(A) Generally.
(1) Sewer design shall be in accordance with and shall meet all requirements of the NCDENR Gravity Sewer Minimum Design Criteria. It is the responsibility of the design engineer to ensure that these standards are met. In cases where statements herein conflict with such requirements, the more restrictive shall apply. A state Professional Engineer must sign and seal all sewer main construction plans and revisions submitted for city review.
(2) Sewer mains, manholes and cleanouts in a private road shall be installed and adjusted in the same manner as in publicly maintained streets and a 30-foot sewer easement dedicated to the city for maintenance purposes.
(3) Sewer mains shall be extended to the end of the development (or across the frontage of the proposed development) to allow for future extensions, as determined by the city.
(4) Easement widths shall be a minimum of 30 feet. Large diameter pipes or deeper installations require additional easement widths, as shown in the standard details and as required by the city.
(5) Sewer main designs shall consider the possibility of future road widening. Projection of future street grades may require increased depth of pipe installation or additional easements.
(6) Sewer design must be consistent with overall needs of watershed. The engineer shall furnish topographic maps, zoning maps and design data to substantiate sizing of all watershed outfalls.
(7) Sewer main in streets shall be extended to the far reach of property, if it could be extended in the future, to serve the remainder of the drainage basin. Sewer outfalls serving a drainage basin shall also be extended to the far property line.
(8) Sewer service to developed property shall be achieved by gravity sewer unless otherwise specifically approved in writing by the city. Low pressure sewer systems are not an alternative and will not be accepted. Pump stations, if approved by the city, shall utilize Flygt City approved pumps.
(B) Sewer design.
(1) There should be at least ten feet of horizontal separation between water and sewer mains. In the event horizontal separation cannot be maintained, vertical separation will govern.
(2) (a) Vertical separation of lines shall be as follows:
1. Twelve inches minimum between storm and sanitary;
2. Twelve inches minimum between storm and water; and
3. Eighteen inches minimum between water and sanitary (water over sewer).
(b) Material for water and sewer mains shall be ductile iron, ten feet each side of the crossing, if vertical separation cannot be maintained.
(3) Proposed sewer mains shall be placed in the center of streets. Manholes shall be located in the center of the street. Off-street manholes shall not be located in ditchlines.
(4) Proposed sewer lines shall be placed a minimum of five feet off the edge of pavement of all NCDOT roads and existing ribbon-paved roads. A NCDOT right-of-way encroachment agreement will be required for work within the right-of-way of any state maintained road.
(5) Minimum diameter pipe shall be eight inches.
(6) (a) Sanitary sewer pipe eight inches through 15 inches shall be PVC SDR 35. Pipe 18 inches through 36 inches shall be PVC ASTM F679.
(b) PVC for cover of three feet to 14 feet. Stone bedding is required for all PVC pipe a minimum of four inches below the pipe extending to the top of the pipe as shown on the standard drawings.
(c) Ductile iron for all other installations, including creek crossings and drop manholes (the last joint of pipe into the top of the drop pipe).
(d) Ductile iron restrained joint pipe inside encasements.
(7) The minimum grade on sewer is 0.5% for pipe eight inches in diameter or greater. Grades shall be a minimum of 1% for dead-end lines and where low flows are expected. Bores shall be installed with a minimum of 1% slope.
(8) Minimum pipe size for laterals is four inches. Four-inch laterals may connect into the main with a wye or into a manhole (cored hole with flexible sleeve). Six-inch laterals or larger must connect into manholes.
(9) (a) Manholes shall be placed a maximum of 400 feet apart and at all angle points. Pipes shall run straight between all manholes. End manholes shall extend a minimum of ten feet past the lot line of last lot served and/or to the back of the cul-de-sac pavement.
(b) Typical depth of manholes shall be six to seven feet so that cleanout depth at the right-of-way is 48 inches minimum.
(10) Manhole stations shall be shown on plan view and profile view (For example, Prop. MH Sta. 10+00.00). All manholes shall be stationed in the plan and profile view.
(11) All manholes shall have invert elevations shown on profile view. Standard drop through the manhole shall be two-tenths of a foot or one-half foot with pipes at angles.
(12) Sanitary sewer shall be designed to avoid spilling inverts since these can lead to odor and maintenance problems. Inverts into and out of manholes will be smooth hand-built or precast. Vertical distance between invert in and invert out shall be a minimum of two-tenths of a foot for straight through with one-half foot at any angle.
(13) Inside drop manholes are required where the vertical distance between outgoing and incoming lines is 30 inches or more. Distances of less than 30 inches shall be redesigned to eliminate the spilling condition. Show both top and bottom of drop and centerline invert elevations on plans.
(14) Sanitary sewer lines shall not be located less than 25 feet from a private well or 50 feet from a public water supply well. Sewer lines less than 100 feet from a well shall be constructed of ductile iron.
(15)
Off-street sewers shall show bearings and distances with a minimum of 30-foot permanent easements. Large pipes or deep sewers may require a wider easement. Outfalls shall have street access for maintenance unless otherwise approved by the city.
Pipe Size (Inches)
|
Minimum Easement Width (Feet)
|
8 | 30 |
12 | 30 |
15 | 30 |
18 | 35 |
24 | 35 |
30 | 35 |
36 | 40 |
42 | 40 |
(16) The top of manholes on sanitary sewer outfalls shall be two feet above the finished grade and have a vented, bolted ring and cover. Manholes in a yard may be flush with the ground. All rings and covers shall be bolted to the manhole cone with four three-quarter inch stainless steel expansion bolts (no adjustment rings allowed) unless under paved areas. Manholes in paved areas may be adjusted up to ten inches vertically using concrete grade rings or full beds of brick and mortar.
(17) Water-tight ring and covers shall be used within the 100-year flood plain. The top of the manholes shall be two feet above the ground. The vent pipes shall be extended two feet above the 100-year flood elevation. Vent pipes are to be placed on every other manhole. Water-tight manholes may be required in areas that are subject to flooding but not covered by the FEMA mapping.
(18) Rings and covers shall be:
(a) Standard vented for manholes in the street right-of-way;
(b) Vented, bolted down for off-street manholes not in a floodway; and
(c) Bolted, water-tight for outfall manholes in a floodway.
(19) Label in the profile view for all outfalls the type of ring and cover if other than standard.
(20) When connecting to an existing manhole, show invert elevation, shelf elevation, top of manhole elevation, type construction of existing manhole (brick or precast concrete), vent pipe elevation (outfalls only) and alignment of existing line. Connections into existing precast manholes shall be made by coring and installing a flexible sleeve (to be noted on plans).
(21) Aerial sewers will be allowed where cover cannot be maintained over sewer line. The maximum unsupported clear span is 40 feet. Suspended joints shall be mech-lok rigid restrained joint by Griffin (or equal). Piers or piles are required to support pipe for spans greater that 40 feet. For stream crossings, the bottom of the sewer pipe shall be located above the 25-year flood elevation. Calculations or FEMA studies shall be submitted to substantiate the 25-year flood elevation.
(22) Ductile iron pipe is required for sewers that cross under streams or creeks. Concrete anti-seepage collars shall be placed downstream of the crossing on ductile iron pipe.
(23) Slopes at creek crossings and ditches shall be no steeper than four-to-one to allow crossing by maintenance equipment. Disturbed creek banks shall be protected with rip rap as shown in the standard details and as designed by the engineer.
(24) (a) Sanitary sewers that parallel creeks or streams shall be located at depths that are below the creek or stream being paralleled. The top of the sanitary sewer pipe shall generally be a minimum of one-foot below the creek bottom elevation.
(b) Creek elevations shall be shown in the sewer design profile for all sewer outfalls that parallel creeks. Sewer mains shall cross creeks at or near 90-degree angles.
(25) Restrained joint or mechanical joint pipe shall be required inside all encasements (label on plans).
(C) Sewer specifications.
(1) Sewer main line.
(a) PVC sewer pipe shall be installed with a minimum cover of three feet and a maximum cover of 14 feet. Ductile iron pipe must be used outside of these limits and approved by the Utilities Department.
(b) Install pipe in accordance with ASTM D-2321 with stone bedding a minimum of four inches below the pipe and extending to the top of the pipe.
(c) Pipe shall be marked with the manufacturer’s name or trademark, size, thickness class or dimension ratio, and the material designation (PVC).
(d) Polyvinyl chloride (PVC) pipe for four-inch to 15-inch diameter gravity shall conform to all requirements of ASTM D-3034. Minimum class shall be SDR 35 and shall be capable of withstanding the overburden pressures determined by the depth of burial in the field.
(e) Material shall be clean virgin, NSF approved PVC compound conforming to ASTM D-1784. Reruns or reclaimed materials are not acceptable.
(f) Laying length shall be the standard 20 feet plus one inch.
(g) The pipe shall have bell and spigot end push-on, O-ring rubber gasket, compression type joints conforming to the requirements of ASTM D-3212. Elastomeric gaskets shall conform to the requirements of ASTM F-477.
(h) PVC fittings shall be as manufactured and furnished by the PVC pipe supplier and shall have bell and spigot configurations compatible with that of the pipe.
(I) Force mains shall be installed using welded joints.
(2) Precast manholes.
(a) Manholes shall conform to ASTM C-478 and the minimum standards herein. Each section shall clearly show all of the markings required by ASTM C-478 and be designed for H-20 loading.
(b) Minimum wall thickness: five inches for four-foot and five-foot diameter manholes, six inches for six-foot diameter manholes, seven inches for seven-foot diameter manholes and eight inches for eight-foot diameter manholes.
(c) The base section shall be cast monolithically or have a waterstop cast in the cold joint between the wall and base slab. Reinforcing steel in the base shall conform to ASTM A615; Grade 60 and wall steel shall conform to ASTM Al 85. Inverts shall be cast-in-place concrete. Bases with preformed inverts are not acceptable.
(d) Cone sections shall be eccentric with the inside face of one side vertical and flush with the inside face of the barrel sections.
(e) Joints between sections shall meet ASTM C-443. Seal the joints with rubber gaskets per ASTM-443, Forsheda 114, or with a flexible joint sealant compound meeting federal specifications SS-S-00210A and AASHTO M-198, Type B. Mortar may be required to provide a water-tight joint.
(f) Joints of precast sections shall be sealed on the outside of the manhole with butyl adhesive tape (minimum six inches wide). Tape shall be EZ-Seal manufactured by Press-Seal Gasket Corp EZ-Wrap or approved equal.
(g) Cement shall be Type II with a maximum tricalcium aluminate (3CaOA12O3) content of 8%. Aggregate shall be sound, crushed angular granite stone in substantial conformance with ASTM C-33, excepting the gradation standard. Alternately, manholes shall have Type III cement with calcareous (limestone) aggregate forming a complete mix with minimum alkalinity of 78%. Certified lab tests results shall be submitted to substantiate the alkalinity of the cement mix and chemical content.
(h) Pipes shall have flexible watertight sleeves conforming to ASTM C-923. The sleeves shall be as manufactured by Press-Seal Gasket Corporation, EPCO, Inc., NPC, Inc., or approved equal. Sleeves shall have a maximum deflection of seven degrees (12%). Slopes greater than 12% require sleeves designed for higher deflection.
(I) Manholes over existing pipelines shall have doghouse openings cast in the bottom section so the pipe may be set over the existing pipe. Contractor shall pour a concrete base and invert around the bottom section and the pipe.
(3) Manhole steps.
(a) Manhole steps shall not be provided unless specifically allowed, in writing, by the city. It is not allowable to remove steps from manhole structures after manufacture.
(b) If allowed, manhole steps shall be of Grade 60 steel reinforcing rod (minimum one-half inch). The steel shall be completely encapsulated with a wear and chemical resistant copolymer polypropylene plastic.
(c) Minimum tread width is 12 inches. Minimum depth is nine and one-eighth inches. Minimum vertical load resistance is 400 pounds. Minimum pullout resistance is 1,000 pounds. Manufacturer’s certification of pullout resistance is required. Steps shall be embedded in the manhole wall to a depth of three inches, 16 inches on center.
(4) Manhole frames and covers.
(a) Manhole frames and covers shall be cast iron, produced in a plant with a recognized reputation and experience with the specified standards. The name of the foundry and part number shall be cast permanently on the ring and cover.
(b) Cast iron shall be tough, closed-grained gray iron conforming to ASTM A-48 Class 30B.
(c) The castings shall conform to ASTM A-126 and shall be free from holes, cracks or other defects and support H-20 wheel loading.
(d) Cover shall measure 23 and one-half inch in diameter. The minimum clear opening shall be 22 inches. The minimum average frame weight shall be 190 pounds, and the minimum average cover weight shall be 125 pounds.
(e) Frames and covers shall have two vent holes, two pick holes, have “SANITARY SEWER” cast in the top, and be U.S. Foundry Frame 669 with KL cover, Vulcan V-13 84, or approved equal.
(f) Vented, bolt-down ring and covers shall be Vulcan Ring V-2384, Cover V-1385, or USF Ring 669-2, Cover KL-2.
(g) Watertight rings and covers shall be USF 669-KL-BWTL or approved equal.
(5) Sewer laterals (Schedule 40 PVC).
(a) Pipe shall be marked with the manufacturer’s name or trademark, size, thickness class or dimension ration, and the material designation (PVC).
(b) Polyvinyl chloride (PVC) Pipe for four-inch to six-inch diameter drain, waste, vent pipe shall be Schedule 40 PVC conforming to ASTM D-2665, NSF 14, and ASTM D-1785. Fittings shall be socket-type in accordance with ASTM D-2466. Joining shall be through solvent cement in accordance with ASTM D-2564.
(c) Minimum class pipe shall be Schedule 40 and shall be capable of withstanding the overburden pressures determined by the depth of burial in the field.
(d) Sewer services shall connect to the main line with standard 45-degree pattern wyes or saddles. Pipe fittings shall be supplied by the pipe manufacturer and shall meet the requirements of ASTM D-2466. The pipe manufacturer shall supply solvents that meet ASTM D-2564.
(e) Clean-out caps shall have a raised nut.
(6) Sewer lateral installation.
(a) All laterals will have clean-outs located four inches inside the property line but in no case closer than 24 inches to walls, buildings or other obstructions. Clean-outs shall not be located in driveways, sidewalks or streets. Cleanouts shall be located in the center of subdivision lots.
(b) Clean-outs shall be located inside an ASTM-A48 class 30B gray iron box, Sigma P-107 valve box with sewer lid. Cover shall be marked “sewer” or with an “S”.
(c) Use either one 45-degree or two 22 and one-half-degree bends of the same material and joint as the line to tie the lateral to the cleanout. Joints shall be gasketed.
(d) Laterals shall be located to minimize the length of service line and bends.
(e) Installation criteria: Minimum slope is one-eighth of an inch per foot (1%). Minimum cover is four feet. Maximum depth at the property line (right-of-way) is six feet unless greater depth is needed to serve the building and approved by the city.
(f) The service pipe shall be installed to the proper line and grade from the sewer line to the property line without horizontal bends or deviation.
(g) Wyes shall be located at least five feet from any manhole.
(h) All new taps in existing mains shall be made with saddles placed over cored holes.
(I) Wyes and bends shall be firmly supported and placed at the proper angle and direction to provide smooth hydraulic flow and to facilitate cleaning.
(j) All tees, saddles and bends shall be completely encased in #67 washed stone.
(k) Stack pipe shall be installed flush with the existing grade, carefully aligned and adequately supported.
(l) Lateral connections into manholes shall be the same as those for main lines (cored with flexible sleeves).
(7) Couplings.
(a) Couplings shall be Mission Flex-Seal ARC or Femco Strong Back Repair coupling.
(b) Couplings shall have stainless steel shear rings.
(8) Sewer installation. Pipe laying for sanitary sewer shall be as specified for water mains in § 153.083(C)(7)(e). Trench width and bedding shall be as shown on the standard drawings.
(9) Air testing.
(a) After the sewer line has been installed and manholes constructed, or replacement sewer pipe reconnected to an existing manhole, the contractor shall proceed to test all sewer lines to determine if sewers are free of breaks or other defects which would permit excessive infiltration or exfiltration in accordance with ASTM C-828 or as stated below.
(b) On all gravity flow sewers, the contractor shall conduct low pressure air tests of the various sections of pipe by use of equipment manufactured for this purpose. The equipment shall include a regulator to avoid over-pressurizing and possibly damaging an otherwise acceptable line.
(c) The low pressure air test shall be conducted by plugging each opening in the reach of pipe to be tested. All plugs shall be braced against slippage due to internal pressure, and no one shall be allowed in the manhole during the testing procedure. One of the plugs provided must have an inlet tap or other provision for connecting an air hose. After connecting the air control equipment to the air hose, monitor the air pressure so that the internal pressure does not exceed five psig. After reaching four psig, the air supply shall be throttled to maintain between four and 3.5 psig for at least two minutes in order to allow equilibrium between air temperature and the pipe walls. If plugs are found to leak, the contractor shall bleed off the air, tighten the plugs, and again begin supplying air. After the temperature has stabilized, the pressure is allowed to decrease to 3.5 psig. At 3.5 psig, the contractor shall begin timing to determine the time required for the pressure to drop. The pipe shall be presumed free of defects if the time, in seconds, for the air pressure to decrease one psig is greater than that shown.
Minimum Test Time for Various Pipe Sizes
| |
Nominal Pipe Size (Inches)
|
T (Time) Minutes per 100 Feet
|
8 | 1.2 |
10 | 1.5 |
12 | 1.8 |
15 | 2.1 |
18 | 2.4 |
21 | 3.0 |
24 | 3.6 |
(d) The low pressure air test shall be performed as specified in the latest revision of ASTM C828. If the line pressure drops more than one psi during the required test time, then the section of pipe has failed the test.
(e) If by use of the procedure in division (C)(9)(d) above, defective section(s) of line are found, the line segment shall be tested at 20-foot intervals to determine the exact location of the defect(s). Repairs shall be made in defective section(s), and the entire line segment shall then be retested.
(f) If the top of the sewer pipe to be tested is below the ground water table, an infiltration test may be required. Infiltration shall not exceed 100 gallons per inch diameter per mile of pipe per 24 hours. Obvious leaks in any section shall be corrected even if the section passes testing. The contractor shall furnish and install weirs or other measures as required for measuring infiltration.
(10) Mandrel testing.
(a) Polyvinyl chloride pipe sewer lines shall be mandrel tested as follows.
1. Flexible sewer pipes shall be mandrel tested with a rigid device sized to pass 5%or less deflection (or deformation) of the pipe.
2. The mandrel (go/no-go) device shall be cylindrical in shape and constructed with either nine or 16 evenly spaced arms or prongs. Mandrels with fewer arms (in odd or even numbers, respectively) will be rejected as not sufficiently accurate. The contact length of the mandrel’s arms shall equal or exceed the nominal diameter of the sewer to be inspected. Critical mandrel dimensions shall carry a tolerance of plus or minus one one-hundredth of an inch.
3. Pipe dimensions as contained in ASTM 2680, latest revision, shall be used to compute the mandrel dimensions. Allowances for pipe wall thickness tolerances or ovality (from shipment, heat, shipping loads, poor production and the like) shall not be deducted from the base ASTM data, but shall be counted as a part of the 5% or lesser deflection allowance.
4. The mandrel shall be hand-pulled by the contractor through all sewer lines. Any sections of sewer not passing the mandrel shall be uncovered and the contractor shall rebed, reround or replace the sewer to the satisfaction of the city. These repaired sections shall be retested.
(b) The inspection shall be conducted no earlier than 30 days after reaching final trench backfill grade, provided, in the opinion of the city, that sufficient water densification or rainfall has occurred to thoroughly settle the soil throughout the entire trench depth. If this cannot be achieved in the time after installation prior to the project completion date, then the mandrel size shall be increased to measure one-third less of a deflection allowance.
(c) Drawings of the mandrel with complete dimensioning shall be furnished by the contractor to the city for approval for each diameter and specification of pipe.
(d) Contractors or owners shall supplement the mandrel testing procedures with CCTV camera or sewer-line rapid assessment technology as required by city inspectors at no cost to the city.
(11) Vacuum Testing of Manholes.
(a) Each manhole constructed by the contractor shall be vacuum tested by the contractor after assembly of the manhole. The test shall be conducted in accordance with ASTM C-1244. The test shall be performed after all grade rings and rings and covers have been installed. After the testing equipment is in place, a vacuum of ten inches of mercury shall be drawn on the manhole. The time for the vacuum to drop to nine inches of mercury must be greater than the minimum time listed below.
Minimum Vacuum Test Time (Seconds)
| |||
Manhole Depth (Feet)
|
Diameter of Manhole (Inches)
| ||
48 Inches |
60 Inches
|
72 Inches
| |
0-10 Feet | 60 seconds | 75 seconds | 90 seconds |
10-15 Feet | 75 seconds | 90 seconds | 105 seconds |
15-25 Feet | 90 seconds | 105 seconds | 120 seconds |
25-30 Feet | 105 seconds | 120 seconds | 135 seconds |
(b) The City Inspector shall be present during the entire testing process. Any repairs to manholes which fail the vacuum test must be made on the inside and outside of each manhole.
(D) Construction.
(1) Installation must meet these specifications and the standard drawings.
(2) Sewer connections shall be stamped into the curb at the exact location of the crossing (“S” for sewer).
(3) Contractors will be responsible for a one-year warranty beginning the date final construction acceptance is given by the city.
(4) The city will not maintain any newly installed infrastructure until final acceptance of the project is granted by City Council. The one-year warranty period will not begin until final acceptance. The applicant must submit one set of as-builts and a digital copy to the Utilities Department. The developer may not request final acceptance until all deficiencies have been satisfactorily addressed as determined by the city and a set of as-built drawings certified by the engineer of record have been submitted, reviewed and accepted by the city. It shall be the responsibility of the developer to request the final acceptance.
(Ord. passed 9-27-2021)
Penalty, see § 153.999