Wells are considered abandoned when they have not been used for six consecutive months. Many accidents have taken place in which people or animals have fallen into abandoned wells.
Abandoned wells also provide a direct route for contaminants to enter aquifers below the surface. When open to more than one aquifer, abandoned wells may also allow deeper, salty aquifers to contaminate shallow freshwater aquifers. In addition, abandoned wells contribute to regional depletion of pressure head within an aquifer.
Find more information at our site on Abandoned Well Plugging.