1) Sewer service laterals shall not be connected into manholes unless approved in writing by the City Engineer on a case-by-case basis. Where lateral connections to manholes are allowed, the crown of the lateral pipe shall be installed at or above the crown of the manhole outlet pipe.
b. Mainline Sewer Cleanouts.
1) Mainline cleanouts will not be approved as substitutes for manholes. Cleanouts shall only be allowed at the upper end of lateral or main sewers less than 150 feet long which will be extended on the same grade and alignment during the next construction phase of a multiphase development, and which does not have any laterals.
2) All mainline cleanouts will be considered on a case-by-case basis and approved by the City Engineer. In all cases, plan and profile showing the alignment and depth of the anticipated future extension from the proposed cleanout to the next manhole shall be submitted prior to approval of cleanouts.
c. Manhole Size.
1) For pipe 21-inches in diameter and smaller, the minimum diameter of manholes shall be 48 inches.
2) For pipe 21-inches or 27-inches in diameter, the minimum diameter of manholes shall be 60 inches.
3) For pipe larger than 27-inches in diameter, the minimum diameter of manholes shall be 72 inches unless otherwise approved by the City Engineer.
4) Larger manholes may be required for multiple pipe connections.
5) Manholes sizes for drop structures or metering manholes will be reviewed on a case-by-case basis.
d. Manhole Location:
1) Manholes shall be placed at the following locations:
a) Upper end of all lateral sewers, except as provided above.
b) Every change in grade or alignment of a sewer.
c) Every change in size of a sewer.
d) Each intersection or junction of sewers, excluding four (4) inch service laterals
e) Adjacent to the center radius point of a cul-de-sac.
f) In front of the last property or lot being served, a minimum of 10 feet past the common lot line of the adjoining parcel served.
g) At intervals of 350 feet or less.
2) Where practical, manholes shall be located at street intersections. All manholes from which future sewer line extensions are anticipated, shall have a pipe stub designed and installed at the grade and direction of the anticipated sewer main extension. Pipe stubs shall be a minimum of eight inches in size and shall protrude at least five (5) feet outside the manhole base, and end with a watertight gasketed cap acceptable to Public Works.
3) Manholes shall not be located in the curb or in the gutter. Placement of manholes behind the curb shall be reviewed on a case-by-case basis for approval. Consideration shall be given to those sewer or public utility lines which already exist behind the curb.
4) Two manholes shall be installed when the horizontal deflection angle between two sewers is an acute angle less than or equal to 80°. Spacing of such manholes shall be a minimum of ten feet outside to outside. The intent is to prevent lateral sewer connections from discharging into sewers against the direction of flow.
e. Manhole Rim Elevation.
1) The rims of all manholes located within paved or other hard surfaced areas shall be set to finished grade.
2) Concrete riser rings shall be used to bring casting to grade. The height from the top of the cone or flattop section to the rim shall not exceed 18-inches.
3) The rims of all manholes located outside of paved or other hard surfaced areas shall be set 6-inches above surrounding finish grade. Finish grade shall be defined as the final ground surface after grading and landscaping, as shown on the standard manhole rim adjustment details.
4) Manholes within easements shall have lockdown lids only where specifically required by the City Engineer.
f. Drop Across Manhole Structure.
1) The minimum vertical drop across a 4-foot diameter manhole is required as shown below.
a) Straight through runs: 0.1' minimum drop
b) Bends greater than 45°:0.2' minimum drop
2) Maximum vertical drop across a 4-foot diameter manhole shall not exceed 18- inches with a beaver slide channel.
3) Where pipes of different sizes enter the same manhole, the design shall generally provide that the crowns of the pipes are set at the same elevation.
4) In cases where two pipes discharge into a manhole from opposite directions and one pipe has a slope more than 4% steeper than the pipe opposite, the invert of the pipe with the lower slope shall be set a minimum of 0.35 feet or ½ the pipe diameter, whichever is greater, above invert of the steeper pipe.
5) Manhole Flow Channels.
a) Flow channels in manholes shall be of such shape and slope to provide smooth transition between inlet and outlet sewers and to minimize turbulence.
b) Flow channel height shall be to the crowns of the sewers. Benches beside flow channels shall be sloped from the manhole wall toward the channel to prevent accumulation of solids.
c) Beaver slide channels shall be shaped to allow the insertion of a 6-inch diameter by three (3)-foot long TV camera into the downstream sewer.
g. Drop Manholes.
1) All drop manhole installations must be approved in writing by the City engineer on a case-by-case basis.
2) When allowed, outside drop assemblies shall be provided for pipe lines 12 inches in diameter and smaller when entering a manhole more than 24 inches above the invert of the outlet line. The vertical displacement shall be measured at the inside manhole walls and not the manhole centerline. Pipe lines larger than 12-inches shall be introduced into the manhole at the manhole invert.
3) When allowed, inside drop manholes shall be a minimum of 60 inches in diameter. All inside drops shall be constructed with pipe with stainless steel support structures. No partitions will be allowed.
h. Manhole Taps.
1) When an existing manhole is tapped to install a new sewer which will drain into the manhole, the crown of the new sewer shall generally match the crown of the existing pipes.
2) When the size of the new pipe being tapped into the existing manhole is the same size as the existing pipe exiting the manhole, the invert of the new pipe should be a minimum of 0.35 feet above the invert of the existing pipe or higher as required to be above the normal sewage flow level.
3) A detail drawing showing the steps, bench and proposed connection is required for connections to existing manholes.
4) The drawing shall include notes to the effect that openings for connections to existing manholes shall be made by core-drilling the existing manhole structure and installing a rubber boot. Small chipping hammers or similar light tools which will not damage or crack the manhole base may be used to shape channels. Use of large pneumatic jackhammers shall be prohibited.
5) Unless otherwise approved by the City Engineer, manhole steps shall be installed in any manhole tapped which does not have existing steps.
i. Metering & Sampling Manhole.
1) A metering and sampling manhole shall be installed on all systems meeting the following criteria:
a) Industry or business which discharges high strength wastewater or wastewater with characteristics not commonly found in domestic sewage.
2) Metering and sampling manholes shall include provisions for continuous and composite sampling, continuous flow monitoring and recording, and flow paced sampling.
3) Sampling and flow monitoring may be required at the discretion of the City Engineer. All machinery, equipment, supplies and labor required to carry out the sampling and flow monitoring program shall be provided by the Developer, and shall meet the City engineer's prior approval.