Conference Abstracts

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

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

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

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

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 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

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

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

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

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

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

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

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

A cycle of research is under way to investigate sustainable farming practices and business development on emerging farms in the lowveld of the Limpopo Province of South Africa. One of the main limiting factors for intensive agricultural production in this region is water availability. The objectives of this study were: i) to determine the spatial extent of occurrence of shallow groundwater (<20 m deep), in particular along dry river beds; and ii) to determine the sustainability of shallow groundwater abstraction for irrigation on emerging farms.

A case study was investigated in the Molototsi River catchment, a torrential tributary of the Letaba River. The geology consists of well-developed, medium-textured alluvial/colluvial soils overlying predominantly Goudplaats gneiss. Geophysical surveying and mapping was carried out with a Model G5 proton memory magnetometer and an EM-34 electrical resistivity meter. Groundwater level data were collected from the GRIP database (Groundwater Resource Information Project - Department of Water and Sanitation) and selected boreholes were monitored with Solinst water level loggers. Groundwater abstraction data, borehole logs and digital elevation models were also collected.

A methodology was developed to map the extent of shallow groundwater using measured groundwater levels, a National Land Cover map (NLC 2013/14), the wetland map of the National Freshwater Ecosystem Priority Areas (NFEPA), satellite remote sensing (MOD16 evapotranspiration data) and ground-truthing. Groundwater level monitoring indicated that the water bearing features may not be directly connected to the alluvium and sand river bed (alluvial aquifer), resulting in limited baseflow estimated to be ~15 m3 a -1 for a river reach of 100 m. Episodic recharge of the alluvial aquifer occurs predominantly via surface runoff. The hydraulic conductivity of the river sand aquifer was estimated to be >20 m d-1 , and one order of magnitude smaller in the fractured rock aquifers. Groundwater modelling with MODFLOW was done at farms abstracting groundwater from fractured bedrock aquifers and directly from the sand bed of the Molototsi River to investigate how much water can be abstracted for sustainable irrigation. Both modelling and monitoring results indicated that there is limited scope for large scale expansion of irrigation, given the competition for water in the area, in particular for drinking water supply. However, the volume of water stored in the dry river bed could represent a useful reserve during periods of severe drought, with recharge from occasional flood events being essential. Given the porosity of the river bed aquifer of about 40%, it was estimated that a 100 m reach of the Molototsi River would retain about 7,200 m3 of water that could be abstracted if numerous wells are established and recovery periods are allowed. A water volume of 7,200 m3 is sufficient to irrigate 1.8 ha of vegetables for one season. This volume could be augmented to a certain extent by establishing river bed sand dams.

Abstract

With increasing pressure on Cape Town’s potable water supply, the responsibility of diversifying supply for small, medium and large volume water users has fallen to the user to ensure sustainable use of potable water, and utilising all feasible non-potable sources where available.

With estate and sectional title living becoming more common in South Africa, it is possible to develop holistic groundwater development models and strategies for the implementation of mini wellfields within these, in general, more densified living areas. This is well aligned with the Water Conservation and Water Demand Management Strategy of the City of Cape Town, where conjunctive use of groundwater for non- potable uses such as irrigation is implemented, as well as aligning itself with the current water restrictions within the Cape Metropole.

Unlike standard residential neighbourhoods, estate development allows for the implementation of well- managed abstraction and monitoring of groundwater levels, as well as the possibility of shared groundwater usage in situations where legislation allows. The installation of fewer higher yielding boreholes (versus individual wellpoints on each residential section) to supply water to all communal areas and private gardens, allows for targeted data collection, interpretation and reporting.

Implementation of shared water use from a single water use licence (likely issued to the legal entity of the body corporate) within sectional title property has its own complications, where licensed water use would generally be restricted to communal areas.

The multi-phase assessment, implementation and licensing of groundwater supply for a life-rights retirement estate is presented as a case study. This enabled the investigation into shared water usage for irrigation of communal areas, as well as gardens of individual dwellings, eliminating the installation of dozens of wellpoints on estate properties thus ensuring sustainable usage and continued monitoring of the groundwater.

Concurrent development of the groundwater infrastructure during the housing estates development brings its own challenges, and requires special consideration during early phases of the project, where infrastructure damage is commonplace on large construction sites. Holistic water conservation strategies were implemented, such as the construction of permeable pavements to increase the amount of recharge to the underlying aquifer storage below the estate instead of trying to store rainwater in the limited surface space.

Utilising installed borehole equipment, an Aquifer Stress Test (AST) was undertaken to determine the aquifer parameters, sustainable yield of the individual boreholes and the wellfield as a whole, as well as inter borehole interactions. An AST allows for real world scenario aquifer testing to prove sufficient groundwater availability.

Abstract

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

Abstract

The UNESCO-IHP initiated a project on “Governance of Groundwater Resources in Transboundary Aquifers” in 2013. Three aquifers were selected for case studies: Trifinio (Central America), Pretashkent (Central Asia), and the Stampriet Transboundary Aquifer System (STAS) in southern Africa shared between Botswana, Namibia and South Africa. The project aimed to conduct a detailed assessment of the characteristics, current state and management of transboundary aquifers and to lay the foundations for a multi-country consultation body. It is expected that this will lead to enhanced water security, transboundary cooperation in groundwater management, and improved environmental sustainability in the aquifer region. Phase 1 of the project focused on desktop activities to acquire existing data and information with respect to three components: Hydrogeological, Socio-economic & Environmental, and Legal & Institutional. The integrated assessment determined that the recharge is taking place in Namibia during heavy rain periods, and that is where the resource is mostly used - Namibia (91.2%), Botswana (8.6%), South Africa (0.2%). Lack of time-series data made it difficult to determine aquifer properties. Groundwater quality is mainly impacted by agricultural activities and geological properties. The STAS area depends mainly on groundwater since the rivers are ephemeral. The Information Management System was developed in order to encourage information sharing among countries and to store interpreted and processed data from the assessment of the groundwater resources for use as a tool to support decision makers and relevant stakeholders’ actions. Water Diplomacy training offered involves hydro-politics of water to support cooperative agreements and increasing institutional capacity of sharing countries to reduce conflict and enhance cooperation over shared resources. This formed basis for the development of a Multi-Country Consultation Mechanism, a body that will provide the vision and direction towards governance and sustainable management of the STAS. The project is on-going with Phase 2 expected outcomes including numerical model, among other outcomes, using FREEWAT which is openly available. It is anticipated that ultimately, a joint governance model shall have been drawn amongst the three countries to ensure a mutually sustainable resource management.

Abstract

In coastal areas worldwide terrestrial groundwater resources and the coastal sea are generally hydraulically connected thus allowing continuous groundwater/seawater interaction. This major form of land-ocean interplay is associated with two potential pathways of dissolved matter transport, namely (1) flux from the marine to the terrestrial environment in form of seawater intrusion into terrestrial aquifers and (2) flux of terrestrial groundwater into the coastal ocean manifested as submarine groundwater discharge (“SGD”). The sea-to-land pathway is of relevance due to the risk of irreversible salinization of coastal groundwater resources and is in most cases a manmade (and hence manageable) phenomenon set off by excessive groundwater exploitation that is not balanced by groundwater recharge. The land-to-sea pathway (i.e. SGD), on the other hand, occurs naturally everywhere an aquifer with a positive hydraulic head is connected to the ocean. It is of interest due to two potential threats, namely (i) the loss of freshwater to the ocean, an issue that is particularly relevant in climate zones characterized by water scarcity, and (ii) the detrimental impact of nutrient- or contaminant-laden groundwater discharge on the coastal water quality, an aspect that is of relevance along urbanized coastlines worldwide. The latter implies that SGD localization and quantification is of major relevance with regard to (i) the evaluation of the vulnerability of the coastal sea to groundwater pollution and for (ii) understanding the associated matter cycles including nutrients, organic compounds or inorganic contaminants. We present results of an environmental tracer based approach that aimed at evaluating short-term SGD dynamics into the Knysna estuary, South Africa. Both natural components of SGD, terrestrial freshwater (FSGD) and recirculated seawater (RSGD), were estimated individually. We conducted an end-member mixing analysis for time series of radon (222Rn) and salinity over two tidal cycles in order to determine four water fractions within the estuary: seawater, river water, FSGD and RSGD. The results were backed by stable isotope data (18OH2O and 2HH2O). End-member mixing ratio analyses revealed the mixing ratios that fit best to the observations at every time-step of the 24 h time series, which was carried out near the estuary mouth. Results indicated highest FSGD and RSGD fractions in the estuary water during low tide amounting to 0.2 % and 0.8 % for FSGD and RSGD, respectively. A radon mass balance for the whole estuary revealed a radon flux via SGD of 41 ± 7 Bq m^-2 d^-1, which equals a total FSGD of 4.6 *10⁴ m³ d^-1  and RSGD of 1.5 *10⁵ m³  d^-1 . The results do imply that the majority of nutrient fluxes (DIN) into the estuary are SGD-derived.

Abstract

Households in many rural areas worldwide rely on septic tanks, simple pit latrines or other means of wastewater disposal. Many such households are not served by a piped mains water supply, but rather obtain their water supplies from local wells. Sampling studies of private wells in Ireland and elsewhere have shown many wells to be contaminated, with sources of microbial contamination known to include domestic wastewater treatment systems, as well as practices associated with intensive agricultural production. While the microbial quality of private well water is commonly assessed using faecal indicator bacteria (FIB), such as E. coli, FIB are not source-specific, and provide no information as to the origin of the contamination. A range of chemical and microbiological fingerprinting techniques has been investigated in an attempt to identify a robust method for apportioning private well contamination to a specific source. Fingerprinting methods evaluated include ionic ratios, fluorescent whitening compounds, faecal sterol profiles, artificial sweeteners, caffeine, pharmaceuticals and human specific Bacteroidales 16S rRNA genetic markers. A total of 212 Irish households that depend on private wells and domestic wastewater treatment systems, commonly septic tanks, were evaluated by site assessment surveys. A once-off sampling and analysis campaign of these wells found that 15% were contaminated with E. coli. Subsequent monitoring of 24 selected wells found 45% to be contaminated with E. coli on at least one occasion. The application of fingerprinting techniques to these monitored wells found that ionic ratio analysis, specifically the use of chloride/bromide and potassium/sodium ratios, is a useful low-cost fingerprinting technique capable of identifying impacts from human wastewater and organic agricultural contamination, respectively. The artificial sweetener acesulfame was detected on several occasions in a number of monitored wells, indicating its conservative nature and potential use as a fingerprinting technique for human wastewater. However, fluorescent whitening compounds, faecal sterols and caffeine were not detected in any wells, suggesting low suitability. Whilst human specific Bacteroidales genetic markers were detected, further work is required to identify how the culture-independent nature of the method relates to faecal contamination.

Abstract

This paper describes the characteristics of the deep aquifer systems in South Africa as derived from the available data. The study formed part of the larger WRC project K5/2434 (Characterisation and Protection of Potential Deep Aquifers in South Africa). A review of the available literature relevant to potential deep aquifers in South Africa was done to allow characterisation of these aquifer systems. In addition, data obtained from the geological logs of the SOEKOR and KARIN boreholes were considered.

This paper focuses on deep aquifers in 1) the Karoo Supergroup, 2) the basement and crystalline bedrock aquifers, 3) the Table Mountain Group, 4) the Bushveld Igneous Complex and 5) the dolomites of the Transvaal Supergroup. From the available data the deep aquifer systems are described in terms of the following characteristics: lithology, occurrence, physical dimensions, aquifer type, saturation level, heterogeneity and degree of isotropy, formation properties, hydraulic parameters, pressurisation, yield, groundwater quality, and aquifer vulnerability.

The results of the study show that the deep aquifer systems of South Africa are generally fractured hard-rock aquifers in which secondary porosity was developed through processes such as fracturing and dissolution. The primary porosity of most of the rocks forming the aquifers is very low. Apart from the dolomite aquifers, most of the water storage occurs in the rock matrices. Groundwater flow predominantly takes place along the fractures and dissolution cavities which act as preferential pathways for groundwater migration. The aquifers are generally highly heterogeneous and anisotropic.

The deep aquifers are generally confined and associated with positive hydraulic pressures. The groundwater quality generally decreases with depth as the salinity increases. However, deep dolomite aquifers may contain groundwater of good quality. Due to the large depths of occurrence, the deep aquifer systems are generally not vulnerable to contamination from activities at surface or in the shallow subsurface. The deep dolomite aquifers are a notable exception since they may be hydraulically linked to the shallower systems through complex networks of dissolution cavities. The deep aquifers are, however, very vulnerable to over-exploitation since low recharge rates are expected.

Abstract

New Vaal Colliery (NVC) is an opencast mine in the northern Free State, located within a meander of the Vaal river and underlain by the Transvaal Supergroup dolomitic aquifer. Dewatering of the pits results in high-sulphate water that needs to be stored in the Maccauvlei dam, the main unlined pollution control dam. In 2011 the mine was issued a water use license containing challenging conditions, one of which was the requirement for all water pollution dams on site to be lined. The conditions were viewed as impractical and unnecessary as the mine impacted water did not pose a risk to the surrounding environment, in particular to the underlying dolomitic aquifer. In order to motivate for the amendment of the license conditions, a hydrogeological conceptual site modelling (CSM) process was initiated in order to identify and quantify the groundwater balance and assess the extent of interaction between the dolomite aquifer and the mine.

The CSM formed the basis for the development of a detailed and robust numerical model and triggered the re-evaluation of the mine’s land rehabilitation plan. The results were to be used to ensure the risks associated with water management on site were addressed and for submission of a water use license amendment application. This paper summarises the CSM development. A history of hydrogeological studies provided the initial understanding of the hydrostratigraphy which is characterised by three main units, namely the shallow weathered and mine aquifers, the Karoo aquifers and aquiclude as well as the pre-Karoo aquifer and aquiclude. The available site data indicated that while the Maccauvlei dam may have a hydraulic connection to the shallow artificial mine aquifer, it was unlikely that water from the dam impacted on the dolomitic aquifer.

This was supported by water levels measured in boreholes targeting the dolomite aquifer, which generally recorded an elevation above that of the Vaal River, confirming the confined or semi-confined nature of the aquifer. The pressure heads suggested that water flow is from the dolomitic aquifer to the mine and not the other way around. Of significance to the mine’s water management were the findings that 1) a geological graben forming the boundary between NVC and the defunct Cornelia mine could provide substantial groundwater flow into the mine and 2) that the flooded old underground mine working still to be mined are likely to exceed the site’s infrastructure capacity for water storage and limit coal production. The CMS was sufficient to illustrate that it is not likely that the mine water has an impact on the dolomitic aquifer water quality, a finding later supported by the numerical model. The modelling process provided the necessary platform to negotiate a progressive implementation of license conditions that are specific to the mine and cost effective over the life of mine, despite the gaps identified.

Abstract

The paper provides an outline of the recently published National Groundwater Strategy and of the approach to its implementation. According to the National Water Resource Strategy, development of groundwater resources will be crucial for sustaining water security in the light of increasing water scarcity in South Africa. Already groundwater’s role in South Africa has undergone a major change during the water sector transformation post-1994, from an undervalued resource and a ‘private water legal status’ to a source of domestic water and general livelihood to more than 60% of communities in thousands of villages and small towns country-wide. However, there are major concerns that local groundwater resources are very poorly managed and that major aquifers are under pressure in many locations through over- abstraction, declining water levels and water quality degradation. In the light of these general challenges, there has been a recognition, world-wide, that, with increasing level of groundwater development, there has to be an incremental institutional path, moving from technical development of the resource to groundwater management and ultimately to groundwater governance as part of IWRM. This is the path South Africa is intending to follow in the development of a national groundwater strategy initiated in 2015. At the heart is an agreed strategic framework of groundwater governance and a stakeholder-driven process to roll out the framework over the next 10-20 years. Appropriate governance is particularly important for groundwater, because of its ubiquitous nature and relative ease of local access. Focus on local stakeholder involvement will be essential. Thus major issues that will have to be addressed from the beginning to encourage stakeholders to be more willing to contribute to the management efforts include proper valuation of groundwater, scientific understanding and accessible data and information and broad-based education to build social support for management. The strategy framework will address three essential levels, namely the local action level, the national/regional regulatory, planning and institutional development level and an enabling policy level. A major challenge at the enabling level is the present lack of a well-capacitated national groundwater champion to guide and coordinate the overall roll-out process. Different ways for a much greater involvement of the groundwater sector as a whole are suggested. A risk-based approach is proposed to achieve increased focus and levels of management for more stressed aquifers on a priority basis. This must be seen as a major paradigm shift from national management to facilitated local level participative management of groundwater resources within the overall IWRM framework.

Abstract

A hydrogeologist studies the ways that groundwater (hydro) exists within and moves through the soil and rock of the earth (geology). How we use this knowledge for the good of the environment and society will lead to our success as hydrogeologists and environmental game-changers. Within the broad field of hydrogeology there exist several specialist domains. One may be more of a specialist in groundwater supply, resource management and monitoring issues. Or one may concentrate on subsurface contamination issues. Or be more slightly removed in areas such as geophysics and specialised modelling. Field experience as a young hydrogeologist is essential to establish a foundation for good science. Early specialisation is however occurring to the detriment of first understanding the essentials of basic hydrogeology. Data collection, collation, interrogation and interpretation all contribute to the report. It is the presentation of the findings in a manner that can be understood by the layman, general public and authority groups that is important. For the field of hydrogeology to obtain the recognition it deserves in South Africa, the hydrogeological fraternity will need to become more ‘heard’ and ‘active players’ in managing the country’s scarce water resources. It is one thing to develop a groundwater supply scheme, but the role of the hydrogeologist must continue with the long term monitoring and management of that supply scheme to ensure its success. This presentation draws on the more than 30 years of experience that the author has had as a practising hydrogeologist in South Africa. The oral presentation of this paper has as its intention to excite passion for the profession of hydrogeology. Reminisces made will show the pleasure of experiences gained and provide guidance to young entrants to the profession. Being a hydrogeologist provides one with the opportunity to be a ‘player in the field’ and contribute to sustainable life and societal well-being. Being a player is more exciting than being a spectator, so engage in how you can enjoy your game.

Abstract

The presence of shallow groundwater at locations with limited spatial coverage in drylands have since time immemorial supported plant and animal communities. These locations often have in comparison to the surrounding dry landscapes high biomass production and biodiversity. The presence of groundwater makes these locations attractive for development of groundwater dependent human activities such as irrigated crop production, and livestock production. Groundwater abstractions from locations that are not necessarily close to these plant and animal communities, but tapping into the same aquifer systems have also a potential to affect the availability of water to these ecosystems which is critical for their existence. The importance of these groundwater dependent ecosystems is not well understood due to limited knowledge about their spatial coverage. Some of the groundwater dependent ecosystems occur in areas that are not accessible such as mountain slopes, or in remote areas. The long-term impact of groundwater usage on some of these ecosystems has not been evaluated, with most of the knowledge about these impacts being based on anecdotal information obtained from the respective land owners.

Remote sensing offers an opportunity to map the spatial coverage of groundwater dependent ecosystems in drylands. A distinguishing characteristic of these systems is the active plant growth especially during periods when throughout the landscape, there is limited or no water to support plant growth. Monitoring plant growth during the dry season using indices such as the NDVI enables detection of groundwater dependent ecosystems. Knowledge about the rates of actual evapotranspiration at locations with these ecosystems enables an estimation of the amount of water required to support them during the dry season. The MODIS 16 actual evapotranspiration rates (ETA) which are globally available can be used for evaluating water use by groundwater dependent ecosystems.

This paper explores the mapping of the spatial coverage of groundwater dependent ecosystems using remote sensing based vegetation indices in parts of the Gourizt River basin in South Africa. The rates of waters use by the identified groundwater dependent ecosystems are estimated using actual evapotranspiration rates based on MODIS 16. The paper also examines possible long-term changes to the spatial coverage of groundwater dependent ecosystems.

Abstract

In South Africa and neighboring countries such as southern Zimbabwe, Botswana, southern Angola and Namibia, most river systems are non-perennial due to semi-arid/arid climatic characteristics. In such river systems, the interaction between groundwater and surface water is of significance in terms of developing appropriate methods for determining ecological water requirements among others. However, the interaction is not well understood in terms of the influence on the volume and quality of water on the gaining and losing water bodies. In past years, research on non-perennial rivers (NPRs) has not been widely published for various reasons. In certain cases, NPRs experience extended periods of water ponding within their channels. This could possibly be caused by groundwater seepage that is sufficient to maintain pools but insufficient to generate channel flow (gaining stream) and overcome evaporation losses. The opposite can also occur, whereby some reaches of the river channel are recharging the underlying aquifer (losing stream). Abstraction of either groundwater or surface water thus impacts on both water resources.

The objectives of the study are to investigate the role of the Tankwa River in recharging the underlying aquifer and the role of the aquifer in recharging the Tankwa River. Preliminary findings through literature review and field observations seem to suggest that the groundwater flow in terms of the regional perspective is driven by recharge in the far upland TMG Mountains. However, on a local scale, field observations seem to suggest that there is some aquifer-river interaction, whereby the aquifer is maintaining the pools in some parts of the channel whereas some parts of the river are dry. These findings suggest that the river contains both losing and gaining reaches thereby providing indication of an exchange of water between the water resources. This has implication on the quantity and quality of water in gaining and losing water bodies in aquifers and rivers. Future work will involve installing piezometers at points where permanent pools are located and along the river riparian zone. Monitoring of groundwater levels and the river will be carried through the different seasons. Samples will be collected from the aquifer, surface water bodies and rain gauges to integrate with the groundwater chemistry. The overall purpose of the present study is to develop a regional hydrogeological conceptual model of recharge for the Karoo in order to improve understanding of the recharge mechanism in non-perennial river systems especially in the semi-arid environment, using the Tankwa River as a case study.

Abstract

Amongst groundwater users, the importance of a scientific borehole yield test is often highly underrated. From experience, a vast number of groundwater users make use of a method of yield testing known as the ‘farmer test’ or even just the air lift yield obtained when the borehole is drilled. In many cases, a scientific yield test is only conducted so that the borehole can be licensed with the Department of Water and Sanitation. A recent yield test undertaken near Stellenbosch demonstrated the importance of a scientific yield test, and the short comings associated with the “farmer method”. The case study pertains to a borehole where the air lift yield was much higher than expected for the area. The borehole was drilled into a high transmissivity aquifer of limited extent. As such, the yield testing was able to quite quickly detect and demonstrate impacts from aquifer boundary conditions. The case study demonstrates the need for hydrogeological conceptualization of the aquifer and flexibility in designing and modifying the yield test. The safe yield potential of this borehole was reduced from an expected 15 L/second to 0.5 L/second. Aquifer boundary conditions occur at most boreholes to some degree, and this case provides a demonstration of the effect on yield testing.

Abstract

An investigation of surface and groundwater chemistry was undertaken as part of a resource assessment of water-supply for potash solution-mining in the Danakil Depression of the Afar Rift, situated in northern Ethiopia on the N/S-trending Ethiopia-Eritrean arm of the East African Rift System. Four hydrostratigraphic units are recognised in the area: 1) Basement Tsaliet Group rocks, low yielding and with poor water quality; 2) Adigrat Formation and Antalo Group fractured sandstones and karstic limestones, high yielding with good water quality; 3) Danakil Group and Zariga Formation fine-grained sediments, forming a good regional aquifer; 4) Dogua Formation alluvial fans, forming a major, regional, primary aquifer with high yields and poor water quality (yields of >50 l/s but 3 times the salinity of sea water). In the mining concession area the only available target for groundwater exploration is the Dogua alluvial-fan system that extends off the Dogua Mountain range to the west. During 2015 and 2016, 5 production and 5 exploration/monitoring boreholes were drilled into the fans, thereafter test pumped and sampled for hydrochemical and isotope analysis. The aquifer stress test proved that there is sufficient groundwater available for the life of mining, but that the water quality is poor. The hydrochemical analysis found that in general, water quality is poor (brine with TDS values >100 000 mg/l and a density >1.05 g/cm3 ) and with temperatures of ~50°C. Water quality degrades from south to north, possibly due to recharge of fresh water from the Antalo limestones in the south and lesser quality water from the Tsaliet basement in the north. The high salinity and temperature found throughout the fans is due to hydrothermal influx along rift-boundary faults that extend downwards into the thermally active, volcanic rift zone. Prolonged pumping results in the degradation of the water quality in the southern boreholes and improvement of quality in the northern boreholes; this is likely as the groundwater heads towards equilibrium, with a similar hydrochemical signature to that of the dominant hydrothermal influx. Stable and radiogenic isotope sampling and analysis was undertaken to determine the source of the recharge, the results showing that it is likely a combination of evaporation from fresh water, lateral recharge of ancient sea water along faults from the Red Sea, and hydrothermal recharge from the sub-surface leaching of young Afar and Red Sea Basalts in the active rift zone.

Abstract

Three dimensional numerical flow modelling has become one of the best tools to optimise and management wellfields across the world. This paper presents a case study of simulating an existing wellfield in an alluvial aquifer directly recharged by a major perennial river with fluctuating head stages. The wellfield was originally commissioned in 2010 to provide a supply of water to a nearby Mine. Ten large diameter boreholes capable of abstracting ±2 000 m3 /hour were initially installed in the wellfield. The numerical groundwater flow model was used to evaluate if an additional 500 m3 /hour could be sustainably abstract from the alluvial aquifer system. A probabilistic river flow assessment and surface water balance model was used to quantify low and average flow volumes for the river and used to determine water availability in the alluvial aquifer over time. Output generated indicated that the wellfield demand only exceeded the lowest 2% (98th percentile) of measured monthly river flow over a 59 year period, thereby proving sufficient water availability. Conceptual characterisation of the alluvial aquifer was based on previous feasibility studies and monitoring data from the existing hydrogeological system. Aquifer parameters was translated into the model discretisation grid based on the conceptual site model while the MODFLOW River package was used to represent the river. Actual river stage data was used in the calibration process in addition to water levels of monitoring boreholes and pump tests results. The input of fluctuating river water levels proved essential in obtaining a low model error (RMSE of 0.3). Scenario modelling was used to assess the assurance of supply of the alluvial aquifer for average and drought conditions with a high confidence and provided input into further engineering designs. Wellfield performance and cumulative drawdown were also assessed for the scenario with the projected additional yield demand. Scenario modelling was furthermore used to optimise the placement of new boreholes in the available wellfield concession area.

Abstract

This paper describes the results of study aimed at consolidating the available data sources on deep aquifers and deep groundwater conditions in South Africa. The study formed part of the larger WRC Project K5/2434 (Characterisation and Protection of Potential Deep Aquifers in South Africa). Since very little is known about the aquifer conditions below depths of 300 m, all groundwater information from depths greater than 300 m was considered to represent the deep aquifer systems. Various confirmed and potential sources of data on deep aquifers and groundwater conditions were identified and interrogated during this study, namely:

1. Boreholes of the International Heat Flow Commission (IHFC). The IHFC database indicates the location of 39 deep boreholes ranging in depth from 300 to 800 m, with an average depth of 535 m.
2. The Pangea database of the International Council for Science (ICSU). The Pangea database has information on 119 boreholes in South Africa, of which 116 are deeper than 300 m.
3. A database on deep boreholes at the Council for Geoscience (CGS). This database contains information on 5 221 boreholes with depths exceeding 300 m.
4. Information on the deep SOEKOR boreholes drilled during the 1960s and 1970s (at least 38 boreholes).
5. Information on deep boreholes from the database of the Petroleum Agency SA.
6. The National Groundwater Archive (NGA) of the Department of Water and Sanitation (DWS).
7. Information derived from the thermal springs in South Africa.
8. Boreholes drilled as part of the Karoo Research Initiative (KARIN).
9. Information on the locations and depths of underground mines in South Africa. Information on the occurrence of deep groundwater could potentially be obtained from these mines.

The study shows that, although information on a vast number of deep groundwater sites is listed in the various databases, the data relevant to the geohydrological conditions are scant at most sites. This paucity of geohydrological data implies that the deep aquifers of South Africa are currently poorly understood.

Abstract

The need to diversify energy resources for South Africa has brought developing shale gas to the forefront. Consequently, the semi-desert Karoo basin in South Africa is being explored as a potential source for shale gas resources. South Africa’s limited water resources have caused concern because groundwater resources are the main source of water for irrigation, drinking and for sustaining groundwater dependent ecosystems. Groundwater dependent ecosystems are found across the South
African landscape, affecting the environment and ecological processes where groundwater flow to and discharge from aquifers. The current study assesses potential impacts of shale gas developments on groundwater dependent ecosystems in the Karoo area. Groundwater dependent ecosystems were identified and categorized based on a combination of hydrogeological and morphological type setting. Direct methods based on terrestrial setting and indirect methods based on hydrogeochemistry for determining interaction between groundwater and the groundwater dependent ecosystem were assessed. Preliminary results lean towards potential risks to groundwater dependent ecosystems and shallow aquifer systems from surface processes during shale gas developments instead of subsurface processes. Therefore, it is suggested to ecologically assess groundwater dependent ecosystems and further study the influence of shale gas development on groundwater dependent ecosystems at regional scale perspective in South Africa to inform a level of protection and risk management.

Abstract

The legacy of mining in South Africa in general and in KwaZulu-Natal (KZN) province in particular, continues to affect the quality of surface water and groundwater resources. Rehabilitation of Northern KZN abandoned coal mines and their discard coal mine dumps had been undertaken by Government in the 1990’s following the emergence of stricter environmental legislation. The purpose of this study was to study the success of the rehabilitation of these abandoned mines in improving the quality of surface water and groundwater resources around the area. Hydrochemical data for the past seven years including data generated during this research was analysed through hydrochemical plots, trend analysis, bivariate and multivariate statistical analyses and calculation of saturation indices using various software, including AqQA, SPSS and PHREEQC. These hydrochemical analyses results were interpreted along with groundwater level and environmental isotope data. The results show that since the start of the monitoring period seven years ago, the groundwater is characterized by circumneutral pH and contains relatively low concentrations of metals. Ionic concentrations of groundwater were assessed and found to correlate with neutralization reactions, specifically calcite and dolomite Acid Mine drainage (AMD) buffering reactions. Time series analysis of saturation indices revealed slight fluctuations for calcite and dolomite, although groundwater appeared to remain oversaturated with respect to these minerals. This was due to the generation of Ca2+, Mg2+ and SO4 2- ions from carbonate- AMD neutralization reactions. Time series data of EC, SO4 2- and total Fe indicated no anomalous values except with few episodes of elevated levels. The main groundwater hydrochemical facies identified was Ca-Na-HCO3. The surface water samples displayed elevated EC at various sampling points, indicative of the impact of both the neutralization reaction and the AMD. The analysis of all available data and information show that the rehabilitation operation has been largely successful, with exception of a few possible seepage zones that have been impacting surface water quality.

Abstract

The Omaruru River Basin encompasses an area of approximately 19 625 km2 in central west Namibia. The headwaters extend to the area north of the Etjo Mountains, ephemeral surface runoff and groundwater flow is generally directed south-westward until they reach the Atlantic Ocean. Annual rainfall decreases steadily from 380 mm at the headwaters to <50 mm at the river mouth implying that majority of runoff is generated in the upper headwaters. The alluvial aquifer is recharged indirectly from seasonal floods whose runoff reduces significantly towards the coastal aquifers by transmission losses. Groundwater abstraction is controlled through a permitting system by the Department of Water Affairs, embracing the principles of Integrated Water Resource Management.

The alluvial aquifer is a major contributor to bulk water supply in the basin. Four bulk water schemes were established along the aquifer for domestic and industrial use while the alluvial aquifers also sustain riparian and sensitive ecosystems established along the river. The current water demand of the Omaruru River Basin has been estimated at 12.7 Mm3 /a, of which 59 % is abstracted from the alluvial aquifer. An integrated geohydrological model was developed using dynamic system modelling software. Hydrological and geohydrological information was made available to highlight runoff and groundwater recharge as key indicators for integrated water resources management. River compartments were defined adopting the concept that the ephemeral rivers are characterised by pools and ridges formed by basement highs. Therefore, groundwater levels are regulated mostly by flood recharge, evapotranspiration and groundwater abstraction and to a lower extent by groundwater through-flow from the alluvium upstream. Sub-basin parameters such as rainfall, basin size, alluvial aquifer compartment length, width and depth were derived to estimate surface runoff produced per sub-basin, transmission losses and first estimate of groundwater recharge to the alluvial aquifer.

Model results indicated total volume of saturated alluvium to approximately 377 Mm3, with recharge from transmission losses amounting to approximately 14.8M m3 for the entire basin. Groundwater recharge potential is highest in the upper part and decreases significantly towards the coast. Groundwater abstraction needs to be reconciled with the protection of sensitive ecosystems established along the ephemeral river. The model results have implications on management of the entire alluvial aquifer. The Geohydrological model provides fast assessment of the impact of groundwater abstraction on water levels and available water resources in downstream compartments. This can be a great benefit to the Department of Water Affairs and Forestry in processing abstraction permits as well controlling abstraction in times of prolonged drought. The resulting model shows that abstraction strategies downstream the river should be optimized to protect the aquifer against over-abstraction. In its simplicity the model can be adapted to other strategic alluvial aquifers.

Abstract

This paper reports the results of groundwater level variability analysis across KwaZulu-Natal (KZN) Province of South Africa and its relationship with rainfall. The study used 32 groundwater level monitoring sites and 15 rainfall stations.

The main objective of the study was to understand groundwater level trends for the monitoring period, i.e. from 2004 to 2015 and understand its controls. The Mann-Kendall test was used to explore the presence of trends in groundwater level and rainfall data at 10% statistical significance level. The slope of the trend has been estimated using Sen’s slope estimator. The results revealed that within the Usuthu-Mhlathuzi Water Management Area (WMA), both groundwater level and rainfall have a declining trend for the entire record period. Tembe and Mbazwana areas showed a groundwater level decline of 0.7 and 2.7 m, respectively; while areas around Richards Bay experienced a groundwater level reduction between 0.7 and 6.3 m from 2004 to 2015. During the same period, rainfall was significantly reduced around Tembe, Mbazwana and Richards Bay areas by 26, 6 and 18% from the mean, respectively. The uThukela WMA, around Dundee and Newcastle exhibited an increase in groundwater levels by about 1.5 m between 2004 and 2010 but later declined by 1.2 m in the period from 2014 to 2015. During the period from 2004 to 2010, the rainfall showed increasing trend by 8%, but decreased by 22% in 2015. The central part of the uThukela WMA, around Tugela Ferry and Greytown, showed a decrease in groundwater level and rainfall by 3.2 m and 15%, respectively for the entire record period. The northern Mvoti- uMzimkhulu WMA around Maphumulo showed groundwater level decline by 11 m for the period from 2005 to 2011. However, the groundwater level recovered by 8 m between 2012 and 2013 following an increase in rainfall by 21%. Areas around Durban, groundwater level showed an increasing trend from 2005 to 2008 which coincided with an increasing rainfall amount by about 13%. The rainfall decreased by 21% from 2012 to 2015 resulting in the decline of groundwater level by 0.4 m for the same period. The steady decline in the groundwater level across the province appears to be a response to prolonged reduction in rainfall, which consequently reduced the amount of groundwater recharge reaching the aquifer. The response of the groundwater level to changes in rainfall across KZN has a lag time between 1 to 4 months.

Abstract

The benefits of the commercial plantation forestry sector (income generation, job provision, etc.) come at considerable environmental costs, particularly the impact of the industry on water resources. Plantation forests exhibit higher evapotranspiration rates when compared to that observed in indigenous forests/grasslands. A reduction of the water yield in a catchment is one of the most frequently reported impacts of afforestation. Afforestation also significantly impacts groundwater, which is becoming an increasingly important resource for water supply in South Africa. Very few studies have however quantified in detail the impact of different commercial forests grown in South Africa on groundwater and the interactions with surface water. This study seeks to contribute to addressing this important knowledge gap. The main objective was to comprehending groundwater recharge dynamics in commercial plantation forests, i.e. an environment where evapotranspiration losses is a major component of the water balance. The HYDRUS-2D model was used to simulate the hillslope hydrological dynamics in a commercial plantation forest (Pinus radiata) during the period 8 July 2016 to 12 June 2017. The model was used to simulate the interaction between the vegetation, unsaturated zone and the saturated zone in order to better understand the groundwater recharge dynamics evident in the area. As a precursor to model application a detailed conceptual model of the recharge processes occurring in the study areas was developed. The model considered the prevailing geomorphological and hydrogeological conditions. HYDRUS-2D was able to adequately simulate the soil hydraulic properties characterising the study area. The hydrological dynamics of the simulation results also conform to the conceptual understanding of groundwater recharge processes evident in the study area. Over the entire simulation period (340 days), the model quantified potential groundwater recharge to be 31.5 mm. This primarily occurred during a 60 day period (20 September 2016 - 19 November 2016) in response to significant rainfall events of 76.96 mm (DOS 56 – 58) and 45.98 mm (DOS 71 – 72). This groundwater recharge dynamic conforms to the notion that groundwater recharge is driven by single or multiple events and not by annual averages. The results of the investigation are promising and provide motivation for the application of HYDRUS-2D to estimate groundwater recharge in environments which are deemed to be suitable for model application. The model provides the ability to study the dynamics of groundwater recharge at short time scales, as opposed to annual average responses which are derived from commonly applied techniques.

Abstract

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

Abstract

A fault system may form preferential flow paths for groundwater along fault planes. In an industrial and mining environment, such geological structures pose a geohydrological challenge when delineating and managing groundwater pollution. A geophysical investigation, employing electric resistivity tomography (ERT) and electromagnetics (EM), was conducted along a section of a graben system to improve the geological understanding, define groundwater flow paths and pollution distribution in a mining and industrial setting. Additionally, the geophysical survey assisted in the siting of monitoring boreholes to gain an understanding of the geohydrological properties within the fault system. A total of 35 profiles were completed along a 12 km section of the graben including a refined grid around a water-filled quarry with elevated salinity. The geophysical results confirmed the presence of faults and indicated zones of lower apparent resistivity along the graben. Areas of elevated conductivity were modelled near industrial and mining operations, such as ash tailings, discard dumps and mine-water dams, suggesting that leachate could potentially seep into the underlying aquifers. A refined ERT model around the quarry indicated areas of high conductivity at dolerite contacts, fault planes and within a backfilled area which could form preferential groundwater flow paths from and to the quarry. This study showed that a fault system underlying industrial and mining activities with high conductivity zones could distribute seepage along secondary geological structures but could also aid as a barrier between different aquifer systems. An outstanding groundwater chemistry analysis is expected to provide further insight whether the detected groundwater flow paths along the fault planes contribute to the distribution of pollutants across the industrial site. Overall, the geophysical survey and consequent siting of monitoring boreholes were useful tools to identify groundwater flow paths for pollutants across a large scale structure to implement future water management plans.

Abstract

Arsenic is a common contaminant typically found in effluent from gold mine operations and copper smelters throughout the world. The geochemical behaviour of arsenic in contact with dolomite underlying an arsenic containing waste rock pile was investigated. The interaction between the arsenic and the dolomite is an important control in the subsequent transport of the arsenic in the dolomitic aquifer. Rocks with varying dolomite content were tested to investigate the interaction between the arsenic and dolomite. From the modelling and test results it was estimated that in the aquifer, between 60 - 90% of arsenic is present in the solid phase under oxidation conditions at >50 mV. At 50 to -25 mV about 40 - 60% of the arsenic is estimated to be present in the solid phase and below -25 mV about 0 - 10% of arsenic will be present in the solid phase. Although some arsenic is removed by the dolomite in the aquifer the arsenic would still be present above acceptable guidelines for drinking water. The arsenic in the solid phase will be in equilibrium with the aquifer water and could be remobilised 1) under more reducing conditions or 2) with a decrease in arsenic in the aquifer.

Abstract

To control the impact of nitrate and its sustainable mitigation in groundwater systems used for drinking water production, it is crucial to understand and quantify sources as well as biochemical processes which (permanently) remove nitrate.

In an alluvial aquifer in Germany (Hessian Ried) that serves as major drinking water recourse for the Frankfurt metropolitan area, water quality is challenged by nitrate contamination from intensive agricultural land use locally by far exceeding the drinking water limits of 50 mg/L.

In order to evaluate the capability of the aquifer for natural mitigation of the nitrate contamination, we investigated the denitrification potential with respect to the availability of electron donors and the predominant reduction pathways in different sections of the aquifer. The content of sedimentary sulfide and organic carbon was quantified by solid-phase analyses of drill core samples from aquifer sediments. Water samples from vertical profiles gave access to information on the isotope-hydrochemical composition of the groundwater (multi-parameter profiles, major ions, nitrate isotope signature, sulfate isotope signature). Using this hydrochemical and isotope information in concert with the results of a groundwater flow model allowed determining the nitrate input and the average nitrate reduction kinetics along the flow path upstream of selected groundwater monitoring wells. Batch and column experiments provided detailed information on prevailing reaction pathways and the associated isotope fractionation pattern enabling the recognition and quantification of processes on field scale. Our results suggest that litho-autotrophic denitrification using sedimentary sulfide as an electron donor is preferably responsible for the nitrate degradation in the aquifer. However, due to the low sulfide content (max. 123 mg-S/kg), the potential for autotrophic denitrification is very limited. Consequently, if no active measures reducing the input of fertilizer-derived nitrate will be implemented in the near future, the limited potential for autotrophic denitrification will ultimately exhaust and a severe deterioration of the groundwater quality can be expected.

Abstract

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