multi-layered aquifer system hosting large population densities particularly in Lagos where nearly half of the population rely on the groundwater for domestics and industrial purposes. The vulnerability evaluation involves determining the protective cover and infiltration condition of the unsaturated zone in the basin. This was achieved using the PI vulnerability method of the European vulnerability approach. The PI method specifically measures the protection cover and the degree to which the protective cover is bypassed. Intrinsic parameters assessed were the subsoil, lithology, topsoil, recharge and fracturing for the protective cover. While, the saturated hydraulic conductivity of topsoil, infiltration processes and the lateral surface and subsurface flow were evaluated for the infiltration bypassed. The results were depicted in vulnerability maps. Map of the protective cover ranges from high to very high. This means a very effective cover over the groundwater resources. The I map revealed a low to very low degree of bypass. The final vulnerability map shows that the Dahomey Basin vulnerability ranges from moderate to very low vulnerability areas. Low vulnerability areas were characterised by lithology with massive sandstone and limestone, sub soils of sandy loam texture, high slopes and high depth to water table. The moderate vulnerability areas were characterised by high rainfall and high recharge, low water table, unconsolidated sandstones and alluvium lithology. The vulnerability map was validated with hydrochemical properties of the groundwater. Chloride and TDS concentration of the groundwater reveals high chloride concentration for low groundwater vulnerability areas while low chloride concentrations were observed for moderate vulnerability areas. Low to moderate groundwater vulnerability areas show low TDS concentrations according to the WHO standards except for the coastal areas with relatively higher TDS concentrations. The groundwater vulnerability maps will be a useful tool for planning land use activities which will minimise groundwater contamination and enhance the protection of the Dahomey Basin groundwater resources.
{List only- not presented}
Keywords: PI method, Dahomey Basin, aquifer vulnerability, protective cover, groundwater resources.

Abstract

Based on a modified DRASTIC model and GIS techniques, shallow groundwater vulnerability assessment was carried out in the Federal Capital City of Abuja, Nigeria. The results indicate that the studied area can be divided into three zones, namely: low groundwater vulnerability zone (vulnerability index <100) which covers about 60% of the City; moderate vulnerability zone (vulnerability indexes 100-140) which covers 35% of the City and high vulnerability zone (vulnerability index >140) which covers only 5% of the City. The highest groundwater vulnerability zone mainly locates in the central solid waste disposal site area in the outskirt of the City. The findings correlate well with the results of the physicochemical and microbiological investigation. The general low contamination vulnerability signature of the City may be attributed to absence of industries, limited agricultural activities, and preponderance of clayey top soil which effectively forms the first defence against contamination of the underlying aquifers as well as the presence of central sewage collection facility that covers about 25% of the City.

Abstract

VLF-Electromagnetic and geoelectric soundings were carried out at Ibuso-Gboro area via Ibadan, Oyo state. The objective was to delineate the groundwater potentials of the area. VLF-Electromagnetic method was adopted for reconnaissance survey with a view to locating bearing fractured zones in the basement bedrock. Sixteen (16) VLF-Electromagnetic profiles whose length ranges from 90-290 m were occupied with station interval of 10 m. The VLF-Electromagnetic results were presented as profiles. Linear features, suspected to be fractured zones, which were from the anomaly curves of the VLF-Electromagnetic were delineated in seven localities along the profiles. These localities were further confirmed by Vertical Electrical Soundings (VES). The seven Schlumberger Vertical Electrical Soundings (VES) were occupied with the electrode spacing (AB/2) varying from 1 m to 100 m with the total spread length of 200 m. The VES data were presented as sounding curves and interpreted by partial curve matching and computer assisted 1-D forward modeling. The results were presented as geoelectric sections, which showed the subsurface geoelectric images. Two out of the seven delineated linear features were test drilled and the fractured zones were met at depth range of between 25.0 m and 38.2 m beneath borehole (1) and 43.0 m and 52.1 m beneath borehole (2) for confined fractured. The pumping test analysis revealed borehole yield varied from 4.8 m3/hr and 5.2 m3/hr, where three (3) abortive boreholes had earlier been drilled. {List only- not presented} Key Words: VLF-Electromagnetic, Linear features, Geoelectric Soundings and Pumping test.

Abstract

Abstract

Electromagnetic (EM) techniques were used to map groundwater salinity and clay layers in the Netherlands. The EM method used the so-called time domain system, is towed behind an ATV and is therefore called towed TEM. The results revealed a detailed 3-dimensional insight into the subsurface’s sequence of clay and sandy layers. Also, shallow saline groundwater, far from the coast, has been detected related to a subsurface salt dome. The rapid, non-destructive data acquisition makes the tTEM a unique tool. Electromagnetic (EM) techniques detect electrical conductivity contrasts in the subsurface with depth. EM data can often be interpolated into a 3D model of electrical conductivity. Expert knowledge of the regional geohydrologist, together with existing (borehole) data, is paramount for the interpretation. The towed Transient Electro-Magnetic system (tTEM) is developed to acquire data up to 60-80m depth by driving a transmitter and a receiver behind an ATV. With a speed of 10-15 km/h, measurements are collected every 5m. On fields, the distance between lines is typically 20m, resulting in a dense network of data that is inverted into 1D resistivity models, showing the variation of conductivity with depth. Interpolating 1D resistivity models into a 3D model allows for further interpretation in terms of geology, lithology, and groundwater quality. The tTEM technique bridges the gap between point measurements and more expensive and lower-resolution airborne EM data collection. The technique is sensitive to disturbance by man-made conducting infrastructure.

Abstract

Faced with climate change and population growth, Dutch drinking water company Dunea is looking for additional water resources to secure the drinking water supply for the coastal city of The Hague. One of the options is to enhance the existing managed aquifer recharge (MAR) system in the coastal dunes by extracting brackish groundwater. Extracting brackish groundwater provides an additional drinking water source, can protect existing production wells from salinization, and can effectively stabilise or even grow the freshwater reserves in the coastal dunes, according to numerical groundwater modelling. To test this concept in the field, a three-year pilot commenced in January 2022 at Dunea’s primary drinking water production site, Scheveningen. Brackish groundwater is extracted at a rate of 50 m3 /h with multiple well screens placed in a single borehole within the brackish transition zone (85-105 meters below sea level). The extracted groundwater is desalinated by reverse osmosis, whilst the flow rate and quality of extracted groundwater are continuously monitored. The hydraulic effects and the dynamic interfaces between fresh, brackish and saline groundwater are monitored with a dense network of piezometers, hydraulic head loggers and geo-electrical measurement techniques. At the IAH conference, the monitoring results of the pilot will be presented. Based on the results of the field pilot and additional numerical modelling, the feasibility of upscaling and replicating the concept of brackish groundwater extraction to optimize MAR and increase the availability of fresh groundwater in coastal areas is reflected.

Abstract

The National Environmental Management Waste Act, 59 of 2008 (NEMWA) clearly identifies the status and risk of contaminated sites and provides a legislative mechanism for remediation activities to be implemented and controlled. The Draft National Framework for the Management of Contaminated Land (henceforth Framework) provides national norms and standards for the practical implementation of remediation activities in compliance with NEMWA. A soil-screening value (SSV) for the protection of water resources is based on a two-phase equilibrium partitioning and dilution model which includes a dilution factor (DF) and partitioning coefficient (Kd) which converts the water quality guideline to a total soil-screening value. This paper presents a methodology to use soil-specific Kd  values to improve the accuracy of the new South African guideline for contaminated land.

Appropriate Phase 1 screening assessments are important due to the potential consequence it holds. Some uncertainty exists in the Phase 1 screening values due to variability in Kd values for different soil. This study shows that the Kd  values selected for the Framework is not representative of typical South African soils. Cu Kd values exceed the value provided by the Framework in all soils, but are lower that the Framework V Kd value in all soils. For Pb, low clay content weathered soils have lower Kd, but higher clay content soils are up to four orders of magnitude higher that the Kd in the Framework. Furthermore, due to the large variability (three to four orders of magnitude for Cu and Pb) point estimates of a single Kd value cannot be used for all soil types. However, for V only one order of magnitude variation is found. 

A way of addressing the uncertainty would be to determine the water soluble portion during the assessment. This would dramatically increase the certainty with which screening is conducted and could prevent significant inappropriate screening. Additional cost incurred be offset by saving as a result of unnecessary Phase 2 assessments or the reduction of undetected risks that later could impact the environment. 

Phase 1 screening could also be improved by including soil classification and some basic soil properties in the site assessment and adjusting Kd values, accordingly. Soil properties that can be used are typically clay content, pH and organic matter content. From these properties more appropriate Kds can be estimated for use in setting screening values.

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

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

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

Abstract

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

Abstract

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

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

Abstract

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

Abstract

The benefits of numerical groundwater modelling in resource management and scenario-testing are well known; it provides quantitative predictions of aquifer responses to stresses not yet experienced, albeit with uncertainties. Modelling is hence a widely used tool in Environmental Impact Assessment (EIA), in which prior to project commencing, the likely impacts must be assessed quantitatively to determine their significance. Based on these results mitigation measures can be proposed such that the residual impact is deemed acceptable.

At the stage of an EIA there is often very little data on which to base a model. Generally one is required to predict timescales in the order of hundreds of years with only very short-term time series data, and required to predict the response to stresses far beyond those used in the calibration. The very nature of the problems posed at EIA stage therefore render the accuracy of most modelling conducted at EIA phase severely limited. Recognising this, an appropriate model for the problems at hand can still be constructed and provide useful results.

The model results need to  be seen  as  the first phase  in  an  adaptive management cycle, rather than  a standalone prediction which a mine can use for future operation. To strengthen the resulting predictions, the cycle in which monitoring results are used to update the model, and thus update predictions and update future requirements for monitoring repeating the cycle, needs to be entrenched into the mine phases by ensuring the recommendation as detailed in the Environmental Management Plan. Thus, what started as a useful demonstrative tool, but with large uncertainties, becomes an accurate quantitative prediction tool for operation, closure and post-closure planning.

This paper outlines a case study of a proposed open-pit zinc mine on an inselberg in South Africa, within which these themes are explored. Limited initial data was sufficient to build a useful yet simplified model. The purpose and known limitations of the model approach dictated the spatial discretisation of the model, its dimensions, and the geometry of the aquifer units, yet the simplification of the aquifer systems into the numerical model was only feasible once the complexity of the aquifer systems had been recognised, else over- or unjustified simplification is a risk.

The paper concludes with a framework for integrating the adaptive groundwater management into the mine life cycle through applying appropriate models at each phase, which would strengthen the use of groundwater models in mining.

Abstract

Water plays a significant role in the economies of the agricultural, business and industrial sectors. Expanding populations, economies and climate change have put pressure on the quality and availability of water resources in South Africa, therefore water resource protection becomes increasingly important for sustainable water supply management. Hence, a review of the state-of-the-art of water resource protection in South Africa has been undertaken on behalf of the WRC, applying the water resource governance framework. Gaps in scientific understanding and implementation with regards to water resource protection have been identified through literature review and discussions with stakeholders and experts. Aiming to improve the water resource protection in South Africa, a research strategy has been developed to tackle the most relevant of the identified gaps. The legislation in South Africa with respect to water resource protection is state-of-the-art and one of the best in the world. However, there is still space for improvement in that the different acts need to be aligned better to facilitate cooperative governance and improve the implementation of the legislation. Regulations and guidelines are plentiful covering most of the relevant activities and various water resources. The main challenge for implementing the intent of the National Water Act with respect to groundwater resource protection is that the standard methodology for determining Resource Directed Measures (RDM) was developed for surface water resources and is not applicable to groundwater or wetlands. Furthermore, classification and Reserve determination are mostly carried out at a scale that is insufficient for effective groundwater resource protection. The methodology requires update to incorporate potential impacts of climate change, changing land use and changing demographics. The different elements of the RDM methodology need to be aligned. There is also often an insufficient spatial and temporal distribution of monitoring networks to effectively manage groundwater resources. Integrated catchment management can provide a solution to the current state of water resource protection. However, this must be based on a scientific understanding of the complex natural system. The different challenges, research needs and possible solutions are demonstrated on a case study of Stanford Aquifer.

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

Variability in both rainfall and raw water demands at South African mines and lack of accurate predictive planning tools often leads to water shortages or spillages of excess dirty water. The demand varies due to changing production rates, scheduled and unscheduled maintenance, while available water resources are greatly influenced by droughts and untimely storm events. Using averages in static water balances or planning for “worst case scenarios” by increasing storm water capacity or securing larger volumes from external sources “for in case”, is expensive and could still be inadequate.

A dynamic simulation model can integrate all the variables above with available ground- and surface water resources. Groundwater is  often underestimated as  a  source.  A  simulation model can  test  strategies to optimise its role before expensive dams or pipelines are considered.

In the case studies presented, Arena simulation software (from Rockwell) are used with hourly time steps to dynamically simulate water flows/levels, evaporation, seepage and rainfall runoff. All flows and dam levels are recorded to Excel for statistical analysis after simulation runs. To calculate the significance of overflow events and maximum demands the model runs multiple iterations which render specific confidence intervals for results, for example a 95% confidence level that a specific dam will not overflow more than once during the life of mine. Models may span several shafts, concentrator plants and smelter complexes. One model integrated over 1 000 flows and 75 dams with respective flow logic on the backdrop of a Google map of operations. Highlights of recent case studies include: 

• Groundwater from shallow anthropogenic aquifers greatly reduced external raw water requirements.
• This also prevented the clean water from overflowing into the underground workings where it is then pumped from depth as dirty water. 
• Artificial recharge of an aquifer with sporadic excess surface water increased the groundwater in storage that was used as a buffer for drought periods. 
• Optimised models proved that external raw water requirements and overflows into the environment could be significantly reduced and in some cases eliminated.

A dynamic water balance simulation model integrates business components with all related flows and storages and is the best tool available to accurately predict water resource demands and overflows to the environment. It enables the testing and optimization of water management strategies long before capital is spent and enhances the understanding, buy-in and decision support for all affected parties.

A picture is worth a thousand words... A (good) simulation is worth a thousand pictures!

Abstract

In recent years there is an increased awareness of hydrocarbon contamination in South Africa, and the need for remediating sites affected by these contaminants. Hydrocarbon contamination of groundwater can be caused by a large variety of activities at industrial, mining or residential areas. Once these contaminants are discovered in groundwater where it poses risks to human health and/or the environment, remediation is often required. Remediation of groundwater has become a booming industry for groundwater practitioners and often there is an attitude of more sophisticated and expensive solutions are better. This paper will show that this attitude is not always the best solution, but rather recommend an approach where a combination of low cost/low maintenance system need to be investigated and applied to reach clean-up goals. Determination of natural attenuation potential and on-going monitoring forms an integral part of this type of solution.

Abstract

This study explores some of the principle issues associated with quantifying surface  water and groundwater interactions and the practical application of models in a data scarce region such as South Africa. The linkages between the various interdependent components of the water cycle are not well understood, especially in those regions that suffer problems of data scarcity, and there remain  urgent  requirements  for  regional  water  resource  assessments.  Hydrology  (both  surface water and groundwater hydrology) is a difficult science; it aims to represent highly variable and non- stationary processes which occur in catchment systems, many of which are unable to be measured at the scales of interest. The conceptual representations of these processes are translated into mathematical form in a model. Different process interpretations, together with different mathematical representations, result in the development of diverse model structures. These structural uncertainties are difficult to resolve due to the lack of relevant data. Further uncertainty is introduced  when  parameterising  a  model,  as  the  more  complex  the  model,  the  greater  the possibility that many different parameter sets within the model structure might give equally acceptable results when compared with observations. Incomplete and often flawed input data are then used to drive the models and generate quantitative information. Approximate implementations (model structures and parameter sets), driven by approximate input data, will necessarily produce approximate results. Most model developers aim to represent reality as far as possible, and as our understanding of hydrological processes has improved, models have tended to become more complex. Beven (2002) highlighted the need for a better philosophy toward modelling than just a more explicit representation of reality and argues that the true level of uncertainty in model predictions  is  not  widely  appreciated.  Model  testing  has  limited  power  as  it  is  difficult  to differentiate  between  the  uncertainties  within  different  model  structures,  different  sets  of alternative parameter values and in the input data used to run a model. A number of South African case studies are used to examine the types of data typically available and explore the extent to which a model is able to be validated considering the difficulty in differentiating between the various sources of uncertainty. While it is difficult to separate input data, parameter and structural uncertainty, the study found that it should be possible to at least partly identify the uncertainty by a careful examination of the evidence for specific processes compared with the conceptual structure of a specific model. While the lack of appropriate data means there will always be considerable uncertainty surrounding model validation, it can be argued that improved process understanding in an environment can be used to validate model outcomes to a degree, by assessing whether a model is getting the right results for the right reasons.

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

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 Department of Water and Sanitation reviewed and re-designed (optimised) the national water resources monitoring networks. During the re-design, monitoring objectives were formulated and prioritised. The highest priority, i.e. to make available data and information related to quantity and quality of present and future water resources is through planned infrastructure development and other interventions. The data and information dissemination aims at providing strategic decision support for the equitable and sustainable allocation of resources to the population, environment and other economic sectors of society. In setting up the groundwater monitoring network, an approach was followed which allowed for the incorporation of local and international best-practice; hydrogeological information combined with expert knowledge. We used the following criteria to establish the baseline or background sites for the national groundwater monitoring network: borehole spatial densities; pristine areas (no land-use activities); aquifer yield; recharge; baseflow; sites for background monitoring related to groundwater reserve determinations and the setting of resource quality objectives; springs; and international obligations. Trend monitoring sites were selected around baseline sites and around towns who were groundwater dependent. The trend monitoring sites allow for trends to be determined in terms of: (i) over-exploitation/abstraction of groundwater; (ii) groundwater quality degradation from various land use practices; and (iii) groundwater water use. Regional Spatial Design Workshops were held to compare the existing water resources monitoring network with the newly designed network and the existing monitoring network were optimised accordingly. Google Earth was used to query the detail of the monitoring sites, consider land-use coverages and incorporated expert input to position sampling points in line with the monitoring objectives. The implementation of the updated groundwater monitoring network will rely predominantly on hydrogeological considerations and field-
based investigations and observations. When the networks are optimised, statistical techniques will be useful to ascertain monitoring point location, redundancy and frequency.

Abstract

Groundwater in South Africa is an essential source of potable water for rural communities, farms and towns. Semi-arid conditions of South Africa, a growing population and surface water resources almost entirely being exploited to their limits, increase  the demand for groundwater resources. Therefore,  the  relation  between  the  geology  and  geohydrology  of  South  Africa  becomes  an important tool in locating groundwater resources that can provide sustainable quantities of water for South Africans. A document was therefore compiled, providing valuable geohydrological information  on  the  geological  formations  of  the  whole  of  South  Africa.  The  information  was gathered by means of interviews with experienced South African geohydrologists and reviewing of reports and articles of geohydrological studies. The geohydrological characteristics discussed include rock/aquifer parameters and behaviour, aquifer types (primary of secondary), groundwater quality, borehole yields and expected striking depths, and geological target features and the geophysical method  used  to  locate  these  targets.  Due  to  the  fact  that  90%  of  South  Africa’s  aquifers  are classified as secondary aquifer systems, groundwater occurrence within the rocks of South Africa is mainly controlled by secondary fractured systems; therefore, understanding the geology and geological processes (faulting, folding, intrusive dyke/sills and weathering) responsible for their development and how they relate, is important. However, the primary aquifers of South Africa (Coastal Cenozoic Deposits) should not be neglected as these aquifers can produce significant amounts of groundwater. Drilling success rates and possibility of striking higher yielding boreholes can be improved dramatically when an evaluation of the structural geology and geohydrological conditions of an area together with a suitable geophysical method is applied. The ability to locate groundwater has been originally considered (even today) a heavenly gift and can be dated back to the Biblical story of Moses striking the rock to get water: “behold, I will stand there before thee there upon the rocks thou shalt smite the rock and there shall come water out of it” (Exodus 17:6).

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

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

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

Because the quality of groundwater is influenced by the host rock through which it moves, it differs on a site-specific basis, and is often naturally brackish or even potentially harmful to people. In spite of this, many practitioners incorrectly use the SANS 241 Drinking Water Standard as “compliance requirement” to compare groundwater quality against. This standard only applies to water that has been purified to be suitable for potable purposes at a water treatment works in terms of regulations made under the Water Services Act 108 of 1997. The only circumstance in which it could be used to compare the quality of natural groundwaters against, is where such groundwater is (to be) used, for potable purposes (with or without treatment), and then only to provide guidance on the level of treatment required to facilitate suitability for such domestic use, and not to determine possible ‘unacceptable’ levels of contamination. Therefore, the comparison of groundwater quality results against the SANS 241 Drinking Water Standard is not only a scientifically flawed practice, it has no basis in law. It is furthermore a scientifically flawed practice to refer to groundwater quality as ‘good’, ‘bad’, or ‘poor’, as it reflects a judgemental anthropocentric perspective that has no place in modern discussions on judicious environmental management and monitoring.

 This then raises the question, what are, or should the limit values be against which groundwater quality results should be compared to determine if it has been negatively affected by anthropogenic activity to such an extent that a scientifically substantiated claim can be made that the groundwater has been ‘polluted’, an allegation with criminal liability implications?

This paper aims to answer this question in the context of South African Framework law and policy, and propose a methodology to determine appropriate site-specific limit values for groundwater quality.

Abstract

Carbon Capture and Storage (CCS) in deep saline aquifers is a viable option for Green House Gas (GHG) mitigation. However, industrial-scale scenarios may induce large-scale reservoir pressurization and displacement of native fluids. Especially in closed systems, the pressure buildup can quickly elevate beyond the reservoir fracture threshold and potentially fracture/ reactivate existing faults on the cap rock. This can create pathways, which could act as conduits for focused leakage of brine and/or CO2 up-dip and mobilization of trace elements into capture zones of freshwater wells. Careful pressure management can ensure the reservoir’s hydraulic integrity. This can theoretically be achieved through simulation with appropriate mathematical tools. This research aims to quantify pressure buildup at a CO2 injection well by applying fractional derivatives to the pressure diffusivity Differential Equation (PDE). A numerical solution has been developed to (1) predict and assess the consequence of pressure buildup within the storage formation on groundwater flow in shallow aquifers and (2) assess the impact of pressure-mobilized contaminants (CO2 , brine and/or trace elements) on the quality of usable groundwater, if there is a leakage. The efficiency of each derivative is shown to depend on the type of reservoir heterogeneity. The Caputo derivative captured the long tail dependence characteristic of fracture flow, while the ABC derivative was able to model the cross-over from matric into the fracture flow. The numerical tools presented here are useful for successful risk assessments during geo-sequestration in basins with freshwater aquifers.

Abstract

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

Abstract

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

Abstract

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

Abstract

The South African government is actively pursuing unconventional oil and gas (UOG) extraction to augment energy supplies in South Africa, but it risks damaging water quality. The Department of Water Resources and Sanitation recently released regulations to protect water resources during UOG extraction for public comment.

Regulations are one of the main tools that can be used to minimise UOG extraction impacts on water resources and enhance an environmentally sustainable economy. This tool must however be used correctly. Many states in the US and Canada have extensive regulations to protect water resources during UOG extraction but they are often ineffective, either because they were poorly drafted or because they are not properly enforced. Since South Africa is a water-scarce, groundwater-dependent country, we asked South African groundwater experts what regulations are needed and how to enforce them. Focusing on the interface between science and public policy, we critically analyse and recommend the most appropriate fracking regulations to protect groundwater resources. Additionally, we consider the enforcement mechanisms required to ensure the proper regulation of fracking.

The results from this study can assist the government in ensuring that regulations that they are currently drafting and finalising, are appropriate to protect groundwater resources, and that they would be able to enforce them effectively.

Abstract

This paper outlines the core factors related to the economic assessment of groundwater resources. Included in the discussion is a delineation of the factors that determine the economic value of groundwater as well as a thorough description of the range of ecosystem services that are derived from groundwater resources.

Several factors affect the economic value of aquifers, but these factors can split into two categories, natural asset values and ecosystem services values.

Ecosystem services are the benefits that humans receive from ecosystems, and are officially defined by the Millennium Ecosystems Assessment. Ecosystems produce these ecosystem services on an annual basis, and the value of these services accrue on a country’s national income statement, and should ideally be measured through indicators that relate to Gross Domestic Product (GDP).

Aquifer themselves are natural assets. They form part of the ecological infrastructure of a country and the values of these assets theoretically appear on a country’s natural resources balance sheet. The asset value can be determined by calculating the Net Present Value (NPV) of the perpetual stream of aquifer ecosystem services delivered.

By understanding the full range of factors that underlie the natural asset values of aquifers, along with their ecosystem service values and the full range of inter-temporal and inter-ecosystem service characteristics, we can begin to adequately assess the economic value of groundwater resources.