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The Association of Clean Water Administrators (“ACWA”) submitted October 31st comments to the United States Environmental Protection Agency (“EPA”) on an August 31st Federal Register Notice soliciting input on:

. . . possible approaches to updating the National Pollutant Discharge Elimination System (NPDES) regulations related to the management of peak wet weather flows at Publicly Owned Treatment Works (POTWs) treatment plants serving separate sanitary sewer collection systems. . .

ACWA describes itself as an independent, nonpartisan, national organization of state, interstate, and territorial water program managers, who on a daily basis implement the water quality programs of the Clean Water Act.

As EPA has previously noted:

. . . During periods of wet weather, flows received by POTW’s collection system and treatment facility typically increase. Significant increases in influent flow caused by wet weathers conditions (e.g., due to infiltration and/or inflow of water into the collection system) can create operational challenges for treatment facilities and potentially adversely affect treatment efficiency, reliability, and control of unit process operations for the treatment plant. Activated sludge systems are particularly vulnerable to high volume peak flows. Peak flows that approach or exceed design capacity of an activated sludge unit can shift the solids inventory from the aeration basin to the clarifier(s) and can result in excessive solids losses from the clarifiers (i.e., wash out the biological mass necessary for treatment).

Various design and operational methods are often utilized to enhance treatment of wet weather flows.

ACWA notes in its October 31st comments that the states have expressed a diversity of opinions on management of peak wet weather flows. However, the organization indicates that half the states have expressed potential for support of EPA “exploring a blending rule, depending on how blending was defined.”

Points raised in ACWA’s comments include:

• States generally support limiting EPA’s rulemaking to separate sanitary sewer systems (noting that sanitary sewer systems are managed differently than combined sewer systems)
• States support further discussion and consideration of both technology and water quality-based approaches (arguing limiting discussions to one side of the equation could undermine information exchange that would provide a complete picture of options)
• States request greater certainty and clarity regarding peak flow management
• A need for a brighter line to be drawn between allowable blending and unallowable bypass is requested
• Most states would not support a definition for blending that allows the mixing of completely untreated waste with partially treated effluent (and then discharging it)
• Approximately ¾ of the states surveyed indicated future support of a blending rulemaking (depending on how blending was defined)
• States supporting a blending rule also advocate for further consideration of appropriate operations, infrastructure, asset management, maintenance programs, inflow and infiltration reduction efforts, and general feasibility

ACWA states that questions were raised during the organization’s discussions which include:

1. Whether EPA’s policy of discouraging blending has changed;
2. Will a blending rule significantly increase the number of water quality standards variances issued;
3. How will EPA void sending mixed signals to the public;
4. What role does “no feasibility analysis” have going forward;
5. Is there any data showing that blending increases the amount of viruses coming out of the facility; and
6. Should we be linking cost-benefit of blending to the designated uses in the affected watershed?

A copy of the ACWA comments can be found here. A survey summary can be found here.