Septic Tanks
A septic tank is a settlement tank in which raw incoming sewage is retained long enough for organic matter to undergo anaerobic decomposition. A scum forms on top of the tank consisting of fats and soaps, and sludge settles at the bottom of the tank. A standalone septic tank will reduce the `strength` of raw incoming sewage by 30-50% under ideal conditions. The relatively clear liquid, called septic tank effluent, which is inbetween the scum and sludge, leaves the tank and then undergoes secondary treatment e.g. a soakaway, reed bed or sewage treatment plant.
Important Note: If your septic tank discharges effluent directly into a watercourse or ditch you are committing an offence under Section 85 of The Water Resources Act 1991. Such an offence carries a prison sentence and/or a fine. This does not mean however that the tank must be replaced. Quite often secondary forms of treatment like a soakaway, sewage treatment plant or reed bed, can treat the septic tank effluent to a level that it can be discharged to the environment under an Environment Agency Permit (Consent) or Exemption. By contacting us we can advise you further on your own system. We will need to survey the tank to check its structure, size and location. Septic tank systems were first reported being used for serving the sewage disposal needs for properties in France around 1870. The septic tank invention is credited to Frenchman John Louis Mouras, who patented the septic tank invention in September 1881. The first recorded septic tank in full use in the UK was installed in 1896 and served the entire town of Exeter.
Types of Septic Tank
Historically septic tanks were built of engineering brick or stone and pointed, or built of concrete block and rendered. Often the inlet dip pipes were salt glazed clay 4” pipe work. The tank would consist of one, two or infrequently three chambers. The chambers where often connected using dip pipes or gaps in the partition wall, as shown in the diagram below. Wooden baffles might also be found within older tanks to hold back the scum and prevent carryover into the soakaway. Often a separate pipe would supply air to the tank via a nearby vent.
Common Septic Tank Problems
There are a number of common septic tank problems that can lead to bubbling toilets, frequent rodding of drains, soakaway failure and environmental pollution. The simple explanations below are designed to help you diagnose your septic tank problem. For further information contact us on 01984 623404.
The original septic tank may now be too small for modern usage.
Over the past years household water usage has increased and we now produce higher volumes of waste water. If a septic tank is undersized the retention time within the tank is reduced which might cause solids to carry over into the soakaway, reducing the longevity of the soakaway. Building Regulation under Approved Document H state ‘septic tanks should have a capacity below the level of the invert of at least 2,700 litres (2.7m3) for up to 4 users’, i.e. 2 double bedrooms.
Roof or surface water entering the septic tank.
All fresh water from rooves or surface water drains should NOT enter the septic tank. The reason is that under storm conditions huge quantities of water will enter the tank, mix up the settled solids and carry them through into the soakaway, reducing the longevity of the soakaway. This can be represented by a lack of solids within the septic tank. Fresh water also includes water entering the tank due to damaged pipe work or damaged tank structure.
A primary indicator of pollution: sewage fungus (grey/ white cotton wool in appearance) caused by a septic tank, without any secondary treatment, discharging into the ditch
Damaged dip pipes inlet and/or outlet.
If the dip pipes are damaged or have broken off, solids can carry through into the soakaway without adequate settlement. This can lead to soakaway failure. Dip pipes can usually be repaired or replaced without too much expense.
Misuse of chemicals entering the tank.
When large amounts of bacteria damaging chemicals enter the drains (eg. Jeyes Fluid) the breakdown of solids within the septic tank will be adversely affected. Often this is represented by a lack of crust and a foul odour. Contact WCI now for a list of prohibited substances.
Infrequent desludging.
Most modern septic tanks (fibreglass onions) are designed for complete emptying/desludging every 12 months. I should note that the rate of desludging does depend on the number of people using the system and the working capacity of the tank. Why is desludging important? As the amount of solids increase within a septic tank the retention time of incoming foul water decreases and the treatment quality of the wastewater decreases. Sludge can carry over into the soakaway and block the surrounding stone and soil meaning the septic tank effluent cannot soak away. This will result in the septic tank filling up and waste water backing up the drains. Eventually wastewater will exit out of the top of the septic tank and manholes. A badly congested tank can also cause water to back up as the solids prevent water entering the tank. A telltale sign that your system is surcharged or backed up is your toilet bubbling when you flush it!
Collapsed Baffles.
Fiberglass septic tanks can, on occasion, suffer the collapse of the internal baffles (shown on the preceding diagram as a black suspended ‘petticoat’). This can occur when the tank has not been emptied for a long period of time and the tank is the emptied incorrectly. If the solids are left to hang on the baffle as the effluent is removed the sheer weight of the solids could cause the baffle to collapse and fall to the bottom of the tank. This end result is that solids are not able to settle out properly within the tank and soakaway longevity is reduced.
Pumping macerated solids to an existing septic tank.
When levels do not allow for a gravity system, sometimes raw sewage enters a pump chamber and is pumped via a macerator pump to a septic tank. During this process solids are cut up into smaller pieces which require a much longer retention time to settle out in the tank. Often the existing tank’s working capacity is inadequate to allow the necessary settlement and large amounts of solid material passes into the secondary treatment causing problems. Such problems include gravel blockages in a reed bed or soakaway which can lead to failure.
By contacting us we can advise you further on your own system. We may need to survey the system and carry out some basic tank calculations which allow us to check if the tank is suitable. Contact us now on 01984 623404 for more information.