Septic Tank

[wcavanagh]

I have the following question from Building control. How do I go about finding this? House was build in 1900 and it was 2 semi detached now one 4 bedroom cottage. I am not sure where I would go for this information.

Confirm capacity of existing septic tank (in litres) and demonstrate the suitability of the existing outfall (see clause 3.8.5).

 

[Hugh Jaleak]

Either measure the height, width/length/diameter of the tank and work out the capacity from that, or get it emptied and ask the tanker driver how much has been removed. Under no circumstances make any attempt to enter the tank when empty.

What are the current outfall arrangements, soakaway, leach field, reed bed or straight into a watercourse?

 

[oilboffin]

Yes stay out of the tank deadly gasses.hughs right lxbxdepth do it in ft3cos I cubic foot is 6.2 galls.

 

[wcavanagh]

Yes I work in the petrol business and know all about confined space entry (actually fully trained on this, so could do entry) but would not want to.
They are pushing for me to scrap the old tank, and install a new Mini Treatment Plant, as they tell me I don't need the drainage field then.

So much to look into.

 

[Hugh Jaleak]

What would the plan be for disposal of the final effluent if the Treatment Plant was installed?

 

[wcavanagh]

I have no idea, don't know how it works. Can it go into a soak away?

 

[Hugh Jaleak]

I have no idea, don't know how it works. Can it go into a soak away?

Yes. That's why I was confused. Virtually every drop of water that goes into the system, needs to come out again. Cant understand why they said you wont need the drainage field, that final effluent has to go somewhere.

I would imagine they're asking if the existing drainage arrangements are still fit for purpose, some can silt or clog up, especially if the tank hasn't been maintained properly, and the final effluent has a high concentration of suspended solids.

A septic tank relies totally on settlement, and natural bacteria to break down the sewage, provided the tank is correctly operating and maintained, then the outflow is permitted to be discharged into the subsoil via a soakaway or leachfield.

A package plant, such as those from Klargester, provides a higher level of treatment for the sewage. https://www.kingspanenviro.com/wastewater-management/sewage-treatment-plants Look at either the Biotec or Biodisc for examples for domestic usage, although the Biodisc can be specified in sizes capable of treating a large number of properties. The final effluent from these, provided the unit is operating and maintained correctly, is of such a standard it can sometimes be discharged straight into a watercourse.

 

[wcavanagh]

Thank you very much. We had planned to use the original tank so never looked into any of this.

When you say watercourse what exactly is that? I have no mains drainage at all, at the moment, all house, and gutter go into this tank (yes I know) and it seems its been like this for the last 60 years.... anyway, my plan was to separate the rain water drainage, and put in a soak away using them crates. So would I need a similar setup after this package plant to deal with the outflow?

Will have to do this all myself as I dont really have budget for this. I have access to a 1.5T digger, and very able to deal with all plumbing, etc. Just never had to work on one of these before.

 

[Hugh Jaleak]

Watercourse, ditch, stream etc. Septic tank outfall should always go into the ground to give the final level of treatment, as the final effluent is far from pure. Have seen some going into a ditch, but these are the ones the Environment Agency will be jumping on and forcing to upgrade to a package plant.

Rainwater should never go into a septic tank, in times of heavy rainfall it'll stir everything up, and possibly wash solids into the soakaway, which will soon bung it up. Modern living produces a lot more grey water than 60 years ago, dishwashers, automatic washing machines and people are bathing more often. Often these tanks are now overwhelmed by the flow going into them, which far exceeds anything they were designed for. Remember, every drop of water you put down the drain will go to the tank, and out again. A 'Cesspool' which is basically a holding tank for sewage, has to be pumped out when full, (very rarely used due top this fact), but as a minimum now I think they have to be 30000 litre capacity for a single domestic property. That sounds a lot but wont take long to fill. (5000 toilet flushes at 6litres a flush!)

Assuming there is not a ditch you could look at discharging the treated effluent into, then a soakaway is the only option. (Check with the Environment Agency for any permissions or licences you may need to discharge.) Keep it separate from the rainwater soakaway, you don't want the tank backfilling with rainwater in wet periods.

If you've not installed one before I wouldn't recommend doing it unless you're totally confident, drainlaying to connect the tank up is easy enough, but installing the tank will need to be done in accordance with the manufacturers specifications, or you'll not only render any guarantee void, there is also the risk of damage to the tank, or in extreme circumstances I've known them 'pop' back out the ground after being emptied as the water table in the surrounding soil was so high and the tank hadn't been installed correctly for the ground conditions!

Most, if not all, package plants will need a power supply too. The Biodisc has rotating paddles, the Biotec uses a compressor to bubble air through media to assist with breakdown of bacteria.

 

[wcavanagh]

Thank you. I have experience I fitting large Petrol Station Fuel Tanks, of 100,000L etc, so I don't think I will have any issues from this point of view.

Thank you very much for the very detailed reply, and very helpful. I will make 2 separate soakaways then, no issues, the rainwater one will be to the side of the property and the new tank one will be towards the bottom of the property, I have a fair amount of land, etc.

Electrical is also no issues, I can deal with this as the whole house is being rewired also.

I guess there is some kind of control and alarm system in place, as it is not often we go to the bottom of the garden to check the tank.

 

[Hugh Jaleak]

I think an alarm is an optional extra from Klargester, depending on which you unit you go for. Personally I think the Biodisc is the superior unit, simple in operation, just a small motor turning the discs. I work for a water company, and we have a number of the larger units in service, providing treatment for the sewage from smaller villages. Discharge from these usually goes into a settling tank or small lagoon, and from there into a ditch or stream, such is the quality of the treated final effluent.

Basically the only major problem you could have then is the motor or drive belt failing, but a rotation sensor can be fitted to provide an alarm in the event of that happening. Plant will continue to function adequately for a few days whilst repairs can be organised. Desludging should be carried out, probably on an annual basis, to maintain the correct balance and operation within the tank.

Lastly, if you've not had a septic tank before, please try and keep use of detergents and particularly bleaches, to an absolute minimum, and any discharge from a water softener is strictly prohibited. Brine is antiseptic, and anything else that could upset the essential bacteria involved in the process of breaking down the sewage, must be avoided as much as possible.

 

[wcavanagh]

Fantastic, thank you for all the information. I have looked at a couple of units and install of tank looks very straightforward, compared to what we do for a petrol tank. So no issues, with that. Will have a good look in the new year as I have some time to get this done etc. Thank you again for the help.