Nebraska Administrative Code › Topic - ENVIRONMENT AND ENERGY › Title 123 - NEBRASKA DEPARTMENT OF ENVIRONMENTAL QUALITY › Chapter 5 - DESIGN STANDARDS AND SPECIFICATIONS › Section 123-5-002 - Gravity Sewers

Current through June 17, 2024
00 2.01 Gravity
  sewers will be designed to achieve a minimum velocity of 2.0 feet per second
  when flowing full based on Manning's Equation, using an "n" value of 0.013
  (Refer to Chapter 6, 002 for approval of alternative designs).
002.02 The minimum diameter of public gravity
  sewer mains carrying raw domestic wastewater will be eight inches, except that
  six-inch sewers may be used if the distance between manholes is not greater
  than 400 feet, the total length of six-inch sewer is not greater than 800 feet,
  and the sewer is located where it will not need to be extended for future
  growth.
002.03 Gravity sewers will
  be designed with a uniform slope between manholes. This does not apply to
  inverted siphons.
002.04 Where
  velocities greater than 15 feet per second are attained, special provisions
  will be made to protect sewers from displacement by impact forces and
  erosion.
002.05 Sewers with slopes
  of 20% or greater will be reinforced with concrete anchors. Erosion collars
  will be provided around steep sewers where migrating storm water could cause
  erosion of pipe bedding.
002.06
  Curvilinear sewers are restricted to simple curves. The radius of curvature
  will not be less than the pipe manufacturer's recommendation or be less than
  100 feet. Elbows or couplings with deflections greater than three degrees will
  not be used at pipe joints to create a curvilinear sewer. Curvilinear
  alignments are not to be achieved by bending the pipe barrel.
002.07 Inverted siphons will include at least
  two barrels, each not less than six-inches in diameter. Adequate head will be
  provided to assure velocities of at least 3.0 feet/second in all barrels when
  flowing at their maximum hydraulic capacity. Inlet and outlet control
  structures will be designed with adequate clearances for inspections and
  cleaning to occur. For two-barrel siphons, the inlet and outlet control
  structures will be designed so that flow can be diverted to either barrel to
  accommodate cleaning.
002.08 Sewers
  will be laid at least 10 feet horizontally from any existing or proposed water
  main. The distance will be measured from the outside edges of the two pipes.
  Where it is not practical to maintain the 10 foot horizontal separation, the
  sewer may be laid closer if the water main is in a separate trench or on an
  undisturbed earth shelf located on one side of the sewer, and the bottom of the
  water main is at least 18 inches above the top of the sewer. Where 10 feet of
  separation cannot be met, both the sewer and water main will be constructed of
  water main quality pipe and pressure tested to 150 pounds per square
  inch.
002.09 Sewers crossing water
  mains will be laid to provide 18 inches of vertical separation, measured from
  the outside edges of the two pipes. A full length of sewer pipe will be
  centered on the crossing so that its joints are as far as possible from the
  water main. When providing 18 inches of vertical separation is not achievable,
  one of the following two alternatives will be met to protect the water main:
(a) either the sewer main will be constructed
  of water main quality pipe and pressure tested to 150 pounds per square inch,
  or
(b) one of the mains will be
  encased in a watertight encasement pipe. Where the crossing is at a right
  angle, the protection will extend for 10 feet on each side of the crossing.
  Where the crossing is at an acute angle, the protection will extend to all
  points within 10 feet of the water main, measured perpendicular to the water
  main.