Peatlands as Filters for Polluted Mine Water?—A Case Study from an Uranium-Contaminated Karst System in South Africa—Part I: Hydrogeological Setting and U Fluxes

2011

Water

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Abstract:As the second part of a series of four, this paper reviews a number of case studies of natural uranium attenuation in peat, as well as underlying chemical mechanisms reported in literature. Based on this review, a generic, conceptual, model for peat to act as filter for dissolved uranium (U) is developed for guiding subsequent field investigations. The model consists of a chemical and an hydraulic component which is derived largely from data reported in literature as well as from limited field observations. For the chemical model component 10 different processes, each controlled by factors relating to water chemistry, have been identified to govern the attenuation of U in peat via a net balance of immobilization and remobilization. For the hydraulic aspect of the filter model, five different principal modes of U polluted water coming in contact with peat are discussed, focusing on the associated peat-water contact time as a crucial parameter controlling chemical U attenuation. Moreover, links between the two model components are discussed and, based on the integrated conceptual model, possible effects of natural and anthropogenic events on U attenuation in peatlands are outlined. Guided by the model, various site-specific field and laboratory investigations are finally designed to verify how far the identified generic factors and processes are indeed applicable to the Gerhard Minnebron Peatland.

Section: +mentioning

confidence: 89%

Section: Project Backgroundmentioning

confidence: 99%

Peatlands as Filters for Polluted Mine Water?—A Case Study from an Uranium-Contaminated Karst System in South Africa—Part II: Examples from Literature and a Conceptual Filter Model

2011

Water

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“…Whilst the mega-compartment concept has largely been addressed exclusively on a speculative basis, Swart et al 51 provided the only existing study employing a scientific methodological approach (based on Darcy's Law) in order to approach the issue on a hydraulic basis. Consequently, Van Niekerk and Van der Walt 32 and Winde and Erasmus 74 propose that the existing research on the topic (i.e. hydraulic consequences of piercing of dykes) is insufficient to reach any firm conclusions.…”

Section: Hydrogeological Characterisation Of Dolomitic Compartmentsmentioning

confidence: 99%

“…The existing uncertainties complicate the assessment of post-mine closure scenarios with regard to aquifer conditions and the associated environmental aspects. As a result, even in investigations into other aspects, an assumption is made about the hydrogeological future by choosing one of the two opposing scenarios 58,74 (i.e. reactivation of spring flow or formation of a mega-compartment in which springs remain dry) or taking both possibilities into account 70 .…”

Section: Hydrogeological Characterisation Of Dolomitic Compartmentsmentioning

confidence: 99%

Unearthing a hidden treasure: 60 years of karst research in the Far West Rand, South Africa

Schrader

2015

S. Afr. J. Sci.

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Karstified dolomitic formations situated in the Far West Rand goldfield of the Witwatersrand Basin constitute a significant groundwater resource in semi-arid South Africa and would be of strategic importance for alleviating the increasing water stress in nearby metropolitan areas. The deep-level gold mines operating below the dolomites have suffered from large volumes of dolomitic groundwater flowing into the mine voids, rendering mining both expensive and hazardous. In order to secure safe and economical mining, the overlying dolomites were dewatered. Here we review research over 60 years, conducted in three of the four major dolomitic compartments affected by dewatering. After more than six decades of research, these aquifers are arguably the most investigated karst systems in South Africa, and possibly worldwide. The data generated are, in many respects, unique, as many measurements can never be repeated, covering stochastic events such as a major water inrush into mine workings and some of the most catastrophic sinkhole developments ever recorded. Given the potential value for improving the understanding of general and local karst hydrogeology, our main goal for this paper is to alert the scientific community to the existence of this resource of mostly unpublished data and research. A no less important aim is to support a systematic collation of these studies which are in danger of being irretrievably lost as mines increasingly close down. Ecological and economic impacts of the flooding of mines in and around Johannesburg emphasise the lack of reliable historical mine data to optimally address the matter. We provide the first comprehensive, yet not exhaustive, overview on the existing studies, briefly discussing scientific content as well as obstacles for utilising the scattered, and often non-peer reviewed, information sources.

“…A focal point of the investigations was the question if and to what degree the remaining (i.e., unmined) peat may act as a filter for uranium (U) as the main contaminant of concern emanating from upstream mining activities. Apart from assessing current conditions, this also includes possible future post-mining scenarios in which large volumes of highly polluted, acidic mine water may flow into the peatland [1]. Based on a literature review, a conceptual model on the U filter function of peat was developed that consists of a chemical component characterizing the mechanisms responsible for the attenuation and release of U in and from peat as well as a hydraulic component that addresses the rate and mode of contact between (polluted) water and the peat.…”

Section: Open Accessmentioning

confidence: 99%

Peatlands as Filters for Polluted Mine Water?—A Case Study from an Uranium-Contaminated Karst System in South Africa—Part III: Quantifying the Hydraulic Filter Component

2011

Water

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Abstract:As Part III of a four-part series on the filter function of peat for uranium (U), this paper focuses on the hydraulic component of a conceptual filter model introduced in Part II. This includes the quantification of water flow through the wetland as a whole, which was largely unknown and found to be significantly higher that anticipated. Apart from subaquatic artesian springs associated with the underlying karst aquifer the higher flow volumes were also caused by plumes of polluted groundwater moving laterally into the wetland. Real-time, quasi-continuous in situ measurements of porewater in peat and non-peat sediments indicate that rising stream levels (e.g., during flood conditions) lead to the infiltration of stream water into adjacent peat deposits and thus allow for a certain proportion of flood water to be filtered. However, changes in porewater quality triggered by spring rains may promote the remobilization of possibly sorbed U.