N.J. Admin. Code § 7:14A-23.17 - Settling tanks

(a) Multiple units or independent compartments shall be provided except in small installations of less than 150,000 gpd design flows.

(b) Channels shall be designed to maintain a velocity of one foot per second at 50 percent of design flow.

(c) Baffling shall be provided to dissipate inlet velocity and diffuse flow equally across the cross section of the tank. Baffles shall also be provided to retain scum in primary tanks. Scum collectors shall be provided.

(d) Weirs shall be adjustable.

(e) The minimum slope of the side walls of sludge hoppers shall be 1.7 vertical to 1.0 horizontal.

(f) The use of upward flow settling tanks may be considered when accompanied by supporting data on their hydraulic characteristics and results of operation in actual plants.

(g) Walls of settling tanks shall extend at least 18 inches above the surrounding ground surface.

(h) Mechanical means shall be provided for the collection and removal of sludge from settling tanks, and shall meet the following design requirements:

1. Primary tanks, except those preceding the activated sludge process, shall have a surface settling rate that does not exceed 600 gallons per square foot per day of design flow, and a minimum water depth of six feet;

2. Inlets shall be designed to dissipate inlet velocity promptly so as to diffuse the flow and to prevent short-circuiting; and

3. Adjustable outlet weirs shall be provided.

(i) Final settling tanks shall be designed according to the following:

Maximum Surface
Settling Rate
Side Water	gals./sq. ft./day
Type of Treatment	Depth	(At Design Flow)
Standard Rate Trickling Filter	6 feet minimum	1,000
High Rate Trickling Filter	8 feet minimum	800
Activated Sludge
(2.0 m.g.d. and less design flow)	8 feet minimum	800
Activated Sludge
(Over 2.0 m.g.d. design flow)	10 feet minimum	1,000

Notes

N.J. Admin. Code § 7:14A-23.17