Aquifer Contamination
Aquifer Contamination is when bad stuff gets into water stored deep under the ground.
Think of it this way
A kitchen sponge soaks up water and holds it inside its tiny pores. Now pour a drop of food dye onto the top of the sponge. The dye seeps down through the sponge and mixes into the water trapped inside. The clean water in the sponge is now stained, and you cannot easily separate the dye from the water again.
Explaining aquifer contamination by grade level
Rain soaks into dirt and fills up spaces in rocks below. That underground water is what many people drink. If something bad spills on the ground, rain can wash it down into that water. Dirty soil on a hillside can send pollution deep underground.