250 feet under the Bronx, N.Y. — Murky shadows. Dynamite fumes. Jagged, rough-hewn tunnels carved out of solid bedrock. Stout-hearted, burly miners journeying to work up to 800 feet below the surface, down farther than many skyscrapers go up.
A coal mine in West Virginia? A diamond mine in South Africa?
No, these miners, called ''sandhogs,'' are digging rock, much of it granite and none of it precious. They are at work on New York City's long-awaited third water tunnel, or as one engineer said with a bit of a smile and a lot of poetic license, ''the Taj Mahal of tunnels.''
The Taj Mahal it's not. But in the section this reporter visited the other day, the tunnel was 60 feet high, 40 feet wide, and two football fields long. It's like some kind of primitive stone cathedral, where both time and sunlight have been eclipsed.
When the first phase of the city's third water tunnel is completed about 1990 , more than 1.2 billion gallons of water will flow through it daily.
Last month, four construction companies were awarded a contract for ''holing through'' the last unexcavated portion of the first phase of tunnel No. 3, as well as lining 17,500 feet of the tunnel with concrete. The contract may eventually exceed $130 million.
''This contract brings us a step closer to the completion of the first stage of the third water tunnel, a project that is essential to ensure the future of the city's water supply,'' says Joseph T. McGough Jr., New York City's environmental protection commissioner. The Bureau of Water Supply, spearheading construction of the third tunnel, is a division of the city's Department of Environmental Protection.
On a map, this first phase runs roughly from Van Cortlandt Park in the Bronx south under the Harlem River to a spot some 600 feet below Central Park just south of the Metropolitan Museum of Art. Then the tunnel turns east under the East River into Queens. The other three stages of the construction of Tunnel 3 will wind it deep into Queens, Brooklyn, Staten Island, and Lower Manhattan. But these latter three stages are not expected to be completed before the next century.
Officials say the total price tag for the third water tunnel may exceed $5 billion. More than $800 million has been allocated for the project since its start in 1969 - and not a dime of this money has been from either the state or federal government, Bureau of Water Supply spokesmen are quick to point out.
But no official is likely to tell you that this billion-dollar subterranean cavern will mean a drop ''more'' water for the nation's biggest city. Even after recent conservation efforts, New Yorkers still consume a whopping 1.3 billion gallons of potable water every day. This is approximately 130 gallons per capita , but this figure is inflated because it includes heavy industrial and commercial water use.
What the third tunnel will be, in effect, is a $5 billion ''safety valve'' in case trouble develops in the other two older tunnels. A major concern of officials is that if they ever wanted to close the mammoth six-foot-in-diameter valves in the other tunnels for tunnel repairs, these valves might not reopen. As a result, vast areas of the city would be without water.
Tunnel No. 1, completed in 1915, is 18 miles long, up to 15 feet in diameter, and runs through rock at an average depth of 365 feet. The second tunnel, completed in 1936, is 20 miles long, up to 17 feet in diameter, and has an average depth of 500 feet. Both tunnels, and the third tunnel now under construction, will tap water from the same upstate New York reservoir system.
For now, however, the third water tunnel is filled with 400 sandhogs working around the clock. Their equipment is equal to their dinosaur-sized task: Gigantic yellow ''front-end loaders,'' which look a lot like tanks in the dust-filled light; 40-ton locomotives that haul tons of debris, called simply ''muck,'' out of a not-so-silent, dynamite-blasting world up to 800 feet below the sidewalks, parks, and skyscrapers of New York.
One reason the tunnels occasionally run to such depths is that they have to be cut far under natural faults in the rock.