8.7.3.

(1) The total length of distribution piping shall,

(a) not be less than 30 m when constructed as a shallow buried trench, or

(b) not be less than 40 m for any other absorption trench.

(2) Except as provided in Sentences (1), (3), and (4) every leaching bed constructed by means of absorption trenches shall have a total length of distribution pipe not less than the value determined by the formula,

where,

L = total length of distribution pipe in metres

Q = the total daily design sanitary sewage flow in litres

T = the design percolation time

(3) Except as provided in Sentence (1), where the treatment unit is described in Article 8.6.2.2.v1, the leaching bed may have a total length of distribution pipe not less than the value determined by the formula,

where,

L = total length of distribution pipe in metres

Q = the total daily design sanitary sewage flow in litres

T = the design percolation time

(4) Except as provided in Sentence (1), where the leaching bed is constructed as a shallow buried trench, the total length of the distribution pipe shall not be less than the value determined by Table 8.7.3.1.

where,

Q = the total daily design sanitary sewage flow in litres, and

T = the design percolation time.

(1) Except as provided in Sentence (2), absorption trenches shall be,

(a) approximately the same length and not more than 30 m in length,

(b) not less than 500 mm and not more than 1 000 mm in width,

(c) not less than 300 mm and not more than 900 mm in depth,

(d) centred not less than 1 600 mm apart,

(e) located so that the bottom of the trench is not less than 900 mm above the high ground water table, rock or soil with a percolation time more than 50 minutes, and

(f) backfilled, after the installation of the distribution pipe with leaching bed fill, so as to ensure that after the leaching bed fill settles, the surface of the leaching bed will not form any depressions.

(2) Absorption trenches constructed as shallow buried trenches shall be,

(a) approximately the same length and not more than 30 m in length,

(b) not less than 300 mm and not more than 600 mm in width,

(c) not less than 300 mm and not more than 600 mm in depth,

(d) centred not less than 2 000 mm apart,

(e) not less than 900 mm at all points on the bottom of the absorption trench above the high ground water table or rock, and

(f) backfilled, after the installation of the distribution pipe with leaching bed fill, so as to ensure that after the leaching bed fill settles, the surface of the leaching bed will not form any depressions.

(1) Except for shallow buried trenches, the distribution pipe used in the construction of a leaching bed shall be,

(a) of not less than 3 in. trade size for gravity flow systems, or 1 in. trade size for pressurized systems,

(b) installed with a uniform downward slope from the inlet with a drop of not less than 30 mm and not more than 50 mm for each 10 m of distribution pipe, and

(c) installed within a layer of stone conforming to Sentence (5).

(2) Prior to backfilling, the stone layer required in Clause (1)(c) shall be protected in such a manner so as to prevent soil, or leaching bed fill from entering the stone by completely covering with,

(a) untreated building paper, or

(b) a permeable geo-textile fabric.

(3) Every pressurized distribution pipe shall be self-draining so as to prevent freezing of its contents.

(4) Every pressurized distribution pipe shall have orifices of at least 3 mm in diameter, spaced equally along the length of the pipe.

(5) The layer of stone required by Clause (1)(c) shall,

(a) be comprised of washed septic stone, free of fine material, with gradation conforming to Table 8.7.3.3.A.,

(b) be not less than 500 mm in width,

(c) extend not less than 150 mm below the distribution pipe, and

(d) extend not less than 50 mm above the distribution pipe.