Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences, Shijiazhuang, China; Hebei Key Laboratory of Groundwater Remediation, Shijiazhuang, China.
Haikou Marine Geological Survey Center, China Geological Survey, Haikou, China.
Sci Total Environ. 2022 Mar 20;813:151890. doi: 10.1016/j.scitotenv.2021.151890. Epub 2021 Nov 23.
Establishment of natural background levels (NBL) of groundwater in urbanized areas such as the Pearl River Delta (PRD) is challenging. Pre-selection methods are the most common approaches for NBL assessment, but it will overestimate (or underestimate) contaminated groundwater in urbanized areas by using present pre-selection methods with empirical definite values because of complicated human activities. Unlike present pre-selection methods, this study aims to establish a new pre-selection method with the indicative of Cl/Br ratios to identify contaminated groundwaters with convincing evidences. Specifically, this new method consists of indicatives of the oxidation capacity and the Cl/Br ratio combining with contaminated-markers. In addition, factors controlling NBL of Cl and NO in groundwater in various hydrogeological units in the PRD were also discussed. Main procedures of this new method: contaminated-markers in various hydrogeological units are extracted by a hierarchical cluster analysis, thereby determining threshold values of Cl/Br ratios and Cl concentration in various hydrogeological units for identifying contaminated groundwater; After that, groundwater chemical datasets was selected by the oxidation capacity, and then tested by Grubbs' test until normal distributions. Groundwater Cl and NO concentrations in datasets before and after this new method are dependent and independent of urbanization levels, respectively, indicating that the new method is useful for groundwater NBL assessment in urbanized areas such as the PRD. Both the seawater intrusion and the diffusion of Cl from marine deposits are likely to be responsible for the much higher NBL-Cl in coastal-alluvial and marine aquifers than in other hydrogeological units. Groundwater Cl enrichment resulted from groundwater recharge and evaporation is mainly responsible for the higher NBL-Cl in alluvial-proluvial aquifers than in lacustrine aquifers, fissured aquifers, as well as karst aquifers. More than double times NBL-NO in alluvial-proluvial and fissured aquifers than in other hydrogeological units is probably attributed to more oxidizing conditions of their vadose zones and groundwaters.
建立珠江三角洲（PRD）等城市化地区的地下水自然背景水平（NBL）具有挑战性。预筛选方法是 NBL 评估最常用的方法，但由于复杂的人类活动，使用目前具有经验确定值的预筛选方法会高估（或低估）城市化地区受污染的地下水。与目前的预筛选方法不同，本研究旨在建立一种新的预筛选方法，该方法以 Cl/Br 比值为指示，以确定具有令人信服证据的受污染地下水。具体来说，这种新方法由氧化能力和 Cl/Br 比值的指示物与污染标志物相结合组成。此外，还讨论了 PRD 不同水文地质单元中地下水 Cl 和 NO NBL 的控制因素。该新方法的主要步骤：通过层次聚类分析从各种水文地质单元中提取污染标志物，从而确定各种水文地质单元中 Cl/Br 比值和 Cl 浓度的阈值，以识别受污染的地下水；然后，根据氧化能力选择地下水化学数据集，然后通过 Grubbs 检验进行测试，直到达到正态分布。新方法前后的地下水 Cl 和 NO 浓度分别与城市化水平相关和独立，表明该方法可用于 PRD 等城市化地区的地下水 NBL 评估。海水入侵和海洋沉积物中 Cl 的扩散都可能导致滨海冲积含水层和滨海含水层中的 NBL-Cl 远高于其他水文地质单元。地下水补给和蒸发导致的地下水 Cl 富集主要导致冲积-洪积含水层中的 NBL-Cl 高于湖泊含水层、裂隙含水层和岩溶含水层。冲积-洪积含水层和裂隙含水层中的 NBL-NO 是其他水文地质单元的两倍以上，可能归因于其包气带和地下水的氧化条件更多。
