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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.

Truck WashCleaning, Vehicle Washing

Road Rail Air Water

This section provides information about wastewater from vehicle washing operations, including washing of trucks, locomotives/railcars, and aircraft.

Other types of cleaning operations are covered elsewhere on TERC, including:

For wastewater topics related to vehicle cleaning see:

Who is covered by the regulations?

Wastewater generated by any type of vehicle cleaning operation, carried out by any business, is considered to be industrial wastewater. It cannot be discharged or disposed of without a permit. All industrial wastewater discharges are regulated by federal, state and in most cases, by local regulatory agencies.

What is the purpose of the regulations?

With aqueous (water-based) cleaning processes there are two major environmental concerns:

  • Oil, sludge, sediment and similar concentrated wastes that are removed from cleaning operations (e.g., cleanout of sumps).
  • Wastewater, which may be contaminated with cleaning compounds, dissolved and suspended solids, oil/grease, and/or metals such as lead and zinc.


Vehicle washing is usually performed in one of three ways:

  1. On-site mobile washing - vehicles are washed by facility owners or a commercial wash service that comes on-site with portable equipment such as high pressure hot water (including steam) hoses or wands, brush cleaners, dry washing with aerosols, and self-propelled washing units.
  2. On-site permanent wash facilities - vehicles are washed at a fixed system in a building or outside. Permanent facilities include drive-through brush systems and multi-step pressure wash bays.
  3. Off-site commercial washing - trucks may be driven to wash facilities operated by a commercial company other than the company that owns the trucks being washed. The facilities operate similar to permanent wash facilities.

With methods 1 and 2, the transportation facility is responsible for complying with wastewater discharge/disposal regulations. With method 3, the burden of wastewater discharge/disposal compliance is with the off-site commercial washing operation.

Vehicle washing can create a significant volume of wastewater, which is regulated in one of several different ways, depending on how it is disposed.

There are seven primary options for disposing of wastewater vehicle washing:

  1. Haul it to a treatment facility.
  2. Discharge it to a municipal sanitary sewer system (also know as a Publically Owned Treatment Works or POTW).
  3. Discharge in accordance with an NPDES permit.
  4. Evaporate it.
  5. Allow it to percolate into the ground.
  6. Discharge to a septic system, well drain field, cesspool or similar disposal feature.
  7. Utilize a water recycling system

The most common form of non-compliance is to discharge the vehicle wash wastewater into a storm sewer system or into a city street that drains to a storm water inlet. Most storm drainage systems discharge directly to streams or other water bodies without treatment, which means anything that discharges into a storm drain is the same as putting it directly into the stream.

Each of the seven options is discussed below.

Option 1 - Hauling
Option 1 is an economical solution when there is a sufficiently small volume of wastewater generated, for example where extensive on-site recycling is employed and only a small concentrated volume of wastewater is 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 Publicly 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 transportation 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.
  • 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 vehicle washing wastewater include pH adjustment and settling processes. For more information see Pretreatment Standards and Limits.

Option 3 - Discharge to a Stream
Discharging to a stream or other water source including ditches or culverts that lead to streams are termed "direct discharge." This is a potential option for vehicle washing wastewater disposal, but one that requires a National Pollutant Discharge Elimination System (NPDES) permit or state equivalent. In some states, a "general NPDES permit" for vehicle washing (see example general permit) may be obtained and in other states, you will need to apply for an individual permit. If you obtain this type of permit, you may be required to meet discharge standards (usually more stringent than indirect discharge standards) and demonstrate that you are in compliance by collecting samples of your wastewater and having them analyzed at a laboratory. You may also have reporting and recordkeeping responsibilities. For more information see NPDES.

Persons responsible for new wastewater discharges requiring a NPDES permit for vehicle washing are required to apply for an individual permit or seek coverage under a general permit at least 180 days before discharge of vehicle wash wastewater is scheduled to begin.

Option 4 - Evaporation
With this option, a facility constructs a berm on an impervious surface to capture vehicle wash wastewater and hold for a sufficiently long time period that it evaporates. Obviously, this option is only viable for small vehicle washing operations in dry climates. With this option, if your vehicle wash wastewater does not reach a stream or ditch/culvert that leads to a stream or other water body, then there are no permitting requirements under the federal Clean Water Act.

Note that state or local regulations may preclude the use of this option, so check with your state environmental agency and local government before implementation.

Option 5 - Discharge to the Ground
NPDES permit requirements may be avoided and impacts on local streams minimized if vehicles are washed without the use of chemicals in a vegetated or grassy area where the wash water will percolate into the ground instead of allowing it to run into the street and then into a storm drain. This option is usually limited to very small operations. Also, there may be additional requirements if chemicals (detergents, waxes, etc.) are used or if the absorbed water will reach an underground water body.

Note that state or local regulations may preclude the use of this option, so check with your state environmental agency and local government before implementation.

Option 6 - Discharge to a Septic Tank
Discharging vehicle washing wastewater to a septic tank is a viable option as long as the septic tank is not being used as a "motor vehicle waste disposal well," it is designed to handle the volume and characteristics of the vehicle washing wastewater, and no state or local regulations preclude its use for this purpose. Further, there must be no significant potential for discharge of industrial, hazardous or toxic liquids and the wastewater must have constituents similar in concentration to domestic wastewater (including animal or vegetable matter, soap solutions, and diluted domestic-use cleaning solutions).

If a septic tank is to be used for wash water disposal, then engine, undercarriage, and transmission washing is prohibited. [Wash water from engine, undercarriage and transmission washing and from the cleaning of the interior of truck trailers and other large commodity-carrying containers must be collected and discharged to a municipal sewer system, treated in a closed-loop, wash water recycling system or some other acceptable method.] Also, vehicle washing operations should minimize the detachment of paint residues, heavy metals, or other potentially hazardous materials from vehicle surfaces. The use of acids, bases, metal brighteners, degreasing agents or steam is also prohibited. EPA recommends the use of non-toxic, phosphate-free cleaners with cold water as cleaning agent.

Note that state or local regulations may preclude the use of this option, check with your state environmental agency and local government before implementation.

Option 7 - Utilize a Water Recycling System
This option involves the purchase of treatment equipment that is capable of removing a sufficient percentage of contaminants from wash water so that it can be recycled over and over. Wash water recycling systems can be owned and operated on-site by transportation companies, contractor-owned and operated at the fleet owner's site or airport using mobile units, or stationary systems located at the contractor's facility. Commercial units are available as systems that include spray washing, water collection, pumping/piping, and treatment equipment. Treatment typically consists of various filtering and clarification processes to remove solids. Individual components are also available that can be retrofit to existing washing operations. The systems generate a sludge or concentrated wastewater that must be disposed of. A hazardous waste determination must be made before disposal. Water recycling is generally more expensive than once-through water use, due to high equipment costs. However, it is especially applicable to situations where water use is limited or controlled due to droughts and/or where discharge options (e.g., POTW) are unavailable.

Best Practices

A number of states publish best management practices for vehicle and equipment washing. Although these guidance documents are mostly intended for washing trucks and heavy equipment, many have applicability to locomotives/railcars and aircraft. Examples include:

Small aircraft can be effectively cleaned using a dry wash technique. This method involves no water and therefore eliminates the wastewater permit issues that come with wet washing an aircraft. Dry wash is performed using a foaming cleanser that removes dirt, stains and blemishes off of the aircraft’s exterior.

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