PURPOSE: The following criteria have been prepared as a guide for the design of sewers. This rule is to be used with rules 10 CSR 20- 8.110–10 CSR 20-8.220 for the planning and design of the complete treatment facility. This rule reflects the minimum requirements of the Missouri Clean Water Commission as regards adequacy of design, submission of plans, approval of plans and approval of completed sewage works. Deviation from these minimum requirements will be allowed where sufficient documentation is presented to justify the deviation. These criteria are taken largely from Great Lakes-Upper Mississippi River Board of State Sanitary Engineers Recommended Standards for Sewage Works and are based on the best information presently available. These criteria were originally filed as 10 CSR 20-8.030. It is anticipated that they will be subject to review and revision periodically as additional information and methods appear. Addenda or supplements to this publication will be furnished to consulting engineers and city engineers. If others desire to receive addenda or supplements, please advise the Clean Water Commission so that names can be added to the mailing list. 10 CSR 20-8

Editor’s Note: The secretary of state has determined that the publication of this rule in its entirety would be unduly cumbersome or expensive. The entire text of the material referenced has been filed with the secretary of state. This material may be found at the Office of the Secretary of State or at the headquarters of the agency and is available to any interested person at a cost established by state law.

1. (1) Definitions. Definitions as set forth in the Clean Water Law and 10 CSR 20-2.010 shall apply to those terms when used in this rule, unless the context clearly requires otherwise. Where the terms shall and must are used, they are to mean a mandatory requirement insofar as approval by the agency is concerned, unless justification is presented for deviation from the requirements. Other terms, such as should, recommend, preferred and the like, indicate discretionary requirements on the part of the agency and deviations are subject to individual consideration.
2. (2) Exceptions. This rule shall not apply to facilities designed for twenty-two thousand five hundred (22,500) gallons per day (85.4m3) or less (see 10 CSR 20-8.020 for the requirements for those facilities).
3. (3) Approval of Sewers. In general, the agency will approve plans for new systems, extensions to new areas or replacement sanitary sewers only when designed upon the separate plan, in which rainwater from roofs, streets and other areas and groundwater from foundation drains are excluded.
4. (4) Design Capacity. In general, sewer capacities should be designed for the estimated ultimate tributary population, except in considering parts of the systems that can be readily increased in capacity. Similarly, consideration should be given to the maximum anticipated capacity of institutions, industrial parks, etc. Where future relief sewers are programmed, economic analysis of alternatives should accompany initial permit applications. In determining the required capacities of sanitary sewers, the following factors should be considered: maximum hourly domestic sewage flow; additional maximum sewage or waste flow from industrial plants; inflow and groundwater infiltration; topography of area; location of sewage treatment plant; depth of excavation; and pumping requirements. The basis of design for all sewer projects shall accompany the plan documents. More detailed computations may be required by the agency for critical projects.

5. (5) Design Flow.

   1. (A) Per Capita Flow. New sewer systems shall be designed on the basis of an average daily per capita flow of sewage of not less than one hundred (100) gallons per day (.38m3/day). This figure is assumed to cover normal infiltration but an additional allowance should be made where conditions are unfavorable. For existing sewer systems an additional per capita allowance shall be made where the average annual flow exceeds this value and immediate remedial measures are not proposed.
   2. (B) Peak Design Flow. Sanitary sewers shall be designed on a peak design flow basis using one (1) of the following methods: the ratio of peak to average daily flow as determined from the quotient of eighteen (18) plus the square root of the population in thousands divided by four (4) plus the square root of population in thousands or values established from an infiltration/inflow study acceptable to the agency. Use of other values for peak design flow will be considered if justified on the basis of extensive documentation.
   3. (C) Combined Sewer Interceptors. In addition to the requirements in subsection (5)(B) of this rule, interceptor sewers that will receive combined sewage shall have sufficient additional capacity to insure attainment of the appropriate state and federal water quality standards.

6. (6) Details of Design and Construction.

   1. (A) Minimum Size. Gravity collector sewers conveying raw sewage shall be no less than eight inches (8") (20 cm) in diameter, except in unusual circumstances where smaller diameter pipe can be justified.
   2. (B) Depth. In general, sewers should be sufficiently deep so as to receive sewage from basements and to prevent freezing and to protect them from superimposed loads. Insulation shall be provided for sewers that cannot be placed at a depth sufficient to prevent freezing.

   3. (C) Slope.

      1. 1. All sewers shall be so designed and

constructed to give mean velocities, when flowing full, of not less than two feet (2') per second (0.61m/s), based on Kutter’s formula using an “n” value of 0.013. The following are the minimum slopes which should be provided; however, slopes greater than this are desirable: Minimum Slope in Feet Per 100 Feet Sewer Size (m/100 m) 8 in. (20 cm) 0.40 9 in. (23 cm) 0.33 10 in. (25 cm) 0.28 12 in. (30 cm) 0.22 14 in. (36 cm) 0.17 15 in. (38 cm) 16 in. (41 cm) 18 in. (46 cm) 21 in. (53 cm) 24 in. (61 cm) 27 in. (69 cm) 30 in. (76 cm) 36 in. (91 cm)

1. 2. The pipe diameter and slope shall be

selected to obtain the greatest practical velocities to minimize settling problems. Slopes slightly less than those required for the 2.0 feet per second (0.61m/s) velocity when flowing full may be permitted. Decreased slopes will only be considered where the depth of flow will be 0.3 of the diameter or greater and the velocity from partial flow determination will be 0.9 feet per second (27.4 cm/s) or greater based on design average flow. These reduced slopes may result in better flow characteristics at design flow than minimum slope in a larger pipe. Whenever the decreased slopes are selected, the design engineer must furnish with his/her report computations of the anticipated flow velocities of average and daily or weekly peak flow rates. The operating authority of the sewer system will give written assurance to the agency that any additional sewer maintenance required by reduced slopes will be provided.

1. 3. Sewers shall be laid with uniform

slope between manholes.

1. 4. Where velocities greater than fifteen

feet (15') per second (4.6m/s) are attained, special provision shall be made to protect against displacement by erosion and shock.

1. 5. Sewers on twenty percent (20%)

slope or greater shall be anchored securely with concrete anchors or equal, spaced as follows: not over thirty-six feet (36') (11m) center-to-center on grades twenty percent (20%) and up to thirty-five percent (35%); not over twenty-four feet (24') (7.3m) center-to-center on grades thirty-five percent (35%) and up to fifty percent (50%); and not over sixteen feet (16') (4.9m) center-to-center on grades fifty percent (50%) and over.

1. (D) Alignment. Sewers twenty-four inches (24") (61 cm) or less shall be laid with straight alignment between manholes. The alignment shall be checked by either using a laser beam or lamping.

2. (E) Changes in Pipe 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 point of both sewers at the same elevation. Sewer extensions should be designed for projected flows even when the diameter of the receiving 0.15 sewer is less than the diameter of the pro- 0.14 posed extension. The agency may require a 0.12 schedule for future downstream sewer relief. 0.10 (F) Materials. Any generally accepted 0.08 material for sewers will be given considera- 0.067 tion but the material selected should be 0.058 adapted to local conditions, such as character 0.046 of industrial wastes, possibility of septicity, soil characteristics, exceptionally heavy external loadings, abrasion and similar problems. 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 the trench. Where necessary to withstand extraordinary superimposed loading, special bedding, concrete cradle or special construction may be used.

   1. (G) Installation.

      1. 1. Standards. 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.

   1. 2. Trenching.

      1. A. The width of the trench shall be

   ample to allow the pipe to be laid and jointed properly and to allow the backfill to be placed and compacted as needed. The trench sides shall be kept as nearly vertical as possible. When wider trenches are dug, appropriate bedding class and pipe strength shall be used.

   1. B. Ledge rock, boulders and large

   stones shall be removed to provide a minimum clearance of four inches (4") (10 cm) below and on each side of all pipe.

   1. 3. Bedding.

      1. A. Concrete or well-graded granular

   material (bedding classes A, B or C as described in ASTM C12-74 or WPCP MOP No. 9) shall be used for all rigid pipe provided the proper strength pipe is used with the specified bedding to support the anticipated load.

   1. B. Concrete or well-graded granular

   material (bedding classes I, II or III as described in ASTM D2321-74) shall be used for all flexible pipe provided the proper strength pipe is used with the specified bedding to support the anticipated load.

   1. 4. Backfill.

      1. A. Backfill shall be of a suitable mate-

   rial removed from excavation except where other material is specified. Debris, frozen material, large clods or stones, organic matter

or other unstable materials shall not be used for backfill within two feet (2') (0.61 m) of the top of the pipe.

1. B. Backfill shall be placed in a man-

ner as not to disturb the alignment of the pipe.

1. 5. Deflection test.

   1. A. Deflection tests shall be performed

on all flexible pipe. The test shall be run not less than thirty (30) days after final backfill has been placed.

1. B. No pipe shall extend a deflection of

five percent (5%).

1. C. If the deflection test is to be run

using a rigid ball or mandrels, they shall have diameters equal to ninety-five percent (95%) of the inside diameter of the pipe and the tests shall be performed without mechanical pulling devices.

1. (H) Joints and Infiltration.

   1. 1. Joints. The installation of joints and

the materials used shall be included in the specifications. Sewer joints shall be designed to minimize infiltration and to prevent the entrance of roots throughout the life of the system.

1. 2. Leakage tests. 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 two hundred (200) gallons per inch of pipe diameter per mile per day (0.19m3/cm of pipe dia./km/day) for any section of the system. An exfiltration or infiltration test shall be performed with a minimum positive head of two feet (2') (0.61m). The air test, if used, as a minimum shall conform to the test procedure described in ASTM C- 828-76T, entitled Tentative Recommended Practice for Low-Pressure Air Test of Vitrified Clay Pipe Lines. The testing methods selected should take into consideration the range in groundwater elevations projected and the situation during the test. For the purpose of leakage tests, manholes shall be considered pipe of equivalent diameter and shall be tested by an appropriate test method.

1. (7) Manholes.

   1. (A) Location. 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 four hundred feet (400') (120 m) for sewers fifteen inches (15") (38 cm) or less and five hundred feet (500') (150m) for sewers eighteen inches to thirty inches (18"–30") (46 cm–76 cm), except that distances up to six hundred feet (600') (180m) may be approved in cases where adequate modern cleaning equipment for such spacing is provided. Greater spacing may be permitted in larger sewers. Cleanouts may be used only for special conditions and shall not be substituted for manholes nor installed at the end of laterals greater than one hundred fifty feet (150') (46m) in length.
   2. (B) Drop Type. A drop pipe should be provided for a sewer entering a manhole at an elevation of twenty-four inches (24") (61 cm) or more above the manhole invert. Where the difference in elevation between the incoming sewer and the manhole invert is less than twenty-four inches (24") (61 cm), the invert should be filleted to prevent solids deposition. Drop manholes should be constructed with outside drop connection. Inside drop connections (when necessary) shall be secured to the interior wall of the manhole and provide access for cleaning. Due to the unequal earth pressures that would result from the backfilling operation in the vicinity of the manhole, the entire outside drop connection shall be encased in concrete.
   3. (C) Diameter. The minimum interior diameter of manholes shall be forty-two inches (42") (1.07m) on eight-inch (8") (20 cm) diameter gravity sewer lines and forty-eight inches (48") (1.22m) on all sewer lines larger than eight inches (8") (20 cm) in diameter. Larger diameter manholes are necessary for large diameter sewers in order to maintain structural integrity. A minimum access diameter of twenty-two inches (22") (56 cm) shall be provided.
   4. (D) Flow Channel. The flow channel through manholes should be made to conform in shape and slope to that of the sewers.
   5. (E) Watertightness. Manholes shall be of the precast concrete or poured in place concrete type. Manholes shall be waterproofed on the exterior. Inlet and outlet pipes shall be joined to the manhole with a gasketed flexible watertight connection or any watertight connection arrangement that allows differential settlement of the pipe and manhole wall to take place. Watertight manhole covers are to be used wherever the manhole tops may be flooded by street runoff or high water. Locked manhole covers may be desirable in isolated easement locations or where vandalism may be a problem.
   6. (F) Electrical. Electrical equipment installed or used in manholes shall conform to 10 CSR 20-8.130(4)(C)5.
2. (8) Inverted Siphons. Inverted siphons should have not less than two (2) barrels, with a minimum pipe size of six inches (6") (15 cm) 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 10 CSR 20-8

feet per second (0.92m/s) for average flows. The inlet and outlet details shall be arranged so that the normal flow is diverted to one (1) barrel and so that either barrel may be cut out-of-service for cleaning. The vertical alignment should permit cleaning and maintenance.

1. (9) Sewers in Relation to Streams.

   1. (A) Location of Sewers on Streams.

      1. 1. Cover depth. The top of all sewers

entering or crossing streams shall be at a sufficient depth below the natural bottom of the stream bed to protect the sewer line. In general, the following cover requirements must be met: one foot (1') (0.3m) of cover is required where the sewer is located in rock; three feet (3') (0.9m) of cover is required in other material (in major streams, more than three feet (3') (0.9m) of cover may be required); in paved stream channels, the top of the sewer line should be placed below the bottom of the channel pavement. Less cover will be approved only if the proposed sewer crossing will not interfere with the future improvements to the stream channel. Reasons for requesting less cover should be given in the project proposal.

1. 2. Horizontal location. Sewers located

along streams shall be located outside of the stream bed and sufficiently removed therefrom to provide for future possible stream widening and to prevent pollution by siltation during construction.

1. 3. Structures. The sewer outfalls, head

walls, manholes, gateboxes or other structures shall be so located that they do not interfere with the free discharge of flood flows of the streams.

1. 4. Alignment. Sewers crossing streams

should be designed to cross the stream as nearly perpendicular to the stream flow as possible and shall be free from change in grade. Sewer systems shall be designed to minimize the number of stream crossings.

1. (B) Construction.

   1. 1. Materials. Sewers entering or cross-

ing streams shall be constructed of castor ductile-iron pipe with mechanical joints or shall be so otherwise constructed that they will remain watertight and free from changes in alignment or grade. Material used to backfill the trench shall be stone, coarse aggregate, washed gravel or other materials which will not cause siltation.

1. 2. Siltation and erosion. Construction

methods that will minimize siltation and erosion shall be employed. The design engineer shall include in the project specifications the method(s) to be employed in the construction of sewers in or near streams to provide adequate control of siltation and erosion. Specifications shall require that clean-up, grading, seeding, planting or restoration of all work areas shall begin immediately and exposed areas shall not remain unprotected for more than seven (7) days.

1. (10) Aerial Crossings. Support shall be provided for all joints in pipes utilized for aerial crossings. The supports shall be designed to prevent frost heave, overturning and settlement. Precautions against freezing, such as insulation and increased slope, shall be provided. Expansion jointing shall be provided between above-ground and below-ground sewers. For aerial stream crossings, the impact of flood waters and debris shall be considered. The bottom of the pipe should be placed no lower than the elevation of the fifty (50)-year flood.

2. (11) Protection of Water Supplies.

   1. (A) Water Supply Interconnections. There shall be no physical connections 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 supply. No water pipe shall pass through or come in contact with any part of a sewer manhole.
   2. (B) Relation to Water Works Structures. While no general statement can be made to cover all conditions, it is generally recognized that sewers shall meet the requirements of 10 CSR 60-2.010 with respect to minimum distances from public water supply wells or other water supply sources and structures.

   3. (C) Relation to Water Mains.

      1. 1. Horizontal separation. Sewer mains

shall be laid at least ten feet (10') (3.0m) horizontally from any existing or proposed water main. The distances shall be measured edgeto-edge. In cases where it is not practical to maintain a ten foot (10')-separation, the agency may allow deviation on a case-by-case basis, if supported by data from the design engineer. This deviation may allow installation of the sewer closer to a water main, provided that the water main is in a separate trench or on an undisturbed earth shelf located on one (1) side of the sewer at an elevation that the bottom of the water main is at least eighteen inches (18") (46 cm) above the top of the sewer.

1. 2. Crossings. Sewers crossing water

mains shall be laid to provide a minimum vertical distance of eighteen inches (18") (46 cm) between the outside of the water main and the outside of the sewer. This shall be the case where the water main is either above or below the sewer. The crossing shall be arranged so that the sewer joints will be equidistant and as far as possible from the water main joints. When a water main crosses under a sewer, adequate structural support shall be provided for the sewer to prevent damage to the water main.

1. 3. Special conditions. When it is impos-

sible to obtain proper horizontal and vertical separation as stipulated previously, the sewer shall be designed and constructed equal to water pipe and shall be pressure tested to assure watertightness prior to backfilling.

AUTHORITY: section 644.026, RSMo Supp. 1993.* Original rule filed Aug. 10, 1978, effective March 11, 1979. Amended: Filed May 17, 1994, effective Dec. 30, 1994. *Original authority 1972, amended 1973, 1987, 1993.