Wastewater discharge limits and regulations

Corrosives (pH)

When wastewater is too acidic or too alkaline it can corrode the sewage system. Maximum and minimum limits are set for wastewater discharged into the sanitary sewer. Limits are measured by pH.

Fats, oils, and grease (FOG)

There are two types of Fats, oils, and grease (FOG):

• Nonpolar FOG
• Polar FOG

Nonpolar FOG

The King County limit for nonpolar FOG is 100 milligrams per liter of discharged wastewater. Nonpolar FOG can harm the biological phase of sewage treatment where microbes are used to break down wastes.

Industries use oil and water separators to pretreat waste water that contains nonpolar FOG. Separator plans must be approved by King County Industrial Waste (KCIW). KCIW has also given some local sewer utilities the authority to approve separator plans. 

View the KCIW oil and water separator fact sheet for plan submittal information installation guidelines (401KB)

Free-floating polar FOG

Free-floating polar FOG can block sewer lines. Dischargers are asked to minimize free-floating polar FOG. King County rules require:

• Wastewater should not be discharged if free-floating polar FOG is visible on the surface or sides of a storage container.
• A sample should contain less than 0.25 inches of free-floating polar FOG in a sample, per the KCIW-approved sampling method.
• Dischargers do not add agents that emulsify free-floating polar FOG. 
  
  

FOG control plan

Some companies that discharge polar FOG in King County may need to complete a FOG control plan. The goal of the plan is to implement common sense controls of free-floating polar FOG. The basic components of the plans should include:

• A written policy detailing support and commitment for the plan from management and corporate
• A description of the facility type and a summary of what the facility is used for
• The quantity of all FOG brought into the facility and quantities discharged to the sewer
• Schematics of process areas that illustrate drains and discharge points connected to the sewer.
• A description of current reduction, recycling, and treatment activities
• Detail potential FOG reduction opportunities
• Detail the reduction and control methods selected for implementation
• Detail the processes that will be affected and the estimated reductions
• List specific performance goals and the implementation schedule

Heavy metals and cyanide

King County waste discharge permits contain aqueous concentration limits, typically in units of milligrams-per-liter (mg/L); however, these permits also can contain mass-based limits for metals. The mass allocation procedure that the Industrial Waste Program uses involves reviewing the influent data for the applicable King County wastewater treatment plant and statistically determining the loading amount, in pounds-per-day (lb/day), associated with one standard deviation of the average flow rate. The reasoning behind this is that on any given day a single discharger should not be allowed to discharge a mass of metal that would exceed the typical range of fluctuation of the wastewater treatment plant. As a pretreatment program we need to make sure that the concentration or mass limits that are in our permits will not cause problems at the wastewater treatment plants. 

Loading Limits for Metals, July 2014 (85KB)

King County local limits are set for total metals, not dissolved metals. Companies that are not classified as significant industrial users and that discharge less than 5,000 gallons of wastewater per day only need to comply with the instantaneous limits.

*Cyanide amenable to chlorination, not total cyanide

Hydrogen Sulfide

Hydrogen sulfide gas can be dangerous to breathe and causes serious odor problems (the smell of rotten eggs). When hydrogen sulfide reacts with water it forms sulfuric acid. Sulfuric acid can cause corrosion and destroy sewage pipes.

There are two types of hydrogen sulfide:

• Atmospheric sulfide
• Soluble sulfide (dissolved in water)

Atmospheric sulfide

The following are atmospheric hydrogen sulfide limits as measured at a monitoring station designated by King County:

• 15.0 parts per million volume (ppmv) as a 15-minute average
• 10.0 ppmv as an 8-hour average
• 3.0 ppmv as a 7-day average

Soluble sulfide

King County may restrict soluble sulfide discharges on a case-by-case basis. For guidance, King County has a screening limit of 0.1 mg/liter.

Organic Compounds

Organic compounds discharged into the sewer may cause toxic gases and fumes, which can harm sewer workers. Examples of organic compounds include:

• Solvents
• Cleaners
• Thinners
• Pesticides
• Laboratory chemicals 

The King County Industrial Waste Program (KCIW) has developed screening levels for certain volatile organic compounds (VOCs). We provide VOC screening levels (25KB) as guidance to industrial users of the King County sewer system. These screening levels are not an authorization to discharge. Businesses can get authorization to discharge industrial wastewater with a discharge authorization or waste discharge permit issued by KCIW.