In this study, the formation mechanism and water quality of groundwater in the northwest of Nansi Lake Catchment (NNLC) were analyzed through mathematical statistics, hydrochemical analysis and entropy weighted water quality index (EWQI), and the human health risk of nitrate was also evaluated. To this end, 89 wells in the NNLC were sampled, and the groundwater samples were divided into three groups (I, II, and III) according to cluster analysis results and spatial distribution. The main results are as follows: Topographically, Groups I, II, and III correspond to the alluvial plains, apron plain, and low hills and its front margin, respectively. According to the Piper diagram, the hydrochemical types of Groups I and II groundwater are Na–SO₄·Cl and Ca·Mg–HCO₃, respectively, and that of Group III is more concentrated, mostly corresponding to the Ca–HCO₃ type. Hydrochemical analysis indicated that the development of groundwater hydrochemistry is mainly attributable to water–rock interactions, with the primary process being the dissolution of minerals such as calcite, dolomite, gypsum, and albite. Evaporation exhibited an increasing trend from the northeast to the southwest. Groups I and III presented obvious effects of human activities, with Group I showing sulfate pollution and Group III mainly showing nitrate pollution. Analysis of the characteristics and causes of the groundwater hydrochemistry revealed the proposed approach has excellent performance for classification in areas with complex hydrogeological conditions. The results of EWQI showed that the overall water quality was good, following the order Group III > Group II > Group I. The overall human health risk of nitrate in groundwater was low, but the risk was slightly higher for children than for adults. Therefore, the effects of nitrate contamination should be considered when exploiting hilly and peri-urban groundwater for drinking water.

本研究通过数理统计、水化学分析和熵权水质指数（EWQI）分析了南四湖流域（NNLC）西北部地下水的形成机制和水质，并评估了硝酸盐对人体健康的风险。 . 为此，对NNLC的89口井进行了采样，根据聚类分析结果和空间分布将地下水样品分为三组（I、II和III）。主要结果如下： 地形上，Ⅰ、Ⅱ、Ⅲ组分别对应冲积平原、坪平原、低丘陵及其前缘。根据Piper图，I组和II组地下水的水化学类型分别为Na-SO ₄ ·Cl和Ca·Mg-HCO ₃, 并且第 III 组的浓度更集中, 主要对应于 Ca-HCO ₃类型。水化学分析表明，地下水水化学的发展主要归因于水-岩相互作用，主要过程是方解石、白云石、石膏、钠长石等矿物的溶解。蒸发量呈现由东北向西南增加的趋势。Ⅰ组和Ⅲ组表现出明显的人类活动影响，Ⅰ组表现为硫酸盐污染，Ⅲ组主要表现为硝酸盐污染。对地下水水化学特征和成因的分析表明，该方法在水文地质条件复杂的地区具有良好的分类性能。EWQI结果显示，总体水质良好，顺序为Ⅲ组>Ⅱ组>Ⅰ组。地下水中硝酸盐的总体人类健康风险较低，但儿童的风险略高于成人。因此，在开采丘陵和城郊地下水作为饮用水时，应考虑硝酸盐污染的影响。