MORE than 350 feet below the city's streets, nine big and grimy sandhogs straddle a metal deck and guide a six-ton concrete form as it is lowered by an American 9260 crane. Working in misty darkness spotlighted by arc lamps, the team spends its eight-hour shift lining about 10 feet of a 20-foot diameter shaft with pressurized concrete. The shaft plummets into the cavernous depths of the city's partially completed third water tunnel. The painstaking and dangerous procedure typifies work in ``the hole,'' as workers call the tunnel, which has been under construction since 1970.
The third tunnel is designed to handle most of New York's water needs. Its network of huge pipes will be able to deliver 1.2 billion gallons of water per day to points throughout the city. Officials believe it will not be completed until well into the next century.
By the time the last valve is in place, the tunnel's price tag is expected to total $5 billion - the most expensive project financed by the city. In 18 years of blasting through the Fordham gneiss bedrock, 23 workers have been killed.
Despite the cost in lives and dollars, the third tunnel will not bring more water to slake the city's lusty thirst. New Yorkers consume about 200 gallons of water per person each day, according to Tina Casey, a spokeswoman for the city's Department of Environmental Protection, which oversees the Bureau of Water Supply.
The tunnel will carry water from a holding reservoir in Yonkers, rather than from new sources, but officials promise better delivery and pressure throughout the city.
``Every city has its own unique set of water problems,'' said the assistant resident engineer for the project, Ted Dowey, as he stood at the bottom of the third tunnel's west shaft. ``New York's biggest problem is in bringing water to the city from reservoirs that are 125 miles away.''
More troubling is the city's inability to monitor the condition of the two aging, mammoth tunnels that distribute all its water. Tunnel No. 1, built in 1917, and tunnel No. 2, opened in 1937, deliver close to 2 billion gallons of water during the city's hottest summer days - about 60 percent more than they were designed to handle, according to Jack Ledger, resident engineer for construction of tunnel No. 3.
Because the two tunnels are filled with water and cannot be emptied, they have never been inspected. To inspect one would require shutting it down - something the city cannot afford. A shutdown of one of the tunnels, or a cave-in, would leave much of the city without water.
Officials say that a crippling accident in one of the tunnels is unlikely. Yet they acknowledge that stress, age, and no opportunity for maintenance may be exacting a heavy price in water losses. The city states that perhaps 10 percent of its water is lost to leaks in the delivery system, a figure that State Assembly Environmental Conservation Committee chairman Maurice Hinchey calls a ``gross underestimate.'' Noting that many parts of the aging system date from before the turn of the century, Mr. Hinchey estimates that the city may be losing 30 to 40 percent in leaks.
Sometime around the turn of the 21st century, construction will be far enough along to enable the third tunnel to deliver water to much of the city. Engineers will then be able to close one of the other tunnels to make inspections and repairs.
With the swivel of a faucet, New Yorkers drink and bathe in water that is pulled downstream by gravity from the Catskill Mountains and the watersheds of the Croton and Delaware rivers, through 6,000 miles of tunnels, aqueducts, and pipes to each of the 800,000 commercial and residential buildings along its route.
The delivery process is differing from that of water systems in other big cities. Only about 10 percent of New York's water is pumped and filtered. Cities such as St. Louis, Cincinnati, and Louisville rely on river water that must be pumped and treated.
NEW YORK'S water supply system is the result of a remarkable feat of engineering that has contributed mightily, according to experts, to the technology of constructing dams and aqueducts.
The system was pushed into the hinterlands 150 years ago by farsighted planners, who obtained the rights to vast stretches of upstate watershed. The city has built three major reservoir systems over a period of 125 years that collect up to 550 billion gallons in rainfall and runoff.
``[New York's water supply system] is the envy of professionals throughout the country,'' said Jim Hayes, a spokesman for the American Waterworks Association of Denver. ``You couldn't build that system today.''
Despite the accolades, three droughts in the last decade, combined with the growing water demands of 8 million users, are taxing New York's aging water storage and transmission system, some of whose parts date as far back as 1870.
New York's businesses, residents, and industry use a large amount of water and have been increasing their consumption yearly, from 1.1 billion gallons a day in 1960 to 1.4 billion in 1970. New York's water consumption has now swollen to an average of 1.5 billion gallons a day, well above the mayor's goal of 1.1 billion.
Despite the increases, the city is attempting to expand the supply of its reservoirs by cutting per capita consumption. To do this, the city recently enacted regulations requiring ultra-low-flow fixtures for toilets. Water officials believe that in 10 years the fixtures will save 20 million gallons of water per day. The city is also working to meter actual water consumption in each building, and it is spending $100 million annually to detect and repair leaking water mains.
In a fenced-in area on Roosevelt Island in the East River, 140 sandhogs enter the third water tunnel each weekday in three shifts around the clock. They are lowered in a cage down an 800-foot shaft to the tunnel's muddy floor, where they drill holes, install bolts and wire mesh on the face of the red-banded rock, and continue lining the tunnel with concrete.
Many sandhogs have fathers, grandfathers, and even great-grandfathers who mined silver and gold as well as subway and water tunnels. Though proud of their craft, they see some irony in all of their sweat and toil.
``Here we are, breaking our backs in this tunnel,'' said sandhog Adin Sullivan, during a lunch break. ``But we'll never live long enough to see it finished.''
Leaning against a battered locker, he chewed on a hamburger and added, ``But hey, maybe our grandkids will drink from it.'' Tonight, NOVA (PBS) will include the third water tunnel in its special report on ``The Hidden City.'' Check local listings for the time.