Identification of Sources and Mechanisms of Salt-Water Pollution Affecting Ground-Water Quality; A Case Study, West Texas
Identification of Sources and Mechanisms of Salt-Water Pollution Affecting Ground-Water Quality; A Case Study, West Texas
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查明影响地下水质量的咸水污染的来源和机制；
DOI：
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发表时间：
1990
期刊：
影响因子：
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通讯作者：
C. Kreitler
中科院分区：
文献类型：
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作者：
B. Richter;A. Dutton;C. Kreitler
在康乔河流域及其与西德克萨斯州科罗拉多河的汇合处以及德克萨斯州和美国的其他半干旱地区，地下水和土壤盐碱化的情况很多。盐碱化是自然过程和人为过程的结果，它们可以共同发生，也可以单独发生。为了识别区域咸水来源，了解康乔河谷的盐化机制，我们研究了与咸化地下水相关的化学和物理特征。通过对以往研究中1200多个水样的化学分析和本次调查中76个水样的分析，我们通过绘制水文地质控制的盐度模式和水化学相，以及通过图形分析同位素组成和离子比来区分盐渍化机制。在研究区东部，位于Runnels县，灌溉用水和浅层含水层地下水的蒸发是盐渍化的主要原因。在研究区域的西部，位于利昂县和汤姆格林县，大部分咸水和半咸水地下水被解释为从米德兰盆地向东流动的地下盐水和在康乔河流域补充的浅层循环大气水的自然混合物。对淡水底部以下深度的测试钻探证实了二叠纪浅层地层中存在地下盐水。在向西数十公里的60至275米（200至900英尺）的浅层中，二叠纪岩石中含有相对淡水的含水层也含有盐水和碳氢化合物。试验钻井还帮助记录了地下盐水和浅层地下水局部混合的两种人为机制：(1)废弃的油气勘探孔允许盐水向上流动，其中地表套管和钻孔塞位于淡水底部之上；(2)以前的盐水处理坑下土壤中积累的盐的浸出，即使在这种盐水处理方法停止20年后，这一过程仍在继续。第三种机制，即通过废弃的水井混合盐水和浅层地下水，无法进行测试。据报道，钻探到含水层含盐部分的深水井在没有堵塞的情况下就被废弃了，目前还没有相关记录。在二叠纪和宾夕法尼亚地层中，地下盐水的化学成分构成了两个端元群之间的连续阵列。通过(1)钙、镁、钠和硫酸盐浓度的图形分析，(2)氯化物浓度的BrICI比，(3)硫酸盐浓度和Na/Ca比的CIISO比，可以区分端元基。康乔河流域浅层地下水的大多数盐水样品在化学上与二叠纪地层盐水末端成员相似。科尔曼结地层卤水不能从化学上与其他二叠纪地层卤水区分开来。有关有机酸阴离子、除溴化物以外的微量成分、氢、氧、碳和硫的同位素的信息也可用于区分二叠纪和宾夕法尼亚的盐水，但可能并不总是确定浅层地下水盐碱化来源的有用测量方法。
Occurrences of ground-water and soil salinization are numerous in the Concho River watershed and its confluence with the Colorado River in West Texas and in other semiarid regions of Texas and the United States. Salinization results from both natural and anthropogenic processes, which can occur together or separately. To recognize regional salt-water sources and understand salinization mechanisms in the Concho River valley, we investigated chemical and physical characteristics associated with saline ground water. Using more than 1,200 chemical analyses of water samples from previous studies and 76 analyses of samples from this investigation, we differentiated salinization mechanisms by mapping hydrogeologically controlled salinity patterns and hydrochemical facies and by graphically analyzing isotopic compositions and ionic ratios. In the eastern part of the study area, located in Runnels County, evaporation of irrigation water and ground water from a shallow aquifer accounts for most salinization. In the western part of the study area, located in lrion and Tom Green Counties, much of the saline to brackish ground water is interpreted as being a naturally occurring mixture of subsurface brine flowing eastward from the Midland Basin and shallowly circulating meteoric water recharged in the Concho River watershed. Test drilling to depths below the base of fresh water confirmed the presence of subsurface brine in shallow Permian formations. Aquifers that contain relatively fresh water in outcropping Permian rocks also contain brine and hydrocarbons at depths as shallow as 60 to 275 m (200 to 900 ft), tens of kilometers to the west. Test drilling also helped document two anthropogenic mechanisms for local mixing of subsurface brine and shallow ground water: (1) upward flowing of brine allowed by abandoned oil and gas exploration holes, where surface casing and borehole plugs are above the base of fresh water, and (2) leaching of accumulated salt from soil beneath former brine-disposal pits, an ongoing process even 20 years after this brine-disposal method was discontinued. A third mechanism, mixing of brine and shallow ground water via abandoned water wells, could not be tested. No records exist on deep water wells that reportedly were drilled into saline portions of aquifers and were abandoned without being plugged. Chemical compositions of subsurface brines make up a continuous array between two endmember groups in Permian and Pennsylvanian formations. The end-member groups are distinguishable by graphical analysis of the (1) calcium, magnesium, sodium, and sulfate concentrations, (2) BrICI ratio plotted against chloride concentration, and (3) CIISO, ratio plotted against sulfate concentration and Na/Ca ratio. Most saline samples of shallow ground water in the Concho River watershed are chemically similar to the Permian formation brine end member. Coleman Junction Formation brines cannot be chemically distinguished from other Permian formation brines. Information about organic-acid anions, minor and trace constituents other than bromide, and isotopes of hydrogen, oxygen, carbon, and sulfur also can be used to differentiate between Permian and Pennsylvanian brines but may not always be useful measurements to determine sources of salinization in shallow ground waters.