Visualizing Ammonia Nitrogen Transport in Groundwater Using MODFLOW and MT3DMS: A Case Study from Xinxu, Xiamen, China 
WengChen1  LvChencan2  CaiKexuan1  ZhongChuxian1  LiuYu3(Correspondence)

1 Xiamen Institute of Geological Engineering, Xiamen, 316008;

2 School of Land Science and Space Planning Hebei GEO University, Shijiazhuang, 050031;

3 Xiamen Institute of Environmental Science, Xiamen, 361021;

Abstract：In response to the increasing risk of groundwater pollution in rapidly urbanizing coastal environments, this study develops a high‑resolution three‑dimensional model to simulate the transport of ammonia nitrogen (NH₄⁺) in Xinxu Town, Xiamen, China. Integrating 148 borehole datasets, multi‑source monitoring data, and a 5 m resolution digital elevation model, we constructed a heterogeneous groundwater flow model with a 50×50 ×5 m grid using MODFLOW. Boundary conditions reflect regional recharge–discharge patterns and continuous leachate input from a municipal solid waste treatment facility. The subsequent MT3DMS-based solute transport simulation examines NH₄⁺ migration under varying hydrological scenarios over a six‑year period. Model results reveal predominant southeastward contaminant migration aligned with hydraulic gradients, with shallow layers exhibiting faster transport velocities than deeper strata. Critical discharge zones were identified in low‑lying northeastern areas, highlighting potential risks to downstream water users. The model provides a robust tool for visualizing pollutant plumes, assessing long‑term impacts of waste facility leachate, and informing targeted management strategies.

Keywords：Groundwater flow field; Numerical simulation; MODFLOW; MT3DMS; Ammonia nitrogen transport

References

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