Fosse Toutes Eaux
Fosse Septiques
Before the new regulations
came into force the water from toilets was directed into a concrete
tank called a Fosse Septique. The water from showers, baths and
sinks could be discharged into any local ditch or waterway - and
often was!
Fosse Toutes Eaux
Now all the water has
to go into one tank - hence the name. The systems that are now required
include the concrete tank and a filter bed that varies in type depending
on ground conditions.
Bluepools and Fosse
Toutes Eaux
Bluepools can undertake
the installation of Fosse Toutes Eaux when concurrent installation
of fosse and pool is required
This section of the website
describes everything that you need to know about Fosse installations.
History and Background
Historically the French
seperated the grey water (eau usee ) from showers, sinks, washing
machine etc and the sewage from the WC (eau vanne).
The eau usee was taken
anywhere convenient such as into the ditch alongside the road or
even into a local stream.
The eau vanne was either:
-
piped into a fosse
septique with an outlet to a rudimenary filter bed that normally
consisted of a trench filled with stone (tranchee d'epandage)
-
or piped into a fosse
d'etanche that was supposed to be emptied regularly.
The invention of the
septic tank is attributed to a French man named Jean-Louis Mouras
who built the first septic tank in Vesoul in 1860 and the first
use of a septic tank in France dates back to 1881.
The fosse septiques (septic
tank) were often very small but the fosse d'etanche can be 4 cubic
metres or more. Fosse d'etanches were often tampered with to reduce
emptying costs - by simply knocking a hole in the bottom - but this
only worked in areas where the limestone rock or gravel prevailed
and the water could drain down and pollute the same acquifer that
was being used for drinking water. It also often backfired because
in non-draining soils the tanks will often fill up with rainwater
and require even more frequent emptying. Many people wonder why
their tanks need to be emptied more in the winter and cannot understand
why they "use more water in the winter than in summer".
Once in the tank the
waste starts to divide itself - the lightest parts of the waste
(fat, oil, grease) starts to float to the surface where they form
a crust called Suspended Solids. These will be digested by aerobic
bacteria and transformed into carbon dioxide and water. (Aerobic
bacteria : a micro-organism that requires oxygen to live).
The heavier solids will
drop and settle at the bottom of the tank. This is called the sludge.
They will be digested by anaerobic bacteria. (Anaerobic: opposite
of aerobic) and the liquid will circulate in between the two masses.
Pre-treatment
The septic tank does
not really treat waste. Its main purpose is to store the waste for
a period during which the waste will undergo its first transformation
called the pre-treatment. This "pretreatment" only removes
about 30% of the pollutants and the remaining 70% contains germs
and pathogens (such as hepatitis, polio, cholera, para typhoid etc)
which pose real threats of life threatening disease.
The remaining 70% is
purifed by the filter bed that is now required for every installation
- this is the "treatment" that just does not exist in
most existing installations. It has been estimated that about 3
out of 4 French rural properties do not comply.
European law has forced
the French government to act - and not before time!
Septic Tanks and
main drainage connections
The
new regulations on the installation of fosse toutes eaux are tough
and now in place. On the 3rd of January 1992, all towns and villages
in France saw their responsibilities increased and the Maire is
now responsible for every aspect of wastewater treatment, be it
collective or individual and is directly responsible for the control
and regular maintenance of your septic tank.
The
new laws impose an obligation on each commune to prepare a map -
called "Carte d'aptitude des sols" that designates the
area that should have systems "collectif" or "non-collectif"
. In the areas where non-collectif systems (fosse toutes eaux) are
designated each commune has to have a pollution monitoring system
in place by the end of 2005 that will control the disposal of all
sewage.
Because most of the Maires
are not specialists in the field of wastewater treatment, they have
in many cases appointed a syndicate or a professional body to enforce
the law. They are often (but not always) known as S.P.A.N.C. (Service
Public d’Assainissement Non Collectif) and will service a group
of communes from a local office.
The responsible regional
body is "Les Directions Regionale et Departmentales des Affairs
Sanitaires et Sociales (DRASS) de your region." Each department
in each region will also have a "Les Directions Departmentale
et Departmentales des Affairs Sanitaires et Sociales (DDASS) de
your department" These offices will monitor and administer
the implementation of the new laws by the mairies of each commune.
The law is all about pollution control and does not impose any construction
obligation on communes that have designated "collectif"
systems. So if a commune does not have the money for a system "collectif"
then do not buy a house in the designated area because you will
probably not get consent for a "non-collectif" fosse toutes
eaux.
If your property is in
a designated "collectif" area, where the main drains have
been installed you will eventually be obliged to stop using your
existing fosse septique and connect to the mains drainage in the
road.
Many of you will have
noticed that your water bill contains a line called “Redevance
Service Public d’Assainissement Non Collectif”. This is
a charge applied by your water company to help finance the implementation
of the law. The cost does vary depending on where you live.
The main purpose of the
control is to ensure that all the systems which are not, or which
cannot be, linked to the main sewage system are in good condition,
function properly and are capable of dealing with the amount of
wastewater to be treated.
A visit to your property
will be arranged by SPANC and during the visit the technician will
verify the :
You will then receive
a report that will indicate whether or not your system is working
correctly and that will explain to you how to proceed with any required
changes.
Requirement for
documentation
All recent installations
should have been documented and the records placed with the Mairie.
If you are purchasing
an old house in the country ask to see the legal certificate of
approved drainage - It is unlikely that there is one and it will
be the responsibility of the new owner to get it. The notary will
need it before you can resell the property in the future.
A visit to the Mairie
is probably all that will be necessary to decide whether or not
a new fosse toutes eaux or mains drainage connection is required.
Bluepools can undertake the application on behalf of the client
where required
Application for
a new Fosse Toutes Eaux
This is known as the
"Demande d'installation d'un dispoitif d'assainissement non
collectif"
The application requires:
The application form
completed and signed - including number of main rooms, slope of
the land, the ground water level and the type and size of filter.
A location plan (1:25,000 or 1:10,000)
A layout plan showing existing and future buildings, the proposed
location of the fosse installation, any wells or streams and the
slope and direction of slope of the land.
Costs of Fosse Toutes
Eaux
The costs of Fosse toutes
eaux installations depends on the number of main rooms - because
this directly affects the size of the fosse elements.
The cost of concrete
tanks can vary between 400 and 800 euros depending on the size and
the builders discount from the merchants.
The cost of polymer tanks
will probably lie in the same range even though the published price
lists of many major suppliers such as Frans Bonhomme indicate much
higher prices. The polymer tanks do need sand backfill around them
and need more careful installation.
The pipework and fittings
between the house and the filter bed will also cost several hundred
euros. Additional drainage runs can add a day to the programme and
increase the cost by up to 1000 euros.
The cost of the filter
bed materials bed will be approximately 30 euros per square metre.
A straightforward installation
for a 5 main room residence will take about 4 days - this could
increase to 7 for a large complex installation. A team of builders
with their plant and equipment will cost about 750 euros per day.
Hence total costs are
likely to be as in the following table. The cost of carting the
excavation arisings off site can increase the cost by 500 euros
or more depending on the filter size and the haulage distance to
the local tip (dechetterie).
Indicative costs
The costs exclude pipe
connections, pumping, vent stacks, travelling and accommodation
costs
|
Number of main
rooms (No of bedrooms + 2)
|
Fosse toutes
eaux costs in euros
|
|
less than or
equal to 5
|
5000
|
|
6
|
6000
|
|
7
|
7000
|
|
Each extra room
on top
|
1000
|
The conclusion to be
drawn is - do not overestimate the number of rooms and never build
a fosse now for a future dwelling
Costs can be quite a
bit more for several reasons including:
-
The requirement for
a pumping chamber(s)
-
The number of drain
connections from the property
-
The difficulty of
installing the vent stack above the roof
-
The builders travelling
/ accommodation costs
Mains Drainage
If mains drainage has
been or is about to be installed then the house-owner will have
been asked where they would prefer the connection point to be located.
When this request is not answered the communes drainage contractor
will make the decision and mark the connection point on a plan.This
will be available for reference in the future and the connection
location will be required before your installation contractor will
be able to provide a fixed quotation.
The mains drainage connection
needs to be planned before the installation of a pool because it
is surprising how often the best locations for both result in a
clash. Hence the pool and main drainage connections need to be just
as carefully planned as a pool and fosse toutes eaux installations.
The mains drainage connections
will cause quite severe damage to an established garden (As fosses
also do) and so it is preferable to install pool and these connections
at the same time both to reduce cost and some of the disruption.
Mains drainage connection
costs
These can vary more than
fosse toutes eaux costs because the number of manholes and length
/ depth of drain runs will vary significantly from project to project.
However in broad terms most mains drainage connections should be
a bit less than the cost of a fosse installation.
Maintenance of Fosse
Systems
The law requires that
the fosse toutes eaux in emptied at 4 year intervals or less. It
is essential that the property owner retains the invoice (facture)
from the licensed fosse evacuation contractor as the Mairie will
ask to see this during any inspection in the future.
When a fosse has been
emptied it should be refilled with fresh water and treated with
a packet of EPARCYL (can be bought in most supermarkets). This also
applies to old septic tanks after they have been emptied. A fosse
that has stopped working for any reason can also be kickstarted
by emptying, refilling and treating with EPARCYL.
Troubleshooting
| Smells
in the house |
- No
water seal in toilets and traps
- Evaporation
of water seals
- Lack
of high level ventilation
|
| Smells
outside the house |
- Fosse
vent pipes <100 mm
- Fosse
vent pipe blocked or not carried above the roof
- Lack
of extractor on top of vent
- Lack
of primary vent on the WC pipe
- Fosse
vent pipe not installed properly
- Manholes
on fosse out of position
|
| Corrosion
of the steel reinforcement in the fosse |
- Lack
of fosse ventilation
|
| Blockages
in internal drains |
- Grease
- Insufficient
falls on pipework
- Pipe
diameters too small
|
| Fosse
full |
- Fosse
needs emptying
- Fosse
to small for loading
|
| Foreign
materials in the entry manhole to the filter bed |
- Fosse
needs emptying
- Fosse
is too small
- Rainwater
getting into the fosse network
- Prefilter
in fosse needs to be changed
|
| Blockage
of the final manhole in the filter |
|
Fosse Toutes Eaux
Technical Details
The
installation will always consist of two main systems:
- The pretreatment chamber (the
fosse toutes eaux ) - a concrete or polymer type tank
Occasionally a grease
trap (bac degraisseur of 500 litres) may be required but this should
not be necessary in non commercial premises and should be avoided
if possible because it is just something else to maintain or go
wrong. If it is not possible to keep the distance between the kitchen
and the fosse down to 10 metres or less a grease trap is advisable
and will probably be a technical requirement of the consent documentation.
When an existing fosse
system is being replaced it must be cut out of the pipework system
entirely. It can be sealed up and left full of water - any odour
from it should reduce to nothing within a few days. Alternatively,
depending on its location, it may be preferable to have it pumped
dry and filled with sand.
Fosse Toutes Eaux
Volumes
The volume of the fosse
toutes eaux can be determined from the following table:
|
Number of
main rooms (No of bedrooms + 2
|
Fosse toutes
eaux volume in cubic metres
|
|
less than
or equal to 5
|
3
|
|
6
|
4
|
|
7
|
5
|
|
Each extra
room
|
+ 1
|
Tank sizes
These are shown in the
following table:
|
Number of main
rooms
|
4
|
5
|
6
|
7
|
|
Fosse toutes
eaux capacity (m3)
|
3
|
3
|
4
|
5
|
|
Depth of tank
|
1.35m
|
1.35m
|
1.72m
|
1.85m
|
|
Length of tank
|
2.52m
|
2.52m
|
2.52m
|
2.52m
|
|
Width of tank
|
1.19m
|
1.19m
|
1.19m
|
1.40m
|
|
Weight
|
1600kg
|
1600kg
|
1950kg
|
2050kg
|
Vents
Two vents are always
required and these are the most important part of the installation
if odours are to be avoided. Both vents must be taken above the
property roof eaves levels
Primary vent - 100 mm
and taken from the downpipe from the WC straight up through the
roof
Secondary vent - 100mm
and taken from the top of the fosse outlet pipe, back to the property
and then up an outside wall - can be taken through or outside the
roof tiling.
Filter Beds
The size and type of
filter bed is a function of the number of main rooms, permeability
of the soil, the maximum ground water levels and the slope of the
land on which it is to be built.
The size can be determined
from the following table:
|
Soil type
|
Filter type
|
Length of trenches
or minimum surface area of sand filter
|
|
5 main rooms
or less
|
Each extra room
|
|
Permeable sand
or silt with a minimum thickness of 1 metre
|
Land drain trenches
500 mm wide
x 500 mm deep filled with 10/40 mm gravel surrounding slotted
pipes
|
45m
|
15m
|
|
A thick layer
of soil on fissured permeable rock
|
Vertical sand
filter without drainage
Slotted pipes
in 200 mm gravel over a 700 mm deep sand bed covered with
a minimum 200 mm topsoil
|
25 m2
|
5m2
|
|
Impermeable soil
such as clay or when there is a risk of contaminating an underground
water resource
|
Vertical sand
filter with drainage
As filter without
drainage but with a system of slotted water collection pipes
in a 200 mm layer of gravel below the sand filter. The water
is then piped or pumped to a suitable ditch
|
25 m2
|
5 m2
|
|
Land prone to
flooding or where the ground water is very near the ground
surface
|
An above ground
sand filter with sloping sides
As vertical sand
filter without drainage but above ground
|
Base area - 60
m2
Top area - 25
m2
|
Base area - 20
m2
Top area - 5
m2
|
ILLUSTRATIONS OF
FOSSE INSTALLATIONS
Scheme
in principal
Clearance
distances
Fosse
Ventilation
Trench
filter
Vertical
filter without drainage
Vertical
filter with drainage
Above
ground filter
|
