(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 600 mm and not more than 900 mm in depth,
(d) centred not less than,
(i) 1 600 mm apart where used in conjunction with,
(A) a distribution pipe,
(B) a Type I leaching chamber, or
(C) a Type II leaching chamber constructed in leaching bed fill, or
(ii) 2 400 mm apart where used in conjunction with a Type II leaching chamber, other than a Type II leaching chamber constructed in leaching bed fill,
(e) located so that the bottom of the absorption trench is not less than 900 mm above the high ground water table, rock or soil with a percolation time of more than 50 minutes, and
(f) backfilled, after the installation of the distribution pipe or leaching chamber 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 a shallow buried trench 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.