8.7.5.

(1) The total daily design sanitary sewage flow shall not exceed 5 000 L where the treatment unit is a septic tank, or 10 000 L where the treatment unit is described in Article 8.6.2.2.v1

(1) The effective area of the surface of the filter medium in each filter bed shall be at least 10 m² and not more than 50 m².

(2) The area described in Sentence 8.7.4.2.(1) shall be designed such that the loading rate does not exceed, for soil having a percolation time set out in Column 1 of Table 8.7.4.1.A., the maximum value set out opposite thereto in Column 2 of Table 8.7.4.1.A.

(3) Except as provided in Sentence (5), where the total daily design sanitary sewage flow does not exceed 3 000 L, the effective area shall be such that the loading on the surface of the filter medium does not exceed 75 L/m² per day.

(4) Except as provided in Sentence (5), where the total daily design sanitary sewage flow exceeds 3 000 L,

(a) the effective area shall be such that the loading on the surface of the filter medium does not exceed 50 L/m² per day, and

(b) the leaching bed shall be comprised of more than one filter bed, each of similar size and adjacent to each other.

(5) Where a treatment unit designed to produce effluent not exceeding the maximum concentrations stipulated in Column 2 of Table 8.6.2.2.A.v1 is used in conjunction with a filter bed, the effective area shall be such that the loading on the surface of the filter medium does not exceed 100 L/m² per day.

(1) Sentences 8.7.4.2.(1), (2) and (4) to (11) apply to the construction of a filter bed.

(2) The lines of distribution pipe shall be evenly spaced over the surface of the filter medium to which the sanitary sewage is applied.

(3) The filter medium shall have a minimum depth of 750 mm below the stone layer and shall be clean sand comprised of particles ranging in size between the limits of,

(a) an effective size of 0.25 mm with a uniformity coefficient not less than 3.5,

(b) an effective size of 2.5 mm with a uniformity coefficient not greater than 1.5, and

(c) having a uniformity coefficient not greater than 4.5.

(4) The filter medium shall be unsaturated for its entire depth.

(5) Where there is more than one filter bed in a leaching bed, the filter beds shall be separated by at least 5 m between the distribution pipes of the filter beds.

(6) The base of the filter medium shall extend to a thickness of at least 250 mm over an area meeting the requirements of the following formula:

where,

A = the area of contact in square metres between the base of the filter medium and the underlying soil,

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

T = the lesser of 50 and the percolation time of the underlying soil.

(7) The stone layer required by Clause 8.7.3.3.(1)(b) shall be not less than 900 mm above the high ground water table, rock or soil with a percolation time more than 50 minutes,