Recommended Design Criteria...
Engineer's Report, Plans, and Specifications...
Information for sewer systems must be submitted as required by Chapter 10, Recommended Standards for Wastewater Works, 1978 or the latest edition.
Types of Sewers...
1. Community Sewers : In general, and except for special reasons, the Department will approve plans for new systems, extensions, or replacement sewers only when designed upon the separate plan, in which rain water from roofs, inflow from streets and other areas, and groundwater from foundation drains is excluded. "Combined" sewers are not permitted unless provisions have been made for directing and treating the overflows.

2. House Sewers : House sewers conveying raw wastewater to public sewers should meet all requirements of the State Plumbing Code and the plumbing code of the local authority having jurisdiction, as well as the following :

a. They shall be of asbestos cement, plastic, cast iron, concrete, vitrified clay or other material of 1,200 pound crush strength or heavier.
b. They shall have a nominal inside diameter of not less than four inches.
c. House sewer joints and connections to public sewers should be watertight and root proof.
d. House sewers should be laid on a slope of 1/4 inch per foot and in no case less than 1/8 inch per foot.
e. House sewers shall not be directly connected to manholes.
f. Abandoned disposal systems shall be disconnected from buildings and plugged. All receptacles or excavations in which such receptacles were contained shall be filled with earth. Prior to filling, receptacle contents shall be pumped out and disposed of in a manner to eliminate pollution.

3. Industrial Sewers : Any industrial hook-ups; such as restaurants, rendering plants and service stations should have adequate pretreatment facilities for grease and grit collection in order to prevent clogging of collection lines and wear of components in discharge lines.
Design Period...
Refer to Chapter I.
Design Factors...
In determining the required capacities of sanitary sewers, the following factors should be considered :

1. Peak hourly wastewater flow from residences.
2. Additional maximum wastewater flow from industrial plants and institutions.
3. Groundwater infiltration and inflow.
4. Capacity of pumps in wastewater pumping stations.
Design Basis...
1. Per Capita Flow : New sewer systems shall be designed on the basis of an average daily per capita flow of wastewater of not less than 100 gallons per day. This figure is assumed to cover a small amount of infiltration, but an additional allowance should be made where a large amount of infiltration is present.

a. Design capacity for laterals and sub-mains - Full running capacity of not less than 4 times the design average daily flow per capita per day.
b. Design capacity for large sewers - Full running capacity of not less than 2.5 times the design average daily flow per capita per day or peak hourly flow, whichever is greater.

2. Alternate Method : If water consumption records are available, refer to Chapter I. When deviations from the foregoing per capita rates are demonstrated, a description of the procedure used for sewer design shall be included.
Gravity Sewer Design and Construction...
1. Minimum Size : No community sewer receiving raw wastewater shall be less than six inches in diameter, however, eight inch diameter sewers are recommended. Six inch diameter pipe may be used as laterals where there are relatively low flows, a small number of people to be served, future extensions not anticipated and the sewer is capable of handling the design flows. The justification for using the six-inch pipe shall be provided by the consultant. The operating authority shall be made aware of the added possibility of cleaning problems which shall require their acceptance of any additional maintenance. Sewers receiving treated or partially treated wastewater and capable of handling the design flows may be four inches in diameter where adequate justification and documentation is provided. See Section N in this Chapter for EPA funded projects criteria.

2. Depth : Gravity sewers should be placed deep enough to serve all basements, assuming a 2 percent grade on house sewers (absolute minimum of 1 percent). They should be well below the frost line at all points and lower than any water lines placed in the same street. Where freezing conditions could occur, sewer lines should be provided with sufficient insulation or a raised berm for cover.

3. Slope : a. All sewers shall be so designed and constructed to give mean velocities, when flowing full, of not less than 2.0 feet per second, based on Manning's formula using an "n" value of 0.013. Based on an "n" value of 0.013, the following are the minimum slopes which should be provided; however, slopes greater than these are desirable :

Sewer Diameter ( inch )	Minimum Slope ( Ft / 100 feet )
4	1.05
6	0.60
8	0.40
10	0.28
12	0.22
14	0.17
15	0.15
16	0.14
18	0.12
21	0.10
24	0.08
27	0.067
30	0.058
36	0.046

b. Depending on the type of pipe, other practical "n" values may be permitted by the Department if deemed justifiable on the basis of research or field data presented. Slopes slightly less than those required for the 2.0 feet per second velocity when flowing full may be permitted. Reduced slopes will be permissible if a minimum velocity of 1.8 feet per second can be maintained and if detailed justifiable reasons are given; such as, a sewer serving a limited area or the elimination of a sewage lift station. Such decreased slopes will only be considered where the depth of flow will be 0.3 of the diameter or greater for design average flow. Whenever such decreased slopes are selected, the design engineer must furnish with his report his computations of the depths of flow in such pipes at minimum, average, and daily or hourly rates of flow. The operating authority shall be made aware that decreased slopes may cause additional sewer maintenance expense and septic conditions. Sewer size shall be based on design flows and not the grade that is available.

c. Sewers shall be laid with uniform slope between manholes.

d. Sewers on 20 percent slope or greater shall be anchored securely with concrete anchors or equal, spaced as follows :

( 1 ) Not over 36 feet center to center on grades 20 percent and up to 35 percent.
( 2 ) Not over 24 feet center to center on grades 35 percent and up to 50 percent.
( 3 ) Not over 16 feet center to center on grades 50 percent and over.

1. Alignment : Sewers 24 inches or less shall be laid with straight alignment between manholes except where street or road layouts are such that straight alignment between manholes is impractical, sewers may be curved to conform with their curvature. The radius of curvature shall not be less than 100 feet and the deflection angle shall not exceed the manufactures recommendations at any joint or point on the pipe. It is suggested that the sewer curvature be made concentric with the street curvature to simplify layout work and locating the lines at a later date. An alignment test such as "balling" must be conducted on curved sewers. The entity responsible for maintenance should be cognizant of the fact that additional maintenance may be necessary and small diameter sewers will require jet-cleaning machines.

2. Increasing Size : When a smaller sewer joins a larger one, the invert of the larger sewer should be lowered sufficiently to maintain the same energy gradient. An approximate method for securing these results is to place the 0.8 depth of flow point of both sewers at the same elevation. Generally, sewers should not decrease in size in the downstream direction.

3. High Velocity Protection : Where velocities greater than 15 feet per second are attained, sewers shall be anchored securely with concrete anchors or equal to protect against displacement by erosion and shock. The design shall be such to prevent turbulence and deterioration of the receiving manhole.

4. Materials, Trenching and Installation : Any generally accepted material for sewers will be given consideration, but the material selected should be adapted to local conditions, such as character of industrial wastes, possibility of septicity, soil characteristics, exceptionally heavy external loadings, abrasion and similar problems. Installation specifications shall contain appropriate requirements based on the criteria, standards and requirements established by industry in its technical publications. Requirements shall be set forth in the specifications for the pipe and methods of bedding and backfilling thereof so as not to damage the pipe or its joints, impede cleaning operations and future tapping, nor create excessive side fill pressures or ovalation of the pipe, nor seriously impair flow capacity. The design engineer should consult the various ANSI and ASTM specifications or industry literature for information on pipe bedding classes for each pipe material used in the design. When trenching, all rock shall be removed within 6 inches of the pipe. The trench shall be dewatered for all work. Open trench time should be considered and all pipe ends plugged when installation of pipe is halted.

In all cases, suitable backfill or other structural protection shall be provided to preclude settling and/or failure of the higher pipe. Backfill shall not contain debris, frozen material, large clods or stones, organic matter or other unstable material. Stones larger than 3 inches in diameter shall not be placed within 2 feet of the top of the pipe. Compaction shall be to a density at least equal to the surrounding soil or existing roadway conditions. All sewers shall be designed to prevent damage from superimposed loads. Proper allowance for loads on the sewer shall be made because of the width and depth of trench. When standard strength sewer pipe is not sufficient, the additional strength needed may be obtained by using extra strength pipe or by special construction. Deflection tests shall be performed on pipe after final backfill has been in place at least 30 days. No pipe shall exceed a deflection of 5 %.

5. Joints and Infiltration : The method of making joints and materials used should be included in the specifications. Sewer joints shall be designed to minimize infiltration and to prevent the entrance of roots. Leakage tests shall be specified. This may include appropriate water or low pressure air testing. The leakage outward or inward (exfiltration or infiltration) shall not exceed 200 gallons per inch of pipe diameter per mile per day for any section of the system. The use of a television camera or other visual methods for inspection prior to placing the sewer in service is recommended.

6. Calculations : Computations should be presented, in a tabular form, to indicate depths and velocities at minimum, design average and peak hourly waste flow for the different sizes of sewers proposed.
Manholes...
1. Location : Unless necessary, manholes should not be located in drainageways. If any flooding over manholes is anticipated; they shall be provided with watertight covers. Manholes shall be installed at the end of each line; at all changes in grade, size, or alignment; at all intersections; and at distances not greater than 400 feet for sewers 15 inches or less, and 500 feet for sewers 18 inches to 30 inches, except that distances up to 600 feet may be approved in cases where adequate cleaning equipment for such spacing is provided. Greater spacing may be permitted in larger sewers and in those carrying a settled effluent. The distance between manholes for sewers less than 15 inches in diameter may be increased to 450 feet if justification is provided by the consultant.

2. Cleanouts : Cleanouts may be used only for special conditions and shall not be substituted for manholes nor installed at the end of laterals greater than 150 feet in length. Cleanouts shall be provided on all service lines in accordance with State Plumbing Code. The cleanout shall be constructed using a 45 degrees bend directed downstream on vertical riser pipe to the surface. Size of the cleanout shall be the same as the pipe size.

3. Drop Type : A drop pipe shall be provided either inside or outside for a sewer entering a manhole at an elevation of 24 inches or more above the manhole invert. Where the difference in elevation between the incoming sewer and the manhole invert is less than 24 inches, the invert should be filleted to prevent solids deposition. Inside drop connections shall be secured to the interior wall of the manhole and provide adequate access for cleaning. For exterior drop connections, the entire outside drop connection shall be encased in concrete.

4. Diameter : The minimum diameter of manholes shall be 48 inches. The size of the manhole access shall be 22 inches or larger in diameter.

5. Flow Channel : The flow channel through manholes should be made to conform in shape and slope to that of the sewers.

6. Watertightness : The specifications shall include a requirement for inspection of manholes for watertightness prior to placing into service and shall not exceed leakage limits for sewers. Watertight manhole covers or raised manhole frames and covers are to be used wherever the manhole tops may be flooded by street runoff or high water. Manholes of brick or segmented block should be waterproofed on the exterior with plaster coatings; supplemented by a bituminous waterproof or epoxy coating where groundwater conditions are unfavorable.

7. Safety and Vandalism : It is recommended that entrance into manholes contain provisions for portable ladders. Consideration should be given for providing a means of ventilation for deep manholes. Locked manhole covers may be desirable where vandalism or unauthorized dumping may be a problem.
Inverted Siphons...
Inverted siphons shall require at least two barrels, with a minimum pipe size of six inches and shall be provided with necessary appurtenances for convenient flushing and maintenance; the manholes shall have adequate clearances for rodding; and in general, sufficient head shall be provided and pipe sizes selected to secure velocities of at least 3.0 feet per second for average flows. The inlet and outlet details shall be designed to permit the normal flow to be diverted to one barrel while the other barrel may be taken out of service for cleaning. The joints should not exceed 45 degrees bends to easily accommodate cleaning equipment.
Stream Crossings...
1. Cover Depth : The top of sewers when entering or crossing streams shall be at a sufficient depth below the natural stream bed to protect the sewer line. The following cover requirements should be met :

a. One foot of cover where the sewer is located in rock. b. Three feet of cover or more is required in other material depending on size of stream. c. In paved stream channels, immediately below the pavement. d. Shallow and intermittent streams may require insulating materials.

2. Alignment : Sewers crossing streams should be designed to cross the stream as nearly perpendicular as possible with no change in grade.

3. Materials : Sewers entering or crossing streams shall be constructed of cast or ductile iron pipe with mechanical joints or other watertight materials, encasements, and anchored so no changes in alignment or grade will occur.

4. Sediment and Erosion Control :
a. Refer to Department Guide, BMP's "Best Management Practices".
b. "404" Permit for large streams.
Aerial Crossings...
1. Supports shall be provided to maintain the alignment and support of pipe along the aerial crossing.

2. Precautions against freezing, such as insulation and increased slope, shall be provided. Expansion jointing shall be provided for sections of pipes entering the below-ground sewers.

3. Consideration shall be given to floating debris and flood waters. The pipe should be no lower than the elevation of a hundred year (100) flood.
Outfalls...
Outfall sewers and structures shall be designed and constructed to provide :

a. Protection of the sewer against excessive receiving stream velocities, waves, floating debris, or other hazards which may damage the outfall works.
b. Protection of the sewer from entrance of floodwater.
c. Protection of the sewer from entrance of wildlife.
d. Compliance with mixing zone criteria established in A.R.S.D. 74:03:02:07.
Sewer Extension...
In general, sewer extensions shall be allowed only if the receiving wastewater treatment facility is either :

1. Capable of handling the added hydraulic load and pipe size not smaller.
2. Capable of adequately processing the added hydraulic and organic load.
3. Provision of adequate treatment facilities on a time schedule acceptable to the Department is assured.
Protection of Water Supplies...
1. Water Supply Interconnections : There shall be no physical connection between a public or private potable water supply system and a sewer, or appurtenance thereto, which would permit the passage of any sewage or polluted water into the potable water system. Water main bleeders into sanitary sewers are prohibited. No water pipe shall pass through or come in contact with any part of a sewer manhole.

2. Relation to Water Works Structures : While no general statement can be made to cover all conditions, sewers shall be at least 75 feet from shallow water supply wells, 50 feet from underground water reservoirs and 30 feet from a well if the sewer is constructed as mentioned in section M-3-c.

3. Relation to Water Mains : a. Horizontal Separation - Whenever possible, sewers should be laid at least 10 feet, horizontally, from any existing or proposed water main. Should local conditions prevent a lateral separation of 10 feet, a sewer may be laid closer than 10 feet to a water main if :

1) It is laid in a separate trench; or
2) It is laid in the same trench with the water main located at one side on a bench of undisturbed earth;
3) In either case, the elevation of the crown of the sewer is at least 18 inches below the invert of the water main.

b. Vertical Separation - Whenever sewers must cross under water mains, the sewer shall be laid at such an elevation that the top of the sewer is at least 18 inches below the bottom of the water main. When the elevation of the sewer cannot be buried to meet the above requirement, the water main shall be relocated to provide this separation and reconstructed with slip-on or mechanical-joint cast-iron pipe, asbestos-cement pressure pipe or prestressed concrete cylinder pipe for a distance of 10 feet on each side of the sewer. One full length of water main should be centered over the sewer so that both joints will be as far from the sewer as possible.

c. Special Conditions - When it is impossible to obtain the proper horizontal and vertical separation as stipulated above, the water main should be constructed of slip-on or mechanical-joint cast-iron pipe, asbestos-cement pressure pipe or prestressed concrete cylinder pipe and the sewer constructed of mechanical-joint cast-iron pipe, schedule 40 ABS or PVC or equal and both services should be pressure tested to assure watertightness in accordance with AWWA standard for leakage testing. As an alternative, it is permissible to encase either the water or the sewer main with six (6) inches of concrete for a distance of 10 feet on each side of the crossing; or if PVC or cast iron is used as encasement material, the ends shall be adquately sealed with concrete as well as any joints within the 20 foot section.

d. House Sewers - The requirements in sections M-3-a, M-3-b, and M-3-c shall apply to building sewers and water service lines to buildings except that the separations mentioned in sections M-3-a and M-3-b may be reduced to state plumbing code when water lines are installed with continuous non-jointed material.
Small Diameter Gravity Sewers...
1. General Statement : The innovative and alternative technology provisions of the Municipal Wastewater Treatment Construction Grant Amendments of 1981 (Public Law 97-117) provide for additional Federal grant funding for eligible costs associated with small diameter gravity sewers serving small communities and conveying partially or fully treated wastewater. Septic tank effluent is considered partially treated wastewater, and the costs for design and construction of treatment works which collect and convey it for additional centralized treatment are eligible for additional Federal grant funding, provided that all requirements in this section are met.

2. Administrative Provisions : Alternative technology grant funding for those costs associated with the transport of partially or fully treated wastewater may be provided only if the project serves a small community defined as follows: a. A small community is defined by 40 CFR 35.2005(40) as any municipality with a population of 3,500 or less or highly dispersed sections of larger municipalities as determined by the U.S. EPA Regional Administrator. b. If nonconventional systems are planned for certain sparsely developed subdivisions or parcels of a larger municipality (existing population over 3,500), then each of these subdivisions or parcels could be defined as a small community for the purpose of alternative system funding. Any such area having a density of two households per acre or less could be considered sparsely populated.

3. Small Diameter Gravity Sewer Design Criteria : The following considerations shall be used for the design of small diameter gravity sewer systems :

a. No gravity sewer shall be less than 4 inches in diameter.
b. Since the small diameter gravity sewers will be conveying anaerobic septic tank effluent which will be corrosive and odorous, the pipe, pumping equipment and treatment hardware shall be manufactured of suitable materials to endure these adverse conditions. Acceptable pipe materials are ABS, PVC, poly- ethylene, vitrified clay and fiberglass/ polyester composite. Concrete, asbestos cement, steel, iron and other metals are not acceptable. Bituminous-fiber pipe, commonly known as Orangeburg pipe, is not acceptable for public or community collection systems.
c. The maximum allowable infiltration-exfiltration rate shall be 200 gallons per inch of pipe diameter per mile per day.
d. Small diameter gravity sewers conveying partially or fully treated wastewater will be considered acceptable if they are designed and constructed to provide mean velocities, when flowing full, of not less than 1.5 feet per second based on Manning's formula using an "n" value of 0.013. The following slopes should be provided, however, slopes greater than specified are desirable :

Sewer Diameter ( inch )	Minimum Slope ( Ft / 100 feet )
4	0.47
6	0.28
8	0.19

While insufficient empirical data has been generated to demonstrate the absolute, unqualified acceptability of slopes less than those specified in the preceding paragraph, a system of small diameter gravity sewers conveying settled sewage may be approved if designed and constructed to provide mean velocities, when flowing full, of not less than 1.0 feet per second based on Manning's formula using an "n" value of 0.013, provided that the cost saving qualification of 40 CFR 35.2005(4) is met. The purpose of this is to ensure that the savings to be gained by installing the sewers at these flatter slopes is sufficient to justify the potential risk involved. Under these criteria, the minimum slopes which should be provided :

Sewer Diameter ( inch )	Minimum Slope ( Ft / 100 feet )
4	0.21
6	0.12
8	0.08

It is imperative that septic tanks be properly sized and septic tank maintenance procedures be established to ensure the retention of solids in the septic tanks. While important for flows at 1.5 feet per second, it is especially important below that velocity.

e. It is preferable that cleanouts and manholes be alternated at a spacing of approximately 200 to 250 feet; however, cleanouts will be allowed at deadends and intervals of 300 feet where long sections of pipe can be installed. Manholes should be provided at the junctions of two or more small diameter gravity sewer lines. Manhole and cleanout covers should be watertight and consideration given for vandalism due to grit and inflow problems experienced with conventional covers. Manholes and cleanouts should be located where they will be least susceptible to damage from street grading and snowplowing.
f. Drop type manholes should be avoided where anaerobic conditions exist. Gases generated in the septic tank under anaerobic conditions may be toxic; consequently, the creation of turbulence will enhance the release of gases from the septic tank effluent.
g. Special consideration should be given to protect the sewer against freezing due to construction at ground depths susceptible to frost penetration because the outlet piping of the septic tank is normally shallower than that of conventional gravity building sewers.
h. If severe odor problems are anticipated, peroxide feed stations may be considered for control of odors.
i. Since it is recognized that the key technology to successful operation of these systems is retention of solids in the septic tank, maintenance districts and cleaning procedures for septic tanks shall be established in conjunction with the facility planning and design phases. Sewer use ordinances and/or local health codes shall include adequate provisions to ensure proper operation, use, connection to, and construction of such small diameter sewers. Adequate cleaning equipment, such as a jet machine, shall be provided or through agreement with another entity, be readily available.
Storm Sewer...
1. Protection of Water Supplies : Storm sewers shall be constructed to meet the requirements of section M of this chapter, with the following exception: a reinforced concrete pipe (RCP) storm sewer may cross below a water main with the separation of less than 18 inches or at any height above a water main provided the joints on the RCP that are within 10 feet of either side of the watermain are assembled with preformed butyl rubber sealant meeting federal specification #SS-S-210A and AASHTO M0198, and each of these joints are encased with a minimum 2-foot wide by 6-inch thick concrete collar centered over the joint and re-enforced with the equivalent steel area as that in the RCP; the watermain will not be required when the RCP joints are collared within the 20-foot section.

2. Pipe Sizing : To ensure any debris which enters a drain is carried through the system to the outlet, pipe sizes should not decrease in the down-stream direction even though increased slope may provide adequate capacity in the smaller pipe.

3. Inlet/Outlet Protection : Consideration should be given, especially with large diameter pipe, to providing trash guards or grid work over inlets and outlets to prevent obstructions from debris and as a safety measure to prohibit entry.

4. Erosion Protection : Erosion protection shall be required at the discharge outlet when the slope gradient and pipe discharge capacity are expected to reach erosion velocity for the existing soil conditions.
Deviations from Design Criteria...
The Department may consider and allow deviations where adequate documentation is provided to prove the need for such deviation.