Answer:
Contaminated soil or rock needs to be cleaned in an aquifer because if left uncleaned, it can leach pollutants into the groundwater contained within the aquifer. The polluted water can then spread to wells and water treatment facilities, potentially contaminating the drinking water supply. This can have serious health and environmental consequences, so it's important to clean contaminated soil or rock in aquifers to prevent the pollution of the water supply. The cleaning of such soil or rock is typically done through a process called remediation, which involves removing, treating, or isolating the contaminated material.