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Effective April 28, 2015 Chapter Four Subsurface Sewage Treatment System Regulations (E) The drop box must be covered by a minimum of six inches of soil. If the top of the box is deeper than six inches, access must be provided above, at, or within six inches of finished grade. (F) The drop box must be placed on firm and settled soil. (3) If valve boxes are used, all requirements in Section 14.3(2) apply. (4) Distribution boxes must meet the standards in items (A) to (F). (A) The box must be watertight and constructed of durable materials not subject to corrosion or decay. (B) The distribution box must be covered by a minimum of six inches of soil. If the top of the box is deeper than six inches, access must be provided above, at, or within six inches of the finished grade. (C) The inverts of all outlets must be set and maintained at the same elevation. (D) The inlet invert must be either at least one inch above the outlet invert or sloped such that an equivalent elevation above the outlet invert is obtained within the last eight feet of the inlet pipe. (E) Each trench line must be connected separately to the distribution box and must not be subdivided. Distribution boxes must not be connected to one another if each box has distribution pipes. (F) When sewage tank effluent is delivered by pump, a baffle wall must be installed in the distribution box or the pump discharge must be directed against a wall, baffle, side of the box on which there is no outlet, or directed against a deflection wall, baffle, or other energy dissipater. The baffle must be secured to the box and extend at least one inch above the crown of the inlet pipe. The discharge rate into the drop box must not result in surfacing of sewage from the drop box. Pressure must not build up in the box during pump discharge. (5) Nonpressurized distribution pipes must meet the requirements of items (A) to(C)below. (A) Distribution pipes used for gravity distribution must be at least four inches in diameter. (B) Distribution pipes used for gravity distribution must have at least one row of holes of no less than one-half inch in diameter spaced no more than 40 inches apart. (C) Distribution pipes for gravity distribution must be laid level or on a uniform slope oriented away from the distribution device of no more than four inches per 100 feet. 14.4 Pressure Distribution (1) Pressurized distribution pipes must conform to the requirements of Sections 14.2(2) (A,C,D and E) (2) Pressure distribution pipes and associated fittings must be properly joined together. The pipe and connections must be able to withstand a pressure of at least 40 pounds per square inch. (3) The distribution network must be designed so there is less than a ten percent variance in flow for all perforations. (5) (4) Perforations must be no smaller than'/8-inch diameter and no larger than'/4-inch diameter. The number of perforations, perforation spacing, and pipe size for pressure distribution must be in accordance with Table IV below. The friction loss in any individual perforated lateral must not exceed 20 percent of the average pressure head on the perforations. Perforation holes must be drilled straight into the pipe and not at an angle. Pressurized distribution laterals must be installed level. Perforation holes must be free of burrs. Holes must be spaced no more than three feet apart. A method to introduce air into the pipe after dosing must be provided. The pipes must completely drain after the pump turns off. (6) Pressure distribution laterals must be spaced no further than 36 inches apart in seepage beds and mound absorption beds, and no further than 24 inches from the outside edge of the bed. (7) Pressure distribution laterals must be connected to a header or manifold pipe that is of a diameter such that the friction loss in the header or manifold will be no greater than five percent of the average head at the perforations. The header of manifold pipe must be connected to the supply pipe from the pump. 56 Washington County Development Code