N.J. Admin. Code § 7:9A-9.2 - Dosing tanks

Current through Register Vol. 54, No. 7, April 4, 2022

(a) A dosing tank using a siphon or pump is required for systems using gravity or pressure dosing and shall meet the requirements of (b) through (f) below.
(b) The minimum capacity of dosing tanks using pumps shall be determined as follows:
1. Dosing tanks using pumps shall have sufficient capacity to distribute septic tank effluent equally to all parts of the disposal field during each dosing cycle and to provide adequate reserve storage capacity in the event of a pump malfunction. The total liquid capacity shall be great enough to accommodate the minimum required dose volume (V[d]) determined as prescribed in (b)2 below, plus the minimum required reserve storage capacity determined as prescribed in (b)3 below. Additional volume must be provided above the pumping level to accommodate the volume of water displaced by the pump and controls (V[pd]) as well as any quantity of effluent which will drain back into the dosing tank when the pump shuts off at the end of a dosing cycle (V[cp]). Additional volume must be provided below the pumping level so that the pump may be placed on a pedestal, above the dosing tank bottom, to prevent the pump from drawing in air or whatever solids may accumulate in the bottom of the dosing tank.
2. The dose volume (V[d]) shall be determined based upon the soil permeability or percolation rate, daily volume of sewage (Q) and the total internal volume of the distribution network (V), as shown below. In the case of pressure dosing systems, the volume of the distribution network, V, shall include the volume of the delivery pipe (V[p]), the manifold (V[m]) and the laterals (V[l]).

Soil Percolation Required Required
Permeability Rate Dose Volume Dose Volume
(in/hr) (min/in) Gravity Dosing Pressure Dosing
6-20 3-15 minimum of 75 percent minimum of 10V<2>
V<1>
maximum of 25 percent Q maximum of 25 percent
Q
0.2-6 15-60 minimum of 75 percent V minimum of 10V
maximum of 100 percent Q maximum of 100 percent
Q

[LESS THAN]1[GREATER THAN] In cases where 75 percent V is larger than 25 percent Q, the 25 percent Q maximum rather than the percent minimum shall be observed.

[LESS THAN]2[GREATER THAN] In cases where 10V is larger than 25 percent Q, the 25 percent Q maximum rather than the 10V minimum shall be observed.

3. Reserve capacity is the inside volume of the dosing tank which lies between the level at which the high-water alarm switch is set and the invert elevation of the tank inlet, as shown in Figure 13 of Appendix A. A minimum reserve capacity equal to the daily volume of sewage shall be required except where a stand-by pump is provided which is equivalent in performance capacity to the primary pump and which will switch on automatically in the event that the primary pump malfunctions.
(c) The capacity of dosing tanks using siphons shall be adequate to provide the required dose volume determined as prescribed in (b)2 above. No reserve capacity is required when a siphon is used.
(d) All dosing tanks shall meet the following requirements regardless of whether a pump or siphon is used.
1. The requirements for the construction of dosing tanks shall be the same as those prescribed for septic tanks in 7:9A-8.2(e). Dosing tanks may be constructed as a separate unit or may share a common wall with the pretreatment unit.
2. Materials used for the construction of dosing tanks shall be the same as those allowed for septic tanks as prescribed in 7:9A-8.2(h).
3. Dosing tanks shall be constructed in a manner that will permit venting of the disposal area.
4. Installation requirements for pre-fabricated dosing tanks shall be the same as those for septic tanks, as prescribed in 7:9A-8.2(f).
5. Dosing tanks shall be placed on a firm and stable foundation so that the potential for differential settling or shifting is minimized.
6. Inlets shall be above the highest water level attained when the entire reserve capacity is full. Outlets for dosing tanks using siphons shall conform with the manufacturer's recommendations.
7. Dosing tanks shall be readily accessible for service and repair. A removable watertight cover or a manhole with a removable watertight cover shall be provided. Manholes shall be a minimum of 24 inches in diameter or 24 inches square and shall be located directly over the pump or siphon. The top of the tank or manhole riser, at a minimum, shall be extended to within six inches of finished grade and be equipped with a watertight cover. Where manholes are extended flush with finished grade, the cover shall be bolted or locked to prevent access by children and shall be of cast iron when a concrete riser is used. When the top of the tank or manhole is not extended to finished grade, covers shall be constructed of precast reinforced concrete, fiberglass, polyethylene or other materials as specified by a licensed professional engineer and approved by the administrative authority. The location of the manhole shall be marked on the ground surface by means of a permanent, non-corrosive marker a minimum of three inches in diameter.
8. Requirements for backfilling around dosing tanks shall be the same as for septic tanks, as prescribed in 7:9A-8.2(n).
(e) Dosing may be accomplished by means of an automatic siphon when the low water level in the dosing tank is at a higher elevation than the invert of the highest distribution lateral. When a siphon is used the following requirements shall be met:
1. Siphons shall be constructed of durable materials not subject to corrosion by acid or alkali.
2. Extreme care shall be utilized in the installation of siphons. The installation shall conform exactly and in all details to the manufacturer's recommendations and specifications.
3. The horizontal dimensions of the dosing tank shall be adjusted so that the volume obtained by multiplying the manufacturer's rated siphon drawing depth by the internal horizontal area of the tank will be equal to the required dose volume determined as prescribed in (b)2 above.
4. When installation is complete, the siphon shall be primed by filling it with water at which time the siphon shall be checked for leaks as evidenced by air bubbles rising from the bell casing or piping. Any leaks shall be repaired before final approval is given.
5. In gravity dosing systems, when the delivery pipe between the dosing tank and the distribution box or distribution network is long, the siphon invert shall be set at an elevation sufficiently higher than the invert of the highest distribution lateral to compensate for any head losses due to friction in the connecting pipe. Friction head shall be determined using Figure 16 of Appendix A.
6. In pressure dosing systems, the invert of the siphon shall be set higher than the invert of the distribution laterals by a distance equal to the total operating head determined as prescribed in 7:9A-9.7(a) ii.
7. For facilities from which large quantities of septic tank effluent may be discharged at one time, the design engineer shall make certain that the siphon discharge rate will not be exceeded by the maximum expected rate of inflow at time of peak flow.
8. Each dosing tank shall be equipped with a cycle counter activated by a weighted float or mercury switch to facilitate monitoring of siphon performance.
9. Dosing tanks using siphons shall be equipped with an overflow to the distribution box or distribution network and a high-water alarm meeting the requirements of (f)7iii below. The invert of the overflow shall be just above the level of the high-water alarm switch which shall be several inches above the normal high-water level of the dosing tank.
(f) Dosing may be accomplished by means of a pump when either gravity dosing or pressure dosing is used. Duplicate pumps may be required by the administrative authority. The following requirements shall be met:
1. The pump must be rated by the manufacturer to handle septic tank effluent and all equipment must be listed and identified for the intended use as determined by the design.
2. Pumps used for gravity dosing systems must be rated by the manufacturer, as indicated by the manufacturer's pump performance curve, to be capable of delivering the total required dose volume within a period of 15 minutes or less when working against a total dynamic head equal to the total design operating head. For the purpose of making this determination, the total design operating head shall be considered as the sum of the elevation head and the friction head calculated as prescribed in 7:9A-9.7(a)7.
3. Selection of an adequate pump for pressure dosing is part of the design procedure for pressure dosing systems and shall be performed in conformance with 7:9A-9.7(a).
4. Pumps shall be set on a pedestal so that the intake is elevated several inches above the bottom of the dosing tank.
5. Easy or "quick-disconnect" couplings shall be used to facilitate removal of the pump for servicing.
6. For facilities from which large quantities of septic tank effluent may be discharged at one time, the design engineer shall make certain that the pump discharge rate will not be exceeded by the maximum expected rate of inflow at times of peak flow.
7. The operation of the pump shall be controlled by means of automatic switches which are activated by the rising and falling level of effluent in the dosing tank. Such switches shall meet the following requirements:
i. Switches shall be able to withstand the humid and corrosive atmosphere in the dosing tank. Mercury or weighted float type switches are suitable for this purpose. Pressure-diaphragm type switches are prohibited.
ii. The pump-on and pump-off switches shall be set at appropriate levels to provide a dose volume as required in 7:9A-9.2(b)2. The pump-off switch shall be set six inches above the pump intake. The pump-on switch shall be set at a distance, d, above the pump-off switch, which is calculated by means of the following formula:

d, in = (V[d] + V[cp] + V[pd]) x (1 ft[LESS THAN]3[GREATER THAN]/7.48 gal) x (12 in/1 ft)/(A)

where:

V[d] is the required dose volume, in gallons, determined as prescribed in 7:9A-9.2(a)2;

V[cp] is the internal volume of all pipes which will drain back into the dosing tank at the end of a dosing cycle, in gallons;

V[pd] is the displacement, in gallons, of pump and controls; and

A is the internal horizontal area of the dosing tank, in square feet.

iii. A high-water alarm switch shall be set four inches above the pump-on switch and shall activate visible and audible alarms which can be readily seen and heard by occupants within the building served. The high-water alarm switch shall meet the same requirements prescribed for pump-control switches in (f)7i above. The alarm and its switch shall not be on the same electrical circuit as the pump and its switches.
iv. All electrical splices, junction boxes, contacts and relays shall be located outside of the dosing tank and a gas-tight seal shall be provided where electrical conduits enter the tank.
v. All electrical service lines to or from the pump control panel shall be installed in electrical conduit.

Notes

N.J. Admin. Code § 7:9A-9.2
Amended by R.1993 d.294, effective 6/21/1993.
See: 24 N.J.R. 1987(a), 25 N.J.R. 2704(b).
Amended by R.1999 d.314, effective 9/20/1999.
See: 31 N.J.R. 1416(a), 31 N.J.R. 2741(a).
In (b), inserted symbols throughout; and in (f)7ii, changed N.J.A.C. reference.
Amended by R.2012 d.066, effective 4/2/2012.
See: 43 N.J.R. 478(a), 44 N.J.R. 1047(a).
In (d)8, updated the N.J.A.C. reference; in (f)7iv, inserted "splices, junction boxes,"; and in (f)7v, inserted "to or", deleted "home or facility to the" preceding "pump", and substituted "installed in" for "protected by".

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