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The Pennsylvania Code website reflects the Pennsylvania Code changes effective through 54 Pa.B. 1806 (March 30, 2024).

25 Pa. Code § 73.44. Pressurized distribution design.

§ 73.44. Pressurized distribution design.

 (a)  General requirements are as follows:

   (1)  The piping used in a pressurized effluent system shall have watertight joints.

   (2)  Systems using pressure distribution shall meet the general requirements of § §  73.52, 73.53, 73.55, and 73.166.

   (3)  Delivery pipes from dosing pumps shall be installed to facilitate drainage of the distribution piping back to the dosing tank between doses.

 (b)  Seepage beds of 2,500 square feet or less shall meet the following design standards.

   (1)  Conveyance of effluent from the dosing tank to the absorption area shall be through a delivery pipe sized to minimize friction loss. Check valves shall be prohibited on delivery pipes. Where the system designer determines that water hammer may be a problem, thrust blocks may be installed on delivery pipes.

   (2)  When equally sized absorption areas are dosed simultaneously, a header pipe shall be used to connect the delivery pipe from the tank to the manifolds. The header pipe shall be sized to minimize friction loss. Effluent application rates per square foot of absorption areas served by a common header shall have a maximum design variation of 10%. If the distance from the treatment tank to the absorption area would cause excessive backflow into the dosing tank, a transfer tank may be used between the treatment tank or storage tank and dosing tank.

   (3)  Distribution of effluent to the individual laterals shall be by a central manifold extending into the absorption area from the delivery pipe or header. The manifold shall have the following minimum diameters:

Sq. ft. of Absorption AreaMinimum Manifold Diameter
200 to 1,1991 1/2"
1,200 to 2,5002"

   (4)  Laterals shall be extended from both sides of the manifold by opposing tees or a double sanitary tee.

   (5)  Laterals shall consist of 1 1/2 inch diameter pipe, with holes placed along the bottom of the pipe; an end cap shall be cemented on the terminal end of the lateral. Minimum hole size shall be 1/4 inch.

   (6)  The first hole in the lateral shall be 3 feet from the manifold. Additional holes shall be placed 6 feet on center with the last hole placed directly in the end cap.

   (7)  The maximum length of a lateral from the manifold to the end cap shall be 51 feet and contain nine holes.

   (8)  The location and spacing of the laterals shall conform to §  73.53(3)—(6) (relating to seepage beds).

   (9)  Opposing laterals may not differ in length by more than 6 feet.

   (10)  When less than the maximum length of lateral is used, as described in paragraph (7), the lateral shall be shortened in 6-foot sections with hole spacing maintained as required in paragraph (6).

   (11)  All systems shall be designed to maintain a minimum of 3 feet of head at the terminal end of each lateral.

   (12)  The minimum pump capacity (gpm) shall be calculated by multiplying the total number of discharge holes contained in the laterals of a proposed distribution layout by the gpm factor determined by the hole size at the design head level.

   (13)  Total pump head shall be calculated by addition of all losses incurred due to elevation changes, pipe and fitting friction losses, and the head level to be maintained at the terminal end of the lateral as specified in paragraph (11).

   (14)  For purposes of calculating head loss due to friction, head loss in the standard lateral as described in paragraph (7) shall be assumed to be 0. Head loss due to friction in pipe and fittings used in construction of the pressure system shall be calculated using a friction loss table for smooth-walled plastic pipe (C=150).

   (15)  When siphons are used in a pressure distribution system, each discharge hole shall be at least 5/16 inch in diameter. The discharge from all of the holes in the distribution system may not be less than the minimum rate of the siphon and may not vary from the average discharge rate of the siphon by more than 20%.

 (c)  Seepage beds of greater than 2,500 square feet shall meet the following design standards:

   (1)  The diameter of individual laterals, size and spacing of discharge holes, and minimum diameter of the distribution manifold may not be restricted by subsection (b) except that no discharge hole may be less than 1/4 inch for systems using pumps or 5/16 inch for systems using siphons.

   (2)  The maximum length of a lateral designed under this subsection or subsection (d) shall be 100 feet.

   (3)  Discharge rates from the individual holes of the lateral at design head shall be calculated using the sharp-edged discharge hole equation:

   gpm=11.82(d2) ( {PaCodeERROR}Unknown Element error{PaCodeERROR}Unknown Element error{PaCodeERROR}Unknown Element error{PaCodeERROR}Unknown Element error{PaCodeERROR}Unknown Element errorh)

   gpm=gallons per minute

   (d)=diameter of hole (inches)

   (h)=head to be maintained at the terminal ends of the lateral (in feet).

   (4)  All piping and fittings in the system shall be sized to minimize friction losses to provide as uniform distribution of effluent as possible.

   (5)  The design head at the terminal end of the last lateral shall be at least 3 feet.

   (6)  The head loss due to friction from the beginning of the distribution manifold to the terminal end of the last lateral may not exceed 15% of the head level to be maintained at the terminal end of the lateral.

   (7)  Spacing of laterals and discharge holes in the laterals shall provide for uniform distribution of the effluent over the seepage bed.

   (8)  The arrangement of laterals and discharge holes shall result in the discharge holes being spaced at the apexes of either squares or equilateral triangles.

     (i)   The maximum spacing between discharge holes shall be 10 feet where an equilateral triangle pattern is utilized.

     (ii)   The maximum spacing between discharge holes shall be 8 feet where a square pattern it utilized.

   (9)  The minimum pump capacity shall equal the total discharge from all holes in the laterals when operating at designed head.

   (10)  The permittee shall conduct a test pressurization of the completed distribution system in the presence of the sewage enforcement officer prior to covering the piping system from view. During the test, the permittee shall confirm that all joints are watertight and that a discharge is occurring from each hole.

 (d)  Design of pressure distribution in trenches shall comply with the following:

   (1)  Subsection (c)(1)—(4) and (10) applies to design of trenches utilizing pressurized effluent distribution.

   (2)  Variation in head in the laterals caused by differences in elevation or friction losses shall be compensated for by individual design of the laterals.

   (3)  The effluent application rate per square foot of any two trenches served by a common dosing tank shall have a maximum design variation of 10%.

   (4)  Equalization of loading may be accomplished by variation of discharge hole diameter between trenches, variation of spacing of discharge holes between trenches or another method approved by the Department or sewage enforcement officer.

   (5)  The maximum spacing between discharge holes is 10 feet.

   (6)  The manifold for a trench system shall be placed on undisturbed soil a minimum of 6 inches above the trench bottom.

   (7)  A minimum isolation distance of 3 feet shall be maintained between the manifold and the beginning of any trench. The individual laterals in the trench shall be connected to the manifold using unperforated pipe. The area beneath the manifold and connecting pipe shall consist of undisturbed or compacted soil.

   (8)  The design head at the terminal end of each lateral shall be at least 3 feet.


   The provisions of this §  73.44 amended under section 9 of the Pennsylvania Sewage Facilities Act (35 P. S. §  750.9); The Clean Streams Law (35 P. S. § §  691.1—691.1001); and section 1920-A of The Administrative Code of 1929 (71 P. S. §  510-20).


   The provisions of this §  73.44 adopted August 2, 1971, effective August 14, 1971, 1 Pa.B. 1649; amended August 30, 1974, effective September 16, 1974, 4 Pa.B. 1805; amended January 21, 1983, effective January 22, 1983, 13 Pa.B. 508; corrected May 22, 1992, effective May 13, 1983, 22 Pa. B. 2715; amended November 7, 1997, effective November 8, 1997, 27 Pa.B. 5877. Immediately preceding text appears at serial pages (217327) to (217329).

Cross References

   This section cited in 25 Pa. Code §  73.53 (relating to seepage beds); and 25 Pa. Code §  73.161 (relating to general).

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