Section 605 Installation of Conventional Soilabsorption Systems
A seepage pit shall have not less than an inside diameter of 5 feet (1524 mm) and shall consist of a chamber walled-up with material, such as perforated precast concrete ring, concrete block, brick or other approved material allowing effluent to percolate into the surrounding soil. The pit bottom shall be left open to the soil. Aggregate of 1/2 inch to 21/2 inches (12.7 mm to 64 mm) in size shall be placed into a 6-inch minimum (152 mm) annular space separating the outside wall of the chamber and sidewall excavation. The depth of the annular space shall be measured from the inlet pipe to the bottom of the chamber. Each seepage pit shall be provided with a 24-inch (610 mm) manhole extending to within 56 inches (1422 mm) of the ground surface and a 4-inch-diameter (102 mm) fresh air inlet. Seepage pits shall be located not less than 5 feet (1524 mm) apart. Excavation and scarifying shall be in accordance with Section 605.4. The effective area of a seepage pit shall be the vertical wall area of the walled-up chamber for the depth below the inlet for all strata in which the percolation rates are less than 30 minutes per inch (70 s/mm). The 6-inch (152 mm) annular opening outside the vertical wall area is permitted to be included for determining the effective area. Table 605.3, or an approved method, shall be used for determining the effective sidewall area of circular seepage pits.
EFFECTIVE SQUARE-FOOT ABSORPTION AREA FOR SEEPAGE PITS
|INSIDE DIAMETER OF|
IN FEET PLUS 1 FOOT FOR
WALL THICKNESS PLUS 1
FOOT FOR ANNULAR SPACE
|DEPTH IN FEET OF PERMEABLE|
STRATA BELOW INLET
For SI: 1 foot = 304.8 mm.
Observation pipes shall be provided. Such pipes shall be not less than 4 inches (102 mm) in diameter, not less than 12 inches (305 mm) above final grade and shall terminate with an approved vent cap.
The bottom 12 inches (305 mm) of the observation pipe shall be perforated and extend to the bottom of the aggregate. Observation pipes shall be located not less than 25 feet (7620 mm) from any window, door or air intake of any building used for human occupancy. Not more than four distribution pipelines shall be served by one common 4-inch (102 mm) observation pipe where interconnected by a common header pipe (see Appendix-A, Figure A-4).
Exception: Where approved and where the location of the observation pipe is permanently recorded, the observation pipe shall be not more than 2 inches (51 mm) below the finished grade.