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
|
