Graf Infiltration Tunnel 300 In Lieu Of Perforated Drainage Pipe Field

[EViS]

Does anyone have any experience with using the Graf Infiltration Tunnel 300 in combination with a One2Clean PTP for their foul drainage? Is there much possibility in using these in lieu of a traditional drainage field formed of perforated distribution pipes?

 

I gather that an EA permit will be required for their use. Is it realistic to be granted one?

[Drellingore]

'ello! I've done something almost the same as you describe, in Groundwater Source Protection Zone 1. So the short answer is: yes.

 

The Environment Agency don't like the use of infiltration tunnels, as they allow treated effluent to infiltrate over a smaller area in plan view, even if the surface area in three dimensions is the same. As you've probably discovered the infiltration isn't part of BS6297, although I believe Graf are working with the BSI to have it added as an acceptable option in future. The EA will allow their use if it can be demonstrated that a standard infiltration field or mound isn't practical, and that there is no possibility of discharging to surface water (ie a ditch, stream, or surface water sewer).

 

In my case we couldn't fit an infiltration field in the space available unless it was to be outside the planning redline, uphill, and involving pipe runs going back under the house after having been through the treatment plant. The space that we had was limited owing to root protection areas, the required margins around habitable buildings, and the fact that a right of access was granted by title, over which a farmer needed to drive 50t machinery. Our infiltration tests came out favourably (vp 19.8).

 

I haven't looked up the One2Clean PTP, but we specified a Solido Smart and tertiary treatment via Tricel Puraflo modules. Once we had an assigned officer for our permit application at the EA, they suggested that they'd grant the permit without the tertiary system being necessary because whatever levels the Solido Smart emitted were clean enough. Of course, they encouraged use to use the tertiary system and were trying to give us flexibility, and we intend to install the tertiary system even if it is overkill.

 

The folks at Graf were very helpful in providing documentation and detailed sizing calculations that the EA appreciated receiving. Graf know that their customers face a bit of hurdle using the product, and have experience in helping people negotiate permit application.

 

Given that we're in Groundwater Source Protection Zone 1, there is no higher level of treatment required unless you're within 50m of drinking water borehole. So if you're anywhere other than that, it is indeed possible to get a permit to discharge to ground.

 

If you can demonstrate that infiltration tunnels are the only viable option, it is realistic to be granted a permit to use some.

 

FWIW I phoned about five different drainage consultancies, and every single one of them said "Groundwater source protection zone 1? No chance, mate!" They were all wrong.

[flanagaj]

Can I ask what the cost of the permit was?  We are not in a SPZ1, but whilst I can fit a drainage field into the space.  The logistics of excavating the area is going to be difficult and if I am honest, a right pain to remove so much spoil.   Hence, my motivation to see whether I could instead use the infiltration tunnels.

[ProDave]

How does this work then?  You need a certain area of infiltration field depending on the Vp measurement of your soil from a percolation test.  How can this magic plastic box with some holes in it reduce that area?

 

 

[flanagaj]

1 hour ago, ProDave said:

How does this work then?  You need a certain area of infiltration field depending on the Vp measurement of your soil from a percolation test.  How can this magic plastic box with some holes in it reduce that area?

 

 

The infiltration tunnels can store a large volume of treated water. I assume it  then means the water can dissipate over night from the tanks, where as a conventional field can store a much smaller volume of water in the pipes.  Maybe I’m talking nonsense, but I get your point.

[saveasteading]

I've had a look at the info, such as there is.

It appears to be simply a holding tank with lots of perforation.

It will catch and hold the treated liquid ejected if there is a run on baths and flushing.

Then it soaks away......nothing happens inside the box.

Thus is is not spreading the outfall in the way that a long pipe would.

 

You could as easily build a plastic catchpit with no bottom and optional holes in the side, or make it of brick, the worse quality the better. Or wrap a crate with membrane.

 

I guess the big sales points are. 1. It gets buried and carries a load.

2. It is made by a digester company.

3 fits in a driveway.

4.. A bco feels safe accepting it and will not be blamed for any pollution.

This being the main attraction?

 

Against it.

1. Small footprint so not dispersing the outfall very far. 2 expense. 3. A pipe system in gravel will encourage further treatment of gunk stuck to gravel.

 

In summary it's just a soakaway so is encouraging a reduction in soakaway standards, but will be easy for a builder, and the bco may feel able to accept the nice certificate for the file.