Final answer:
Groundwater contamination in the nearby town is most likely caused by waste disposal at a nearby landfill, where non-decomposing materials like plastics can leach toxic chemicals into the soil and water table.
Step-by-step explanation:
Toxic chemicals filtering through the soil into groundwater, thereby contaminating the drinking water in a nearby town, most likely resulted from waste disposal at a nearby landfill. Landfills are a common source of groundwater contamination because materials like Styrofoam and plastics do not decompose naturally; instead, they may break down into harmful chemicals that percolate through the soil and into the water table.
Continuous dumping in landfills leads to the risk of an increase in groundwater contamination as the landfill sites fill up. The other options provided, such as dumping in the harbor, composting, or using an incinerator, do not directly correlate with the contamination of groundwater through soil percolation.