Design manual

2. Percolation test – EPA (American) method
A hole 15 cm in diameter is filled with water to
the height of 30 cm. After presoaking (similar
to the Polish method) the drop in water
level from 30 cm to 27.5 cm is timed. The
percolation rate, measured in min./25 mm,
is the basis for determining permeability and
filtration rate.
12.3. Hydraulic conductivity
for various types of soil
3. Hydraulic conductivity
In order to be suitable for rainwater
infiltration, hydraulic conductivity of the
soil must be 10 -3 m/s – 10 m/s.
12.4. Guidelines on rainwater infiltration
into the ground
Infiltration systems are usually designed
without drainage. It is possible, however, for
the infiltration system to be equipped with
an emergency overflow, through a settling
chamber to another receptacle of rainwater,
such as a rainwater drainage system. Soil
permeability, tank depth, number and thickness
of drainage layers underneath and around
the box system and groundwater level are
particularly important when designing a solution
of this type.
The useful volume of the box system should be
chosen based on the least favourable conditions,
in practice for precipitation lasting from 15 min
to 360 min. The amount of precipitation should
be based on actual precipitation in the given
2
Water percolation rate
[min./25 mm]
region (data from the Institute of Meteorology
and Water Management).
Infiltration systems should be able to contain
rainwater from the planned catchment area.
The first wave of water from the drainage area
contains the most impurities. For that reason a
chamber with a settling tank should be installed
upstream of the infiltration system in order to
Soil type Permeability [min./cm] Filtration rate [cm/h]
< 1 Gravel < 0.4 < 150
5 Sand 2 30
10 Fine sand 4 15
15 Clayey sand 6 10
20 Sandy clay 8 7.5
30 Clay 12 5
40 Clay 16 3.75
80 Heavy silty clay 32 1.875
120 Very heavy clay 48 1.25
> 120 Silt > 48 > 1.25
3
Permeability
Hydraulic conductivity
Permeability type
coefficient
[m/s] [m/h] [m/d] [Darcy]
Very good: rockfill, gravel, coarse
and uniform sand
> 10 -3 > 3.6 > 86.4 > 100
Good: non-uniform and medium sand 10 -4 - 10 -3 0.36 - 3.6 8.64 - 86.4 10 - 100
Medium: fine sand, loess 10 -5 - 10-4 0.036 - 0.36 0.864 - 8.64 1 - 10
Poor: silty and clayey sand, loam, sandstone 10 -6 - 10 -5 0.0036 - 0.036 0.0864 - 0.864 0.1 - 1
Semipermeable rock: clay, aggregate mud,
mudstone, sandy silt
10 -8 - 10 -6 0.000036 - 0.0036 0.000864 - 0.0864 0.001 - 0.1
Impermeable rock: silt, claystone, compact
silty clay, silty marl