<p>Groundwater seepage is one of the primary drivers for the migration of contaminants at a site. Currently, the long-term direction of groundwater seepage is critical to the service life of vertical pollution-barrier walls in engineering design. Based on the convection–diffusion equation, we created a numerical model in three dimensions for this investigation. The site’s horizontal hydraulic gradient was 0.02 and the barrier’s insertion depth was fixed at 12&#xa0;m. This was done to examine how the angle (α) between the suspended vertical barrier’s length direction and seepage direction affected the barrier’s resistance to breakthrough from flow around the bottom for contamination containment. The numerical model is then validated against experimental and analytical results in order to demonstrate its accuracy. According to simulation results, changing α alters the distribution of maximum bypass flow velocities and resulting in an uneven flow-field distribution inside the barrier-controlled area. The position of the breakthrough failure gradually moves from the middle of the downstream bottom of the barrier to the end of the barrier when the value of α falls between 45° and 90°. The service life against breakthrough can be increased by up to 10.7%. There is only one breakthrough failure point at the bottom of the barrier for a range of α values. The study demonstrates that the best barrier efficiency occurs when seepage is perpendicular to the length of the upstream and downstream barriers (α = 90°), which is followed by α = 60° with the highest barrier efficiency. Therefore, while building or optimizing suspended anti-pollution barriers, it is necessary to take geological factors into consideration when choosing the α value for sites with stable, long-term groundwater seepage.</p>