The $1 billion fix of New York City’s Delaware Aqueduct will ultimately earn its own chapter in the books that chronicle engineering’s greatest hits.

How can plugging leaks in an 85-mile-long aqueduct possibly compare to building it – the world’s longest tunnel – in the first place?

Easily.

In 1939-44, when the city’s Department of Environmental Protection built this companion to the Catskill Aqueduct, it was only a supplement to the water supply for a burgeoning population. Today, the Delaware Aqueduct provides upwards of 50 percent of the 1 billion gallons that 9.5 million people use every day – 1 million of them in the Hudson Valley, including 100,000 in Orange and Ulster counties.

“How to fix it – and still maintain that supply – was an overwhelming challenge,’’ said Paul Rush, the DEP’s deputy commissioner for water supply and a Sullivan County native. “We spent a lot of time figuring out how to do it.”

Then an equal challenge became how to move the fix to the top of the DEP’s, and the mayor du jour’s, to-do list.

After all, the rate of the leaks, which ranged from 15 million to 35 million gallons a day, hadn’t changed since they were discovered in the towns of Newburgh and Wawarsing in early 1990s.

The leaks in Newburgh, responsible for 95 percent of the water loss, were pooling along the Hudson and draining into the river. The leaks in Wawarsing, however, exacerbated over time by floods and high water tables, were forcing the state and the DEP to spend millions of dollars to buy 40-odd homes and repair countless others.

“The leaks were stable, but what if they got worse?’’ said Rush. “We were putting half the city’s water supply at risk. If we lost the Delaware, it would be a disaster. Water is the economic lifeblood of the city. That’s what I saw.”

Sean McAndrew, the fix’s executive director and another Sullivan County native, and Rush credited former Mayor Michael Bloomberg and his DEP commissioner and subsequent deputy, Cas Holloway, with making the project a priority.

In 2010, the DEP announced it would build a 2.5-mile bypass tunnel to circumvent the leaks in Newburgh and seal the leaks in Wawarsing when the aqueduct was drained to connect it.

In 2013, excavation of access shafts in the towns of Newburgh and Wappinger began. In 2016, they were completed and, before 2017 is out, excavation of the tunnel – a five-year process - will begin.

“I remember Paul said to me, when we had the groundbreaking for the shaft (in Newburgh), ‘We’re really going to do this, aren’t we?’” said McAndrew. “And I said, ‘Yeah, we sure are.’”

Safety first

DEP engineers sifted through 10 options for what would be the biggest fix in the 174-year history of the country’s biggest water system – 19 reservoirs and three lakes that sprawl across Delaware, Sullivan, Ulster and five other counties - before settling on the bypass tunnel as the best of the bunch.

Beyond question, it would eliminate the leaks, and it would only take shutdowns of months for both aqueducts, rather than years, to do it. At the same time, it would give communities like New Paltz and New Windsor the lead time to bolster their backup supplies.

“We have one of the strongest in-house design teams in the world,’’ said McAndrew. “They’ve been designing and building water tunnels forever. It’s all they ever do; it’s part of who they are.”

The engineers were aided by the notes and drawings of their 20th century predecessors and abetted by the photographs from a 21st century self-propelled underwater vehicle, but they still enlisted other experts to review their conclusions about the project’s inherent risks.

“At times, you lose a sense of scale here, of how big our responsibility is,’’ said Rush.

Could the Hudson be kept at bay when the tunnel was being built 600 feet beneath it? Would the aqueduct collapse when it was drained for the first time since 1957?

And could they realistically expect to connect the tunnel and the aqueduct in five to eight months, an estimate critical to how long the source of half of the city’s water supply would be shut down.

“The best guess in town is six months,’’ said McAndrew. “Five is working 24/7 and everything goes right. Eight is everything goes wrong.”

The DEP only allowed companies that passed an assessment of their qualifications to bid on the two primary contracts – the shafts and the tunnel - for what is already a marquee project, front-page fodder for industry publications.

Of the ones that didn’t make the cut, said McAndrew: “We didn’t like their safety record.”

The emphasis on safety is everywhere, right down to the bungee-like cords that anchor hardhats to clothing, a best practice stolen from a Thames Water project in London. A hardhat that topples into the Newburgh shaft can transform itself over the 845-foot plunge into a projectile capable of killing a man.

In fact, the degree of risk aversion is perhaps the biggest difference between building the Delaware back then and rebuilding a piece of it now.

“We kill a lot less people (in construction) today," said McAndrew. “We don’t take as many risks as they did. They were careful, but they had nerve. And we benefit, too, from better equipment and techniques."

Drilling the Delaware

Schiavone Construction of Secaucus, N.J., completed the $101 million contract for the shafts in April. They were excavated over three years of drill-and-blast at a rate of roughly 10 feet a day and then lined with concrete: 30 feet in diameter and 845 feet deep in Newburgh and 675 feet deep in Wappinger.

Their location along the path of the aqueduct was determined in part by where the DEP could acquire property with the least impact. It bought 60 acres of forested hillside off Route 9W in Newburgh and turned it into the operational heart of a project that is almost invisible to passersby – sparing Wappinger, where a hamlet crowded a small DEP parcel along the river.

For the past year, Kiewit-Shea of Omaha, Neb., the contractor for the $706 million tunnel, has been carving out a chamber at the bottom of the shaft, 42 feet wide, 100 feet long and 40 feet high, to create a staging area for construction.

The locomotives to power the miniaturized trains that will move crews and materials within the tunnel are on site and ready to be lowered into the shaft. The 230 steel pipes that will line much of the tunnel, reinforcing the concrete to stave off the wear and tear of shifting limestone that caused the leaks in the first place, are being stockpiled at the Newburgh waterfront as they arrive on barges.

And the star of the show, the $30 million tunnel-boring machine, is poised to begin its journey, in pieces, on trucks, from the Robbins Company’s plant in Solon, Ohio. The first pieces will arrive this month and the rest will follow in May and June.

“What makes the Delaware (fix) such a big deal is that we’re building a tunnel through water-bearing rock at 300 pounds per square inch of pressure,’’ said McAndrew. “Your average garden hose is maybe 30 psi. Imagine if it were 300; you’d blast right through your fence and perhaps anybody standing on the other side of it. You’d at least knock them over.”

The DEP gave companies that bid on the contract the option of using a tunnel-boring machine built to its specifications or drill-and-blast, the technique that was used to excavate the shafts and the original Delaware Aqueduct.

“If it were only a mile, everybody would drill-and-blast, even today,’’ said McAndrew. “But we gave them the option because, at 2.5 miles, it’s just about at the cutoff for them, economically speaking.”

The DEP will hold a traditional ceremony to christen the machine before Kiewit lowers it into the shaft in Newburgh – all 469 feet and 2.7 million pounds of it, from cutter head to trailing gear – and puts it together again. In five years, it will be taken apart again and hauled out of the shaft in Wappinger

At the ceremony, the project’s premium ogling moment for the public, the machine will be named “Nora,” after Nora Stanton Blatch Barney, the first woman in the United States to earn a college degree in civil engineering, in 1905 from Cornell. Among her first jobs were building subway tunnels in the city and then the Catskill Aqueduct.

Scrubbing the Catskill

The Catskill Aqueduct, which now accounts for 40 percent of the city’s water supply, will become the dominant source when the Delaware is shut down in 2022. In preparation, it is getting its first wholesale overhaul since it became operational 102 years ago.

“It will be the most complicated project that we have ever done,’’ said McAndrew. “We have to repair, replace and clean simultaneously in a short period of time – and still keep everybody in water. It took a year of regular in-house meetings to decide how to structure the contract.”

The contract, which has yet to be awarded, calls for repairing and cleaning as much of the above-ground aqueduct as is readily accessible, some 59 of its 92 miles between the Ashokan Reservoir in Ulster County and the Kensico Reservoir in Westchester, to restore capacity lost to age.

Biofilm, naturally occurring microorganisms that have accumulated on walls of the aqueduct, has reduced the volume and slowed the flow of water, robbing the Catskill of 40 million to 50 million gallons a day of capacity in the process.

The DEP will shut down the aqueduct for two weeks in October to test the best method for removing the biofilm - scrape? power wash? squeegee? scrub? – and then begin work in earnest in 2018 with a series of 10-week shutdowns over three years.

Rush said many other DEP projects, undertaken independent of the Delaware fix, will inadvertently bolster the water supply during the shutdowns. For example, construction of a $3.6 billion filtration plant for the Croton reservoirs, which the federal government forced the city to idle in the early 2000s, has restored 10 percent of the water supply.

Now, pumping stations in Croton Falls and Cross River are being renovated so they can push additional water from the Croton reservoirs through the Delaware south of the fix to slake the city’s thirst during the shutdown.

Ultimately, Rush said, the $1 billion fix will not only eliminate the leaks but also ensure the system’s ability to deliver water to New York City and its other customers over the long term.

“And we will have fulfilled our responsibility as stewards, our responsibility to leave the system better than how we found it,’’ said Rush.

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