Given a scientific passage and an answer, generate a question for the given answer.
Q: Passage: Pollutants in surface water can filter into the ground and enter a groundwater aquifer. Irrigation water can bring pesticides and other chemicals. Water can seep through landfills. Tanks of gasoline stored underground can leak. Answer: groundwater aquifer
A:
Pollutants in surface water can filter into the ground and enter a what?