New Jersey Administrative Code › Title 7 - ENVIRONMENTAL PROTECTION › Chapter 9A - STANDARDS FOR INDIVIDUAL SUBSURFACE SEWAGE DISPOSAL SYSTEMS › Subchapter 9 - EFFLUENT DISTRIBUTION NETWORKS › Section 7:9A-9.7 - Design procedure for pressure dosing systems

Current through Register Vol. 56, No. 14, July 15, 2024
(a) The
				following procedure shall be used for disposal fields consisting of a disposal
				bed or disposal trenches, which are at equal elevations.
1. Step One: Determine the length, number and
				spacing of distribution laterals based upon the required size of the disposal
				field, determined as prescribed in
				7:9A-10.2, and the requirements for
				spacing of disposal trenches or the requirements for spacing of distribution
				laterals within disposal beds as prescribed in
				7:9A-10.3(d). The
				number of distribution laterals will also depend upon whether a central or end
				manifold arrangement is used.
2.
				Step Two: Select the hole diameter and spacing. The hole diameter shall be a
				minimum of one-quarter inch but no larger than one-half inch. The minimum
				allowed hole spacing shall be 30 inches. The maximum allowed hole spacing shall
				be 60 inches, except in the case of systems installed in soils or fill material
				with a permeability faster than six inches per hour or a percolation rate
				faster than 15 minutes per inch, in which case the maximum allowed hole spacing
				shall be 36 inches.
3. Step Three:
				Based upon the hole diameter and the hole spacing selected and the length of
				the laterals, determine the required diameter of laterals using Figure 14 of
				Appendix A. If the disposal field configuration is such that it is beyond the
				applicable limits of Figure 14, other methods of hydraulically evaluating
				adequate lateral diameter may be used subject to prior approval by the
				administrative authority.
4. Step
				Four: Pressure distribution systems shall be designed so that a minimum
				pressure head of 2.5 feet shall be maintained at the distal end of the
				laterals. Based upon the hole diameter and the design pressure head at the
				distal end of the laterals, determine the hole discharge rate from the table
				below. Determine the lateral discharge rate by multiplying the hole discharge
				rate by the number of holes per lateral.
Pressure
Discharge Rate (gallons
						  per minute)
Head (ft)
based on Hole Diameter
						  (inches)
1/4
5/16
3/8
7/16
1/2
2.5
1.18
1.85
2.66
3.63
4.73
3.0
1.28
1.99
2.87
3.91
5.10
3.5
1.40
2.19
3.15
4.29
5.60
4.0
1.47
2.30
3.31
4.51
5.89
4.5
1.59
2.48
3.57
4.86
6.35
5.0
1.65
2.57
3.71
5.04
6.59
5.
				Step Five: Based upon the number of laterals and the lateral spacing, determine
				the manifold length. Based upon the manifold length, the lateral discharge rate
				and the number of laterals, using Figure 15 of Appendix A, determine the
				required manifold diameter. If the disposal field configuration is such that it
				is beyond the applicable limits of Figure 15, other methods of hydraulically
				evaluating proper manifold diameter may be used subject to approval by the
				administrative authority.
6. Step
				Six: Determine the necessary system discharge rate by multiplying the lateral
				discharge rate by the number of laterals; and
7. Step Seven: For pump systems, select the
				proper pump as follows:
i. Using Figure 16 of
				Appendix A, determine the friction head based upon the system discharge rate
				and the diameter and length of the delivery pipe. If the system discharge rate
				is such that it is beyond the applicable limits of Figure 16, then other
				methods of determining friction head in the delivery pipe may be used subject
				to approval by the administrative authority.
ii. Calculate the total operating head, H[t],
				using the following formula:
H[t], ft = H[f] + H[e] + H[p]
where:
H[f] is the friction head, in feet, determined in (a)7i
				  above;
H[e] is the elevation head, in feet, calculated by
				  subtracting the dosing tank low water elevation from the elevation of the
				  invert of the distribution laterals; and
H[p] is the design pressure head to be maintained at the
				  distal end of the laterals, in feet.
iii. Choose a pump which is rated by the
				manufacturer to deliver a flow rate equal to or greater than the system
				discharge rate calculated in Step Six when working against a total dynamic head
				equal to the total operating head calculated in (a)7ii above.
8. Alternate Step Seven: For
				systems using syphons, determine the syphon elevation as follows:
i. Determine the friction head in the
				delivery pipe as in (a)7i above.
ii. Calculate the velocity head using the
				following formula:
H[v], ft = (D/A)[LESS THAN]2[GREATER THAN]/2g
where:
D = System Discharge Rate, ft[LESS THAN]3[GREATER
				  THAN]/sec.
= (System Discharge Rate, gpm) (1 ft[LESS THAN]3[GREATER
				  THAN]/7.48 gal) (1 min/60 sec)
A = pipe area, ft[LESS THAN]2[GREATER THAN]
= [(internal pipe diameter, in/2) (1 ft/12 in)][LESS
				  THAN]2[GREATER THAN] (3.14)
g = 32.2 ft/sec[LESS THAN]2[GREATER THAN]
iii. Calculate the total operating head,
				H[t], by the following equation:
H[t], ft = H[f] + H[v] + H[p]
where:
H[f] is the friction head, in feet, determined from Figure 16
				  of Appendix A.
H[v] is the velocity head, in feet, determined in (a)8ii
				  above.
H[p] is the design pressure head to be maintained at the
				  supply end of the laterals, in feet.
iv. Choose a siphon rated to discharge at a
				flow rate equal to or greater than the system discharge rate. Install the
				siphon at an elevation such that the siphon invert is higher than the invert of
				the distribution laterals by a distance equal to the total operating head
				calculated in (a)7iii above.