For inspection purposes only. Consent of copyright owner required ...

S OURCE
INFILTRATION
CONTROL
TRENCHES & SOAK-AWAYS
Overflow Berm
* Flood Studies Report, WRAP Classification
SECTION
Construction Cost
PRIMARY CONSIDERATIONS
Maintenance Requirements
LOW
HIGH
Observational Well
with Screw-Top Lid Run-off filters through
grass buffer strip
Pea Gravel Filter Layer
Protective Layer of Filter Fabric
Trench:
Filled with 30 - 60mm diameter
clean stone / gravel
Sand Filter
(or Fabric Equivalent)
BENEFITS
�Water
Quality Control YES
�Water
Quantity Control YES
�Amenity
Value NO
L and Take
LOW
�Habitat
Creation Value NO
�Biological
Treatment NO
Side-entry pits drain to infiltration trench in car-park
DESCRIPTION
DESIGN
n infiltration trench is a gravel /
�The
treatment volume should
�Soils
underlying the site should be
rock-filled trench designed to
completely infiltrate through the trench
permeable, i.e. have a clay content of
Ainfiltrate run-off to the ground.
bottom in 24 hours.
less than 20% and a silt/clay content of
Infiltration trenches are essentially long
�Trenches
should be under-drained, so
less than 40%. (Refer BRE,1991 and
thin soakaways (rock filled pits or large
that in the event of clogging it can act as
CIRIA, 1996). Infiltration controls can
tanks structures). Run-off is stored in
an overflow.
be used on soil types 1 or 2* and where
the voids allowing it to slowly infiltrate it can be demonstrated that the trench �With
long infiltration trenches it is
through the bottom into the soil matrix. will infiltrate the design treatment advisable to provide inspection tubes at
This reduces the volume of water that is volume within 12 hours under average regular intervals along the trench
discharged into receiving watercourses winter rainfall (Campbell, 2000). (CIRIA, 2000).
thereby reducing some of the impacts
�A
pre-treatment device such as a �The
maximum contributing area to
caused by excess flows and pollutants.
swale or filter strip is recommended infiltration trenches should be less than
upstream of the trench to reduce 5 hectares.
incoming velocities and coarser �The
infiltration device should not be
sediments.
constructed within 5m of the
�The
device should be constructed at foundations of buildings or under a
least 1.5m above the maximum road.
groundwater level or bedrock layer and �Do
not construct near drinking water
only where the groundwater wells, septic tanks or drainfields .
classification allows.
�During
construction, measures to
�The
trench should be filled with clean minimise sediment erosion and soil
stones that can retain the required compaction should be used.
volume of water to be treated in their
�The
facility should not come into use
void space.
until construction and landscaping of
�The
stone should be wrapped in a
the site that drains to it is completed.
geo-textile. This fabric should be
�Areas
upstream of the trench should
selected on the basis of durability with
be stabilised.
adequate opening size to resist
clogging.
For inspection purposes only.
Consent of copyright owner required for any other use.
Run-off exfiltrates through
undisturbed sub-soils with a
minimum rate of 1.27 cm per hour
MORE OVERLEAF - 1 of 2
GREATER DUBLIN STRATEGIC DRAINAGE STUDY - ENVIRONMENTAL MANAGEMENT POLICY
EPA Export 24-08-2012:23:55:53