A CITY IS LIKE a mushroom, or an iceberg: Everyone knows the flashy part above the ground, or water. But this protuberance would not exist without a vast unseen substructure below: the nine-tenths of the iceberg that lies underwater; the buried webs of fungal mycelia that send up the spore-bearing appendages we call “mushrooms”; the equally intricate web of tunnels, pipes, bunkers, cables and conduits that transport water, sewage, electricity, steam, light pulses, trains, automobiles, people and even rats under the city. Without these substructures, our bungalows and office towers would be as helpless as plucked mushrooms.

THE BACKSTORY: Pioneer Square’s underground ‘comfort station’ inspired a writer to go deeper

Seattle is more aware than many cities of its lower depths, thanks to two mid-20th-century newsmen: the late Seattle Times columnist John J. Reddin, who tagged along on fire inspections under what were then called Skid Road and Chinatown, and touted the buried “ghost town” there, and Bill Speidel of the rival Seattle Star, who saw the commercial possibilities. But the Underground Tour Speidel founded and the competing Beneath the Streets tour cover just a slice of the world that keeps the city working.

Get to know it, and you might never see the ground beneath your feet in the same way.

WE WON’T GO DOWN as boldly as city sanitary engineer E. French Chase and two colleagues did nearly 90 years ago. They donned rain slickers and gas masks, dropped a collapsible rowboat down a manhole near the baseball stadium on Rainier Avenue and paddled 18 miles through the sewers before emerging near the Ship Canal. Later inspectors would rope up, mount skateboards and snap photos as colleagues at the other end of the line towed them through dry sewers.

Today, Seattle’s sewer managers conduct their inspections safely via closed-circuit television. They and their colleagues in the waterworks get to their pipelines through locked portals scattered almost invisibly throughout the urban landscape. One leads to a tunnel cutting under Interstate 405 in Renton, at whose center runs a raised 54-inch pipe that looks larger, its leak-stopping wrap shimmering like a giant serpent gathering to strike.

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This is Cedar River Pipeline 3, which carries one-fifth of the water used by 1.4 million people in Seattle and neighboring cities. Downstream, it runs under Beacon and Capitol hills and ends at the Maple Leaf Reservoir in northeast Seattle. Upstream from the reservoir, on the uphill side of I-405, this utility corridor rises straight up for 55 feet underground, forming a vertiginous concrete bunker that can be accessed by an open-grate stairway.

“Looks like a missile silo,” says Dave Muto, Seattle Public Utilities’ water systems operations manager.

Muto says this section of Pipeline 3 — built in the early 1990s, with expansion joints between sections and shut-off valves on both sides of I-405 — is one of the seismically sounder links in Seattle’s water system. Not so an older part of the line that runs under downtown Renton, nor sections of the three other Cedar River pipelines and three other major lines in the system. A recent seismic study found that these likely would fail, leaving Seattle and much of the surrounding area without water for up to two months if we had a major earthquake like the 2011 Tohoku and Christchurch quakes — and that there’s a nearly 1 in 5 chance of that happening in the next 50 years.

Muto at least knows what to expect. He was working in Los Angeles’ water department in 1994, when the Northridge quake busted water mains in 2,000 places. He didn’t get a lot of sleep in the weeks afterward.

FOR MOST OF the past 125 years, Seattle’s engineers and officials remained blissfully oblivious to dangers like seismic fault zones. They started digging in 1894, tunneling with shovels and wheelbarrows under Denny and Beacon hills in order to divert some of the sewage that was turning lakes into cesspools. More sewers followed, together with train, water, stormwater and highway tunnels; pedestrian tunnels for hospital patients and downtown shoppers; and a unique bus/rail tunnel.

Then as now, digging through the local glacial stew of sand, gravel, boulders and clay was no cakewalk.

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“The thing about tunneling around here is you always know what conditions you have — right here!” says Sound Transit construction manager Brad Cowles, who has overseen the completion of Seattle’s longest subterranean passageway, a light-rail tunnel from Jackson Street to Northgate Mall. “Three feet away, it can be completely different.”

Cowles and other modern diggers at least have the benefit of boring machines that slide concrete sleeves in place and shoot grout behind them to hold the ground firm. Those who excavated downtown’s Great Northern railroad tunnel 115 years ago had to throw up wooden covers, afterward covered with concrete, to contain the leaky soils above. As those soils settled, ground levels dropped as much as 3 feet, damaging the new Carnegie Library (and drawing lawsuits as late as 1972). A would-be second train tunnel collapsed at Yesler Way three years later, in 1907.

With shovels and wheelbarrows, the Great Northern workers proceeded at a remarkably fast 18 feet each day until they hit cement-like blue clay and had to bore. But not all the interruptions they encountered were, well, boring. At 140 feet below Fourth Avenue and Spring Street, they found the remains of a prehistoric forest, including a solid-looking 3-foot tree trunk that crumbled after meeting the air. More than a century later, crews replacing Seattle’s seawall also uncovered an intact log, and other detritus, from rails and ties to shoe scraps — a city’s story writ in refuse. Jack Johnson, an archaeologist at the University of Washington’s Burke Museum, is piecing together the history of local brewing, distilling and drinking from excavated bottles.

TODAY, SEATTLE’S SOILS contain much more than artifacts. Thousands of miles of tunnels, pipes and cables wind, twine, criss and cross through the ground — the arteries, capillaries, nerves, ducts and guts of the body civic. Seattle Public Utilities delivers water through 1,823 miles of pipeline and takes it back via 1,422 miles of sewers. Another 485 miles of storm drains captures rainwater that would flood the streets and makes sewers overflow.

Seattle City Light keeps the juice flowing through 899 miles of buried primary lines. And, unbeknown to many, 18 miles of underground piping carries steam at about the speed of sound from Enwave Seattle’s (formerly Seattle Steam’s) gas-fired plant on Western Avenue to 192 hotels, hospitals, and residential and office towers around downtown and First Hill. Circulating at 380 degrees, this steam not only heats the buildings, saving the cost of bulky on-site boilers, but also sterilizes the hospitals’ surgical instruments. And, when it leaks, it warms water lines as well.

“Some buildings will get tap water 30 degrees warmer than usual,” says Muto. “I call Seattle Steam, and they say, ‘We don’t have a problem.’ I say, ‘Yes, you do … ’ ”

The University of Washington boils its own steam; 7-plus miles of vaulted tunnels, as deep as 80 feet, carries it throughout the campus, together with electric power, compressed air and chilled water for air conditioning.

Even such a tidy, self-contained system isn’t immune to intrusion. Sound Transit engineers laying light rail under the campus recently nudged one test bore over to spare a sequoia and drilled into a utility tunnel. Luckily, they missed the 22-inch pipes carrying steam from the plant and cooled waters returning to it. “Otherwise, you’d have millions of gallons shooting out,” says UW Campus Utilities assistant director Mark Kirschenbaum — a ready-made disaster movie.

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RUNNING STUFF UNDERGROUND does avoid many problems. Trains don’t tangle with traffic when they’re below the street. Buried wires don’t get gnawed by squirrels or knocked down in storms. Putting lids on reservoirs, as Seattle did post-9/11, protects them from seagull droppings and human mischief, and creates new land for parks.

But going underground also creates new problems. Seattle’s wet, acidic soils corrode the bare neutral wires wrapped around cables laid in the ground in the 1970s and ’80s, before City Light started enclosing them in conduit or ducts. Aging sheaths get brittle and crack, and … zzztt. Lines short, and the lights go out.

Tracing underground shorts can take hours, City Light crew chief Fiel Diaz explains: You dig up the middle of a shorted line, determine which side the short is on, dig at its midpoint … and so on and so on, until you find the short — an electrical Zeno’s paradox.

Worse yet, a short can ignite a fire in one of Seattle’s 1,564 underground electric vaults, sometimes to explosive effect: About eight years ago, a vault fire near Seattle Center blew a 300-pound hatch cover 30 feet in the air. The standard response was to let fires burn themselves out, but that meant long delays and compounded damage. Now City Light pays to keep a fire truck equipped with high-pressure carbon dioxide — a fire extinguisher on wheels — on call to snuff them out.

Those who maintain the sewers and storm drains might wish they had something as clean as fire to contend with. Ray Brown manages the 67 pump stations that keep Seattle’s wastewater going where it should — until nature intervenes.

“This is our Transylvanian crypt,” Brown jokes as we descend into a quaintly gloomy 1929 bunker hidden among Leschi’s view homes. He opens a wall hatch, below which a pungent stream runs down a concrete channel. Just a year earlier, Brown says, “We had a real bad storm, and the system couldn’t keep up. These motors and pumps” — where we’re now standing — “were all submerged in raw sewage.”

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That’s not the worst of it. “The biggest problem is all the rags and things people stuff down the [curb] drains,” says pump station technician Scott Helmbrecht. “We get a lot of jeans and T-shirts. I saw a park bench come through one time, broken in half. Once, in Ballard, a baby seal swam all the way up to the check valve. A guy opened it, saw this face there and took off running.”

Seals are just part of a menagerie of critters that wander up or get flushed down the pipes. “I’ve seen salamanders swim by,” says Helmbrecht. “I saw a frog in a station by Magnuson Park.” And then there are the rats.

SEWERS AND SEATTLE both have reputations as rat havens, and both live up to them. Public Health — Seattle & King County rodent inspectors patrol the sewers, continually hanging test bait in manholes and returning to plant poisonous, anticoagulant-laced “hot bait” wherever the test bait gets bitten. They can’t keep up: “We’re not setting out enough traps,” says Kris Pape, one of the dogged rat patrollers. “In areas that have a history [such as southeast Beacon Hill], we get hits at 80 percent of the test baits.”

The even more determined rats don’t use only the sewers to navigate the city. Running 30 feet deep under First Avenue, a steeply inclined tunnel lined with thick, bundled cables brings electricity to much of downtown.

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“It’s kind of scary here at night,” says Diaz, a man unfazed at being caught atop a ladder bouncing like a pogo stick amid swaying brick walls in Pike Place Market when the Nisqually Earthquake hit in 2001. “These cables become rat and cockroach highways.”

Darkness and secrecy, the qualities that draw rats underground, are irresistible to some members of another species: homo sapiens. Since the dawn of literature, questing heroes have journeyed to the underworld, from Gilgamesh and Odysseus to Alice descending the rabbit hole. A subgenre of movies, TV episodes and novels, beginning with 1973’s “The Night Strangler,” spins spooky tales beneath old Seattle — echoing the strange encounters recounted by tour guides and others working there.

Worldwide, the “urban explorers” movement promotes intrusions into tunnels and other forbidden sites. Once or twice a year, quest-struck students sneak into the UW tunnels. “It’s cool at first,” says Kirschenbaum. “But after you’ve gone 800 feet and the view hasn’t changed, it’s not so cool anymore …. We finally got The Daily to stop listing this as one of the things every UW student should do. But we still get a spike every time something gets posted.”

Others have sought refuge rather than thrills underground: More than 50 years ago, a thief fled from the Market into the Great Northern Tunnel and was never seen again; vagrants tried to roast a salmon purloined from a waterfront cannery there but were chased out before a train could crash their party. Today’s homeless people sometimes camp in the city’s water and wastewater tunnels, which weren’t locked until recent years: “It just wasn’t needed when they were built,” says Brown.

Seattle’s underworld guards many secrets. “Native history goes back at least 13,000 years here,” says Johnson, the UW archaeologist. “Basically any landform that’s been stable since that day will contain native artifacts.”

Reddin, the newsman who introduced Seattle to its buried “ghost town,” warned that tours would never reach “the really interesting parts of the underground.” Indeed, Pioneer Square’s buried treasure, the elegant restrooms built 111 years ago beneath the pergola, has been sealed and left for another era’s archaeologists to discover — along with who knows what else.

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