Section 410IAC6-8.3-78. Subsurface trench pressure distribution on-site sewage systems: design and construction requirements

   (a) Subsurface trench pressure distribution on-site sewage systems shall meet all of the requirements of:

(1) section 74 of this rule; and

(2) this section.

  (b) Each pipe connected to an outlet in the manifold of a subsurface pressure distribution on-site sewage system shall be counted as a separate distribution lateral.

  (c) An inline residual pressure of two and five-tenths (2.5) to three (3) feet of head shall be maintained in the pressure distribution lateral at the highest elevation in the soil absorption system during pumping.

  (d) The effluent pump shall be sized and its controls set as follows:

(1) When a subsurface pressure distribution on-site sewage system is designed using a soil loading rate of less than one and two-tenths (1.2) gallons per day per square foot, the pump shall deliver the DDF to the soil absorption field in each dose.

(2) When a subsurface pressure distribution on-site sewage system is designed using a soil loading rate of one and two-tenths (1.2) gallons per day per square foot, the pump shall deliver four (4) doses each day, each dose being approximately one-fourth (1/4) of the DDF.

  (e) The effluent force main shall drain unless it is installed below the frost line, as listed in Table VIII in section 76(d) of this rule and designed so that no effluent remains in any portion of the effluent force main located above the frost line.

  (f) The liquid holding capacity of the dosing tank shall be determined as follows:

(1) If the effluent force main drains to the subsurface pressure distribution on-site sewage system, or if it does not drain between doses, the dosing tank volume shall be the dose calculated using subsection (d)(1) or (d)(2), whichever is applicable.

(2) If the effluent force main drains back to the dosing tank, the dosing tank volume shall be the dose calculated using subsection (d)(1) or (d)(2), whichever is applicable, plus the volume contained in the effluent force main.

(3) Additional dosing tank capacity must be provided to:

(A) keep the dosing tank effluent pump submerged at all times; and

(B) provide sufficient freeboard for a high water alarm.

  (g) For installation for a subsurface trench pressure distribution on-site sewage system, the effluent force main shall be stabilized and backfilled without damaging the pipe with debris-free soil material to prevent the movement of effluent along the outside of the pipe.

  (h) The minimum inside diameter of the effluent force main shall be one and one-half (1 1/2) inches. The maximum inside diameter of the effluent force main shall be four (4) inches.

  (i) Tables IX and X in section 76(h) of this rule shall be used in determining friction losses in the effluent force mains and manifold when plastic pipe is used.

  (j) The minimum inside diameter of the manifold shall be one (1) inch. The maximum inside diameter of the manifold shall be six (6) inches. The manifold pipe diameter shall be determined from Table XI as follows:

  (k) The minimum inside diameter of the pressure distribution laterals from the manifold shall be one (1) inch. The maximum inside diameter of the pressure distribution laterals shall be three (3) inches.

  (l) Table XII, as follows, may be used to calculate pipe volumes:

Table XII - Pipe Volume for Various Diameter Pipes (gal/ft)
Pipe Diameter (in)	1	1 1/4	1 1/2	2*	3*	4*
Volume (gal/ft)	.045	.078	.106	.174	.384	.650
*These diameters and pipe volumes are for calculating the total volume of the effluent force main. They are not used for calculating volumes of pressure distribution laterals.

  (m) The pressure distribution laterals shall have one (1) row of holes spaced in accordance with Table XIII as follows:

Table XIII - Soil Loading Rates Versus Pressure Distribution Lateral Hole Spacing for Subsurface Trench Pressure Distribution Systems
Soil Loading Rates: Gallons per Day per Square Foot	Lateral Hole Spacing Feet Between Holes
1.2	3
0.75	3 to 5
0.5 and 0.6	3 to 6
0.25 and 0.3	3 to 7

  (n) The holes in the pressure distribution laterals shall be placed in the trenches facing down, and all burrs shall be removed from the edges of the holes.

  (o) The hole size in the pressure distribution laterals shall be one-fourth (1/4) inch.

  (p) The perforation discharge rate shall be determined in accordance with the formula used to compute the flow from a hole in the pressure distribution lateral at inline head as follows:

Where:	Q	=	the volume of the flow from the hole.
	d	=	the diameter of the hole in the pipe.
	H	=	the inline head at the hole.
Table XIV, as follows, gives the discharge rates at varying heads that would be obtained using the formula above in which "d" equals one-fourth (1/4) inch diameter holes:

Table XIV - Perforation Discharge Rates in GPM at Varying Inline Heads for 1/4 Inch Diameter Hole Size
Inline Head (feet)	Perforation Discharge Rate (gallons per minute)
2.5	1.17
3.0	1.28
3.5	1.38
4.0	1.47
4.5	1.56
5.0	1.65
5.5	1.73

  (q) Effluent pump selection for soil absorption systems using pressure distribution shall be based on the manufacturer's pump curves for the required pump discharge rate at the total head imposed on the pump. The pump discharge rate for level on-site sewage systems is calculated by using the following formula:

Pump discharge rate = Perforation discharge rate × total number of perforations

To obtain the pump discharge rate required for sloping sites, the rate must be calculated individually for each pressure distribution lateral using the pump discharge rate formula based on the pressure on that line, and the sum of the calculated discharge rates determined for each individual line.

  (r) The end of each pressure distribution lateral shall be capped, and a one-fourth (1/4) inch hole shall be drilled in the upper half of the end cap.

  (s) All joints, including the end cap, shall withstand the pressures exerted on them. (Indiana State Department of Health; 410 IAC 6-8.3-78; filed Oct 19, 2012, 2:06 p.m.: 20121114-IR-410120156FRA)