020-11 Wyo. Code R. § 11-9

Current through April 27, 2019

Section 11-9 - Design of Sewers

(a) Separate sewers. Separate sewers shall be provided for collection of stormwater and wastewater. Roof, areaway, drive or foundation drains shall not be connected to sanitary sewers.

(b) Pipe materials.

• (i) Wastewater characteristics. Pipe materials shall resist acid and alkaline solutions, organic solvents, and other wastewater constituents and environmental conditions encountered.

• (ii) Pipe loadings. Pipe materials shall be chosen and the pipeline shall be designed to withstand all trench and superimposed surface live loads with a minimum factor of safety. Rigid pipes shall have a minimum factor of safety of 1.5, and flexible pipes shall have a minimum factor of safety of 1.25.

• (iii) Soil characteristics. Pipe materials shall be chosen to resist corrosion due to aggressive soil characteristics by the soil it contacts. Iron or steel pipe shall be protected from corrosion with polyethylene encasement or cathodic protection.

• (iv) Joints. Pipe joints shall be flexible, durable and designed to minimize infiltration/exfiltration and exclude roots.

• (v) Performance tests. Piping shall be subjected to leakage tests. Leakage tests shall be infiltration, exfiltration, or air tests.
  • (A) Infiltration. Maximum of 200 gallons per inch diameter per mile per day (1200 liters/cm/km/day) with a minimum of two feet (0.6 m) of head over the top of the pipe.
  • (B) Exfiltration. Maximum of 200 gallons per inch diameter per mile per day (1200 liters/cm/km/day) with a minimum of two feet (0.6 m) of head over the top of the pipe.
  • (C) Air. Air tests shall conform to ASTM C-828-80. (D) Deflection. Maximum five percent deflection after flexible pipe is backfilled for thirty (30) days. A mandrel of 95 percent of pipe diameter shall be used. No mechanical pulling of mandrel is permitted.

• (vi) Approved pipe material specifications. Type of commercial pipe approved for gravity sanitary systems include:
  • (A) Extra strength and standard strength vitrified clay pipe: ASTM C700-78a.
  • (B) PVC sewer pipe and fittings: ASTM D3034-80, SDR35, ASTM F679-81, or ASTM F794-83.
  • (C) ABS composite sewer pipe: ASTM D2680-80.
  • (D) Reinforced plastic mortar pipe: ASTM D3262-81.
  • (E) Asbestos cement nonpressure sewer pipe: ASTM C428-80.
  • (F) Reinforced concrete sewer pipe: ASTM C76-82.
  • (G) Concrete Sewer Pipe: ASTM C-14.
  • (H) Ductile iron sewer pipe: ASTM A746-77.

    Types of commercial pipe approved for pressure sanitary sewer systems include:

  • (I) PVC water pipe: ASTM D2241-80, or AWWA C900.
  • (J) Asbestos cement pressure pipe: AWWA C400-80.
  • (K) Ductile iron pipe: AWWA C151-81.
  • (L) Glass Fiber-Reinforced Thermo-setting-Resin Pressure Pipe: AWWA C950-81.

(c) Collection piping design, construction and testing. A sewage collection line is any conduit that carries wastewater that originates from two (2) or more separate buildings or from a single building that generates more than 2,000 gpd (7.6 m³/d) of average daily flow.

• (i) Gravity system.
  • (A) Depth. Sewers shall be located to protect them from freezing and frost heave as prudently possible.
  • (B) Size. Sewers to be aligned straight shall be 8-inch (20.3 cm) diameter or larger except 6-inch (15.2 cm) sewers may be used in cul-de-sacs, or other dead end locations where the sewer cannot be extended in the future. 18-inch (45.7 cm) or larger sewers may be laid on curves. Lines shall be sized for 200 percent of maximum daily flow or more. In the absence of data deriving maximum daily flow, the chart on Figure 1-1 shall be used to determine maximum daily flow.
  • (C) Slope. Sewers shall be laid with uniform slope between manholes. Minimum slopes shall be:

    Sewer Size Inch (cm)	Minimum Slope in Feet Per 100 Feet (m/100 m)
    6 (15.2)	0.60
    8 (20.3)	0.40
    10 (25.4)	0.28
    12 (30.5)	0.22
    14 (35.6)	0.17
    15 (38.1)	0.15
    16 (40.6)	0.14
    18 (45.7)	0.12
    20 (50.8)	0.11
    21 (53.3)	0.10
    24 (61.0)	0.08
    27 (68.6)	0.067
    30 (76.2)	0.058
    33 (83.8)	0.051
    36 (91.4)	0.046

    Maximum slopes without the use of concrete anchors shall be 20 percent. The following spacing of concrete anchors shall apply to slopes greater than 20 percent:

    Slopes (percent)	Concrete Anchor
    20-35	36 ft (11 m)
    35-50	24 ft (7.3 m)
    More than 50	16 ft (4.9 m)

  • (D) Velocity. Minimum velocities shall be 2 fps (0.6 mps) when flowing full. Velocities greater than 10 fps (3.0 mps) require special design considerations.
  • (E) Increasing size. All sewer pipe size changes shall be at manholes. Pipe size shall not be decreased in the direction of flow. The energy gradient line should be maintained when a smaller sewer joins a larger one.
  • (F) Excavation, bedding installation, backfill.
    • (I) Excavation. Trench width from the trench bottom to a point one foot above the top of the pipe shall be no less than the outside diameter of the pipe plus 8 (8) inches (20.3 cm) but not more than twenty-four (24) inches (61 cm) plus the pipe O.D. The trench bottom shall be excavated for the pipe bell. All rock shall be removed within six (6) inches (15.2 cm) of pipe. The trench shall be dewatered for all work.
    • (II) Bedding. Bedding shall be designed in accordance with:
      • (1.) Rigid pipe. Types A, B, C (Water Pollution Control Federation Manual of Practice No. 9) or ASTM C12-81.
      • (2.) Flexible pipe. Types I, II, III, ASTM D2321-74.
    • (III) Backfill. Backfill shall be performed without disturbing pipe alignment. Backfill shall not contain debris, frozen material, unstable material, or large clods. Stones greater than three (3) inches (7.6 cm) in diameter shall not be placed within two (2) feet (0.6 m) of pipe. Compaction shall be to a density equal to or greater than the surrounding soil.

• (ii) Force mains and pressure sewers.
  • (A) Depth. Force mains shall be located to protect them from freezing and frost heave.
  • (B) Size. Force mains shall be four (4) inches (10 cm) diameter or greater. Pressure sewer collection system piping shall be one (1) inch (2.5 cm) minimum.
  • (C) Velocity. Minimum velocity shall be 2.5 fps (0.76 mps).
  • (D) Air release. Air release facilities shall be provided at the high point in the piping whenever the pipe crown elevation falls below the pipe invert elevation. Access to air release manholes shall not be in traffic-ways.
  • (E) Cleanouts. Cleanouts shall be provided at 400-foot (122 m) maximum spacing in pressure piping four-inch diameter or less.
  • (F) Pressure sewer systems. Pressure sewer collection systems shall be preceded by grinder pumps or septic tanks.
  • (G) Pressure sewer collection system pumps. Pumps shall be provided with isolation and check valves. If a septic tank is not provided before the pump, a grinder pump shall be required. Pump holding sumps shall not be steel, iron, or coated metal. The sump chamber shall be fifty (50) gallon (189 liters) volume, minimum.

• (iii) Service connections. A service connection is any conduit that carries wastewater that is not defined as a sewage collection line. Service connections shall conform to the requirements for sewage collection lines (Section 9(c)(i) and (ii) ) with the following modifications:
  • (A) Size: minimum size shall be four (4) inches (10.2 cm).
  • (B) Slope: minimum slope shall be 2 feet/100 feet (2 m/100 m).
  • (C) Flow: flow shall be determined from a fixture unit count and the sewage size based on flowing full.
  • (D) Connections: all service connections to sewage collection lines shall be made with a wye or tee for new construction and a tapping saddle for connection to existing collection lines.

(d) Manholes and cleanouts.

• (i) Location. Manholes shall be located at all changes in pipe size, vertical or horizontal alignment, pipe intersections, and the end of lines. Maximum spacing for various line sizes are as follows:

  Line Size (In)	(cm)	Maximum M.H.	Spacing
  15 or less	(38 or less)	400 ft	122 m
  16 - 30	(40.6 - 76)	500 ft	152 m
  31 or more	(78 or more)	600 ft	183 m

  Terminal sewer cleanouts may be provided at the end of sewer lines if they are not more than 150 feet (45.7 m) from the nearest downstream manhole. The cleanout shall be constructed using 45-degree bends to the upturned pipe coming to the surface of the ground. The diameter of the cleanout shall be the same as the pipe size. Lampholes shall not be used.

• (ii) Size. Minimum manhole interior size is four (4) feet (1.2 m).

• (iii) Drop manhole. Drop manholes must be constructed where the change in elevation between two lines is greater than twenty-four (24) inches (0.6 m). Concrete encasement shall be provided around the drop pipe.

• (iv) Invert. Manhole inverts shall be constructed to conform to the shape of the sewer. The bench shall drain to the invert. Connections to the manhole shall be watertight and allow differential settlement between the manhole and pipe. Minimum fillet height shall be one half of the pipe diameter.

• (v) Cover. The manhole cover shall be suitable to withstand all loads, including impact loading without deformation, slip or rattle. The manhole cover shall be watertight in areas subject to flooding and a bolt-down type in areas subject to unauthorized dumping or vandals.

• (vi) Steps. Access to manholes shall be with portable ladders, or with cast iron manhole steps spaced at sixteen (16) inches (40.6 cm) maximum.

• (vii) Materials. Manholes shall be constructed watertight and durable using cast-in-place concrete, or precast concrete with gasketed joints. Where precast concrete bases are used, the first twelve (12) inches (30 cm) of wall will be monolithically cast with the base.

• (viii) Access. A twenty-two (22) inch (56 cm) minimum diameter clear opening shall be provided on all manholes. All manholes shall be located to be accessible by motorized equipment for maintenance.

(e) Special structures.

• (i) Inverted siphons. Inverted siphons shall have a minimum of two (2) six (6) inch (15.2 cm) barrels. The inlet and outlet shall be arranged to cause only one (1) pipe to be used during normal flows. The minimum velocity shall be 3 fps (1 mps) at average flow, and occur at least daily. The siphon shall be designed for flushing and maintenance.

• (ii) Aerial crossings. Aerial crossings shall be designed to prevent freezing, leaking, settlement, lateral movement, and damage from expansion/contraction. It shall be located with proper vertical clearances for highway vehicles and the 100-year flood.

• (iii) Stream crossings. Stream crossings shall be within 10° of the perpendicular direction of the stream. Pipe shall have a minimum cover of one (1) foot in rock, and three (3) feet under other surfaces. The crossing shall be made with an inverted siphon or without a grade change. Pipe materials shall be steel, cast iron, or ductile iron pipe.

(f) Potable water supply protection.

• (i) Cross connections. There shall be no cross-connections between sewer lines and potable water lines.

• (ii) Horizontal and vertical separation from water mains. Minimum horizontal separation shall be ten (10) feet (3 m) where the water main is less than 1.5 feet (0.46 m) above the elevation of the sewer. Minimum vertical separation shall be 1.5 feet (0.46 m) at crossing. Joints in sewers at crossing shall be located at least ten (10) feet (3 m) from water mains. The upper line of a crossing shall be specially supported. Where vertical and/or horizontal clearances cannot be maintained, the sewer shall be placed in a separate conduit pipe.

020-11 Wyo. Code R. § 11-9

Amended, Eff. 6/29/2018.