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Keep Austin Sustainable: The Unique Case Of Water Treatment Plant No. 4 With people flocking to the trendy Texas metropolis, Austin needed a new treatment plant to sustain its growth — but a "sensitive" touch was required to complete the project while protecting the environment. By Larry Laws, Katy Perrino, and Joseph Sesil F or years, Austin, TX, has ranked as one of the fastest-growing major cities nationwide. Between 2000 and 2010, the city's population grew by 20 percent, and today nearly 165 people move to Austin daily. Consequently, water demand will increase sharply for years to come. Growth projections predict that the popula- tion will increase by 500,000 people by 2040; this is on top of the more than 1.8 million current residents of the Austin metropolitan area. Matched with increasing population, Austin's aging water infrastruc- ture has magnified water challenges. The Green Treatment Plant was built in 1925 and decommissioned in 2008, leaving Austin with just two water treatment plants: the Davis Water Treatment Plant, built in 1954, and the Ullrich Water Treatment Plant, built in 1969. Both draw water from the same source, Lake Austin, and both are decades old, thereby increasing the risk of shutdown. Planning And Execution At Austin's Water Treatment Plant No. 4 Austin's Water Treatment Plant No. 4 (WTP4) was completed, commis- sioned, and started up in November 2014. The plant, which is located on Lake Travis, is capable of treating 50 MGD with room to expand to 300 MGD. This investment adds reliability by giving utility customers an additional plant that draws from Lake Travis instead of Lake Austin, saves energy in serving Austin's north and northwest desired develop- ment zone, and provides continuous service during shutdowns and repairs of Austin Water's two other aging treatment plants and pump stations. WTP4 featured an unprecedented environmental commis- sioning process that worked to protect the environment at every step of construction and into the future. The facility includes an intake system in Lake Travis, a raw water tunnel and pump station, the treatment plant, and the Jollyville Transmission Main. The water's journey from lake to distribution starts at the raw water intake structure in Lake Travis. Fully submerged in the deepest part of the lake, the intake is a series of three stainless steel mesh filters and screens that remove large debris. Buoys mark the perimeter of the intake area to prevent boaters and swimmers from entering the area. Raw water travels from the intake system via a 9-foot tunnel to a raw water pump station, which moves water to the raw water transmission main, which then goes to the treatment plant. Once the water reaches the treatment plant, it goes through an upflow clarifier water treatment process. The Jollyville Transmission Main (JTM) is a 6.5-mile, 84-inch-diameter tunnel that connects the water treatment plant to the Jollyville Reservoir. From this reservoir, the treated water enters the water distribution system. WTP4 replaced the capacity lost when the Green Water Treatment Plant was decommis- sioned in 2008. WTP4 buildings have achieved a silver rating through the Leadership in Energy and Environmental Design (LEED) national rating system. All facilities are designed to integrate into the surround- ing landscape. Design And Construction Of The Facility Austin hired Carollo Engineers to design the plant and MWH Constructors to serve as the construction manager-at-risk (CMAR) on the plant, intake structure, and transmission mains. Time was added to the project schedule to incorporate value engineering changes developed by the team. The project was also extended to inspect and protect karst features that were encountered during exca- vation. The project team used Primavera scheduling tools to monitor and control the schedules of the more than 385 subcontracts. The team created an on-site "trailer village" where staff from public works, Austin Water Utility, MWH, subcontractors, consultants, subcon- sultants, and inspectors all worked together daily. Monthly executive team meetings were held at the plant site so project leaders could witness progress firsthand. It was crucial that the project team collaborate on a daily basis. For instance, a significant construction challenge was creating the foundation to install the raw water intake tunnel. The foundation was built using a temporary trestle on top of the water on the edge of Lake Travis — one of the largest recreational lakes in Texas. The original concept called for a concrete gravity base that required extensive dredging. However, due to the limited amount of dredging allowed by the permit from the U.S. 18 wateronline.com n Water Innovations