(a) Horizontal Flow Grit Chambers.
  (1) Velocity through a horizontal flow grit chamber must range from 0.8 feet per second to no more than 1.3 feet per second.
  (2) A horizontal flow grit chamber channel must minimize turbulence and provide uniform velocity across the channel.
  (3) The channel size of a horizontal flow grit chamber must accommodate the grit removal equipment capacity and grit storage.
(b) Aerated Grit Chambers.
  (1) The air diffuser and baffle arrangement in an aerated grit chamber must not interfere with the removal of particles with the design particle size and density.
  (2) The aeration equipment must be capable of varying air feed rates along the length of an aerated grit chamber from 3.0 standard cubic feet per minute (scfm) per linear foot to no more than 8.0 scfm per linear foot.
  (3) An aerated grit chamber must have a hydraulic detention time of at least 3.0 minutes.
  (4) An aerated grit chamber must include a grit hopper located under an air diffuser.
(c) Mechanical Grit Chambers.
  (1) The velocity through mechanical grit chambers must be no greater than 1.0 foot per second at design flow.
  (2) Each mechanical grit chamber channel must include a grit hopper at the side of a tank contiguous to a grit removal mechanism.
  (3) An inlet must include baffles to prevent short-circuiting.
  (4) Grit removal must be provided by one of the following mechanisms:
    (A) reciprocating rake;
    (B) screw conveyor; or
    (C) air lift pump.
(d) Cyclonic Degritters.
  (1) A cyclonic degritter must prevent an inlet-to-outlet short circuit.
  (2) A cyclonic degritter must include an adjustable apex with a quick disconnect assembly to remove any oversized object.
  (3) Detention time in a cyclonic degritter must be at least 1.0 minute at the design flow.
  (4) The flow velocity in a cyclonic degritter must be at least 1.0 foot per second but not more than 2.0 feet per second at the design flow.
  (5) A screening unit must be installed upstream of a cyclonic degritter.
(e) Vortex Grit Chamber.
  (1) An inlet channel must include a straight length in order to deliver smooth flow into the vortex grit chamber.
  (2) The inlet velocity must be at least 2.0 feet per second at peak flow.
  (3) A vortex system must include rotating paddles in the center of the grit chamber, and must rotate at a maximum of 21 revolutions per minute.
  (4) An outlet channel must maintain a constant elevation.
  (5) Grit removal from a grit storage chamber must be achieved using pumps specifically designed to handle grit.

Source Note: The provisions of this §217.125 adopted to be effective August 28, 2008, 33 TexReg 6843; amended to be effective December 4, 2015, 40 TexReg 8254