1978-09-14 Septic System Design Report

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• III. DISTRIBUTION OF EFFLUENT 1. BY GRAVITY FLOW OVER THE SOIL TREATMENT AREA A. Level Ground Where the elevation difference of the ground surface does not exceed 28 inches in any direction within the soil treatmrit area, the sewage tank eff- ant may be directed to the soil tr atment area through a distribution box. (1) ,The box shall be watertight with a removable cover and shall be constructed of durable materials not subject to excessive corrosion or decay. The minimum inside dimen- sion shall be at least ten inches. (2) The inverts of all outlets shall be at the same elevation as measured from a liquid surface in the bottom of the box. (3) The inlet invert shall be at least one inch above the outlet inverts. (4) The outlet inverts shall be at least four inches above the distribution box floor. • (5) Each drainfield trench line shall be connected separately to the distribution box and shall not be subdivided. When sewage tank effluent is delivered to the distribution box by pump, either a baffle wall shall be installed in the distribution box or the pump discharge shall be directed against a wall or side of the box on which there is no out- let. The baffle shall be secured to the box and shall ex- tend at least one inch above the crown of the inlet flow line. B. Sloping Ground Where the elevation difference of the ground surface exceeds 28 inches in any direction within soil treatment area a drop box shall be installed at the head end of each lateral line. Connec- tions between drop boxes shall re b_, wa' right pipes. (See Figure 2) (1) The drop box shall be watertight and constructed of durable material- not subject to excessive corrosion or decay. The minimum inside dimension shall be at least ten inches, un- less the box is to be used as a valve box. Then each outlet shall have at least eight inches of sidewall space and the side of any outlet shall be at least six inches from any corner. - 7 -