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Integrated site-wide water quality models linked to dynamic water balances have been developed in GoldSim to link aqueous chemistry to the physical system of the site-wide water balance. Geochemical mechanisms are determined from site water monitoring and the most important processes to be included in the model are loading rates, pH-buffering, and water quality data. Water balance components include seasonal flow variability, waste facility water storage and system lags, run-off variability, milling processes and tailings production as a function of ore types, simulation of automated and scheduled maintenance of settling points, water re-routing for water treatment, and freshwater demand, usage and storage. The models can be used for regulatory submissions and mine feasibility studies in a variety of climatic and regulatory environments at different stages of mine life. The model is being used at a mature poly-metallic mine in South America to study the effects of various planned initiatives and potential water options on water flow and quality, and in the support of water treatment design, regulatory submissions and mine closure planning., Integrated site-wide water quality models linked to dynamic water balances have been developed in GoldSim to link aqueous chemistry to the physical system of the site-wide water balance. Geochemical mechanisms are determined from site water monitoring and the most important processes to be included in the model are loading rates, pH-buffering, and water quality data. Water balance components include seasonal flow variability, waste facility water storage and system lags, run-off variability, milling processes and tailings production as a function of ore types, simulation of automated and scheduled maintenance of settling points, water re-routing for water treatment, and freshwater demand, usage and storage. The models can be used for regulatory submissions and mine feasibility studies in a variety of climatic and regulatory environments at different stages of mine life. The model is being used at a mature poly-metallic mine in South America to study the effects of various planned initiatives and potential water options on water flow and quality, and in the support of water treatment design, regulatory submissions and mine closure planning.

A dynamic simulation to predict the variability of sediment discharges has been used for risk-based impact assessment of aquatic ecosystems over the life of a proposed South Pacific mine. The site is in rugged terrain with high annual rainfall and the mine will be located across two adjacent valleys which have streams discharging into the same river. A sediment and hydrology model of two major sediment ponds was developed to provide daily estimates of run-off flow and sediment concentrations. An algorithm based on a water balance model was incorporated into the model. A Revised Universal Soil Loss Equation assessment was carried out and a subcatchment erodibility vector calculated for different land-use types. These gave predictions of daily sediment concentrations which were used in a sediment settling model to predict the daily efficiency of the sediment ponds and the discharged sediment concentrations. The effects of these concentrations on aquatic ecology can be used to assess the risks due to the presence of suspended solids. The water-balance model used was found to be effective and, in combination with a cost-benefit assessment, can be used to compare options for reducing sediment releases from the mine site., A dynamic simulation to predict the variability of sediment discharges has been used for risk-based impact assessment of aquatic ecosystems over the life of a proposed South Pacific mine. The site is in rugged terrain with high annual rainfall and the mine will be located across two adjacent valleys which have streams discharging into the same river. A sediment and hydrology model of two major sediment ponds was developed to provide daily estimates of run-off flow and sediment concentrations. An algorithm based on a water balance model was incorporated into the model. A Revised Universal Soil Loss Equation assessment was carried out and a subcatchment erodibility vector calculated for different land-use types. These gave predictions of daily sediment concentrations which were used in a sediment settling model to predict the daily efficiency of the sediment ponds and the discharged sediment concentrations. The effects of these concentrations on aquatic ecology can be used to assess the risks due to the presence of suspended solids. The water-balance model used was found to be effective and, in combination with a cost-benefit assessment, can be used to compare options for reducing sediment releases from the mine site.

Waste generation is a widespread phenomenon around the world, of which the majority is disposed by landfilling. In landfills, waste constitutes an integral part of the hydrological system, and thus poses a threat to down-gradient groundwater and surface water receptors. This research was undertaken with the purpose of determining the interactions between landfill and the underlying Karoo aquifer, investigating the impacts of a domestic waste landfill on the aquifer and further predicting the magnitude of future contamination. A domestic waste landfill site at Sasol Synfuels (Secunda), located on the Karoo aquifer, was investigated in order to achieve these objectives. This site (Charlie I Landfill) has been used by the refinery to dispose of all non-hazardous/general waste produced for the past twenty years. It is not lined. There is no information available on the type and volume of waste disposed, and the impact on groundwater was not quantified. The landfill is classified as GMB+ (i.e. producing significant amounts of leachate), with the bord-and-pillar mining method taking place underneath the site at the depths of 90- 120m. This implies a lower probability of subsidence at this position. Field investigations indicate that there is a contaminant plume emanating from the landfill, which is mostly concentrated in the upper part of the soil horizon. This horizon is mainly composed of clayey loams and clay, averaging 3m in depth with a laboratory estimated maximum hydraulic conductivity of 0.0128 m/day. It is underlain by the Karoo sediments (sandstones and shales). Regional groundwater levels have been disturbed by the presence of the landfill site, with the higher water table closer to the site and the deeper water table moving away from the site. According to the blow yields obtained, slug tests for boreholes and piezometers, as well as the pumping tests, an average K- value of 10-2 was obtained for the aquifer, except in regions where a dolerite sill or fracture

English: In the first part of this study the typical physico-chemical processes involved in Acid Mine Drainage (AMD) generation were discussed. This included a detailed description of mineralogical reactions, oxygen migration processes and heat conduction typically found in coal mine wastes. In the second part of the study the mineralogy as well as the AMD generation potential of coal mine spoils and discard in South Africa was assessed. A geochemical model of the AMD generation at a rehabilitated backfilled open-cast mine was constructed that simulated the oxygen diffusion process. Coal mine wastes produce Acid Mine Drainage (AMD) due to the ingress of oxygen and the subsequent oxidation of pyrite in the waste rock. As coal mine wastes consume oxygen, oxygen molecules will spontaneously diffuse into the coal mine waste rock along the concentration gradient. Oxygen migration into coal mine wastes also occurs through the passive process of advection. Mechanisms for advection include 1) air convection due to heat differences or changes in gas composition, 2) barometric pumping or 3) changes in water saturation. Heat is generated in coal mine waste mostly through pyrite oxidation and spontaneous combustion of coal. Heat flow occurs by means of conduction, convection, radiation and latent heat. Heat has an indirect influence on every aspect of Acid Mine Drainage (AMD) including microbial activity, gas migration, the rate of chemical reactions etc. Coal discard analysed in this study showed a high net acid generation potential, whether subjected to spontaneous combustion or not. Overall it can be concluded that coal discard has a high potential to generate AMD in South Africa. In spoil material it was found that some trace to dominant minerals were present that were also identified in other studies. These minerals include quartz, kaolinite, calcite, dolomite, mica, K-feldspar, plagioclase, siderite, pyrite, illite/smectite, smectite and anatase. The average pyrite conten, Afrikaans: In die eerste gedeelte van hierdie studie is die fisies-chemiese prosesse wat ‘n rol speel in die produksie van suur-mynwater bespreek. Hierdie gedeelte sluit ‘n gedetaileerde beskrywing van die mineralogiese reaksies, die suurstofmigrasie prosesse en die hitte-generasie wat tipies gevind word in steenkoolmyn afvalprodukte. In die tweede gedeelte van hierdie studie word die mineralogie sowel as die suur-mynwater produksie potensiaal van die steenkoolmyn afvalprodukte in Suid-Afrika ondersoek. ‘n Geochemiese model van die suur-mynwater produksie by ‘n gerehabiliteeerde oopgroefmyn is gebruik om die diffusie van suurstof in die myn in te simuleer. Steenkoolmyn afvalprodukte genereer suur-mynwater weens die infiltrasie van suurstof en die gevolglike oksidasie van piriet in die afvalmateriaal. Soos wat die materiaal suurstof verbruik sal suurstofmolekules spontaan diffundeer in die material in, in reaksie op die konsentrasiegradiënt wat geskep word. Suurstofinfiltrasie kan ook passief plaasvind naamlik deur adveksie. Meganismes van adveksies sluit in 1) lugkonveksie weens hitte- of lugsamestellingsverskille, 2) barometriese drukking of 3) veranderinge in waterversadiging. Hitte word geproduseer in steenkoolmyn afvalmateriaal deur die oksidasie van piriet, en deur die spontane verbranding van steenkooluitskot. Hittevloei vind plaas deur geleiding, konveksie, radiasie en latente hitte. Hitte het ‘n indirekte invloed op elke aspek van die produksie van suur-mynwater, insluitend mikrobiese aktiwiteit, gasmigrasie, chemiese reaksie tempo’s ens. Steenkooluitskot van die veredelingsproses het in hierdie studie ‘n hoë potensiaal getoon om suur-mynwater te genereer. Dit was selfs ook die geval vir steenkooluitskot wat onderhewig was aan spontane verbranding. In steenkoolmyn afvalgesteentes is spoor tot dominante minerale teenwoordig wat ook in ander studies geïdentifiseer was. Hierdie minerale sluit in kwarts, kaoliniet, kalsiet, dolomiet, mika, K-veldspaat, plagiokla

English: The objective of this research is to characterise fractured aquifers contaminated with DNAPLs in South Africa. The site characterisation approach is conducted in two case studies by integrating a range of site assessment techniques. It started with the noninvasive methodologies that provide rapid and cost-effective ways for screening. After developing the initial conceptual model, the investigation proceeded to invasive techniques that provide more information on DNAPLs and fractures on a local scale. This research indicated that fracture “hunting” is extremely difficult with the current technology, making DNAPL characterization very challenging. It also indicated that no single technique provides an unequivocal indication of fracture position and orientation, but that best results were obtained when several invasive techniques were used in a toolbox approach. These tools were most appropriate when integrated with hydraulic testing methods. The site characterisation was done in a continuous and iterative process, and each phase of investigation was used to refine the conceptual model of the site. The non-invasive techniques applied included: • General assessment of Test Site 1 by site inspection, interviewing employees, documentation studies and aerial photo analysis. • Hydrocensus • Direct observing for DNAPL contamination using UV light and Sudan IV shake tests. • Soil gas surveys by using various models of PIDs to delineate the organic vapour plumes. • Surface and airborne geophysics for outlining major structures that may play an important role for DNAPL migration pathways. This did not yield useful results at Test Site 1 due to noise interference from industrial activities and infrastructure. The non-invasive techniques were not applicable for direct evaluation of DNAPLs migrating in fractured aquifers; however, they were essential in understanding DNAPL-release zones and vapour plumes. They were also found to be relatively cost and time efficient. The, Afrikaans: Die doelwit van hierdie navorsing is om Suid Afrikaanse fraktuurakwifere, wat besoedel is met DNAPLs, te karakteriseer. Die die terrein karakterisering is benader deur die integrasie en toepassing van verskillended ondersoek metodes by twee gevalle studies. Eerstens is nie-binnedringend en vinnige, effektiewe ondersoek tegnieke gebruik. Nadat die aanvangs konseptuele model gekonstrueer is, is daar voort gegaan met binnedringende tegnieke om meer inligting te verskaf oor DNAPLs en frakture op ‘n lokale skaal. Hierdie navorsing het gewys dat fraktuur opsporing baie moelik is met beskikbare tegnologie, wat DNAPL karakterisering baie uitdagend maak. Dit het ook bewys dat geen enkele tegniek die fraktuur posisie en orientasie kan aandui nie, en dat binnedringende tegnieke wat saam gebruik word, die beste resultate gelewer het. Hierdie tegnieke is mees geskik as dit geintegreer word saam met hidroliese toets metodes. Die terrain karakterisering was gedoen as ‘n aaneenlopended en herhalende proses, waar die konseptuele model tydens elke fase opgedateer is. Die nie-binnedringende tegnieke wat toegepas is sluit die volgende in: •Algemene ondersoek tegnieke soos terrein inspeksie, onderhoude met werknemers, dokument studies en lugfoto interpretasie. •Hidrosensus •Direkte obserwering van DNAPL besoedeling met die hulp van UV-lig en Sudan IV kleurstof skud toetse, van die boonste grondlaag. •Die organiese gas pluim is gedelinieer, deur grond gas opnames met verskillende modelle “PIDs”. •Grond en lug geofisika is gebruik om belangrike geologiese strukture en kenmerke op te spoor wat ‘n rol kan speel in die beweging van DNAPLs. (Hierdie tegnieke was egter nie suksesvol op Toets Terrein 1 nie, aangesien daar baie agtergrond geraas was weens die industriële aktiwiteite en infrastrukstuur.) Die nie-binnedringende tegnieke was nie toepasbaar vir direkte evaluering van DNAPL migrasie in die gefraktureerde akwifere nie, maar het bygedra tot die insig in die DNAPL bron a, Water Research Commission (WRC)

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English: Huge volumes of mine water, impacted on by acid mine drainage, are presently produced as a result of mining activities. These waters are mostly neutralised either as a result of seepage through neutralising geological strata, or artificially by the addition of lime. Mine drainage is, therefore, often saturated with gypsum. Gypsiferous mine water can thus be regarded either as one of the greatest problems associated with mining, or as a potential asset. Large amounts of waste water could be made available to the farming community, and utilised for the irrigation of highly productive soils in the coalfields. Concentrating the gypsiferous soil solution through evapotranspiration, thereby precipitating gypsum in the soil profile, will reduce environmental pollution, as these salts are removed from the water system. However, the regulatory authorities have raised some concerns regarding the possible impact of largerscale irrigation on water resources. This research attempts to provide meaningful answers. Five different irrigation sites were selected for research. Monitoring indicates that very little salinity applied on surface during irrigation reaches the water table. Soil analysis indicates that most of the salts are captured in the upper one or two meters of the soil profile. The data indicate that the clay layers, which playa major role in the vertical flux of the water, also have an influence on the salt distribution through the soil profiles. The porous cups data suggest that the majority of the salts is currently contained within the uppermost portions of the soil profile, showing a steady decrease in sulphate concentrations with depth. Geochemical modelling indicates that soil water in the uppermost meter is saturated with gypsum, and precipitation occurs. Virgin solts: The chloride values at all the different irrigation sites showed a decrease value with depth, indicating bimodal flow. The saline water moving through the soil profile contributes approx, Afrikaans: Groot volumes water, geimpakteer deur suurvorming, word huidiglik geproduseer as gevolg van mynbou aktiwiteite. Hierdie water word meestal geneutraliseer as gevolg van vloei deur geologiese strata wat neutralisering aanhelp, of deur die toevoeging van kalk. Water afkomstig van mynbou is dus dikwels versadig met gips. Hierdie gipsryke water kan beskou word as een van mynbou se grootste probleme, of as 'n potensiële bate. Groot hoeveelhede afval water kan tot die beskikking van die landbou gemeenskap gestel word vir gebruik in besproeiing op die hoë-potensiaal gronde van die steenkoolveld. Deur die gipsryke water te konsentreer deur evapotranspirasie, kan gips in die grond gepresipiteer word. Dit sal die omgewingsbesoedeling verminder deurdat saute verwyder word uit die waterstelsel. Die betrokke owerheid is egter besorg oor die impak wat grootskaalse besproeiing kan hê op die grondwater reserves. Hiedie navorsingsprojek poog om sulke vrae te beantwoord. Vyf verskillende besproeiings persele is geselekteer vir die projek. Monitering van die persele oor tyd toon dat baie min van die saute wat deur die water op die grond toegedien word, die water tafel bereik. Grond analises toon dat meeste van die saute in die boonste twee meter van die grond profiel vasgevang is. Die klei lae speel 'n groot rol in die vertikale beweging van die water. Analises toon ook dat dit 'n invloed het op die sout verspreiding deur die grond profiel. Poreuse koppie data het hierdie bevinding bevestig, en aangetoon dat daar 'n afname van sulfaat konsentrasie met diepte is. Geochemiese modelering toon dat die grondvog in die boonste meter van die profiel versadig is met gips, en dat presipitasie plaasvind. Onversteurde grond: Die chloried konsentrasie by al die verskillende persele wys 'n afname in konsentrasie met diepte. Dit dui op voorkeur vloei. Die soutryke water wat afbeweeg in die profiel dra ongeveer 15% of minder by tot die vermenging van die water om die laer chloriedwaardes t, Water Research Commission, Coaltech

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Petroleum liquids are a basic building block of our modern lives. Uses include fuels, lubricants, and the raw material for manufactured products. The by-product of these uses has been the inadvertent release of petroleum liquids. A result of our utilization of petroleum liquids is a legacy of soil and groundwater impacted by petroleum liquids. The aim of this research is to provide an overview of LNAPLs in South African urban areas, transport mechanism of the LNAPLs in the subsurface, framework for detecting and evaluating LNAPLs under South African conditions. LNAPL is a convenient label for petroleum liquids in soils and groundwater. The acronym stands for Light Non Aqueous Phase Liquid. “Light” highlights the fact that petroleum liquids (i.e., gasoline) are less dense than water; “Non Aqueous” highlights the fact that petroleum is not completely miscible in water. An LNAPL contamination assessment was conducted at a service station after a complaint was raised by a resident who found free product (petrol) in her borehole. A multitude of private boreholes were found during the hydrocensus survey. A petroleum contamination assessment was done through soil vapour survey (SVS), hand auger holes and rotary percussion drilling. No significant petroleum vapours were detected due to clay soil which has low transmission of vapours. Hand auger holes were restricted to shallow depth due to the lack of penetration though the clay soils. Percussion drilling was needed to gather groundwater information (i.e., quality and quantity). Free product (petrol) was found within the percussion and some of the private boreholes. Groundwater samples were collected and analyzed for BTEX (Benzene, Toluene, Ethyl benzene and Xylenes) compounds. No detectable levels of BTEX were found in the soil samples. Risk assessment was done suing the RBCA approach and BP RISC software. BTEX concentrations of groundwater samples have triggered the Tier 1 risk based screening level for the risk values of

English: The generation of waste material associated with Gold Mining is a known fact. Research on these waste materials has currently expanded worldwide in an attempt to scientifically characterise and understand their interaction with the natural environment. These materials contain certain amounts of sulphide minerals and other harmful substances, associated with the exploited ore bodies and the beneficiation processes. It is even more important to understand certain impacts and to develop a logical approach to assess the impacts on receiving water bodies, towards mine. The increase in awareness of environmental issues and a desire for a cleaner environment by the public has caused gold mining companies to place greater emphasis on the continuous rehabilitation of deleterious effects caused by mining operations. Ongoing rehabilitation is also a requirement of the Government Departments involved in mining in South Africa. The biggest concern for the relevant Government Departments is the possible uncontrolled pollution of water resources in the vicinity of these mines, after they have closed. Investigations have shown that receiving water bodies, which mainly include rivers, streams, and the more complicated geohydrological system, are part of the primary end-receivers of harmful contaminants from identified waste bodies. The need for a cost effective method to assess site hydrology and geohydrology, to understand the associated legal responsibility of contaminated streams and aquifers, is recognised. In the compilation of this thesis, the unique nature of the South African situation has been considered - this refers to a legally acceptable approach towards current legislation and policies. Throughout this document, the emphasis falls on what can reasonably be achieved, without compromising on information that would lead to early detection of water pollution. This study leads to the construction of a logical approach towards mine closure specifically in the field, Afrikaans: Die produksie van afvalstowwe, as by-produkte gedurende die myn van goud, is 'n bekende feit. Tans word die navorsing van hierdie afval materiaal as baie belangrik beskou sodat moontlike interaksies tot die natuurlike omgewing beter verstaan kan word. Die materiaal bevat sulfied minerale asook ander elemente wat moontlik nadelig kan wees vir die natuurlike omgewing. Die graad en hoeveelheid van die spesifieke elemente hang grootendeels af van die tipe erts liggaam wat gemyn word asook die prosessering van die erts. Soos wat 'n myn neig na sluiting raak dit dus belangrik om moontlikke impakte op natuurlikke water bronne te bepaal. 'n Toenemende bewustheid oor omgewings kwesies vanuit 'n publieke oogpunt, en 'n groter drang na 'n skoner natuurlike omgewing, het veroorsaak dat goud myne meer klem op grondwater rehabilitasie en omgewings bestuur lê. Staats Departemente, betrokke in die goudmyn bedryf, verreis ook die voortdurende rehabilitasie van besoedelde areas. Die grootste besorgdheid vir die Staats Departemente is dus die potensiaal vir onbeheerbare besoedeling van water bronne, deur myne wat sluiting in die oog staar. Studies het gewys dat dit oorwegend riviere, strome en grondwater is wat die ergste deurloop onder besoedeling afkomstig van goud myne. Dit is as gevolg hiervan dat die behoefte ontstaan om 'n koste-effektiewe manier te ontwikkel en saam te stelom hierdie water bronne wetenskaplik te ondersoek en ook om die grondwater probleme vanuit 'n wetlike oogpunt te verstaan. Gedurende die samestelling van hierdie verhandeling is die uniekheid van die Suid Afrikaanse wetgewing en beleidspunte deurentyd in ag geneem - dit verwys grootliks na die wetlike aanvaarbare benadering wat gevolg is. Die klem word deurentyd gelê op redelike en praktiese oplossings tot grondwater besoedeling sonder om die insameling van inligting te beperk. Hierdie studie lei tot die samevoeging van 'n logiese benadering om grondwater te ondersoek tydens die sluiting van 'n gou

English: South Africa has only recently realized that organic groundwater contamination occurs in this country and that it can have a serious effect on the groundwater quality. The Water Research Commission (WRC) recently launched studies to investigate Non Aqueous Phase Liquid (NAPL) pollution, and Dense NAPL in specific. The understanding of NAPL pollution problems, is however, still very limited. Hence groundwater practitioners confronted with NAPL pollution problems have burning questions regarding amongst others the characterization of the pollution, which is much more sophisticated than in the case of inorganic pollution. While in this phase, groundwater practitioners can not even begin to consider remedial efforts for contaminated sites, which continue to pollute the groundwater. It is therefore of paramount importance to get up to speed with technologies and practices accepted worldwide for characterization. Much improvement is still needed on these characterization methods, but South Africa can learn from past mistakes made by other countries in addressing NAPL pollution. In order to begin contemplating addressing NAPL characterization, it is important to understand the nature of the problem, which is why Chapter 2 describes the current situation of organic groundwater pollution and the associated vulnerability of aquifers in South Africa. The general understanding of groundwater pollution by NAPL is distorted, not only in the eyes of the public, but also in the eyes of experts in the groundwater field. A general misconception is that NAPL pollution only occurs at heavy industries such as ISCOR and SASOL, but Chapter 2 clearly shows that organic pollution is much more widespread and sinister in nature than would have been thought before. Smaller urban activities and small industries have been identified to be just as large a contributor towards organic pollution as the heavy industries. Shortcomings in the current understanding of NAPL pollution have been h, Afrikaans: Suid Afrika het eers onlangs besef dat organiese grondwater besoedeling in die land voorkom en dat dit ‘n groot effek op die grondwater kwaliteit kan hê. Die waternavorsings kommissie (WNK) het onlangs ondersoeke geloods na organiese besoedeling, en spesifiek swaar olie besoedeling. Die vlak van kennis van organiese besoedeling is egter nogsteeds baie laag. Grondwater kundiges het dus brandende vrae aangaande byvoorbeeld die karakterisering van organiese grondwater besoedeling, wat soms meer gespesialiseerd is as in die geval van anorganiese besoedeling. Dit is dus van kardinale belang dat Suid- Afrika homself verwitting van internasionale standaard en praktyk in terme van die aanspreek van organiese grondwater besoedeling. Die internasionale gemeenskap kan nog baie verbetering aanbring op die terrein van karakterisering, maar Suid-Afrika kan baie uit die foute van ander lande in hulle pogings om organiese grondwater besoedeling aan te spreek, leer. In ‘n poging om die karakterisering van organiese grondwater besoedeling te verstaan, is dit nodig om die omvang van organiese besoedeling in Suid-Afrika te verstaan. Dit word in Hoofstuk 2 beskryf. Die hoofstuk spreek ook die kwesbaarheid van grondwater vir organiese besoedeling aan. Die publiek en grondwater kundiges het oor die algemeen ‘n wanopvatting van organiese grondwater besoedeling in Suid-Afrika, waarvan een die opvatting is dat organiese grondwater besoedeling net by swaar industrieë soos byvoorbeeld ISCOR en SASOL voorkom, maar Hoofstuk 2 lig dit duidelik uit dat organiese grondwater besoedeling baie meer algemeen en en van groter omvang is as wat voorheen gemeen is. Die afleiding is gemaak dat kleiner industrieë en klein stedelike aktiwiteite net so ‘n groot bydrae kan lewer tot organiese grondwater besoedeling as swaar industrieë. Tekortkominge in die huidige vlak van kennis van organiese grondwater besoedeling is in Hoofstuk 2 uitgelig en verdere studies kan daarop fokus om die impak van verski

Acid mine drainage was evaluated at three opencast collieries in the Witbank coalfield, South Africa. Test pits were dug into the spoils to characterise the in situ conditions of spoils of varying age. Static testing was carried out on surrounding drill holes and additional samples were taken from the test pits. Selected samples were tested using acid-base accounting (ABA), mineralogy and kinetic tests. Groundwater monitoring boreholes from the areas surrounding the spoils were also used for the characterisation. The ABA results compared favourably with the in situ determinations. ABA results indicated that acidic test pits were potentially acid even when the samples had neutral paste pH. Kinetic test results showed these samples to yield low pH leachate over the test period. NAG pH-values and final observed water chemistry were in agreement for the cells predicted by ABA to acidify, but compared poorly in cells that did not acidify. Results from the non-acidic spoils were consistent with the in situ observations. Duplicate samples were tested in humidity cells and in aerated trays that were manually wetted on a regular basis. The results showed excellent correlation. The ABA results were consistent with those expected from the mineralogy. In most cases ABA provides information that can be correlated to field, mineralogy and humidity cell data., Acid mine drainage was evaluated at three opencast collieries in the Witbank coalfield, South Africa. Test pits were dug into the spoils to characterise the in situ conditions of spoils of varying age. Static testing was carried out on surrounding drill holes and additional samples were taken from the test pits. Selected samples were tested using acid-base accounting (ABA), mineralogy and kinetic tests. Groundwater monitoring boreholes from the areas surrounding the spoils were also used for the characterisation. The ABA results compared favourably with the in situ determinations. ABA results indicated that acidic test pits were potentially acid even when the samples had neutral paste pH. Kinetic test results showed these samples to yield low pH leachate over the test period. NAG pH-values and final observed water chemistry were in agreement for the cells predicted by ABA to acidify, but compared poorly in cells that did not acidify. Results from the non-acidic spoils were consistent with the in situ observations. Duplicate samples were tested in humidity cells and in aerated trays that were manually wetted on a regular basis. The results showed excellent correlation. The ABA results were consistent with those expected from the mineralogy. In most cases ABA provides information that can be correlated to field, mineralogy and humidity cell data.

not available, Water Research Commission