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Virginia Administrative Code
Title 9. Environment
Agency 25. State Water Control Board
Chapter 790. Sewage Collection and Treatment Regulations
11/16/2024

9VAC25-790-510. Grit removal facilities.

A. Grit removal unit operations facilities shall be provided for all sewage treatment works with a design capacity of 0.15 million gallons per day or greater and are required for treatment works receiving sewage from combined sewers or from sewer systems receiving substantial amounts of grit. Grit removal facilities should be provided at all sewage treatment works.

1. Grit removal facilities should be located ahead of pumps and comminuting devices. Coarse bar racks and other suitable screens should be placed ahead of mechanically cleaned grit removal facilities.

2. Treatment works treating wastes from combined sewers shall have at least two mechanically cleaned grit removal units, with provisions for unit bypassing.

3. A single manually cleaned or mechanically cleaned grit removal unit, with a unit bypass, is acceptable for those sewage treatment works with a design capacity of less than 0.15 million gallons per day and serving separate sanitary sewer systems.

4. Minimum facilities for larger treatment works serving separate sanitary sewers shall be at least one mechanically cleaned unit with a unit bypass.

B. Design. The design of grit removal facilities shall be based on the requirements of the downstream treatment units. Local conditions and wastewater characteristics shall be evaluated in selecting the design size of particle to be removed. Flow turbulence into and through grit removal basins shall be minimized.

1. Horizontal flow basins shall be designed so as to provide controlled velocities as close as possible to one foot per second during average design flow conditions. The detention period shall be based on the size of particle to be removed. The design should take into consideration hydraulic inefficiencies and positioning of inlets and outlets.

2. Aerated chambers shall be designed to provide a minimum detention time of three minutes at average flow. An air flow of three to five cubic feet per minute per foot of chamber length should be maintained. Aerated chambers shall have adequate and flexible controls for agitation and air supply devices.

3. Other types of degritters will be approved on a case-by-case basis upon evaluation of satisfactory performance data.

4. Wherever possible, grit removal facilities should be located in open areas with easy access. Grit removal facilities located in deep pits shall be provided with mechanical equipment for pumping or hoisting grit to ground level. Such pits shall have a stairway, elevator, or manlift, adequate ventilation, and adequate lighting in accordance with VOSH requirements.

5. Provisions shall be made for dewatering each unit. Drain lines shall discharge to points within the system such that maximum treatment of the contents of the drained unit is provided.

6. The provision of grit washing facilities shall be a function of the ultimate disposal and transportation methods provided for the grit. Impervious surfaces with drains shall be provided for grit handling areas. If grit is to be transported, conveying equipment shall be designed to avoid loss of material.

Statutory Authority

§ 62.1-44.19 of the Code of Virginia.

Historical Notes

Former 12VAC5-581-570 derived from Virginia Register Volume 18, Issue 10, eff. February 27, 2002; amended and adopted as 9VAC25-790-510, Virginia Register Volume 20, Issue 9, eff. February 12, 2004.

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