Septic tank outflow problem

[Keith Dunbar]

Since moving into our new house, which is 350 years old, we've been aware of problems of sewage backing up and the septic tank outflow chamber never properly emptying. Previous owner for 20 years tells me it never properly emptied for them!!!

Tank will be at least 40 years old, may be a lot older. The outflow chamber is connected to a 110' long outflow pipe laid in 1" gravel parallel to, but not connecting with, a ditch. The pipes are about 1' long, laid end to end but not sealed or cemented together in any way. They are grooved on the outside, and look as if they are porous rather than glazed, so presumably the waste water is meant to pass through their walls as well as down them, into the gravel and thence into the ground and eventually the ditch.

Rodding indicated a blockage a about 60 feet. We were enormously lucky to find the far end of the pipe when we were digging rather randomly where we thought the end might be, and rodding upwards indicated a blockage at exactly the same place, so we knew where to dig. What we found strange was that the far end of the outflow just seemed to end in the ground, with no pipe work across to the ditch or anything like that, and not even any trace of a soakaway. The hole we dug to expose it has filled with water and remained filled.

Digging at the site of the blockage we have managed to expose the pipe and lift one section. Again, very luckily, we managed to open up the channel above the blockage so at least the water can get away no, and seem to be soaking away into the ground very easily. Our next task is to try and sort out the blockage.

Is it possible that if the pipe was originally porous it may have lost its porosity because it has been sludged up for perhaps 20 years +? And if so, is there anything we can do about it (e.g. send a chimney brush down on the rods)? Do we need to do anything about it? We're planning to put an inspection chamber where we've opened the pipe to make it easier to rod if it gets blocked again. Should we dig a new soakaway at the bottom, and if so, how big? Are there any other observations people might have as to how to get a more satisfactory result from rather an antiquated system?

TIA

Keith

[The Natural Philosopher]

Keith, you are going to hate me for saying this,but its not dissimilar from the situation at this property, except someone had dug up ALL the pipe and relayed plastic, down to a ditch, which stank in summer. I have found sections of the porous when doing other groundwork in the garden.

I rebuilt the house from scratch, and the BCO took one look and said 'that tank's got to go'

I put in a Klargester Biodisc, which probably would have cost £7500 installed, but we did it ourselves with the builders for about £6k.

Its been running 5 years, and apart from a pulley falling off, it hasn't needed to be emptied. It doesn't smell. As long as the pulley is on anyway. I guess the belt will break in 7-10 years. It is legal to dump straight into a ditch, and it does. Whiff free clear water. I put down loads of stuff I shouldn't. It takes it.

The old three chamber got its lids removed, filled with rubble and earth pushed over. The grass round there is VERY green.

My point? sometimes it ain't worth repairing crap or systems that don't deal with crap very well. Bite the bullet, get in a small digger, and a Klargester or equivalent,. make your BCO a happy man, and enjoy life insytead of pushing rods up shot pipes.

Heck, it may be something you can claim off insurance..because as sure as eggs is eggs, if the BCO did know that you are doing major remedial work on a system like this, he would like as not tell you to replace it completely.

[robgraham]

Keith I'm no expert other than I have a similarly antique system. Judging actually from a recent thread here on septic tanks, (within the last month or so so have a hunt for it as it was very informative), having an old system has it's benefits as it is far more tolerant to abuse in one form or another (long periods between cleaning out, household chemicals, etc)

Anyway I'm afraid I can't help you about your outflow problem really. I too have a double chamber system (modern ones seemingly only have one chamber) and obviously when it was built (1928 I think) it was acceptable to discharge into the local burn. Certainly the outflow is quite clean. But the outlet (some 15 ft long) to that point in my case was similarly unglazed pipes which some 15 years blocked totally with the consequent backing up and unpleasantness. I replaced it with modern 'holey' plastic laid in gravel.

Not really a lot of help I'm afraid !

Rob

[Roger]

The message from "Keith Dunbar" contains these words:

It sounds to me that the pipe itself was intended as your soakaway in which case that the dead end at the end of the pipe run is only to be expected. I think the clay pipes you describe are the traditional porous pipes used in land drains. Even if they have sludged up the gaps between should still be able to to let the water out into the surrounding ground.

IIRC the second chamber in a two chamber septic tank should also be full (of water, not sludge) and the drainage system connected as an overflow. You would only have a problem if the water level in the septic tank was markedly above the outflow pipe. I also think the adjacent ditch may be normal land drainage and a bit of a red herring. Septic waste outfalls should percolate away in the ground if you don't have a reed bed system to act as a buffer.

You don't say what the gradient is or how much land is available but AIUI the normal drainage pattern these days is a herringbone pattern. You are constrained by the ditch on one side but you could increase the soakaway area by adding branches to your main pipe on the side away from the ditch. Plastic perforated pipe is pretty cheap. When I diverted a land drain a few years ago I found the cost of the surrounding gravel was more than the cost of the pipe.

Digging out can be hard in some soils but you only need the trenches to be a spade width.

[The Natural Philosopher]

I completely disagree actually.

Thats a reasonable bodge..slightly better is perforated clay pipes in gravel.

But it cots a fair bit..

[Keith Dunbar]

I seem to have slightly mislead folk with my talk of a second chamber. This is only a 1' diameter, 2-3' deep chamber. It takes the outflow from the tank, via some sort of u-bend (which itself has got blocked two or three times because of lumps of white fat/soap? that have collected under the crust in the tank. It also has an inlet for some of the house rainwater (the house has been extended twice). And of course it has the outlet to the

110 foot row of porous clay pipes. It is this chamber which apparently has had 4 -6 inches of water in it pretty permanently for the last 20+ years.

I am in fact quite reassured by what is being said. The tank itself is very healthy - barely any smell at all and obviously doing its job exceedingly well. Once we clear this blockage it may well be the system will run as intended, given that there will be an extra 40 feet of pipe or so distal to the blockage for water to drain into the ground from, and perhaps the proximal end of the pipe was only not draining away because of the amount of sludge that has collected over the years because of the blockage. Now that did smell, but it wasn't horrendous.

I guess I need to suck it and see - put an inspection chamber for easier rodding of any future blockages where we've exposed the pipe half way down, leave the far end open to see if there is a problem with the water level there, and if so dig a soakaway to help it on its way. And keep a very low profile as far as the BCO is concerned!!!!!

Keith

[David Hansen]

On Thu, 10 Jan 2008 08:23:43 GMT someone who may be "Keith Dunbar" wrote this:-

I suggest you take a book out of the library which covers septic tanks. You can then work out which bit is which.

It sounds like your installation has the final stage, filtration, done by subsoil irrigation rather than a filter bed. If that is the case then the best way of doing this via a dosing system. This will accumulate effluent in a catchpit and then discharge it in one go. This ensures the effluent reaches all parts of the drains (there should be more than one in a fan shape) and allows the soil/bacteria to recover between doses.

[Huge]

I wouldn't ...

[Roger]

The message from "Keith Dunbar" contains these words:

I don't suppose that running the rainwater into the drain helps but at least it isn't directly into the septic tank. We had 1" of rain overnight here. That is about 20 cu feet of water off the roof (over 500 litres) which is a good deal more than the average sewerage output of the average house.

I would be surprised if the outlet from the second chamber wasn't at least a few inches above the bottom of the chamber and if the soakaway is horizontal there will need to be some head to get the water moving. However now you have the far end open you should know what the minimum level is. The chamber would have been put there for a reason and that reason might just be a sludge trap so if you periodically clear that out your drainage field shouldn't block up again unless the cause of the block was the inward movement of earth rather than the downward movement of sludge.

It's 30 years since I had a septic tank so I am a bit rusty on the subject and attitudes have changed markedly over that time. There now seems a presumption that septic tanks have never worked as intended (without mechanical assistance) and need regular emptying but if you have a crust and a good smell yours still has some aerobatic life in it which should have taken care of the fat. (Some people of course tip large quantities of fat directly down the drains which has the capacity to bugger main sewers let alone septic tanks).

Don't forget the Environment Agency (or whatever they call themselves these days) as well. :-)

[Keith Dunbar]

The second chamber is really like a drain inspection chamber, and from what has been said I guess it was installed when the house was extended so that at least some of the rainwater goes straight into the outflow pipe instead of via the septic tank, which is where most of it goes.

The outflow pipe does have a very adequate slope - around 1 in 40 - so once I sort out this blockage it may be the whole system will work very adequately.

Keith

[Keith Dunbar]

Perhaps you would be kind enough to suggest a suitable title?

Keith

[The Natural Philosopher]

I can just see teh microbes leaping from the surface, doing a double Immelman followed by a Hanmmerhead stall before spinning back into the sludge.. ;-)

[David Hansen]

On Thu, 10 Jan 2008 12:50:10 GMT someone who may be "Keith Dunbar" wrote this:-

"Home Plumbing" by Ernest Hall goes into enough detail without being too deep. It should allow an understanding of what is what.

[Keith Dunbar]

Thank you