Chapter 14.36 — DESIGN CRITERIA FOR SEWER CONSTRUCTION

The approval by the city manager of plans for construction of sewers by private developers shall be based upon good engineering practice and upon the standards set forth in this chapter.

(Code 1972, § 14.36.010; Ord. No. 352, § 701, 1970)

Pipe materials shall be chosen for their strength, durability, and ease of maintenance, with due consideration for dead and live loads, beam strength, and resistance to corrosion. Pipe joints shall be selected to provide positive protection against entrance of roots and groundwater, and sufficient flexibility to adjust to the trench bedding. Joints shall be nonrigid, and the joint sealer shall be restrained against lateral and axial movement.

(Code 1972, § 14.36.020; Ord. No. 352, § 702A, 1970)

The following pipe materials are acceptable for construction of sewers: Extra-strength vitrified clay pipe, asbestos cement pipe, nonreinforced concrete pipe, reinforced concrete pipe, cast iron pipe, steel pipe, and plastic pipe.

(Code 1972, § 14.36.030; Ord. No. 352, § 702B, 1970)

Gravity sewers having slopes less than the standard minima specified in section 14.36.170 shall be made only of clay pipe or of other corrosion-resistant material approved by the city manager. Clay or other corrosion-resistant pipe shall also be used for sewers downstream from sewers of substandard slope, to a point where, in the judgment of the city manager, there is no longer a substantial danger of corrosion due to septicity of the sewage. Cast iron or steel pipe shall be used where the sewer may be subjected to physical forces that would threaten the integrity of other materials and, generally, for sewers aboveground, but shall not be used otherwise. Clay pipe, nonreinforced concrete pipe, and plastic pipe shall not be used aboveground unless encased.

(Code 1972, § 14.36.040; Ord. No. 352, § 702C, 1970)

The drawings shall show the acceptable type or type of bedding, the maximum allowable trench width at the top of the pipe, and the strength class of the acceptable pipe materials. The strength class shall be

sufficient so that the properly installed pipe will not be endangered, as calculated according to good engineering practice.

(Code 1972, § 14.36.050; Ord. No. 352, § 702D, 1970)

The minimum pipe diameter for public sewers shall be six inches.

(Code 1972, § 14.36.060; Ord. No. 352, § 702E, 1970)

The city manager will require such tests and certifications as he deems necessary to show that the specified materials are being used on the work. Notwithstanding prior factory or yard inspection, the city manager will have the right to reject any damaged or defective materials found on the job which in his opinion will affect the durability of the installation, and may order its removal from the site.

(Code 1972, § 14.36.070; Ord. No. 352, § 702F, 1970)

Sewers shall be laid on a straight alignment and grade between manholes, except that curved sewers may be used subject to the following requirements:

(1)

Minimum radius shall be 100 feet;

(2)

Minimum invert slope shall be 0.01 except that sewers with a radius of 200 feet or more will have the same requirements as straight sewers;

(3)

Total deflections. The total of all deflections due to curves in the sewer between any two manholes shall not exceed 60 percent;

(4)

Maximum deflection at any joint shall be as recommended by the manufacturer, but in no case more than three degrees.

(Code 1972, § 14.36.080; Ord. No. 352, § 703, 1970)

Sewers shall not be located in the parkway or within four feet of the curb except with special permission of the city manager. On divided highways, a separate sewer shall be installed to serve each side of the highway.

(Code 1972, § 14.36.090; Ord. No. 352, § 704A, 1970)

The sewer interline shall not be closer than ten feet horizontally to the centerline of any parallel water line nor five feet to the centerline of a gas line or other utility except with special permission of the city manager.

(Code 1972, § 14.36.100; Ord. No. 352, § 704B, 1970)

In curved streets the sewer shall, in general, parallel the street curvature, at least to the extent of avoiding unnecessary crossings of the centerline.

(Code 1972, § 14.36.110; Ord. No. 352, § 704C, 1970)

Where a sewer cannot be installed in a public street it shall be located in an easement conveyed to the city and shown as such on the tract map. Sewer plans shall show easement descriptions wherever practicable.

(Code 1972, § 14.36.120; Ord. No. 352, § 704D, 1970)

Sewer easements shall be 12 feet wide where access is provided at both ends, and 15 feet wide where access is provided at one end only.

(Code 1972, § 14.36.130; Ord. No. 352, § 704E, 1970)

Deeds for easements shall provide for restriction of permanent construction so that access to the sewer for maintenance operations will not be impaired.

(Code 1972, § 14.36.140; Ord. No. 352, § 704F, 1970)

Where easements follow common lot lines, the full easement width shall be on one lot, in such a manner that access to manholes will not be obstructed by walls, trees, or permanent improvements. Where this requirement cannot be met without interfering with existing buildings, easements may straddle lot lines.

(Code 1972, § 14.36.150; Ord. No. 352, § 704G, 1970)

Sewers shall be installed at a depth which will provide suitable service to the properties connected and will allow subsequent installation of water lines in accordance with the regulations of the county governing separation of sewers and water supplies, with a minimum of special construction of the water lines other than joint spacing.

(Code 1972, § 14.36.160; Ord. No. 352, § 705, 1970)

Minimum slope requirements are necessary to ensure self-cleansing and self-oxidizing velocities in order to avoid significant generation of hazardous, odorous, and corrosive sulfur compounds. The standard minimum slope shall be 0.6 percent except where the sewer will serve more than 400 connections. Slopes below the standard minimum slopes may be used only if justified in an engineering report, approved by the city manager, showing that it is not reasonably feasible to attain the standard slopes.

(Code 1972, § 14.36.170; Ord. No. 352, § 706, 1970)

Manholes shall be located at all abrupt changes in alignment and at junctions, and elsewhere as required so that the spacing shall nowhere exceed 400 feet.

(Code 1972, § 14.36.180; Ord. No. 352, § 707A, 1970)

Manholes shall be provided with steps made of bent Type 304 stainless steel rod, five-eighths inch in diameter. The steps shall be formed so that a foot cannot slip off laterally, and shall have a clear width not less than 12 inches. The vertical spacing shall not exceed 14 inches. The channel shall be of a well-formed U-shape, with a depth equal to the diameter of the pipe and with the lower half continuous with the lower half of the pipe. The bench shall slope one-half-inch per foot toward the channel. The drop of invert elevation through the manhole, even on curves, shall be only the drop due to a continuation of the slope of the pipe. At a junction of two sewers of the same size, however, the invert of a branch shall be one-tenth foot above the invert of the main stream, or more if necessary to avoid retardation of flow in the branch. Drop manholes should be avoided insofar as possible.

(Code 1972, § 14.36.190; Ord. No. 352, § 707B, 1970)

The upper end of a sewer may end in a terminal cleanout if the distance to a manhole is not more than 200 feet, or if the slope is not less than one percent and the distance to a manhole is not more than 300 feet. Otherwise, it shall end in a manhole.

(Code 1972, § 14.36.200; Ord. No. 352, § 708A, 1970)

A terminal cleanout shall be constructed generally as illustrated on drawings furnished by the city manager.

(Code 1972, § 14.36.210; Ord. No. 352, § 708B, 1970)

Wherever it is known or can be reasonably assumed that a building sewer connection is required, a service lateral shall be shown on the plans and installed to the property line as a part of the street sewer construction prior to paving; provided, however, that a subdivider will not be required to pay for service laterals from off-tract sewers.

(Code 1972, § 14.36.220; Ord. No. 352, § 709A, 1970)

A service lateral serving a single dwelling shall be at least four inches inside diameter. All others shall be at least six inches inside diameter.

(Code 1972, § 14.36.230; Ord. No. 352, § 709B, 1970)

Where a service lateral will not be needed because the public sewer will be on private property, or where for some other reason it may not be feasible during main sewer construction, to construct a lateral for future use, yet there is a strong possibility that a connection will be needed, the city manager may require that a wye or tee be installed.

(Code 1972, § 14.36.240; Ord. No. 352, § 709C, 1970)

Unused wyes of service laterals shall be tightly sealed and supported in a manner to facilitate their future location and use. Locations shall be indicated on the plans and marked on the curb, or as otherwise approved by the city manager.

(Code 1972, § 14.36.250; Ord. No. 352, § 709D, 1970)

The making of connections to wyes, tees, and service laterals, the tapping of the main sewer where there is no wye or service lateral, and the maintenance of service laterals are subject to the requirements of chapter 14.20.

(Code 1972, § 14.36.260; Ord. No. 352, § 709E, 1970)

The construction specifications shall contain adequate provisions, satisfactory to the city manager, describing the conditions of excavation so as to minimize hazard or nuisance to the public and to safeguard the integrity of the sewer being installed. Methods of backfilling also shall be specified that will avoid trouble from damaging the pipe or from subsequent sinking of the surface.

(Code 1972, § 14.36.270; Ord. No. 352, § 710, 1970)

The specifications shall require that the sewer line pass a test for tightness before its acceptance by the city, the test to be not less strict than set forth in sections 14.36.290 through 14.36.310.

(Code 1972, § 14.36.280; Ord. No. 352, § 711A, 1970)

The finished sewer shall be tested either by air or water, at the expense of the builder.

(Code 1972, § 14.36.290; Ord. No. 352, § 711B, 1970)

After plugging all openings and providing thrust blocking as necessary, air shall be admitted to the section under test at an inlet pressure not exceeding five psi from a source regulated by an adjustable pressure control valve and measured by a sensitive pressure gauge calibrated from zero to ten psi. When the internal gauge pressure has reached three and five-tenths psi under stabilized temperature conditions, the air supply to the test section shall be cut off. The inspector shall then observe the time interval during which the internal pressure drops one psi from three to two psi. The length of time for the one psi loss shall not be less than that shown in the following table for the sewer size being tested.

Sewer Diameter Minimum Time for One psi Loss

6 inches through 14 inches 1 minute

15 inches through 20 inches 2 minutes

21 inches through 30 inches 3 minutes

31 inches through 36 inches 4 minutes

(Code 1972, § 14.36.300; Ord. No. 352, § 711C, 1970)

Water shall be applied until the head over the lower end of the reach is ten feet, or the head over the upper end is five feet, whichever requires the higher water level, except that a lower head may be applied where necessary to avoid overflowing a manhole or exceeding the safe working pressure of the pipe. The leakage shall be determined from the loss of water from a standpipe or manhole. The water level shall not drop more than two feet during the measurement. The rate of loss of water shall not exceed 0.05 gallon per day per inch of pipe diameter per foot of length tested, including the length of service laterals.

(Code 1972, § 14.36.310; Ord. No. 352, § 711D, 1970)

It is recognized that unusual conditions not anticipated in the composing of these criteria may arise, of such nature that strict conformance would lead to designs not indicative of the application of proper

engineering skill. The criteria shall not be interpreted to excuse the designing engineer from the need to develop an all-around good design. On the other hand, rigid conformance to the criteria may not be required in situations where no useful purpose would be served. Therefore, the city manager may reject a design that he considers unsatisfactory even though it may not specifically violate any criterion listed in this chapter, and he may grant exceptions to the criteria of this chapter where the exercise of sound engineering judgment requires such exceptions.

(Code 1972, § 14.36.320; Ord. No. 352, § 712, 1970)