Pretreatment is the reduction, the elimination, or the alteration of pollutants in wastewater to a less harmful state prior to discharge of the wastewater to a sanitary sewer system.

It is an EPA-mandated program that requires the WSSC to regulate industrial discharges to WSSC's wastewater collection system, thereby reducing the amount of pollutants released into the environment from the WSSC's treatment plants.

The Clean Water Act established the responsibility of Federal, State, and local government to implement National Pretreatment Standards in order to control pollutants from non-domestic sources that discharge to a Publicly Owned Treatment Works (POTWs). The WSSC operates 6 wastewater treatment plants that treat wastewater from domestic and industrial sources. These plants in turn discharge treated wastewater to the environment. Each of WSSC's treatment plants hold permits issued by the Maryland Department of the Environment (MDE). These permits regulate the WSSC's plant effluent discharges to State waterways. Each permit contains requirements to implement a pretreatment program to prevent pollution of the waterways.

All industrial users located within the WSSC's jurisdiction must comply with the WSSC's Industrial Waste Regulations. However, industrial users that perform processes deemed "categorical" by the EPA and/or significant by WSSC, must comply with additional requirements.

The term Significant Industrial User as defined by the EPA means: (1) All industrial users subject to Categorical Pretreatment Standards under 40 CFR 403.6 and 40 CFR chapter I, subchapter N; and (2) Any other industrial user that: discharges an average of 25,000 gallons per day or more of process wastewater; contributes a process wastestream which makes up 5 percent or more of the average dry weather hydraulic or organic capacity of the treatment plant; or is designated as a SIU by WSSC on the basis that the industrial user has a reasonable potential for adversely affecting the operation of the WSSC's wastewater treatment plants.

Potential SIUs under construction should apply for a WSSC Discharge Authorization Permit at least 90 days prior to discharging to the WSSC's sanitary sewer. Existing SIUs should apply as soon as possible.

To obtain a WSSC Discharge Authorization Permit you must complete a WSSC Industrial User Survey   and submit it to this office. If your industry meets the definition of a Significant Industrial User, you do not have to fill out the Industrial User Survey; however, you must complete a WSSC Discharge Authorization Permit Application   and submit it to this office in the timeframe mentioned above.

If an Industrial User does not comply with pretreatment program requirements, it will be subject to enforcement action in accordance with the guidelines established in the WSSC's Enforcement Response Plan (ERP)  .