Abandonment of a drywell, known as decommissioning, is very straightforward, but not necessarily simple. According to the Arizona Department of Environmental Quality (ADEQ), decommissioning activities should only be undertaken by a qualified drywell drilling contractor. After a thorough cleaning, the standard procedures include removal of all internal drywell components such as piping, screens, and shields and then pumping grout down the main injection pipe. Next, all concrete chamber material should be removed creating a large, circular hole. Once the chamber has been removed, the resulting hole should be filled with clean fill such as silt, clay, or engineered material and compacted as it is placed.
Too many times, inexperienced contractors simply fill the drywell chamber with whatever material is readily available and then walk away. However, decommissioning a drywell improperly can be a risky endeavor for a number of reasons. First, neglecting to pump grout down the main injection pipe provides a conduit for contaminants. Second, if the fill material is not compacted, subsidence is likely to occur at the ground surface. Finally, since the main purpose of the decommissioning process is to seal the original excavation in order to prevent contaminants from migrating into the ground, the quality and type of fill material used in the process is critically important.
According to ADEQ staff, decommissioning a drywell is serious business and proper procedure should definitely be followed. If alternate procedures are employed, the drywell owner must demonstrate that the procedures employed are at least equivalent to those defined above.
