Delineation of groundwater source recharge area in confined aquifers based on particle tracking techniques

Accurately delineating the groundwater source recharge area is of great importance for assessing environmental risks and ensuring the supply of drinking water. In this study, taking the Chengxi Wellfield of Suzhou City, Anhui Province, as an example, the typical groundwater source recharge area with high extraction intensity was studied. Innovatively combining the MODFLOW–MODPATH particle tracking method, a three-dimensional transient groundwater flow model was established for the delineation of the dynamic recharge area. Model calibration showed strong agreement between simulated and observed hydraulic heads, reliably capturing groundwater level dynamics. The simulated results revealed significant head decline at the wellfield center and the formation of an expanding cone. The particle trajectories progressively extended outward, and the boundary of the capture zone was delineated after 12 050 days. Sensitivity analysis identified hydraulic conductivity, specific storage, and pumping rate as the main factors controlling recharge extent and flow dynamics. In addition, the nonlinear response model quantitatively characterized the gradual expansion of the recharge area over time and with pumping intensity. The study confirms the reliability of particle tracking methods for dynamic recharge delineation in complex aquifer systems and provides practical insights for adaptive and sustainable groundwater management under intensified extraction.