Hydraulic Model – The Nexus of White Plains’ Future Water System Improvements

Authors:

  • Meg Roberts, Anni Luck, Richard Hope, Robert Guena

Hydraulic models can be used for a variety of planning tasks related to water treatment and distribution systems. They are often employed for master planning, to analyze and improve operations and system hydraulics, select pumps, analyze fire flow availability, prioritize water system rehabilitation or replacement, as well as plan for specific distribution needs like a disinfectant conversion, address water quality concerns, or design flushing programs.

The City of White Plains, NY, has a population of nearly 58,000 people with an average daily demand (ADD) of approximately 8 million gallons per day (mgd). It is currently undergoing upgrades to its 1.2 mgd microfiltration (MF) water treatment plant to help supplement supplies purchased through Westchester County. White Plains has one 9 million gallon water storage tank that supplies equalizing, fire, and emergency storage to its entire distribution system. The tank dates from the 1930s and because it is the sole tank for the system, the City does not have the ability to take it out of service for extended periods of time for maintenance.

The City also recently measured high concentrations of the five regulated haloacetic acids (HAA5), a group of regulated disinfection byproducts, in their distribution system. Preliminary investigations suggest the elevated levels may be due to booster chlorination practices, unlined cast-iron pipe with high chlorine demand, and/or high water age in certain parts of the distribution system. Because much of the city was constructed before the end of World War II, many of their distribution mains are unlined cast-iron and the City’s need for replacement or rehabilitation of existing water infrastructure is also great.

In addition as part of Westchester County’s system-wide treatment improvements, the County will be installing two ultraviolet disinfection facilities (25 mgd and 20 mgd) immediately upstream of White Plains’ Central Avenue Pump Station and Orchard Street Pump Station to serve the County and surrounding municipalities. Hydraulic analysis is needed to identify any impacts that construction, testing, start-up, and long-term operation of the UV facilities may have on the operation of the City’s pump stations. As such, a hydraulic model is being used to tie these needed water system evaluations and improvements together.

This presentation will use examples from the City of White Plains to illustrate the interconnectedness of water system improvements. It will highlight how the hydraulic model was used with considerations for water supply, treatment plant operations, storage facilities, and aging infrastructure to evaluate distribution system hydraulics and water quality. Emphasis will be placed on the storage analysis and water quality concerns in the distribution system. This presentation will appeal to both operators and managers as it will underscore the “big picture” for water system master planning and the benefits associated with it.

For more information, please contact the author at mroberts@hazenandsawyer.com.

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