CHAPTER 7 - Design and Construction Standards for Sanitary Sewers
7.01 Introduction
7.02 General Requirements
7.03 Design Standards
7.04 Easement and Right-of-way Dedication
7.05 Town's Participation in Cost
7.06 Specifications and Special Provisions
7.07 Standard Details
7.01 INTRODUCTION
All subdivisions and developments, regardless of size within the corporate limits or under the control of Town, shall include provisions for the construction of sanitary sewage facilities designed and constructed in accordance with this chapter.
7.02 GENERAL REQUIREMENTS
All subdivisions shall be designed so the proposed sanitary sewer system does and accomplishes the following:
- Conforms to the Town of Normal Comprehensive Plan;
- Extends interceptor sanitary sewers through the proposed
subdivision to serve upstream properties in the natural drainage
area;
- Provides sanitary sewer services with separate service connections
terminating not less than two feet inside the property or easement
line of each proposed lot of record,
- Has adequate capacity to drain the portions of the subdivision
proposed to be served by the sewer and any property upstream
thereof which drains into or may drain into that sewer, based
on the effluent discharge reasonably expected from development
of the type and to the maximum density permitted by the then-existing
zoning ordinances of the Town for property within the corporate
limits and the land use element of the Town's Comprehensive
Plan for property outside the corporate limits;
- Maintains separation from public water supply system.
- Discourages the use of sewage pumping facilities.
- Permits the use of private sewage disposal systems only
in the following situations:
- Where public sanitary sewers are not within 200 feet
of an area included in the subdivision's preliminary plan,
and
- Where the subdivision contains no lots less than 20,000
square feet in area, not more than two lots of more than
20,000 square feet but less than 30,000 square feet and
not more than five lots with more than 30,000 square feet
but less than one acre, and
- All requirements of the Town Sewer Code are complied
with.
- Where public sanitary sewers are not within 200 feet
of an area included in the subdivision's preliminary plan,
and
- Designed to prevent installation of sanitary sewers in rear
or side yard easements.
- Meet requirement for pump stations if required.
7.03 DESIGN STANDARDS
- Design Formula. Sanitary sewers shall be designed
to provide adequate capacity without surcharge, using Manning's
Formula.
Metric English 1 2/3 1/2 1.486 2/3 1/2 V = n R S V= n R S V = Velocity of flow in meters V = Velocity of flow in feet per second per second per second n = Roughness Factor n = Roughness Factor R = Hydraulic Radius (meters) R = Hydraulic Radius (feet) S = slope of energy grade line S = slope of energy grade line for For conduit running full (meter
per meter)conduit running full (feet per foot) For new Smooth walled sewer pipe n = 0.013
Sanitary sewers shall flow with a desired minimum velocity of 0.8 meters per second (2.5 feed per second) with an absolute minimum velocity of 0.6 meters per second (2 feet per second). Proposed sanitary sewage flow shall be based on the population after full development of the area. For undeveloped areas where the details of future development are not known, design population will be estimated by the Town Engineer based on the zoning classification and expected use conforming to the Town of Normal Comprehensive Plan.
FLOW CRITERIA:
Sanitary sewers shall be sized to accept the following peak design flows:Domestic: 400 gallons (1500 liters) per day per capita for lateral sewers. Average flow of 375 liters (100 gallons) per capita peaked by a factor per Exhibit Q in the Appendix plus 110 liter/mm Dia/Hectare (300 gal/inch/dia/acre) for infiltration. Commercial: 95,000 liters/hectare (10,000 gallons/acre) per day for lateral and industrial sewers. 66,000 liters/hectare (7,000 gallons/acre) per day for trunk sewers.
- Materials. All sanitary sewer pipes shall be Vitrified
Clay Pipe ASTM Designation C-700 (extra strength) or Ductile
Iron Pipe conforming to ANSI A 2151 or Polyvinyl Chloride
(PVC) Pipe conforming to ASTM D 3034, type PSM for sizes up
to 10" diameter. Minimum acceptable Standard Dimensional
Ratio (SDR) for PVC Pipe shall be 21. Vitrified Clay pipe joints
shall conform to ASTM C-425. Ductile iron pipe joints shall
be mechanical or rubber ring (slip seal or push-on) joints.
The Town Engineer prior to their installation must approve use
of other materials for sanitary sewers in writing. (Amended
4/17/06 by Ord. No. 5068)
- Minimum Size. All public sanitary sewers shall be
a minimum of 8" (200 mm) in diameter. All service sewer lines
shall be a minimum of 6" (150mm) diameter.
- Alignment. All sewers shall be laid straight in both
horizontal and vertical planes between manholes unless otherwise
approved by the Town Engineer.
- Sewer Size Changes. When sanitary sewers of different
diameters join in a manhole, the invert elevations shall be
adjusted to maintain a uniform energy gradient. Alignment of
the 0.9 depth points of the sewers shall be implemented to meet
this requirement.
- High Velocity Protection. Where velocities greater
than 10 feet per second (3 mps) will occur, in a sanitary sewer
when flowing full, special provisions shall be taken to prevent
scouring or displacement of the pipe.
- Manholes.
- Provide public manholes at the end of each line, at
all changes in grade, size or alignment, at all intersections
and at distances not greater than 400 feet (125m). The Town
Engineer in large sewers and in those carrying a settled
effluent may permit greater spacing.
- Provide a drop pipe for sewers entering a manhole at
an elevation of 24 inches (600mm) or more above the manhole
invert. Where the difference in elevation between the incoming
sewer and the manhole invert is less than 24 inches (600mm),
the invert should be filleted to prevent the depositing
of solids. Drop manholes shall be constructed in accordance
with Standard Detail 7.07B-1.
- Provide public manholes in improved streets or other
hard surfaced public rights-of-way accessible to vehicular
access, not more than 800 feet (240 m) measured in a straight
line along the sanitary sewer.
- Provide public manholes at the end of each line, at
all changes in grade, size or alignment, at all intersections
and at distances not greater than 400 feet (125m). The Town
Engineer in large sewers and in those carrying a settled
effluent may permit greater spacing.
- Service Drops in Manholes:
- New construction: Outside service drops shall be provided as per Standard Detail 7.07 B-1 in new construction when a proposed sanitary service enters a proposed manhole more than 600 mm (2 feet) above the invert of the manhole. With the permission of the Town Engineer, for existing manholes an inside drop connection as per Standard Detail 7.07 B-2 may be used.
7.04 RIGHT-OF-WAY DEDICATION
Generally, all sanitary sewers shall be installed in public easements or dedicated public rights-of-way. Such easements and rights-of-way are to be of sufficient width and the sewers to be installed at such locations as to permit open cut installation, maintenance and repair within the confines of the easement or right-of-way without relocation or other unreasonable interference with other public utilities located therein and so as to meet the following minimum standards:
- 15 foot (5m) width plus 5 feet (1.5m) for each additional
utility except water main or other sewers.
- Sewers exceeding 15 feet (4.5 m) in depth, additional width may be required.
7.05 TOWN'S PARTICIPATION IN COST
- Where installation of sanitary sewer lines of larger capacity
than required to serve land owned by the developer is required
by the Board of Trustees to serve future growth in the vicinity
of the development, the developer shall pay for only his portion,
based on the Code requirements for his development, of the total
cost of installation; the balance to be borne by the Town. Provided
funds are available, the Town will pay the difference in cost
between the size required for the developer's land and the larger
size required. If there is, in the Town's records, an existing
tap-on charge requirement, then the developer shall abide by
it.
- Engineering Costs. The developer will be responsible for all engineering costs for design of sanitary sewer facilities including pump stations within his/her development.
7.06 SPECIFICATIONS & SPECIAL PROVISIONS
All sanitary sewers shall be installed in accordance with all applicable sections of the Standard Specifications for Water and Sewer Main Construction In Illinois, the current edition as then modified, supplemented and amended by this Manual or the Town Engineer. These modifications, amendments and amplifications have been provided in this Chapter of the Manual.
Special Provisions for Sanitary Sewer
Granular Cradle: A granular cradle (bedding and haunching) will be required for all sanitary sewers as shown in the Standard Details and in accordance with Section 20-2.20B of the “Standard Specifications for Water and Sewer Main Construction.” and for Vitified Clay Pipe (VCP) per ASTM C12-04. The bedding and haunching material for VCP shall be crushed stone with a size range of 3/4" - 1/4" which meets the requirements of IDOT Gradation CA 11 and that the installation shall have a minimum Bedding Class of Class B which results in a minimum Safety Factor of 1.20 as calculated per ASTM C 12-04. (Amended 4/17/06 by Ord. No. 5068)
Trench Backfill: All trenches under another sewer or water main, or under existing or within 0.6 meters (2 ft) of existing or proposed streets, existing sidewalks and driveways shall be backfilled with trench backfill material in accordance with Section 208 of the “Standard Specifications For Road and Bridge Construction”.
Compaction of Trench Backfill: All sewer trenches under streets, driveways or sidewalks shall be compacted by jetting, mechanical compaction, or as directed by the Town Engineer.
Leakage Test: The leakage test will be by the low-pressure air method. The Town will supply all labor and material. The contractor shall notify the Town Engineer when the sewer is ready for testing. The ground shall be leveled and all manholes shall be accessible to the air testing equipment.
Sewer Service Markings: The contractor shall place 2x4’s (50 x 100 mm) extending from the bottom of the sewer service to two feet (0.6 m) above the ground at the location where each sewer service terminates. These markers shall be installed at the time the services are constructed.
Curb Marking of Sewer Services: At the time the curb and gutter is poured, the contractor shall mark the top of the curb with an “S” to mark location of said sewer service.
Sewer Service Laterals: All services shall terminate at a point at least two (2) feet inside the proposed property line or two (2) (0.6m) feet beyond any easement where a Town owned utility is located, unless otherwise directed, and at a maximum depth of nine (9) feet (2.75m) below the proposed curb grade unless otherwise approved by the Town Engineer. Breaking the joints without breaking the seal may make the change in elevation on the services or the contractor may provide fittings to adjust for the change in grade. The last length of pipe at the property line shall be laid at a uniform grade of 1.0% (separation between laterals shall be a minimum distance of one pipe length).
Adjustment of Manhole Casting: Final grade for all manhole castings will be determined after the curb and gutter has been poured and the sub-grade and/or base have been constructed. Final adjustment of the frame and grate shall be made in the following manner: After the curb and gutter has been poured and the base constructed the final elevation will be determined by the Engineer. The frame and grate will be adjusted to this elevation in accordance with the Standard Specifications. Any material disturbed while adjusting the frame and grate will be disposed of and all fill made with lean concrete. A maximum of eighteen (18) inches (450 mm) of adjusting rings shall be allowed. For manholes located in easements outside public right-of-way or paved surfaces, the frame and grate shall be adjusted six (6) inches (900 mm) above the final elevation as determine on the approved lot grading plan with temporary adjusting rings in a manner that will allow Town maintenance staff to remove after finished grading.
Special Provisions Modifying Standard Specifications for Water and Sewer Main Construction in Illinois
30-3.01 E & F DUCTILE IRON PIPE
Add:
Inside of all pipes shall have standard cement mortar lining and the inside and outside shall be tar (seal) coated.
30-3.01G POLYVINYL CHLORIDE (PVC) SEWER PIPE
Change minimum acceptable SDR shall be 21.
31-1.11 A (1) SELECTION OF TEST SECTIONS
Delete paragraphs two, three and four
and substitute the following:
All sections of the sewer shall be tested, except for those designated
portions of the sewer that are placed into service during the construction
process.
32-2.07 CAST IRON FRAMES, COVER AND STEPS
Add the following:
Covers shall be Neenah, East Jordan or equal. Neenah numbers are given as examples.
For Sanitary Manholes: Standard Type 1 Frame and Grate - Neenah R-1772 B with Type "B" Lid and NF-9204 pick hole. All lids for sanitary manholes shall be self-sealing.
Steps shall be M.A. Industries PS1-PF Manhole Step or equal conforming to ASTM C-478.
32-3.05 PRECAST MANHOLES
Add the following to paragraph 3:
No bitumastic material shall be used on the inside of manholes. Inside of all joints shall be finished with non-shrink type grout and rubber gaskets.
32-3.09 PLACING CASTINGS
Change to read:
Castings placed on concrete or masonry surfaces shall be set in a full mortar bed or on approved solid bituminous gaskets.
32-3.09 A STREETS AT GRADE
Change 12 inches (300 mm) to 8 inches (200 mm).
32-3.09 B STREETS OR ALLEYS WITH NO ESTABLISHED GRADE
Change 12 inches (300mm) to 8 inches (200 mm).
32-3.09 C MANHOLES NOT WITHIN STREET OR ALLEY AREAS
Change 18 (450 mm) inches to 24 inches (600 mm).
Change second paragraph to read:
Unless otherwise directed, the top of manhole castings shall be at grade of existing surface.
32-3.11 PIPE CONNECTIONS
Add the following sentence:
Bituminous material shall be used on the outside of the manhole only.
