Most septic tanks and soak-aways have problems at some point, these usually involve the drain pipes backing up, the septic tank overflowing and the effluent backing seeping into ditches and polluting the environment.
Usually problems with the septic tank are to do with the soak-away and not the septic tank itself.
Unfortunately soakaways are pretty much designed to fail – how quickly depends on several factors, including;
- how the septic tank has been maintained,
- the soil type and quality
- the height of the winter water table
- the specification of the septic system itself
The common signs of a soakaway failure are;
- effluent pooling on the ground surface,
- foul odours (bad smells) coming from the septic tank or drains,
- visible pollution of nearby ditches or streams,
- slow flushing toilets and gurgling sounds from the drains,
- overflowing toilet, shower, bath or any other drain appliance,
- dips in the ground surface near to the septic tank and drain runs, as a result of wash away,
If you have any of these signs it is advisable to lift the drain inspection chambers to see if there is any standing effluent in them, they should be clear flowing with no material buildup.
The main reasons for septic tank and sewage system failure
Septic Tank Maintenance
All septic tanks require emptying at least once every 12 months as they only have a capacity for storing 12 months of sludge. If the sludge gets washed into the soakaway system, it very quickly reduces the soils porosity, preventing the effluent from soaking away.
Most septic tanks are poorly maintained with owners often under the misguided belief that they are saving money.
Onion shaped septic tanks have a lower quality effluent than the traditional brick (concrete or fibreglass) two chamber septic tanks.
Septic tank soakaways should be constructed in aerobic soil (contains oxygen in the air spaces of the soil) which is only found in the top metre of soil.
As well as acting as a medium to disperse the effluent the ground is used as part of the system to break up and digest the effluent. This is carried out by aerobic bacteria in the soil. If the soakaway depth is greater than a metre below ground level (including the 300mm gravel bed beneath the pipe) then it will be trying to operate in anaerobic conditions. Under these conditions (no oxygen) a different type of bacteria exists and rather than breaking down the effluent a slime is produced which reduces the length of life of the soakaway by reducing the soils porosity.
Surprisingly most modern ‘onion’ shaped septic tanks have outlet levels that are set at greater than a metre below ground – resulting in a soakaway using anaerobic conditions, contrary to Section H of the Building Regulations 1.39 which states that ‘ Drainage fields should be designed and constructed to ensure aerobic contact between the liquid effluent and the subsoil’.
In soils with a low porosity such as clay and clay based soils it is impossible to disperse the effluent satisfactorarily. In these soils the porosity is so bad that soakaways will often fail in the first 5 years of their life. The air voids are filled with high levels of suspended solids (often greater than 1200mg per litre). This level of suspended solids can also be found in badly maintained sewage treatment units,and also results in the reduced life of the soakaway. Even if the ground consisted of a sand based soil, the porosity will eventually be reduced by the high level of suspended solids and the black slime created as a result of the anaerobic process – the period in which this may occur will be extended to 15 to 25 years but the result the same at the end.
Winter water table
If the winter water table is higher than the septic tank outlet level, then the soakaway acts as a water collection system and back fills the septic tank, this process can cause the settlement chambers to mix with the clarified effluent. When the water level subsides the resulting effluent is full of solids which then reduces the soils porosity.
Because of the corrosive environment in a septic tank metal parts and mortar joints detiorate over time, this includes the internal divisions/fins/rods and metal struts and bolts in the ‘Onion’ type septic tanks, and the mortar joints in thebrick built septic tanks.
When the septic tank is unable to clarify the sewage as a result of an internal collapse the level of suspended solids in the final effluent rises dramatically causing the soakaway to fail shortly after.
Excess sodium (salt) in soils with fine particles of silt or clay can cause Sodium Binding. This is when the clay particles bind together, resulting in a waterproof layer forming alongthe soakaway trench.
This sodium comes from washing powder, detergents, sweat and the water from cooking vegetables.
Soakaways are designed to cope with a certain volume of daily use. If there is an increase in the volume then the soakaway needs to be redesigned to match.
How to solve a soakaway failure problem
Unfortunately adding a ‘friendly bacteria’ to a system after a soakaway failure has occurred will not help as the porosity has been reduced so badly that there is no flow to allow the bacteria to get to where it needs ro be.
High pressure water jetting of the soakaway drain run will force more solids into the soils air spaces, resulting in even poorer porosity.
You can scrap the entire septic system and install a full sewage treatment unit which can, with the relevant permits discharge to a ditch, stream, land drain etc.
You can fit a conversion unit inside the septic tank, but you need to be sure that the septic tank is sound and will remain so, and is sufficiently sized to
allow for the unit and adequate settlement.
Many ‘bottle’ septic tanks need to have their internal tank divisions removed prior to fitting as they were never designed to become a sewage treatment unit, this does remove the need for any groundworks which may be important for sites with no JCB access or extensive extensive landscaping features.
Septic Tank Conversion Unit
You can use your septic tank, as the first settlement stage of a full 3 stage sewage treatment unit if the inside struts are broken.
The Septic Tank Conversion Unit is installed as a retro fit and is connected to the septic tank outlet pipe so converting your system into a full sewage treatment unit.
The septic tank conversion unit adds the missing aeration chamber and final settlement chamber or, in the case of the Biorock sewage treatment plant, filters and digests the effluent without the need for electricity.
The final effluent from an aeration septic tank conversion unit is the same standard as a full sewage treatment unit, i.e. 20BOD* : 30S.S.* :20NH3* and from a filter system, five times better.
Unlike septic tank effluent, the resulting water can be discharged to a watercourse etc.
By using what you already have as part of the system you can save as much as 60%.
Because the septic tank has a greater capacity than an ‘all in one’ sewage treatment unit the time between tank emptying can be 12 months or more.
The units are small and the damage to gardens, etc. is limited.
For further information please call GoEnviro 02920 553370 to speak to a B.Eng (hons) engineer.
GoEnviro also provide blocked drain cleaning, CCTV camera surveys, drain and odour investigation, basic plumbing services to Barry, Penarth, Cowbridge, Vale of Glamorgan, and surrounding areas.