Chapter 13.35
SANITARY SEWAGE SYSTEM CONSTRUCTION SPECIFICATIONS
Sections:
13.35.010 Materials.
(a) All sanitary sewers, including house or service connections, within the public streets, alleys or easements shall be constructed of either vitrified clay, cast iron or polyvinyl chloride pipe.
Vitrified clay pipe and fittings shall meet the requirements of ASTM tentative specifications for extra strength clay pipe, designated C200. Vitrified clay pipe joints: all vitrified clay pipe and fittings shall be furnished with a factory fabricated joint meeting the requirements of ASTM specification for vitrified clay pipe joints having resilient properties, designation C425, for either types I, II or III material combinations.
Cast iron sewer pipe shall be Class 150 pipe meeting the requirements previously specified for cast iron pipe for water mains.
Plastic pipe may be used under approval from the town engineer, but with a specification of at least an SDR of 35.
(b) Manholes. All manholes shall be constructed of pre-cast reinforced concrete with an eccentric-cone top section and a 48-inch inside diameter. The pre-cast manhole sections shall meet the requirements of ASTM standard specification for reinforced concrete manhole sections being made using type V Portland cement.The pre-cast sections shall be installed on a plain concrete base slab. In fabricating the pre-cast sections allowance shall be made for thickness of the vitrified clay pipe as the base slab on which the bottom pre-cast section is placed shall be formed to the elevation of the outside bottom of the pipe. The bottom pre-cast section shall be fabricated with a flat base. Blocked out openings shall be provided in the sections for the incoming and outgoing sewer pipe or as an alternate such openings may be cut in the field.
Manhole steps shall be cast iron steps equal to the Clow F-3650 step. Wrought iron or steel steps will not be accepted.
Manhole rings and covers shall be the Comco No. 250C ring and cover or approved equal with the total weight of ring and cover to be not less than 275 pounds. The ring shall be provided with an interior retaining lip and shall have a net of five and one-half inches.
Concrete for manhole base slabs and interior concrete fill shall be mixed in the following proportions based on a one-yard batch:
|
Cement |
564 lb. (6.0 sack) |
|
Water |
284 lb. (34.0 gal.) |
|
Fine aggregate |
1310 lb. |
|
Coarse aggregate |
1755 lb. |
|
Air entraining agent |
As required to entrain four and one-half percent air. |
Water content above has been on an allowance of two percent moisture in the aggregate.
Water content shall be adjusted in the field to obtain a slump of three inches maximum. Grout for filling of the joints in the pre-cast concrete manhole sections and for grouting-in of pipe through the walls of the manhole shall consist of one part by volume of type V Portland cement to two and one-half parts volume of concrete fine aggregate with just sufficient water to make a workable mix that can be packed into the openings to be grouted. Mortar for grouting-in of the manhole ring and cover shall consist of the same mix with the addition of one-fourth parts by volume of hydrated lime to increase workability. [Ord. 419 Appx. 2 § 5, 1976. 1996 Code § 7-119.]
13.35.020 Applicability.
These regulations shall apply to the design of all sanitary sewerage facilities installed in streets, alleys or public easements within the corporate limits of the town. The regulations shall likewise apply to the design of sanitary sewerage facilities in areas contiguous or adjacent to the corporate limits which are planned to be connected with either now or in the future the sewerage systems of the town. [Ord. 419 Appx. 2 § 1, 1976. 1996 Code § 7-120.]
13.35.030 Agreements.
To assure continuity of the present town system, owners of area platting within one mile of the town boundaries shall negotiate written agreements as to the timing, design and construction of sanitary sewage treatment and collection facilities prior to the mayor’s signature being signed on any plats within such one mile area. Such agreements may also call for the time of annexation of such parcels. [Ord. 419 Appx. 2 § 1, 1976. 1996 Code § 7-121.]
13.35.040 Inspection.
There shall be no installation of any new sewer pipe which, in the judgment of the town engineer, would be maintained by the town, unless a representative of the town engineer is present. All costs for inspection shall be paid for by the installer. [Ord. 419 Appx. 2 § 2, 1976. 1996 Code § 7-122.]
13.35.050 Permits.
Sanitary sewerage facilities coming within the scope of these regulations shall be constructed only after a permit for construction has been issued by the town. The permit will not be issued until after plans and specifications covering the proposed construction have been submitted to the town and approved by the town engineer. [Ord. 419 Appx. 2 § 1, 1976. 1996 Code § 7-123.]
13.35.060 Design.
(a) Generally. The design of any particular sewage system shall conform to the long-range sewage system plans adopted by the town. Features of the long-range plan shall be incorporated into the design of the particular addition or subdivision. In the case of unusually large sizes required by the long range plan, the town shall pay its proportionate share.
All sanitary sewers and appurtenances shall be designed to carry the design flows from all contiguous or adjacent areas which may within a reasonable period in the future be tributary thereto. Contiguous or adjacent areas to be included in the design and the tributary population to be provided for shall be subject to approval by the planning commission.
(b) Flow. Where actual flow measurements are not available or where data from existing water usage or sewage flows are not applicable, trunk or main sewers shall be designed on the basis of an average per capital flow of not less than 250 gallons per day; and lateral and sub-main sewers shall be designed for an average per capital flow of not less than 400 gallons per day. If design flows are based on sewer gaugings or flow measurements or on an analysis based on water usage records or similar data, an outline of the design procedure used shall be presented with the plans and specifications submitted for approval.
(c) Minimum Size. No public sanitary sewer shall be less than six inches in diameter. Six-inch sizes shall be used only in cul-de-sac or other special areas if approved by the town engineer. All other sewers shall be a minimum of eight inches in diameter.
The minimum size of all house connections shall be four inches. The minimum size of a connection for commercial and industrial service shall be six inches.
(d) Velocity. All sewers shall be signed and constructed with hydraulic slopes sufficient to give mean velocities when flowing full or not less than two feet per second based on Manning’s formula using a value for “n” of thirteen-thousandths.
The following shall be minimum slopes to be provided:
|
Sewer size in inches |
Slope in feet per foot |
|---|---|
|
8 |
0.0040 |
|
10 |
0.0028 |
|
12 |
0.0022 |
|
14 |
0.0018 |
|
15 |
0.0016 |
|
16 |
0.0014 |
|
18 |
0.0012 |
Under special conditions, slopes slightly less than those required for the two feet per second velocity when full may be permitted. Such decreased slopes will only be considered where the depth of flow will be not less than four-tenths of the diameter for the design average flows and where computations of the depth of flow in such pipes at minimum, average and peak rates of flow are submitted showing the basis of design.
Maximum slopes for vitrified clay pipe shall be two-tenths for eight-inch, 10-inch and 12-inch sizes and twelve-hundredths for larger sizes. Cast iron pipe shall be used where steeper grades are required to drop manholes provided to reduce the slopes to the maximum specified.
House connections shall be installed on a minimum slope of two percent.
(e) Depth of Cover. Sanitary sewers shall be designed of sufficient depth to permit floor drains from basements to be connected unless in subdivisions or areas in which nonbasement houses are to be constructed. In no case shall sanitary sewers be designed for a depth of cover of less than 36 inches over the top of the pipe. Where shallower depths are unavoidable concrete encased pipe with or without insulation as circumstances may direct may be used. Proper allowance for loads on the sewer shall be made, because of the width of the depth of trench, by using concrete cradles or concrete encasement where required to increase the supporting strength of the pipe.
(f) Location of Sewers. Sewers shall be designed for uniform slope and alignment between manholes. Where alleys are provided sewers shall be installed as per approved plan. Where alleys are not provided sewers shall be installed within the dedicated public streets, manholes shall be located so that the required horizontal clearance from water mains can be maintained and no portion of the sewer shall be under curb, gutter or private property. The centerline of manholes shall be closer than six feet from the flow line of any gutter. On any individual street the sanitary sewer shall be located on one side or the other of the street water main with unavoidable crossings of the water main to be made at approximately 90 degrees to the water main.
(g) Clearances. Sanitary sewers shall be located to maintain a horizontal clearance of not less than 10 feet from any water main with a minimum vertical clearance of one foot between the outsides of the pipes and with the sewer to be installed below the water main. Where the required vertical clearance cannot be obtained or where the sewer must cross above the water main regardless of the clearance the sewer pipe shall be encased with a distance of 10 feet on each side of the water main. Sanitary sewers shall have a minimum clearance of six inches between the outside walls of the pipe from gas mains, drains and similar utilities other than water.
(h) House connections to the sanitary sewer shall also maintain the clearances from water services and other utilities as specified above.
(i) Manholes. Manholes shall be installed at the end of each line; at all changes in grade, size or alignments; at all intersections; and at distances not greater than 400 feet apart. Lampholes will be accepted as a substitute for manholes. Drop manholes shall be provided for a lateral sewer entering a manhole at an elevation of 24 inches or more above the manhole invert. Where sewers change in size at a manhole the tops of the sewers shall be placed at the same elevation.
A one-tenth foot drop shall be provided through manholes to allow for transition losses, except where conservation of grade is critical.
(j) House connections to any public sanitary sewer shall be made only by the use of a Y-branch or T-branch or approved type of cutting-in saddle. Saddles, if used, shall be of a type that will not project into the sewer or otherwise interfere with the flow in the pipe or the use of sewer cleaning equipment. Connections to the sanitary sewer system shall be made only after the necessary permit to do so has been obtained from the office of the town engineer. House connections within public streets, alleys or easements shall be constructed only of vitrified clay pipe, cast iron pipe or plastic pipe installed in accordance with applicable sections of these regulations.
In all subdivisions house sewer connections shall be extended to the property lines of each lot from the lateral or street sewer prior to the installation of curbs, gutters and street paving.
(k) Roof and Foundation Drain. Under no circumstances shall roof drains, foundation drains or sub-drains be connected to the sanitary sewer system. [Ord. 419 Appx. 2 § 4, 1976. 1996 Code § 7-124.]
13.35.070 Installations.
(a) Generally. Trenches and excavations shall be kept free from water during excavation, fine grading, pipe laying and jointing. Where the trench bottom is mucky or otherwise unstable because of the presence of groundwater and in all cases where the static groundwater level is above the bottom of the trench, the groundwater shall be lowered by means of pumps or well points to the extent necessary to keep the trench free from water and the bottom stable.
The bottom of the trench at pipe grade shall be clean and free from rock, boulders or hard lumps and graded to provide a uniform and continuous bearing and support for the pipe on solid undisturbed soil at every point between bell holes. Bell holes of sufficient size to permit proper making up of joints shall be provided at each joint.
Under no circumstances shall water and sewer service connections be installed in the same trench.
(b) Trench Depths. All trenches for sewers shall be excavated to such depths that the invert grades of the finished sewer will be as specified on the drawings and as staked in the field.
Machine excavation shall be carried lower than four inches above the specified grade elevation. The remainder of the excavation shall be done by hand at the time the pipe sub-grade is prepared and immediately prior to installing the pipe. The bottom of the trench at pipe sub-grade shall be shaped to fit the outside surface of the bottom quadrant of the pipe and to the exact grade required in such manner that the pipe shall have a continuous bearing on undisturbed soil for the full length of the pipe except for such distance as required for bell holes. The sub-grade shall be so shaped and graded that the spigot end of the pipe will be accurately centered in the adjacent pipe socket when laid without the raising or lowering of the pipe after installation in the trench.
Where the sub-grade is found to be sufficiently unstable to prevent proper placing and bedding of the pipe the installer shall excavate the trench not less than four inches below the specified pipe sub-grade and the full width of the trench filled to not less than four inches above pipe sub-grade with a pit-run sand or sand-gravel or other approved noncohesive material in which the pipe shall be bedded as provided above.
(c) Trench Width. The minimum trench width for sewers at the center of the pipe shall be not less than 12 inches greater than the nominal diameter of the pipe or as may be required for the proper making up of joints. In order that trench loadings will not exceed the allowable loading on the pipe for the bedding conditions specified above, the maximum trench-width at a point one foot above the top of the pipe shall not exceed three feet for sewers up to 10 feet in depth.
(d) Excavation for Manholes. Excavation for manholes shall be of such dimensions as to allow for the proper forming of the concrete base, the installation of the pre-cast concrete manhole sections and the grouting-in and making of connections to the manhole barrel. Finished excavation for the base slabs shall not extend below the exact grade of the bottom of the concrete.
(e) Backfill. Trenches shall be backfilled immediately after the pipe installation has been approved for backfilling. All backfill material shall be carefully placed to avoid displacement or damage to the pipe or adjacent structures. Backfill from the bottom of the trench to approximately one foot over the top of the pipe shall be placed by hand unless otherwise approved taking particular care to completely fill under the pipe haunches. This portion of the backfill for the full width of the trench shall be thoroughly compacted by either pneumatic or mechanical compaction equipment. Thorough compaction of this portion of the backfill is particularly important in order that the trench loading on the pipe can be properly distributed.
Backfill from approximately one foot over the top of the pipe to the surface of the ground or pavement sub-grade, where applicable, may be placed by either hand or equipment and shall be thoroughly compacted by either the placing of the backfill in 12-inch maximum lifts and compacting each lift with mechanical tamping equipment, or by the partial filling of the trench in maximum lifts of three feet and compacting each lift with a mobile trench compactor. Care shall be taken in the backfilling around manholes to avoid unequal loadings on one side of the structure that would tend to displace the entire structure or open up the joints in one or more of the barrel sections.
(f) Backfill Material. From the bottom of the trench to at least one foot over the top of the pipe, backfill material shall be material as excavated from the trench selected to eliminate rock, stones or similar hard objects that might damage the pipe during subsequent backfill compaction or future earth movement or settlement. The remaining backfill shall be material as excavated from the trench without selection.
(g) Laying. The laying of pipe shall be commenced at the lowest point so that the spigot ends point in the direction of flow. Pipe shall be laid with ends abutting and true to line and grade. They shall be fitted and matched so that when laid in the work they will form a sewer with a smooth and uniform invert.
Trenches shall be kept free from water during jointing. The interior of the pipe and the outside of the spigot shall be kept clean during laying operations. Pipe shall be laid with ends abutting and true to line and grade. They shall be fitted and matched so that when laid in the work they form a sewer with a smooth and uniform invert.
Trenches shall be kept free from water during jointing. The interior of the pipe and the outside of the spigot shall be kept clean during laying operations. Pipe shall be lowered into the trench by such methods as will avoid damage and unnecessary handling in the trench.
Sewers shall be laid continuously through manhole locations, and the manhole built later. Pipe sections within the manholes shall not be broken out until after the manhole has been set and the interior concrete fill has hardened. Where, due to change in alignment, it is not practical to lay the sewer through the manhole by use of straight pipe or fittings, a portion of the manhole invert may be made of concrete formed to match the semicircular section of the sewer pipe.
The grade and alignment of sewers shall be determined and maintained by the use of a line parallel to the grade and line of the sewer. This line is to be supported above the ground surface on batter boards. Not less than three batter boards shall be kept in position at all times as a check on the accuracy of the grade line. Equivalent methods of maintaining grade and alignment may be used if approved by the town engineer.
The factory fabricated joint shall be installed in strict accordance with the manufacturer’s instructions therefor. Care shall be taken that the jointing surfaces are wiped clean before jointing, that the spigot end of the pipe is seated evenly against the face of the bell and that the sealing gasket, if used, is properly seated in the gasket groove. Due to the close tolerances of this type of joint, it is essential that the spigot end of the pipe being installed is in exact alignment with the bell of the pipe before pushing the joint together; that spigot and bell ends are free from sand or other material; and that joint lubricant, if recommended for the type of joint furnished, is applied. Cutting of cast iron pipe shall be done with mechanical pipe cutters in such a manner as to avoid damage to the pipe and leave a smooth cut at right angles to the axis of the pipe. The cut end shall be tapered with a grinder or filed about one-eighth inch back at an angle of approximately 30 degrees. In making up the push-on type of joint, the gasket shall be placed in the bell, the large round side of the gasket first, so it will spring into place over the bell head. The inside surface shall be lubricant furnished with the pipe. The joint shall be pulled together by the use of choker slings or by use of a bar used as a lever against the bell end of the pipe.
Manholes shall be constructed to the details shown on the town’s standards manhole drawing. The concrete manhole base shall be formed and placed prior to the setting of the manhole barrel sections unless otherwise approved by the town engineer. In forming the concrete base at manholes having an invert drop, the base shall be formed to the elevation of the pipe being blocked-up to the invert drop elevation specified. After the manhole sections have been installed all joints shall be grouted-in and pointed-up and the interior concrete fill placed and floated to a smooth surface. After the concrete has hardened, the pipe within the manhole shall be broken out flush with the concrete fill and the walls of the manhole and pointed-up to form a smooth continuous invert channel through the manhole.
The full depth of the manhole cover shall be at the elevation of the surface of the street paving unless otherwise directed by the town engineer. [Ord. 419 Appx. 2 §§ 4, 6, 1976. 1996 Code § 7-125.]
13.35.080 Infiltration.
All sanitary sewers shall be constructed such that infiltration of groundwater into any section of the sewer, including house or sewer service connections, or infiltration of sewage from the sewer shall not exceed 250 gallons per inch of diameter per mile of sewer in 24 hours. The completed sewers or any section thereof shall be subject to infiltration or infiltration tests at the discretion of the town engineer. [Ord. 419 Appx. 2 § 7, 1976. 1996 Code § 7-126.]
13.35.090 Plans.
Three complete sets of plans and specifications shall be submitted for approval. In general plans shall consist of a detailed layout of the area to be served by the proposed construction, including any contiguous or adjacent areas which might be affected, together with the relationship of the project with the entire physical drainage area and sufficient details and supplemental drawings as may be necessary for complete review of the proposed construction.
Plans for sanitary sewers must include profiles of each individual sewer line and invert and top of ring elevations of each manhole. Plans shall show the elevation and location of existing facilities to which the proposed construction will connect, together with all utilities the proposed construction will cross or be affected by.
Specifications covering the materials to be used and construction requirement shall accompany the plans.
Plans shall be drawn on standard plan and profile sheets no larger than 24 inches by 36 inches and bound with the details and cover sheet of the same size.
All elevations shown on plans shall be referenced to mean sea level and referenced to a United States geological survey benchmark or town benchmark run from such USGS elevation. Benchmarks used for the preliminary and construction surveys shall be shown on the plans.
In compliance with the state statutes, all designs, plans and specifications shall be prepared by a registered professional engineer licensed to practice in the state, and shall be submitted to the State Department of Environmental Quality, Water Quality Division, for their approval.
Within 30 days after completion of construction one reproducible copy and two sets of prints of “as constructed” drawings shall be submitted for the permanent records of the town. [Ord. 419 Appx. 2 §§ 1, 3, 1976. 1996 Code § 7-127.]