Section 450. Treatment works design

Article 3. Sewage Treatment Works

A. The sewage treatment process consists of a sequential, upstream to downstream, arrangement of unit operations that remove or modify contaminants through several treatment phases, including (i) primary, (ii) secondary, and (iii) tertiary. A conventional or established secondary treatment process will include primary treatment. Advanced wastewater treatment works include all three phases of treatment. Sewage treatment works should be designed to provide waste water treatment for the tributary sewage flows from either the estimated population 10 years hence or a capacity required by applicable state or federal requirements.

B. Location. A sewage treatment works site shall be located as far as practicable from any existing built-up commercial or residential area, which will probably develop within the design life of the treatment works. The treatment works site shall be (i) protected by a buffer zone, (ii) located to avoid flooding, (iii) provided with year-round access, and (iv) provided with ample area for any future expansion. The minimum distance between the locations of effluent discharges from separate treatment works on the same watershed shall be 500 feet.

C. Restrictions. All new primary and secondary sewage treatment unit operations shall provide the minimum buffer zones as shown in Table 2 (found in 9VAC25-790-460) unless they qualify for reduced requirements as provided in this chapter. Buffer zones for advanced treatment (AWT) and natural treatment operations will be established on a case-by-case basis considering the reliability requirements and process design. Buffer zones are areas of controlled or limited use.

1. Within buffer zones, neither residential uses, high density human activities, nor activities involving food preparation are to be established within the extent of the buffer zone. The extent of the buffer zone perimeter is measured from the treatment units. Buffer zone requirements for sewage sludge incinerator restrictions shall be established in accordance with applicable state and federal regulations.

2. The department may approve a reduction of up to one half of the listed buffer zone requirements based on one or more of the following factors: (i) site topography, (ii) prevailing wind directions, (iii) existence of natural barriers, (iv) establishment of an effective windbreak, (v) type of adjacent development, and (vi) provision of enclosed units, as described in this chapter.

3. The prevailing wind direction should be determined by on-site data. Local weather station records may be utilized if they are demonstrated to be applicable. Attention should be paid to both moderate and high speed winds since the high velocity winds often have a prevailing direction different from the prevailing direction of moderate winds.

4. A windbreak should be located on both sides of the treatment works normal to a line projected through the treatment works and the area that is to be protected, as close to the treatment works as practicable. An effective windbreak may be comprised of man-made or natural barriers that extend from the ground surface to a height of 16 feet. Alternatively, a cultivated tree windbreak may be developed by planting at least four rows of fast-growing evergreen trees (pine family preferred), planted on staggered 10-feet centers. Rows should be spaced no greater than 16 feet apart. The minimum tree height at planting shall be six feet, unless taller trees are required in order to provide a windbreak which will be immediately effective. The variety of tree used should be readily adaptable to the soil and climate at the treatment works site.

5. Reduced buffer distances will be established for enclosed treatment unit operations or processes. Covered units shall be provided with screened intake openings and positive forced draft ventilation and shall have provisions for removal of aerosols and odors from the exhaust.

6. Owners of existing sewage treatment works or those treatment works proposed for upgrading shall take whatever steps possible to provide as much of the required buffer as is reasonably possible under the specific existing conditions at each treatment works site. Wherever a demonstrated nuisance problem does exist, corrective action (wind breaks or odor control measures, for example) shall be undertaken.

7. The required buffer zone shall be maintained by adequate legal instruments such as either ownership, recorded easements, or restrictive zoning throughout the life of the treatment works.

8. The director may consider exceptions to the listed buffer zone requirements in accordance with this chapter.

D. Flooding. All mechanical and electrical equipment that could be damaged or inactivated by contact with or submergence in water (motors, control equipment, blowers, switch-gear, bearings, etc.) shall be physically located above the 100-year level or otherwise protected against the 100-year flood/wave action damage. All components of the treatment works shall be located above or protected against the 25-year flood/wave action level and remain fully operational. Consideration should be given to designing the treatment works in such a way as to facilitate the removal of vital components during more extreme flood events.

E. Closure. A closure plan shall be submitted to the department in accordance with this chapter.

Historical Notes

Former 12VAC5-581-510 derived from Volume 18, Issue 10, eff. February 27, 2002; amended and adopted as 9VAC25-790-450, Virginia Register Volume 20, Issue 09, eff. February 12, 2004.

Statutory Authority

§ 62.1-44.19 of the Code of Virginia.