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Technology Transfer Network - OAR Policy and Guidance





  • On March 31, 2006, the Environmental Protection Agency (EPA) announced a decision to amend the applicability section of the current rule that limits emissions of toxic air pollutants from industrial process cooling towers. See more information below to obtain a copy of the final amendments.
  • EPA analyzed emissions from these facilities after implementation of the 1994 air toxics rule and determined that the risks to human health and to the environments are low. Therefore, EPA need not require further emissions reductions.
  • An industrial process cooling tower is a cooling system for an industrial process. Hot water travels from an industrial process to the cooling tower where the water partially evaporates, cooling the water. Water treatment chemicals must be added to the cooling water to inhibit corrosion, control scaling and fouling, limit the growth of microorganisms and control the pH of the cooling water. A small amount of the water treatment chemicals may be emitted during the cooling process.
  • EPA issued a national rule to limit emissions of toxic air pollutants from these facilities in 1994. That rule is one of 96 rules called maximum achievable control technology (MACT) standards that require 174 industry sectors to eliminate 1.7 million tons per year of 187 toxic air pollutants. Congress listed these toxic air pollutants in the Clean Air Act.
  • The 1994 MACT standards for industrial process cooling towers eliminates the use of chromium-based water treatment chemicals that EPA suspects cause cancer or have other serious health or environmental effects. The rule prevents 25 tons per year of chromium from being emitted into the air. Currently, some industrial process cooling towers may emit one of three toxic air pollutants: methanol, ethylene thiourea, and chloroform.
  • The Clean Air Act requires EPA to assess the risk remaining after the application of the 1994 MACT standards. These are called residual risk assessments.
  • The Clean Air Act also requires EPA to review and revise, as necessary, the 1994 standards by taking into account developments in practices, processes, and control technologies.
  • EPA considered the public comments received on the proposal and we are amending the applicability section of the rule in response to these comments.
  • EPA is making a final decision that no further controls are necessary, because:
    - The risk assessment found that after application of the standards, the chronic cancer, noncancer, and acute risks to humans, as well as ecological effects, from these facilities are low enough that further controls are not warranted.
    - The technology assessment did not identify any advancements in practices, processes, or control technology.
  • The final action responds to public comments on the residual risk assessment and technology review and announces EPA’s final decision to amend the applicability section of the rule.

  • The Clean Air Act requires EPA to regulate air toxics from large industrial facilities in two phases.
  • The first phase is “technology-based,” where EPA develops standards for controlling the emissions of air toxics from sources in an industry group (or “source category”). These maximum achievable control technology (MACT) standards are based on emissions levels that are already being achieved by the better-controlled and lower-emitting sources in an industry.
  • Within 8 years of setting the MACT standards, EPA is required to assess the remaining health risks from each source category to determine whether the MACT standards appropriately protect public health. Applying this “risk-based” approach called residual risk, EPA must determine whether more health-protective standards are necessary.
  • Also, every 8 years after setting the MACT standards, the Clean Air Act requires that EPA review and revise the standards, if necessary, to account for improvements in air pollution controls and/or prevention.
  • When the rule was promulgated, we had no information that indicated that air toxics other than chromium compounds were emitted from industrial process cooling towers. Consequently, we did not address emissions of other air toxics in the rule. Because the rule prohibits the use of chromium-based water treatment chemicals in industrial process cooling towers, we believe that chromium compound emissions from industrial process cooling towers have been eliminated by the rule.
  • To determine the residual risk for the source category, however, we considered emissions of other air toxics from industrial process cooling towers. We determined that some water treatment chemicals may contain or form air toxics and subsequently be emitted from industrial process cooling towers. These air toxics include chloroform, methanol, and ethylene thiourea.
  • EPA's residual risk analyses show that there is not a significant health risk associated with any of the facilities in the United States.

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