RWTH Aachen University, Department of Engineering Geology, Lochnerstrasse 4-20, 52064 Aachen, Germany.
Sci Total Environ. 2009 Dec 20;408(2):245-54. doi: 10.1016/j.scitotenv.2009.09.046. Epub 2009 Oct 23.
Intrinsic vulnerability assessment to groundwater contamination is part of groundwater management in many areas of the world. However, popular assessment methods estimate vulnerability only qualitatively. To enhance vulnerability assessment, an approach for quantitative vulnerability assessment using numerical simulation of water flow and solute transport with transient boundary conditions and new vulnerability indicators are presented in this work. Based on a conceptual model of the unsaturated underground with distinct hydrogeological layers and site specific hydrological characteristics the numerical simulations of water flow and solute transport are applied on each hydrogeological layer with standardized conditions separately. Analysis of the simulation results reveals functional relationships between layer thickness, groundwater recharge and transit time. Based on the first, second and third quartiles of solute mass breakthrough at the lower boundary of the unsaturated zone, and the solute dilution, four vulnerability indicators are extracted. The indicator transit time t(50) is the time were 50% of solute mass breakthrough passes the groundwater table. Dilution is referred as maximum solute concentration C(max) in the percolation water when entering the groundwater table in relation to the injected mass or solute concentration C(0) at the ground surface. Duration of solute breakthrough is defined as the time period between 25% and 75% (t(25%)-t(75%)) of total solute mass breakthrough at the groundwater table. The temporal shape of the breakthrough curve is expressed with the quotient (t(25%)-t(50%))/(t(25%)-t(75%)). Results from an application of this new quantitative vulnerability assessment approach, its advantages and disadvantages, and potential benefits for future groundwater management strategies are discussed.
地下水污染固有脆弱性评估是世界上许多地区地下水管理的一部分。然而，流行的评估方法仅定性地估计脆弱性。为了增强脆弱性评估，本文提出了一种使用水流和溶质运移的数值模拟以及瞬态边界条件和新的脆弱性指标进行定量脆弱性评估的方法。基于具有明显水文地质层和特定于站点的水文特征的非饱和地下的概念模型，分别对每个水文地质层在标准化条件下进行水流和溶质运移的数值模拟。对模拟结果的分析揭示了层厚、地下水补给和迁移时间之间的功能关系。基于不饱和带下部边界处溶质质量突破的第一、第二和第三四分位数以及溶质稀释，提取了四个脆弱性指标。指标迁移时间 t(50)是溶质质量突破的 50%通过地下水位的时间。稀释是指当进入地下水位时，进入地下水位的渗流水中的最大溶质浓度 C(max)与注入的质量或地表处的溶质浓度 C(0)的关系。溶质突破持续时间定义为地下水位处总溶质质量突破的 25%和 75%之间的时间段(t(25%)-t(75%))。突破曲线的时间形状用商(t(25%)-t(50%))/(t(25%)-t(75%))表示。讨论了这种新的定量脆弱性评估方法的应用、优点和缺点，以及对未来地下水管理策略的潜在益处。
