Earth Sciences Department, Sciences Faculty, University of Zaragoza, Pedro Cerbuna, 11, 50009 Zaragoza, Spain.
Sci Total Environ. 2014 Jan 15;468-469:791-803. doi: 10.1016/j.scitotenv.2013.09.007. Epub 2013 Sep 23.
This paper presents the mixing modelling results for the hydrogeochemical characterisation of groundwaters in the Laxemar area (Sweden). This area is one of the two sites that have been investigated, under the financial patronage of the Swedish Nuclear Waste and Management Co. (SKB), as possible candidates for hosting the proposed repository for the long-term storage of spent nuclear fuel. The classical geochemical modelling, interpreted in the light of the palaeohydrogeological history of the system, has shown that the driving process in the geochemical evolution of this groundwater system is the mixing between four end-member waters: a deep and old saline water, a glacial meltwater, an old marine water, and a meteoric water. In this paper we put the focus on mixing and its effects on the final chemical composition of the groundwaters using a comprehensive methodology that combines principal component analysis with mass balance calculations. This methodology allows us to test several combinations of end member waters and several combinations of compositional variables in order to find optimal solutions in terms of mixing proportions. We have applied this methodology to a dataset of 287 groundwater samples from the Laxemar area collected and analysed by SKB. The best model found uses four conservative elements (Cl, Br, oxygen-18 and deuterium), and computes mixing proportions with respect to three end member waters (saline, glacial and meteoric). Once the first order effect of mixing has been taken into account, water-rock interaction can be used to explain the remaining variability. In this way, the chemistry of each water sample can be obtained by using the mixing proportions for the conservative elements, only affected by mixing, or combining the mixing proportions and the chemical reactions for the non-conservative elements in the system, establishing the basis for predictive calculations.
本文呈现了用于拉法尔地区（瑞典）地下水水文地球化学特征的混合模型结果。该地区是在瑞典核废物管理公司（SKB）资助下，作为可能的候选场址之一进行调查的两个场址之一，用于长期储存乏核燃料。经典地球化学模型，结合系统古水文地质历史进行解释，表明该地下水系统地球化学演化的驱动过程是四种端元水之间的混合：深部古老盐水、冰川融水、古老海水和大气水。在本文中，我们使用一种综合方法，将主成分分析与质量平衡计算相结合，重点研究混合及其对地下水最终化学成分的影响。该方法允许我们测试几种端元水的组合和几种组成变量的组合，以便找到混合比例的最佳解决方案。我们已经将该方法应用于由 SKB 收集和分析的拉法尔地区 287 个地下水样本的数据集。发现的最佳模型使用四种保守元素（Cl、Br、氧-18 和氘），并根据三种端元水（盐水、冰川和大气）计算混合比例。一旦考虑了混合的一阶效应，就可以用水-岩相互作用来解释剩余的可变性。通过这种方式，仅受混合影响的保守元素的混合比例或系统中非保守元素的混合比例和化学反应可以用来获得每个水样的化学性质，为预测计算奠定基础。
