Soakaway Problem

[vanessajackson]

Can anyone offer advice on my Soakaway problem?

We moved into our present property approx 2 years ago which had an existing ceptic tank and soakaway. 2 people lived there before us and supposedly had had no problems. There are now 4 people at the property so water usage etc is higher now. After approx 6 months waste started backing up the drains towards the house. We had the ceptic tank emptied at a cost of £140 and the problem seemed to go away for a couple of weeks. Then the same thing happened again. We determined that the soakaway was obviously not working properley, so decided to dig another soakaway next to the existing one. We dug further down than the existing soakaway to be on the safe side until we reached what we assumed to be the rock bed (in excess of 15 feet) and filled with the appropriate size rubble. Again the problem went away, this time for approx 6 - 8 months. When waste started backing up the pipes to the house again we were at a loss as to what to do. We researched all about anaerobic/aerobic bacteria etc and, ensuring all the levels would be right, we now have in place a float switch pump and hose which takes the liquid from the ceptic tank to the top of the garden (approx 40-50ft away) which disperses into a newly installed French Ditch (this has a length of land drain in it, covered with a breathable fabric and soil, which sits on a bed of gravel). We placed an inspection hole half way up the garden to be able to monitor how things were working. We thought we had the problem solved but over the past few months, we can see via the inspection hole that liquid is still not draining away fully, and when we have heavy rain the levels rise and we have to resort to having the ceptic tank emptied again and again and again. We've cut down on using bleach products etc so that the bacteria in the soakaway doesn't get harmed and can do its job, but unfortunately our garden soil is of a clay consistency so this obviously doesn't help the situation. We really don't know what to do next. One option is to install a home sewage treatment operation as we do have access to a nearby stream (we have priced this up and it could cost anything in the region of £6000-£9000) but this would have to be a last resort and we really don't want to go down that route. So can anyone offer any advice at all as we are in a desperate situation?

 

[Static]

Clay soils and soakaways is never a good mix.. they dont allow for decent infiltration rates so tend to just not work.. how free draining is your garden.. do you get alot of water puddling on it or soft spongy patches after rainy days.?
Also is the tank suitably sized for the number of people in the house?

 

[vanessajackson]

Clay soils and soakaways is never a good mix.. they dont allow for decent infiltration rates so tend to just not work.. how free draining is your garden.. do you get alot of water puddling on it or soft spongy patches after rainy days.?
Also is the tank suitably sized for the number of people in the house?

The garden is pretty flat but we don't tend to get puddles of water on the garden, but when it rains quite heavily it sort of feels squelchy underfoot and can remain that way for several days. I'll have to check the size of the ceptic tank cause thats one thing we havent done.

 

[IanAnderson]

You have my sympathy, who needs this kind of problem, especially as you are doing everything right.

Makes you wonder about the muppet, sorry, 'expert' that specified this kind of set up in an obviously inappropriate soil and of course the mother lode of all muppetry, sorry, competence, the Building Control office that passed it.

Without seeing the layout of your land, its difficult to go into specifics. Need to find a local 'drain God' down your way.

Might be worth calling the local BCO at the authorities and describe the problem, you never know.....

 

[Static]

A test for calculating a soakaway is to dig a hole in the ground about 1mx1mx1m and full it full of water, then time how long it takes to 1/2 drain and fully drain.. normally should only be 1-12hrs but if it takes longer than about 24hrs to fully drain then soakaways simply wont work and you need to consider alternative drainage..

 

[jeds]

I was put on alert about septic soakaways when I designed one for a project a few years ago. The size of the filtration system was absolutely massive. I checked my calculations and at first thought they couldn't be right but I had them checked and if anything I was rounding down. For a 4 bedroom house the length of the system was 88 linear metres over an area of more than 200m². Fortunately it was an old farmhouse and they had the space but not everybody would do.

I would follow static's advice. Do a percolation test and work from there.

 

[theoldun]

Will throw in our little bit of knowledge with regards to septic tanks, though mind you the last septic tank we installed was approx12 years ago and the last wastewater management plant 10 years ago.
It would appear that the previous occupants or builders never did a water table test or percolation test to establish the (Vp).. It would appear that you also did not when you dug your new soak away. A percolation test is very easy to do, its just a matter of getting your head round the formula.
Technically waste water from a septic tank should not discharge into a soak away as it requires secondary treatment, either through a drainage field, drainage mound or reed bed. Providing nobody is aware that you have drained into a soak away, then fair enough. You say you dug 15 ft deep which equals 4.5m, but you do not say width or length. Depth 4.5, less an invert level of say 700mm gives you a depth of 3.8m by lets assume. 2m square gives you a storage capacity with no percolation of 15.2m3. Now you say that you filled the soakaway with the appropriate size rubble thus reducing soak away storage capacity by approx 75%. You are now left with a storage capacity of 3.8m3 which is 3,800 litres. From memory the average water consumption is 150litres per day per person. Lets assume the percolation Vp of soak away is zero and soak away is full the septic tank is probably 2,600ltres and will require emptying every 4 days.
YOU QUOTE: We thought we had the problem solved but over the past few months, we can see via the inspection hole that liquid is still not draining away fully, and when we have heavy rain the levels rise and we have to resort to having the ceptic tank emptied and again and again. END QUOTE. Now you know the reason why., but at least as long is not being emptied every 4 days, you know that soak away is working to some extent. You could get a very good idea of your filtration rate by how often your tank needs to be emptied. As Jed has said a drainage field takes up a very large area and can be very expensive and at the end of the day may not work. If you have a drainage length in excess of 200m for a 2800 litre tank, it is considered to be more economical to go for a bio disc.
Couple of other points. If you really get water wise you could possibly reduce your daily consumption from 150 litres per day per person down to 50 litres. We do not know how water rise you are at present. It is worth noting that 38% of water used is for washing and bathing, 30% toilet flushing, 12% clothes washing and 11% dish washing Read up on water wise.
Take it that you are to far from main drainage to consider a pumping station?
Depending on how near stream is, your only real answer is a bio disc management plant and run outlet through reed bed to be on safe side, although to best of our knowledge the latest models can discharge straight in to stream with the Dept of Environments’ permission. Plastic reed beds can be bought now that just drop into ground like a pond. Have no prices to hand for Klargester Bio Disc, but feel your budget is about right.
We find Drain Store to be the most helpful drainage outlet around at present, and they do a Nation wide installation service. Google them and if they have a local branch they will supply all the information you require. Sorry can not be of further help.
oldun

 

[Diggerjohn]

Firstly, a soakaway 'pit' is ONLY to be used for surface roof water, not septic tank effluent. Pits do not work for septic tank effluent as, unlike rainwater, you will be discharging into it every day and it never gets a chance to empty. Pits are not allowed under Section H2 of the Building Regulations 2002 Start reading about page 30 for septic tanks, percolation test method and soakaway design.

Have you thought about installing a Jewel septic tank conversion unit? You have the septic tank already and the Jewel fits after it to supply the missing biozone and humus tank, converting the whole thing to a full sewage treatment plant. Much cheaper than buying a package sewage treatment plant, much smaller and you should be able to buy and install it for under £2500. I find WTE Ltd very helpful and they can arrange a free survey.

 

[vanessajackson]

Will throw in our little bit of knowledge with regards to septic tanks, though mind you the last septic tank we installed was approx12 years ago and the last wastewater management plant 10 years ago.
It would appear that the previous occupants or builders never did a water table test or percolation test to establish the (Vp).. It would appear that you also did not when you dug your new soak away. A percolation test is very easy to do, its just a matter of getting your head round the formula.
Technically waste water from a septic tank should not discharge into a soak away as it requires secondary treatment, either through a drainage field, drainage mound or reed bed. Providing nobody is aware that you have drained into a soak away, then fair enough. You say you dug 15 ft deep which equals 4.5m, but you do not say width or length. Depth 4.5, less an invert level of say 700mm gives you a depth of 3.8m by lets assume. 2m square gives you a storage capacity with no percolation of 15.2m3. Now you say that you filled the soakaway with the appropriate size rubble thus reducing soak away storage capacity by approx 75%. You are now left with a storage capacity of 3.8m3 which is 3,800 litres. From memory the average water consumption is 150litres per day per person. Lets assume the percolation Vp of soak away is zero and soak away is full the septic tank is probably 2,600ltres and will require emptying every 4 days.
YOU QUOTE: We thought we had the problem solved but over the past few months, we can see via the inspection hole that liquid is still not draining away fully, and when we have heavy rain the levels rise and we have to resort to having the ceptic tank emptied and again and again. END QUOTE. Now you know the reason why., but at least as long is not being emptied every 4 days, you know that soak away is working to some extent. You could get a very good idea of your filtration rate by how often your tank needs to be emptied. As Jed has said a drainage field takes up a very large area and can be very expensive and at the end of the day may not work. If you have a drainage length in excess of 200m for a 2800 litre tank, it is considered to be more economical to go for a bio disc.
Couple of other points. If you really get water wise you could possibly reduce your daily consumption from 150 litres per day per person down to 50 litres. We do not know how water rise you are at present. It is worth noting that 38% of water used is for washing and bathing, 30% toilet flushing, 12% clothes washing and 11% dish washing Read up on water wise.
Take it that you are to far from main drainage to consider a pumping station?
Depending on how near stream is, your only real answer is a bio disc management plant and run outlet through reed bed to be on safe side, although to best of our knowledge the latest models can discharge straight in to stream with the Dept of Environments’ permission. Plastic reed beds can be bought now that just drop into ground like a pond. Have no prices to hand for Klargester Bio Disc, but feel your budget is about right.
We find Drain Store to be the most helpful drainage outlet around at present, and they do a Nation wide installation service. Google them and if they have a local branch they will supply all the information you require. Sorry can not be of further help.
oldun

Many thanks for taking the time... the info you have given is extremely helpful