(1) Pressure distribution with timed dosing of LOSS effluent to the drainfield is required.

(2) The maximum spacing between the outside laterals and the edge of the trench or bed must be one-half of the selected orifice spacing, with a variance of one-half foot or less.

(3) All pressure distribution laterals must be equipped with cleanouts and monitoring ports at the distal ends and accessible at finished grade.

(4) Required distribution system minimum residual pressure head:

(a) Is two feet or 0.87 psi for distribution systems with three-sixteenth inch diameter orifices and larger; and

(b) Is five feet or 2.18 psi for distribution systems with orifices smaller than three-sixteenth inch diameter.

(5) If any portion of the pump fittings or effluent transport line is at a higher elevation than the drainfield, the distribution system must be equipped with an air vacuum release valve or other device to prevent siphoning.

(6) Duplex alternating pumps that provide timed dosing to the drainfield are required.

(7) Quick disconnect couplers or an equivalent quick disconnect system for all sewage pumps are required.

(8) If float switches are used, they must be mounted independent of the pump discharge and transport line.

(9) All mechanical and electrical components must be rated for wastewater applications.

(10) The control panel for the pressure distribution pumps must:

(a) Contain an elapsed time meter and a dose counter;

(b) Be in an enclosure that is secure from tampering and, if outside, resistant to weather; and

(c) Be equipped with both audible and visual alarms.

(11) The drainfield dose frequency must be a minimum of six doses per day.

(12) Except where subsurface drip distribution is used, the volume of each dose must be at least five times the internal volume of the pipe dosing network to be pressurized.

(13) The variation in orifice discharge rates within any one lateral must not be more than ten percent.

(14) The variation in orifice discharge rates over the entire distribution system must not be more than fifteen percent.

(15) Orifices must be no smaller than one-eighth inch in diameter.

(16) Orifices must be evenly distributed along the laterals and spaced as follows:

(a) In soil types 1, 2, and 3, and in sand filters, sand-lined trenches and beds, recirculating gravel filters and mounds, the maximum orifice spacing must be:

(i) One orifice per six square feet of infiltrative surface when not using gravelless chambers; or

(ii) One orifice per nine square feet of infiltrative surface when using gravelless chambers.

(b) In soil types 4 and 5, the maximum orifice spacing must be one orifice every six feet on center along the lateral.

(17) When using gravelless chambers with pressure distribution, the orifices must be oriented in the twelve o'clock position.

(18) Pressure distribution systems with design flows greater than 14,500 gpd must include:

(a) The capacity for remote or off-site operation and alarm notification; and

(b) A means to connect to an emergency power generator.

(19) Electrical components and wiring must comply with WAC 296-46B-501, Special occupancies NEC Class I locations.

(20) Electrical control and other electrical components must be approved by Underwriters Laboratories (UL) or an equivalent rating agency.