Fosse again - exit from the sand filtre?

[friend of stouby]

Sorry to start another thread but this doesn't really go into my other thread re costs of a fosse installation.

With both visits from prospective fosse fitters they both had the same question " where is the ditch that the water exiting the sand filter will run into ? "

The filter bed will be pointed downhill to the hedge dividing us from a neighbouring field. this is around 200m away but with no ditch on either our or our neighbours land.

At this they both appeared puzzled as to how to complete the drainage but with one accepting the idea of a UK type soak away 10m down slope of the sand filtre.

Is there a standard proceedure in the absence of a ditch?

Thanks

[pachapapa]

Exutoire assainissement....épandage....puit d'infiltration.

All depends on natural drainage....permeabilité of sub soil....geology.

What happens with the rain?

[friend of stouby]

The slope continues downhill from the filtre for maybe 250m.

The vegetation is a hay field starting about 35m below the filtre.

There is an occassional 'source' about 200m away but not in a direct line with filtre, maybe 40m to the right.

There is an underground sandstone area about 100m below the filtre.

The soil is loam for about 25cm under pinned by clay and sandstone rock in small and large pieces.

We have one area which is very wet in a tropical storm type situation which is above and over the brow of the slope so doesn't affect the fosse area. This we think is from drainage of our neighbours large roof?

That apart water doesn't ever lay unless it's tropical, then for only maybe a few minutes and maybe once or twice each year.

Thanks

[pachapapa]

where is the ditch that the water exiting the sand filter will run into ? "

Suggests you plan an FSVD. The implication from not planning an FSVND is that the permability is outside the prescribed limits. By inference therefore that the rest of the land is the same.

Note that for an FSVND the permeability must lie between a value such that drainage into the subsoil will not occur or a value to allow vertical drainage from the base of the filtre and complete aerobic purification of the effluent before harm can be done to any aquifers.

For example an extreme involving too low a permeability would be an FSVND in a karstic region with the effluent reporting immediately to underlying caves.

Loam,clay,sandstone? Loam 25 cms and the clay is how much.

The source? How intermittent? Which horizon? Where does it run to when it flows?

[pachapapa]

Simplest alternative is to use natural run off.

But the crux of the permeability issue is contained below.

Article 11 de l'arrêté du 7 septembre 2009
Les eaux usées traitées sont évacuées, selon les règles de l'art, par le sol en place sous-jacent ou juxtaposé au
traitement, au niveau de la parcelle de l'immeuble, afin d'assurer la permanence de l'infiltration, si sa
perméabilité est comprise entre 10 et 500 mm/h.
Sous-section 3.2 : Cas particuliers : autres modes d'évacuation
Article 12 de l'arrêté du 7 septembre 2009
Dans le cas où le sol en place sous-jacent ou juxtaposé au traitement ne respecte pas les critères définis à
l'article 11, les eaux usées traitées sont :
- soit réutilisées pour l'irrigation souterraine de végétaux, dans la parcelle, à l'exception de l'irrigation de
végétaux utilisés pour la consommation humaine et sous réserve d'absence de stagnation en surface ou de
ruissellement des eaux usées traitées ;
- soit drainées et rejetées vers le milieu hydraulique superficiel après autorisation du propriétaire ou du
gestionnaire du milieu récepteur, s'il est démontré, par une étude particulière à la charge du pétitionnaire,
qu'aucune autre solution d'évacuation n'est envisageable.

Article 13 de l'arrêté du 7 septembre 2009
Les rejets d'eaux usées domestiques, même traitées, sont interdits dans un puisard, puits perdu, puits désaffecté,
cavité naturelle ou artificielle profonde.
En cas d'impossibilité de rejet conformément aux dispositions des articles 11 et 12, les eaux usées traitées
conformément aux dispositions des articles 6 et 7 peuvent être évacuées par puits d'infiltration dans une couche
sous-jacente, de perméabilité comprise entre 10 et 500 mm/h, dont les caractéristiques techniques et conditions
de mise en oeuvre sont précisées en annexe 1.
Ce mode d'évacuation est autorisé par la commune, au titre de sa compétence en assainissement non collectif,
en application du III de l'article L. 2224-8 du code général des collectivités territoriales sur la base d'une étude
hydrogéologique.

[friend of stouby]

Good morning

The source is so far away as to not be very relevant, also we are discussing the filtered water not pure effluent.

We are in rolling countryside, the land falls away in 3 directions away from our house. Quite complex to describe but only one direction is of any relevance... the site of the fosse and filtre.

Re the sandstone area, perhaps I didn't explain clearly enough. It is at or very near the surface about 100m down slope of the filtre bed.

Sorry, but don't understand your acronyms.

There is no ditch that I know of although there is a damp area/tiny stream on occassion about 400m away. We back onto fairly continuous grazing farm land and forest.

My question is, what is the technical/official norm if there is no ditch?

Thank you

[pachapapa]

Posted in between.

FSVD filtre sable verticale drainé     vertical sand filter drained.

FSVND filtre sable verticale non drainé   undrained vetical sand bed filter.

Supplementary What would be the vertical depth between bottom of filter and the sandstone bed and is the sandstone inclined or flat ?

[friend of stouby]

I have to guess as to inclination as all sandstone in the lower field has a soil covering.

That said, due to a small quarry to one side of the area under discussion, it's possible to see a side view.

On mentioning this, the quarry base is never waterlogged either. So, as this is a much lower point than the surrounding areas on all sides, it has just occurred to me that the soil/rock is very permeable...

The sandstone area is inclined following the soil surface.

The base of the sand filtre is around level or just above the soil above the sandstone.

[Dave&Olive]

hi ok

                      here is a drawing of both types of the fosse systems           one for well drained land and the sand filter one for land that has failed the perculation test ..

             [IMG]http://i83.photobucket.com/albums/j311/daveolive/sawdust-burner/img007.jpg[/IMG]

     Dave

[friend of stouby]

Thanks Dave

We have a diagram from SIVOM for the drain type filter they want us to use, but the item that the two potential ground workers are puzzling over is item 13 on your drawing.

As we neither have a ditch or a stream within about 400m of the filter exit (No.13), they want to know what they should do with the exit water.

I didn't think we would have the only property without a ditch downstream, but both of these companies are pondering this problem?

Thanks

[Dave&Olive]

hi OK

                 Did you say in an earlier post that it was on a slope ???

                   Why is an experienced firm struggling with a simple common question , I would question their qualifications !!!

                             Dave

 

[friend of stouby]

Good question Dave!

Both companies (listed as groundworkers in PJ and middle aged men) so far have pondered the same question.

Yes we are on slopes with one continuous one falling away from the house and new fosse site.

That's the reason for posing the question here as we don't understand the problem with adequate fall and adequate space to build whatever is required???

We have a third man arriving on Monday, this chap has worked for us before. He is recommended by everybody so we will wait and see but was trying to understand the problem before he arrived.

Thanks for your interest.

[Dave&Olive]

 Hi Ok

                    Have you had SVL or your own local  water board to come out to the site , they usually come out to inspect the site before work can commence , it`s to see if you are fitting the correct size tank ,  the size of the filter bed to suit the tank etc , they normally tell you were they would like the things, I always find if you keep them sweet at this stage they will  bend a little if you have a problem . 

                           You can run the waste water in to a soak away , incendiary etang ( fire pond ) or just throw some rocks on were the pipe comes out of the ground and make a feature of it, if you don't have to put the filter in a bag not that much water comes out of it most of it will soak away as it percolates down the filter system .

                     You will get amount out of the fosse  ( this is how they work out the size of the fosse )  number of persons the house can sleep X   145   X  3  =

so if you have 2 double bedrooms and say 2 single bedroom =  6

145 litres is the amount of water a person uses in a day

the tank must hold 3 days stock

so       6  x 145 x 3 =2610 ltrs

hence a 3000 ltr tank and a 25 m3 sand filter

you could push it to 7 people =3045 ltrs    some inspectors will some will not

Get back if your " Man " cannot work it out and I will draw out what I used to do

                Dave

[pachapapa]

Frankly doubt the competency of your local SIVOM.

Probably the ANC examination is run by a brother_in _law of a local mayor.

The lack of surface water in sloping country suggests the subsoil and rock is permeable and probably a FSVND would be OK.

The selection of this method requires a permeability test.

The quip on page 10 of the Sotralentz Users Manual that the ground should be permeable is not sufficient.

http://baryblanc.free.fr/utilisateur.pdf

But the Manual is more of a catalogue than a serious guide to the selection and installation of an ANC service.

The selection of an FSVD is always simpler for a SIVOM type organisation as it places all the extra cost on the householder and requires little if any analysis by the SIVOM chappie.

[Dave&Olive]

[quote user="pachapapa"]

Frankly doubt the competency of your local SIVOM.

Probably the ANC examination is run by a brother_in _law of a local mayor.

The lack of surface water in sloping country suggests the subsoil and rock is permeable and probably a FSVND would be OK.

The selection of this method requires a permeability test.

The quip on page 10 of the Sotralentz Users Manual that the ground should be permeable is not sufficient.

http://baryblanc.free.fr/utilisateur.pdf

But the Manual is more of a catalogue than a serious guide to the selection and installation of an ANC service.

The selection of an FSVD is always simpler for a SIVOM type organisation as it places all the extra cost on the householder and requires little if any analysis by the SIVOM chappie.

[/quote]

    Please please please

                                                If  I ever suffer from   " saline dimensions  "  and start cooking my food on a" George Formby " grill would some one put a plastic bag over my head ......6 years today mum died  ...I will not mock 3 p o again

                                                               Dave

[pachapapa]

2nd Sat in june...a birthday!

2nd Tues in june...13 Microsoft security updates!

My cup runneth over!

Uncle jesus is so kind to PPP.

[pachapapa]

An FSVD may not be the correct filière...

and

L’appel en garantie ne peut être invoqué
en cas de :

• mauvais choix de la filière partielle ou complète.[:-))]

[friend of stouby]

We do have all the relevant paperwork to start the fosse construction Dave and thanks to pacha for the link.

The paperwork is very basic which may be because the inspector asked if we or an artisan were to complete the works. Only the the most basic info is shown...  fosse size, pre-filtre size required, dimensions of drained sand filtre. My guess is he thought the artisan would complete the run off to whatever was usual for our area and that it would be no big deal?

Having now read specs for other area drain fosse systems, it appears that without a water course to hand it's best to use land drains to dissipate the small amount of water, or I may ask for a gravel filled soak away.

Many thanks for all comments as they have been a great help. They have expanded my knowledge of fosse installation and also clarified my own original thoughts. The inspector was a fairly relaxed and helpfull chap and we will go back to him before we accept a devi, but we return to the UK next Tuesday and may not have time to contact him before we leave (Monday holiday), so the final detail (water run off) for any of these devis may not be settled for 3 or 4 weeks. Therefore asked here to try to speed up the final design.

I placed a separate question elsewhere on the forum re the depth we are allowed to bury the fosse, but think we will also have address this to the inspector directly as he will have to pass it.

Once again thanks to all.

[pachapapa]

Might be an idea to load the BRGM Geology plug-in to Google Earth and get an idea of the underlying geology of your locality.

As an example an image of my local area below.

[IMG]http://i282.photobucket.com/albums/kk244/pachapapa/GourgGeology.jpg[/IMG]

[pachapapa]

The GeoPortail site can be useful due to the layer options.

The Hydrography of your local area could give an example of surface drainage.

Example below with blue bits.

http://www.geoportail.fr/?c=4.80666,43.5616&l=Photo(100),Hydro(100)&z=7

[Patf]

In our last house here there was a fairly modern fosse system and the exit of the ejets was down a steep hill and , we assumed , onto the field below which was our own land.An orchard in fact.

We had an inspection from SPANC who said it was ok as it drained onto our own land ( I have it in writing.) The earth was pure clay.