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Pollution Prevention Storage Criteria for Toxic, Hazardous or Polluting Materials

These storage criteria were established 2-19-1998 in accordance with Section 5.4 of the Washtenaw County Pollution Prevention Regulation, which provides that, "all parties who store toxic, hazardous, or polluting materials shall do so in a manner that will assuredly prevent contamination of the environment."

Due to the diversity of materials and packaging volumes covered by the Regulation, this document presents above ground storage requirements in terms of general standards.

Underground storage is governed by the Michigan Department of Environmental Quality. Storage of specific materials or container types may also be controlled by other state federal or local agencies.


  • Combustible Liquid - A liquid material with a flash point at or above 100 degrees Fahrenheit.

  • Compatible - Materials that will not react violently or produce dangerous gases or vapors when mixed.

  • Contamination - The presence or introduction of a substance into the environment above naturally occurring concentrations.

  • Environment - The air, water and land outside a workplace.

  • Flammable Liquid - A liquid material with a flash point below 100 degrees Fahrenheit.

  • Primary container - The container that is in immediate contact with a substance.

  • Secondary Containment - Spill control devices that are external to the primary container of a substance. The concept of secondary containment is to prevent environmental contamination or human exposure to chemicals when a primary container is damaged or spilled.

  • THP - Toxic, Hazardous, or Polluting.

General Storage Conditions (above ground)

  1. All liquids must be stored with secondary containment.

  2. Materials used for secondary containment must meet the following conditions:

    • Must be compatible with, and impermeable to, all substances stored within the structure.
    • Must be resistant to weathering.
    • Must be able to bear any load that would result from the rupture of a primary storage container.
    • Must be noncombustible if flammable or combustible liquids are in the area.
  3. A secondary containment area must be large enough to withhold a complete spill of the largest primary container, even if other items are in the containment area.

  4. All materials stored within a secondary containment unit must be compatible with each other and with all primary containers in the area.

  5. Primary containers must be placed to allow for inspection of both primary and secondary containers.

  6. Storage rooms for flammable liquids must have mechanical venting. All electrical fixtures must be explosion proof. The rooms must be free of open flame furnaces and other ignition sources.

  7. Solid materials must be in sound packaging protected against moisture and other potential damage.

  8. Compressed gas cylinders must be secured to a stationary object or affixed in a welding cart.

  9. Storage rooms for compressed gases must have accurately calibrated low oxygen monitors and must be mechanically vented. All heat sources and electrical fixtures must be explosion proof if flammable gases are stored.

  10. Gas specific monitors are required for storage of gases identified by SARA Title III as extremely hazardous.

  11. Compressed gases stored outdoors, including liquid propane, must be protected from vehicles, vandalism, and other sources of damage.

  12. Floor drains are discouraged. They will only be accepted in three situations:

    • The drain discharges to a municipal sanitary sewer system where treatment plant officials agree that the system can accept a full release of the materials stored.
    • The drain discharges to a sealed holding tank that is pumped by a transporter who is licensed to handle the waste.
    • A permit has been received from the Michigan Department of Environmental Quality to discharge the drain into the environment.

Design Considerations

The specific design of secondary containment systems involves a number of considerations, including function and practicality. Many prefabricated secondary containment units are available, however they are not universally suited. In some situations, the floor of a building will provide adequate secondary containment. The following issues should always be considered when designing or selecting a system:

  1. What are the types of materials to be stored? This will dictate limitations on construction material and may impact required capacity.
  2. How much will be stored, and what is the largest container? This will determine the storage capacity of secondary containment.
  3. What are the logistics involved?
      • Proximity to work areas.
      • Methods of transferring the substance.
      • Indoor verses outdoor storage. Precipitation must be controlled for outdoor storage. It may be necessary to dispose of accumulated water as hazardous or liquid industrial waste.
      • Above ground vs. underground storage.


Guide to Understanding Secondary Containment Requirements in Michigan
Michigan Department of Environmental Quality
Environmental Assistance Division
P.O. Box 30473
Lansing, MI 48909

Small Business Guide to Secondary Containment
Clinton River Watershed Council
8215 Hall Rd.
Utica, MI 48087
(248) 739-1122

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