25 Pa. Code § 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 Area | Minimum Manifold Diameter |
| 200 to 1,199 | 1 1/2" |
| 1,200 to 2,500 | 2" |
(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.
Notes
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).
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