Connecting Across the Ages:  The World’s Largest Treatment Facility


  • Kurt Matscherz – Hazen and Sawyer
  • Jasmin Rivera – NYC DEP

The Cat-Del UV facility, seen here under construction, was recently awarded an ACEC National Grand Award.

Our forefathers who planned, designed and built NYC’s water supply system were able to create one of the engineering wonders of the world and leave for future generations a water supply sytem that enabled growth, prosperity and improved public health in NYC and its surrounding areas. These engineers did not know what the future would hold in terms of supply needs and water treatment, but they did have the wisdom and foresight to design in the flexibility for future generations of engineers to enhance and modify the system to meet the needs and challenges of their times. One hundred years after being conceived, it was put to the test and passed with flying colors, proving invaluable in its ability to facilitate UV treatment for the Cat-Del supply.

This paper will focus on the planning, design, coordination, and details needed to enable the successful and timely connection of the world’s largest Ultraviolet Light (UV) disinfection facility to physical infrastructure and connections of the early and mid 20th century.

This enormous, 2,020-mgd UV facility is New York City’s newly-commissioned disinfection system for its Catskill and Delaware water supplies. The facility allows New York City to provide an unfiltered supply while protecting its quality through the innovative UV process to inactivate cryptosporidium and giardia. Its huge capacity presented major challenges in connecting the facility to existing infrastructure.

The UV Facility is not only at the sole location where all water supplied from the upstream watersheds comes together for unique treatment of a size and capacity unparalled in the world, it is also the new control center or the largest supply in the world. These two key components – water treatment and flow control – have been accomplished at a scale like no other, and it has been done in a way that reflects the forward thinking of those planners and engineers that have come before us. Specifically, the single facility incorporates UV treatment and NYC’s flow control from which water passes to 8 million people. The design was influenced by the thinking of the original sytem designers and done in a way that our forefathers would be proud of – leaving flexibility for the unknown in the areas of future treatment and connecting to future supply aqueducts.

Construction of the UV facility required connections to two separate conveyances – the Catskill Aqueduct, constructed in the early 1900s, and the Delaware Aqueduct, constructed in the 1940s. Foresight by the engineers who designed these conveyances made it much less daunting to connect the UV facility; however, the age of the aqueducts and changes in standards of construction and design required considerable care and planning in order to successfully make the necessary connections. The unearthing of the 70-year old Delaware Aqueduct and 100-year old Catskill Aqueduct connection structures did reveal some features that required adjustments to be made during construction.

For more information, please contact the author at

Hear about new publications with our email newsletter

We will never share your details with anyone else.


Newsletter Newsletter

Horizons Fall 2017 (pdf)

Horizons showcases significant water, wastewater, reuse, and stormwater projects and innovations that help our clients to achieve their goals, and can help you achieve yours. Articles are written by top engineers and process group leaders, demonstrating and explaining the beneficial application of a variety of technologies and tools.

View previous issues »