Various hydrogeochemical processes can modify the quality of river water during riverbank filtration (RBF). Identifying the subsurface processes responsible for the bank-filtered water quality is challenging, but essential for predicting water quality changes and determining the necessity of post-treatment. However, no systematic approach for this has been proposed yet. In this study, the subsurface hydrogeochemical processes that caused the high concentrations of total iron (Fe) and sulfate (SO₄²⁻) in the bank-filtered water were investigated at a pilot-scale RBF site in South Korea. For this purpose, water quality variations were monitored in both the extraction well and the adjacent river over five months. The volumetric mixing ratio between the river water and the native groundwater in the RBF well was calculated to understand the effect of mixing on the quality of water from the well and to assess the potential contribution of subsurface reactions to water quality changes. To identify the subsurface processes responsible for the evolution of Fe and SO₄²⁻ during RBF, an inverse modeling based on the chemical mass balance was conducted using the water quality data and the calculated volumetric mixing ratio. The modeling results suggest that pyrite oxidation by abundant O₂ present in an unsaturated zone could be a primary process explaining the evolution of total Fe and SO₄²⁻ during RBF at the study site. The presence of pyrite in the aquifer was indirectly supported by iron sulfate hydroxide (Fe(SO₄)(OH)) detected in oxidized aquifer sediments.

在河岸过滤 (RBF) 期间，各种水文地球化学过程可以改变河水的质量。确定导致河岸过滤水质的地下过程具有挑战性，但对于预测水质变化和确定后处理的必要性至关重要。然而，目前还没有提出系统的方法来解决这个问题。在本研究中，导致高浓度总铁 (Fe) 和硫酸盐 (SO ₄ ²⁻) 在韩国的一个中试规模的 RBF 站点进行了调查。为此，在五个月内对提取井和邻近河流的水质变化进行了监测。计算 RBF 井中河水和天然地下水之间的体积混合比，以了解混合对井水质量的影响，并评估地下反应对水质变化的潜在贡献。为了确定在 RBF过程中导致 Fe 和 SO ₄ ^2-演化的地下过程，使用水质数据和计算的体积混合比进行了基于化学质量平衡的逆向建模。模拟结果表明黄铁矿被丰富的 O ₂氧化存在于不饱和带中可能是解释研究地点 RBF 期间总 Fe 和 SO ₄ ^2-演变的主要过程。含水层中黄铁矿的存在间接得到了氧化含水层沉积物中检测到的硫酸铁氢氧化物 (Fe(SO ₄ )(OH)) 的支持。