Stormwater-based managed aquifer recharge in a rural agricultural catchment: Design, monitoring, and hydrogeochemical impacts from a pilot site in Bavaria, Germany

Managed aquifer recharge (MAR) is increasingly recognized as a key strategy to enhance groundwater sustainability, yet the use of stormwater as a recharge source remains limited, particularly in rural and agricultural settings. Key uncertainties persist regarding stormwater quality variability, treatment performance, and potential impacts on groundwater quality.We present the technical design, operational testing, and hydrogeochemical assessment of a stormwater-based MAR pilot site implemented in November 2024 in Hüll (Hallertau region, Bavaria, Germany), an area characterized by intensive agriculture, recurrent local flooding, and strong groundwater demand for irrigation. The MAR system combines a stormwater retention basin for buffering flash-flood dynamics, treatment units, and recharge via an infiltration well targeting a highly heterogeneous Tertiary aquifer.Initial results demonstrate robust system performance under variable stormwater conditions. The treatment units effectively reduce suspended solids and pesticide concentrations, enabling controlled recharge while minimizing risks to groundwater quality. Beyond quantitative water resource augmentation, the scheme shows potential qualitative benefits for agricultural groundwater systems.