Eliminate the pollution source: An underground tank must be pumped dry and then dug out from the ground. A factory must be required to stop releasing toxic chemicals. Farms must be more careful about the chemicals they put on their fields.
Monitor the extent of the pollutant: Scientists test water in wells. Sometimes they drill wells to test water. They learn how the groundwater is flowing: how fast and in what direction. They study the contaminants in the groundwater. Then they determine where the contaminant plume is going.
