Septic Tank Problems and Solutions

Most septic tanks and their soakaways have problems sooner or later, with the septic tank overflowing, drainage effluent appearing at ground level, seeping into ditches or backing-up the pipes. These are common problems.

How quickly the septic tank soakaway becomes a failure depends on several factors which include how well the septic tank has been maintained, the nature of the soil, the height of the winter water table and the deterioration of the septic tank itself.

The Environment Agency has confirmed to us that DEEP BOREHOLE soakaway solutions are not acceptable to them.  BEWARE of adverts on the internet.

Signs of a failed septic tank soakaway:

Septic tank effluent surfacing on your land  (see photo below)

The reasons for septic tank and sewage system failure

1. Septic Tank Maintenance

All septic tanks require emptying at least ONCE A YEAR.  They only hold 12 months sludge storage and if sludge starts to empty into the soakaway soil, it very quickly blocks the air spaces (porosity) in the soil, the effluent cannot soak away, you suffer a soakaway failure and the septic tank fills up, backing up the system.  Most Septic Tanks are very poorly maintained and I hate to think how many Clients have told me (when their septic system has failed!) that septic tanks never need emptying!  I have STOOD on the solid mass, covered only by inches of liquid, inside the septic tank on many occasions!

Onion shaped septic tanks have a poorer quality of effluent than the traditional 2 chamber brick/concrete/fibreglass septic tanks.

2.  Depth of the soakaway

All septic tank soakaways must be constructed in the AEROBIC soil layer. This is soil which has oxygen in the air spaces between the particles and only occurs within the top metre of the soil.

This is because a septic tank soakaway has two functions - the first is to soak the septic tank liquid away and the second is to treat the septic tank effluent and digest it via aerobic ( oxygen breathing ) soil bacteria.

Aerobic bacteria cause no problems for soil porosity.

Unfortunately, if the septic tanks soakaway is deeper than one metre below ground level; and this includes the 300mm. gravel bed underneath the pipe, then it is in the ANAEROBIC soil layer and the bacterial growth is anerobic.

Anaerobic bacteria cause huge problems as they produce a slime which blocks the soakaway and the porosity of the soil.

The ridiculous fact is that most modern 'onion' shaped septic tanks have outlet levels deeper than one metre as standard! This almost certainly ensures that the soakaway is constructed in the anerobic layer, making soakaway failure inevitable.

As Section H of the Building Regulations 1.39 states that ' Drainage fields should be designed and constructed to ensure aerobic contact between the liquid effluent and the subsoil', why do manufacturers design septic tanks that do not comply? If you buy one of these septic tanks, then reduce the height of the neck before installation to raise the outlet height.

 3.  Nature of the soil

It is impossible to soak septic tank effluent away into a clay or clay-based soil in a normal soakaway. The porosity is so bad that soakaways often fail within the first 5 years as their air spaces become filled with the high levels of suspended solids, often above 1200mg/litre, in the septic tank effluent. (This level of suspended solids can also be found in badly maintained sewage treatment units, and the same thing applies - you ruin your own soakaway!)   In any case, even with a sandy soil, the porosity is eventually destroyed by the high level of suspended solids and by the black slime that results during the decomposition, although it may take 15 to 25 years. The air spaces fill with solids and the soil turns from a 'sponge' into a 'brick'.  Adding a pump to the septic system to try to force the septic tank effluent into the soakaway only makes matters worse.  The solids are 'blasted' into the soils air spaces, blocking the porosity even quicker and hastening your soakaways demise! Adding commercially available 'friendly bacteria' sachets is also useless once a soakaway failure has occurred. Because there is then no flow into the septic tanks soakaway, they can do NOTHING to restore the soil's porosity.

4.  Winter water table

If the winter water table becomes higher than the septic tank outlet level, then the outlet pipe to the soakaway starts to drain water from the soakaway back into the septic tank.  There is one thing that is certain: water ALWAYS finds the level.  This usually causes the septic tank to fill and settlement chambers mix with clarified effluent with the result that, when the level subsides, the resulting effluent is full of solids which then block the soil porosity in the soakaway.  It is USELESS to try to jet out the outlet drain as all you are doing is forcing even more solids into the soil air spaces, making the situation worse.

5.  Deterioration of the tank

Many septic tanks' internal divisions/fins/rods and particularly the metal struts and bolts, (in the case of 'Onion' septic tanks) and mortar joints (in the case of brick built septic tanks), etc deteriorate,  as raw sewage is a very corrosive environment.   When the inside of the septic tank is no longer able to clarify the sewage due to internal collapse, then the level of suspended solids in the final effluent rises dramatically and it is only a short time before soakaway failure occurs.

6.  Sodium Binding in the soil

7.  Another house joining the system

How to solve the soakaway failure problem

• 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. The effluent is gone from your property and with it, all the hassle of soakaways.

• You can fit a 'conversion' unit inside the septic tank, but you MUST be CERTAIN that the septic tank has a long lifespan ahead of it without leaking water in or out or it will not work.  The septic tank must also be large enough 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. We can fit them but we DO NOT offer service agreements on them as we have had too many Emergency Call-Outs in the past due to blocked air-lift pumps and backed-up drains.  They do, however, prevent the need for any groundworks which may be important for sites with no JCB access, extensive landscaping features, etc.  Call us for details and prices.

• You can utilise your septic tank, even if the inside struts are broken, as the first settlement stage of a full 3 stage sewage treatment unit. The Septic Tank Conversion Unit is installed AFTER the septic tank, connected to the septic tank outlet pipe and will convert your system into a full sewage treatment unit.  The septic tank conversion unit either 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.  The savings can be up to 60% by using what you already have as part of the system.  The septic tank, having a greater capacity than in an 'all in one' sewage treatment unit, can still last at least 12 months between emptyings.  The units are small and the damage to gardens, etc. is limited.

• If you have bought a house with a defective system, it is sometimes possible to use the Legal System to make your Solicitor pay for the repair or replacement works. Contact Maureen Webb on 01757 288022 to discuss.