Conference Abstracts

All Abstracts were presented at the Groundwater Conferences

Displaying 101 - 150 of 574 results
Title Presenter Name Presenter Surname Area Conference year Keywords

Abstract

The geographic positioning of the Western Cape results in a Mediterranean climate - receiving majority of its rainfall during the winter months. A demand on the water supply throughout the year is typically met by storing water from winter rainfall in large dams. The Western Cape experienced a significant drought between 2015 and 2019. As a result, the supply dams have not been filled to capacity and drastic water restrictions had to be implemented. In the search for alternative water sources, groundwater exploration became a priority. Groundwater development projects were implemented rapidly in attempt to alleviate the implications caused by severe water restrictions and ultimately prevent running out of water. As a local groundwater institution, GEOSS got involved in several fast-tracked groundwater development projects for Department of local government, local municipalities, as well as other industrial and agricultural corporations. For obtaining the required water volumes, alternative measures were implemented. Previously under developed aquifers were targeted. In certain instances, in order to target the Table Mountain Group Aquifer (TMG), horizontal exploration drilling was conducted. The results of exploration and drilling yielded valuable learnings in terms of relevant hydrostratigraphy within the study areas. Additionally, there were learnings in terms of managing projects of this nature. In fast-tracked projects, careful management of the contractors, data collation (and storage) and public perception is critical to the success of the project. In this paper on water supply development for Municipalities, the various components of groundwater development are detailed along with relevant learnings from the recent emergency drought response measures.

Abstract

The groundwater quality in semi-arid aquifers can be deteriorated very rabidly due to many factors. The most important factor affecting the quality of groundwater quality in Gaza Strip aquifer is the excess pumping that resulting from the high population density in the area. The goal of this study to investigate the future potential deterioration in groundwater salinity using scenario analysis modeling by artificial neural networks (ANN). The ANN model is utilized to predict the groundwater salinity based on three future scenarios of pumping quantities and rates from the Gaza strip aquifer. The results shows that in case the pumping rate remains as the present conditions, chloride concentration will increase rapidly in most areas of the Gaza Strip and the availability of fresh water will decrease in disquieting rates by year 2030. Results proved that groundwater salinity will be improved solely if the pumping rate is reduced by half and it also will be improved considerably if the pumping rate is completely stopped. Based on the results of this study, an urgent calling for developing other drinking water resources to secure the water demand is the most effective solution to decrease the groundwater salinity.

Abstract

A conceptual hydrogeological and numerical groundwater flow modelling study is being undertaken around and within the proposed ESKOM Thyspunt Nuclear Site, located 120 km west of Port Elizabeth. The study aims to improve the understanding of the prevailing hydrogeological condition around the Thyspunt area. The area is characterized by folded and jointed geological conditions. The local geology comprises the Table Mountain Group (TMG) and the Bokkeveld Group rocks of the Cape Supergroup, and Quaternary to recent sand deposits of the Algoa Group. The study area receives mean annual precipitation (MAP) of 922.6 mm. The mean annual estimated evapotranspiration is 821 mm and the average annual recharge rate estimated using the Water Table Fluctuation method is about 71 mm. A robust conceptual hydrogeological model is developed through detailed aquifer characterisation including pumping test analyses, determination of groundwater occurrence, storage, and flow, hydrogeochemical and environmental isotope analyses. Groundwater occurs within intergranular of the Algoa Group and fractured quartzitic aquifers of the TMG. The depth to groundwater ranges from 4.5 to 28.9 m below ground level (b.g.l.) and though the local groundwater flow is complex, the general groundwater flow direction is from west to east, towards the Indian Ocean. The upper unconfined intergranular Algoa aquifer and the deeper semi-confined fractured TMG aquifer are characterised by wide range of hydraulic properties, including aquifer thickness (2.2 - 22.0 m and 18.0 - 138 m), hydraulic conductivity ( 4.5 - 19.1 m/d and 8.9x10-3 -1.58 m/d), transmissivity (108.3 - 275 m2/d and 0.4 - 44.0 m2/d), specific yield (1.5x10-2 - 0.1) and storativity (5.0x10-5 - 5.9x10-3), respectively. The main hydrochemical facies of groundwater in the shallow Algoa is Ca-Mg-HCO3 type and groundwater circulating in the deep TMG aquifers are Na-Cl type. Environmental isotope signatures (?2H, ?18O) results indicate groundwater - surface water interactions

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

Hydraulic behaviour of an aquifer is defined in terms of the volumes of water present, both producible and not (specific yield and specific retention), and the productivity of the water (hydraulic conductivity). These parameters are typically evaluated using pumping tests, which provide zonal average properties, or more rarely on core samples, which provide discrete point measurements. Both methods can be costly and time-consuming, potentially limiting the amount of characterisation that can be conducted on a given project, and a significant measurement scale difference exists between the two. Borehole magnetic resonance has been applied in the oil and gas industry for the evaluation of bound and free fluid volumes, analogous to specific retention and specific yield, and permeability, analogous to hydraulic conductivity, for over twenty years. These quantities are evaluated continuously, allowing for cost-effective characterisation, and at a measurement scale that is intermediate between that of core and pumping tests, providing a convenient framework for the integration of all measurements. The role of borehole magnetic resonance measurements in hydrogeological characterisation is illustrated as part of a larger hydrogeological study of aquifer modeling. Borehole magnetic resonance has been used for aquifer and aquitard identification, and to provide continuous estimates of hydraulic properties. These results have been compared and reconciled with pumping test and core data, considering the scale differences between measurements. Finally, an integrated hydrogeological description of the target rock units has been developed.

Abstract

The City of Cape Town (CoCT) and surrounding areas in the Western Cape is experiencing one of the worst droughts recorded in over a century and has been declared a disaster area. The need to develop the underlying, shallow Cape Flats Aquifer (CFA) has become of utmost importance to increase the resilience of the CoCT during times of drought. Since early 2018, over 180 boreholes have been drilled into the CFA and undergone test pumping and hydrochemical sampling. Hydrochemical analyses include macrochemical, dissolved metal and microbiological analytes to investigate the hydrochemical character of the CFA, identify potential contamination sources and better understand rock and groundwater interactions. In recent times, Contaminants of Emerging Concern (CEC) have become an important role player in groundwater hydrochemistry. Limited CEC data in South Africa prompted detailed investigations and analyses of CEC within the CFA. Groundwater within the CFA can be characterised into 3 types, predominantly linked to aquifer heterogeneity: Ca-HCO3 type (Mitchells Plain WWTW-Strandfontein), Na-Cl type (Philippi-Hanover Park) and Ca-Na-HCO3 (Bishop Lavis-Swartklip). Water quality varies across the aquifer with some areas being poor and highly contaminated, not meeting SANS 241:2015 drinking water standard. Exceedances include EC, TDS, sodium, chloride, sulphate, ammonia and TOC. Dissolved metals which exceed the standards are aluminium, iron, manganese, chromium and arsenic. These pose considerable risks to ecological functioning of the CFA and to human health if not properly treated, managed and monitored. Poor water quality within the CFA is predominantly a result of anthropogenic contamination, such as industrial pollution, unlined WWTW, leaking canals and sewage lines, agricultural fertilizers and irrigation return flow. Further sampling of surrounding surface water bodies and groundwater from boreholes will lead to the identification of contamination sources and an understanding of temporal changes in water quality to inform treatment options and costs when considering bulk supply

Abstract

Hydrogeochemical and environmental isotope investigation of the Thyspunt area, located in Eastern Cape South Africa, has been undertaken to understand the hydrogeological conditions in the area. Fifty-nine water samples from springs, wells, streams and ocean were collected for major ions, metals, and environmental isotope analyses. The hydrogeochemical and environmental isotope signatures were used to identify the interaction between various waters bodies, major hydrogeochemical processes, and possible sources of moisture in the Thyspunt area. The groundwater is characterised by electrical conductivity (EC) that varies between 286 and 7040 ?S/cm, dominant alkaline pH conditions and calcium-magnesium-bicarbonate hydrochemical water type. Hydrochemical evolution of groundwater is observed along the groundwater flow direction (west to east), from fresh calcium-magnesium-bicarbonate water type to saline sodium-chloride water type. Furthermore, mixing of calcium-magnesium-bicarbonate and sodium-chloride type groundwater is apparent in the analysed spring samples, indicating deep circulation. Gibbs plot of major ion hydrochemical data indicates that the groundwater hydrochemistry is primarily controlled by water-rock interactions (mineral dissolution) and evaporation processes. Isotopically, water samples from springs and wells have depleted isotope signatures indicative of rainfall recharge from either high attitude moisture source or recharge during colder seasons or both. None of the groundwater samples have isotope signatures similar to ocean water, signifying that there is no seawater intrusion in any of the sampled aquifers. Deuterium excess values range between -0.71 ? and 22.64 ?, suggesting the presence of numerous moisture sources. Tritium activity in groundwater varies between 0.2 T.U and 3.2 T.U, showing submodern to modern (5 - 10 years) recharge. Hydrochemical and environmental isotope similarities between spring and borehole samples confirm the fact that springs are a surface manifestation of the local groundwater flow conditions.

Abstract

Millions of tons of coal ash are produced across the globe, during coal combustion for power generation. South Africa relies largely on coal for electricity generation. The current disposal methods of coal ash are not sustainable, due to landfill space limitations and operational costs. One way/means of disposing of coal ash that could provide environmental and financial benefits; is to backfill opencast mines with the ash. However, a limited number of studies have been conducted to assess the feasibility of this method in South Africa. Thus the aim of the experiment is to monitor bulk ash disposal under field conditions to improve the understanding of the geochemical and hydrogeological processes occurring during the actual deposition of coal ash in opencast coal mines. To achieve the aim (1) a gravity lysimeter will be built containing both mine spoils and coal ash representing field conditions; (2) the factors (CO2, water level and moisture content) affecting acid mine drainage will be monitored in the lysimeter and (3) the change in the quantity and quality of the discharge released from the lysimeter.

Abstract

In the management of water resources especially groundwater resources, implementing existing regulations is one of the much needed aspects ensuring water security through the regulated use. However, such regulations are not regulated to ensure that they served the intended purpose in their original formulation. In South Africa, a study was carried out to assess the relevance and efficient of adhering to procedural requirements during water use licence application (WULA) process. Lived-experiences and observation methods were used to collect data. The department of water and sanitation was used as a case study. Interpretative analysis approach was used to provide the meaning on the analysed information. The WARMS database was accessed where the number of days that WULA process was extracted. The regulation No. 40713 about WULA process was analysed. The five-year-data prior and post the promulgation of regulation No. 40713 were extracted from WARMS database and evaluated in terms of the duration each application took to be processed for WULA. Data on water use for abstractions from all the regions were obtained from WARMS database and assessed. Dates when applications were submitted and when such applications were finalised were analysis per month and per years for temporal analysis. The number of entitlements received during the particular period and the number of applications recommended to be declined and issued were assessed using exploratory data analysis methods. Graphical method was adapted to increase results visualisation on water use entitlements. Key results showed that the process of WULA was generally slow and reasons were provided for such outcome. However, the temporal analysis revealed an increasing trend in the post promulgation of regulation No. 40713 suggesting that regulations when re-regulated serve its intended purpose. Although such findings are not conclusive but they inform a basis for re-regulating enforcement regulations in Southern African countries with issues similar to South Africa on water entitlement.

Abstract

Stable Hydrogen and Oxygen isotopic technique were used in studying the water resources interaction in Wonderfonteinspruit Valley, North-western South Africa. The objective of this study is to refine the understanding of recharge processes in typical watersheds representative for karstic semiarid areas. This study investigated the isotopic composition of 35 boreholes, 5 surface water, 4 Dams, 4 springs, 1 canal, 2 pipelines, 1 cave and 4 rain stations for two periods October and Mars. Oxygen-18 (?18O?SMOW) and deuterium (?D?SMOW) isotopic data of the karst aquifer reflects the identification of different sources of recharge controlled mainly by the rainfall for the majority of samples and by bank filtration of the main rivers (Wonderfonteinspruit, Middelvieinspruit, Renfonteinspruit) for some samples. Stable isotopes,

Abstract

As part of supporting the National Development Plan (NDP) vision 2030, Council for Geoscience has been tasked by the Department of Mineral Resources to embark on an integrated and multidisciplinary geoscience mapping programme to systematically map South Africa in a more detail manner. With the idea of groundwater resource development and preservation purposes, a 1:100 000 geohydrological map, explanatory booklet, geohydrological data base for all data obtained from various sources and an ISO document was produced. The map is situated in the middle reach of Kuruman River and covers an area of 2750 km2. Mapping process commenced by sorting existing geological and hydrogeological data sourced from the Council for Geoscience database, Department of Water and Sanitation, Department of Agriculture and Kuruman municipalities. The process also includes filling identified gaps through extensive hydrocensus which entailed site surveying, hydrocensus, measuring and groundwater sampling, determination and demarcating of groundwater units, legend standardization and GIS cartography. Different aquifer types were categorised by analysing factors which control groundwater occurrence in the area; these factors includes lithostratigraphy, groundwater quantity, geological and linear structures. These were later used as datasets in Arc GIS for map processing. Before being used to determine aquifer media and geohydrological boundary conditions, these factors were closely studied through different approaches by interpreting geological and remotely-sensed data, field verification and survey of historical information. Four aquifer types were identified, namely; Intergranular aquifer covering an area of 152.9 km2; Intergranular and fractured aquifer which covers 696.4 km2 area; Fractured aquifer which covers an approximate area of 408.5 km2 and Fractured karst aquifer with a total size of 1486.1 km2. The insert groundwater quality map show completely unfit water (Class 4) for use in the central and south-eastern side of the map. Electrical conductivity in most parts of the map fall within recommended operational limit.

Abstract

The National Water Act (Act 36 of 1996) aims at redressing inequalities in water allocation. Historically, water resources were allocated to few white people who owned land and actively participated in agribusinesses. The need for widening access to water-related business was agreed and water allocation reformed (WAR) model was developed and implemented to re-dress such past inequality. However, limited progress has been registered because there is no real-time model to monitor, evaluate and report the progress of the four water entitlements. The current study focused on groundwater abstraction/use to assess the reported limited progress in WAR. Data report and active groundwater use from WARMS database were collected, filtered and analysed for parameters as set out in the water use license conditions. WARMS database contains information on parameters regarding water use in the water allocation process. Statistical techniques were utilised to establish change detection, trend analyses and correlations including multiple regression analysis in order to establish the magnitude and direction of relationships between factors. Preliminary results showed that several communities did not make significant improvement with regard to WAR. When population groups were compared, results showed that majority of black people lagged behind in accessing water resources for economic use implying that they will continue facing difficulties to participate in agribusiness-related activities. When WAR targets were assessed, findings showed such targets were not achieved. Further analysis showed that water use entitlements and participating in the economic activities are attached to land ownership. The current study recommends that a real-time model is required to monitor, evaluate and report the progress of four water entitlements and to fast tracking land reform tasks which promote the transfer of land from white people to black people because this has been viewed as one of the ways through which progress on water allocation reform process can be fast tracked.

Abstract

Precision agriculture continuously seeks improved methods to enhance productivity whether it is for greater crop yields or economic viability regarding labour inputs and satisfying the demand in a shorter time span. Soil moisture is one important factor that drives the agricultural industry and is therefore of utmost importance to manage it correctly. A shortage of water may result in reductions in yield, while excess irrigation water is a waste of water resources and can also have a negative impact on plant growth. Knowledge of the spatial distribution of soil moisture is important for determining soil moisture storage and soil hydraulic transport properties. Capturing field heterogeneity without exhaustive sampling and costly sample analysis is difficult. Electromagnetic induction, Frequency Domain Reflectometry, Neutron Scattering and conventional soil sampling have been utilised to determine the spatial variability of soil moisture within a field. Emphasis has been placed on practicality and accuracy of all the methods. Electromagnetics have proven itself to be the primary method to determine soil moisture within the field by comparing the results of the volumetric soil water content present in the field together with a combination of various soil properties such as clay and silt content, sand fraction, concretions, density and soil depth that contribute towards the accumulation of soil water. Electromagnetic induction has the highest resolution of data collected for a specific time period of all considered methods making it economically the best option for soil moisture management within a variable rate irrigation system. Electromagnetic induction has proven to be successful in delineating a field into management zones consisting of different classes based on observed conductivity values. Higher conductive zones are considered with small water demand. Lower conductive zones are considered with a greater water demand through a variable rate irrigation system. These water management zone maps could be informative for modelling, experimental design, sensor placement and targeted zone management strategies in soil science, hydrogeology, hydrology, and agricultural applications.

Abstract

Underground coal gasification (UCG) is an unconventional mining method that gasifies coal in situ to produce a synthetic gas that can be used for industrial purposes. This mining method is still to go commercial and one of the challenges to its sustainable development is the potential risk to groundwater pollution. There is therefore a need to quantify the environmental risks associated with UCG in order for authorities to regulate this emerging sector. The knowledge attained through this work has provided for a simple but comprehensive groundwater risk assessment of a spent UCG chamber via an integrated model. The model follows the source-pathway-receptor model where the sources are identified as ash, char, roof and floor. The risk to groundwater pollution is then assessed by subjecting these sources to the following tests; mineralogical and element analysis, petrography and chemical assessment, leaching tests and acid generation assessments. Groundwater was identified as the only natural medium that can access the spent geo-reactor and transport contaminants to secondary locations. The pathways that pollution from the UCG geo-reactor can be transmitted through were identified as; natural faults, heat induced fractures, boreholes, local aquifers. This research has laid a firm foundation in understanding groundwater contamination from UCG operations.

Abstract

Groundwater forms an important part of the water resources of South Africa, especially in Karoo region, where groundwater is an important source of fresh water. Beaufort West is a town that uses groundwater as a major source of municipal and private water supply. Groundwater samples were collected from a network of 43 boreholes, between November 2015 to December 2018 within Beaufort West town and 10km radius surrounding. The water samples were analysed for inorganics, organics, stable isotopes and radioactive isotopes. The hydrogeochemical results indicate that all the boreholes onsite are collecting water from the shallow aquifer with neutral pH. From the 228 groundwater samples analyses, the total dissolved solids (TDS) concentrations averaged 1041 mg/L. This falls within the SANS 241:2015 guideline standard of ? 1200 mg/L for TDS. The high nitrates and sulphates in the water indicate that shallow aquifer has aerobic conditions. Generally, the water type is Calcium Magnesium Bicarbonate and Magnesium Sulphate. Both the inorganic chemistry and the stable isotopes have a signature of water that is recently recharged. The carbon dating results indicate that water has been underground for no more than 3 000 years. The groundwater samples generally show no contamination of organic compounds with the exception of boreholes located in the Karoo National Park, which showed high amounts of organic compounds (xylene and ethylbenzene). The interaction of the known uraniferous deposit of the Poortjie Formation in the Beaufort West area has possibly influenced the groundwater. This has resulted in groundwater with elevated average amount 17.58 ?g/L of uranium against background values of 10 ?g/L. This is however below the SANS 241:2015 standard of 30 ?g/L.

Abstract

The original City of Cape Town (CCT) Table Mountain Group (TMG) Aquifer Feasibility Study and Pilot Project was initiated in 2002, the purpose being to evaluate the feasibility of augmenting the CCT's bulk water supply using groundwater from the TMG (specifically the fractured Peninsula and Nardouw Aquifers). CCT TMG groundwater exploration/development was fast tracked under the "New Water Programme" (NWP; from 2017-present) as a result of two interrelated water scarcity/demand factors, namely periodic drought (including the major 2015-2017 1:590-year event) and rapid urban growth. Initial NWP TMG groundwater development (including additional exploration via detailed geological mapping and heliborne geophysics) has occurred in the vicinity of the CCT-operated Steenbras Dam, in the form of a minimum 15-20 Ml/day wellfield scheme. The planned "Steenbras Wellfield" targets both TMG aquifers along the Steenbras-Brandvlei Megafault Zone on the southeastern limb of the Steenbras Syncline (which regionally occurs within the high groundwater potential Cape Fold Belt Syntaxis). Current drilling activities have included ultra-deep (up to 975 m depth, representing the deepest groundwater-specific boreholes outside of mining/resource activities in South Africa), wide diameter abstraction (using rotary air percussion, reverse circulation and hydraulic/water hammer techniques) and core exploratory boreholes into both TMG aquifers. Tested abstraction borehole yields range between 10-70 l/s, while artesian-discovery core holes into the Peninsula Aquifer from Steenbras towards Theewaterskloof Dam have surface pressures and flows of up to 800 kPa and 4 l/s respectively (from BQ-sized holes intersecting water strikes between 840-910 m). Further CCT TMG groundwater exploration and wellfield scheme development (potential total combined supply of ~50-150 hm3/a or ~140-400 Ml/day) is planned along major TMG structures within the Grabouw-Eikenhof and Theewaterskloof basins, Wemmershoek, Voelvlei, Berg River and the CCT South Peninsula region. This has, and will continue to include, monitoring of surface/groundwater-dependent ecosystems as a geo-ethical approach to minimise ecological/environmental impact.

Abstract

South Africa utilizes coal for energy and chemical feedstock thereby generating millions of tons of ash every year. The ash is stockpiled in surface waste facilities where it poses a risk of leaching and contaminating groundwater. This study utilizes standard leaching tests, TLCP and SPLP, to evaluate and predict the mobility of different elements that leach from fly ash. Two different fly ash samples (Ash M and Ash T) were used in the study. A QEMSCAN analysis was also performed on the samples as well as the coal to determine the elementary and mineralogical compositions. Both Ash samples were generated from bituminous coals and had similar physical properties. Both ash samples were mixed respectively with the two different leachates one more acidic (Leachate A) the other more basic (Leachate B). Trace elements are present in ash in small amounts, but still at lower levels still pose threat to the environment and human health. Only three trace elements were found present in both ash samples. The detected trace elements in an increasing concentration order are: Manganese>Chromium>Copper. It appears the leaching behaviour of these trace elements is similar to the other metals, being insoluble at near neutral and alkaline pH range while dissolvable at low pH ranges. The results show that Leachate B was found to extract more material than Leachate A on a milligrams per gram of ash basis. The risk to groundwater contamination can be minimized by understanding the leaching dynamics and water retention of fly ash dumps as the results show.

Abstract

The Eastern Cape Province has been severely impacted by the current drought period, particularly within the Butterworth town and surrounding communities. This study, conducted within the Mnquma Local Municipality of the greater Amathole District Municipality, presents the approach undertaken in mitigating and augmenting the current water shortage. The area generally experiences annual rainfall of 596 mm and is mostly reliant on surface water with a population of over 250 000 residents. The supply of water to the communities is abstracted from the Gcuwa, Toleni and Xilinxa dams with water levels at 44, 21 and 0.6% respectively. Groundwater source development remained the most feasible solution to alleviate the drought within the area.

The geophysical techniques that were applied include the airborne technique (aeromagnetic and gamma[1]ray spectrometric) and the ground geophysical techniques (magnetic and em34) at the targeted airborne sites to verify the dolerite structures. The airborne method was used to obtain more in-depth knowledge of the geological and hydrogeological conditions within the study area. The total distance in kms’ flown for the airborne survey amounted to ~1200 km. The flight-line pattern was (N-S) and tie-line pattern (E[1]W) of the survey was conducted by AeroPhysX, and the flight-lines were flown at a 200m line spacing and tie-lines at 750m spacing at 60m flying height.

The study area consists of a vast network of E-W trending geological structures such as regional dolerite dyke and sill intrusions, faults and lineaments. Although many dykes are present within the lower Ecca and Dwyka Formations and even the Nama age basement, the bulk of the dykes are strata bound and concentrated in the Upper Ecca and Beaufort Group (Chevallier and Woodford, 1999; Woodford & Chevallier 2002). The airborne geophysical technique assisted by accurately mapping out prominent and inferred dolerite dykes located at inaccessible areas due to steep undulating hills.

 The drilling success rate on the airborne sites is 98% so far with depths ranging from 60 to 300 m with blow yields of between 2 and 50 l/s. A total of 25 prioritized drilling positions have been identified based on the airborne survey.

The hydrochemical status of the successfully developed boreholes is indicative of class 3 water quality according to the SANS 241-1:2015 minimum standards due to turbidity, sodium, chloride, iron and fluoride as common constituents in the developed boreholes. The developed boreholes will be connected  to the existing bulk water supply to the Water Treatment Plant (WTP) for treatment prior human consumption.

Airborne survey has proven to be a useful method in locating new groundwater potential areas as well as identifying unmapped dolerite structures. This paper is based on quantitative and factual findings of actual work conducted on site so far.

Abstract

Water has been recognized and acknowledged as a fundamental natural resource that sustains environmental diversity, social and economic development (Liu et al., 2017; Fisher et al., 2017). With increasing populations, climate change and limited monitoring networks for both ground and surface water, freshwater resources are becoming difficult to assess due to rapid changes in water supply and uses. Several efforts have been devoted towards the monitoring and management of water resources and discovery of alternative sources of freshwater. One of the more recent efforts is using gravity information to track changes in water storage on the earth's surface. The Gravity Recovery and Climate Experiment (GRACE) mission (https://www.nasa.gov/mission_pages/Grace/index.html) holds great potential for assessing our water resources in areas with little monitoring data. The increasing interest in the use of GRACE as a water resource information and monitoring tool, is due to its cost effectiveness and user-friendly system which affords a broad understanding of the world we live in and its processes, specifically in water resource management and hydrological modelling. South Africa's National Water Act (NWA) of 1998 highlights the importance of the sustainable development of water resources. However, it is difficult to sustainably manage South Africa's groundwater resources due to the difficultly in measuring and understanding our complex aquifers. The challenges in establishing sustainable monitoring of groundwater resources and its Reserve, are due to insufficient knowledge about the contribution that groundwater makes to surface water, and methods which reliably monitor groundwater resources. The GRACE is a joint satellite mission by the Deutschen Zentrum fur Luftund Raumfahrt (DLR) in Germany and the United States National Aeronautics and Space Administration (NASA). The satellite was launched on 17 March 2002 and provides monthly temporal differences of earth's gravity field and its mean gravity field (Schmidt et al., 2008). It can afford insights into the location of groundwater resources, and their changes. GRACE can however, only determine the change in total water storage and therefore information on other components of the water balance are required to isolate the groundwater component. Therefore, the integrated Pitman Model is ideal to be applied together with GRACE and the Model can isolate surface water, soil moisture and groundwater into various components. Many studies have evaluated GRACE-derived groundwater storage changes as a response to drought (Famiglietti et al. 2011; Scanlon et al., 2012), while Thomas et al. (2017b) evaluated a groundwater drought index based on GRACE observations in an effort to understand and identify groundwater drought. Typically, GRACE is applied at scales of 150 000 km2, however Thomas et al., (2017) has developed a recent method that allows for the application of his GRACE derived Groundwater Drought Index (GGDI) at smaller scales. This study applies Thomas et al. 2017 GGDI in South Africa to the Crocodile, Sedgefield and Doring catchments, in hopes to to evaluate drought characterisation using data from GRACE satellites, focusing on the total water storage deficits to characterise groundwater drought occurrence.

Abstract

South Africa is generally a dry country, it receives an average rainfall of approximately 500 mm/a, which is below the global average rainfall of 860mm/a. The annual average temperature in the study area was 25?C from 1995 to 2016. South Africa has made an improvement since 1994 with supplying domestic water of suitable standards, communities in rural areas, mostly have groundwater as the best option for satisfying their water demands. In the study area (Bushveld Igneous Complex), which falls within the Olifants and Limpopo Water Management Area (WMA), groundwater is used in various sectors for various. In both WMA's the irrigation sector is the highest water user. In 2015 irrigation accounted for approximately 72% of the total water requirements in the Limpopo WMA, with 57% of the irrigation requirements fulfilled by groundwater resources. In the Limpopo WMA groundwater resources supply also 44.5% of the domestic water requirements, while surface water resources account for only 21% and water transfer schemes account for 34.5%. In the Olifants WMA the mining sector uses 28 million m3/a of groundwater resources and 58 million m3/a from surface water resources. The aim of this research is to determine the hydrochemical variation and the suitability of groundwater for irrigation and drinking purpose for a sustainable agriculture and basic human needs. There are chiefly five hydro-chemical facies on regional scale identified based on the piper diagrams, namely the Ca-HCO3, mixed Ca-Mg-Cl type followed by Ca-Cl, Na-Cl and mixed Ca-Na-HCO3 water type. The suitability of groundwater is determined based on the water type, the mixed-Ca-Mg-Cl and Ca-HCO3 water types are generally suitable for domestic purposes as per SANS drinking water standards, while the mixed Ca-Na-HCO3, Ca-Cl and Na-Cl water types are mostly not suitable drinking water unless treated.

Abstract

It has been shown over many years that the efficient management of water resources is almost impossible without a database containing historical and up-to-date information and data of high integrity. When it comes to groundwater the situation is even worse as groundwater was often not seen as a viable resource, and if it was used, then in many cases, it was poorly managed due to the lack of monitoring and poor data collection. This has changed in recent years as groundwater now forms a large part of the used water resources in several communities, towns and metros. Therefore, the need for properly managed groundwater data has increased tremendously, leading to urgent requirements for a water database in whatever form. Unfortunately off-the-shelf groundwater databases relevant to the South African market did not really exist for many years, while international packages are expensive and need a lot of adaptation to work for South African conditions. Therefore, most groundwater practitioners used various forms of database software and/or spreadsheets without much integrity leading to data hosted on various computers around South Africa, but not one central system available to be accessed by groundwater managers, scientists or even the public. The Water Research Commission therefore Initiated a research project for the "Development of an integrated Groundwater Database and visualisation tools for the City of Cape Town and Environs", a system that should be so versatile that it could also be applied in other metros, provincial or national offices. This research project will have a huge impact on water resources decision making for the City of Cape Town, as the recent drought has put the City water managers under immense pressure, which was increased by the need to start using more and more groundwater resources, especially for critical City and province institutions like hospitals, clinics and care centres around the Western Cape. The outcome of the project is a "complete" groundwater resources database with links to surface water and meteorological stations and a number of visualisation tools, including an online web-based mapping tool, which is fed by live data from the database and may be used even by the public for groundwater education purposes.

Abstract

The current Grahamstown/Makhanda drought has once again highlighted the vulnerability of the local surface water resources. The two local dams supplying the western part of town (and the university) are fed by a typical Eastern Cape river which requires a very large amount of rainfall to generate runoff into the dam. Rainfall records since 1860 indicate that statistically, the current drought is not the worst drought the town has endured and there have been many similar droughts in the past, most recently in the mid-1990s, and early 1980s. The severe drought in the 1980s led to the municipality commissioning a groundwater feasibility study carried out by Dr Andrew Stone, employed by Rhodes University at the time. The study included the drilling and testing of 13 boreholes, as well as a report on incorporating groundwater into the town's water infrastructure. All but two of these boreholes are destroyed, and they, along with the report were forgotten about. Around 4 years ago, we discovered the report at the university and began building on the work undertaken by Andrew Stone by monitoring 31 of the town's boreholes and carrying out a detailed analysis of the towns local groundwater fed spring, which many of the town's residents rely on. The current drought reignited the interest in groundwater, particularly with the arrival of Gift of the Givers who drilled a further 15 boreholes in town. The renewed focus on groundwater development came with its own complexities since the western part of town that the university resides in and the historically white area, is the only part of town to yield good quality groundwater. The local synclinal fold structure has resulted in a bowl type landscape in which much of the town is situated. Resistant Witteberg quartzitic sandstone rocks are observed as high-lying ridges which border the south-western margin of the town. The less resistant Dwyka tillite and Witteberg shales are generally found in the low-lying areas. This paper discusses the current water crisis, and how groundwater could be used on an on-going basis to relieve the water deficit in drier times caused by the vulnerable local dams.

Abstract

South Africa has a looming water supply crisis, with 98% of its surface water already developed, demand outstripping supply in most catchment areas (WRC, 2015). Based on current usage trends, South Africa is expected to face a water deficit of 17% by 2030, and this shortage will only be worsened by climate change (WWF, 2017) which is mainly characterized by prolonged period of drought. There are many challenges facing the sustainability of groundwater, among others there are issues such as climate change, human errors in data handling, over abstraction due increasing water demand, damage of borehole infrastructure in remote areas and poor groundwater management systems.

Groundwater resources within the D41L quaternary catchment occurs in abundance. Aquifers in the area are classified as karst and fractured dolomite aquifers with a median yield of >5 L/s. These aquifers are compartmentalized by several impervious dykes that sub-divide the D41L area into sub-catchments and smaller sub-compartments. With the probable impacts of extended drought period in the Gasegonyana Local Municipal area, increased water demands and density of abstraction points in some sub-catchments/sub-compartments the water resources have become stressed and at risk of being over-exploited. To sustainably and secure future water supply in the region, it has become essential that a comprehensive assessment is undertaken of the sustainable water supply potential of the D41L and delineate various groundwater resource units (GRU's).

The paper highlights why is it imperative to conduct the groundwater feasibility studies on a regional scale in order to protect the sole aquifer resource for semi-desert areas such as Gasegonyana municipal zone. Secondly, the importance use of appropriate geophysical techniques which include regional gravity surveys on dolomitic aquifers with emphases to sustainability on exploitable resources as these karst aquifers are highly vulnerable to over-abstraction if not properly investigated.

Groundwater water potential and large aquifer zones were delineated explicitly with the regional gravity results and exploration drilling of these zones proved to be sustainable compared to existing boreholes that were drilled in limited/smaller dolomitic compartments. The predictive scenario of the groundwater assessment confirms that the water demand could be achieved with half of the simulated abstraction rates while an increase in water demand should be managed accordingly by distributing the yields of the borehole between the existing boreholes and the newly drilled production boreholes.

The study results will ensure sustainability of water supply in the region and the document will assist the town planners and stakeholders to manage high population growth in a groundwater secure zone, and it will mitigation against climate change impact for the municipality.

Abstract

Groundwater in the West Coast has been utilised for many years as there are not many surface water resources in the area, and is therefore extremely important. Despite studies being conducted on the aquifer systems since 1976, they are still poorly understood especially with regards to their recharge and discharge processes. This means that the amount of water entering and leaving these systems are unknown, which may lead to over abstraction. It is therefore important to investigate these systems to prevent overexploitation of the groundwater as it will have adverse effects for both humans and ecosystems dependent on it. As part of a managed aquifer recharge (MAR) project for the Saldanha Bay Municipality, this study aims at providing better insight and understanding on the natural resource volumes. The study focusses on groundwater recharge, flow paths and discharge processes and aims at quantifying the volume of water related to each. The study will be conducted by identifying aquifer characteristics through Frequency Domain Electromagnetic and Electrical resistivity geophysical methods. Groundwater flow paths through the unsaturated zone, into the groundwater and towards the discharge area will be determined using Chloride Mass Balance calculations and water isotope analyses. The mass balance equations along with isotope analyses will then aid in the identification of natural recharge and discharge areas of the West Coast aquifer systems, as well as quantifying the volume of water moving through each aquifer. Temperature profiles will also be generated to identify specific layers of the aquifer systems and to determine their groundwater-surface water interactions. The aquifer characteristics will be used in numerical models to test the conceptual understanding of recharge and flow through the systems as well as assessing the volumes of water available to the users of the system.

Abstract

For sustainable water resource management it is crucial to assess the water budget. However, estimating a region's spatiotemporal water budget is fraught with difficulties. The heterogeneous nature of every hydrological system poses major obstacles, particularly at the regional scale where monitoring data are scare. This is further complicated by rapidly changing climatic and land use trends. When estimating water availability and its distribution, the presence and sustainability of groundwater is a vital factor to consider: adequate recharge, whether natural or artificial, can ensure both the productivity of an aquifer as well as the health of its associated aquatic habitats. In order to ameliorate water budget estimates at the regional scale (>1000 km2) we investigate the capability of a multiparameter data-assimilation approach for the Thur catchment in Switzerland, with a focus on the exchange of surface water and groundwater in unconfined aquifers. With a catchment size of ~1700 km2, a dynamic topography (elevation ranging from 356 - 2505 m.a.s.l.), underlain by both consolidated and unconsolidated lithologies, no major barriers along the length of its course (~130 km), naturally variable discharge rates (3 - 1129 m3s-1), an annual average rainfall of 2,701 mm, and 10 operational gauging stations, the Thur River is well suited to this study. We aim to determine 1) the usefulness of multiparameter techniques, particularly when used in conjunction with remotely sensed data, 2) the catchment-wide spatiotemporal water distribution and budget, and 3) the groundwater storage potential within the catchment. Historic and current precipitation data, along with evapotranspiration estimates, a product derived from the MODIS sensor on board the Terra satellite, was used in conjunction with measured long-term hydrological discharge data, groundwater levels, and hydrogeochemical parameters. A remotely sensed water balance was determined for the years 2001 - 2017 and compared to spatiotemporal and statistical geochemical water characteristics from long-term surface water and groundwater monitoring sites. The results are used to determine the primary physical processes involved in regulating the catchment's water distribution. Our working hypothesis suggests that, when coupled with available hydrogeochemical water quality data and geological information, the remotely sensed water budget can be used as a tool to determine the physical processes governing the distribution of a catchment's available water. We aim to determine 1) the usefulness of multiparameter techniques, particularly when used in conjunction with remotely sensed data, 2) the catchment-wide spatiotemporal water distribution and budget, and 3) the groundwater storage potential within the catchment. Historic and current precipitation data, along with evapotranspiration estimates, a product derived from the MODIS sensor on board the Terra satellite, was used in conjunction with measured long-term hydrological discharge data, groundwater levels, and hydrogeochemical parameters. A remotely sensed water balance was determined for the years 2001 - 2017 and compared to spatiotemporal and statistical geochemical water characteristics from long-term surface water and groundwater monitoring sites. The results are used to determine the primary physical processes involved in regulating the catchment's water distribution. Our working hypothesis suggests that, when coupled with available hydrogeochemical water quality data and geological information, the remotely sensed water budget can be used as a tool to determine the physical processes governing the distribution of a catchment's available water. Understanding a catchment's spatiotemporal water distribution will help determine where water bodies could be suitably buffered, either through the rehabilitation and protection of wetlands and river reaches or via managed aquifer recharge, in order to abate the effects of increasing water demand, and climate and land use change on the water budget.

Abstract

The most used methods for the capturing of shallow groundwater contamination are the use of abstraction wells and infiltration trenches. The use of trenches for the interception of shallow groundwater contamination has become a popular choice of remediation method due to the lower cost than a comparable pump-and-treat system. Trenches have large surface areas which limits the tendency of filter media clogging with suspended media as well as only a single pump and lower maintenance requirements. An important consideration of the use of trenches is determining the effectivity before design and construction. To date, limited information on the effectivity of trench designs are available, therefore a method to determine the effectivity of a trench was devised. This paper will discuss this evaluation method and look at some cases where planned trenches were successful and some cases where they were not.

Abstract

Groundwater is vulnerable to contamination from various anthropogenic sources. The degree of groundwater vulnerability can be assessed using various methods, which are grouped into three major categories: index-and-overlay methods, process-based computer simulations and statistical analyses. This study attempts to produce a groundwater vulnerability map of the eThekwini Metropolitan District Municipality using the index-and-overlay method of DRASTIC in a GIS environment for the first time. The advantage of this method is that it provides relatively simple algorithms or decision trees to integrate large amount of spatial information into maps of simple vulnerability class es and indices. The main objective of the study is to identify areas of high groundwater contamination potential based on hydrogeological conditions so that management interventions are undertaken timely. DRASTIC is a groundwater vulnerability assessment method based on the intrinsic property of groundwater systems to human or natural impacts. It uses seven hydrogeological parameters, namely, Depth to groundwater, net Recharge, Aquifer media, Soil media, Topography, Impact of the vadose zone and hydraulic Conductivity of the aquifer. These DRASTIC parameters characterize the hydrological setting and are known to control the vulnerability of aquifers to surface derived pollutants. Various studies show that depth to groundwater and impact to vadose zone impose larger impact on aquifer vulnerability followed by recharge, topography and soil media. The application of DRASTIC to the greater Durban area resulted in vulnerability index values in the range from 71 to 168. Based on these index values, greater Durban area is classified into zones of low, moderate and high vulnerability of groundwater to pollution. The low vulnerability areas (Drastic Index. DI: 71-114) are located in the northern region around Magangeni which are underlain by the intergranular and fractured aquifer due to essentially deep groundwater table (>25 m), vadose zone sediments, low hydraulic conductivity and recharge rate. The moderately vulnerable areas (DI: 114-127) cover more than 50% of the study area that is underlain by fractured and Intergranular, and fractured aquifers. The moderate vulnerability areas are located in the western region (Hammarsdale and Kloof), northern region (Mount Edgecombe and Tongaat) and southern region (Amanzimtoti). The moderate vulnerability pattern is mainly due to variation in the hydraulic conductivity of the aquifer and the vadose zone and less by the recharge and the depth to groundwater. The region around central Durban, the Bluff area, Yellowwood Park and areas along the coast that are underlain by intergranular aquifer are mapped as "hotspots" characterized by high vulnerability to groundwater pollution (DI: 127-168) and needs immediate management intervention.

Abstract

Historically Finsch Diamond Mine has experienced groundwater inflow in the underground workings of the mine. The inflow results in unsafe and undesirable working conditions. Sampling was conducted over a three month period in order to determine the source of the groundwater inflow. The sampling consisted of various underground samples, monitoring borehole samples as well as surficial water body samples. The samples were analysed for major and minor chemical constituents as well as O18 and H2 isotopes. In order to determine the source of inflow in the underground workings the samples were compared to that of the South African drinking water standard (SANS), graphically interpreted via Piper, expanded Durov and Stiff Diagrams as well as isotopically analysed by comparison to the Global Meteoric Water Line (GMWL). Geochemical modelling was employed in order to determine the typical chemical constituents where groundwater interacts with tailings material and to calculate mixing ratios. Comparison to SANS and the geochemical modelling indicated that elevated sulphate and sodium is associated with fine residue deposit (FRD) water. The Piper and expanded Durov diagrams indicated the presence of three major water types namely: calcium-magnesium-bicarbonate, calcium-magnesium-sulphate and sodium-sulphate types. The isotope analysis indicated the presence of three major water types namely: samples which correspond well with the GMWL, samples which do not correspond well with the GMWL but fall along a mixing line and water which does not correspond with the GMWL. From the analyses, it was clear that water with a sodium-sulphate signature and an evaporated nature, as seen from the isotope data occurred in the underground workings of the mine. These samples corresponded well with water from a nearby FRD and indicate that the FRD is responsible for inflow on shallow levels of the mine.

Abstract

Compliance values for Water Use Licenses are based on Water Quality Objectives for the catchment and require each monitoring point to be below the stipulated criteria. This approach neither considers the site geohydrological elements nor the characteristics of point source plumes, meaning that the management of existing groundwater contamination cannot achieve compliance. This deadlock is problematic for both the authorities and for industry/mining in South Africa that cannot adhere to the specific conditions in terms of water quality as specified in most Water Use Licence water quality conditions.

Geo Pollution Technologies (GPT) would like to introduce the development of compliance levels which are risk based and achievable taking site specific conditions and the Water Quality Objectives into account. The approach is well established for soil contamination under the Framework for the Management of Contaminated Land and international best practice, and can be extended to groundwater using the following two methods.

Firstly, the Compliance Level Approach entails the development of compliance levels to protect receptors in terms of land use. Example: land use criteria can be domestic, irrigation, livestock, aquatic as from Department of Water and Sanitation. Secondly, the Analytical Approach calculates the human health Tier 1 and Tier 2 risks and calculation of Site Specific Target Levels (SSTLs) that can be used as target levels for site clean-up; if required.

Both these approaches need a firm understanding of the underlying Conceptual Site Model (CSM) which illustrates the interrelationship between the sources of contamination, pathways of transport and potential receptors on which groundwater (and soil) as our pathways can impact. Before Groundwater Compliance values or Site Specific Target Levels can be determined it is important that consensus should be reached between all stakeholders for different CSM scenarios. These scenarios look at different source-pathway-receptor relationships that can exist at a site for activities during the operational and decommissioned phases of a facility.

This paper would like to illustrate that a single groundwater compliance value for a groundwater plume is not only unachievable but cannot be defended scientifically in a modern industrial world. Both the proposed approaches are risk based which is the driver for the implementation of remedial actions and will incorporate Water Quality Objectives at a point of compliance.

We hope through this paper that our authorities will reconsider the blind application of surface water quality standards to groundwater.

Abstract

The recent Western Cape drought initiated large scale development of the Cape Flats Aquifer (CFA) and refurbishment of the Atlantis Water Resource Management Scheme (AWRMS). Both aquifers are comprised of primary sediments of the Sandveld Group. Lithologies and depositional environments of the two aquifers are often directly compared and linked, but recent borehole drilling in these two aquifers is highlighting their inherent differences. The use of conventional mud rotary drilling techniques in these aquifers and changing nomenclature over time, has created uncertainty in their lithological character, leading to complications in borehole design and interpretation of test pumping results. Sonic drilling - Atlantis (20) and CFA (25) - was undertaken and incorporated with approximately 200 mud rotary borehole drill logs and geophysical survey results to investigate aquifer geometry and hydro-lithological characteristics. Results to date indicate the CFA is more heterogenous and has greater lateral variation compared to the Atlantis Aquifer. The CFA is interspersed with clay lenses, organic rich layers, calcrete and thick basal shell units. Whilst the Atlantis Aquifer displays a more homogeneous character with limited clay lenses, minor organic layers, interspersed calcrete and a near non-existent basal shell layer. Results of the sonic drilling have led to increased confidence in boreholes design, test pump analyses and numerical model results. The influence of CFA's heterogeneity on test pumping interpretation is displayed in the results through a variety of unconfined, confined, semi-confined and leaky type curves. Atlantis however, typically displays unconfined Neuman-type curves. Delayed gravity drainage signals, test pump duration, varying hydraulic conductivities of different lithological units and other boundary effects not only have an economic impact on test pump design, but can lead to the misinterpretation of test pump data which greatly influences planning for the aquifers' response to large scale abstraction and Managed Aquifer Recharge (MAR) alike.

Abstract

Continued population growth, economic development and climatic change have increased the demand for water supply in South Africa. As a result, most surface water systems have been exhaustively developed, increasing dependency on groundwater, including on meager aquifers during dry spells. This study aims to characterize the hydrogeology of the Pietermaritzburg Formation, a poorly productive aquifer that has been targeted for borehole sitting during drought years though with poor success rate. Pumping test analyses, monthly monitoring of groundwater level, electrical conductivity (EC), pH, water temperature and environmental isotopes (?2H, ?18O) were undertaken in 2018. Analyses of the pumping test data of the pumping well using the Theis and Cooper-Jacob method has returned hydraulic conductivity (K), transmissivity (T) and storativity (S) values of 4.12*10-6 m/day, 1.56*10-4 m2/day and 1.52*10-4, respectively. Analyses of observation well data located west 20 m from the pumping well gave K, T and S values of 1.79*10-7 m/day, 6.95*10-6 m2/day and 2.8*10-10, respectively. A second observation well located 33 m north from the pumping well did not show any water level response to the pumping. Additionally, the rate of water level recovery was very slow both in the pumped well and one of the observation wells. These test results indicate that the investigated aquifer is not only poorly productive but also heterogeneous, compartmentalized in nature and not feasible for sitting water supply wells. Rainfall recharge estimated using the water table fluctuation method (WTF) based on monitored groundwater level data is about 28 mm/a or 3.5% of mean annual precipitation (MAP). The groundwater level, temperature and EC monitoring indicate that as new rainfall recharge reaches the aquifer, the groundwater level and temperatures increases while the EC decreases as a result of salinity reduction because of dilution. Similarly, as the groundwater level declines as a result of prolonged dry seasons, the groundwater temperature drops, while EC increases due to increased salinity. Furthermore, monthly environmental isotope monitoring shows that all the samples plot along the local meteoric water line (LMWL) indicating that groundwater is recharged from local precipitation. The groundwater at the studied site is characterized by Ca-Na-HCO3 hydrochemical facies indicating an early stage of rock-water interaction

Abstract

The generation of acid mine drainage (AMD), as a result of mining activities, has led to the degradation of groundwater quality in many parts of the world. Coal mining, in particular, contributes to the production of AMD to a large extent in South Africa. Although a vast number of remediation methods exist to reduce the impacts of AMD on groundwater quality, the use of a coal fly ash monolith to act as a reactive and hydraulic barrier has not been extensively explored. This study, therefore, aims to investigate how different ways of packing ash affect the hydraulic conductivity of ash and influence leachate quality when acid-mine drainage filters through the ash. Coal ash is highly alkaline due to the existence of free lime on the surface of the ash particles. Previous studies that investigated alternative uses of coal ash, particularly in AMD treatment, suggest that coal ash has the potential to neutralise pH in acid water and remediate acidic soils. To test the effects of different packing methods of coal ash on the hydraulic conductivity and quality of acid mine leachate flowing through it, several Darcy column tests will be conducted. During the course of these experiments, the following parameters will be measured, electrical conductivity, pH discharge, lime (CaCO3) and selected elements of environmental concern.

Abstract

The rainfall situation in the Western Cape became a focal point in 2015; 2016 and 2017. The rainfall in 2015 was half the long term average; in 2016 it was still below the long-term average and in 2017 it was again about half the long-term average. In 2018 the rainfall was better and was about the same as the long term average. These consecutive years of low rainfall were really problematic and with the declaration of the "Day Zero" campaign the media brought the plight of the City of Cape Town into the global headlines. However it was not only the City of Cape Town that was under dire stress but the whole of the Western Cape Province (and beyond). The neighbouring District Municipalities (DM) also embarked on frantic groundwater development and augmentation programmes. GEOSS South Africa (Pty) Ltd was fortunate to be involved in the DMs surrounding the City of Cape Town.

This presentation focusses more on the groundwater aspects per se rather than the technical; aspects of boreholes; pumps etc, with specific reference to case studies including the Sandveld; Saldanha Bay Local Municipality and the Stellenbosch Local Municipality (specifically the Franschhoek area). The Sandveld (which is within the Berg River District Municipality) has a significant agricultural sector and 25 years of regional groundwater monitoring indicates that even with significant groundwater abstraction for the agricultural activities within the area, the groundwater volumes are robust enough to support further development of groundwater to meet the increasing water requirements for the town supply of Graafwater and Lamberts Bay. This expansion is currently underway.

The West Coast District Municipality (specifically the Saldanha Bay Local Municipality) committed significant resources to groundwater development in the times of the drought. The Langebaan Road Aquifer wellfield was expanded with additional production boreholes and a new wellfield, known as the Hopefield Wellfield was also fully developed and equipped with all infrastructure in place. The wellfields have also set up to implement Managed Aquifer Recharge. Although these schemes are not yet operational, the groundwater levels held up well during the drought, indicating these wellfields should play a major role in times of future drought. Groundwater within the Franschhoek area (Winelands District Municipality) is utilized by many sectors and from detailed and long term monitoring the drought had little impact on the resources supporting the development of groundwater supply schemes for Municipal augmentation. From widespread work in the Western Cape Province it is evident that the drought had little impact on the groundwater levels of the region and it bodes well as a resource to be utilised in times of severe stress, so long as it is properly authorised, monitored and managed.

Abstract

Note: This case study was submitted and reported in the Publication Advances in Groundwater governance. The demand on fresh water has increased to such an extend that supply cannot keep up with demand, especially in areas where desalination of seawater is not an option. There is a large gap between the water user, the water supplier and the capacity of the resource/s. The water user sees it as his/her right to be provided with clean water in sufficient volumes to sustain their most basic needs.At the same time people want higher levels of service, especially where sanitation is concerned. The recent droughts in Cape Town and in Port Elizabeth have put significant focus on groundwater and we've seen uncontrolled drilling for groundwater reaching new heights, which is a problem on its own. We can no longer afford not to bring the groundwater user into the water planning cycle, so that the users, on all levels of society, can be educated to understand that the quantity and quality of fresh water (ground -and surface water) is limited and dependent on recharge from rainfall, size of the catchment, topography and all that takes place on the surface. This education must be specific to a target audience and must take into account the existing knowledge and understanding of the user profile. As an example, a case study will be discussed where there are large groundwater users operating within the upper parts of a catchment, followed by municipal abstractions and private abstractions within the central parts of the same catchment. Four profiles of users are therefore present: (1) large-scale irrigation by farmers, (2) large-scale municipal abstractions, (3) private residents and (4) formal / informal settlements, with the latter probably competing for top pot in terms of water use, with the irrigation. They key deliverable of the presentation / paper will be to (1) make people aware of the problem/challenge, and (2) suggest ways to bridge gaps and get all users and service providers to work together to save water and to understand that there are limits to the quantities available.

Abstract

Groundwater exploration in crystalline basement aquifers is often more complex as its occurrence and characteristics are largely a consequence of the interaction of several processes related to recharge and groundwater through-flow within a particular system. An integrated approach of geological mapping and hydrogeophysical investigations can nevertheless be useful in mapping the subsurface characteristics that are likely to control groundwater occurrence in such formation. In this study, multiple geological mapping and hydrogeophysical methods were applied to identify potential groundwater bearing targets as controlled by several geologic structures within the Houtriver gneiss crystalline basement aquifer system in Limpopo province of South Africa. The results from magnetic and frequency domain electromagnetic surveys were combined with geological observations and used to identify anomalous points where vertical electrical resistivity sounding was done in order to infer the thickness and layering of weathered and fractured zones, as well as to assess the area for groundwater potential targets. The magnetic method, horizontal and vertical frequency domain electromagnetic geophysical methods presented herein managed to delineate the main hydrogeological features associated with groundwater occurrence in typical basement aquifers. The vertical electrical sounding (VES) sections done on ten (10) sites suggest that groundwater occurrence is characterized by a multiple layer of varying depths inferred to be caused by different levels of weathering, geology and fracturing within the study area. VES sections are further correlated with the reconstructed drill samples from boreholes drilled within project framework in order to develop a lithological conceptual understanding of weathering and fractured regions that influence groundwater occurrence within the study area. The integration of several geophysical methods for groundwater evaluation in study provided a more detailed approach for the for resource assessment in crystalline basement aquifers as compared to the traditional VES, thereby resulting in increased accuracy in borehole siting.

Abstract

The overexploitation of water resources has resulted in a global decline in groundwater levels. Managed aquifer recharge (MAR) is a globally acceptable practice to manage the depletion of water in overexploited aquifers in regions with limited water availability. The West Coast of South Africa experiences a semi-arid climate with predominantly dry summers. This study aims to identify potential areas suitable for MAR in the Saldanha Bay area to maximize the water available to these areas during the dry season. This will be done through the delineation of the aquifer(s) units to determine the distribution of suitable aquifers, understanding the aquifer(s) hydraulic and hydrogeological characterises and investigate the water quality. This study focuses on 1) Frequency domain electromagnetic and electrical resistivity geophysical methods to characterise the subsurface; 2) Aquifer testing, to estimate the hydraulic properties of the aquifer(s); 3) Water quality sampling and analysis for water quality investigations. Practical considerations like distance from suitable water sources will also be considered. The expectations for this study, based on the results that should be obtained from these methods, should include the identification of several zones that would allow for MAR practices

Abstract

Hydrogeology no longer only relies on understanding of phreatic systems. Highly heterogeneous and anisotropic conditions in soil and rock comprising intergranular, fractured and karstic porosity affect groundwater vulnerability, recharge rates, drainage and dewatering practices, soil corrosivity, natural attenuation of contaminants, and integrity of infrastructure, to name a few examples. Movement of water at partial and highly variable saturation is very complex, depending on very small-scale variations in ground conditions as well as very subtle changes in moisture content. In contributing to this, a number of research projects were conducted, focused around physical experiments in the laboratory or mimicked in the field, and subjected to differing conditions pertaining to gravitational acceleration to scale the vertical dimension. Studies contribute to flow mechanisms and flow regimes of variably saturated soils and rocks, as well as the interface between, and link available theoretical understanding and empirical approaches to physical experiments and field verification experiments. Where possible, hydraulic parameters are estimated to improve the quantification of said parameters at discreet scale rather than assuming single values for bulk systems. Obvious limitations and assumptions are understood to the extent that updated flow scenarios are proposed to contribute to variably saturated flow systems. Behaviour is inferred for fractures of changing orientation, changes in medium from soil to rock, and for alternation between wetting and drying of different media. Selected experiments will be presented to highlight novel findings and the way forward

Abstract

Saline groundwater in semi-arid to arid areas is typically ascribed to evaporative concentration of salts on or near the surface followed by dissolution of salts during episodic rainfall events and then percolation of saline downwards. This has been previously postulated for large parts of the west coast of South Africa where groundwater electrical conductivity (EC) ranges between 804 ?S/cm and 21 300 ?S/cm. However, due to the spatial variability of groundwater salt concentrations, it is unlikely that simple evaporation is the only process leading to elevated salinity levels in this region. Palaeo-termite mounds, known as heuweltjies (meaning little hills), are common surface features along the west coast of South Africa, covering an estimated 14 to 25% of the land surface. These structures consisting of aerated and nutrient-rich sediments, containing elevated levels of micro- and macro elements, including salts, compared to the surrounding sediments. For this reason, it is postulated that heuweltjies are an important source of groundwater salts. In the Buffels River valley, exchangeable ions from sediments in the centre of the heuweltjies are up to 20 times higher than in the inter-heuweltjie material and are consistent with elevated heuweltjie salts determined via in-situ EM38 scanning. 36Cl/Cl ratios are highly variable ranging between 25.94 x10-15 and 156.19x10-15, indicating that recharge occurs inland. Groundwater 87Sr/86Sr ratios in the same area are extremely elevated, up to 0.78240, suggesting a direct link to the underlying radiogenic granitic gneisses but decrease to the west suggesting interaction or mixing between different water sources. We propose that in this case, the two water sources are older groundwaters mixing with direct recharge that contains elevated salts but lower 36Cl/Cl and 87Sr/86Sr ratios derived from preferential flow paths through the heuweltjies.

Abstract

In southern Africa, crystalline basement aquifers constitute approximately 55% of the land area and therefore it is important to understand these aquifers and the mechanisms that control them. These aquifers have been well documented in the northern parts of South Africa however the amount of research done on the central Namaqualand basement aquifers is severely lacking, especially in the area surrounding Kakamas in the Northern Cape (the study area). Therefore a detailed hydrogeological study was conducted in the area by means of a thorough hydrocensus, pumping tests and a geological evaluation of the area. The hydrogeological tests were conducted on various boreholes in the study area, close to Kakamas. In an attempt to better hydrogeologically classify the aquifers that are prevalent in the area, the data from the hydrocensus and pumping tests were evaluated in conjunction with the specific geology of the area, as Namaqualand aquifers are very much structurally controlled by the geology. There are three types of aquifers (alluvial, weathered zone and fractured basement rock) that are superimposed on each other throughout the study area. These aquifers are strongly interlinked as groundwater flows from one to the other. The data obtained from the boreholes varies across the study area. When evaluating both the pumping test data and the site specific geology it is evident that on geological contact zones and areas where the geology is more faulted the boreholes have higher yields. The study indicates that boreholes targeting alluvial aquifers that overlay basement aquifers in faulted valleys or contact zones are the best source for sustainable groundwater in central Namaqualand.

Abstract

Industrial areas are major sources of surface and groundwater pollution. As a result, constant monitoring of water quality is of vital importance to detect pollution incidences in time and to take corrective actions. This integrated hydrogeological, hydrochemical and environmental isotopes (?2H, ?18O, 3H) study has been undertaken to investigate the hydrogeological conditions around the Kusile coal-fired power station located in the quaternary catchment B20F. The study area is characterized by mainly weathered and fractured and fractured aquifer systems. The weathered and fractured aquifers are made up of the Ecca Group shale lithologies, with weathering depths ranging between 5 and 12 m below ground surface (b.g.l.), while the fractured aquifer system is made up of the Pretoria Group quartzites, chert and shale units. Both aquifer systems have borehole yields ranging from 0.1 to 2 L/s. The depth to groundwater ranges from few cms to 22.7 m, with an average depth of 7.6 m b.g.l. Regional groundwater flow direction is from south-east to north-west, following the topographic gradient. The hydrochemical analysis from 25 boreholes, 6 springs, and 19 surface water points show electrical conductivity (EC) values less than 70 mS/m, pH values in the range from 5.2 to 9.6. High concentrations of Fe, Mn and Zn were measured in some samples that have high turbidity (> 5 NTU). The hydrochemical data shows six hydro-chemical facies with Mg-HCO3 as the most dominant indicating a shallow circulating less evolved recharge area groundwater. Multivariate statistical methods in the form of factor and cluster analyses were applied in the analyses of the hydrochemical data collected. The results of Factor analysis indicated three factors which explained 81.5% of the total variance in the hydrochemical data. The first factor is characterised by strong loadings of EC, Mg, SO42-, Ca, and Cl which could explain the contribution of the major ions to the salinity. The second factor has high positive loadings of Fe, turbidity, and a strong negative loading of dissolved oxygen indicating reducing conditions. Factor three shows high positive loadings of HCO3-, pH and Na, where the positive correlation of HCO3- and pH shows carbonate buffering on the pH of the system. The Hierarchial Cluster Analysis subdivided the samples into two clusters and two sub-clusters. Cluster 1 is dominated by surface water samples which are characterised by elevated concentration of HCO3-, turbidity, and SO42-. The second cluster has two sub-clusters. Cluster C-2-1 is characterised by lower Cl and K concentrations while cluster C-2-2 contains boreholes which are dominated by Mg-HCO3 water type. Environmental isotope data indicates that groundwater recharge is from a mixture between sub-modern and recent precipitation. Four surface water samples along a stream line show a similar isotopic signature as the groundwater samples indicative of an interaction between the groundwater and surface water. The preliminary results of the inorganic hydrochemical data doesn't indicate pollution from the Kusile coal-fired Power Station.

Abstract

A large number of groundwater investigations have been carried out in the Western Cape over the last decade or so. Most of them were related to water supply options for individuals, agriculture, businesses, industries, government departments and municipalities. Some of these developments have confirmed what we already knew about the groundwater characteristics and aquifers of the Western Cape, while others provided us with surprises - surprises so significant that we may have to re-write what we thought we knew. This paper will not be able to cover all the interventions and groundwater studies that have been done. Two case studies linked to the major geological structure in the Western Cape, namely the Colenso Fault (also known as the Franschhoek-Saldanha Fault), will therefore be used as an illustration of the lessons that were learnt by comparing them with our historical understanding of the associated groundwater characteristics. It will also show that there is a need for updated groundwater maps on smaller scale and a reassessment of the aquifers status.

Abstract

Due to its location in a dry and arid part of South Africa, Beaufort West relies on groundwater as a crucial source of freshwater for the town. Although there have been fluctuations over the years, groundwater levels in the area have progressively dropped due to unsustainable abstraction from wellfields. The general flow of groundwater in the town, which is from the North where the Nuweveld mountains are situated to the town dyke in the South, is dictated by major dykes in the area. In 2011, flooding resulted in extreme groundwater recharge with groundwater levels North East of Beaufort West recovering tremendously, from 45m below ground level to approximately 10m below ground level; and the general groundwater levels of Beaufort West becoming relatively higher. The purpose of this study was to gain a better understanding of episodic groundwater recharge around extreme climatic conditions of high precipitation events in a semi-arid region. This was done by analyzing data for surface water levels, groundwater levels, rainfall and evaporation from Beaufort West; using Sentinel 1 in InSAR (interferometric synthetic aperture radar) to utilize remote sensing as a tool to examine land surface fluctuations with regards to the changes in the groundwater levels; as well as studying the hydrogeological setting and lineaments in the area

Abstract

Many groundwater models are commissioned and built under the premise that real world systems can be accurately simulated on a computer - especially if the simulator has been "calibrated" against historical behavior of that system. This premise ignores the fact that natural processes are complex at every level, and that the properties of systems that host them are heterogeneous at every scale. Models are, in fact, defective simulators of natural processes. Furthermore, the information content of datasets against which they are calibrated is generally low. The laws of uncertainty tell us that a model cannot tell us what will happen in the future. It can only tell us what will NOT happen in the future. The ability of a model to accomplish even this task is compromised by a myriad of imperfections that accompany all attempts to simulate natural systems, regardless of the superficial complexity with which a model is endowed. This does not preclude the use of groundwater models in decision-support. However it does require smarter use of models than that which prevails at the present time. It is argued that, as an industry, we need to lift our game as far as decision-support modeling is concerned. We must learn to consider models as receptacles for environmental information rather than as simulators of environmental systems. At the same time, we must acknowledge the defective nature of models as simulators of natural processes, and refrain from deploying them in a way that assumes simulation integrity. We must foster the development of modelling strategies that encapsulate prediction-specific complexity supported by complexity-enabling simplicity. Lastly, modelers must be educated in the mathematics and practice of inversion, uncertainty analysis, data processing, management optimization, and other numerical methodologies so that they can design and implement modeling strategies that process environmental data in the service of optimal environmental management.

Abstract

Until 1998 groundwater was managed separately from surface water and was seen as a private resource. The National Water Act of 1998 (Act 36 of 1998) (NWA) was forward thinking in that it saw groundwater as an integrated part of the water resource system and as a common resource to be managed by the Department of Water and Sanitation (DWS) as custodian. Various tools had been provided to manage the water resources equitably, sustainably and efficiently. A limited understanding of groundwater and the prevalence to revert to engineering principles when managing water resources had led to an Act that is mostly written with surface water in mind. The tools and principles that had been tested for surface water was used directly for groundwater without considering the practicalities in applying and enforcing the NWA. This did not provide too many problems, as groundwater was not considered a viable, sustainable water resource, and the use of groundwater was mostly limited to private use for garden irrigation, in agriculture for irrigation and for bulk supply in a number of small towns where surface water was not available. This has changed drastically during the recent drought that affected the whole country, but especially the Western Cape. Groundwater was suddenly seen as the solution to the problem of water availability. The problem was that the understanding of groundwater has not increase sufficiently over the years, and water resources management is still skewed to hydrology principles that apply to surface water. Groundwater sustainability is at the heart of the questions of scale and measurements. The Department has been flooded by the large number of water use licence applications that have been submitted by municipalities, industries and agriculture as a result of the drought. This article will look at groundwater resource assessment and allocation methodology in a South African context.

Abstract

Limpopo Province is one of the wealthiest areas of South Africa with respect to geothermal spring occurrences, which were classified according to the residing mountains: Soutpansberg, Waterberg and Drakensberg. Mphephu, Sagole, Siloam and Tshipise geothermal springs fall within the Soutpansberg. This study is aimed at understanding the origin and age, geochemical processes controlling the water chemistry. Analyses of major ion hydrochemistry and environmental isotopes (?18O, ?2H and ?3H) were undertaken, which is supported by conventional hydrogeological information. The dominant hydrochemical facies for geothermal springs within Soutpansberg are Na-Cl and Na-HCO3. The results indicate that geothermal spring water chemistry is controlled by water-rock interaction, silicate/carbonate weathering, mineral dissolution, cation exchange and inverse cation exchange. The isotopic composition of the springs range from ?0.48? to ?5.41? for ?18O, from ?33.3? to ?24? for ?2H, and from 0 to 1.6 TU for tritium. The hydrogen (?2H) and oxygen (?18O) isotope signatures reveal a significant infiltration before evaporation takes place. This implies that the geothermal water has been originating from local precipitation with evidence of paleoclimate effect. ?3H values show that the present rainfall contributes more to the geothermal spring recharge particularly in summer compared to winter season. This corroborates with findings from the geothermal water age obtained by radiocarbon method, which placed the recharge period during the Holocene. Hence, this is clearly indicated that this water is originating from the deep circulating local meteoric water.

Abstract

South Africa relies heavily on coal to generate electricity and meet the countries energy demands (National Electricity Regulator, 2004). Numerous opencast coal mines are decanting acid mine water (AMW) as a result of coal mining activities, causing elevated salt concentrations in nearby surface and ground water bodies. Additionally, the burning of coal for power generation produces large amounts of coal combustion residues (CCR's) annually (Reynolds-Clausen and Singh, 2016), which are disposed of in holding ponds or landfill sites, with limited space. To keep the generation of coal-energy sustainable, there is a need to prevent AMD generation from abandoned mines, whilst concurrently disposing of coal ash. A potential solution is to backfill opencast coal mines with CCR monoliths (large single ash blocks), however, limited studies have focussed on understanding this applications behaviour to determine whether this activity will have a positive, negligible or negative effect on groundwater quality. This study addresses this gap by assessing the flow and transport characteristics of CCR's under numerous generic numerically modelled backfilling scenarios: (1) No CCR's, (2) CCR's placed above water table, (3) CCR's placed below water table, (4) CCR's placed in middle of pit, (5) CCR's on down gradient side of the pit, and (6) CCR's placed from the base up to the weathered zone. Results display that CCR backfill scenarios that intercept the water table experience a 10 - 12 % rise in water levels, whereas, scenarios that do not intercept the water table have no significant effect on the flow regime. This is due to the low hydraulic conductivity of CCR's that act as a hydraulic barrier. CCR backfill scenarios experienced significantly reduced salt loads leaving the pit. The contaminant plume migrates southwards down gradient in all scenarios, with the exception of scenario 5 which successfully contains the plume. The modelling results thus indicate that all CCR backfilling scenarios provide a positive environmental improvement.

Abstract

Groundwater is often used as an alternative source of drinking water in many places of the world mostly in rural areas. There is a perceived claim that groundwater is clean and safe. This study was carried out to assess the quality of various groundwater sources in the Vhembe District of South Africa. Questionnaires were distributed to residents of the area to evaluate the water use practices. Water quality indices were employed to estimate the usefulness of the groundwater water resources. Heavy metals and major ions were analysed using ICP-MS. E. coli and total coliforms were determined using membrane filtration method. Health risk of the heavy metals in the water was estimated using standard protocol. The results of the study showed that most of the metals complied with the South Africa National Standards. Some of the anions exceeded the recommended limit. Majority of the groundwater sources were fit for other uses except drinking due to the levels of E. coli determined. Sources of contamination determined were both natural and anthropogenic. Adequate monitoring of groundwater resources is recommended to avoid possible risk to public health.

Abstract

The paper presents the groundwater monitoring data collected at Eskom's Thyspunt Site over the eleven-year period from January 2008 to January 2019. The Thyspunt site is underlain by an upper unconfined intergranular aquifer of the Algoa Group sediments, called the Algoa Aquifer, and a deeper semi-confined fractured-rock aquifer of the Table Mountain Group, called the TMG Aquifer. In the Algoa Aquifer, the highest water levels were recorded after the very good winter rains of 2011 and 2012. Between 2013 and January 2019 the recorded water levels in this aquifer have been declining to the lowest measured levels since monitoring started in 2008. This decline varies from 11.0 m in the Oyster Bay dune field recharge zone to 0.8 m in the Langfonteinvlei discharge zone. The deeper TMG Aquifer shows a similar decline over the last four years ranging from 10.1 m in the inland recharge zone where the TMG outcrops to 1.3 m at the near coastal discharge zone.

Abstract

It's been said that you cannot manage what you cannot measure. This is especially true with groundwater management; where we have limited data allowing us to 'see' the underground source. All over the world, people are spending aquifers full of money (bucket loads) on monitoring programmes and hydro census's. They capture borehole locations, water levels, abstraction rates, rainfall measurements and water quality analysis, then typically store the product, the deliverable, their valuable data, in a massive amount of spreadsheets. They have measured, but struggle to manage effectively because the data has not been stored in a centralised, consolidated fashion. Join us for a journey through Dagbreek, an open cast pit at Sishen mine, one of the largest open cast iron ore pits in the world and certainly part of the biggest dewatering project in South Africa. See how Sishen utilised technology to eliminate manual, paper-based data collection and spreadsheets. See how they utilised a cloud-based information management system to centralise and consolidate their data before transforming the data into valuable visualised information. See how this is equipping Sishen's decision makers with easy to interpret and up-to-date information, empowering them to make more effective operational and management decisions about their dewatering and groundwater management strategy