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Sewage Treatment: I Smell A Rat

Posted by Crofter , 30 January 2015 · 2,128 views

I'm a little over a week away from the expected decision date for planning permission on my little house project. I've spent this time getting on with percolation testing and researching how to proceed with the unglamorous yet vital task of sewage treatment and disposal.

As is usual around this part of the world, mains sewerage is not an option, so I am limited to some form of private treatment. Just to complicate things, my existing house's septic tank lies on the path of what will eventually be the driveway to the new house. This, coupled with the fact it is 40 years old, means its days are numbered. The new system will then have to deal with both houses. Decision made, the only thing left was- septic tank or treatment plant? If only it was that easy...

I've lost track now of how many hours I have put into finding a solution to this part of the project. For one thing, as soon as you go off-piste with your sewage treatment design (i.e. move away from a conventional septic tank and soakaway system) you are outside the comforting confines of the building regulations and the ever useful Technical Handbook. No bad thing, some might say, but without the backup of the regulations how do you that what you are building is going to satisfy BCO, or even work properly?

Then there is the almost comical matter of the different manufacturers and suppliers. There are hundreds of websites where bold fonts and exclamation marks entice you towards certain products. Seeds of doubt are sewn around competitors' systems. Glossy PDF brochures aim to impress whilst failing to deliver critical information. Phone calls to the same people yield similar results.

Here's one example of competing claims, on the apparently controversial issue of 'Soakaway Crates':
SOAKAWAY CRATES AND TUNNELS etc. are not allowed for foul water drainfields as they do not comply with either Section H2 of the Building Regs. Or BS6296.....BEWARE of adverts on the internet and report the cowboy traders to Trading Standards.” (www.wte-ltd.co.uk)

On the other hand...
Are Soakaway Crates Approved by Building Regs? YES. Section H of UK Building Regulations section 1.4 States...soakaways can consist of different materials, as long as biological treatment takes place in the soil... Soakaway crates that are installed in the topsoil legally meet this requirement... Why do some websites say soakaway crates are not approved? We find some companies have an agenda to sell you their products based on misinformation and scare tactics...” (www.septictank.co.uk)

This same sort of claim vs. counter-claim is present in the competing world of treatment plants too. Most of them claim 'class leading' performance, whether that refers to low power usage, or one of the many variables by which treatment efficacy is measured. De-sludging intervals is another grey area. The information you actually need is very simple: the 3 magic numbers (BOD, SS, NH3), whether these are given on a mean or 95% basis, the power usage, and the de-sludging interval. How hard can it be to put this information into a 20 page brochure? Yet some companies are incapable of doing so.

So, other than hugely confused, where does this leave me? Well, my percolation tests were virtually pointless as I have a layer of fractured rock just below the surface. So anything relying on a conventional soakaway, with aerobic breakdown in the topsoil, is out- the soil simply isn't deep enough. SEPA have given me agreement in principle for discharge so long as the BOD etc is no more than a limit they have set me. The hunt is on for a way of meeting this that is reliable, affordable, and practical.

Come back, septic tank, all is forgiven...

You have my sympathy.

The other problem you might face (like me) is the planners give PP for something only to find building control don't like it. There really is no joined up thinking between them.

I'll let you know when I get a resolution to my own difficulties as that may or may not help you.
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this is all good info, I think I will also be in this position as I know clay is only about 400mm below the surface. I have done some searching for good plant so would like to hear what others have found to be good for them.
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One thing that I'm struggling to find is the ongoing costs, especially desludging intervals. I've just had my septic tank emptied after what could well be decades of use (the lid was mortared on...) so I can't help myself taking manufacturers' recommendations of annual desludging with a pinch of salt. Is the annual desludging partly a means of the manufacturers avoiding problems? Are people actually going to two, three, five year intervals?
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We have our conventional septic tank emptied every 2 or 3 years. It costs about £150 each time, so say £75 per year. Still cheaper than paying a sewage charge if a mains sewer were available.
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Same here.
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02 Feb 2015 08:57 AM
Well, Crofter, (ProDave, Joe90) we've both (all) got to the same point, via different routes. I long for simplicity, clarity and a reasonable amount of standardisation in information structure, and accountability.

First job this week is to have a conversation with a local trustworthy partner in developing an off mains drainage plan. That means finding an organisation whose focus is the customer and not simply reassurance and sales. There are any number of snake-oil sales folk in this sector. This is the only blog about off-mains drainage I have found that appears remotely to address this area of house building.

Thanks for your blog.
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Thanks, useful blog there.

A thought: can you extend desludging intervals by speccing an oversized tank? Intuition would suggest so but perhaps it's not as simple a that?
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02 Feb 2015 06:34 PM
Our local council provides the opportunity for an annual desludging service (up to a threshold volume) to properties not serviced by mains sewers. I wouldn't say we get this free, but it must be paid for by part of our "Rates" (council tax), as long as you remember to lift the phone to arrange it!

Does your council tax bill make a distinction for properties that are not on mains sewers?
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Here in Scotland, water rates are charged with your council tax bill.

There's one charge for mains water supply and another charge for sewage. Obviously if you son't have one of them it's not included.

Scottish Water will desludge your tank, but I have always found the local independent operator cheaper.
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My reasons for wanting to extend the desludging interval aren't so much to do with costs, but because I think the tanker is going to struggle to get down the drive to within 4m of the tank's elevation. It'll be by far the largest vehicle that ever has to use the driveway, which in one place has to be built up significantly from existing ground levels, and I think it could cause a fair bit of settlement and surface wear. So I'd rather turn this into a once-every-five-years headache instead of an annual one, if possible.
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I'm going for a Biopure 3 (suitable for 12 People) check them out I think they are pretty good (according to neighbors recommendations and the drainage expert). My soak-away site is fractured granite but I'm pumping it up from the plant a little bit due to the contours of the land. I will also be dumping a bit more soil on top to achieve the minimum 1m head of soil required by SEPA.
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