(A) The following leaching areas are required for the seepage rates indicated:
Minimum uniform seepage rate time to drop one inch | Square feet of effective seepage area required per bedroom | |||
1 | 2 | 3 | 4 | |
(1) 5 minutes or less | 125 | 250 | 375 | 500 |
(2) 6 to 10 minutes | 165 | 330 | 495 | 660 |
(3) 11 to 20 minutes | 225 | 450 | 675 | 900 |
(4) 21 to 30 minutes | 250 | 500 | 750 | 1000 |
(5) More than 30 minutes | Special consideration needed to avoid nuisance conditions. In some soils it may be impracticable or impossible to use subsurface disposal. | |||
(6) Where a seepage rate slower than one inch in 30 minutes or high ground water is found, no sewage disposal system shall be built. In impervious soil, swamp or rock it may not be feasible to provide subsurface sewage disposal.
(B) All trenches shall follow contours with the bottoms of the individual trenches level. Depth of trenches should normally be not more than 30 to 36 inches, but depths up to 48 inches or greater may be used if warranted by conditions of topography or more favorable absorption capacity of soil at that depth. The width of the trench shall not exceed 36 inches and the spacing between adjacent sides of trenches shall be at least 3 times the width of the trench. The length of individual trenches shall not exceed 75 feet except that in installations where dosing apparatus is used, a maximum length of 100 feet may be used. Distributing pipe shall be laid near the top of a layer of one inch screened gravel or one inch broken stone placed to a depth of at least 18 inches in the trenches. The depth of stone under the pipe invert shall be at least 12 inches. Distributing pipes may be unglazed drain tile, at least 4 inches in diameter, laid with open joints. Pipe of vitrified tile or other acceptable material with suitable perforations or adequate spacing may also be used. The upper portions of joint openings shall be protected by strips of tar paper or other suitable material. Tile lines shall be laid on a grade not exceeding 2 to 4 inches per 100 feet. A layer of salt hay or tar paper shall be placed over the gravel before backfilling the trenches.
(C) Construction shall be such as to provide for proper distribution of settled sewage to trenches. Better distribution, particularly for large systems with several trenches, is secured in tile fields by using siphon dosing apparatus to apply the septic tank effluent. Diverting boxes with several outlets of the same elevation to individual trenches may be used to distribute the sewage. Where trenches are at different levels, serial distribution may be used with high-level overflows from upper to lower trenches.
(D) In seepage beds where space between trenches is also excavated and .backfilled with one inch stone or one inch screened gravel, only 1/3 of the total bottom area shall be considered effective. Distributing pipe shall be laid 6 feet to 8 feet on centers. Installation of stone and distributing pipe shall be the same as that required for leaching trenches. The bottom of the entire bed shall be at the same elevation.
(E) Leaching cesspools shall be spaced 3 times the diameter between sides of adjacent cesspools. Cesspool walls shall be constructed with masonry laid with open joints below the maximum liquid level. The walls shall be surrounded by 12 inches of screened gravel or broken stone.
('66 Code, § 57-17)