The Microbiology of The Maqarin Site, Jordan - A Natural Analogue for Cementitious Radioactive Waste Repositories
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THE MICROBIOLOGY OF THE MAQARIN SITE, JORDAN - A NATURAL ANALOGUE FOR CEMENTITIOUS RADIOACTIVE WASTE REPOSITORIES JULIA M WEST, PATRICIA COOMBS, SUSAN J GARDNER AND CHRISTOPHER A ROCHELLE. Fluid Processes Group, British Geological Survey, Keyworth, Nottingham NG12 5GG, UK. ABSTRACT The Maqarin site, Jordan is being studied as a natural analogue of a cementitious radioactive waste repository. The microbiology has been studied and diverse microbial populations capable of tolerating alkaline pH were detected at all sampling localities. Dissolved organic carbon was identified as the potentially most important reductant with sulphate identified as the main oxidant, both supplying energy for microbial life. Calculations on upper limits of microbial numbers were made with a microbiology code (MGSE) using existing information but the results are overestimates when compared with field observations. This indicates that the model is very conservative and that more information on, for example, carbon sources is required. INTRODUCTION The Maqarin site in northern Jordan is an unusual area containing highly alkaline (up to pH 12.9) groundwaters. These are produced by the interaction of bicarbonate groundwaters infiltrating zones of metamorphosed rock (formed by in-situ combustion) hosted in Cretaceous to Tertiary pyritic organic-rich marls and limestones [1. 2. 3. 4]. Hydration of the calcined rocks has produced a mineral assemblage similar to that found in hydrated cements and thus provides an analogue of a cementitious radioactive waste repository. As part of a large project designed to examine further the mineralogy, petrology and geochemistry at the site, NAGRA (National Cooperative for the Disposal of Radioactive Waste), Switzerland funded an examination of the microbiology of Maqarin. Laboratory studies have shown that microbes, particularly sulphate reducing bacteria, can grow in hyperalkaline conditions containing repository structural materials [5]. As microbes are important catalysts in many geochemical processes (thereby gaining necessary energy and nutrients), it is important to establish if they
are present in this analogue site and quantify their significance in this unique environment. The work also provides a guide to the significance of microbes in a cementitious repository. Previous studies of the Maqarin site [3] have shown the presence of sulphate reducing bacteria. Denitrifiers were not detected. The aims of the current study were: to isolate microbial species focussing on sulphur bacteria; determine their distribution, pH tolerance and morphology by developing isolation and culturing techniques in hyperalkaline conditions; and review geochemical information and feedstuffs in order to determine their significance to biological growth requirements. The data were also to be used to test the generic microbiology model MGSE (Microbe Growth in Subsurface Environments) [6] and will be used in the future to test NAGRA's near-field microbiology model EMMA [7]. MGSE is a model designed to automate conventional calcu
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