Read as much as you want on BostonGlobe.com, anywhere and anytime, for just 99¢.

Tragedy beneath Boston Harbor

In 1999, two divers died deep in the nearly 10-mile-long Deer Island sewer tunnel. This selection from a new book follows the detective who investigated their fatal mission.

Only the start of the tunnel had lighting and ventilation when the final mission began.

MWRA

Only the start of the tunnel had lighting and ventilation when the final mission began.

Adapted from Trapped Under the Sea: One Engineering Marvel, Five Men, and a Disaster Ten Miles Into the Darkness by Neil Swidey. Copyright 2014 by the author and reprinted by permission of Crown Publishers.

‘POTENTIAL FATALITY at Deer Island.”

Mary McCauley hung up the phone and looked at her watch. It read 3:20 p.m. McCauley was a Massachusetts state trooper assigned to the Suffolk County district attorney’s office, focusing on death investigations. The plainclothes detective did not fit the typical trooper profile. She’d gone to law school and served for several years as an assistant district attorney before enrolling in the police academy. A big reason for her career switch was that, as a prosecutor, she had often felt frustrated trying to understand a case simply by reading the police report and reviewing photos. That approach never satisfied her type-A personality. She regularly reinterviewed witnesses and visited crime scenes, so she could be more persuasive when she had to stand before a jury. After three years of doing this, working 60-hour weeks for pay so low that she had to continue waitressing on the side, McCauley decided that if she became a cop, it might be simpler for everyone involved.

Continue reading below

This call about the Deer Island incident, coming on a brilliant July afternoon in 1999, contained few details. She most likely wouldn’t investigate the case unless someone actually died. But even if that happened, her involvement wasn’t a sure thing. Massachusetts’s blurry jurisdictional lines led to frequent turf battles among its various law enforcement agencies. On more than one bridge-jumper investigation, McCauley had been able to take the lead only after establishing that the suicide victim had jumped from a state-owned bridge and had landed in a spit of water that fell under state jurisdiction. At 3:53 p.m., her supervisor cleared her to head to the scene.

An athletic 34-year-old with shoulder-length dirty-blond hair, McCauley had grown up in Mattapan, on the southern edge of Boston, and had the street smarts and accent to show for it. Coming from a tightknit Irish family, she had married a guy from the North Shore and was now raising a family there with him, yet areas north of the city remained somewhat foreign to her. The only thing she knew about Deer Island was that there was some kind of sewer plant there, and she had once gone for a run along the coastal route leading to it.

On tiny, out-of-the-way Deer Island, work crews had spent nearly a decade erecting the second largest sewage treatment plant in the country, not to mention using the island as the base for building the longest tunnel of its kind in the world. That nearly 10-mile-long dead-end Deer Island Outfall Tunnel, which was constructed hundreds of feet below the ocean, would eventually carry waste water from the plant into the deep Atlantic waters of Massachusetts Bay. The plant and the tunnel were the two most important components of the multibillion-dollar cleanup of Boston Harbor, which was designed to make “the dirtiest harbor in America” once again a source of pride rather than ridicule. But all this work had gone largely unnoticed by lots of people around Boston, including the State Police detective.

Bill Brett/Globe file

One of the stricken divers is transported to Boston Medical Center.

McCauley and her partner drove in their unmarked cruiser across the strip of land that had connected the town of Winthrop to Deer Island ever since 1938, when a hurricane moved around enough sand to close up a little channel. By the time they arrived at quarter past 4, the site was a swirl of commotion. McCauley saw fire engines, ladder trucks, and ambulances from multiple departments, marine rescue units, and mobile command units. So many emergency vehicles were clogging the island that she had to park her cruiser and hoof it to the bustle around the entrance to the 420-foot shaft leading to the tunnel.

As she approached, the last of the ambulances was clearing out. She tracked down a deputy fire chief who seemed to have a handle on the chaos, and he quickly filled her in. He pointed to the ocean and told her that five commercial divers had been working as part of a “dry penetration” job nearly 10 miles into the sewer tunnel, to remove a series of 65-pound safety plugs before the tunnel could be filled with treated waste water. They had used a retrofitted Humvee to drive more than 9 miles into the tunnel, until it became too narrow to drive farther. At that point, three of them had trudged on foot to the end of the tunnel, while two stayed in the Humvee. Because there would not be enough room even to turn around the Humvee, they’d towed a second one, facing in the opposite direction, which they would use for the drive back. Around 1:45 p.m., when the three divers returned to the Humvees, they’d found the other two lying unconscious. By 4 o’clock, the two unconscious divers had been airlifted, one to Boston Medical Center and the other to Massachusetts General Hospital, where the three other divers had been taken by ambulance for evaluation.

Then the deputy chief added another crucial detail. Deep into that endless tunnel, there was no light or oxygen to speak of. Nodding, McCauley hurriedly jotted notes onto her white steno pad. But it all sounded like the setup for some half-baked science fiction novel.

Even the lines of authority for this project were confusing. The Massachusetts Water Resources Authority owned the tunnel, but there was a contractor building it for the water and sewer agency, which also had a separate company supervising the job. The two divers who’d lost consciousness worked for different diving companies, one based in Spokane, Washington, the other in Portsmouth, New Hampshire.

Within 15 minutes of McCauley’s arrival, at least one aspect of the investigation became clearer. Word came in from both Mass General and Boston Medical: The two divers who’d been airlifted had been pronounced dead. McCauley called her boss, and he gave her the confirmation she needed. This was now officially a State Police-run investigation, and she would take the lead.

McCauley knew that in these critical early hours she had to focus on controlling what she could. That boiled down to preserving all the evidence and documenting everything she and her partner, John O’Leary, heard and saw. As she did this, questions began throbbing in her head. How had these two men died? Was the cause a freak accident? Could it have been suicide? Negligence? Homicide? And if it was a crime, who was responsible?

***

Suzanne Kreiter/Globe staff/file

All those billions and all that brainpower, and this is what these divers were given to keep them alive? — Mary McCauley, Massachusetts State Trooper

THE DAY AFTER the accident, McCauley returned to Deer Island. The “man cage,” a tubular metal basket attached to a crane, jerked and swayed as it was lowered down the shaft. Inside it, McCauley kept busy taking notes, trying to distract herself from the stomach-tightening descent she was making 40 stories into the earth. As unsettled as she was, she realized this trip would have been a lot more frightening if she had been allowed to journey all the way out to the actual crime scene, the spot where the two divers had lost consciousness. Her request to do that had been denied. The federal safety agency OSHA had jurisdiction over the tunnel work site and had ruled that no one would be allowed to venture past the base of the shaft until mechanical ventilation had been reestablished.

It was still a puzzle to McCauley why the people who had designed and overseen the construction of the tunnel — the best and brightest minds — had decided to remove its elaborate ventilation system before sending the divers in for the final mission. That ventilation “bag line” had provided crews with plenty of ambient air for the years they had spent building the tunnel. The divers’ destination at the end of the tunnel was impossibly remote — 3 miles farther from the surface than the Challenger Deep valley of the Mariana Trench, the deepest ocean point on earth. That distance made the use of more conventional breathing supplies — such as bottles of high-pressure compressed air — impractical. Instead, she had been told, the mission’s project manager, a Canadian engineering whiz by the name of Harald Grob, had given the divers an innovative system. It supplied their breathing air by mixing, right there in the tunnel, the vapors of liquid oxygen with liquid nitrogen.

Clearly, something had gone horribly wrong with that system, robbing two divers of the oxygen they needed to live. But since all five divers had been breathing off the same system, McCauley still couldn’t understand how the pair sitting in the Humvees, monitoring the breathing system for the team, had died while the three crawling into 30-inch-wide pipes at the end of the tunnel had managed to live. Even more pressing for the detective was the overarching question of accountability: Who should be held responsible for the deaths?

She’d spent hours the night before at Mass. General, grilling the three surviving divers. She felt guilty about that, given how traumatized they seemed, but felt she had no choice, just in case they’d been hiding some important details. By now, though, she suspected they’d simply been pawns in a much bigger game of risk.

The man cage touched down, and McCauley headed over to the deck to examine the Humvee the divers had used to return to the shaft. She couldn’t get over how jampacked it was. Every inch of the interior seemed to have some kind of hose or valve or tool taking up space. There were also everyday artifacts, like the crumpled-up green Nature’s Valley granola-bar wrapper on the driver’s-side floor, which now served as an unnerving reminder of the dead divers’ presence. Examining the components of the innovative “mixed-gas” breathing system, McCauley had two intense yet contradictory thoughts. First, it seemed incredibly complicated, with hoses going in every direction and attached to all kinds of contraptions. Second, the incredibly complicated system seemed so jury-rigged. The gas cylinders looked old and rusty. The manifolds where the various hoses met were made of plywood — plywood! And the quarter-turn valves were labeled with pieces of tape.

McCauley couldn’t believe it. If this Grob guy, the Canadian engineer and project manager, was as brilliant as she’d been told, how could he have possibly come up with a plan that should have flunked even a layperson’s common-sense test? And how could the people who hired him have signed off on it? McCauley was no expert on the harbor cleanup project, but she knew it had a price tag of several billion dollars, and she now knew it involved some of the country’s top contractors and design and engineering firms. All those billions and all that brainpower, she wondered, and this is what these divers were given to keep them alive?

***

MWRA

Diver DJ Gillis checks out the breathing equipment before heading into the tunnel.

IN THE WEEKS AFTER the accident, McCauley became a regular visitor to Deer Island, where she had secured a locked storage garage to hold evidence. She’d gotten one crack at interviewing Harald Grob, two days after the accident, but realized she needed to talk to others to know exactly which questions she and her partner should be asking him.

One conversation that was particularly illuminating was with the safety manager for Airgas Northeast, the company that had supplied the tanks of liquid gas for the mission. After inspecting the setup and the Humvees, he rattled off a host of examples of its poor design. The valves bumped up against one another. The disabled interior dome lights in the Humvee, while helping to conserve battery power, had made it much harder for the divers to monitor the gas mixer and accurately note the levels. The process for measuring the oxygen content of the breathing air was unreliable, and the access to the backup air supplies was poor. And then he said something that blew her away. He insisted no one had ever informed his company that the liquid gas was going to be used to supply breathing air for humans. Company policy and industry practice, he said, prohibited doing that. It would be too risky.

Disturbed by the safety manager’s findings, McCauley realized she needed a diving expert who was a neutral party. She found the person she was looking for at the US Navy. Dr. Marie Knafelc was a leading authority on diving and the senior medical officer of the Navy’s Experimental Diving Unit, based in Panama City, Florida. It didn’t take long for the physician to show up on Deer Island.

McCauley was impressed that for all her credentials, the Navy doctor was a straight shooter like herself. When Knafelc inspected the sophisticated oxygen-injection system that each Humvee had been equipped with to function in the tunnel, then compared it with the improvised mixed-gas breathing system the divers had been given, she couldn’t hide her disgust. “Oh, my God,” she said at one point. “They cared more about that Humvee than they did about the divers.” She told McCauley that she would reserve final judgment until returning to Florida to review her notes and write a full report. But McCauley had little doubt which way it would fall.

Based on her growing knowledge of the events leading up to the incident, the detective knew she needed to reinterview Grob, who had returned to Canada shortly after the accident. He was clearly the man behind the curtain. And yet she was becoming just as convinced that ultimate responsibility would not end with him.

MWRA

A two-way trailer attached to a pair of Humvees holds tanks of liquid oxygen and liquid nitrogen for mixing.

McCauley would spend six months on her investigation, which at times would feel like a series of intense graduate school seminars on new subjects ranging from oxygen deprivation to mega-project construction. There were a couple of bombshell revelations along the way, none more shocking than the one involving the MAP Mix 9000, the machine the divers had been given to blend liquid oxygen and liquid nitrogen for their breathing air. As it turned out, the Danish-made mixer was designed for industrial uses, such as packaging supermarket burritos and cheese, to give the products longer shelf life. It was not intended for human use.

The deeper McCauley dug, the more convinced she became it hadn’t been an accident that had killed the two divers. Given all the bad decisions that had preceded those divers into the tunnel, she argued, “the results were completely foreseeable. To suggest it was some accident is absurd.” That conclusion naturally led to another one: “If it wasn’t an accident, and people died, somebody should be held accountable.”

Still, from her previous life as a prosecutor, McCauley knew how challenging it might be to assign clear blame. Although she’d come to believe that Grob had made a host of horrible and fateful decisions, she also knew that many parties above him had enabled that to happen.

She had to remind herself that she wouldn’t be deciding who would be prosecuted, if anyone. Her job was simply to investigate and, if appropriate, demonstrate probable cause. Confident she had done that, McCauley submitted her report to the district attorney’s office.

Neil Swidey, a staff writer for the Globe Magazine, will discuss Trapped Under the Sea on February 26 at Harvard Book Store and on February 27 at Newtonville Books. E-mail him at swidey@globe.com or follow him on Twitter @neilswidey.

Loading comments...
Subscriber Log In

You have reached the limit of 5 free articles in a month

Stay informed with unlimited access to Boston’s trusted news source.

  • High-quality journalism from the region’s largest newsroom
  • Convenient access across all of your devices
  • Today’s Headlines daily newsletter
  • Subscriber-only access to exclusive offers, events, contests, eBooks, and more
  • Less than 25¢ a week
Marketing image of BostonGlobe.com
Marketing image of BostonGlobe.com