雄安新区唐河污水库残留污染物对地下水水化学动态的作用机制

唐河污水库位于雄安新区白洋淀西侧，污水库渗漏和污水灌溉历时长达40 a，包气带中累积大量污染物.识别污水渗漏和灌溉复合系统残留污染物对地下水水化学动态的作用机制，对雄安新区的水环境保护至关重要.利用水化学离子示踪及改进的氯碱指数等水文地球化学方法，解析浅层地下水水化学时空特征及演化机制.结果表明，污水库区地下水水化学类型为SO₄ ·HCO₃-Na型，平均污水混合比例为48.4%，阳离子交替吸附作用和岩盐溶解作用分别为地下水提供了29.9%和8.6%的钠离子；污灌区地下水水化学类型为SO₄ ·HCO₃-Na ·Mg型，平均污水混合比例为58.3%，阳离子交替吸附作用降低了地下水中8.1%的钠离子；降水和灌溉水的混合稀释作用导致残留污水混合比例和矿物饱和指数降低，促进地下水中钠离子与土壤胶体吸附的钙镁离子的交换作用.含水层反硝化作用能有效减少地下水硝酸盐污染.此外，污水库修复前后污水比例分别为61.5%和49.3%.污水渗漏和灌溉复合系统中长期滞留的污染物将在降雨和灌溉模式驱动下以不同程度的污水物理混合和水岩相互作用持续影响浅层地下水水质.

Dynamic Mechanisms of Groundwater Quality by Residual Contaminants of the Tanghe Wastewater Reservoir in Xiong'an New Area

Tanghe wastewater reservoir(TWR) is located on the west side of Baiyangdian Lake in Xiong''an New Area, where sewage infiltration and irrigation has been taking place for 40 years, and a large number of contaminants have accumulated in the unsaturated zone. Identifying the mechanisms by which this combined system contributes to groundwater hydrochemical dynamics is important for the protection of the water environment in the area. Hydrogeochemical methods such as tracing and improved chlor-alkali index are used to analyze the spatial and temporal characteristics and evolution mechanisms of shallow groundwater. The study shows that the groundwater chemistry in the sewage reservoir area is SO₄·HCO₃-Na type, with an average sewage fraction of 48.4%, and the contribution of Na⁺ from ion exchange and halite dissolution is 29.9% and 8.6%, respectively. The chemical type of groundwater in the sewage irrigation area is SO₄·HCO₃-Na·Mg, the average sewage fraction is 58.3%, and Na⁺ consumption of ion exchange is 8.1%. The mix dilution of precipitation and irrigation leads to a reduction in the effluent fraction and saturation index in the groundwater, and promotes the adsorption of Na⁺ from groundwater into the soil. Denitrification in aquifers can effectively reduce groundwater nitrate pollution. In addition, the sewage fraction before and after the restoration of the reservoir was 61.5% and 49.3%, respectively. Pollutants retained in the sewage infiltration and irrigation combined system will continue to affect the quality of shallow groundwater with varying degrees of mixing and water-rock interaction driven by rainfall and irrigation.