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EPA Self-Audit and Inspection Guide
Organic Finishing of Metals

Table of Contents

Aqueous Cleaning: Regulatory Requirements

As part of the Clean Water Act, Effluent Guidelines and Standards for Metal Finishing (40 CFR Part 433) have been established that limit concentrations of conventional pollutants, and heavy metals in wastewater streams. Aqueous cleaning solutions may have a non-neutral pH, and may contain chemical additives and/orimetal ions, depending on their intended use. Used solutions will also contain dirt, oils and grease. These materials can enter the wastewater through liquid dripping off of parts, when cleaning equipment or changing solution, and from accidental spills or leaks in equipment. Actual limits for effluent constituents depend on the size of the operation and the amount of wastewater generated from the facility. If the facility discharges directly to receiving waters, these limits will be established through the facility's National Pollutant Discharge Elimination System (NPDES) permit (40 CFR Part 122). Facilities which are indirect dischargers releasing to a POTW must meet limits in the POTW's discharge agreement. Wastewater streams with concentrations exceeding permit limits will require pretreatment prior to discharge to receiving waters or to a publicly owned treatment works. Pretreatment may include separation of liquid wastes to remove solvents, and settling or precipitation of solid materials.

Solid and Hazardous Waste
Under the Resource Conservation and Recovery Act (RCRA), organic finishing facilities are required to manage listed and characteristic hazardous wastes (40 CFR Part 261). Used aqueous cleaning solutions may contain constituents listed or characterized as hazardous wastes, such as oils and grease. Hazardous waste management (40 CFR Part 262) includes obtaining permits for the facility in order to generate wastes, meeting accumulation limits for waste storage areas, and manifesting waste containers for off-site disposal.

The Emergency Planning and Community Right-to-Know Act (EPCRA) requires facilities to notify employees, customers and the surrounding community of certain hazardous chemicals and substances that are present on-site. Large aqueous cleaning operations may contain hazardous substances in sufficient quantities to subject a facility to several EPCRA requirements. Facilities may be required to inform the local emergency planning committee (LEPC) and the state emergency response commission (SERC) of the materials stored and used on-site, devise emergency response plans for reacting to spills, and notify authorities of accidental spills and releases (40 CFR Parts 302 and 355). In addition, due to the materials used in organic solvent cleaning solutions, facilities may be required to submit Material Safety Data Sheets (MSDS) for these materials to state, regional, and local organizations, while disposed volumes of the material may have to be documented on annual Toxic Release Inventory reports (40 CFR Part 372).


  • Do aqueous cleaning solutions come in contact with water streams? If so, do concentrations of pollutants exceed limits established by the facility NPDES permit or POTW discharge agreement?
  • Are all aqueous cleaning solutions and wastes labeled and packaged in accordance with 40CFR Part 262, Subpart C? Are manifest forms completed for wastes to be shipped for disposal?
  • Has the facility participated in local, regional, or state emergency response planning activities? Have facility response plans been developed and coordinated with local authorities?
Aqueous Cleaning: Common Causes of Violations
  • Aqueous cleaning solutions are liquid materials that can contaminate water streams. Contamination may occur accidentally, as with spilt material entering a storm sewer. Contaminated water streams may contain pollutants, including surfactants, residual sludges, and oils, in concentrations that exceed the limits established by facility NPDES permits or POTW discharge agreements. The water stream may also have a non-neutral pH. Effluent, then, may not be directly released to water systems or to publicly owned treatment works without pretreatment.
  • Aqueous cleaning solutions containing oils, grease, and other contaminants may be classified as hazardous waste according to RCRA. These materials must be labeled, stored, and disposed in accordance with 40CFR Part 262, Subpart C.
  •  Organic solvent cleaning solutions may contain substances defined as hazardous chemicals. Depending on the quantity of material on-site, facilities must have an MSDS for each solution, maintain records for TRI reporting, and cooperate with local emergency planning committees.
Aqueous Cleaning: Sources of Pollution
  • Used aqueous cleaning solutions with non-neutral pH levels, and/or containing grease, oils, phosphates, and heavy metals may spill due to improper handling or leaks in tanks, pipes, hoses, or other containers. The liquid material may enter storm sewers if not properly contained.
  • Used aqueous cleaning solutions may contain grease, oils, and heavy metals which would classify the solutions as hazardous waste.
  • Grease, oils, and heavy metals may be separated from aqueous cleaning solutions as sludge. The sludge may be classified as a hazardous waste and require disposal in accordance with 40 CFR Part 262.
  • Parts experiencing flash rusting of the substrate due to incompatibility with aqueous cleaning solutions will necessitate rework or possibly disposal.
Aqueous Cleaning: Pollution Prevention Alternatives
  • Aqueous cleaning may be considered a pollution prevention alternative since it aids in proper application of coating materials thereby reducing rework or reject parts.
  • Substituting aqueous cleaners for semi-aqueous cleaners or organic solvents reduces the problems associated with volatile organic compounds and hazardous substances and wastes.
  • Use a higher quality cleaner at a lower concentration to minimize consumption of additive, water, and time.
  • Restrict traffic in storage areas to reduce spills and accidents. Keep storage and work areas clean so that spills and leaks are more noticeable and reaction time is reduced.
  • Optimize aqueous cleaning processes to clean properly with minimal water and additives. Proper adjustment of operating parameters, such as time, agitation, solution concentration, temperature, and water type, will improve cleaning without creating additional wastewater or using more additives. Modify part orientation or racking to ensure that the cleaner reaches all surfaces.
  • Conserve energy by operating at optimum temperature; and by covering baths, using insulated tanks, or using waste heat from other processes to heat cleaning solution.
  • Remove contaminants from aqueous cleaning solutions to retain cleaning effectiveness. Separate soils, dirt, oils, and other contaminants using filtration, gravity separation, or membrane technologies (crossflow filtration). Reducing heat and stopping agitation will promote separation of contaminants in batch systems.
  • Segregate non-hazardous wastewater and other materials from hazardous organic solvents, and label containers to prevent mixing. Separation of the materials reduces the amount of hazardous waste that is produced.
  • Minimize water consumption by utilizing counter-current rinse baths. Backflow water from final rinse, to pre-rinse, to cleaning baths before disposing.
  • Check aqueous cleaning equipment regularly for leaks and repair them. Items to check include tanks, pumps, pipes, hoses, valves, fittings, and storage containers.
  • Minimize accumulation of soils, dirt, and oils by practicing good housekeeping. Keep the facility clean and use proper part handling procedures to reduce part contamination initially. Perform regular maintenance of machinery to remove excess oil, grease, and dirt; use gloves when handling parts to reduce oils.
  • Train employees on safe handling of materials and wastes and encourage continuous improvement. Training familiarizes workers with their responsibilities, which reduces spills and accidents.

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