Chapter 5.20 DESIGN STANDARDS

Chapter 5.20
DESIGN STANDARDS

Sections:

5.20.010 Design criteria.

The following criteria for the design of gravity sewers within the jurisdiction of the Sanitary District No. 5 is hereby established.

(1) Population Density. Population densities for determining the ultimate tributary population shall be based on actual count, current general plan of the agency exercising jurisdiction, or based upon the character of proposed development, whichever is the greatest.

(2) Average Single-Family Unit. The average single-family unit shall be taken as two and one-half persons per residence.

(3) Per Capita Domestic Sewage Flow. The average per capita dry weather domestic sewage flow shall be taken as 80 gallons per day.

(4) Design Flows – Areas Containing Less Than 2,000 Persons. In the design of sewers for residential tributary areas containing 2,000 persons or less, the unit design flow used shall be 400 gallons per capita per day. This factor includes appropriate allowance for storm water infiltration.

(5) Design Flows – Areas Containing More Than 2,000 Persons. For tributary areas containing more than 2,000 persons, the total design flow shall be determined by multiplying the average dry weather sewage flow times the ratio of peak flow to average flow and adding an appropriate allowance for storm water infiltration.

(a) Ratio of Peak to Average Sewage Flow. The ratio of peak to average dry weather sewage flow is a function of the tributary population, and the values tabulated below shall be used.

Population Range	Rate of Peak to Average Dry Weather Sewage Flow
2,000 – 5,000	2.5
5,000 – 7,000	2.3
7,000 – 9,000	2.2
9,000 – 13,000	2.1
13,000 – 18,000	2.0

(b) Storm Water Infiltration. Investigation has shown that areas of the existing sewerage system constructed prior to 1962 contribute significantly higher amounts of storm water infiltration than can be expected from more recently constructed sewers. Accordingly, the following allowances shall be made for storm water infiltration flows:

Areas sewered prior to 1962 – 6,000 gallons per acre/day.

Areas sewered after 1962 – 2,500 gallons per acre/day.

Areas sewered after 1975 – 1,000 gallons per acre/day.

(6) Commercial or Industrial Flows. Unit design flows used for commercial or industrial areas shall be used on the type of existing or proposed development and shall be determined by special study subject to the review and approval of the District.

(7) Manning Formula. The diameter of gravity sewers shall be determined by use of the Manning formula, using a roughness coefficient, “n,” of 0.013 or the pipe manufacturer’s recommendation, whichever is greater.

(8) Special Design Problems. Special design problems involving siphons, pumps, pump stations, force mains, nonresidential connections, or other unusual features require individual study and approval by the District Engineer.

(9) References. Reference is made to WPCF and ASCE manuals, and to Minimum Design Standards of the Federal Housing Administration (FHA-G-4518.1). [Ord. 2014-2 (Att. § 4-01).]

5.20.020 Prohibited wastes.

(1) Prohibited Materials. It shall be unlawful for any person to connect any drain into the public sewer system. Dumping of garbage or septic tank sludge into manholes or sewers is strictly prohibited as set forth in District Ordinance 112. It shall be unlawful to discharge any industrial waste or any solid or semisolid or liquid substances resulting from any industrial manufacturing or commercial process or from any garage, service station or wash rack, into any sewer in the District without first having obtained a permit to do so from the Sanitary District.

Except as hereinafter provided, no person shall discharge or cause to be discharged any of the following described waters or wastes to any public sewer.

(a) Any solid or viscous pollutants in amounts which will cause obstruction to the flow in the system, or which will require unusual attention or expense to convey and/or treat. In no case shall there be discharge of any solid material not capable of passing through a three-eighths-inch mesh screen.

(b) Pollutants which create a fire or explosive hazard in the system, including, but not limited to, wastestreams with a closed-cup flashpoint of less than 140 degrees Fahrenheit (60 degrees Celsius) using the test methods specified in 40 CFR 261.21.

(c) Heated discharges in amounts which will inhibit biological activity in the treatment facility resulting in interference. Heated discharges in such quantities that the temperature at the treatment plant exceeds 104 degrees Fahrenheit (40 degrees Celsius), or which pose a hazard to District personnel.

(d) Any discharge which has been diluted as a partial or complete substitute for treatment to achieve compliance with this title, the user’s waste discharge permit, or the National Categorical Standards.

(e) Any discharge of hazardous waste, as defined by Cal. Code Regs. Title 22, without the written approval of the District.

(f) Any discharge which causes noxious or malodorous gases at or near the District’s facilities or which otherwise creates a public nuisance.

(g) Pollutants which result in the presence of toxic gases, fumes, or vapors within the District’s facilities in a quantity that endangers the health or safety of District personnel.

(h) Any storm water, surface water, ground water, roof runoff or subsurface drainage, except in cases of discharge of contaminated ground water in accordance with Section 8.

(i) Any radioactive wastes, except as allowed under the “California Radiation Control Regulations,” Cal. Code Regs. Title 23, § 30100 et seq.

(j) Any discharge of any pollutant, including oxygen demanding pollutants (BOD, etc.), released at a flow rate and/or concentration which will cause interference with the system.

(k) Any discharge containing petroleum oil, nonbiodegradable cutting oil, or products of mineral oil origin in amounts that, alone or in conjunction with other discharges, will cause interference or pass-through.

(l) Any discharge which, alone or in conjunction with a discharge or discharges from other sources, will compromise the use of District’s treated wastewater for any adopted reclamation use.

(m) Pollutants which will cause corrosive structural damage to the system.

(n) Substances containing greater than five percent copper by weight, added to control roots or for any other purpose.

(2) Interceptors Required. Grease, oil, and sand interceptors shall be provided when, in the opinion of the District, they are necessary for the proper handling of liquid wastes containing grease in excessive amounts, or any flammable wastes, sand and other harmful ingredients; except that such interceptors shall not be required for buildings used for residential purposes. All interceptors shall be of a type and capacity approved by the District and shall be so located as to be readily and easily accessible for cleaning and inspection.

(3) Maintenance of Interceptors. All grease, oil and sand interceptors shall be maintained by the owner, at his expense, in continuously efficient operation at all times.

(4) Swimming Pools. It shall be unlawful for any person to discharge the contents of a swimming pool into a sanitary sewer except in the manner specified herein. The size of pipe carrying discharge water shall not be larger than two inches and shall not be under a head to exceed 20 feet. If the water is discharged by pumping, the rate of flow shall not exceed 50 gallons per minute. Each swimming pool discharging to a sanitary sewer shall be equipped with an approved separator to preclude any possibility of a backflow of sewage into the swimming pool or piping system. [Ord. 2014-2 (Att. § 4-02).]

5.20.030 Sewer pipes.

(1) Pipe Materials. All main sewer and lateral sewer pipes shall be PVC plastic pipe, polyethylene pipe, ductile iron pipe, cast iron pipe, or reinforced concrete (large diameter – special situations), unless otherwise specifically required or approved by the District. Selection of the pipe type for a given project shall be made by the job engineer, subject to the approval of and final selection by the District. The type of pipe used for side sewer installations shall conform to the “Approved Side Sewer Pipe Materials List,” on file in the District office. The type of pipe used for force mains shall be PVC plastic pipe, polyethylene pipe, cast iron pipe or concrete steel cylinder pipe, as specifically approved for the particular project by the District. Special pipe and/or design provisions may be required by the District.

(2) Minimum Pipe Sizes. The minimum pipe size for main sewers shall be eight inches in diameter unless otherwise specifically allowed by the District. The minimum pipe size for side sewers shall be four inches or the same size as the building plumbing stub, whichever is greater. Where more than 150 fixture units are to be connected, the side sewer shall have a six-inch minimum diameter. When more than one building sewer is allowed to be connected to a single side sewer, the side sewer from the point of intersection of one or more building sewers to the main sewer shall be not less than six inches in diameter.

(3) Minimum Slope – Main Sewers. The slope of the sewer shall be such that the velocity of flow in the pipe when flowing full shall be equal to or greater than two feet per second. The minimum acceptable slopes for various main sewer sizes are tabulated below. For construction in filled marshland or bay mud, or other areas subject to possible differential settlement, the District may specify acceptable minimum slopes greater than those shown.

Pipe Size in Inches	Minimum Slope Ratio in Feet per Foot
6	0.006
8	0.004
10	0.0028
12	0.0022
15	0.0015
18	0.0012
21	0.0010
24	0.0008

(4) Minimum Slope – Side Sewers. The minimum slope for four-inch diameter side sewers shall be one foot per 100 feet (one percent). The minimum slope for side sewers greater than four inches shall be seven-tenths foot per 100 feet (seven-tenths percent).

(5) Steep Slopes. For sewers installed in areas with steep ground slopes, special design features may be required. Depending upon conditions of the specific installation, such items as check dams, rip-rap, trench dams, special anchorage or special pipe materials may be required by the District.

(6) Minimum Pipe Cover. The following minimum pipe covers shall be attained in design and construction of sanitary sewers. If certain conditions exist which make it impractical to meet the minimum cover and clearance requirements, special pipe, bedding, encasement, rip-rap, and/or backfill will be required as directed by the District Engineer.

(a) Main Sewers. The minimum pipe cover for main sewers within street rights-of-way shall be three feet. The minimum cover for mains within easements or other rights-of-way not expected to become streets shall be three and one-half feet. Lesser pipe cover may be approved by the District with use of special pipe materials or concrete slab protection.

(b) Side Sewers. That portion of a side sewer within a street right-of-way (lateral sewer) shall have a minimum cover of three feet. The minimum cover for side sewers from the property line to the building drain (building sewer) shall be three feet. However, when the cover over the side sewer is less than 24 inches, special pipe, bedding and/or concrete encasement may be required by the District.

(7) Pipe Strengths and Maximum Depths. The minimum pipe strengths and classes given as standard in these specifications (see SD5MCC 5.70.020 and 5.70.030) and in the “Approved Side Sewer Pipe Materials List,” are based upon the attainment of standard bedding conditions (see SD5MCC 5.65.050(8)), maximum allowable trench widths (see SD5MCC 5.65.050(2)), and upon the assumption of average pipe depths (depths up to 12 feet). Where, for any reason, the standard bedding conditions cannot be attained, or the maximum allowable trench width is exceeded, or the pipe depth is greater than average, special pipe, bedding, backfill and/or encasement may be required as directed by the District. Where pipe depths or other known conditions require pipe strengths other than those specified as standard, the job engineer shall indicate the required pipe classes on the plans.

(8) Pipe Clearance. All sewer pipes and structures shall be designed and contracted to have a minimum of 10 feet from domestic water lines and 24 inches’ clearance from all other utilities and/or improvements, unless a special approval is received from the District.

(9) Horizontal and Vertical Curves. Horizontal curves may be used on curved streets when the alignment can be kept concentric with street improvements and when pipe deflection requirements can be met. Vertical curves may be used in hilly terrain, when permitted by the District, in order to reduce the number of required manholes. The deflection in the joint between any two successive pipe sections shall not exceed 70 percent of the maximum deflection as recommended in writing by the pipe manufacturer. Shorter pipe joint lengths may be used for vertical or horizontal curves with approval by the District.

(10) Sewer Connections to Existing System. Connection of new main sewers to the existing sewer system shall be made at existing manholes or by constructing a new manhole at the point of connection. The elevation of new sewer mains or laterals connecting to a manhole shall be set so that the pipe crowns match. Side sewer connections to existing main sewers shall be accomplished by connecting to wye or tee branches or laterals where they exist, by installing a spliced-in-wye, by installing a Tap-Tite drilled connection or by connecting to an existing manhole. Inserta Tee lateral connection may not be used on sewer mains with a diameter less than 12 inches. Side sewers eight inches and larger shall be connected with manholes only.

(11) Individual Sewage Ejector Pumps. Special application must be made for installation of an individual sewage pump where gravity service is not feasible. All pumping systems shall be installed in accordance with all applicable codes. The District will inspect the pump station and pressure line from the sewage pump to the point of connection to the District sewer system.

The gravity discharge line from the building outlet to the sewage pump holding tank shall be gravity flow. When the distance between the building outlet and the sewage pump holding tank is greater than five feet, the District shall have jurisdiction, and the gravity line shall be inspected by the District Inspector.

The holding tank, pumps and electrical work are under the jurisdiction of the District.

(12) Sewer Alignment. Where sewer lines are to be installed within street rights-of-way, they shall, wherever practical, be designed and installed five feet off the center line of the existing or future street (usually the side opposite the water line). In streets in hilly areas, the sewer shall be installed on the uphill side of the street where possible. Where practical, all sewer lines within easements shall be designed and installed with not less than five feet between the center line of sewer and the edge of the easement. All sewer lines and structures shall be designed and installed well in the clear of all other improvements and utilities (see “Pipe Clearance,” subsection (8) of this section).

(13) Sampling Manhole. Dischargers of nondomestic wastes may be required to install a sampling manhole at the location where the lateral sewer connects to the sewer main as designated by the District.

(14) Manhole Accessibility. Insofar as possible, all manholes shall be situated so that they are accessible to the District’s cleaning vehicles.

(15) Sewer Pipe Stubs. Sewer pipe stubs shall be designed and installed in all manholes from which future sewer line extensions are anticipated. Pipe stubs shall be minimum eight inches in size or as directed by the District and shall be of an approved type of pipe. Stubs shall protrude a minimum of five feet outside of the manhole base and shall be channeled as though a regular sewer line within the manhole. A rubber coupling on the outside of the pipe shall be encased in the manhole base to prevent leakage. The outboard end of stubs shall be a standard bell joint end and shall be plugged with a standard watertight plug and cap, as supplied by the pipe manufacturer.

(16) Sewer Line Extensions. In all new streets, where sewer lines are expected to be extended, the sewer line shall be designed and installed to the end of the proposed street improvements, prior to street construction. The sewer extension shall terminate with a manhole, at a location which will minimize the amount of pavement to be disturbed by future sewer extensions.

(17) Sewers to Be Installed in Existing Improved Streets. Where sewers are being designed for installation in existing City and/or County streets, the job engineer shall submit the plans for the proposed work to the City and/or County Public Works Department for location and encroachment permit approval.

(18) Sewers to Be Installed in or Across Utility, Highway, Railroad Rights-of-Way or Creeks. Where sewers are to be constructed across or within utility, railroad rights-of-way, or creeks requiring tunnels, bores and/or special pipe, the special pipe or construction shall extend the full length of the sewer line within the particular right-of-way. The permittee shall secure all necessary encroachment permits or joint use permits for utility, highway, railroad rights-of-way or creek crossings.

(19) Separate Side Sewers Required. Each individual building site shall be connected to the main sewer with a separate side sewer. Combined side sewers for buildings under the same ownership will be permitted only on specific approval of the District when the property is not likely to be subdivided in the future. A common side sewer may be used for connected buildings (i.e., buildings with common walls or multistory buildings) under different ownership where the covenants, conditions and restrictions (CC&Rs) provide that the homeowners’ association maintains all common laterals.

(20) Side Sewer Connections. Side sewers shall be installed into manholes where possible. Side sewers shall connect near the bottom of the manhole, matching pipe crowns, unless a formal external drop connection is provided.

(21) Side Sewer Cleanouts Required. Cleanouts shall be installed in the side sewer as provided in the Uniform Plumbing Code. The cleanout riser shall be equal in size to the side sewer (see Drawing SD-5, SD5MCC 5.105.010).

Cleanouts shall be installed at the following locations:

(a) At the junction of the house plumbing and side sewer two feet outside the building.

(b) At each bend or change in direction of the side sewer 45 degrees or over.

Note: All cleanouts, except the blowoff cleanout, shall be brought to grade, properly capped and completely watertight.

(22) Backwater Prevention Devices. All side sewers shall be equipped with an approved backwater prevention device, as detailed on the standard drawings (see Drawing SD-6, SD5MCC 5.105.010).

(23) Check Valve. If the difference between the elevation of the lowest fixture and the backwater prevention device is less than six inches, a check valve shall be installed between the backwater prevention device and house (see Drawing SD-7, SD5MCC 5.105.010).

(24) Abandoned or Unused Side Sewers. Any abandoned or unused side sewers connected to District mains, including side sewers from homes or buildings that are demolished, or any side sewer from property line to District mains shall be dug out and followed to the District main, and the old wye or tee or old connection area shall be cut away and spliced with a solid piece of pipe of the same size and dimension. The District Inspector shall be present when this procedure is done. [Ord. 2014-2 (Att. § 4-03).]

5.20.040 Sewer structures.

(1) Manholes. Manholes shall be placed at all intersections of sewer lines other than side sewer connections less than eight inches in diameter, at all vertical or horizontal angle points, and at intervals not greater than 350 feet. Where practical, manholes shall be located near the center of street intersections and shall be accessible to maintenance vehicles. All manholes from which future sewer line extensions are anticipated shall have a pipe stub planned and installed at the grade and the direction of the anticipated sewer extension. The pipe stub shall be installed with permanent watertight plug in bell of five-foot pipe stub out of manhole. The following regulations shall also apply:

(a) A standard drop manhole with external hubbed ductile iron drop connection shall be installed when the invert elevation of the incoming sewer is greater than two feet higher than the outgoing sewer. Otherwise, the crown elevation of the incoming sewer must match the crown elevation of the outgoing sewer, allowing for the appropriate slope through the manhole. The District must specifically approve all proposed drop manholes.

(b) Where there is to be more than 30 degrees deflection between any inlet line and the outlet line of a manhole, the fall through the manhole shall be a minimum of one-tenth of a foot.

(d) Unless special arrangements are made, all lines connecting to existing manholes shall conform to the standard drawings for new manholes.

(e) A manhole shall be located at the terminus of all main sewers in street.

(2) Rodhole. A rodhole may be installed only in easements out of the road right-of-way at the terminus of a main sewer where there is no possibility that the sewer will be extended to serve upstream properties. The distance from a rodhole to the nearest manhole shall be no greater than 200 feet.

(3) Flushing Inlets. A flushing inlet shall be installed on the force main near each new pump station, at a location specified by the District, in order to provide easy access for flushing the system for a temporary pumping connection if the pump station is out of service.

(4) Test Fittings. All test fittings shall, unless otherwise approved, be tees or wye branches of the same size, type and quality as that of the line in which they are being installed. The branch of all test fittings shall be installed in an upright position and shall be brought to grade as a cleanout or removed after testing.

(5) Pressure Frame and Covers. Pressure (watertight) frames and covers shall be installed when specified by the District, where drainage conditions may cause storm waters to inundate sewer structures.

(6) Remodeling Structures. All structures to be remodeled shall comply with the standard drawings. Any remodeling of any structure shall be specified and/or detailed on the plans and approved by the District prior to any remodeling work.

(7) Special Structures. Trunk sewer manholes, siphons, pumping systems, and other unusual structures require specific design approval by the District.

(8) Locator Wire and Detection Tape. An AWG No. 14 locator wire and plastic detection tape shall be installed above all gravity sewers and force mains between manholes. There shall be a minimum of one-foot of separation between locator wire and detection tape. The locator wire shall terminate with a minimum of three feet of coiled wire inside the manholes at each end of the sewer. Wire shall be neatly rolled with ends securely taped and hung in an out-of-the-way location. Wire is to be brought into manhole through a neat hole drilled through riser ring on top of taper a maximum of one foot from the bottom of the casting. [Ord. 2014-2 (Att. § 4-04).]