A vulnearbility-based framework for assessing impact and risk in source water protection

水源保护已成为加拿大的一个高度优先问题。 传统上，通过建立井口保护区来保护地下水源，该井口保护区表示污染物从污染源行进到井的平均时间。 这种方法可能会忽略一些可能影响污染物对井的实际影响的过程，例如分散、非均质性的影响、化学反应和稀释。 此外，目前使用的大多数模型在如何表示地表水和地下水之间的相互作用以及如何处理非饱和带方面做出了某些假设。 此外，它们通常假定补给和抽水率恒定。 这些假设的影响仍然知之甚少。 风险通常以定性或半定量的方式表示，没有现成的定量评估手段。 我们将通过应用新的水井脆弱性概念来评估污染源对饮用水井的影响，从而将井口保护提升到一个新的水平。 油井脆弱性考虑污染物从源到受体的整个地下路径，并考虑所有相关的地下过程。 它以水井饮用水目标被破坏的时间、相对于污染源强度的稀释系数以及暴露于污染的时间来表示影响。 将评估通常简化假设的效果，并评估井口保护中使用的标准模型的性能。 将在油井脆弱性方面比较模型的可靠性和有效性，从而更好地了解控制过程和不同建模方法的优点。 将对不确定性的影响进行评估，并制定定量方法来评估一口井未能达到饮用水目标的风险。 这将为水源保护制定更强有力和更合理的基本规则，并为地下水资源的保护和长期管理提供更好的决策基础。

Source water protection has become an issue of high priority in Canada.  Conventionally, groundwater sources are protected by establishing wellhead protection areas that express the average time a contaminant will travel from a contamination source to a well.  This approach may neglect some processes that can affect the actual impact of contamination on a well, such as dispersion, the effect of heterogeneities, chemical reactions, and dilution.  Also, most of the models that are  used at present make certain assumptions in how they represent the interaction between surface water and groundwater, and how they deal with the unsaturated zone.  Furthermore, they generally assume constant recharge and pumping rates.  The effect of these assumptions is still poorly understood.  Risk is generally expressed in a qualitative or semi-quantitative way, without a ready means for quantitative assessment.      We will take wellhead protection to the next level by applying the new concept of well vulnerability to assess the impact of a contamination source on a drinking water well.  Well vulnerability considers the entire subsurface pathway of a contaminant from source to receptor, taking into account all relevant subsurface processes.  It expresses the impact in terms of the time when drinking water objectives at the well would be breached, the dilution factor relative to the source strength, and the time of exposure to the contamination.  The effect of commonly made simplifying assumptions will be evaluated, and the performance of standard models used in wellhead protection will be assessed.  Models will be compared with respect to reliability and validity in the context of well vulnerability, leading to a better understanding of the controlling processes and the merits of different modelling approaches.  The effect of uncertainty will be evaluated and quantitative approaches for assessing the risk of a well failing drinking water objectives will be developed.  This will lead to more robust and defensible ground rules for source water protection, and an improved basis for decision making in the protection and long-term management of our groundwater resources.