Reliable Infrastructure Planning of Water Treatment Facilities in Nashville TN

Authors:

  • Scott M. Alpert, PhD, PE, Brent Fulghum, PE - Hazen and Sawyer

For many utilities, the increase in frequency of extreme weather events has exposed vulnerabilities in capacity and treatment capabilities at their facilities. Metro Water Services (MWS) of Nashville (TN) currently operates two water treatment plants, each rated at a nominal capacity of 90 mgd. Nashville experienced a 500-year flood event in May 2010 that disrupted treatment at one of the plants for nearly a month. As public awareness and expectations for a reliable drinking water source increase in the face of ever-changing regulatory requirements and slowing demand, the significance of careful planning in large capital projects has never been greater. For these reasons, MWS conducted a comprehensive study to identify and evaluate alternatives for increasing capacity and improving reliability for the treatment of its drinking water.

In this project, MWS identified potential future regulatory compliance concerns and operational issues, established finished water quality goals, reviewed future system capacity requirements, and established levels of redundancy to best meet system capacity and reliability goals. Using these parameters, alternatives were identified for expanding and/or improving existing raw water supply and water treatment facilities, including evaluating potential sites for a new water treatment plant. Multiple alternatives, assembled to meet the capacity and reliability objectives, were analyzed based on cost and non-cost criteria. A decision matrix approach was used to help compare the proposed alternatives and select the most advantageous option. The results included the benefits of a new 25-mgd advanced treatment facility (expandable to 100 mgd) that would increase capacity, improve reliability, and ultimately replace aging infrastructure at one of the existing facilities. The new plant would offer several key advantages including higher site elevations providing increased flood protection, utilization of existing distribution system high service mains adjacent to the site, the ability to share the raw water intake with one of the existing facilities, and compatibility with existing staff organization. Construction of a new facility also provides the opportunity to design processes with improved redundancy and reliability, to consider processes that will help meet future regulatory requirements, to replace aging infrastructure at the existing plants, and to serve as a foundation for phasing of capacity increases beyond the planning period of this study.

In this poster, the alternative analysis flow chart, decision matrices, and reliability hierarchy will be presented to help viewers understand the critical components of capital planning including the evaluation of key cost and non-cost criteria. Lessons from this project can be applied to both large and small utilities that are faced with developing strategic plans for infrastructure rehabilitation and replacement.

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

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