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首页> 外文期刊>Journal Of The South African Institute Of Mining & Metallurgy >Qualitative hydrogeological assessment of vertical connectivity in aquifers surrounding an underground coal gasification site
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Qualitative hydrogeological assessment of vertical connectivity in aquifers surrounding an underground coal gasification site

机译：地下煤气化地区含水层垂直连通性的定性水文学评估

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摘要

Underground coal gasification (UCG) is the conversion of coal in situ into a usable synthetic gas. One of the major environmental concerns with UCG is the possibility of groundwater from the coal seam aquifer contaminating the shallow aquifers via hydraulic connections. The coal seam aquifers are usually confined aquifers but can have hydraulic connections to the shallow aquifers due to faults/fractures or any man-made connections, including boreholes. The aim of this paper is to study groundwater hydraulic connections across various aquifers at the UCG site at Majuba, using hydrochemistry and stable isotope (δ~(18)O and δ~2H) tools. Physical and chemical processes such as diffusion and condensation generate isotopic differentiation in natural waters that can be used to deduce the origins of different waters, and in groundwater the spatial isotopic distribution can be used to deduce hydraulic connections between different aquifers. The Majuba UCG site consists of shallow, intermediate, and saline deep aquifer systems at a depth of 70 m, 180 m, and 300 m respectively. Samples were taken from each aquifer system together with supplementary samples from an on-site water storage dam. The analyses of isotopic compositions led to the determination of the possible sources of each sample. The deep aquifer is represented by an isotopic signature that is depleted in heavy isotopes with average values of-41.7% and -7.02% for δ~(18)O and δ~2H respectively, while the shallow aquifer is enriched with corresponding average values of-19.9% and -3.3%. Hydrochemical data also showed different water types; a sodium chloride type in the deep aquifer and a sodium bicarbonate water in the shallow aquifer. The results indicate that the shallow aquifer and the deep aquifer are not hydraulically connected, and therefore it is unlikely that groundwater from the gasification zone would contaminate the shallow aquifer.
机译：地下煤气化（UCG）是将煤的转化为原位进入可用的合成气体。 UCG的主要环境问题之一是通过液压连接污染浅含水层的煤层含水层的地下水的可能性。煤层含水层通常是受限的含水层，但由于故障/骨折或任何人造连接，包括钻孔，可以具有与浅含水层的液压连接。本文的目的是使用麦芽化和稳定同位素（δ〜（18）o和δ〜2h）工具研究在Memuba的不同含水层的地下水液压连接。诸如扩散和缩合的物理和化学方法在天然水域中产生同位素分化，可以用于推导出不同水的起源，并且在地下水中，空间同位素分布可用于推导不同含水层之间的液压连接。 Majuba UCG位点分别由浅，中间和盐水深含水层系统组成，深度分别为70米，180米和300米。将样品从每个含水层系统与来自现场储水坝的补充样品一起取出。同位素组合物的分析导致了每个样品的可能源。深含水层由同位素特征表示，分别在较重的同位素中耗尽，平均值-41.7％和-7.02％，分别为δ〜（18）和δ〜2h，而浅含水层富含相应的平均值-19.9％和-3.3％。水化学数据也显示出不同的水类型;深层含水层中的氯化钠类型和浅含水层中的碳酸氢钠水。结果表明，浅层含水层和深含水层没有液压连接，因此来自气化区的地下水不太可能会污染浅层含水层。

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