The DigIndy tunnel is a lot of things: a massive feat of engineering that will cost more than $2 billion; a nearly 15-year project that is more than halfway finished; and a 28-mile system that is the savior of water quality in the White River. Supposedly.

One thing the project, questionably, is not: big enough.

This underground river, carved more than 200 feet beneath the surface, was designed to keep as much as 5 billion gallons of poop-laden wastewater out of Indianapolis’ waterways in any given year. Officials promised it would slash the number of annual overflow events that dump sewage from 60 to four.

That said, the project was also imagined two decades ago, well before global warming increased the severity of rainstorms in the region. Now, more water is funneling into the system.That leaves some worrying that by the time the tunnel is completed in five years, it will already be obsolete.

And the same is true of more than 100 similar projects across the state. More rainfall means more sewer overflows. And sewer operators across Indiana worry they will be forced to build even bigger tunnels, at even greater expense.

But state environmental officials recently changed the rules to ensure that Indianapolis cannot be forced to expand its project to capture that increased flow. And some water quality advocates are crying foul.

“I don’t know where that leaves us,” said Jill Hoffmann, executive director of the White River Alliance. “It’s a moving target, and I know that’s hard, but that doesn’t mean we get a pass. We’re moving the goalpost to make it okay for pollution to happen.”

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With such a big price tag for the project, everyone wants what they were promised. Cities and utilities want to be in compliance with water quality standards. Communities and environmentalists want a clean river free of sewage.

Matt Greller, executive director of Accelerating Indiana Municipalities, wonders if there is a way that both can be happy.

"Or, will the billions of dollars we've been spending over the last 20 years all be for naught?" said Greller, whose nonpartisan group represents more than 460 cities and towns across the state.

'How big is big enough?'

For nearly a century, toilet water — and everything in it — overflowed from Indianapolis' combined sanitary and storm sewer system into the White River and its tributaries any time it rained more than a quarter of an inch.

In 2006, the city of Indianapolis reached an agreement with the U.S. Environmental Protection Agency, the U.S. Department of Justice and the Indiana Department of Environmental Management that pollution of the White River would no longer be tolerated.

This consent decree laid out a 20-year plan to curb the use of Indianapolis’ waterways as an open sewer. The federal Clean Water Act required water bodies to be swimmable and fishable, and this plan worked toward that benchmark.

More specifically, it required capturing roughly 95% to 97% of overflows in a massive underground tunnel so it could be treated before being discharged into the river. Under the consent decree, if the city met that standard, it would be exempted from the swimmability requirement whenever there was a discharge.

On Jan. 8, IDEM's Environmental Rules Board did just that. The board approved a new rule that, in essence, says the utility will stay in compliance, even if more sewage makes its way into Indianapolis waterways.

The rule lifts the swimmable standard and replaces it with a "limited wet-weather" standard for four days after each sewage discharge. The rule does not, however, have any cap on the number of discharges allowed.

That means more sewage could go into the river than people previously thought.

That's because rainfall is changing. In developing its long-term plan, Indianapolis was required to identify the average rainfall during a five-year span. The city picked 1996 to 2000 — it had some wetter and some drier years, Citizens Energy said, so it provided a good mix. Twenty years ago, that is.

“We design as if the statistics stay stationary,” said Alan Hamlet, a professor of civil and environmental engineering at the University of Notre Dame. “But statistics are anything but static, they change through time.”

Already, before the project is even complete, Indiana is seeing more rain than when it began. The five-year average that is the basis for DigIndy’s design is 40.45 inches of rain in a year. The average annual rainfall in Indianapolis over the last five years, however, is 46.61 inches, according to data from the National Oceanic and Atmospheric Administration.

That number is only expected to increase. The state will likely see about 6% to 8% more annual rainfall by mid-century, according to the Indiana Climate Change Impact Assessments research from Purdue University. That jump could be as high as 27% in the winter and spring.

And the outlook gets worse. The average number of days per year with extreme precipitation events — the kind that dump a lot of rain fast, and are particularly prone to causing overflows — could rise one to two days, as cited in the climate report.

The situation is all too familiar for Indianapolis' Midwest neighbor. Chicago was one of the first in the nation to build a mega-tunnel to address its sewage problem. This 109-mile system first began nearly 50 years ago and has helped revive the Chicago River.

But now, Chicago's multibillion-dollar project — which is being replicated in the likes of Indianapolis as well as Washington D.C. and London — is not up to the task to manage all the storm and wastewater coming in.

“They built all this storage, but the impacts have mounted over time,” Hamlet said. “They are better than where they would be without it, but are by no means where they’d hoped.”

Hitting a moving target

More than 100 communities across the state have their own agreements and expensive projects to address their sewer overflow problems. And many are now facing a new set of problems: The projects they planned years ago will fall short.

“Cities are very worried because they’ve made this big investment trying to reach a moving target,” Hamlet said. “It keeps coming back to the question of what the design standards should be? How big is big enough?”

Citizens — which took over the project when it became the city's water utility in 2011 — thinks it got it right.

Indianapolis' project is on track to exceed the standards laid out in its consent decree, based on rainfall averages from 20 years ago.

“It is very difficult to predict future precipitation levels and patterns, and that is why EPA requires communities do a typical year analysis,” said Citizens spokesman Dan Considine. He added that their analysis meets EPA guidelines while also “providing cost certainty that our customers and community demand.”

To capture additional sewage discharges would be cost prohibitive, according to Joe Sutherland, Citizens’ director of government and external affairs. It could as much as double the financial burden for ratepayers, who are footing the bill for the multibillion-dollar project through incremental increases in their utility bills.

And Citizens emphasizes that the project is a significant improvement, arguing that the number of overflows once the project is complete will be drastically reduced.

In some ways, utilities are in a position of “being damned if they do and damned if they don’t,” said Hamlet.

If they take the more innovative approach and use modeling for the future, someone will say they made the project bigger than it needed to be and spent too much money. And if they don’t build big and a storm causes more overflows, Hamlet said, then someone will say they should have known better and been more prepared.

A free pass for pollution?

Hoffmann said she can't fault Citizens for wanting to be conservative with ratepayer dollars when designing the tunnel. Still, the community was sold this deal and supported it because of the promised endgame.

"I wouldn’t want to be raising rates to do this," she said, "and then 10 years from now it’s shown they aren’t meeting what we originally talked about.”

Harlon Wilson, a resident of the Christian Park neighborhood along Pleasant Run, said that the community has held up its end of the bargain: “We followed up on the promise, and we paid to be able to do this.”

Wilson has been involved in the planning side of things, so the president of the My Christian Park Association said he understands the technical difficulty involved. But as a community representative, he said “if residents are seeing their bills go up, then they expect to see the benefits, too.”

There will be benefits of the current project, Gabe Filippelli said, but even just six or eight overflows — double the four originally expected — could create a breeding ground for E. coli. “We don’t have the answers to that yet,” said the director for IUPUI’s Center for Urban Health, “but we are working to get them.”

Hoffmann had hoped the state would study the precipitation numbers to get a better idea of just how many overflows can be expected — the agency doesn't know what it's giving the stamp of approval to, she said.

But Indiana's climate numbers, both current and projected, have not been modeled to see how DigIndy would fare in such conditions, according to Hoffmann.

“I don’t know that anyone has looked at the climate forecast and asked how big should the tunnel be?” she said.

Or if they have, those numbers have not been made available to Hoffmann’s group nor IndyStar.

She sees IDEM's action as being premature. “It closes a chapter and gives Citizens an end point to their work, but it also closes a chapter to abating sewage overflows,” Hoffmann said. “It seems to me like this is creating a massive loophole. No bounds is just a free pass for continued pollution.”

Officials at Citizens and IDEM both said that they do not believe they are creating a loophole — rather, they are closing the loop on the consent decree, said Nancy King, general counsel at the state agency. The rule still requires EPA approval before going into effect.

Hoffmann said that Citizens and the state "are not the bad guys," they are just doing what was in the consent decree. Still, just because it's what they're supposed to do, she added, doesn't mean it's the best thing for the river.

"I understand it's not fair to move the goal post on Citizens in the middle of the game," Hoffmann said. "But the playing field has changed and the entire game is different."

There are ways to work to level the field and address the problem without expanding or building additional tunnels. The key is to lessen the stormwater going into the system from the start, she said.

That can be done through green infrastructure projects, such as installing rain barrels and gardens at homes, using pervious pavers on roads and parking lots and building in “green requirements” including storage to zoning ordinances. Those actions still come with a cost, according to Hoffmann, but it often is minor in comparison.

That is Chicago’s latest strategy. Its metropolitan water agency is encouraging initiatives around the city including green roofs and retention ponds.

Citizens has an initiative to plant 10,000 trees around the city to help catch water and let it soak into the ground. But Hoffman said city government needs to play a bigger role.

“How committed is the city really to having the river as an asset?” she asked. “Because they definitely should be part of these conversations.”

City officials declined questions from IndyStar, saying that the tunnel and its responsibility lies with Citizens. However, the city has continued to tout the importance of DigIndy to realizing its White River Vision Plan — which involves beach areas, restaurants and stores along the river.

Hoffmann said that Indianapolis is in trouble if DigIndy is the only thing in the prevention plan for sewage overflows.

“We are having a lifespan discussion before it is even done,” she said. “Any other industries would have to react to current market conditions, so that’s what we are asking. Where is this really taking us?”

Call IndyStar reporter Sarah Bowman at 317-444-6129 or email at sarah.bowman@indystar.com. Follow her on Twitter and Facebook: @IndyStarSarah. Connect with IndyStar’s environmental reporters: Join The Scrub on Facebook.

IndyStar's environmental reporting project is made possible through the generous support of the nonprofit Nina Mason Pulliam Charitable Trust.