The Department of Public Works and Environmental Services regulates industrial users of the sanitary sewer system in accordance with the Clean Water Act. Inspectors survey, inspect, and monitor wastewater from county businesses to prevent toxic or harmful substances from entering the sewer collection system and reaching the treatment plant.

Federal, state, and county regulations require some industrial users to pretreat their wastewater before it enters the sewer.; Pretreatment removes some pollutants from wastewater, and makes it compatible with the county’s sewer system and with wastewater treatment plants. Fairfax County may require installation and maintenance of pretreatment devices such as grease traps or interceptors, sediment traps, and oil-water separators. County businesses must maintain records of maintenance of their pretreatment systems for three years, and make these records available to county inspectors on request. Fairfax County Code Chapter 67.1 Article 3 establishes county pretreatment requirements. Fairfax County annually submits a summary report of program activities to the Virginia Department of Environmental Quality.