BNA

Wastewater treatment plants should be allowed to “blend” partially treated and fully treated wastewater when necessary during heavy rains under any new rules governing sanitary sewer systems, the leading industry association said in recent comments to the Environmental Protection Agency.

“The use of blending is absolutely essential for many [publicly owned treatment works] to treat wet weather flows and still meet effluent limitations,” the National Association of Clean Water Agencies said.

Permitting agencies should be allowed to incorporate blending as an alternative in National Pollutant Discharge Elimination System permits “under appropriate conditions and circumstances” as long as the treatment plant uses appropriate practices for managing flow and treatment capacity, according to NACWA.

The utility association was among a number of groups submitting comments to EPA, which is considering proposing a rule to modify NPDES regulations as they apply to municipal sanitary sewer overflows (SSOs) and municipal sanitary sewer collection systems (160 DEN A-9, 8/20/10).

EPA also wants to resolve long-standing issues surrounding a 2005 proposed draft “peak wet weather flow” policy that was never finalized.

EPA said in a Federal Register notice it was considering whether to adopt this policy, revise it, or address the peak wet weather flow issue as part of an approach for sanitary sewer overflows “to allow for a holistic and integrated approach to reducing SSOs while at the same time addressing peak flows at the POTW treatment plant” (75 Fed. Reg. 30,395; 102 DEN A-7, 5/28/10).

Sanitary sewer systems are designed to carry sewage only, while combined sewer systems carry both sewage and stormwater. EPA issued a combined sewer overflow policy in 1994, but it has not issued a final policy on sanitary sewer overflows.

Redesigning Systems Called Infeasible
During wet weather conditions, NACWA said, treatment plants must treat flow volumes many times greater than dry weather flows. Collection systems and plants were not designed to store and treat this excess flow, “and it would be both inefficient and technologically infeasible to redesign these facilities to accommodate all wet weather conditions.
“As long as a POTW is meeting its permit limits, EPA should not be concerned with the treatment processes used at the plant or involved in monitoring water quality within the plant,” the association told EPA.

NACWA told EPA that as it considers new SSO rules, “all options regarding peak flows must be on the table, including a final SSO regulation that authorizes peak flow treatment scenarios at POTWs without classifying such peak flow treatment under the current bypass regulation.”

EPA's 2005 proposed policy attempted to clarify its interpretation that the existing “bypass” provision in NPDES regulations applies to peak wet weather diversions at publicly owned wastewater treatment plants, which are recombined with flows from secondary treatment units prior to discharge.

EPA's rule at 40 C.F.R. Part 122.41(m) prohibits bypasses except where necessary for essential maintenance to assure efficient operation. All other bypasses are subject to enforcement action unless there are no feasible alternatives or to prevent loss of life, personal injury, or severe property damage.

Blending Considered a Bypass
The draft policy, which NACWA and the Natural Resources Defense Council helped develop, said blending was considered a bypass and thus subject to the original rule's requirements that an “anticipated bypass” be approved only if there were “no feasible alternatives” to peak wet weather flow diversions around secondary treatment units.

Secondary treatment typically uses biological methods, including bacteria, to treat the wastewater after it has gone through primary treatment. The draft policy would have required sanitary sewage treatment plants to provide full secondary treatment to wastewater, including during peak wet weather flows.

But NACWA said in its comment that the draft 2005 policy “was conceived and developed at a time when collection system standard conditions were lacking. A solution to the peak flows issue was attempted, but the underlying collection system issues were not part of that solution.

“The issue of peak flow management at the treatment plant is inextricably linked to collection system management and utilities must be able to develop a system-wide program for collection system and wet weather management that meets their Clean Water Act mandates and the needs of their communities,” NACWA said.

NACWA urged EPA not to pursue policies or regulations that create disincentives to installing new types of filtration technology that can provide high levels of treatment

Peak Flows Should Be Handled in Larger Rule
How to address peak wet weather flows that overwhelm sanitary sewer systems during heavy rains should be part of a comprehensive sanitary sewer system regulation, not a separate policy, NACWA said.

During a recent EPA “listening session,” one agency official indicated this appears to the direction the agency is taking after hearing various views on the issue (134 DEN A-14, 7/15/10).

The Natural Resources Defense Council called the 2005 draft policy “a good framework,” but said in its comment that “the goal of every NPDES permit should be to phase out blending as rapidly as possible.”

The Water Environment Federation strongly recommended that EPA not use the term blending in any context “because of conflicting interpretations.”

“Rather, EPA must focus on developing appropriate new regulatory language providing for peak wet weather treatment and not rely on existing bypass provisions” to regulate wet weather actions, the federation said.

In another comment, the Iowa Department of Natural Resources recommended that EPA incorporate the 2005 draft peak flows policy into a holistic wet weather rulemaking effort.

“The regulation needs to clearly establish what is acceptable rather than leave that to be determined case-by-case using unwritten, subjective, and inconsistent determinations based on EPA's enforcement discretion,” wrote Charles Corell, the department's Water Quality Bureau chief.

Pending Lawsuit
In July, the Iowa League of Cities sued EPA to force it to review its interpretation of Clean Water Act rules and policies governing how wastewater treatment plants handle wet weather (Iowa League of Cities v. EPA, 8th Cir., No. 10-2646, 7/26/10; 147 DEN A-13, 8/3/10).

The league alleged EPA has been implementing the draft policy from 2005 without going through the rulemaking process. In addition, it alleged EPA has been dictating the type of secondary treatment that must be used at wastewater treatment plants even though the same water quality results might be achieved in a different manner.

For example, in Lawrence, Kan., the league's attorney told BNA, EPA has maintained that the type of chemical treatment used for secondary treatment at the wastewater treatment plant was not an acceptable alternative to biological treatment.
EPA has classified the municipality's secondary treatment device, called Actiflo, which adds chemicals to the water and returns it to be disinfected, as an illegal treatment process, according to the petition.

Importance of Meeting Effluent Limits
“Peak flows at treatment plants should be handled in a cost-effective manner that allows for discharge of peak flows if the effluent from the wastewater treatment facility meets water quality-based limits,” wrote Michael Tate, chief of the Kansas Department of Health and Environment's Technical Service Division, in a comment to EPA.

High-rate treatment systems for wet weather should be considered as “additional treatment trains” in wastewater plants, not bypasses, Tate said.

“Therefore, if EPA chooses to pursue the interpretation that individual treatment trains in wastewater plants must independently meet secondary treatment units, we believe EPA should clarify that stance in this rulemaking.”

The Kansas department in a comment expressed concerns that EPA's interpretations relating to bypassing and SSOs “could have profound impact on Kansas municipalities, perhaps with little environmental benefit.”

By Linda Roeder