Wyoming Administrative Code › Agency 020 - Environmental Quality, Dept. of › Sub-Agency 0011 - Water Quality › Chapter 11 - DESIGN AND CONSTRUCTION STANDARDS FOR SEWERAGE SYSTEMS, TREATMENT WORKS, DISPOSAL SYSTEMS OR OTHER FACILITIES CAPABLE OF CAUSING OR CONTRIBUTING TO POLLUTION AND MOBILE HOME PARK AND CAMPGROUND SEWERAGE AND PUBLIC WATER SUPPLY DISTRIBUTION SYSTEMS › Part B - MUNICIPAL AND DOMESTIC SEWERAGE SYSTEMS, TREATMENT WORKS, AND DISPOSAL SYSTEM › Section 11-13 - Primary Treatment

Current through July 13, 2024
(a) Sedimentation.
(i) Number of basins. For plants having an
				  average design capacity greater than 100,000 gpd (378.4
				  m3/d) and where primary settling is provided,
				  multiple units capable of independent operation shall be provided.
(ii) Design parameters.
(A) Performance. Unless full-scale data is
				  available, primary settling shall be assumed to remove one third of the
				  influent BOD and 55 percent of the influent suspended solids. It is
				  unacceptable to return waste activated sludge to the primary
				  clarifier.
(B) Water depth. The
				  minimum side water depth shall be seven (7) feet (2.1 m).
(C) Surface overflow rates. Surface overflow
				  rates shall not exceed 1,000 gpd/sq ft (41
				  m3/m²d) of surface area at the average design
				  flow nor 1,500 gpd/sq ft (61 m3/m²d) of surface
				  area at the maximum day flow rate. Maximum day flow is the highest flow over a
				  24 hour period that is projected to occur during the design year.
(D) Weir loading rates. Circular basins (or
				  basins with center inlets) shall be provided with a full periphery weir.
				  Rectangular basins shall be provided with end weirs that provide less than
				  80,000 gpd/ft (9,920 m3/m d) weir hydraulic loading
				  at peak instantaneous flow rates.
(iii) Clarifier inlet and outlet.
(A) General. Clarifier inlet structures shall
				  be designed to achieve the following:
(I)
				  Dissipate the inlet kinetic energy.
(II) Distribute the flow evenly into the
				  tank.
(III) Prevent short
				  circuiting.
Inlet channels or piping shall be designed for minimum
					 velocities of one (1) fps (0.3 mps). Where minimum velocities are less, mixing,
					 flushing or other means of resuspending solids shall be provided.
Circular basins shall be provided with symmetrical baffling
					 to distribute flow equally in all radial directions.
Rectangular basins shall be provided with inlet parts
					 uniformly distributed along the entire end of the basin and shall be provided
					 with baffles.
(B) Weirs. Weir plates shall be adjustable
				  for leveling and sealed against the effluent channel.
(C) Baffles. Provide scum baffles at the
				  water surface to intercept all floating materials and scum prior to the weir.
				  Baffles should extend three (3) inches (7.6 cm) above the weir plate elevation
				  and eight (8) inches (20.3 cm) below the water surface.
(D) Clarifier effluent channel.
(I) Size. The effluent channel shall be sized
				  to prevent weir submergence at the peak hourly flow.
(E) Freeboard. The outer walls of
				  sedimentation tanks shall extend at least six (6) inches (0.15 m) above the
				  surrounding ground and shall provide at least twelve (12) inches (0.3 m) of
				  freeboard to the water surface. Where basin walls do not extend four (4) feet
				  (1.2 m) above the surrounding ground, a fence or suitable barrier to prevent
				  debris from entering the basin shall be provided.
(F) Basin equipment and access. Provide
				  walkways and accessways to collector drive units, effluent launders and manual
				  skimmer. Handrail shall be provided.