It can be dangerous to clean a well that has remained closed for a long time because of the buildup of toxic gases and other harmful substances that can accumulate in the well. This can include gases such as hydrogen sulfide, carbon dioxide, methane, and nitrogen, which can pose a risk to human health if they are inhaled in large quantities. Additionally, the water in the well may contain high levels of bacteria, pathogens, and other harmful substances that can cause illness if ingested.
Furthermore, if the well has been closed for an extended period of time, the water inside may have become stagnant and the quality of the water may have deteriorated. If the well is opened and the stagnant water is disturbed, it can release the toxic gases and other harmful substances into the air, which can be inhaled by those nearby.
For these reasons, it is important to exercise caution when cleaning a well that has remained closed for a long time and to seek the assistance of a professional if necessary. A professional well inspector or pump technician will have the necessary equipment and expertise to safely clean the well and test the water quality to ensure that it is safe for use