1-14. SOIL ABSORPTION SYSTEM
a. Location. When a soil absorption system is determined to be usable, the
location of the components must be determined. A safe distance must be maintained
between the site and any source of water supply. Since the distance that pollution will
travel underground depends upon numerous factors, including the characteristics of the
subsoil formations and the quantity of wastewater discharged, no specified distance
would be absolutely safe in all localities. Ordinarily, of course, the greater the distance,
the greater will be the safety provided. In general, when not in conflict with local
ordinances, the location of components of wastewater disposal systems should be as
shown in Table 1-2.
Horizontal Distance (feet)
*Where the water supply line must cross the sewer line, the bottom of the water service
within 10 feet of the point of crossing shall be at least 12 inches above the top of the
sewer line. The sewer line shall be of cast iron with leaded or mechanical joints at least
10 feet on either side of the crossing.
Table 1-2. Minimum distances between components of wastewater disposal system.
b. Design. A soil absorption (disposal) field consists of a field of 12-inch lengths
of 4-inch agricultural drain tile, 2- to 3-foot lengths of vitrified clay sewer pipe, or
perforated, nonmetallic pipe. The individual laterals preferably should not be over 100
feet long and the trench bottom and tile distribution lines should be level. Use of more
and shorter laterals is preferred because most of the field will still be serviceable if
something should happen to disturb one line. Many different designs may be used in
laying out subsurface disposal fields. The choice may depend on the size and shape of
the disposal area, the capacity required, and the topography of the disposal area.