Hundreds of feet below one of the world's most famous cities, a different breed of men dig and blast their way through solid rock. These urban miners create the tunnels that ensure the survival of the city above. Meet Walking Boss Morgan Curran and the Sandhogs of Local 147. Under great pressure, these men work to complete the Croton Filtration Plant, a facility that will help ensure the safety of the city's water supply. In one tunnel they use the "Mole", an enormous tunnel-boring machine that relentlessly eats away at the rock. In the other tunnel, they're using large quantities of dynamite to blast their way through the earth. When a void develops along one of the tunnel walls, the hogs race to put up ring steel to prevent a cave in. And while the Brooklyn Bridge celebrates its 125th anniversary, the Sandhogs continue to toil below, preparing and detonating their next blast.

The Sandhogs begin construction on the first new subway tunnel expansion in over 20 years. Working in the heart of downtown Manhattan, Walking Boss Martin Hostetter and Foreman Ryan McGinty lead a gang of Sandhogs through a series of test blasts to determine the effect the explosions will have on the city above. At the Croton Filtration site in the Bronx, one of Walking Boss Morgan Curran's foremen loses his fingers in an on-the-job accident, and Morgan promotes his young Sandhog protégé Anthony Aviles to fill the position and lead the gang on the mole. In Croton's lower tunnel, the gang detonates an historic blast that successfully unites their new tunnel with the century-old New Croton Aqueduct tunnel, built by fellow Sandhogs over a hundred years ago.in over 20 years. Working in the heart of downtown Manhattan, Walking Boss Martin Hostetter and Foreman Ryan McGinty lead a gang of Sandhogs through a series of test blasts to determine the effect the explosions will have on the city above. At the Croton Filtration site in the Bronx, one of Walking Boss Morgan Curran's foremen loses his fingers in an on-the-job accident, and Morgan promotes his young Sandhog protégé Anthony Aviles to fill the position and lead the gang on the mole. In Croton's lower tunnel, the gang detonates an historic blast that successfully unites their new tunnel with the century-old New Croton Aqueduct tunnel, built by fellow Sandhogs over a hundred years ago.

At the Croton Filtration Plant in the Bronx, the sandhogs continue to mine deep beneath the city. After "punching through" to the 118-year old New Croton Aqueduct tunnel, Repete and his crew prepare for the project's next step of permanently joining the two tunnels. In the upper tunnel newly appointed foreman Anthony Aviles is pushing his mole crew too hard. ensions build until the gang finally snaps and a fight breaks out on the mole, forcing Walking Boss Morgan Curran to take matters into his own hands. Meanwhile, in the heart of Manhattan, at the new #7 subway extension site, Walking Boss Martin Hostetter is out for the day, leaving Foreman Rya McGinty with the greatest challenge of his career...his first solo blast.

Discover a world under New York City where injury and death on the job are common occurrences. Watch as these workers toil underneath the streets of New York City just as they have for the past 150 years--they are an instrumental part of the development of the city. Their union, their identity and their culture have been forged in iron and steel, and it is a bond that is truly shared as a brotherhood.

Morgan and the gang in the Croton Filtration site's upper tunnel begin a critical turn with the mole. As they steadily close in on their goal of mining 3745 feet, the gang has little margin for error. But mid-way into the turn the mole's navigation system goes down, making it so they may have to go forth 'blind'. While on Manhattan's west side, young sandhog Jason Durkin commits the rookie tunnelworker's gaffe known as hanging a steel and his fellow hogs don't let him off the hook easily. Back at Croton, the mole mines the final stretch of rock in the upper tunnel as Morgan plans an important explosion which will allow the sandhogs to back the mole out of the tunnel. As Morgan and his gang wrestle the jackleg drill, the sandhogs at the #7 subway line site get a reminder of how dangerous the jackleg really is when Jason is injured by the mammoth machine. Finally, Morgan and gang attempt a tricky double explosion, out in front of the mole.

At the Croton Filtration Plant in Bronx, NY, Walking Boss Morgan Curran and his gang work to complete the new tunnel's connection to the 118-year old New Croton Aqueduct. As the concrete pour begins, signaling the winding down of this job, Morgan begins his search for the next big drill and blast job. Morgan is reminded of why he hates concrete so much when clogs in the lines slow progress and injuries strike the crew. On the east side of town, the sandhogs are working on the first major upgrade to the LIRR in over a century. And new tunneling technology is moving in that could make drill and blasting obsolete - signaling the end of an era for NY's hard rock miners. Back at Croton, the completion of the lower tunnel forces Morgan to face the worst part of being a boss laying off some of his gang.

On Manhattan's west side, a tunnel said to be the largest public works construction project in the history of the western hemisphere nears completion: New York City's Water Tunnel #3. After 38 years, the sandhogs prepare for the final blasts in this tunnel. With vital tunnel infrastructure dangerously close to the blast site, Master Blaster Eddie Greenan is brought in to supervise. But unexpected collateral damage from the first blast creates problems. Meanwhile, a few blocks away at the #7 Subway expansion site, Martin and Ryan reach a milestone as they finish the shaft and begin mining forward. But there's problems with the blasting plan, and the gang reaches out for help. Back at water tunnel #3, Eddie and the hogs wrestle to complete the final blast, which would conclude the Sandhogs biggest project ever.

At East Side Access, a rock face loaded with dynamite is primed for a blast that will clear a crossover tunnel space for the Roadheader. At the last second, a meltdown at Grand Central Terminal causes the blast to be delayed, leaving undetonated powder in the tunnel wall. All work at East Side Access grinds to a halt while the sandhogs wait for permission to shoot. Meanwhile, frustration builds on Martin and Ryan’s 7-line subway line gang. Already plagued by technical difficulties, they find undetonated dynamite from a previous blast lodged in the rock face. These “bootlegs” are one of the biggest threats any Sandhog crew can face, and prevents them from drilling and blasting. Back at East Side Access, veteran walking boss Billy Orr—who witnessed a failed attempt to use the Roadheader five years before—leaves this site for a traditional drill and blast job in the Bronx. Finally, the Roadheader arrives at the staging area. If it works, it will change the face of Sandhogging at this site.

The moment of truth has arrived for the Sandhogs using the Roadheader at East Side Access. But before it can do battle against Manhattan's diamond-hard subterranean rock, near-disaster strikes. As Little Al's crew tries to maneuver the giant machine into place, it pierces a water line. Meanwhile, on the West Mole dayshift, a member of the gang has gone AWOL, forcing foreman Gregg Ryan and Wes Telesford to break in a "shaper"--a young, inexperienced Sandhog. The hazing is relentless, as are the mining problems that continue to plague the gang. Over on the #7 subway site, tension builds between Jared and his father, walking boss Martin Hostetter. Back at East Side Access, the Roadheader finally smashes into the rock: will it be a $4 million bust, or is it the future of mining for the Sandhogs?

On the #7 Subway line extension project on the west side of Manhattan, Walking Boss Martin Hostetter and Foreman Ryan McGinty ready their gang for an important two weeks. They are preparing the final few blasts to complete the giant subterranean cavern, the last step before tunneling north and south for the new subway line. Over the past 4 months this relatively inexperienced crew of sandhogs has refined their skills and come together as an effective gang of drill and blasters. To meet this deadline, the crew will have to put all they have learned to use. But as they work, mechanical problems slow their progress, and frustration mounts. Over at the East Side Access site, the West Tunnel mole gang confronts one obstacle after another in their efforts to mine 25 feet a day. Broken components on the mole shut down production and the gang must go out in front of it to get it fixed. When the 300-ton mole derails, the gang is thoroughly tested, using hand-tools and ingenuity to get it back on track so mining can continue. Back at the #7 Line Subway extension, Foreman McGinty challenges his younger cousin Jason on his dedication to the fraternity of miners, forcing Jason to rise to the occasion by leading the gang through it's biggest blast yet.

At the Croton Filtration Plant in Bronx, NY, Walking Boss Morgan Curran and his gang of Sandhogs finish prepping the mole for it’s third and final tunnel. With work picking up again Morgan rehires Elom, Mikey Bones and Romo, returning his old gang to full strength. With Morgan thinking forward to the next job, he needs his gang to begin this final segment without incident, to ensure their future prospects. Over at the East Side Access site in Queens, Sandhog foreman Tom Kelly oversees a series of precise blasts. But a nagging shoulder injury sends him to the doctor where he is told to stay off of ladders and away from heavy equipment. Ignoring the doctor’s advice, Tommy returns to the job the next day to build a protective bulkhead, helping to secure to tunnel against the blast. He pays for his efforts with a dislocated shoulder, but his hard work saves the day for the hogs. Back at Croton, the mole gang encounters a string of bad luck, and mining production falls below average. Morgan, concerned that this will tarnish the reputation of his gang, pushes his crew to step in up - or else.