Compliance Summary
Compliance Summary Tool
Transportation Modes
Service Functions
All Topics
Please note: This summary is provided to help you understand the regulations. Consult the references provided for links to the full text of the regulations.

Locomotive Coolant Discharge

Unlike car and truck engines, most locomotives in the U.S. are cooled with water that contains anti-corrosion inhibitors, but does not contain antifreeze compounds. Because of this, locomotive cooling systems may need to be drained when engines are shut down during road operation in cold weather. Failure to do so can result in serious engine damage due to freezing of the coolant.

This page covers rules for the discharge of locomotive coolant.

Related topic: Engine Emissions (Locomotives).

Who is covered by the regulations?

When discharged, locomotive coolant is considered industrial wastewater. The Clean Water Act made it unlawful for all businesses to discharge industrial wastewater unless a permit was obtained.

What is the purpose of the regulations?

To protect the cooling system from corrosion, locomotive coolants contain a dilute additive package, which is basically a mixture of sodium borate and sodium nitrate

If coolants are discharged to the ground or a receiving stream, these additives, although dilute, may pollute the nearby drinking water supplies or waterways.


The Clean Water Act made it unlawful to discharge any pollutant from a point source into navigable waters, unless a permit was obtained. The CWA also limits discharges from businesses to a municipal sewer system (also called Publically Owned Treatment Works or POTW).

Wastewater discharged from locomotive cooling systems is regulated in one of several different ways, depending on how it is disposed. There are three primary options for disposing of locomotive coolant wastewater:

  1. Haul it to a treatment facility.

  2. Discharge it to a municipal sanitary sewer system (also known as a Publically Owned Treatment Works or POTW).

  3. Discharge it to a stream or other water body.

Most railroad operators use option 1 or 2 for locomotive coolant. Each option is discussed below.

Option 1- Hauling
Option 1 is an economical solution when there is a sufficiently small volume of wastewater generated. Before you haul wastewater you must perform a Hazardous Waste Determination. This may involve getting it tested by a laboratory. If the wastewater is "hazardous" you must manage, transport and dispose of it using special procedures. For more information, see the TERC Hazardous Waste section. If the wastewater is non-hazardous, then you should maintain test records that support your determination.

Option 2 - Discharge to a POTW
Discharging to a Publically Owned Treatment Works is referred to as an "indirect discharge," because your wastewater is going to a POTW before it is subsequently discharged to a stream or other water body. This is viable when the facility is located in an area served by a municipal sanitary sewer system. Before you initiate option 2 you must acquire a permit or written notification from either your local sewer district or state environmental agency. You will also have to meet certain rules found in federal and state regulations, including:

  • You are prohibited from discharging any pollutant, including oil, that may upset or interfere with the sewage treatment processes or pass through the system untreated;

  • You cannot discharge pollutants (e.g., solvents) that may cause a fire in the sewer system; and

  • You cannot discharge pollutants such as sludge (e.g., grease, dirt) that may clog the sewer system.

To meet sewer discharge standards, you may need to install equipment such as an oil/water separator to prevent oil and sludge from being discharged to the sewer. This is referred to as "pretreatment." The oil and sludge collected by pretreatment equipment will have to be periodically removed and disposed of, possibly as a hazardous waste (you must make a hazardous waste determination). Other types of treatment that are commonly employed with wastewater include pH adjustment, settling, and metals precipitation processes. For more information see Pretreatment Standards and Limits.

Option 3 - Discharge to a Stream
Discharging to a stream or other water source (called "direct discharge") is a potential option, but one that requires a National Pollutant Discharge Elimination System (NPDES) permit (or state equivalent). If you obtain this type of permit, you will be required to meet discharge standards (usually much more stringent than indirect discharge standards) and demonstrate that you are in compliance by frequently collecting samples of your wastewater and having them analyzed at a laboratory. You will also have significant reporting and recordkeeping responsibilities.

More Resources

Environmental Aspects of Railroad Locomotive Coolant Discharge (Ted A. Ronning, Christopher P. L. Barkan), possibly available through Association of American Railroads.