Pollution Prevention Guides for 
Auto Body Shops - Fact Sheet 12

Waste Water and Sludge

Auto body shops can generate wastewater from either cleaning service bay floors or washing vehicles prior to body work. In most auto body shops, wastewater drains into a sump, where dirt and sand settle out and collect at the bottom, forming a sludge. Wastewater may then be discharged to the sanitary sewer system where it is treated at the municipal wastewater treatment plant.

If the floors of the shop are kept clean of spills and less hazardous products are used, the wastewater and sludge should not be hazardous. However, when good housekeeping is not practiced, wastewater and sludge may be contaminated with heavy metals, chlorinated solvents, and grease. The result is sludge and wastewater that may have to be managed as hazardous waste.

To prevent pollution caused by the mismanagement of your shop's wastewater and sludge:

  • Never discharge them into a storm sewer -- storm sewers generally flow directly into local surface waters.
  • Never release waste to sumps or drains that discharge directly to groundwater supplies -- this could pollute local groundwater supplies (a violation of state and federal water quality regulations).
  • Never release hazardous materials to your septic system -- chemicals can pollute local groundwater supplies (a violation of state and federal water quality regulation).
  • Contact your local municipal wastewater treatment plant prior to discharging wastewater into the sanitary sewer. The plant may require testing or pretreatment (such as an oil/water separator) prior to accepting your waste.
  • Prior to disposal, determine if the sludge is hazardous or not. If the sludge is hazardous, it must be disposed as such. If non-hazardous, allow the sludge to dry and dispose in a local solid waste management facility, such as a landfill, with its approval.

Wastewater And Sludge
1) Do you practice good housekeeping?

Good housekeeping practices, such as cleaning up spills and leaks right away, can help prevent your wastewater and sludge from becoming contaminated with hazardous materials.

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2) Do you use less hazardous products in your shop?

Using less hazardous products not only improves worker safety but can help keep your wastewater and sludge from being contaminated or prevent a release of hazardous materials into the environment.

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3) Do you run a "dry shop?"

A "dry shop" is one that does not have floor drains and uses dry floor cleaning methods such as sweeping and vacuuming instead of using water.

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4) If you have a sump, do you test your wastewater to determine if it is hazardous prior to disposal?

You may have to determine if your wastewater is hazardous prior to discharging it to the municipal wastewater treatment plant. If you do not use hazardous materials in your shop, there is a good chance the wastewater is not hazardous. For help, contact your local wastewater treatment plant.

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5) If you have a sump, do you test your sump sludge to determine if it is hazardous prior to disposal?

You must determine if your sump sludge is hazardous prior to disposal. If you do not use any hazardous materials in your shop, there is a good chance the sludges are not hazardous and could be treated as a solid waste. Note that it may have to be dried prior to disposal before a landfill will accept it.

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6) Are you on a septic system?

Septic system users have to use extreme caution when dumping fluids down the drain. Hazardous chemicals could find their way to local water supplies, causing serious contamination problems. Drains not connected to the city sewer should be sealed and less hazardous products should be used.

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7) Do you use an oil-water separator in your sump?

Commercial oil-water separators or oil skimmers are available that use an oil-attracting material immersed or run over the top of the water to absorb oil only. Once separated, the oil can be transferred to a used oil container for recycling.

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8) Do you wash vehicles on-site?

If you wash vehicles on-site, use less hazardous soaps to help prevent wastewater and sludges from becoming hazardous waste.

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Montana State University Extension Service
Pollution Prevention Program Taylor Hall Bozeman, Montana 59717
(406) 994-3451
funded by
The United States Environmental Protection Agency
(Fact Sheet 12 of 18)

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