Evaluating the Impact of Treated Effluent Recharge on Groundwater Using Solute Transport Model: A Case Study of Khan Yunis

Background: This study evaluates the impact of recharging treated effluent from the 2Khan Yunis Wastewater Treatment Plant on groundwater levels and quality, using a coupled groundwater flow and solute transport model (MODFLOW integrated with MT3DMS). The study area, located in the semi-arid region of Khan Yunis in the Gaza Strip, faces acute groundwater depletion and salinity issues. Key factors, including municipal and agricultural abstraction, rainfall, and leakage from water transmission pipelines, were considered. Methods: Five management scenarios were simulated to assess changes in groundwater levels and quality, including a no-action baseline, recharging treated wastewater with varying total dissolved solids (TDS) concentrations, and the transport of contaminants such as biological oxygen demand (BOD), chemical oxygen demand (COD), and nitrate (NO₃). Results: The results showed that treated wastewater recharge significantly improved groundwater levels, raising water heads by 8.5 m above mean sea level by 2040 compared to the no-action scenario. The treated effluent, with low concentrations of Biological Oxygen Demand (BOD) (9.75 mg/L) and Chemical Oxygen Demand (COD) (29.5 mg/L), disperses from the recharge basin to nearby areas. Notably, the average nitrate concentration in the aquifer (168.8 mg/L) significantly decreases due to the much lower nitrate levels in the treated wastewater (4.375 mg/L). This results in substantial improvement in groundwater quality, with a continuous reduction in nitrate concentration observed at and around the recharge basin. Conclusion: These findings highlight the potential benefits of expanding treated wastewater recharge practices. However, rigorous monitoring of recovery wells is essential to address any potential risks associated with this approach.