Soil
Percolation
Soil
texture determines how quickly wastewater
will be absorbed in the drainfield.
The ability of soil to absorb water
is known as soil percolation. Soils
containing a balance of coarse and
fine particles are the best types
for drainage, or percolation, of
wastewater. Soil
containing a high amount of clay
is not a good choice for siting
a septic drain field. In
specifying the size and type of
absorption field (drain field, leach
field, seepage pits) a soil percolation
test or "perc test" should
be performed.
To
perform a perc test, identify the
most-likely location on the lot
for placement of the septic drain
field, dig a hole about 5 ft. deep.
If groundwater immediately fills
in the hole a different location
or field design must be considered.
Summer
months and periods of dry weather
are times when the groundwater table
is at its lowest level. Test results
done during these periods will not
necessarily reflect year-round conditions.
After
digging the hole, pour 5 or more
gallons of water into the hole.
Make note of the time it takes for
the water to drain from the hole.
A one-inch drop in water level in
three minutes is considered very
good. If the water drains very slowly
or remains in the hole with no drop
in level by the next morning, the
soil percolation is considered bad
and will require soil exchange or
other special design measures.
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