Leaching pits are preferred where their installation
is possible.
The leaching area required shall be determined in accordance with the provisions of Article III. The leaching area shall be considered as the sidewall areas of the excavation below the invert of the inlet. Impervious area of the sidewall below the inlet shall not be considered as available leaching area.
When more than one leaching pit is installed,
they shall be designed such that they will function in parallel, and
the distance between excavation sidewalls shall be no less than twice
the effective width of the pit, whichever is greater.
Leaching pits shall not be constructed in areas
where the maximum groundwater elevation is less than four feet below
the bottom of the excavation.
There shall be a minimum of one inspection manhole
per pit. For systems designed for over 20,000 gallons per day, the
manholes shall be at least 18 inches in diameter, with metal frames
and covers to finished grade.
The lining of the pit shall be constructed of
brick perforated concrete or interlocking concrete blocks laid dry
with open joints on a manner to prevent displacement. At least 12
inches, and not more than 48 inches, of 3/4 inch to 1 1/2-inch
stone shall be placed around the liner. The liner shall be built to
allow the liquid to pass easily through openings to the surrounding
stone. The cover shall be constructed of reinforced concrete or other
approved material.
The stone shall consist of washed stone ranging
from 3/4 inch to 1 1/2 inch in size and shall be free of iron,
fines and dust in place. The stone shall be covered with at least
a two-inch layer of washed stone, ranging from 1/8 inch to 1/2 inch
in size, and shall be free of iron, fines and dust in place. All stone
must have less than 2% material finer than a No. 200 sieve as determined
by the AASHTO Test Methods T-11 and T-27 (latest edition).
A reserve area sufficient to replace the capacity
of the original leaching area must be provided. The area between the
leaching pits may not be used for part of the reserve area.
Excavations through impervious material may be allowed if at least four feet of naturally occurring pervious material, as demonstrated by a percolation test, remains beneath the lowest point of excavation. All construction after excavation through impervious material shall be in accordance with § 223-20.
The grade above and adjacent to a leaching pit
system shall slope at least 2% to prevent accumulation of surface
water.
The minimum depth of cover material over the
stone shall be 12 inches. Earth materials used to cover leaching pit
systems shall be free of large stones, frozen clumps of earth, masonry
or waste construction material. Machinery which may crush or disturb
the alignment of pipe in the disposal system shall not be allowed
on any part of the disposal system.
When pits are built at different elevations,
construction shall be such as to prevent the sewage from upper pits
from flowing into lower pits.
Excavation may be made by machinery, provided
that the soil at the bottom of the disposal system is not compacted.
The bottom of each system shall be level.
When leaching pit systems are constructed under
areas subject to vehicular traffic, the pits shall be capable of withstanding
H-20 wheel loads.
No pits shall be constructed in frozen soil.
Pits may be constructed in cases where the construction elevation
is below the depth of the frost line.
