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.