The filling procedures apply to the entire well cavity from the bottom of the well to three feet below the land surface. The well cavity is filled with clean sand or gravel, or one of the grout sealant materials. For small diameter shallow wells a sealant may be an easy, relatively inexpensive way to completely fill the well cavity. For larger diameter and deeper wells it will be more economical to use sand and gravel as the fill material and use a sealant at the required locations. One of the most critical steps in well plugging is placing the fill and sealant materials.
Special equipment is required to place slurried materials to prevent dilution and separation.
Granular bentonite, sand and gravel can be placed directly into the top of the well. However, you must take care to avoid bridging of granular materials within the well cavity. Fine sand will be more susceptible to bridging than gravel. Bridging will create a partially plugged well that may eventually collapse. The result is a continued safety hazard and potential for ground water pollution.