On-Site Wastewater Treatment and Disposal Systems - Forced ...

Soils with high clay contents (greater than 25% by weight) are very
susceptible to damage, while sands are rarely affected. Careful con-
struction techniques minimize this soil damage. They include:
1.
2.
3.
4.
5.
6.
Excavation may proceed in clayey soils only when the moisture
content is below the soil's plastic limit. If a sample of soil
taken at the depth of the proposed bottom of the system forms a
" wi re" instead of crumbling when attempting to roll it between
the hands, the soil is too wet.
A backhoe is usually used to excavate the system. Front-end
loaders or bulldozer blades should not be used because the
scraping action of the bucket or blade can smear the soil se-
verely, and the wheels or tracks compact the exposed
infiltrative surface.
Excavation equipment must not be driven on the bottom of the
system. If trenches are used, the equipment can straddle the
excavation. If a bed is used, the bed should be divided into
segments so the machinery can always operate from undisturbed
soil.
The bottom of each trench or bed must be level throughout to
ensure more uniform distribution of effluent. A level and tri-
pod are essential equipment.
The bottom and sidewalls of the excavation should be left with
a rough open surface. Any smeared and compacted surfaces
should be removed with care.
Work should be scheduled only when the infiltrative surface can
be covered in one day, because wind-blown silt or raindrop im-
pact can clog the soil.
c. Backfilling
Once the infiltrative surface
operations must be done careful
is properly prepared, the backfilling
ly to avoid any damage to the soil.
1. The gravel or crushed rock used as the porous media is laid in
by a backhoe or front-end loader rather than dumped in by
truck. This should be done from the sides of the system rather
than driving out onto the exposed bottom. In large beds, the
gravel or rock should be pushed out ahead of a small bulldozer.
2. The distribution pipes are covered with a minimum of 2 in. (5
cm) of gravel or rock to retard root growth, to insulate
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