SIST-TP CEN/TR 12566-2:2005

SLOVENSKI STANDARD
01-september-2005
0DOHþLVWLOQHQDSUDYHGR3(±GHO6LVWHPL]DLQILOWUDFLMRY]HPOMR
Small wastewater treatment systems for up to 50 PT - Part 2: Soil infiltration systems
Kleinkläranlagen für bis zu 50 EW - Teil 2: Bodeninfiltrationssysteme
Petites installations de traitement des eaux usées jusqu'a 50 PTE - Partie 2: Systemes
d'infiltration dans le sol
Ta slovenski standard je istoveten z: CEN/TR 12566-2:2005
ICS:
13.060.30 Odpadna voda Sewage water
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL REPORT
CEN/TR 12566-2
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
June 2005
ICS 13.060.30
English version
Small wastewater treatment systems for up to 50 PT - Part 2:
Soil infiltration systems
Petites installations de traitement des eaux usées jusqu'à Kleinkläranlagen für bis zu 50 EW - Teil 2:
50 PTE - Partie 2: Systèmes d'infiltration dans le sol Bodeninfiltrationssysteme
This Technical Report was approved by CEN on 19 December 2004. It has been drawn up by the Technical Committee CEN/TC 165.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 12566-2:2005: E
worldwide for CEN national Members.

Contents Page
Foreword .3
Introduction.5
1 Scope .6
2 Normative references .6
3 Terms and definitions.6
4 Symbols and abbreviations.8
5 General .8
6 Design parameters.8
7 Components .12
8 General requirements for the installation of septic tanks.14
9 Construction requirements .14
10 Specific construction requirements .15
11 Maintenance .28
Annex A (informative) Preliminary site consideration.29
Annex B (informative) Soil investigations .36
Annex C (informative) Selection of suitable sands.45
Bibliography.49

Foreword
This document (CEN/TR 12566-2:2005) has been prepared by Technical Committee CEN/TC 165 “Wastewater
engineering”, the secretariat of which is held by DIN.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights.
CEN shall not be held responsible for identifying any or all such patent rights.
This document is considered as Code of Practice and provides the general requirements for packaged and/or site
assembled treatment plants used for domestic wastewater treatment for a total number of inhabitants and
population equivalents (PT) ≤ 50 PT (see Clause 1).
EN 12566 with the generic title "Small wastewater treatment systems up to 50 PT" consists of the following parts:
 Part 1: Prefabricated septic tanks (specifies the requirements and laboratory test method for prefabricated
septic tank units. Requirements and tests for treatment efficiency are not specified),
 Part 2: Soil infiltration systems (applies for in-situ constructed soil infiltration systems. No treatment
requirements are specified; Technical Report),
 Part 3: Packaged and/or site assembled domestic wastewater treatment plants (specifies the requirements
and laboratory test method used to evaluate packaged wastewater treatment plants, which are required to
treat sewage to a predetermined standard),
 Part 4: Septic tanks built in situ from pre-fabricated kits - Execution standard (in preparation),
 Part 5: Filtration systems (including sand filters) (in preparation),
 Part 6: Test methods for the evaluation of the effectiveness of treatment on users site.
The application of the parts of EN 12566 is shown in the following scheme:
Key
A Domestic wastewater (influent) 2 Infiltration system (into the ground) (see CEN/TR 12566-2;
in preparation)
B Pre-treated wastewater
3 Wastewater treatment plant (see prEN 12566-3)
C Infiltration into the ground
4 Septic tank built in situ (see prEN 12566-4)
D Outlet of treated wastewater (effluent)
5 Filtration systems (see prEN 12566-5)
1 Prefabricated septic tank (see EN 12566-1)
NOTE National regulations may specify different arrangements between the products described in the standards
series EN 12566.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to announce this Technical Report: Austria, Belgium, Cyprus, Czech Republic, Denmark,
Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom.

Introduction
This document gives guidance for soil infiltration systems which can be used together with small waste water
systems according to EN 12566-1, prEN 12566-3 or prEN 12566-4 in places of use where legally provisions for soil
infiltration systems do not exist.
National forewords of this document may give information on provisions for soil infiltration in the place of use (see
Clause 5).
1 Scope
This document specifies the recommended requirements for soil infiltration systems ranging in size from a single
house to 50 PT receiving domestic wastewater from septic tanks manufactured according to the requirements
given in EN 12566-1 and prEN 12566-4.
This document gives design parameters, construction details, installation and component requirements for soil
infiltration systems.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references,
only the edition cited applies. For undated references, the latest edition of the referenced document (including any
amendments) applies.
EN 1085, Waste water treatment – Vocabulary
EN 12566-1, Small wastewater treatment systems for up to 50 PT — Part 1: Prefabricated septic tanks
prEN 12566-4, Small wastewater systems for up to 50 PT — Part 4: Septic tanks assembled in situ from
prefabricated kits
EN 12056-2, Gravity drainage systems inside buildings - Part 2: Sanitary pipework, layout and calculation
EN ISO 10319, Geotextiles – Wide-width tensile test (ISO 10319:1993)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 1085 and the following apply.
3.1
biological layer
biological film which grows on the base of the infiltration system or on top of the filter material when pre-treated
effluent infiltrates the subsoil or the filter material
3.2
connection pipe
non-perforated pipe used to connect the septic tank to the distribution chamber
3.3
disposal area
total area of the site where the pre-treated effluent is discharged into the ground using a soil infiltration system
3.4
distribution chamber
chamber allowing even gravity distribution of pre-treated effluent via the distribution pipes
3.5
distribution layer
layer of the system composed of granular fill material in which pre-treated effluent is discharged through infiltration
pipes
3.6
distribution pipe
non-perforated pipe used to connect the distribution chamber to a single infiltration pipe
3.6
dosing chamber
small tank receiving pre-treated effluent and containing a dosing device e.g. a pump, a hydraulic siphon or a tipping
trough, which automatically discharges the desired quantity
3.7
end connection
perforated and non-perforated pipes and fittings that connect the lower ends of any parallel infiltration pipes, to
enable airflow between infiltration pipes. The connecting fittings may incorporate ventilation and access provision.
3.8
filter material
granular inert material, usually sand, placed beneath the distribution layer, the purpose of which is to provide a
degree of filtration to the pre-treated effluent
3.9
geotextile
fabric, which is permeable to liquid and air but prevents solid particles from passing through it and is resistant to
decomposition
3.10
granular fill material
inert material in which the infiltration pipes are placed in the distribution layer
3.11
impermeable film
inert membrane, which is impermeable to liquid
3.12
infiltration
percolation of effluent around the point at which it is discharged
3.13
infiltration bed
wide excavation in which a number of infiltration pipes are placed in parallel and surrounded by fill material
3.14
infiltration pipes
perforated pipes through which the pre-treated effluent is discharged to the infiltration trench or bed
3.15
infiltration system
series of infiltration pipes, placed in either single trenches or one large bed, used to discharge effluent in such a
way that it percolates into the disposal area
3.16
infiltration trench
trench in which a single infiltration pipe is placed and surrounded by fill material and separated from other
infiltration trenches by undisturbed soil
3.17
land drains
surface or subsurface channels for the transportation of rain water. They are used to dewater ground and divert the
natural flow of surface and subsurface water away from infiltration area
3.18
long Term Acceptance Rate
LTAR
amount of pre-treated effluent which the system can infiltrate during its lifetime without water logging or clogging
(l/m /d)
3.19
mesh
fabric, which is permeable to liquid and air but prevents rough solid particles from passing through it and which is
resistant to decomposition. The hole diameters are approximately 1 mm.
3.20
permeability coefficient
k
measure of the percolation ability of the soil (m/d)
3.21
prefilter
device that helps to prevent clogging of infiltration system
3.22
pre-treated effluent
wastewater that has undergone at least primary treatment
3.23
subsoil
unconsolidated material beneath the topsoil and above the bedrock
3.24
topsoil
upper layer of soil
3.25
water table
level below which the soil is saturated with water
3.26
water table level
surface of the groundwater when related to the ground level or other point of reference
4 Symbols and abbreviations
k Darcy's permeability coefficient determined from small tube permeable test (m/d)
k Normalised permeability coefficient determined from falling head percolation test (m/d)
N
k Constant permeability coefficient determined from constant head percolation test (m/d)
C
5 General
Infiltration systems provide a measure of treatment when constructed according to this document or to appropriate
national regulations; their effectiveness is usually not measured.
The systems described are intended to illustrate the main principles of construction and are subject to national
variation. Provisions in the place of use shall be taken into account. The regulatory authorities shall be contacted.
6 Design parameters
6.1 General
To ensure that a sustainable solution is achieved each site shall be assessed (see Annex A and Annex B). The
choice of infiltration system will depend upon the site considerations detailed in 6.2. The preferential order of
systems is:
 Infiltration trench (see 10.2),
 Shallow infiltration bed (see 10.3.1),
 Vertical infiltration bed (see 10.3.2),
 Infiltration mound (see 10.3.3).
Pre-treated effluent discharging to unsuitable sub-soils may result in system failure.
6.2 Site considerations
6.2.1 Climatic conditions
When designing, constructing and locating the soil infiltration system, climatic conditions in the area such as
extremes of temperature, rainfall, snow shall be taken into consideration.
6.2.2 Water table
The seasonally highest groundwater table shall be determined in the disposal area, prior to the construction.
Unless specified in national regulations or guidance, a minimum of 1,0 m of unsaturated soil and/or filter material
shall be present above the determined seasonally highest level of the groundwater table.
Where these dimensions cannot be accommodated, alternative arrangements (e.g. raised disposal area) shall be
adopted to achieve these dimensions (see 10.3.3).
6.2.3 Location
6.2.3.1 General
In order to take into consideration all relevant site features when locating the disposal areas a detailed site
investigation shall be carried out. Annex A lists the site considerations which should be assessed as part of the site
investigation; all or some of these considerations may be defined by the national authorities.

In absence of any national regulations or guidance, the disposal area shall be located according to the following
minimum criteria:
 No part of the soil disposal area shall be closer than 4 m to the nearest point of the nearest habitable
dwelling.
 No part of the disposal area shall be within 4 m of the nearest road boundary or ditch nor within 2 m of the
boundary of the adjoining site. Disposal areas in the vicinity of small water courses shall be at least 10 m
from the highest level. Larger water courses will need special considerations.
 The growth of any type of tree or plant which develops an extensive root system is limited to a minimum
distance of 3 m from the infiltration system. This restriction also applies to the cultivation of crops which
would inevitably necessitate the use of machinery, even light machinery, likely to disturb the materials
installed at a shallow depth.
 Water supply pipes or underground services other than those required by the infiltration system itself shall
not be located within the disposal area.
 Access roads, driveways or paved areas shall not be located within the disposal area.
6.2.3.2 Groundwater protection
Groundwater, in particular any water to be used for drinking shall be protected.
The risk of polluting groundwater is minimised when the disposal area is hydraulically downslope of groundwater
sources.
NOTE The direction of the groundwater flow may be estimated from a trial hole test (see Annex B) and also from the
topography, wells and local knowledge.
Distances are based chiefly on the most important geological and hydrogeological factors, e. g. the type and depth
of subsoil and the depth to the water table, all of which can be assessed as part of the detailed site investigations.
It is not possible to specify with certainty the minimum safe distance between disposal areas and any system,
which collects drinking water. As a guide for countries where no national regulations or guidance exists a minimum
distance of 30 m may be used. However local conditions may require a far greater distance.
6.3 Dimensioning
The biological layer restricts the infiltration into the subsoil. The layer's properties depend on the permeability of the
soil, the loading rate (hydraulic and organic) and oxygen conditions.
Soil properties such as grain size distribution (soil type), relative compaction, discontinuities and saturation (Table 1
and Annex B) affect the permeability.
Table 1 — Relations between K-values and LTAR
k
Soil type k k LTAR
N C
m/d(m/s)
(l/m /d)
m/d m/d
Medium and coarse > 100 > 12 Not applicable Direct infiltration is
gravel not permitted
-3
(> 1 × 10 )
Mixtures of fine gravel 1 to 100 0,8 to 12 1,5 to 12 20 to 50
-5 -3
and coarse sand
(1 × 10 to 1 × 10 )
Fine or silty sand or till 0,5 to 10 0,6 to 2 0,5 to 1,2 15 to 30
-6 -4
(6 10 to 1 10 )
× ×
Silt or sandy silt 0,1 to 1 0,4 to 0,8 0,15 to 0,5 10 to 15
-7 -5
(1 × 10 to 1 × 10 )
Silty clay loam 0,01 to 0,1 0,1 to 0,4 0,15 10
-7 -6
(1 × 10 to 1 × 10 )
Silty clay or clay < 0,001 < 0,1 < 0,15 Direct infiltration
-8
not possible
(< 1 × 10 )
The Figures 1 to 3 show maximum recommended values for LTAR depending on the k coefficient type.
National regulations or guidance may determine which evaluation method should be used and the acceptable
criteria. From the determined LTAR and the anticipated loading, the area of any infiltration system can be
calculated in accordance with equation 1.

Figure 1 — Relation between LTAR and k
Figure 2 — Relation between LTAR and k
N
Figure 3 — Relation between LTAR and k
C
A = Q LTAR (1)
d
where
A is the infiltration system area (m²);
LTAR is the value given either from Table 1 or Figures 1 to 3 or Annex B (B.3.1) (m /m²/d);
Q  is the total daily flow (m /d).
d
Annex B describes some methods of how the soil parameters could be determined and gives some information
about the determination of LTAR.
6.4 Influent parameters
The infiltration system shall be designed to accept the total daily flow from at least one house.
The infiltration systems are intended to receive only domestic wastewater (without any other water such as
rainwater) pre-treated in a septic tank. Systems to treat commercial wastewater (restaurants, hotels, etc.) require
different design.
In the absence of national regulation or guidance or other reliable data, a minimum value of 150 l per day and per
inhabitant may be used for loading calculation.
6.5 Selection of infiltration system
Start with LTAR and progress across the Table 2 considering each parameter in turn. See also informative
annexes.
Table 2 — Infiltration system basic selection matrix
Measured Water table Soil Fissured Slope Replace System
LTAR level stability rock native soil type
Good Low Good No — No Infiltration
trench
Good Low Bad No Shallow No Shallow
infiltration
bed
Low Low — Yes Shallow Yes Vertical
or steep infiltration
bed
Very high High or — Yes — Yes Infiltration
or very none mound
low
7 Components
7.1 General
In the absence of any national regulation or guidance the following requirements apply.
7.2 Pipes
7.2.1 General
All pipes shall be manufactured in accordance with the requirements of the relevant EN, if available or, in their
absence, with the specifications valid in the place of use.
7.2.2 Distribution pipe
The following specific requirements shall be complied with:
 The nominal diameter of the distribution pipe located between the septic tank and the distribution chamber,
shall at least be equal to the diameter of the outlet of the septic tank.
 For the distribution pipes following the distribution chamber, the minimum internal diameter (ID) shall be
80 mm for gravity systems and 32 mm for pressure systems.
7.2.3 Infiltration pipe
7.2.3.1 General
Fields drainpipes shall not be used.
7.2.3.2 Infiltration pipe diameter
The minimum internal diameter of the infiltration pipes shall be 80 mm for gravity systems and 32 mm for pressure
systems
7.2.3.3 Infiltration pipe perforation
The infiltration pipes shall have holes or slots and a smooth internal inner surface.
The perforations shall be dimensioned and spaced to ensure that granular fill cannot enter the infiltration pipe and
that effluent can flow easily through the perforation without clogging.
7.3 Granular fill material
Granular fill materials used in Europe vary greatly, however it is usually sand in the range of 2 mm to 8 mm or
gravel in the range of 8 mm to 32 mm.
Granular fill shall be inert, washed and graded.
7.4 Geotextile and mesh
Infiltration pipes shall be covered, with a suitable geotextile T (Table 3) to prevent contamination of the granular fill
material e.g. by fine particles of soil. In fissured rock, to avoid sand from being washed out into the ground, a more
porous geotextile B (Table 3) or mesh X shall be used.
Geotextile shall be in accordance with EN ISO 10319.
Table 3 — Geotextile and mesh properties
a
Characteristics Geotextile T Geotextile B Mesh X
Tensile strength
≥ 12 kN/m ≥ 6 kN/m ≥ 6 kN/m
-1 -1 -1
Permittivity
≥ 0,05 s ≥ 0,03 s ≥ 0,03 s
Filtration porosity > 140 µm > 140 µm
≤ 125 µm
Class 1 1 -
a
geomesh can replace geotextile B

7.5 Impermeable film
Impermeable film may be used on the sides of the infiltration system to prevent lateral flow.
This film shall be at least 200 µm thick HDPE or an alternative material of an equivalent strength, which will not
puncture or tear.
7.6 Effluent pumping systems
Effluent pumping systems may be used to transport effluent to remote infiltration systems, to raise effluent from
deep septic tanks and/or for pressure infiltration systems.
Effluent pumps shall not be installed directly in septic tanks but in a separate pumping chamber, which may be
constructed as part of other structures on site.
Suitable wastewater pumps with a minimum free passage of 10 mm should be used.
7.7 Dosing system
To provide efficient distribution of the effluent over the full length of the infiltration pipes, the use of a dosing system
is highly recommended.
7.8 Chambers
Chambers shall be watertight, smooth on the inside and be fitted with a removable cover to facilitate maintenance
and inspection.
Dosing and distribution chambers may be combined into a single structure.
To prevent backflow the inlet of the chamber shall be above the highest operating water level within the dosing
chamber.
The outlets from the distribution chamber shall be adjustable to enable even flow to the distribution pipes, and may
also include optional outlets for alternative infiltration areas.
8 General requirements for the installation of septic tanks
8.1 General
Septic tank shall be installed in accordance with national regulations or guidance and manufacturers instructions.
The outlet pipes from the septic tank shall have a fall of at least 0,5 %. Prior to installation, the use of grease
separator shall be considered.
The use of a prefilter shall also be considered.
8.2 Ventilation
Generally, a ventilating stack provides an air outlet. National requirements may specify either a separate ventilation
stack or the buildings ventilating stack. When using building ventilation stack, requirements are given in
EN 12056-2.
An independent ventilation pipe may be required in certain circumstances.
The ventilating stack shall not be fitted with an air admittance valve.
9 Construction requirements
9.1 General
All infiltration systems require a margin of 1 m, which is part of the disposal area. Excavation of trenches or beds
should be carried out very carefully in order to avoid disturbing the surrounding soil.
9.2 Installation on sloping sites
Generally, the infiltration pipes shall be installed parallel to contours of the ground (see Figure A.2).
9.3 Land drains
Land drains shall be installed when it is required to prevent migration of surface water or groundwater into the
infiltration system.
9.4 General precautionary measures for excavation works
Excavation is not recommended when the ground is wet.
Trenches and beds should be covered during rainy weather and back-filled as soon as possible.
The excavation process shall not cause compaction of the ground area which is intended for the infiltration. If
necessary, the sides and base of the excavation shall be raked. Machinery shall not traverse the area after the
work has been completed.
9.5 Installation of chambers
9.5.1 General
Chamber connections shall be watertight and accommodate soil settlement.
9.5.2 Distribution chamber
The chamber should be placed directly on the granular fill material so that it is level and stable. For a gravity
system a minimum gradient of 0,5 % shall be provided between the septic tank and the distribution chamber.
9.5.3 End connections
When used, the end connections shall be installed level within the granular fill material.
9.6 Inspection of infiltration pipes
Before installation, the holes in the infiltration pipes shall be inspected to check that they are of the correct size and
aperture and free from debris.
9.7 Access and inspection
Access points are required at distribution chambers and dosing chambers. Access or inspection points are
recommended at the ends of infiltration pipes. The covers shall be visible and installed to prevent the entry of
water.
The access and inspection points can also provide an indication of the extent of the infiltration systems.
All covers shall be accessible for maintenance and inspection of the system.
9.8 Backfilling
Soil, free from large objects such as stones or lumps may be used as backfill. This soil shall be laid in successive
layers over the geotextile, taking care that the pipes and chambers are not displaced.
Sand or soil shall be used to backfill over the end connections.
In order to accommodate any subsequent settling of the backfill material, an allowance shall be made when
backfilling.
9.9 Covering
The area over the infiltration system shall not, even partially, be covered by a surface, which is air and water
impermeable.
Climatic conditions can require frost insulation which shall be permeable.
9.10 Health and safety
Relevant national health and safety requirements shall be complied with.
10 Specific construction requirements
10.1 General
In addition to the common requirements of clause 9, the following requirements shall also apply in specific
circumstances.
NOTE It is advisable to construct the infiltration system as close to ground level as possible.
Infiltration pipes shall be laid on the fill material with the perforations facing downwards.
10.2 Infiltration trench
10.2.1 General
Figures 4 and 5 show examples of infiltration trenches.
10.2.2 Excavation of trenches for the distribution chamber and distribution pipes
Ensure that adequate fall is available to construct a gravity fed system. If this is not possible, a pumped system
shall be used.
Excavation shall allow for a 0,10 m thick sand layer below the distribution chamber and pipes.
The sides and base of the trench shall be free from any large object. The base shall be level.
10.2.3 Excavation of infiltration trenches
10.2.3.1 General
The base of the trench shall be level. On sites with gradients greater than 5 %, the infiltration trenches shall be
installed parallel to the site contours. The base of the trenches should be at a minimum of 0,60 m to a maximum of
1 m below ground level.
Factors influencing trenches depth include:
 frost cover
 protection from disturbance
 depth of the outlet pipe from the septic tank
 permeability coefficient of the subsoil at the operating depth
 depth to water table and depth to bedrock
The minimum width of the trench base shall be 0,50 m.
The maximum length of a trench shall be 30 m with a maximum of 5 trenches for a gravity system.
The minimum spacing between adjacent trench sides shall be at least 1 m.
Installation of infiltration pipes and end connections
10.2.3.2 Installation of infiltration pipes
a) Preparation of infiltration trench
The trench shall be filled with granular fill material up to the level where the infiltration pipes are to be installed. This
layer shall extend over the entire surface of the trench base.
If necessary, the thickness of the layer can be reduced while increasing trench width (see Table 4).
Table 4 — Thickness of granular fill material in relation to trench width
Dimensions in meters
Trench width Granular fill material thickness below the pipe
0,50 0,30
0,70 0,20
1,00 0,15
1,50 0,15
b) Infiltration pipes
Pipes shall be laid centrally at a gradient of (0,5 ± 0,5) % in the direction of flow.
In order to set the pipes securely granular fill material shall be carefully spread around the infiltration pipes along
the entire length of the trench so that it reaches at least, the top of the pipe.
Material (gravel with the same characteristic as the distribution layer material) with a thickness from 0 cm to 10 cm
shall be laid just above the infiltration pipes. This layer shall be covered with geotextile T so that the granular fill
material of the distribution layer is separated from the soil used to backfill the trench. Several sheets of geotextile T
shall be overlapped by at least 0,20 m to cover the entire surface. The complete geotextile T covering shall be
wider than the trench (see Figure 6).
10.2.3.3 Installation of end connection pipes and ventilation fittings
The system with parallel trenches may be interconnected at the ends of the infiltration trenches using non
perforated or perforated pipes. The connection between these elements should be level and stable and should
include ventilation.
Key
A Longitudinal cross section 8 Backfill D Distribution layer thickness beneath
infiltration pipe, 0,15 m to 0,3 m, see
B Plan 9 Optional end connection with
Table 3
ventilation and access
C Cross section
D min 1 m
10 Geotextile T
1 Subsoil
W Natural ground width between
D Total depth, 0,6 m to 1,0 m
2 Distribution layer
trenches ≥ 1 m
D Backfill depth ≥ 0,2 m
3 Infiltration pipe 2
W Distribution layer width 0,5– m to
D Infiltration pipe diameter + 0 m to
4 Sand layer 3
1,5 m
0,1 m of granular fill material (same
5 Connection pipe
L Distribution layer length ≤ 30 m
as in the distribution layer)
6 Distributon chamber
Area =Σ (L × W )
1 2
7 Distribution pipe
Figure 4 — Infiltration trench, example with 3 trenches
Key
A five trenches 3 Distribution pipe
W Natural ground width between trenches ≥ 1 m
B three trenches 4 Infiltration pipe W Distribution layer width 0,5 m to 1,5 m
C two trenches 5 Sand layer
L Distribution layer length ≤ 30 m
1 Connection pipe 6 Distribution layer Area =Σ (L × W )
1 2
2 Distributon chamber 7 End connection with
ventilation and access
Figure 5 — Infiltration trench, layout examples
Single sheet turned upwards at the edges Two sheets with an overlap between them and their
outer edges turned upwards
Key
4 Backfill
1 Subsoil 5 Geotextile T
2 Distribution layer 6 Natural ground
3 Infiltration pipe O Overlap on the side, upwards, ≥ 0,2 m
O Overlap two sheets, ≥ 0,2 m
Figure 6 — Geotextile T covering, examples
10.3 Infiltration beds
10.3.1 Shallow infiltration bed
The shallow infiltration bed (see Figure 7) may replace infiltration trenches when the soil is of a sandy consistency.
It consists of a single excavation with a level base. The installation procedures, materials and equipment used are
similar to those for infiltration trenches.
The area of the infiltration bed corresponds to that of the infiltration trenches. Bed depth varies depending on the
factors stated in 10.2.3.1.
Maximum length shall be 30 m and maximum width shall be 8 m. The spacing between the infiltration pipes should
be 1 m ± 0,5 m, and these should be spaced evenly across the width of the infiltration bed.
Key
A Cross section 8 Connection pipe L Distribution layer length ≤ 30 m
9 End connection with ventilation and
B Plan
W Side width ≤ 1 m
access
1 Subsoil
W Equal infiltration pipe distance 0,5 m
D Total depth, 0,6 m to 1,0 m
to 1,5 m
2 Distribution layer
D Backfill depth ≥ 0,2 m
3 Infiltration pipe
W Total distribution layer width ≤ 8 m
D Infiltration pipe diameter + 0 m to
4 Geotextile T
O Overlap on the side, upwards ≥ 0,2 m
0,1 m of granular fill material (same
5 Backfill
O Overlap two sheets ≥ 0,2 m
as in the distribution layer)
6 Distribution pipe
Area =L × W
1 3
D Distribution layer thickness beneath
7 Distribution chamber
infiltration pipe, 0,15 m to 0,3 m,
see Table 3
Figure 7 — Shallow infiltration bed, example with 3 infiltration pipes
10.3.2 Vertical infiltration bed
10.3.2.1 Application
A vertical infiltration bed (see Figure 8) may be used in fissured ground or when the native soil is permeable, but
not sufficiently permeable to allow the construction of an infiltration trench system. The replacement of some of the
native soil with suitable sand (see Annex C) facilitates the use of a vertical infiltration system. The vertical infiltration
bed may also be used in situations where the soil characteristics may be improved by replacement of the upper
layers.
10.3.2.2 Dimensions and excavation
The base of the bed shall be level and located a minimum of 0,90 m below the level at which the distribution
chamber outlet is seated.
The base of the excavation should be located between a minimum of 1,10 m and a maximum of 1,60 m below
ground level.
The width of the infiltration bed should be 5 m. The minimum length shall be 4 m and the maximum shall be 30 m.
If the vertical sides of the ditch excavation are fissured, an impermeable film should cover them. In order to provide
the requirements given in Clause 7 for the impermeable surface, several films can be laid overlapping.
If the bottom of the excavation is fissured, it shall be covered by geotextile or mesh B.
10.3.2.3 Bed construction
The sand shall be laid on the base of the excavation (on geotextile B, when required) to a recommended thickness
of at least 0,7 m.
A layer of granular fill material with a minimum thickness of 0,1 m shall be spread over the sand.
The infiltration pipes are spaced regularly with 1 m between centres.
Material (gravel with the same characteristic as the distribution layer material) with a thickness from 0 cm to 10 cm
shall be laid just above the infiltration pipes. This layer shall be covered with geotextile T so that the granular fill
material of the distribution layer is separated from the soil used to backfill the trench. Several sheets of geotextile T
shall be overlapped by at least 0,20 m to cover the entire surface. The complete geotextile T covering shall be
wider than the trench.
Key
A Cross section 9 Distribution pipe D Distribution layer thickness
beneath infiltration pipe, 0,1 m
B Plan 10 Distribution chamber
to 0,3 m, see Table 3
1 Subsoil 11 Connection pipe
D Sand depth, ≥ 0,7 m
2 Geotextile B or mesh, 12 Optional end connection with
L Distribution layer length 4 m to
when required ventilation and access 1
30 m
3 Impermeable film, 14 Vertical acces and ventilation
W Equal infiltration pipe distance,
when required (optional) 1
1 m (or 0,5 m to 1,5 m)
D Total depth, 1,0 m to 1,6 m
4 Sand
W Total bed width 5 m (or less when
5 Distribution layer
D Backfill depth ≥ 0,2 m
required)
6 Infiltration pipe
D Infiltration pipe diameter 0 m to
O Overlap on the side, upwards,
0,1 m of granular fill material
7 Geotextile T
≥ 0,2 m
(same as in the distribution layer)
8 Backfill
O Overlap two sheets, ≥ 0,2 m
Area = L x W
1 2
Figure 8 — Vertical infiltration bed, example with 5 infiltration pipes
10.3.3 Infiltration mound
10.3.3.1 Application
Infiltration mounds (see Figures 9, 10 and 11) may be used in situations where the groundwater table, bedrock or
fissured rock is too close to the ground surface. They may also be applicable in locations with soils of low
permeability.
10.3.3.2 Dimensions and excavation
The construction of the infiltration mound is similar to that of the vertical infiltration bed (see 10.3.2). However,
whereas the vertical infiltration bed was excavated, infiltration mounds are built on the ground on areas that have
been cleared of vegetation. Due to the elevation of the mound, a pump may be necessary to raise the pre-treated
effluent. A pressure distribution system may be used and designed using established hydraulic principles (see
Figure 9).
The width of an infiltration mound should be 5 m at the top. The minimum length at the top of an infiltration mound
should be 4 m. The base of the mound shall be sized to ensure structural stability.
a) Mounds on fissured rock (see Figure 10)
In fissured rock, an impermeable film shall protect the vertical sides of an excavation. If the area requires
several sheets, the edges shall be overlapped. The base of the excavation in fissured rock shall be covered by
geotextile B or mesh.
At least 0,7 m of sand shall be laid on the base. The infiltration pipes shall be laid on a layer of at least 0,1 m
granular fill material.
The pipes shall be covered by granular fill material. Material (gravel with the same characteristic than the
distribution layer material) with a thickness from 0 cm to 10 cm shall be laid just above the infiltration pipes.
This layer shall be covered with geotextile T. Several sheets of geotextile T shall be overlapped by at least
0,20 m to cover the entire surface. The complete geotextile T covering shall be wider than the mound.
The whole mound shall be covered by topsoil to a thickness of at least 0,2 m.
b) Mounds on soils of low permeability (see Figure 11)
Such mounds are constructed similarly to the above, but the base covers a greater surface area than the other
mounds, so that the hydraulic loading is less than the determined LTAR. These mounds shall be constructed
on a site with a depth of at least 0,3 m of unsaturated soil.
The base on which the mound is to be built should be roughened to minimise compaction and smearing of the
soil. The sand shall be laid on a rectangular base that extends along the contours of the land.
A maximum of three parallel infiltration pipes may be used. To ensure an even distribution, a dosing chamber
shall be used.
Key
1 Subsoil 6 Geotextile T 11 End connection with ventilation and
access
2 Geotextile B or 7 Backfill
mesh, when required L Distribution layer length 4 m to 30 m
8 Distribution chamber
3 Sand O Overlap on the side, upwards, ≥ 0,2 m
9a Connection pipe, pre ssure
4 Distribution layer
O Overlap two sheets, ≥ 0,2 m
9b Connection pipe, gravity
5 Infiltration pipe
10 Pumping chamber with pump
Figure 9 — Infiltration mound, longitudinal cross section, example with a pump

Key
A Cross section 10 Connection pipe
D Sand depth, ≥ 0,7 m
B Plan 11 End connection with ventilation L Distribution layer length 4 to 30 m
and access
1 Subsoil
W Equal infiltration pipe distance,
D Total depth, 1,0 to 1,6 m
1 m,(or 0,5 m to 1,5 m)
2 Geotextile B or mesh
D Backfill depth ≥ 0,2 m W Total bed width 5 m (or less
2 2
3 Sand
when required)
D Infiltration pipe diameter + 0 to
4 Distribution layer
0,1 m of granular fill material (same as O Overlap on the side, upwards,
5 Infiltration pipe
in the distribution layer) ≥ 0,2 m
6 Geotextile T
D Distribution layer thickness
4 O Overlap two sheets, ≥ 0,2 m
7 Backfill beneath infiltration pipe, 0,1 m to
Area = L × W
1 2
0,3 m, see Table 3
8 Distribution pipe
9 Distributon chamber
Figure 10 — Infiltration mound, example on sloping fissured rock
Key
A cross section 9 Dosing chamber (pump) D Distribution layer thickness
10 Connection pipe beneath infiltration pipe, 0,1 m
B Plan
to 0,3 m, see Table 3
11 End connection with
1 Subsoil
D Sand depth ≥ 0,3 m
ventilation and access 5
2 Base
W Equal infiltration pipe distance,
L Distribution layer length 5 m 1
3 Sand
1 m, (or 0,5 m to 1,5 m)
to 30 m D Total depth, ≥ 0,8 m
4 Distribution layer
W Distribution layer width 1 m to 3 m
D Backfill depth ≥ 0,2 m
5 Infiltration pipe
W Base width ≥ 1 m
D Infiltration pipe diameter
6 Geotextile T
0 m to 0,1 m of granular fill O Overlap on the side, upwards
7 Backfill
material (same as in the
≥ 0,2 m
8 Distribution pipe, pressure
distribution layer)
NOTE The hydraulic loading on the base defined by L × W shall be less than the determined LTAR.
1 3
Figure 11 — Infiltration mound, example on soil of low permeability
CEN/TR
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