Which of the following mainly causes groundwater pollution?

Groundwater pollution is primarily caused by substances that seep into the ground and contaminate the water supply stored beneath the surface. Leaking storage tanks are a significant source of this pollution because they often contain hazardous materials or pollutants like chemicals, fuels, and other industrial liquids. When these tanks leak, the contaminants can migrate through the soil and into the groundwater, posing serious risks to drinking water supplies and the environment.

In contrast, while invasive species, air pollution, and soil erosion can have detrimental effects on ecosystems and water quality, they do not directly introduce harmful substances into the groundwater in the same way that leaking storage tanks do. Invasive species primarily affect biodiversity and ecosystem balance, air pollution affects atmospheric quality and can lead to acid rain but not direct groundwater contamination, and soil erosion can contribute to surface water pollution but does not typically involve contamination of groundwater directly. Thus, the link between leaking storage tanks and groundwater pollution is more direct and impactful, making it the primary cause in this context.