When your soakaway doesn’t soak away any more, there isn’t much that can be done to resurrect it short of digging it out and starting again.
A soakaway is constructed of a central perforated pipe surrounded with clean stone, and is usually in a straight run but may also be in a herringbone shape. It does 2 jobs if in conjunction with a septic tank – firstly biologically treating sewage from the tank by way of naturally occurring bacteria, and then distributes the effluent into the subsoil. It is this latter job that the soakaway does if it is linked to a sewage treatment plant, as the influent has already been treated within the plant.
Effluent from the tank flows along the full length of the pipe and gets dispersed through the stones to the surrounding ground. Bacteria living on the stones are constantly fed by the nutrients in the flow of liquor, and break down the waste aerobically. Fine suspended solids continually flow from the tank along the soakaway, gradually silting up the spaces between the stones. A black biomass sludge then starts to form on the stones and the soakaway gradually becomes blocked, thereby reducing its efficiency.
A soakaway will from the outset have a limited life expectancy – some 20 to 30 years depending on the quality and quantity of the fluid passing through it. Once the equilibrium between the amount of liquor produced by the household on a daily basis and the amount the soakaway can discharge during the same period is put out of kilter, then problems start to occur and a backing up will commence. The first sign of this is usually smelly effluent breaking out over the surface of the soakaway, or drains starting to back up.
We are often asked to jet a failing soakaway, but this would rarely serve any useful purpose, as it can only clean out the pipe, not the stones around it. Little significant improvement would be achieved, leaving no feasible alternative than to replace the soakaway.