There's something just a little disconcerting in that statement.
Maybe that means tracing the extent of the plume into the water table. Then they could determine which wells were in the plume. They seem to have a rough idea. I don’t know how the water distribution system in Tarawa Terrace was interlinked. I recall there being at least one water tower in the area, which implies everyone was drinking the same concentration of the contaminant, regardless of their position with respect to the toxic plume. I’ll have to ask my Mom if the water was from the tap tasted OK or if we drank lots of bottled water.