The most easily polluted groundwater reservoirs are aquifers?

Water-table aquifers.

The most easily polluted groundwater reservoirs are water-table aquifers.

Infiltration is the process by which rainwater becomes groundwater. In the water cycle, which involves primarily; evaporation, condensation and precipitation. Henceforth, after precipitation comes infiltration in the land areas leaving the rainwater aggregated in a single location which accumulates over time. Then this process is followed by runoff and subsurface flow by which water flows through other bodies of water, either in river, sea or ocean, even lake. Other rainwaters that has segregated and wasn’t able to transport itself stays in the process of infiltration, thus groundwater.