Thousands of water supply wells are drilled every year. Some of these wells are drilled for individual homeowners, new subdivisions or municipalities. The wells may also be drilled for a water source for industrial use or irrigation. In North America, state or provincial regulations work to ensure that wells are properly drilled and do not pose a threat to valued groundwater aquifers. An important aspect of completing a well is to grout the annular space between the drilled borehole and the casing. This void needs to be properly plugged to avoid any migration of surface water down the well into the aquifer. Diagram 1 shows this annular space being sealed by an impermeable bentonite grout. The well contractors who drill the well require licenses and all the proper training to grout and install a groundwater supply well. The location of the well is registered with the state or province.
In Ontario, where I live, the province has been keeping a database of new wells drilled since the early 1990s. Therefore, we know the location and number of legally drilled water wells since that time. If a property owner is drilling a new well, we know whether there are other wells on the property that may need to be abandoned. There are an unknown number of wells that were drilled before it was legally required to document their location and this causes a problem. Many of these wells may not have been properly sealed and may have been left unused for many years. In fact, there are many abandoned wells that nobody even knows exist. In Ontario alone, some estimate that there are as many as 100,000 wells that either need to be upgraded or abandoned.