Septic Tanks

Septic Tank Problems
 
Most septic tank problems and failures are due to the soakaway and not to the septic tank itself.

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 water table and the deterioration of the septic tank itself.

Signs of a failed septic tank soakaway:-

• Septic tank effluent surfacing on your land
• Strong or bad odours coming from the septic tank or drains
• Pollution of nearby ditches or streams with septic effluent
• Slow flushing of toilets
• Gurgling in the drains
• Ground movement (dips) near the septic tank or soakaway drainfield
• Toilet overflowing
• Overflow at washing machine hookup
• Overflows into shower or bath when the sink is discharged
• Drain inspection chambers have standing effluent in them.  These should be empty.

1. Maintenence of the septic tank
 
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 not routinely emptied, most people tend to wait untill they notice a problem.

2.  Depth of the soakaway

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

Aerobic bacteria cause no problems for soil porosity. 

Unfortunately, if the 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.

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 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 occured.  Because there is then no flow into the soakaway, they can do NOTHING to restore the soil's porosity.
 
4.  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. 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 oulet 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 soskaway failure occurs.

Solutions:-
 
Septic tank soakaway

You can build a new soakaway in a completely different part of your garden, if your garden is big enough (often over 100 metres of pipework is involved) and if your soil has passed the mandatory Percolation Test required by Building Control.  You will require a properly designed herringbone drainage system to be installed, designed to BS 6297:1983 NOT a 'PIT FILLED WITH STONES'.  These 'Pits' work until they are full, (not very long!) then the liquid backs-up the pipe again. You are NOT allowed to discharge septic effluent into a land drain, ditch, watercourse, etc.  This is illegal.

You can scrap the entire system and install a full sewage treatment unit which CAN, with the relavent consents, discharge to a ditch, stream, land drain etc.  The effluent is gone from your property and with it, all the hassle of soakaways.

Please call for advice on 0800 61 20 733 or email ususing the form provided on the Contact Us section of this site.