Sodium bentonite is a natural sealant and is used for sealing stock and recreational ponds, dairy and sewage lagoons, and city landfills. It is also effective as a hole plug as well as for controlling dust on highways. Sodium bentonite is one of the “most effective low cost methods” of treating porous soils. It is so effective, that the Federal Government and most states require a liner of sodium bentonite or material comparable, to be used to seal toxic waste lagoons and abandoned water and oil wells. It is environmentally safe, because it contains no chemicals, no additives, nothing toxic. 50 lb. bag.