This thesis studies the environmental impacts of subsurface irrigation and drainage with treated wastewater. Subsurface irrigation and drainage is a new method of agricultural water management that falls under the umbrella of environmental technologies known as managed aquifer recharge (MAR). The use of treated wastewater means that contaminants of emerging concern (CECs) are inadvertently released into the soil. Numerical models, verified with experimental data, show that subsurface irrigation with treated wastewater is not likely to lead to adverse effects on the surrounding environment or on the irrigated crops at an experimental implementation located in the Netherlands. Numerical modelling also reveals that if the biodegradation of CECs in the soil depends on mixing-dependent multicomponent biochemical processes, then it does not seem possible to simplify the problem by using assumptions such as first-order kinetics or soil homogeneity. Analytical solutions on the efficiency of MAR systems in general are also derived and validated.