soakaways and irrigation
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Klargester provides information concerning their design and installation in Technical Data Sheet TDS0005. This follows the guidelines provided in the British Standard, BS 6297.
The function of drainage systems is to receive the clarified sewage from the septic tank and discharge it underground in the soil. The soil environment purifies the liquid further providing a separate biological stage for additional breakdown. The purified liquid moves away by percolation, evaporation, plant uptake and transpiration.
The type of soil and its ability to drain, is of paramount importance when deciding if an irrigation system is acceptable.
It is very important to ensure that the drainage system has been correctly designed and installed. If the effluent is not absorbed by the soil, ponding occurs, allowing untreated effluent to surface. If the effluent passes through the ground too quickly, (without treatment by a subsurface biological mat) then untreated effluent can enter a water supply, and cause other problems if the water is later abstracted for potable use.
Corrugated pipework, because of its intrinsic design is generally not advised (even by the manufacturers) for use in a septic tank irrigation system as;-
- It is difficult to lay evenly, allowing low points where effluent can collect. This can cause over saturation of a local area.
- The corrugations can retain sediments which may over time, cause blockages.
Problems experienced with the irrigation/soakaway system should be referred to your original installer or local drainage contractor.
Incorrectly designed, or old soakaway systems exhibit their problems. Systems that are too short may allow untreated liquid to surface. If the soil is insufficiently porous, the liquid will stagnate and pond to the surface. As soakaway systems age, the biomat may thicken and as a result progressive blockages can occur. Blocked areas may relate to how level the system is laid and the flow pattern through the pipes.
Systems that have been installed where the water table is too high, or where the water table moves upwards, during wet or winter periods exhibit problems. The soakaway system may allow the ground water to drain back into the tank, and sewage may back up in the incoming drains as effluent cannot flow out of the tank.
You should establish the cause of the problem in your particular circumstance and if necessary consider renewing the soakaway system. Occasionally the use of pumps after a septic tank may assist. The use of a BioDisc® should be considered. BioDiscs are package treatment plants which contain an aerobic biological culture and produce a fully treated effluent with low amounts of BOD and suspended solids. (Generally <20 mg/l BOD and <30 mg/l SS). The low levels of pollutants discharged within the fully treated effluent means that a BioDisc can be used where a soakaway cannot be renewed or in place of a septic tank feeding an inadequate soakaway. With EA consent, a BioDisc effluent may be discharged into open watercourses or ditches. Please contact us.
Smells in the irrigation system may be caused by;-
- Ponding, caused when effluent surfaces out of the top of the ground. As the effluent "decays" smells are produced.
- A chemical within the effluent that damages or kills the biological treatment mat within the soil, which then rots and decays.
- Excess bacterial activity, caused by increased nutrient release possibly as a result of a need to desludge the tank.
Septic tank factsheets:
