<![CDATA[The land application system for treated wastewater has a specific hydrogeological carrying capacity that is highly responsive to seasonal fluctuations. This study aims to analyze the hydraulic impacts and contaminant transport risks resulting from the infiltration of treated domestic office wastewater (7,4 m³/day) and healthcare facility effluent (11,2 m³/day) on the reliability of groundwater monitoring wells. Three-dimensional numerical simulations were conducted using MODFLOW and MT3DMS codes to evaluate four flux-loading scenarios under transient-state conditions. Hydrodynamic simulation results confirmed that the spatial placement of the existing upstream (control) and downstream (impact) monitoring wells is scientifically valid along the regional hydraulic gradient. During the rainy season, when the natural water table is exceptionally shallow (2–3 m), implementing Scenario 1 (100% Maximum Capacity) triggers a local Groundwater Mounding of up to 1,45 m, significantly reducing the unsaturated vadose zone thickness. Consequently, the travel time of dissolved solutes, such as Chemical Oxygen Demand (COD), accelerates rapidly, penetrating the downstream well screen within 45 days at a concentration of 18,45 mg/L. Conversely, adopting Scenario 3 (50% loading with a two-day watering rotation) reduces the spatial extent of the contaminant plume by over 70%. This scenario is recommended as the optimum environmental management strategy to preserve the water quality integrity of the unconfined shallow aquifer.]]>
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