Section 10. Definitions

The words and terms used in this regulation shall have the meanings defined in the State Water Control Law and 9VAC25-31, the VPDES Permit Regulation, unless the context clearly indicates otherwise, except that for the purposes of this chapter:

"Department" or "DEQ" means the Virginia Department of Environmental Quality.

"Membrane treatment" means a pressure driven process using synthetic materials to separate constituents from water. Membranes are used for dissolved solids or suspended solids removal. Membrane treatment for dissolved solids removal includes reverse osmosis and nanofiltration. Membrane treatment for suspended solids removal includes ultrafiltration and microfiltration.

"Microfiltration" means a method of membrane treatment designed to remove particles down to 0.1 µm in size. The treatment removes cysts, bacteria, and most (but not all) particulates.

"Municipal separate storm sewer system" or "MS4" means a conveyance or system of conveyances (including roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, or storm drains) (i) owned or operated by a state, city, town, county, district, association, or other public body (created by or pursuant to state law) having jurisdiction over disposal of sewage, industrial wastes, storm water, or other wastes, including special districts under state law such as a sewer district, flood control district or drainage district, or similar entity, or an Indian tribe or an authorized Indian tribal organization, or a designated and approved management agency under § 208 of the Clean Water Act (CWA) that discharges to surface waters of the state; (ii) designed or used for collecting or conveying storm water; (iii) which is not a combined sewer; and (iv) which is not part of a publicly owned treatment works (POTW).

"Nanofiltration" or "low-pressure reverse osmosis" or "membrane softening" means a method of membrane treatment designed to remove multivalent ions (softening) and removes contaminants down to 1 nm (nanometer = 0.001 µm) in size.

"Potable water treatment plant" means an establishment engaged in producing water for domestic, commercial, or industrial use as designated by Standard Industrial Classified (SIC) Code 4941 – Water Supply (Office of Management and Budget (OMB) SIC Manual, 1987), or others as approved by the board.

"Reverse osmosis" means a method of membrane treatment designed to remove salts and low-molecular weight solutes and remove all contaminants down to 0.0001 µm (microns) in size. Reverse osmosis methods apply pressure in excess of osmotic pressure to force water through a semi-permeable membrane from a region of high salt concentration to a region of lower salt concentration.

"Total maximum daily load" or "TMDL" means a calculation of the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards and an allocation of that amount to the pollutant's sources. A TMDL includes wasteload allocations (WLAs) for point source discharges, and load allocations (LAs) for nonpoint sources or natural background or both, and must include a margin of safety (MOS) and account for seasonal variations.

"Ultrafiltration" means a method of membrane treatment designed to remove particles down to 0.01 µm in size. The treatment removes cysts, bacteria, and viruses as well as suspended solids.

Historical Notes

Derived from Volume 25, Issue 06, eff. December 24, 2008; amended, Virginia Register Volume 29, Issue 23, eff. December 24, 2013.

Statutory Authority

§ 62.1-44.15 of the Code of Virginia; § 402 of the Clean Water Act.