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

7.2.2.4 Construction
A frequent cause of early failure of soil absorption systems is the use
of poor construction techniques. The following should be considered for
construction of a soil absorption system:
a. Layout
The system should be laid out to facilitate the maneuvering of construc-
tion equipment so that damage to the soil is minimized.
1. Absorption system area should be staked out and roped off
immediately after the site evaluation to keep construction
equipment and other vehicles off the area until construction of
the system begins.
2. Trenches rather than beds are preferable in soils with signifi-
cant clay content (greater than 25% by weight1 because equip-
ment can straddle the trenches. This reduces the compaction
and smearing at the exposed infiltrative surface.
3. Trenches should be spaced at least 6 ft (1.8 m) apart to facil-
itate the operation of the construction equipment if there is
sufficient area.
4. To minimize sidewall compaction, trench widths should be made
larger than the bucket used for excavation. Buckets are made
to compact the sidewall to prevent caving during excavation.
If the excavation is wider than the bucket, this effect is min-
imized. An alternative is to use modified buckets with side
cutters or raker teeth (see Figure 7-7).
5. Trenches should follow the contour and be placed outside the
drip lines of trees to avoid root damage.
b. Excavation
Absorption of waste effluent by soil requires that the soil pores remain
open at the infiltrative surface. If these are sealed during construction
by compaction, smearing, or puddling of the soil, the system may be
rendered useless. The tendency toward compaction, smearing, and puddling
depends upon the soil type, moisture content, and applied force.
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