Conference Abstracts

Abstract

There is an urgent need to support the sustainable development of groundwater resources, which are under increasing pressure from competing uses of subsurface geo-resources, compounded by land use and climate change impacts. Management of groundwater resources is crucial for enabling the green transition and attaining the Sustainable Development Goals. The United Nations Framework Classification for Resources (UNFC) is a project-based classification system for defining the environmental-socio-economic viability and technical feasibility of projects to develop resources and recently extended for groundwater. UNFC provides a consistent framework to describe the level of confidence in groundwater resources by the project and is designed to meet the needs of applications pertaining to (i) Policy formulation based on geo-resource studies, (ii) Geo-resource management functions, (iii) Business processes; and (iv) Financial capital allocation. To extend use in groundwater resources management, supplemental specifications have been developed for the UNFC that provide technical guidance to the community of groundwater professionals to enhance sustainable resource management based on improved decision-making. This includes addressing barriers to sustainably exploiting groundwater resources, avoiding lack of access to water and also related to ‘common pool resources’ in which multiple allocations are competing with domestic water supply (e.g. geo-energy, minerals, agriculture and ecosystems, and transboundary allocation of natural resources). UNFC for groundwater resources is designed to enhance governance to protect the environment and traditional users while ensuring socio-economic benefits to society. Consequently, it is a valid and promising tool for assessing both the sustainability and feasibility of groundwater management at local, national and international levels.

Abstract

Water scarcity has driven many countries in arid regions, such as Oman, to desalinate seawater for freshwater supply. Episodic problems with seawater quality (e.g., harmful algae), extreme weather events that affect energy supply and hence the desalination process have nurtured the urgent need to store desalinated seawater (DSW) in the aquifers for use during emergency and peak demand time. Aquifer Storage and Recovery (ASR) using injection wells is a possible strategic option for Oman Water and Wastewater Services Company (OWWSC) to augment aquifer storage using excess desalinated water during low demand times. ASR strategically serves as a water supply backup to optimize production capacities against seasonal demand patterns. The technical-economic feasibility of implementing ASR schemes was investigated in Jaalan, Oman, using hydrogeological and geophysical field measurements, groundwater flow and hydraulic modelling, and economic analysis. Analysis of modelled scenarios results revealed that the Jaalan aquifer is suitable for storing and recovering about 4,000 m3 /hr in 2045. Various well field designs have been tested and optimized numerically using MODFLOW 6, showing that with 160 dual-purpose wells, 7.9 Mm3 can be injected and abstracted within the constraints defined for a robust and sustainable ASR system. Simulations with the density-dependent flow model (MF6 BUY) show that the injected volume can be fully recovered considering the drinking water quality standard. Other sites were also studied. ASR capacity was found to be site-specific, and the groundwater developments near the ASR site governed its feasibility

Abstract

South Africa is classified as a semi-arid region where the evapotranspiration sometimes exceeds the annual recharge through rainfall which leads to more drought periods. Combine the before mentioned issue with the water shortages and the impact of mining on water in South Africa, the focus therefore then needs to be placed on the proper estimation of recharge from rainfall and subsequent water management of these water sources. The Ermelo region in Mpumalanga was chosen for the investigation into calculating recharge from rainfall, using water balance methods as the basis on which recharge is calculated. The Ground Water Balance, Saturated Volume Fluctuation, Ground water level fluctuation and Cumulative Rainfall Departure methods was used to calculated recharge and then compare the different methods and their values with each other to compile an accurate estimation of recharge in the area. The data was analysed for each of the methods and then plotted and compared on a simple x-y chart. A new equation was formulated whereby any recharge from the previously mentioned methods can be normalized against the new formula for a more accurate recharge value. As a secondary objective a recharge intensity map was compiled for the area showing the areas of potentially high recharge.

Keywords: South Africa, Ermelo, Recharge Estimation, Water balance methods, Ground Water Balance, Saturated Volume Fluctuation, Ground water level fluctuation, Cumulative Rainfall Departure, Intensity maps.

Abstract

Water and contaminant transport processes in the vadose zone through preferential flow paths can be understood using environmental and artificial tracer methods. Further improvement in tracer techniques can be achieved by applying numerical modelling techniques of both water and solute transport, accounting for additional information on water movement and the matric potential of the vadose zone. The vadose zone is often ignored as a key component linking the land surface to the groundwater table, even though it acts as a filter that removes or stores potential contaminants. The water transit time between the surface and the groundwater table is frequently investigated using artificial tracers that normally show conservative behaviour. The main advantage is that the input function can be clearly defined, even though artificial tracers can generally only be applied over a relatively small area. The research is expected to provide insight into the selection and use of environmental and artificial tracers as markers for detecting and understanding the contaminant transport processes and pathways of contaminants in altered vadose zone environments (open-pit quarry). The impact is improved characterisation of the pathways, transport and migration processes of contaminants, and residence times, leading to the development of appropriate conceptual and numerical models of vadose zone flow processes that consider various contaminant sources. The principal aim is, therefore, to systematically examine the transport mechanisms and associated pathways of different environmental and artificial tracers in an open-pit quarry.

Abstract

The work presented in this paper incorporates spring data for further conceptualizing the hydrogeology of northern Namibia’s so-called “Karst Area”, an area around the towns of Tsumeb, Otavi and Grootfontein. Also called the Otavi Mountainland, it can be described as a mountainous highland of parallel, east-west trending elongated valleys and ranges shaped by the underlying folded units of carbonate rocks of the Damara Supergroup. The karst aquifers are a supplementary source to the central areas of the country during drought. Most of these 35 springs are often found near hilltop crests or high up on the mountain flanks rather than lower down at the valley floors. If flows are generated locally as gravity or contact overflow springs, studying them would not add much to conceptualizing the regional groundwater flow. Fundamental insights are provided if flows arise due to hydraulic pressure from deeper down. As artesian boreholes do not occur as a rule in the Karst Area, artesian springs might indicate the presence of deeper aquifers out of reach at normal drilling depth. One such hypothesis is that the bottom of the dolomitic synclines, structurally weaker at the fold axis, had been subjected to deep-seated karstification. The work presented here investigates that possibility and argues for and against it. In addition, established concepts of groundwater flow mechanisms for the area have been revisited. A conclusion has not yet been reached, but the balance of the arguments is presented.

Abstract

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

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

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

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

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

Abstract

It is estimated that the three coal layers in the Springbok Flats contain about 5 TCF of coal bed methane (CBM). Two sedimentary basins, namely the southern Tuinplaas basin and the northern Roedtan basin, exist with coal layers with a total thickness of 7m which occurs mainly in three mayor seams. The coal layers are located between 20 m to more than 600m.
Farmers in the Flats are concerned about the environmental impact of fracking the coal beds. They are mostly worried about the risk of groundwater pollution; the drawdown of the water table and the producing of a bad quality water during the mining process. They set up an EPA for the Springbok Flats in 2010 and until now, they have stopped more than 6 companies to conducted exploration (stopped strictly on account of the different laws in SA that were not adhered too).
On average, 1000 liters of water is produced for every 2000 cubic feet coal bed methane mined in the USA. The quality of the produced water is not good (with typical Na values of more than 5 000 mg/l) and cannot be used for irrigation purposes.
It is thus expected that about 500 million m3 of bad quality water will be produced for every 1 TCF mined in the Flats. This groundwater will be removed from the system and it is expected that a drawdown of up to 30m will be evident at places in the Springbok Flats. There are also a large number of dykes and faults in the Flats which imply that the upward movement of methane and water will be very probable after abandonment of each coal methane well.

Abstract

The so-called apparent increase of transmisivity (T) or hydraulic conductivity (K) with scale is an artifact and does not exist in the field. The reason for the apparent increase of T with scale is due to the use of the “not applicable” random log Gaussian stochastic models that are used by geohydrologists. In the petroleum field, where deterministic methods are applied, the apparent increase of T with aquifer volume does not occur. Groundwater practitioners have to change their view and use models that do not show this effect.

Abstract

Managed aquifer recharge (MAR) has become increasingly popular in Central Europe as a sustainable, clean, and efficient method for managing domestic water supply. In these schemes, river water is artificially infiltrated into shallow aquifers for storage and natural purification of domestic water supply, while the resulting groundwater mound can simultaneously be designed to suppress the inflow of regional groundwater from contaminated areas. MAR schemes are typically not managed based on automated optimization algorithms, especially in complex urban and geological settings. However, such automated managing procedures are critical to guarantee safe drinking water. With (seasonal) water scarcity predicted to increase in Central Europe, improving the efficiency of MAR schemes will contribute to achieving several of the UN SDGs and EU agendas. Physico-chemical and isotope data has been collected over the last 3-4 decades around Switzerland’s largest MAR scheme in Basel, Switzerland, where 100 km3 /d of Rhine river water is infiltrated, and 40 km3 /d is extracted for drinking water. The other 60 km3 /d is used to maintain the groundwater mound that keeps locally contaminated groundwater from industrial heritage sites out of the drinking water. The hydrochemical/isotope data from past and ongoing studies were consolidated to contextualize all the contributing water sources of the scheme before online noble gas and regular tritium monitoring commenced in the region. The historical and the new continuous tracer monitoring data is now used to inform new sampling protocols and create tracer-enabled/assimilated groundwater-surface water flow models, vastly helping algorithm-supported MAR optimization

Abstract

The use of radiogenic isotope tracers, produced through bomb testing (e.g. 3H and 14C), and the application of these isotopes is yet to be fully explored now that atmospheric abundances have returned to background levels. New isotope-enabled institutions and laboratories have recently been established in developing countries to apply isotopes in practical research. This study utilized several laboratories in South Africa and in Europe to compile a robust hydrochemical (major cations and anions) and isotope (d18O, d2H, 3H, 14C, 86Sr/87Sr) dataset of groundwater from 95 sample locations in the Maputo province of Mozambique. Groundwater is hosted in different aquifers and recharged through variable mechanisms ranging from direct infiltration of exposed alluvial soils to inter-aquifer transfer between fractured aquifer systems in the mountainous regions and the weathered bedrock in the lowlands. A combination of hydrochemistry and isotopes provided insight into the heterogeneous nature of recharge, mixing of modern and fossil groundwaters, and aquifer vulnerabilities when combined with other physical parameters in the region. However, it is also clear that grab sampling over a regional spatial extent and two sampling seasons (wet and dry) did not capture all the system variability, and more regular monitoring would uncover details in the system’s behaviour not captured in this study.

Abstract

A groundwater study at Middelburg Colliery was completed with the emphasis on the investigations into water balances on a rehabilitated coal mining environment. Water balance calculations and water scheduling for collieries in Mpumalanga have become important facets of mine planning over the past years. Opencast mining involves the blasting and removal of rocks overlying the coal layer, which is removed completely. The overburden is then replaced (backfilled) and covered with soil and the terrain is rehabilitated. Rainwater penetrating through the soil into the backfill may become acidic by pyrite and sulphides in the backfill material and ultimately decants on the surface. Decanting generally commences a decade or more after mining ceases. Opencast mining impacts the natural groundwater regime and radically alters the nature of groundwater-surface water interactions. The Department of Water Affairs and Forestry in South Africa requires that mines minimise the release of their polluted water. A groundwater balance is the numerical accounting of the annual recharge to a groundwater resource. It can further be described as a quantitative assessment of the total water resources of a basin over a specific period of time. In a groundwater development program, such a budget is necessary to efficiently manage and utilize the resource. Many of the parameters that determine recharge to an aquifer are measured directly and some are computed from hydraulic characteristics and measured field data. The Middelburg Mine Services has been experiencing excess water problems in past years. Because of the lack of space and the concerns of decanting of mine water out of the rehabilitated pit, it was suggested that mine water treatment should be considered. Geohydrological models were created to determine the decant positions and water volumes for the rehabilitated area. The size of the water treatment plant can then be determined using the calculated decant volumes and positions.

Abstract

POSTER Electrical Resistivity Tomography (ERT) surveys were conducted in the Kruger National park (KNP) as part of a recent Water Research Commission project (titled: Surface water, groundwater and vadose zone interactions in selected pristine catchments in the Kruger National Park). The surveys were carried out in a pristine ephemeral third-order supersite catchment, namely the southern granite (Stevenson Hamilton). This supersite is representative of the southern granite region of KNP as it covers part of the dominant geology, rainfall gradient and dominant land system.

Electrical   resistivity   profiling   provided   valuable   data   on   the   subsurface  geological   material distribution and results depended on soil/rock properties, water content and salinity. The purpose of electrical surveys was to characterise the hydrogeological components of weathering and depth to water level using the subsurface resistivity distribution. The ground resistivity is related to various geological parameters such as the mineral and fluid content, porosity and degree of water saturation in the rock.

Based on the initial ERT survey interpretations, boreholes were drilled providing actual subsurface results in the form of borehole drilling logs, water levels, hydraulic data and in situ groundwater quality  parameters.  Integrating  the  ERT  survey  data  with  the  results  from  the  intrusive  survey enabled an updated conceptualisation of groundwater flow characteristics and distribution across the southern granite supersite.

Abstract

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

Abstract

Underground Coal Gasification (UCG) is an emerging, in-situ mining technology that has the advantage to access a low cost energy source that is currently classified as not technically or economically accessible by means of conventional mining methods. As such it offers significant potential to dramatically increase the world's non-recoverable coal resource.

Groundwater monitoring in the South African mining industry for conventional coal mining as an example, is well established, with specific SANS, ASTM and ISO Standards dedicated for the specific environment, location and purposes. In South Africa a major impact of the coal mining industry can be a reduction in the groundwater quantity and quality. South-Africa's groundwater is a critical resource that provides environmental benefits and contributes to the well-being of the citizens and the economic growth. Groundwater supplies the drinking water needs of a large portion of the population; in some rural areas it represents the only source of water for domestic use. Utilization and implementation of groundwater monitoring programs are thus non-negotiable.

The groundwater quality management mission, according to the Department of Water and Sanitation in South-Africa, is set in the context of the water resources mission and is as follows:

"To manage groundwater quality in an integrated
and sustainable manner within the context of the National
Water Resource Strategy and thereby to provide an
adequate level of protection to groundwater resources
and secure the supply of water of acceptable quality."

The scope of this paper is to propose an implemention strategy and a fit-for-purpose groundwater monitoring program for any Underground Coal Gasification commercial operation. It is thus important to pro-actively prevent or minimise potential impacts on groundwater through long-term protection and monitoring plans. A successful monitoring program is one that consists of
(1) an adequate number of wells, located at planned and strategic points;
(2) sufficient groundwater sampling schedules; and
(3) a dedicated monitoring program and quality control standard.

In order to have an efficient monitoring program and to prevent unnecessary analysis and costs, it is also critical to determine upfront what parameters have to be monitored for the specific process and site conditions.

Abstract

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

Abstract

The Kalahari iron manganese field (KIMF) in the Northern Cape, South Africa, was historically exploited by only three mines, with Hotazel the only town and the rest of the area being largely rural, with agricultural stock/ game farming the major activity. Since 2010, mining activities have increased to more than 10 operational mines with increased water demand and environmental impacts on groundwater. The area is within catchments of the Matlhwaring, Moshaweng, Kuruman and Gamogara rivers that drain to the Molopo River in the Northern Cape. All the rivers are non-perennial, with annual flow occurrence in the upstream areas that reach this downstream area once every 10 years. The area is semi-arid, with annual evaporation nearly five times the annual precipitation. The precipitation is less than 300mm, with summer precipitation in the form of thunderstorms. Vegetation is sparse, consisting mainly of grasslands, shrubs and some thorn trees, notably the majestic camel thorns. The Vaal Gamagara Government Water Supply Scheme imports 11 Ml/d or 4Mm3 /a water for mining and domestic purposes in the KIMF section. The area is covered with Kalahari Group formation of 30 to 150 m thick with primary aquifers developed in the basal Wessels gravels and Eden sandstones for local use. The middle Boudin clay forms an aquitard that isolates and reduces recharge. Water levels range from 25 to 70m, and monitoring indicates local dewatering sinks and pollution. This study will report on the water uses, monitoring and observed groundwater impacts within the current climatic conditions.

Abstract

Gold Mining activities the past 60 years at AngloGold Ashanti polluted the groundwater underlain by 4000 ha of land at the Vaal River and West Wits operations in South Africa. Sulphide material in Tailings Storage Facilities, Waste Rock Dumps and extraction plants produce Saline Mine Drainage with Sulphate, minor salts and metals that seep to the groundwater and ultimately into surface water resources. Water regulation requires mines to prevent, minimise/ reduce or eliminate pollution of water resources. The waste philosophy has matured from tolerate and transfer to treat and termination of pollution sources. The impact of the pollution was determined and possible technologies to treat the impact were evaluated. Source controls of proper water management by storm water management, clean dirty water separation, lined water conveyance structures and reduced deposition of water on waste facilities is crucial. The aquifer character determines the possible remediation technology. From the possible technologies phytoremediation, physical interception and re-use of this water was selected. In future possible treatment of the water would be considered. This paper explain the strategy and report on the phased implementation of these plans and the expected results. The establishment of 750 ha of woodlands as phytoremediation, interception trenches of 1250 m, 38 interception boreholes and infrastructure to re-use this water in 10 water management areas is planned. The total volume of 15 Ml/day would be abstracted for re-use from the boreholes and trenches. The woodlands can potentially attenuate and treat 5 ml/day. The established woodlands of 150 ha proof successful to intercept diffused seep over the area of establishment and reduce the water level and base flow. The 2 implemented trenches of 1000 m indicate a local decline in the water level with interception of shallow groundwater within 1-2 m from surface. The 2 production interception well fields abstracting 50 and 30 l/s respectively indicate a water level decline of between 2 to 14 m with regional cones of depression of a few hundred meters to intercept groundwater flow up to 20 meter. Predictions from groundwater modelling indicate that these schemes can minimise pollution during the operational phase and protect downstream water resources. Predictions from modelling indicate that the pollution sources need to be removed to ensure long term clean-up to return the land to save use. The gold and uranium prize is securing the removal of the sources through re-processing of the tailings and waste rock dumps. After removal of the sources of pollution the remediation schemes would have to be operated for 20 years to return the groundwater to an acceptable standard of stock watering and industrial water use. The water quality is observed by a monitoring network of approximately 100 observation boreholes.

Abstract

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

Abstract

The provision, usage and discharge of water resources are major concerns for coal mines, both underground and opencast. Water resources in a coal mining environment will often account for a significant portion of the daily operational cost. In order to cut costs, the mine will often collect as much runoff as possible to recycle for future use. This on-going recycling of site water and management of the resource demands a complete site water balance model in order to understand the dynamics of the resource within the boundaries of the mine. To improve the understanding of the dynamics of the resource on a much larger scale, and the effect it will have on recharge in an open cast coal mine environment, one must consider alternative modelling approaches which can compensate for such conditions. This amounts to describing recharge as a modelling component in a physically based distributed model. The main goal of this project is to calculate recharge into the main pit at this specific colliery by applying parameters on a quaternary catchment scale. The colliery is located just west of the town of Ogies, Mpumalanga on the peripheral region of the quaternary catchment B20G. The physiography of the quaternary catchment B20F is described as a central Highveld region gently sloping to the north. The geohydrological modeling application MIKE SHE (developed by DHI) was used to develop a fully integrated catchment model. The model was created mainly to simulate the impact of human activities on the hydrological cycle and hence on water resource development and management. Different modules of MIKE SHE that was used during the modelling stage include saturated- and unsaturated flow and a small degree of overland flow.

Key words: Mpumalanga, MIKE SHE, recharge

Abstract

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

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

Abstract

The mineral rich basin of the West African region has vast reserves of gold, diamond as well as iron ore deposits. Throughout the regional geological setting characterised by structural variations and intrusive belts with metamorphic mineral rich sequences covered by saprolite soils, one common chemical constituent remains a constant in the water reserves. Arsenic is in high concentrations throughout the region with chemical ranges commonly above the various country guidelines as well as international IFC and WHO standards. The aqueous chemical species is associated with arsenopyrite rich mineralogy of the regional greenstone belts and highly weathered soils. This conference article and presentation investigates the natural source of the arsenic through baseline data as well as the effect of mining on the already high concentrations of arsenic in both the groundwater and surface water. Natural levels of various chemical species in the regional area are already high at baseline level. One of the main research questions is thus whether mining and other anthropogenic activities will have an impact on the environment or will the changes to concentrations be so insignificant to allow the ecosystems and water users to continue in their current ways without any effect. Various case studies in Burkina Faso, Liberia, Sierra Leone and other countries have been combined to investigate the arsenic-rich resources of the West African region through groundwater specialist investigative methods with emphasis on geochemical modelling of the fluid-rock and fluid-fluid interactions leading to the water quality in the region.

Abstract

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

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

Abstract

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

Abstract

Collecting groundwater information close to the ocean often raises the question whether a tidal effect could be influencing the data. Sometimes this issue leads to speculation that is counterproductive and sometimes it is overlooked thereby causing judgement errors when interpreting data. This paper looks at the theoretical background of tidal influences in coastal aquifers to identify the screening factors to consider when deciding whether a contaminated site assessment needs to take tidal influences into account. The rising and falling of the tides cause a standing wave with varying frequency that is dampened by the neighbouring aquifer as the wave travels into it. Unconfined aquifers generally tend to be affected over a short distance, while the pressure wave can travel significant distances in a confined aquifer. There are indications that the rise and fall of the tides prevent discharge of the LNAPL, but it could cause lateral spreading due to the head changes in the aquifer. The tidal fluctuation also causes uncertainties in the LNAPL measurements. The case study presents data from a site where tidal variation directly influences the distribution of LNAPL in monitoring holes, while the variation in total fluid level is slight. In this specific case the tidal variation has to be accounted for, otherwise skewed measurement data will be collected.

Abstract

Mining site remnants are everlasting and impact the groundwater regime on a long term scale. An integrated approach to geoscience is necessary due to the complexity of nature and the unknown relationships that must be discovered to further the understanding of impacts on the natural environment. Furthermore, groundwater resources are negatively impacted by mining activities affecting the groundwater quality and quantity. Underground coal mining can be accompanied by roof failure events. This may change the matrix which subsequently alters the flow regime; leads to variations within the water chemistry, provided there is inter- aquifer connectivity; and alters the recharge rate. Dewatered mine voids are in direct contact with oxygen initiating oxidation reactions, depending on the geology of the specific site. A change in water chemistry was analyzed, and this coincides with a roof failure event as interpreted from water level measurements. Concentrations of Mg, Ca, and alkalinity indicate anomalous changes that are still in effect, five to six years after the majority of water levels had stabilized. The changes in the system coincides with and correlates to events of roof failure and different parameters. The latter changes are applied as extra tools when interpreting different site specific anthropogenic induced impacts on the system. Also within this study, constant rate pumping tests were conducted for the interest of the hydraulic properties, using three farming boreholes. The results put forward a range of 0.21 – 0.44L/s and 6.5 – 11.5m2 /d, for sustainable yield and transmissivity, respectively. Furthermore, it is recommended that a better understanding can be gained on system behaviors if chemistry correlations can be gathered through certain events causing specific systems to be in disequilibrium. It is also recommended that additional pumping tests will allow more insightful interpretation and delineation between the abovementioned chemical and water level changes. Finally, the combination of parameters during events can aid in deciding the most appropriate analytical models used for further analysis.

Abstract

The Geneva aquifer is internationally recognized for its transboundary resource management agreement between Switzerland and France, described as the first groundwater management agreement in the world. Signed in 1978 and renewed in 2008, this agreement on managing a shared underground resource has long been an example for establishing other agreements worldwide, particularly by UNESCO and its hydrological program via the TBA commission of the IAH. Like many countries worldwide, Switzerland and France experienced a critical summer of 2022 concerning the use of water resources, both surface and underground. The system applied in the cross-border agreement for using the aquifer involves French participation in the costs of managing aquifer recharge (MAR), depending on the total pumping. It shows that the French part, having consumed more water to compensate for the extreme drought of 2022, has seen its bills increase considerably. Development plans show that the population of Greater Geneva will increase considerably by 2030-2040, requiring significant medium-term water availability (30% additional water). Therefore, the French institutions’ political leaders have formally asked the authorities of the canton of Geneva to review the conditions linked to the quotas and calculation methods included in the 2008 agreement. A new agreement could be a real example of positive cross-border coordination for decision-makers finding themselves in a blocked or even conflicting situation due to differences in managing a shared resource revived by the effects of climate change.

Abstract

The so-called apparent increase of transmisivity (T) or hydraulic conductivity (K) with scale is an artifact and does not exist in the field. The reason for the apparent increasing of T with scale is due to the use of the "not applicable" random log Gaussian stochastic models that are used by geohydrologists. In the petroleum field, which uses deterministic methods, the apparent increase of T with aquifer volume does not occur. Groundwater practitioners have to change their view and use models that do not show this effect.

By using intuitive inspection of geological, fracture and connectivity data as well as real pumping test data, this paper shows that up-scaling must be performed with an exponential decaying function, where T always decreases with scale
.
Two types of heterogeneities exists namely a.) horizontal and b.) vertical. Connectivity between fractures is extremely important in both cases, but it is only in semi-confined and watertable aquifers that the vertical heterogeneities are really important (typical case of fracture dewatering)
{List only- not presented}

Abstract

Year-round water security is at risk as socio-economic developments lead to increasing water demands, while climate change affects water availability through higher-intensity rainfall and prolonged periods of drought. Coastal zones and deltas with often high population densities experience additional risks of salinisation and land subsidence. These developments ask for creative solutions to secure sustainable and year-round access to fresh water. The subsurface provides storage capacity to actively infiltrate freshwater, bridging the time-gap between demand and supply. Combining infiltration with extraction and desalination of brackish water prevents the salinisation of aquifers whilst providing an additional water source. We call this COASTAR. A Dutch research consortium with partners like water companies and water boards develops COASTAR. Among COASTAR results are suitability maps for Aquifer Storage and Recovery (ASR) and Brackish Water Extraction (BWE) in the coastal zone of the Netherlands. The maps are based on geohydrological factors. A quick-scan analysis was also performed to quantify the nation-wide potential extractable ASR and BWE volumes. COASTAR develops case study models and local scale pilots on ASR and BWE. For two water supply regions, an analysis has been made to geographically match development in water demand with suitability for ASR and BWE as a step in the search for strategic locations to develop ASR and BWE. The suitability maps provide guidance for initiatives’ development and practical experiences from pilot projects; this provides important information for further upscaling of COASTAR approaches.

Abstract

Test-pumping drawdown curves do not always sufficiently indicate aquifer characteristics and geometry and should never be analysed in isolation. Using derivative analysis and flow dimension theory, inferring the regional geometries and flow characteristics of fractured aquifers that are otherwise unknown or inconclusive is possible. As the drawdown and/or pressure front propagates through the aquifer, it reaches various hydrogeological objects that influence flow regimes and imprints a sequence of signatures in the drawdown derivative curve. The conjunctive interpretation of these flow regime sequences and hydrogeological data results in a robust, well-informed conceptual model (in terms of both local groundwater flow and the aquifer), which is vital for sustainable groundwater resource management. Derivative and flow regime analysis was applied to the test-pumping data of confined and unconfined Nardouw Aquifer (Table Mountain Group) boreholes within Steenbras Wellfield (Western Cape). Major NE-SW trending folding and transtensional Steenbras-Brandvlei Megafault Zone, in association with cross-cutting faults/fractures and younger False Bay Suite dykes, make the Nardouw Aquifer (and deeper Peninsula Aquifer) hydrogeologically complex. The sequential flow regime analyses reveal domains of conceptual flow models, including open vertical fractures, T-shaped channels, double (triple) porosity models, and leaky/recharge boundary models, amongst others. Appropriate analytical flow models (type curve fitting) are then applied for accurate aquifer parameter estimations, which are used to evaluate recommended long-term yields through predictive pumping scenarios. The outcome is an improved hydrogeological understanding and enhanced conceptual model of the aquifer, which informs numerical modelling, ecological protection, and groundwater resource management.

Abstract

POSTER All groundwater is vulnerable to contamination, and natural in homogeneity in the physical environment results in certain areas being more vulnerable to contamination than others. Inherent in the agricultural, domestic and industrial sectors of Pietermaritzburg, is the generation of contaminants which, upon reaching the aquifer, result in the deterioration of the quality of groundwater, thus resulting in the water no longer being fit for its intended use. The DRASTIC method is used to calculate the groundwater vulnerability of a 670 km2 region, including the city of Pietermaritzburg. The suggested ratings of each parameter are scrutinised and adapted, according to their relevance to the region and according to known geological occurrences. The use of this method enables the user to generate a regional scale vulnerability map of the groundwater in Pietermaritzburg. The vulnerability map generated has the ability to effectively highlight vulnerable areas to groundwater contamination, which is of critical importance in correct land-use planning, as well as in indicating areas of particular concern, where further detailed investigations are needed. The results of such an assessment are used as an input, together with a contamination inventory to assess the potential risk of groundwater pollution in a groundwater risk map. Furthermore, the result informs local decision-makers and enables proactive prevention of groundwater pollution, in accordance with section 13 of the 1998 National Water Act. The intrinsic vulnerability of the Pietermaritzburg region was found to range from low to very high. The area found to be highly vulnerable is the region northeast of Springbank which requires investigation at a local scale.

Abstract

The costs of acid mine drainage (AMD) monitoring result in the quest for alternative non-invasive method that can provide qualitative data on the progression of the pollution plume and ground geophysics was the ideal solution. However, the monitoring of AMD plume progression by ground geophysics (time-lapse electrical resistance) proves to be non-invasive but also time consuming. This gave way to a study that focuses on the modeling of different scenarios of the karstic aquifer. The models use the field parameters such as the electrical resistivity of the host rock and the target rock, depth to the target, noise level and electrode configuration in order to ensure that the model outcomes represent the field data as much as possible. This geoelectric modeling process uses Complex Resistivity Model (CRMod) and Complex Resistivity Tomography (CRTomo) to generate geoelectric subsurface images. Different resistivity values are applied to targets in order to assess the difference against the baseline model for each target scenario. The model resistivity difference is reduced to the smallest difference possible between the reference and new models in order to gauge the lowest percentage change in the model at which the background noises start to have impact on the results. The study shows that the behavior of targets (aquifer) could be clearly detected through resistivity difference tomography rather than inversion tomography. The electrode array plays a significant part in the detection of target areas and their differences in resistance because of its sensitivity. This therefore indicates that the electrode array should be chosen according to study requirements. Furthermore, the model geometry also plays a role and this can be seen with the modelling of different target sizes, alignments and shapes. Future studies that can provide a correlation between the field quantitative data from sampling and the model outcomes have the ability to add to the knowledge field of geophysical modelling therefore reducing costs associated with field based plume AMD monitoring300-500 words without references; reach your conclusions rather than only delivering promises.

Abstract

Complementary use of electromagnetic frequency domain and electrosiesmic geophysical exploration methods in groundwater exploration in Zimbabwe.
Joseph M Zulu, Josrum Enterprises No. 129 A Fort Street, Albion Flats, 2nd Floor, Office Suite 5
Room 3, Bulawayo, Zimbabwe. Email Address: [email protected].
Abstract
Geophysical survey methods and divining are commonly used in groundwater exploration. In view of the current costs of drilling boreholes and fear of drilling a dry borehole, most people prefer the use of geophysical survey methods to have their boreholes sited. Some prefer the use of diving methods for initial siting and then confirmation of the identified site using geophysical survey methods. The key principle being complementarity of the methods to confirm the presence of water at the identified site. Electrical resistivity method and electromagnetic frequency domain methods are popular in ground water exploration in Zimbabwe, with electrical resistivity being the method of choice by many investigators. A new approach in groundwater exploration is proposed where complementarity of geophysical methods is exploited. A complementary approach of using geophysical methods in conjunction with geology, where two methods are used in investigating a site is proposed. In the study the latest technology in groundwater exploration, electrosiesmic survey method was used to complement the electromagnetic frequency domain method in various geological environments. Electromagnetic profiles were carried out on the target areas. Inversion was done on the collected and results presented as a pseudo section. Anomalies identified were further investigated using electrosiesmic sounding. The results of the sounding were presented in the form of a sounding curve. The subsurface layer thicknesses were calculated using forward modelling assuming the typical seismic velocity values of waves generated when passing through geological formations in the areas under investigation. The geology of areas studied include granite, greenstone, Kalahari sands, sandstones, mudstones and basalt of the Karoo stratigraphy. The approach produced impressive results. High yielding borehole sites were identified and successfully drilled in areas where it had been accepted that it was difficult to get water or in areas where it had been accepted there was no groundwater. Comparison of driller's log with models generated from geophysical survey results was also done.
Key words: electromagnetic, electroseismic, geology, complementarity, groundwater.
I acknowledge that this work has not been published elsewhere.

Abstract

The drinking water health issues have been considered due to improved living standards in recent years. Finding and developing high-quality groundwater with high-level minerals has become key to improving human health. The hydrochemical test data of 66 springs in Zhaojue County were analyzed using various methods, and the spatial distributions of H2 SiO3 -rich groundwater, hydrogeochemical characteristics, formation conditions and genesis were revealed. The main results including: 1) the groundwater with H2 SiO3 (≥25mg / L) was identified as the low salinity and alkaline water, which distributed in the six areas with the basement rocks of basalt,with a distribution area of about 79 square kilometers. The H2 SiO3 concentration was generally 25.74~46.04 mg/L; the low mineralization characterized the H2 SiO3 -rich groundwater of study area while the main hydrochemical types of groundwater are HCO3 - Ca·Mg, HCO3 -Ca, and HCO3 -Na; the Pearson correlation coefficient between the content of H2 SiO3 in groundwater and the content of pH is relatively high, indicating that the level of H2 SiO3 in groundwater in the study area is significantly affected by the pH value of the solution; the H2 SiO3 -rich groundwater was influenced by the water-rock interactions, the distribution range and solubility of silicate minerals ,the development of surrounding rock fissures, and water conservation and recharge conditions in the county, among which the water-rock interactions play a critical role. The results can provide a basis for the development of mineral water industry and the construction of urban and rural high-quality water sources in Zhaojue County.

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

Fine ash is a by-product generated during coal combustion and gasification. It is often disposed of as slurry and stored on tailings dams over long periods of time, where it is exposed to weathering. Weathering causes soluble ions to go into solution and to be transported along preferred pathways through the tailings dam. This study was conducted to assess the leaching behaviour of fresh and weathered fine ash and to evaluate the impact on the underlying aquifers. A kinetic test was conducted over 21 weeks to analyse the leachate composition of progressively-aged fine ash and to calculate the release rates for major ions and trace metals of environmental concern. The leachate composition was compared to the groundwater composition of the underlying aquifers to assess the environmental impact of long term ash leaching. The study showed that the release rate of Ca decreased with increasing depth and age of the fine ash. The release rate of Mg, Na, K, Mo, V, Ba, Cr and Mo increased slightly between 22 m and 28 m in the tailings dam. Aluminium had a decreasing release rate from 28 m depth onwards. It was concluded that fine ash leaching influenced the water composition of the underlying aquifers because similarities were observed in the water type trend. The shallow aquifer south of the tailings dam contained Ca/Mg/SO4/Cl/NO3 water with a significant increase in Ca, Mg, Na, Cl and SO4 over time. These ions were expected to be found in the pollution plume due to their high release rate observed in the fine ash. The deeper aquifer northeast and south of the tailings dam showed a reverse trend of decreasing Ca, Mg and NO3 with time. This is possibly due to decreasing release rates in the aging fine ash and due to the cation exchange capacity (CEC) of the aquifer retarding the movement of Ca and Mg in the pollution plume. The shallower aquifer northwest of the tailings dam showed a decrease in Ca and Mg but an increase in K, while the water composition of the deeper aquifer increased in Ca, Mg, Na, K and Cl. This indicates that the pollution plume moved from the shallower to the deeper aquifer and that most of the Ca and Mg content in the fine ash has been leached from the tailings dam after more than 30 years of storage. The study confirmed that leaching of elements from the fine ash tailings dam had a negative influence on the underlying aquifers and that the clay lining was not sufficient in retaining the leachate.

Abstract

Water balance partitioning within dryland intermittent and ephemeral streams controls water availability to riparian ecosystems, the magnitude of peak storm discharge and groundwater replenishment. Poorly understood is how superficial geology can play a role in governing the spatiotemporal complexity in flow processes. We combine a new and unusually rich set of integrated surface water and groundwater observations from a catchment in semi-arid Australia with targeted geophysical characterisation of the subsurface to elucidate how configurations of superficial geology surrounding the stream control the variability in streamflow and groundwater responses. We show how periods of stable stream stage consistently follow episodic streamflow peaks before subsequent rapid recession and channel drying. The duration of the stable phases increases in duration downstream to a maximum of 44±3 days before reducing abruptly further downstream. The remarkable consistency in the flow duration of the stable flow periods, regardless of the size of the preceding streamflow peak, suggests a geological control. By integrating the surface water, groundwater and geological investigations, we developed a conceptual model that proposes two primary controls on this behaviour which influence the partitioning of runoff: (1) variations in the permeability contrast between recent channel alluvium and surrounding deposits, (2) the longitudinal variations in the volume of the recent channel alluvial storage. We hypothesise optimal combinations of these controls can create a ‘Goldilocks zone’ that maximises riparian water availability and potential for groundwater recharge in certain landscape settings and that these controls likely exist as a continuum in many dryland catchments globally.

Abstract

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

Abstract

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

Abstract

Groundwater discharge is crucial for transporting terrestrial carbon into streams and rivers, but the effects of groundwater flow paths on terrestrial carbon inputs are poorly understood. Here, we investigated environmental tracers (EC, Cl-, 2H, 18O, 220Rn, and 222Rn) and carbon concentrations in riparian groundwater, streambed groundwater, and stream water over six groundwater-stream monitoring sites. Significantly high 220Rn and 222Rn activities in the stream and endmember analysis results of the environmental tracers reveal that vertical groundwater discharge from the streambed (VGD) and lateral groundwater discharge from the riparian zone (LGD) is of equal importance for the stream. We quantified VGD by modelling the detailed 222Rn and Cl- profiles at the streambed and then combined differential flow gauging to estimate LGD. VGD (2.9 ± 1.4 m2 d-1) prevailed in relatively wide and shallow channels, while LGD (2.6 ± 2.6 m2 d-1) dominated narrow and deep channels. Carbon measurements indicate that LGD had the highest CO2, CH4, DIC, and DOC, while VGD had relatively higher CO2 but lower CH4, DIC, and DOC than stream water. Our findings suggest that LGD is the primary carbon source for the stream, while VGD mainly dilutes the stream (except CO2). Finally, we observed that groundwater discharge and temperature overrode metabolism in controlling stream carbon dynamics, implying the importance of groundwater discharge for understanding stream carbon cycling. Overall, this study identified the impacts of groundwater flow paths on carbon exchanges between terrestrial and stream ecosystems.

Abstract

This study focused on improving the understanding of flow regimes and boundary conditions in complex aquifer systems with unusual behavioural responses to pumping tests. In addition, the purpose was to provide a novel analysis of the hydrogeological properties of aquifers to deduce inferences about the general expected aquifer types to inform new practices for managing groundwater. In this paper, we report that using derivative analysis to improve understanding of complexities in aquifer flow systems is difficult and rarely used in groundwater hydraulics research work. Thus, we argue that if derivatives are not considered in the characterizing flow regime. The heterogeneity of aquifers, boundary conditions and flow regimes of such aquifers cannot be assessed for groundwater availability, and the decision to allocate such water for use can be impaired. A comprehensive database was accessed to obtain pumping tests and geological data sets. The sequential analysis approach alongside derivative analysis was used to systematically perform a flow dimension analysis in which straight segments on drawdown-log derivative time series were interpreted as successive, specific, and independent flow regimes. The complexity of using derivatives analyses was confirmed. The complexity of hydraulic signatures was observed by pointing out n sequential signals and noninteger n values frequently observed in the database. We suggest detailed research on groundwater flow systems using tracer methods like isotopes and numeric models must be considered, especially in multilayered aquifer systems such as the Heuningnes catchment.

Abstract

South Africa is currently considering unconventional oil and gas (UOG) extraction as an additional energy resource to improve the country’s energy security. In a water-scarce country such as South Africa, which has experienced more frequent and more intense climate extremes due to climate change, the water-related impacts of UOG extraction is a concern. The South African government is however determined to proceed with UOG development as soon as regulations to protect natural resources have been drafted. The country’s intricate governance system can however not enforce such regulations effectively, as it experiences repeated inter-departmental miscommunication, fails to collaborate with stakeholders effectively, and lacks human and financial resources for enforcement. A lack of transparency in fracking operations and between stakeholders is another challenge for enforcing UOG extraction regulations. Poor regulatory enforcement presents an obstacle for the protection of groundwater resources if fracking were to commence.

This study, therefore, focuses on addressing the enforcement challenges of UOG regulations aimed at protecting groundwater resources. It proposes the use of civic informatics on a technology platform, specifically via a mobile application (FrackSA), to assist with on-the-ground enforcement of these regulations. While many UOG mobile applications are used internationally, they mostly focus only on UOG related aspects (news, information, pricing, geological information, and fracking well information). FrackSA uses civic informatics to address both groundwater monitoring and management as well as UOG extraction operations in a single platform, to enable regulators to protect groundwater resources more effectively during UOG extraction, while simultaneously enhancing transparency in the UOG industry.

Abstract

The assessment and prediction of mine water rebound has become increasingly important for the gold mining industry in the Witwatersrand basin, South Africa. The cessation of dewatering lead to large volumes of contaminated surface discharges in the western parts of the basin. Towards the eastern extremity of the Witwatersrand basin the detached Evander Goldfield basin has been mined since the early 1950s at depths between 400 and 2 000 m below ground, while overlain by shallower coal mining operations. The hydrogeology of the Evander basin can be categorised by a shallow weathered-fractured rock aquifer comprising of the glacial and deltaic sediments of the Karoo Supergroup, while the deeper historically confined fractured bedrock aquifer consist predominantly of quartzite with subordinate lava, shale and conglomerate of the Witwatersrand Supergroup. The deep Witwatersrand aquifer has been actively dewatered for the last 60 years, with a peak rate of 60 Ml per day in the mid late 1960s. Modelling the impacts of mine dewatering and flooding on a regional scale as for the Evander basin, entails challenges like the appropriate discretisation of mine voids  and  the  accurate  modelling  of  layered  aquifer  systems  with  different  free  groundwater surfaces on a regional scale. To predict the environmental impacts of both the historic and future deep mining operations at Shaft 6, the detailed conceptual model of the aquifer systems and three- dimensional model of the mine voids were incorporated into a numerical groundwater model to simulate the dewatering and post-closure rebound of the water tables for the basin. The presented model could serve as an example for the successful modelling of mine dewatering and flooding scenarios for other parts of the Witwatersrand basin.

Abstract

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

Abstract

Many of South Africa’s coal fields are characterised by a complex lateral and vertical pattern of mine voids, targeting different lease areas and coal seams, and applying different mining methods such as open cast (strip) and underground (board and pillar) mining. Many are at different stages in their life of mine from exploration to closure stage.

Despite the general recognition that the water management or absence thereof at neighbouring mines influences each other (evident for example in the recognition of inter-mine flow in the overall water balance for a site), and the requirement of cumulative impact assessments, very few studies actually attempt to tackle and quantify cumulative impacts of numerous mines on the ambient groundwater environment. While the parameterisation and calibration of a groundwater model for a single mine is often hampered by environmental data scarcity, the absence of cumulative impact assessments is mostly related to the unwillingness of neighbouring and competing mines to share these data. Soft- and hardware as well as budget limitations pose additional challenges for the development of regional groundwater models taking cognisance of complex mining environments.

This paper describes a regional groundwater flow model that takes into account five surface and underground mining areas. The different start and closure dates for the opencast and underground mining areas result in a complex mining schedule, with groundwater abstractions and inflows for the different areas potentially influencing each other during life of mine and post-closure and requiring therefore a simultaneous simulation thereof.

A further complication in the model development was the explicit consideration of cut-and-fill operations, necessitating alterations of the model topography to reflect annual cuts as free seepage boundaries, and to reflect rehabilitated backfilled areas with topography different from the pre-mining environment. The case study has led to numerical model software developments to enable transient changes in layer elevations over a simulation period.

While the model attempted to simulate the cumulative impact of the mines, it was also used to predict the impact of a new mining development on the life of mine and post-closure water balances for the remainder of the neighbouring mines. The model outcomes could therefore theoretically inform apportionment of post-closure liabilities.

Abstract

In order to meet the increasing national and international demand for coal, substantial expansion plans for existing as well as new coal mines were put forward in recent years. The mine developments are often proposed in environmentally sensitive areas and require an appropriate assessment of potential environmental impacts, including impacts on groundwater dependent ecosystems. This paper describes the development of a conceptual and numerical groundwater model as part of a wetland reserve determination in the Witbank coalfields. The model was used to assess potential mining related impacts on the shallow groundwater flow, including surface seepages and spring discharges feeding hill slope and valley bottom wetlands as well as pans. A number of shallow monitoring boreholes were sited, drilled and tested in the focus area around a pan to characterise the shallow perched and weathered aquifers. While these aquifers were generally found to be very low to low yielding, higher yields were encountered in a coarser grit layer intersected by two of the eight boreholes. The grit layer represents a potential preferential groundwater flow path towards the pan and was subsequently further delineated based on the exploration drilling logs from the mine. The different aquifers, the target coal seam, and over 60 mapped hill slope and valley bottom wetlands as well as pans, were incorporated into a numerical groundwater flow model. A free seepage boundary was assigned to the entire surface area to evaluate if the model is able to represent the observed seepages and spring discharges. The simulation of unsaturated flow processes (Richard's equation) was found to be crucial for the representation of discharges from perched aquifers. Following a satisfactory calibration of the model, different open cast mine layouts were then incorporated into the model to assess their impacts on the groundwater contribution to wetlands. The presented quantitative simulation of groundwater contributions towards wetlands and pans based on site specific groundwater investigations and data is considered a best practice example in assessing the groundwater component for a wetland reserve determination.

Abstract

Model calibration and scenario evaluations of 2D and 3D groundwater simulations are often computationally expensive due to dense meshes and the high number of iterations required before finding acceptable results. Furthermore, due to the diversity of modelling scenarios, a standardised presentation of modelling results to a general audience is complicated by different levels of technical expertise.

Reducing computational time
In this presentation we look briefly at the use of Reduced Order Models (ROM's), which is one of the recent developments in groundwater modelling. The method allows significant speed-up times in model calibration and scenario evaluation studies. In saturated flow for example, these approaches show speed-up times of >1000 when compared to full models created with Finite Element of Finite Difference methods. These methods are demonstrated to a case study in the Table Mountain Group, in which we show a simplified parameter calibration and scenario evaluation study.

Standardising presentation
In order to present the results to as wide an audience as possible, the use of a web-browser as a GUI is proposed, where the web-page is coupled to a geo-spatial database and data is presented in a spatial and numeric format. The use of the spatial database manager PostgreSQL with PostGIS is proposed. Through a browser interface, users can run modelling scenarios using the ROM, which is evaluated in near real-time. Following the evaluation of the model, we show how PostGIS can spatially present data on a base-map such as google maps. In keeping with the current trends in online map customisation, viewers can interactively choose to overlay the base-map with a data-type (such as pressure or hydraulic head contours or flow direction) that is most intuitive for their level of familiarity with the data.

Conclusion
In using advanced modelling techniques and a simplified browser based presentation of results, high-level decisions in water resource management can be significantly accelerated with the use of interactive scenario evaluations. Furthermore, by reaching a broader audience, public participation will be significantly enhanced.

Abstract

Several oil and gas companies have applied for licenses to extract unconventional oil and gas (UOG) resources in South Africa (SA) through a process known as hydraulic fracturing or fracking. The South African government is in the process of drafting regulations and procedures to allow the extraction of these resources. It is surmised, based on evidence from fracking examples around the world, that large volumes of wastewater may, however, potentially be generated during the extraction of these UOG resources. The issues arise when it comes to determining the actual volumes of wastewater that may be generated from this process, should it be used in SA, as well as the management of the wastewater. The volume of wastewater generated is dependent on a number of factors, with well properties, rock formation, basin properties and the number of fracturing stages within the well, being some of the dominant factors. In this project an extensive review of existing literature, reports and fracking databases was used to identify the methods used for determining wastewater volumes, which databases were used as well as the assumptions and challenges each data source faced. The data was analysed and interpreted in order to come up with various ranges and averages of wastewater generated through UOG extraction. The potential volumes of wastewater generated through fracking were then modelled into the hypothetical scenarios outlined in the Strategic Environmental Assessment (SEA) on Shale Gas Development in the Central Karoo. This allowed for the determination of potential volumes of wastewater associated with UOG extraction in SA from which management implications for wastewater in South Africa can be determined.

Abstract

Aquifer Thermal Energy Storage (ATES) is increasingly utilised to optimise the efficiency of Ground Source Heat Pump (GSHP) systems. However, the criteria for selecting ATES over Unidirectional GSHP is not well-defined. Inappropriate selection of AETS can adversely impact the long-term viability and the GSHP system itself, as well as regional hydraulic and thermal sustainability due to adverse groundwater levels and temperature change. This is a concern in urban aquifers, where GSHP systems are increasingly common. There is a perception that ATES is always the most efficient; however, there is no clear definition of efficiency and how it can be readily assessed at the GSHP design stage. It is proposed and demonstrated herein that GSHP efficiency can be assessed by modelling borehole pumping in lieu of complex Coefficient of Performance calculations for the whole GSHP system. Borehole pumping is a more readily definable modelling outcome for comparing options at an individual site but is also a suitable proxy for comparing efficiency at different sites when given as a flow per unit rate of pumping. Operational efficiencies for ATES versus Unidirectional systems are presented using the pumping rate criteria for modelled scenarios. Here, three model inputs are varied: 1) the balance of heating and cooling, 2) the configuration of a single borehole pair across a hydraulic gradient and 3) the hydraulic gradient itself. These were assessed using coupled groundwater flow and heat transport modelling in Feflow to refine the Goldilocks Zone, the perfect balance, for these variables.

Abstract

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

Abstract

On a global scale, groundwater is seen as an essential resource for freshwater used in both socioeconomic and environmental systems; therefore forming a critical buffer when droughts occur. Due to its location in a dry and semi-arid part of South Africa, Beaufort West relies on groundwater as a crucial source of fresh water. Thus, proper management of their groundwater resources is vital to ensure its protection and preservation for future generations. Although fluctuations have occurred over the years, groundwater levels in the area have progressively dropped due to abstraction in well fields. However, in 2011, an episodic flooding event resulted in extreme groundwater recharge with groundwater levels North-East of Beaufort West recovering tremendously. This led to the overall groundwater levels of Beaufort West becoming relatively higher. The general flow of groundwater in the town, which is from the Nuweveld Mountains in the North to the town dyke in the South, is dictated by dykes occurring in the area.

This study aims to expand on the understanding of episodic groundwater recharge around extreme climatic conditions of high precipitation events in a semi-arid region. This was done by analyzing historical data for the Gamka Dam spanning over 30 years; estimating recharge in the Beaufort West well fields caused by the flooding event; as well as studying the hydrogeological setting and lineaments in the area. It was found that sufficiently elevated recharge around the observed flooding event only occurred in areas where the correct climatic (precipitation, evaporation), geological and geographical conditions were met. Ultimately, gaining a better understanding of these recharge events should aid in the assessment of the groundwater development potential of Beaufort West.