AGWT's Andrew Stone lends his counsel on this important topic.
In an area where wells penetrate more than one water-bearing layer, contaminants may reach the ground water zone of the old well and then travel on to other portions of the aquifer. If the contamination connects with another abandoned well, it could impact other aquifers and threaten operating wells and water supply sources. Abandoned dug wells typically do not lead to a contamination risk for deep aquifers, but their wide diameter, usually 3 feet to 5 feet, creates a physical safety hazard for construction equipment, in addition to the danger to people and animals that may be injured falling into the well.