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Catskill & Delaware Ultraviolet Light Disinfection Facility Features A-J’s Grilles & Registers

Article courtesy of New York Construction, a McGraw-Hill Company, June 2009

Cost: $1.4 Billion

New York City delivers up to 1.5 billion gallons of drinking water every day to 9 million residents from the largest unfiltered surface water supply in the world.

To maintain the water quality of this immense system, the New York City Department of Environmental Protection is building the nation’s largest ultraviolet water treatment facility.

When completed in December 2010, the $1.4 billion Catskill and Delaware Ultraviolet Light Disinfection Facility in Mount Pleasant, N.Y., will treat 2 billion gallons of water per day from the Catskill and Delaware water systems. The two systems supply over 90% of New York City’s drinking water.

DEP awarded the contract to construct the facility to the joint venture of Skanska USA Civil of Whitestone, N.Y.; ECCO III, Yonkers, N.Y.; and JF White, Framingham, Mass., in February 2008. A joint venture between Malcolm Pirnie, White Plains, N.Y., and Denver-based CH2M Hill will manage the construction.

Under the Federal Safe Drinking Water Act, all drinking water taken from surface-water sources must be filtered unless the U.S. Environmental Protection Agency grants a waiver or Filtration Avoidance Determination. DEP agreed to build the plant in 2001 to satisfy the requirements of a FAD issued by the EPA exempting the city from building a water-filtration plant. At the time, the cost of a filtration plant was estimated at $8 billion.

The 160,000-sq-ft facility, along with office and laboratories, is being built on city-owned property within the towns of Mount Pleasant and Greenburgh, in Westchester County. The above-ground portion of the building is constructed of structural steel with a precast façade and stainless-steel roof.

Gravity, instead of pumps, will convey water in the system. In order to follow the grade of the existing shafts and use gravity to move the water within the facility, a concrete structure will be buried underground. The structure will house the mechanical equipment along with structures and piping for conveying water through the treatment facility. In total, the project will require 10,000 ft of concrete encased piping, ranging from 48 in. to 144 in. in diameter; 121,000 yds of concrete; and 1.3 million sq ft of foundation work. Two 13,000-volt feeder lines will supply electricity to the facility, which will have its own backup generation system.

Construction of the new facility is aided by an onsite uptake and downtake shaft connected to the Delaware Aqueduct. A series of underground structures and waterways tap into the existing uptake Shaft 19 from the Aqueduct, transferring the water to two large concrete holding tanks called the North and South Forebays.

Valves and sluice gates will control the flow of water from the tanks to 56 UV treatment units, each able to process 40 million gallons of water a day. The UV units consist of stainless steel disinfection chambers containing an array of quartz-sleeved UV lamps that are immersed in the water flow.

UV light alters the DNA of water-based microbes, such as giardia and cryptosporidium, and prevents them from replicating. UV water treatment is considered more ecologically friendly than chlorine treatment.

Once treated, water will be transferred via pipes to the downtake shaft for distribution.

Excavation of the site required rock blasting around the existing uptake shaft to build the forebays. Restrictions imposed by the DEP required hand excavation in the area immediately around the shaft.

This UV treatment plant is 10 times larger than any previously built facility in the world, says Keith Chouinard, Skanska’s vice president of operations. The UV units and valves controlling the water flow will be the largest ever built. The team conducted extensive research during the design phase to ensure the manufacturers could build the units to the size required.

In the future, DEP will build a separate, 3,000-ft conveyance tunnel—a 29-ft-diameter pipe encased in concrete—to tie the water supply from the Catskill aqueduct into the plant.