Mechanical Coatings Removal: Regulatory Requirements

EPA Self-Audit and Inspection Guide
Organic Finishing of Metals

Mechanical Coatings Removal: Regulatory Requirements

Air
The Clean Air Act regulates particulate matter in exhaust air (40 CFR Part 50). Large mechanical coatings removal operations can create a sufficient amount of particulate matter consisting of dry blast media and coatings residue to subject a facility to Title V permitting requirements. In addition, specific standards have been established for Mechanical Coatings removal operations at aerospace manufacturing and rework facilities (40 CFR Part 63, Subpart GG).

Water
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 heavy metals, toxic organics, and conventional pollutants in wastewater streams. Residue from mechanical coatings removal methods including residual coatings, blast media, and blast water, may contaminate the water stream, especially when wet-abrasive blasting is used. 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). Waste from mechanical coatings removal operations may be classified as hazardous depending on the type of coating material removed. 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. Responsibilities will vary according to the amount of hazardous waste generated; facilities generating at least 100 kilograms of hazardous waste per month must comply with the hazardous waste generator requirements at 40 CFR Part 262.

Each state and/or region is primarily responsible for the regulation of non-hazardous solid wastes (those not governed by the hazardous waste provisions of RCRA). Contact state environmental agencies for specific information and guidance.

Health and Safety
Mechanical coatings removal creates adverse conditions inside facilities which, while not regulated by EPA, should be addressed. Suspended particulates in confined areas and excessive noise created by equipment can impact worker health and are regulated by the Occupational Safety and Health Administration. Also, workers should be trained properly to avoid accidents and injuries when working with mechanical coatings removal equipment. For example, blasting systems produce a high-pressure stream of dry or wet media that is capable of severely damaging or even severing limbs.

Self-Audit/Inspection

Do dry residual coatings and blast media come in contact with exhaust air streams? If so, do concentrations of particulate matter exceed limits established by facility air permits?

Do mechanical coatings removal media or residual coatings 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 mechanical coatings removal media or residual coatings wastes labeled and packaged in accordance with 40 CFR Part 262, Subpart C?

Are wastes contaminated with residual coatings classified as hazardous? If so, are the wastes handled and manifested in accordance with 40 CFR Part 262, Subpart B? Are the hazardous wastes segregated from non-hazardous wastes?

Mechanical Coatings Removal: Common Causes of Violations

Blast media, coating material, and substrate residue form dust in the blast area. Some particles may be small enough to qualify as respirable particulates capable of penetrating lung tissue. Typical hazards include exposure to silica and lead.

Mechanical coatings removal technologies generate a high level of noise. Equipment used to compress and pump air or water, the exhaust of the air or water stream, and the media striking the substrate create sufficient decibel levels to require process engineering controls and hearing protection.

Wet-abrasive blasting and waterjet blasting create a waste of coating residue and water, which can contaminate water streams. Water streams may also become contaminated accidentally, as with spilt material entering a storm sewer. Contaminated water streams may contain pollutants, including the solvents, residual sludges, and oils in concentrations that exceed the limits established by facility NPDES permits or POTW discharge agreements. As a result, effluent, may not be directly released to water systems or to publicly owned treatment works without pretreatment.

Dry-abrasive blasting creates a waste of blast media and coatings residue. Wet-abrasive blasting creates a sludge of coatings residue. Based on the coating constituents, the waste may be classified as hazardous according to RCRA (40 CFR Part 261).

Mechanical Coatings Removal: Sources of Pollution

Dry-abrasive blasting creates a waste of spent blast media, dislodged coating materials and other contaminants. This material can create a fine dust containing respirable particles in the work area.

Wet-abrasive blasting creates a waste of spent blast media, dislodged coating materials and other contaminants, and water. The blast media and dislodged contaminants may be segregated from the water as a sludge.

Waterjet blasting creates a waste of dislodged coating materials and other contaminants, as well as water. The dislodged contaminants may be segregated from the water as a sludge.

Depending on the constituents of the coating material and other contaminants, the coatings residue or coating sludge may be considered to be a hazardous waste.

Noise is created from the equipment used to compress and pump the air and solid carbon dioxide, from the exhaust of the carbon dioxide stream, and from the blast media striking the substrate.

Mechanical Coatings Removal: Pollution Prevention Alternatives

Mechanical coatings removal may be considered a pollution prevention alternative since it aids in the proper application of coating materials thereby reducing rework or reject parts. It also eliminates or reduces the use of hazardous materials used in chemical coatings removal.

Substitute carbon dioxide blasting for dry-abrasive blasting and wet-abrasive blasting to eliminate the need for solid blast media, water, and their disposal.

Perform mechanical coatings removal in enclosed areas such as blast booths or workcells to contain noise, dust, and water. The enclosures must have adequate ventilation systems to reduce levels of dust, and drainage systems to capture wastewater.

Optimize process to strip properly with minimal aggression. Proper adjustment of operating parameters, such as media size and media exhaust velocity, will improve coatings removal without damaging the substrate. Modify part arrangement to ensure that blast media reaches all surfaces.

Remove residual coatings and other contaminants from blast media so that it can be reused. Dry-abrasive blast media and water from wet-abrasive blasting and waterjet blasting can be separated from coatings through filtration.

Recycle water from wet-abrasive blasting to other processes such as rinse baths, facility clean-up, or other uses where small contaminants will not matter.

Segregate non-hazardous blast media and wastewater from hazardous coatings residue or other facility chemicals, and label containers to prevent mixing. Separation of the materials reduces the amount of hazardous waste that is produced.

Minimize need for coatings removal by improving other process steps. Reduce coating failure by handling parts carefully, and by performing good cleaning, coating application and curing. Determine if time between rework can be lengthened to reduce need for mechanical coatings removal.

Train employees on safe operation of equipment and handling of wastes and encourage continuous improvement. Training familiarizes workers with their responsibilities, which reduces accidents and spills.