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Soakaways

HOW DOES A SOAKAWAY WORK

Perhaps the most important component of the septic tank system is its soakaway, and it is often the “weakest link”. The soakaway system has to be capable of dealing with all the waste water produced by the household, which can often be in the region of 40 gallons per day per person. Such a soakaway would normally be one of three types: a porous chamber, a stonefilled pit or a layout of irrigation drains.

Years ago, the porous chamber or stonefilled pit were most commonly used, but nowadays a layout of subsoil irrigation drainage is normally considered the most appropriate system. This is similar to a herringbone land drainage system but designed to allow water to leak out to the subsoil instead of attracting ground water into the drain. The amount of drainage required depends on (1) the porosity of the subsoil, which can be determined by percolation tests in trial pits and (2) the population being served by the tank.

There are three basic types of soakaway:

1. The preferred method: irrigation drainage, preferably in a looped or closedcircuit design. The drain consists of porous pipe or landdrainage pipe within a stonefilled trench.

2. A soakaway chamber – normally brickbuilt with slots in the sides to allow effluent to soak into the subsoil. (shown above)

3. A simple stonefilled pit. This has little chance of working properly unless in particularly porous ground

The efficiency of a soakaway depends on the porosity of the ground and this should be determined by a percolation test. The less porous the ground, the bigger the surface area of the soakaway has to be.

Septic tank soakaways are unlikely to be successful in areas of heavy clay ground. Often the most effective and cheapest solution / alternative is to use a small package sewage treatment plant instead of a septic tank, particularly if there is a suitable nearby watercourse for the treatment plant to discharge to.

 

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