| (i) Mandrel sizing. The rigid mandrel shall have an
outside diameter equal to 95% of the inside diameter of the pipe.
The inside diameter of the pipe, for the purpose of determining the
outside diameter of the mandrel, shall be the average outside diameter
minus two minimum wall thicknesses for outside diameter controlled
pipe and the average inside diameter for inside diameter controlled
pipe, all dimensions shall be per appropriate standard. Statistical
or other "tolerance packages" shall not be considered in mandrel sizing.
(ii) Mandrel design. The rigid mandrel shall be constructed
of a metal or a rigid plastic material that can withstand 200 psi
without being deformed. The mandrel shall have nine or more "runners"
or "legs" as long as the total number of legs is an odd number. The
barrel section of the mandrel shall have a length of at least 75%
of the inside diameter of the pipe. A proving ring shall be provided
and used for each size mandrel in use.
(iii) Method options. Adjustable or flexible mandrels
are prohibited. A television inspection is not a substitute for the
deflection test. A deflectometer may be approved for use on a case-by-case
basis. Mandrels with removable legs or runners may be accepted on
a case-by-case basis.
(5) Bedding: trenching, bedding, and backfill. The
width of the trench shall be minimized, but shall be ample to allow
the pipe to be laid and jointed properly and to allow the backfill
to be placed and compacted as needed. The trench sides shall be kept
as nearly vertical as possible. As used herein, a trench shall be
defined as that open cut portion of the excavation up to one foot
above the pipe. The engineer shall specify the maximum trench width.
The width of the trench shall be sufficient, but no greater than necessary,
to ensure working room to properly and safely place and compact haunching
materials. The space must be wider than the compaction equipment used
in the pipe zone. A minimum clearance of four inches below and on
each side of all pipes to the trench walls and floor shall be provided.
Bedding Classes A, B, or C, as described in ASTM C 12 (ANSI A 106.2),
Water Environment Federation (WEF) Manual of Practice (MOP) Number
9 or American Society of Civil Engineers (ASCE) MOP 37 shall be used
for all rigid pipes, provided that the proper strength pipe is used
with the specified bedding to support the anticipated load(s). Embedment
Classes IA, IB, II, or III, as described in ASTM D-2321 (ANSI K65.171)
shall be used for all flexible pipes, provided the proper strength
pipe is used with the specified bedding to support the anticipated
load, except that ASTM D-2680 may be used if the pipe stiffness is
200 psi or greater. Secondary backfill shall be of suitable material
removed from excavation except where other material is specified.
Debris, large clods or stones greater than six inches in diameter,
organic matter, or other unstable materials shall not be used for
backfill. Backfill shall be placed in such a manner as not to disturb
the alignment of the pipe. Where trenching encounters extensive fracture
or fault zones, caves, or solutional modification to the rock strata,
construction shall be halted and an engineer shall provide direction
to accommodate site conditions. Water line crossings shall be governed
by special backfill requirements specified in §317.13 of this
title (relating to Appendix E--Separation Distances).
(6) Site inspections. The executive director shall,
on a random basis, perform site inspections.
(7) Protecting public water supply. Water lines and
sanitary sewers shall be installed no closer to each other than nine
feet between outside diameters. Where this cannot be achieved, the
sanitary sewer shall be constructed in accordance with §317.13
of this title and §290.44(e)(1) of this title (relating to Water
Distribution). Separation distances between sanitary sewer systems
and water wells, springs, surface water sources, and water storage
facilities shall be installed in accordance with the requirements
of §290.41(c)(1), (d)(1), (e)(1)(C), and (e)(3)(A), and §290.43(b)(3)
of this title (relating to Water Sources; and Water Storage, respectively),
as appropriate. Where rules governing separation distance are in conflict,
the most strict rule shall apply. No physical connection shall be
made between a drinking water supply, public or private, and a sewer
or any appurtenance. An air gap of a minimum of 18 inches or two pipe
diameters, whichever is greater, shall be maintained between all potable
water outlets and the maximum water surface elevation of sewer appurtenances.
All appurtenances shall be designed and constructed so as to prevent
any possibility of sewage entering the potable water system.
(8) Excluding surface water. Proposals for the construction
of combined sewers will not be approved. Roof, street, or other types
of drains which will permit entrance of surface water into the sanitary
sewer system shall not be acceptable.
(9) Active geologic faults. For systems to be located
in areas of known active geologic faults, the design engineer shall
locate any faults within the area of the collection system and the
system shall be laid out to minimize the number of sewers crossing
faults. Where crossings are unavoidable, the engineering report shall
specify design features to protect the integrity of the sewer. Consideration
should be given to joints providing maximum deflection and to providing
manholes on each side of the fault so that a portable pump may be
used in the event of sewer failures. Service connections within 50
feet of an active fault should be avoided.
(10) Erosion control. Erosion or sedimentation control
that minimizes the effects of runoff shall be provided during the
construction phase of a project. This requirement will be reviewed
on a case-by-case basis.
(b) Capacities.
(1) Sources. The peak flow of domestic sewage, peak
flow of waste from industrial plants, and maximum infiltration rates
shall be considered in determining the hydraulic capacity of sanitary
sewers.
(2) Existing systems. The design of extensions to sanitary
sewers should be based on the data from the existing system. If this
is not possible, the design shall be based on data from similar systems
or paragraph (3) of this subsection, new systems.
(3) New systems. New sewers shall be sized using an
appropriate engineering analysis of existing and future flow data.
The executive director shall have the authority to determine the reliability
and appropriateness of the data utilized for sizing the system. In
the absence of local reliable flow data and engineering analysis,
new sewer systems shall be designed on the basis of an estimated daily
sewage flow contribution as shown in the table in §317.4(a) of
this title (relating to Wastewater Treatment Facilities). Minor sewers
shall be designed such that when flowing full they will transport
wastewater at a rate approximately four times the system design daily
average flow. Main trunk, interceptor, and outfall sewers shall be
designed to convey the contributed minor sewer flows.
(c) Design details.
(1) Minimum size. No sewer other than service laterals
and force mains shall be less than six inches in diameter.
(2) Slope. All sewers shall be designed and constructed
with slopes sufficient to give a velocity when flowing full of not
less than 2.0 feet per second. The grades shown in the following table
are based on Manning's formula with an assumed "n factor" of 0.013
and constitute minimum acceptable slopes. The minimum acceptable "n"
for design and construction shall be 0.013. The "n" used takes into
consideration the slime, grit, and grease layers that will affect
hydraulics or hinder flow as the pipe matures.
Attached Graphic
(3) High velocity protection. Where velocities greater
than ten feet per second will occur when the pipe is flowing full,
at slopes greater than those listed in paragraph (2) of this subsection,
special provisions shall be made to protect against pipe displacement
by erosion of the bedding and/or shock.
(4) Alignment. Sewers shall be laid in straight alignment
with uniform grade between manholes unless slight deviations from
straight alignment and uniform grade are justified to the satisfaction
of the executive director.
(5) Manhole use. Manholes shall be placed at all points
of change in alignment, grade, or size of sewer, at the intersection
of all sewers and the end of all sewer lines that will be extended
at a future date. Any proposal which deviates from this requirement
shall be justified to the satisfaction of the executive director.
Clean-outs with watertight plugs may be installed in lieu of manholes
at the end of sewers which are not anticipated to be extended. Such
installations must pass a leakage test and a deflection test for all
flexible lines.
(A) Type. Manholes shall be monolithic, cast-in-place
concrete, fiberglass, precast concrete, high-density polyethylene
(HDPE), or of equivalent construction. Brick manholes shall not be
used, nor shall brick be used to adjust manhole covers to grade.
Cont'd... |
