Slide Rail System Speeds UV Waterline Construction

By Jeff Griffin, Senior Editor | October 2009 Vol. 64 No. 10

One of the world's largest ultraviolet (UV) water treatment facilities is under construction in Westchester County, NY.

When the $1.4 billion plant becomes operational in late 2012, it will have the capability of treating 2 million gallons of water per day supplied by the Catskill and Delaware aquifers, which provide more than 90 percent of the drinking water for New York City.

UV light purifies water by altering the DNA of water based microbes to prevent them from replicating. Many experts consider UV water treatment to be more ecologically friendly than conventional methods using chlorine.

The project owner is the New York City Department of Environmental Protection. Construction is being performed by a joint venture named SEW. The construction consortium is comprised of: Skanska USA Civil Northeast Inc, Whitetstone, NY; ECCO III Enterprises Inc., Yonkers, NY, and J.F. White Contracting, Framingham, MA. Construction management is a joint venture between consulting engineering firms Malcolm Pirnie, White Plains, NY, and CH2M HILL, Englewood, CO.

Much of the project involves underground work. The facility's design uses gravity to move water within the facility. From there, valves and sluice gates control water flow to 56 UV treatment units, each of which can process 40 million/gpd of water. Stainless steel chambers contain multiple UV lamps below the level of the flowing water. The treated water flows to a down-take shaft and enters into the distribution pipelines. Gravity will convey water throughout the system.

When complete, the facility will have approximately 10,000 linear feet of encased pipe in diameters that range from 48 to 144 inches. Shoring excavations in often challenging conditions required a variety of methods. Slide rail shoring systems are the preferred shoring method with contractors and owners of projects requiring installation of long runs of large diameter pipelines versus conventional steel sheeting methods, which generally require more time and labor.

Extensive excavation

A slide rail system is a component shoring system comprised of steel panels similar to trench shield side walls and vertical steel posts. It is installed simultaneously as the trench or pit is excavated by sliding the panels into integrated rails on the posts – either double or triple rails depending on needed depth – then pushing the panels and posts incrementally down to grade as the pit is dug. Slide rail systems can be used in a variety of configurations.