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Environmental Blog

  • 25
  • October
  • 2013

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EPA Accepts Eighth Circuit’s Ruling Lifting Blending Mixing Zone Prohibitions

In Iowa League of Cities v. EPA, the Iowa League of Cities (“League”) sought direct appellate review of two letters from the U.S. Environmental Protection Agency (“EPA”) relating to the Agency’s water treatment policies governing blending and mixing zones. The League challenged the policies set out in the letters both procedurally and substantively. On March 25, 2013, the U.S. Court of Appeals for the Eighth Circuit found that both letters had the effect of announcing new legislative rules, but because these rules were not subject to notice and comment, they were invalid under the Administrative Procedure Act. Furthermore, the court held that EPA’s policy on blending exceeded its statutory authority under the Clean Water Act (“CWA”).

On July 10, 2013, the Eighth Circuit denied EPA’s petition for rehearing en banc, but, surprisingly, EPA chose not to file a petition for certiorari to the Supreme Court, letting the opinion stand. This decision will have important implications both for industry and EPA.


Publicly-owned treatment works (“POTWs”) are subject to both federal and state regulation under the CWA. EPA sets technology-based effluent limitations but does not mandate the use of a specific type of technology to achieve the requisite levels. As an additional layer of regulation, states categorize their waterways on the basis of designated uses and set water quality criteria sufficient to protect those uses. These standards are then submitted to EPA for approval. When the technology based effluent limitations placed on POTWs do not achieve the desired water quality levels, EPA is authorized to implement more stringent water quality based effluent limitations for those particular point sources.

POTWs channel incoming water flows through both primary and secondary treatment processes. Secondary treatment processes tend to be biologically-based, but the regulations do not explicitly require that they be biologically-based. Oftentimes, the primary treatment capacity of a particular facility exceeds its secondary treatment capacity. This difference in capacity can be problematic in periods of heavy rain because the large influx of storm water can overwhelm the facility’s secondary treatment processes. To avoid this problem, POTWs often use a process, known as blending, to channel a portion of “peak wet weather flows” around a facility’s biological secondary treatment unit and through an alternative non-biological unit. Water from the alternative unit is then combined with the water that traveled through the biological unit. This combined output must still comply with applicable effluent limitations.

For some time, it was unclear what EPA’s policy on blending was and whether the Agency would characterize it as a bypass, i.e., “the intentional diversion of waste water streams from any portion of a treatment facility.” Bypasses are broadly prohibited under the CWA unless there are no feasible alternatives. In 2003, EPA issued a proposed interpretation of the bypass provision in an effort to clarify its application to blending. In that proposal, EPA made clear that blending was not a prohibited bypass. In 2005, however, EPA abandoned its 2003 proposed interpretation and stated that blending does constitute a prohibited bypass. EPA never officially adopted this 2005 policy.

EPA’s September 2011 letter to the League was on the topic of blending. In particular, it addressed a method of treatment called ACTIFLO that some members of the League wanted to use in the secondary treatment procedures at their wastewater treatment facilities. The letter essentially summarized EPA’s 2005 policy on blending and concluded that ACTIFLO could only be used if there were no feasible alternatives.

The League argued that since the 2005 policy was never finalized, EPA’s September 2011 letter announced a new legislative rule without notice and comment. It also argued that by prohibiting the use of ACTIFLO in a portion of a facility’s secondary treatment procedure, EPA was essentially dictating treatment design, which, they contended, clearly violated the CWA. The court agreed, saying the CWA gives EPA no authority to regulate how POTWs treat wastewater before it is discharged.

Mixing Zones

Mixing zones are defined in EPA’s Water Quality Handbook (“Handbook”) as “a limited area or volume of water where initial dilution of a discharge takes place and where numeric water quality criteria can be exceeded but acutely toxic conditions are prevented.” In effect, a mixing zone allows for a higher concentration of pollutants at the point of discharge, so long as it is sufficiently diluted as it moves through the larger body of water.

Whether and when to allow mixing zones is a matter of state policy to be incorporated into a state’s water quality standards. The Handbook contains further guidance for states on mixing zones, directing states to use a holistic approach in determining whether a mixing zone is tolerable. More specifically, it provides that mixing zones should be used in such a way as to create no significant health risks and disallowed where they could endanger critical areas, such as recreational areas. A state’s policy on mixing zones is subject to EPA approval and EPA retains the authority to veto a permit application incorporating an inappropriate mixing zone.

EPA’s June 2011 letter confirms that states may include mixing zone policies in their water quality standards, but it goes on to say that all mixing zones for bacterial effluents (“bacteria mixing zones”) in waters designated for primary contact recreation should not be permitted due to potential health risks. In the League’s view, any federal objection to a state’s policy on mixing zones should occur through EPA’s process for reviewing state water quality standards. They also argued that the June 2011 letter conflicts with the Handbook, which provides that states are authorized to approve bacteria mixing zones, even in waters designated as recreation areas, so long as site-specific factors create scenarios in which there are no health risks and recreational areas are not endangered. The Eighth Circuit vacated this mixing zone prohibition on procedural grounds, which leaves the door open for EPA to formally propose a similar rule in the future.

What this means

So it seems the ban on blending is effectively dead, but EPA may propose a rule governing mixing zones in the future. Until then, the precedential weight of the ruling may be limited to the Eighth Circuit, though it would be persuasive authority in other jurisdictions and EPA may even apply it nationwide to avoid confusion and uncertainty for regulated entities. In addition, the ruling may ignite challenges to other Agency policies governing wastewater treatment plants, such as policies for setting numeric limits based on narrative criteria and EPA’s interpretation of regulations on when infrastructure upgrades to comply with the CWA are “affordable,” which, League lawyers allege, are similarly improper. 

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