When a septic system is overloaded or not properly maintained, the bacterial decomposition can slow or stop, causing untreated liquid and solid wastes to overflow into the soil. Excessive use of bleaches, disinfectants and caustic or acid drain cleaners also deters the bacterial action of the system, and greases and solids can build up until they choke the system and block the flow of the liquid into the soil. When this happens, the drainage field may have to be dug up and replaced – a costly undertaking.