A DEP depiction of one of the 'chlorine contact tanks' it plans to use to decontaminate untreated sewage before it gets released into some of the city's waterways.

The de Blasio administration on Wednesday acknowledged that more public engagement was needed around its plans to clean up the waterways that a flawed sewage system has fouled for decades.

Top environmental officials testified at a City Council hearing on progress toward reducing sewage overflows, which occur when rain overwhelms older parts of the city’s sewage infrastructure where wastewater from toilets, sinks and showers mixes with stormwater from the street.

The billions of gallons of untreated sewage that overflow ever year are the primary reason why places like the Bronx River, Paedargat Basin and Flushing Creek are out of step with the federal Clean Water Act.

After many years of pressure and legal threats to comply with that law, the city is in the midst of a multibillion-dollar effort to reduce overflows and improve those waterways. State officials have approved city clean-up plans for seven waterways and are considering two others submitted by the city. The city is still working on two additional plans.

Some advocates are unhappy with the plans the state has approved because they reduce but do not eliminate overflows. There are also concerns about the methods the city plans to use, like rerouting sewage from the Bronx River to the East River, or chlorinating overflow water to kill fecal bacteria and then dechlorinating it so the chlorine doesn’t kill fish.

At the Wednesday hearing of the Council’s committee on environmental protection, Councilman Donovan Richards asked Angela Licata, deputy commissioner of sustainability at the NYC Department of Environmental Protection, about how the agency engages the public about those plans. She said DEP has typically held three meetings for each waterbody.

“Our last public meeting is a meeting to review the alternatives that we’ve developed,” she said. But once the DEP makes its plan, it has not gone back to the public. “We submit what we believe to be the approvable plan to [the state Department of Environmental Conservation] and heretofore the city has not provided the public inout on the [overflow cleanup plans] before we pick a proposed project and submit it to the state.”

Was there a reason for that, Richards wondered?

“Not a good one,” Licata replied.

So, for the remaining two plans—a citywide blueprint encompassing the East River and another that will cover Jamaica Bay and its tributaries—”We are proposing to build in the timeline to propose the project that we prefer with all the rationale [to the public] and get their feedback,” Licata said.

It is unclear, however, that more public engagement will change the plans the city proposes and the state approves.

Last month, a DEC official told a citywide meeting about sewer overflows that the state saw no role for any public engagement in its approval process.

For its part, the city argues that it is doing as much as it can to control sewage overflows without crowding out other DEP capital projects, like those related to maintaining a clean supply of drinking water. The agency also says it is concerned about forcing water rates—which cover all the bills for maintaining and improving the water and sewer systems—to reach unaffordable levels.

Since it began its effort to clean up waterways in the 1970s, the city has reduced sewage overflows into New York Harbor by 82 percent. The city has already committed $4.1 billion toward overflow reduction and expects to spend another $4.4 billion under the nine plans submitted to the state, with the two outstanding plans pushing the price-tag up further.

The city admits those plans won’t totally end sewage overflows. Doing that, says DEP, would cost $30 billion, and some of the waterways would still not meet health standards all the time because of other problems. Instead, DEP says its current plans will make the waterbodies “fishable/swimmable under existing standards” almost all the time during the annual recreation season.

Groups like the S.W.I.M Coalition and Riverkeeper question that: They believe the city and state are apply outdated scientific standards to their projections of the future health of waterways.

They’re also concerned about the use of chlorination and dechlorination, because DEP acknowledges a level of uncertainty about their plan—which would apply commonly used methods in novel ways. DEP also has yet to study the impact of rerouting sewage overflows to the East River.

Water-quality watchdogs think a more aggressive approach to using green infrastructure, especially on private property, is a way the city could reduce overflows more without putting it all on the city’s tab. Advocates also believe that a better system for water rates that takes account of the stormwater that a property produces could reduce concerns about unfairness to low-income renters and homeowners.

The city seems open to some of those ideas. Licata said the department was preparing requests for proposals for studies of the water-billing system and the creation of a private incentive program for green infrastructure.

The DEP’s revised engagement process won’t affect the plans the state has already approved. The city says those plans cannot be altered. But Larry Levine, a senior attorney at the Natural Resources Defense Council, believes there’s nothing stopping the city from doing more than it has proposed.

“If the mayor of the city of New York decides he wants to do something more and better, he’s completely empowered to do that,” Levine told the Council hearing.