Wells that are unused and have been improperly decommissioned (abandoned) pose a serious risk to ground water quality. Improperly decommissioned wells can directly channel contaminated surface water into ground water. Since ground water flows through soil and rock formations, contamination from an improperly decommissioned well can spread to other wells in the area. Because of these risks, abandoned wells must be filled, sealed and plugged.
There are very good reasons to make sure abandoned wells are properly decommissioned.
Improperly abandoned wells threaten drinking water supplies by providing open conduits into aquifers that have potential to supply drinking water to public or private wells.
Any contaminants entering an abandoned well from the surface can travel easily into different water-bearing formations whether in coarse sand and gravel aquifers or in bedrock fracture zones and can cross-contaminate a number of water-bearing formations within one well.
If a drinking water well is being replaced because of water quality problems in the original well, the abandoned well is a direct threat to the new water supply if it is not properly sealed.
Improperly abandoned wells can create a liability problem at the time of property resale or if the well causes contamination in neighboring wells.
Shallow dug wells create a physical hazard simply because of their large diameter and the potential for animals or people to fall into them. Typically, the older fieldstone-lined wells are the most dangerous because many were finished flush to the ground surface and were covered with wooden covers which now are decayed or non-existent. Most of the well contaminants that commonly cause concern originate above ground, often as the result of human activities. Disease-causing bacteria and viruses, pesticides, fuels and industrial chemicals are examples of pollutants that can contaminate a ground water supply. Spills and careless storage or use of chemicals, and poor treatment and disposal of waste materials often are to blame.
Soil overlying the water table provides the primary protection against ground water pollution. Bacteria, sediment and other insoluble forms of contamination become trapped within the soil pores. Some chemicals are adsorbed or react chemically with various soil constituents, thereby preventing or slowing the migration of these pollutants into the ground water. In addition, plants and soil microorganisms use some potential pollutants, such as nitrogen, as nutrients for growth, thereby depleting the amount that reaches the ground water.
Well owners sometimes are tempted to use illegal wells to dispose of sewage and other wastes. This is unacceptable; it is literally like pouring waste directly into your drinking water, and the health risks can’t be overstated.