Prohibited Discharge Standards:

General prohibitions: These are standards that prohibit the discharge of wastes that pass through or interfere with publically operated treatment works operations (POTWs).

Specific prohibitions: prohibit the discharge from all nondomestic sources certain types of wastes that include the folowing:

• create a fire or explosion hazard in the collection system or treatment plant
• are corrosive, including any discharge with a pH less than 5.0, unless the POTW is specifically designed to handle such wastes. Note: the King County sewage system is not designed to handle wastewater below pH 5.0.
• are solid or viscous pollutants in amounts that will obstruct the flow in the collection system and treatment plant, resulting in interference with operations
• any pollutant discharged in quantities sufficient to interfere with POTW operations
• discharges with temperatures above 104 F (40 C) when they reach the treatment plant, or hot enough to interfere with biological processes. High temperature can cause materials in wastewater to release gases in sewers or can disrupt operations in sewage treatment plants. Industrial wastewater must not exceed 65 C (150 F) at the point where it enters the public sewer system.

• Solids and Food Waste In wastewater, solids capable of settling can restrict or block flow in sewer lines. A company that discharges solids which cause a sewage backup is liable for any damages. King County prohibits discharge to the sewer of materials such as ashes, sand, grass, and gravel. Industrial wastewater must contain less than 7 milliliters per liter of solids capable of settling. Food waste, including food-grinder waste, must be capable of passing through a 1/4-inch sieve.

Authority: Prohibited Discharge Standards (40 CFR 403.5) (external link) and King County Code 28.84.060.