Section 0400-48-01-.12 - DESIGN OF DOSING SYSTEMS(1) Dosing Chamber The dosing chamber, access riser and riser cover shall be watertight, structurally sound and not subject to excessive corrosion or decay. The dosing chamber shall be of one (1) compartment design. They shall be of such construction and size as specified in paragraphs (2), (3), and (4) of Rule0400-48-01-.09, excluding those requirements strictly relating to two (2) compartments.
(a) The access riser shall have a minimum diameter of twenty-four (24) inches and extend to the finished grade or above. Rectangular or square risers may be allowed provided the size of the opening provides the equivalent access as a circular riser. An access riser with a minimum diameter of sixteen (16) inches may be used provided the threaded union on the pump outlet pipe is located within two (2) feet of the top of the access riser. The access riser shall be located near the outlet end of the tank, directly above the pump or siphon, supply line, switches and other fixtures.(b) The dosing chamber volume shall be a minimum of two (2) times daily wastewater flow except when an alternate pump equipped with an in-tank supply line and switch assembly is on-site and ready for use. If the alternate pump, in-tank supply line and switch assembly is on-site and ready for use, the minimum dosing chamber volume shall be a total of the volume of water below the static level plus the designed dosing volume plus one-half (1/2) the daily flow.(2) Design of Pumps, Pipes and Controls(a) The gallons per minute (gpm) flow in a dosing system shall be determined by the distribution network it doses. If the distribution network is of such design that the gpm flow is not confined to specific amounts, the minimum flow shall be ten (10) gpm.(b) Total dynamic head (TDH) shall be determined by adding the following: 1. Elevation head is the difference in elevation between the bottom of the pump and the highest ground elevation at the disposal field. The minimum assigned elevation head shall be five (5) feet.2. Friction head shall be determined from Appendix III plus fittings loss.3. Pressure head is the amount of pressure desired at the distribution network and shall be a minimum of one (1) foot.(c) When pumping uphill, a check valve must be utilized if the volume of effluent which will flow back into the tank exceeds one-fourth (1/4) daily flow.(d) The dosing volume shall be between one-fourth (1/4) and one-half (1/2) daily flow, except in those situations where the minimum dose exceeds one-half (1/2) daily flow, then the calculated minimum dose shall be the dosing volume.(e) Pipe and Fittings 1. All pipe materials shall be a minimum of Schedule 40 PVC.2. All fittings shall be pressure fittings.3. All connections shall be adequately cleaned with cleaning solvent and glued with PVC solvent cement.4. If used, the gate or globe valve(s) and check valve shall be either bronze or PVC.5. The supply line shall be designed and installed to drain after each use unless system design requires a check valve.(f) Pump, Float Controls and Alarm System1. The pump shall be a good quality, effluent pump and be of sufficient size to meet or exceed the gallons flow requirement and the total dynamic head requirement set forth by the system.2. The pump float controls must be adjustable.(i) The controls must be sealed against entry of effluent or gases.3. The alarm system. (i) The high water alarm shall be required and consist of an audible and visible alarm located in a visible place and clearly marked "wastewater system alarm".(ii) The alarm and alarm switches shall be placed on a separate electrical circuit from the pump power line.(iii) The alarm float control shall be placed so as to be activated when the pump chamber water level rises above the "pump on" float control.(g) Pump and Controls 1. The pump must be placed so that the intake is a minimum of eight (8) inches above the bottom of the pump chamber.2. As a means to remove the pump from the pump chamber, a material of sufficient strength and durability must be secured to the pump and access riser.3. The pump control must be positioned so the "pump off" switch is slightly above the top of the pump and the "pump on" switch is at the desired dosing depth. The "pump off" switch for pumps specifically designed to operate with the pump motor casing exposed to air, may be located at a lower elevation provided an adequate depth of wastewater is maintained above the pump intake to insure that the pump intake will not draw in air.4. The pump outlet pipe must be connected to the supply manifold with a threaded union or similar device.5. When a disposal system requires a specific pressure head, a PVC or bronze, gate or globe valve shall be placed in the supply line.6. If the effluent is pumped downhill, a five-thirty seconds (5/32) inch siphon breaker hole must be drilled in the bottom of the supply line inside the pump tank, above the liquid level.7. All electrical installations shall be installed to meet the current wiring methods of the current edition of the "National Electric Code" (NEC) adopted by the State Fire Marshall's office.(3) Where a dosing system is required in accordance with part (3)(c)1 of Rule 0400-48-01-.07, and where elevation permits gravity flow to be utilized, dosing siphons may be used in lieu of pumps to distribute septic tank effluent to the disposal field. (a) Dosing Siphons 1. The single dose volume for siphons shall not exceed a total of one-fourth (1/4) of the daily flow. In the case of dual siphons, this limit shall apply to the single dose volume for each individual siphon.2. If the absorption field is of divided design, dual siphons designed for automatic alternating operation may be installed within a single dosing chamber.3. Dosing siphons shall be fabricated of materials that are non-corrosive, and are of adequate structural strength and durability. Siphons shall be mounted and installed to the precise elevations required to ensure proper operation.(b) Dosing Siphon Chambers 1. The dosing siphon chamber size and volume, and selected siphon drawdown, shall be coordinated in the design so as to produce the desired single dose volume.2. Dosing siphon chambers shall be watertight single compartment round or rectangular precast reinforced concrete structures with an access riser of twenty-four (24) inch minimum diameter.3. Dosing siphon chambers shall be of large enough dimension to allow working room for repair and replacement as required.(c) Splash boxes shall be installed at the head of each absorption field in order to reduce the entry velocity of the dosing chamber effluent. The access riser and cover shall be watertight and have a minimum diameter of twenty-four (24) inches, extending to the finished grade or above, shall be installed on each splash box to allow for inspection and flow verification. Splash box volume and exit pipe dimension shall be adequate to prevent splash box overflow and/or siphon interruption.Tenn. Comp. R. & Regs. 0400-48-01-.12
Original rule filed June 20, 2013; effective September 18, 2013. Rule renumbered from1200-01-06.Authority: T.C.A. §§ 68-221-401 et seq. and 4-5-201 et seq.