FARGO - As Steve Moss marched down Fourth Avenue North sweeping his detector back and forth over the grass, he looked like an impatient treasure hunter.
He walked at a fast clip, listening to the machine's electronic whine, its pitch changing to indicate that a city-owned electric cable is somewhere down below.
A stick-mounted spray can marked the line's route with red paint, warning construction workers building an apartment at the old Woodrow Wilson High School nearby to dig carefully. The treasure here is the one they'll save by not accidentally breaking or rupturing utility lines.
As construction season goes into full swing in Fargo-Moorhead, Moss and other utility locators are in high demand where new buildings are going up and where cable companies expand their network. These are men and women who can look through pavement and dirt to see an underworld of cables and pipes.
Moss, who's worked as a locator for the city for 18 years, said he often sees that world all around even when off duty.
"You'll start to notice the gas marks and flags. You'll drive down and after a while you wonder why they're marking it and what they're going to do," he said.
He'll see markings in the middle of the road and think that must be for a water or sewer project, he said, or he'll see markings in people's yards and think that must be for a fence.
What lies beneath
If the ground were as clear as glass, what you'd see when you look down is a grid of pipes and cables that reflect the grid of streets above.
Beneath the streets are sewer and water mains buried at around 10 feet and 7 feet, respectively. Smaller service lines connect nearby buildings to the mains. Storm sewer mains 5 feet down connect to storm drains on the curbs. Beneath the sidewalks are lines for natural gas, power, telephone, fiber optics and cable TV coaxials buried 2⅛ to 5 feet down.
Sometimes, you'd see ancient pipes or tanks long abandoned by their owner.
Brenda Derrig, Moss' boss and a division leader in Fargo's Engineering Department, said the stuff under sidewalks is especially vulnerable because they're so shallow. And the consequences of damaging those lines are significant, from disrupting emergency dispatchers' communication to causing natural gas explosions, she said.
That's why many states, including North Dakota and Minnesota, have laws requiring those doing excavation to call a "one call" center - the number is 811 in both states - which then contacts the owners of utility lines to come and mark them.
Minnesota's was founded in 1987 after a gasoline pipeline exploded in Mounds View, according to Gopher State One Call. North Dakota's was founded in 1995 at the request of the city of Fargo, where a building boom raised concerns that utility lines would be accidentally damaged, said Ryan Schmaltz, a spokesman for North Dakota One Call.
Seeing through dirt
How do utility locators see underground?
All utility owners have maps of their network, mostly in electronic form. But sometimes very old infrastructure doesn't make it on the map and these owners must rely on equally old paper maps and construction drawings.
Xcel Energy said that when it looked for abandoned pipes from an old gas plant in downtown Fargo last year, it had to use decades-old engineering maps. These pipes were built in 1885 by a company that Xcel later bought and were last used in 1960.
But maps are only rough guides because they can sometimes be wrong, Moss said. When he arrived at Woodrow Wilson school on Wednesday, May 11, his map told him that the only line he needed to worry about on Fourth Avenue was the electric cable that connects the street lights to the grid.
To mark those lines, he needed more precision, which is where a tool called a "cable locator" came in.
The locator has two components: a transmitter and a receiver.
The transmitter causes the utility line to emit a radio wave, essentially a signal that's yelling "I'm over here." Moss prefers to connect the transmitter directly to the utility line with wires because the signal is clearer. When he can't, the transmitter uses a magnetic field to cause a utility line to emit radio waves without touching it.
The receiver, the thing Moss was sweeping back and forth, picks up those waves.
Most utility lines have metal in them that can emit radio waves or have a metal "trace line" attached to them.
The job is usually straightforward and two years of experience is considered pretty good for a utility locator, he said. The problem is when it's not straightforward, he said, and that's when experience comes in. Even with his 18 years on the job, he said, he's still calling more senior locators for advice every week or so.
Moss recalled one section of Broadway that's like the Bermuda Triangle of underground radio waves. "There's a stretch down there that no matter what you do you can't get them to locate."
Reading the signs
For the average person, signs of a utility locator aren't hard to find around town.
They leave colorful spray paint markings on the ground and plant little flags. It's like a secret language read by construction workers that tell them they'd better turn off the excavator and start digging by hand or use a dirt-sucking Vacutron.
But the language is easy to learn.
According to the American Public Works Association, which standardized the markings, red is for lines that have an electric current, orange is telecommunications, yellow is natural gas and other combustible substances, green is for sewers, blue for water and purple for drinking water.
Moss said usually he uses a straight line or a dot to indicate a route of a utility line. A flag is used to call attention to the lines, especially in grass where they're harder to see. When there are several lines together, a diamond with a line on top and bottom is used. Power companies usually use multiple parallel lines to indicate different types of line. Telecommunications companies use a double check mark, which looks like a malformed Z, to indicate fiber optics.
Moss said his job is a fun challenge and he takes pride in being precise so that construction workers don't have to dig and dig to find the utility lines he's marked.
And he knows it's an increasingly important job. When Moss started in 1997, he replaced the city's sole locator. Now the city has six locators and a dispatcher, double what it had two years ago.