NAC445A.9664. Dosing tanks.

     1. Dosing tanks are required where:

     (a) It is necessary to raise the elevation of wastewater for further treatment or disposal of sewage;

     (b) Intermittent dosing of the disposal field is desirable;

     (c) A pressure distribution system is used;

     (d) More than 500 linear feet of absorption trench is required for the on-site sewage disposal system; or

     (e) Soil conditions exist that require dosing, as determined by the design engineer or the Division or other administrative authority.

     2. Alternate dosing is required for an on-site sewage disposal system with more than 1,000 feet of disposal pipe.

     3. The frequency of dosing must be at least four times per day and not more than eight times per day.

     4. A dosing tank must:

     (a) Be designed to withstand anticipated internal and external loads under both full and empty conditions.

     (b) Be easily accessible and have secured covers.

     (c) Be watertight and anti-buoyant.

     (d) Have risers to provide access to the inlet and outlet of the tank for inspection and service of internal components.

     (e) Be vented.

     5. A dosing tank must have sufficient volume for dosing which must be:

     (a) Sufficient to distribute effluent evenly to all parts of the distribution system.

     (b) Not less than 60 percent or more than 75 percent of the volume of the distribution piping, except for a pressure distribution system.

     (c) Not less than 5 times or more than 10 times the volume of the distribution piping in a pressure distribution system.

     6. A dosing tank must have a reserve volume which must be:

     (a) Equal to the volume of the dosing tank between the alarm switch for high levels of effluent and the bottom of the invert of the inlet pipe;

     (b) Of sufficient size to allow the on-site sewage disposal system to respond to a high-effluent level alarm within 2 hours or before the level of effluent in the dosing tank reaches the invert of the inlet pipe, whichever is longer; and

     (c) Increased by the design engineer if the on-site sewage disposal system is located in a remote area.

     7. If dosing tanks are screened, a reduction in the disposal field pipe opening may be allowed by the Division or other administrative authority.

     8. If dosing is performed by an electric pump:

     (a) The size of the pump must be determined according to the performance curves provided by the manufacturer of the pump, the flow rate required and the size of the pumping head as calculated by the design engineer.

     (b) The control system for the dosing tank must include a switch to turn on the pump, a switch to turn off the pump and an alarm switch for high levels of effluent. A switch must be able to withstand the humid and corrosive atmosphere inside the dosing tank. The design engineer must include in the design specifications an information sheet provided by the manufacturer of each pump, switch and alarm to be used in the dosing tank. The alarm switch must be on a circuit that is separate from the circuit for the switches that turn the pump on and off. The alarm float must be located at a level which provides the required emergency reserve volume pursuant to subsection 6. In lieu of floats, a dosing timer may be acceptable and the design engineer must justify its use in the design specifications.

     (c) All electrical contacts and relays must be mounted on the outside of the dosing tank to protect the electrical contacts from corrosion. The design engineer must take any action necessary to prevent sewer gases from traveling through the electrical conduit to the control box.

     (d) A source of backup power must be available for the electric pump.

     (e) The dosing tank vent must be located as far away from the control box as is practical, but in no case may the vent be closer than 3 feet from the control box.

     9. The following is a diagram of a typical dosing tank with an electric pump:

     (Added to NAC by Environmental Comm’n by R194-07, eff. 8-26-2008)