Utah Administrative Code
Topic - Environmental Quality
Title R317 - Water Quality
Rule R317-3 - Design Requirements for Wastewater Collection, Treatment and Disposal Systems
Section R317-3-5 - Screening and Grit Removal

1. Indoor. Screening devices, installed in a building where other equipment or offices are located, shall be accessible only through a separate outside entrance to protect the operating personnel and the equipment from damage and nuisance caused by gases, odors and potential flooding.

2. Outdoors. Screening devices not installed in enclosures or buildings shall be protected from freezing or other adverse environmental conditions.

1. Bar Spacing. Clear openings between bars should be:

2. Bar Slope. Manually cleaned screens, except those for emergency use, should be placed on a slope of 30 to 45 degrees from the horizontal.

3. Approach Velocities. At average design flow conditions, approach velocities should be no less than 1.25 feet per second (38 centimeters per second), to prevent settling; and no greater than three (3) feet per second (91 centimeters per second) to prevent forcing material through the openings.

4. Channels. Dual channels shall be provided and equipped with the necessary gates to isolate flow from any screening unit. Provisions shall also be made to facilitate dewatering each unit. The channel preceding and following the screen shall be shaped to eliminate stranding and settling of solids. Entrance channels should be designed to provide equal and uniform distribution of flow to the screens.

5. Reliability. A minimum of two screens shall be provided. Each screen shall be designed to handle the peak design rate of flow. Where more than two screens are provided, the peak design rate of flow shall be handled with one of the largest units out of service. Where a single mechanical screen handles the peak design rate of flow, then other unit can be a manually cleaned screen.

6. Flow Measurement. The types and locations of flow measurement devices should be selected for reliability and accuracy. The effect of changes in backwater elevations, due to intermittent blinding and cleaning of screens, should be considered in the selection of the locations for flow measurement equipment.

7. Invert. The screen channel invert should be 3.0 to 6.0 inches (7.6-15.2 centimeters) below the invert of the incoming sewer.

1. Railings and Gratings.

2. Equipment Deactivation and Lockout. Each piece of electrical power mechanical equipment shall be equipped with a positive means of deactivating or locking out or isolating from its power source. Such device shall be located in close proximity to the equipment.

3. Removal of Screenings. The design shall provide for mechanical conveying or lifting systems for safe transport of screenings from a subgrade installation to a collection point on grade.

1. Timing Devices. All mechanical units which are operated by timing devices shall be provided with auxiliary override controls which will set the cleaning mechanism in operation at a preset high water elevation or water differential across the screen.

2. Electrical Fixtures and Controls. Electrical fixtures and controls in screening areas where hazardous gases may accumulate shall meet the requirements of the National Electrical Code for Class I, Group D, Division 1 locations.

3. Manual Override. Automatic controls shall be supplemented with a manual override.

1. Facilities shall be provided for removal, handling, storage, and disposal of screenings in a sanitary manner. Separate grinding of screenings and return to the sewage flow is unacceptable. Manually cleaned screening facilities should include an accessible platform from which the operator may rake screenings easily and safely. Suitable drainage facilities shall be provided for both the platform and the storage areas.

2. Screenings may be landfilled. The ultimate disposal of screenings shall conform to and comply with the requirements for the ultimate disposal of residues or sludge management plan.

1. Location. Comminutors should be located downstream of bar screen and any grit removal equipment.

2. Size. Comminutor capacity shall be adequate to handle the peak design rate of flow.

3. Installation.

5. Electrical Power Controls and Motors. Electrical equipment in comminutor chambers where hazardous gases may accumulate shall meet the requirements of the National Electrical Code for Class 1, Group D, Division 1 locations. Motors in areas not governed by this requirement may need protection against accidental submergence.

1. Ventilation. Uncontaminated air shall be introduced continuously at a minimum rate of 12 air changes per hour, or intermittently at a minimum rate of 30 air changes per hour. Odor control facilities are recommended.

2. Access. Grit removal facilities shall be provided with proper and safe access, and egress from equipment and facilities.

3. Electrical Work. All electrical work in enclosed grit removal areas where hazardous gases may accumulate shall meet the requirements of the National Electrical Code for Class 1, Group D, Division 1 locations.

1. Number of Units. For plants treating:

2. Other types. When arrangements other than channel-type of grit removal is considered, equipment for agitation, air supply, grit collection, grit removal, and grit washing shall be provided with controls for handling variations in rates of flow, and providing operating flexibility.

1. General. The designed effectiveness of a grit removal system shall be commensurate with the requirements of the subsequent process units.

2. Inlet Configuration. Inlet turbulence shall be minimized. The inlet flow direction must be parallel to the induced roll direction within aerated grit chambers.

3. Velocity and Detention Time.

4. Grit Washing. Grit should be washed before the disposal.

5. Drains. Provision shall be made for to adequately bypass, isolate and dewater each grit removal unit for maintenance.

6. Water. An adequate supply of service or non-potable plant water under pressure shall be provided for cleanup.

1. Mechanical equipment for hoisting or transporting grit to ground level shall be provided in grit removal facilities located in deep pits. Impervious, non-slip, working surfaces with adequate drainage shall be provided for grit handling areas. Grit transporting facilities shall be provided with protection against freezing and loss of material.

2. Grit may be landfilled. The ultimate disposal of grit shall conform to and comply with the requirements for the ultimate disposal of residues or sludge management plan.