Septic tank.

[scooby1]

We have one of the older brick built, two chamber septic tanks. The first chamber is the one we empty, the second is full of aggregate. With a house full over Christmas our system has become blocked. I know it's not the drains leading to the tanks, we built a replacement dwelling 2 years ago with all new pipework to the tanks.

My question is what happens in the 2nd tank with the aggregate ? I think that this has become "clogged" up over the years with the previous owner and it is not allowing the excess fluid to drain away. I know it can get away because it's down our own fields and I have, for other reasons, been down to the pipe.

I am assuming that the principle is that the fluids get into the 2nd tank and leave the solids behind in the 1st tank and then the aggregate is supposed to act as a filter and if it has become "clogged" then the liquid isn't getting away as it should and is backing up in the system.

If I am right in my thinking that I assume I have to rip the top off the 2nd tank and replace the old aggregate with new. I have my own 3CX so I can get the top off reasonably easy and maybe even get some of the stone out.

Any ideas/comments would be appreciated. Thank you.

 

[Hugh Jaleak]

Nearly all septic tanks work on a similar principle, raw effluent enters the primary chamber, where the solids should start to settle out. The clarified effluent should then move into the next stage, some have a secondary settlement chamber, others, (as it appears in your case) go to soakaway. I would assume the gravel is to act partly as a filter and partly as media, providing a vast surface area for bacteria to flourish and provide a secondary stage to treatment.

Often the case whereby a system has coped for many years and then a sudden influx overwhelms it. Can you see what is going on in the 2nd tank? Is the aggregate submerged? May be a case of digging the aggregate out giving it a quick hose down, (you don't want to remove all the good stuff!), and chucking it back in. Once it has been loosened this maybe enough to allow the percolation rate to keep tally with the outflow from the 1st tank.

 

[scooby1]

Thank you for that Hugh, that seems a perfectly reasonable and sensible explanation. Is there a preferred size for the aggregate in the 2nd chamber ? The reason I ask is that I have a stockpile of 20mm granite but I seem to remember that the existing ag. is larger than that.

 

[Nige F]

You need to keep the original aggregate - it`ll be full of good bacteria - It should be a volcanic larva like stuff , to give a large surface area - the exact opposite to granite . Have a look in the first tank and make sure the dip pipe to the 2nd tank hasn`t dropped off . If you`ve got a straight through pipe to the aggregate, it'll let solids through to block

 

[scooby1]

Thanks Nigel for that. I will have a look at the "dip pipe" when I have the 1st tank emptied again.

But I have a confession to make and I feel a bit of a fraud. I said originally that I knew it wasn't anything to do with the pipework leading to the tanks because it was all renewed. And I also said that we had a houseful of family over Christmas. I should also have taken notice of my Wife's remarks about having to replace toilet rolls sooner that she would have expected.

It would appear that one of my young Grandchildren thought that he would do a "Dulux puppy" impression with regard to the toilet roll because I found reams of the stuff right at the end of the delivery pipe just as it goes into the 1st tank !!

I have spent most of the morning with a large roll of MDPE (hadn't got enough rods) rodding the pipes. Eventually got it to go and now all is well.

I am not amused.

Happy New Year everyone and thanks again for all your help.

 

[Burnerman]

You get all the good, jobs, scooby!
Pleased you got that sorted....I was going to recommend getting the outfalls jetted.
John

 

[scooby1]

Thanks John. I always look for a silver lining in every cloud. Earlier I forbade Mrs. Scooby to use the washing machine because of the problem. And she has loads to do !

So now she is able to catch up a bit so I won some Brownie points there. I was also given a bottle of Chivas Regal for Christmas and I intend to partake of that tonight. And so the day got better as it went along really.

 

[Hugh Jaleak]

Kids and toilets, never a good mix. Pulled plenty of toys out of drains in the past too!

As to tank, the dip pipe(s) should still be visible when the tank is at normal working level, they consist of a T section, with a stub of pipe on the bottom, and should be fitted on inlet and outlet. Idea is to allow inflow and outflow to discharge/draw from below the surface, this allows a crust to form on the top and as Nige says, it stops solids getting washed through to the second chamber. Furnace slag was often used as a media in these situations, traditional methods of sewage treatment use filter beds which are full of that stuff.

If no T pieces are visible (you'll just see a hole where the pipe goes through to the 2nd tank, then chances are the T has fallen off and is laying in the bottom. If it is missing then it would be prudent to replace T on outlet to 2nd tank as a minimum to prevent any problems with outfall.

Something for the warmer weather possibly, enjoy that bottle for now!

 

[scooby1]

Thanks for that HJ. Yes, I will inspect when we next have it emptied by getting inside the 1st tank. I know about potential issues with gases but will have a mate there with me and have made my will anyway.

 

[Hugh Jaleak]

Go in with a rope round your waist, and make sure your mate is capable of dragging your dead weight back out again! If you pass out then he don't want to be trying to get in there after you! Or that'll be both of you needing a half day out with the Undertaker......

I'm trained to enter confined spaces such as that, and we're not allowed in without at least 3 present, and those entering must wear appropriate PPE. There have been too many cases of multiple lives lost when someone has gone in afterwards to rescue the first person who's collapsed.

Please don't make yourself another statistic, you should be able to see all you need to from the surface I hope.

 

[scooby1]

Thanks HJ. I am very much aware of the gas issue in slurry pits and grain silos but didn't think the septic tanks were as bad. I have already been down it once.

So thanks for the advice and it is duly noted

 

[Hugh Jaleak]

I'm sure I don't have to teach you to suck eggs, but anywhere sewage is present is a risk, there is no place in my view for complacency, you wont get a second chance..... The consequences of things going wrong are explained graphically during training to enter these environments, and it is dramatic enough trying to effect an escape under practice conditions in a controlled environment.

I know of a site (treatment works) that was built undercover (to help prevent odour issues!) and now there is a major issue as the entire covering structure is being rotted from the inside out due to gas! It attacks both concrete and metal, and even short term exposure to lower levels can be injurious to health. Over a certain concentration will deaden the body's sense of smell, so you can actually be unaware of it's presence, rapidly becoming another statistic.....

It really isn't worth the risk, and the gas can actually creep up on you. It's not unknown for an area to test negative only for the alarms to go off shortly afterwards, especially if sludge or other decaying matter is disturbed. Please be careful.

 

[scooby1]

Thanks again HJ. That was very informative. You obviously know what you are talking about. Most of the terrible accidents in slurrry pits in my industry are when people couldn't get out but I am sure there have been times when the reason for that is that the victims have been overcome.

Just as a matter of interest, and I should say that you have discouraged me from going down into the tank, is there any way of negating the problem. i.e. maybe blocking the outlet to the 2nd tank and leaving the 1st tank full of water for a period of time ? How do people deal with tank problems if they have to get inside them ? I am only talking about domestic septic tanks here. I suppose breathing apparatus is one way - perhaps the only way ?

 

[HERTS P&D]

At the end of the day, it is sometimes worth calling in professionals to do the job.

As a roofer once told me that if he fell off a roof, he would never work again. "That's why I'm charging £xxx."

Andy

 

[Hugh Jaleak]

The only long term solution is to fix it properly. (This is, of course, assuming there is a problem!) Bear in mind a slurry tank is full of animal waste, a septic tank is full of human waste. Essentially the same thing in this context.

Entry to the tank is perfectly permissible, but it is simply not worth the risk without the correct procedures in place! Ultimately paying someone trained and with the correct kit to make an entry is cheaper than anyone's life. It only takes a couple of breaths of Hydrogen Sulphide to be lethal, this tragic case brings it right home. http://www.bbc.co.uk/news/uk-northern-ireland-19618661

To enter a confined space requires (by law) a minimum of 3 people. Gas monitors are required to be used at all times, harnesses and a man riding winch, also emergency BA, so if the alarm does go off you have a supply of air to allow an exit to be made.

I attended a job recently where it was required to clean a 'wet well', (sewage pumping station). The well in question was pretty large, and in order to clean properly a multiple man entry was required. Such were the possible risks a separate dedicated emergency rescue team were on site should the worst happen.

I can only inform you of the associated risks, but to again quote the late Fred Dibnah, whilst he faced a very different risk, the principle remains the same! 'Get it wrong and it's half a day out with the undertaker.'