Keep Austin Sustainable: The Unique Case Of Water Treatment Plant No. 4
By Larry Laws, Katy Perrino, and Joseph Sesil
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.
For 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 population 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 infrastructure 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, commissioned, 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 development 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 commissioning 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 decommissioned 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 surrounding 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 excavation. 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, subconsultants, 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. Army Corps of Engineers and the water quality restrictions mandated by the Lower Colorado River Authority, the project explored an alternative method to the original design.
To find an economical and feasible alternative method, the CMAR and design team collaborated on constructability of the foundation during the design process. In addition, the CMAR used a unique approach to value engineering: asking contract bidders for additional value engineering ideas. Through this process, the project eliminated all dredging by employing a drilled or driven-pile foundation to support the intake in lieu of the original design. Another benefit of substituting prefabricated steel frames used by the driven-pile method for the original reinforced concrete frames to support the intake was that it cut by 90 percent the amount of time divers had to be in 150 feet of water in Lake Travis.
Addressing Environmental Concerns
The design and construction of WTP4, including its tunneling components, needed to address several environmental factors. In fact, the initial water treatment plant was set to break ground in 1984 until economic and environmental concerns delayed construction. Once the current site of WTP4 was deemed acceptable from economic and environmental standpoints, the city of Austin was able to move forward with its plans.
Completed filter building at WTP4
More than 12 potential sites were evaluated prior to finding this site as having the least negative effect on the environment. Criteria included the impact on migrating birds, karst invertebrates, and vegetation, as well as considerations for drainage, grading requirements, elevation and pumping requirements, and alignment of the tunnels built to distribute water from the site.
Before breaking ground on the project, Austin Water Utility and the city of Austin’s Watershed Protection Department developed an environmental commissioning plan to guide the project in minimizing environmental impact and protecting the nearby environmental resources, sensitive species, and their habitat. The plan outlined a process that integrates environmental review and oversight of the project to meet the environmental goals beyond typical federal, state, and local regulatory requirements. The process specifically included an ongoing audit with recurring meetings, reviews, oversight, inspection, permitting, and other tasks.
The process required a collaboration with the city’s project team, environmental commissioning team, and all contractors working closely together on design and construction methods. For the JTM tunnel, a key challenge was passing under the Balcones Canyonlands Preserve, a system of habitat preserves created to protect eight federally listed endangered species — six karst invertebrates and two bird species — and a threatened salamander known as the Jollyville Plateau salamander. The tunnel was to be built in the Glen Rose formation, which was made up of three limestone units — Edwards, Walnut, and Glen Rose.
The environmental commissioning plan and project team collaboration resulted in a balanced decision-making process for vetting the project design. Through this process, it was decided to shift the JTM tunnel’s access shafts to the perimeter of the Balcones Canyonlands Preserve to avoid disturbing that critical habitat area. The project team conducted extensive groundwater assessments in the early stages of the preliminary design, proving that there are two distinct groundwater systems in the region. One system feeds the springs in the upper Edwards aquifer, and the team is tunneling through Glen Rose, which is the second system. There is very little interaction between the two, but in order to comply with demands from the environmental community for additional contingencies, the team lowered the entire tunnel a further 50 feet to guarantee that the project team would be in the lower aquifer at all times. Lowering the tunnel reduced potential environmental impact in the area’s fragile karst geology.
Construction of the pump station building in Austin
In particular, karst voids within the Edwards formation provide a habitat for endangered cave-dwelling invertebrates, including six listed species of arachnids and insects. Strict controls on groundwater also exist in order to minimize any potential hydrological impacts to the karst system and the Balcones Canyonlands Preserve above, which has been set aside as a habitat for the Jollyville salamander and two species of protected rare birds.
The temporary support design for the shafts is based on groundwater modeling, which showed there are dolomite zones within the Edwards formation that contain most of the permeability. But there is very little vertical connection between these zones, so the project team wanted to keep water that was found at its same elevation. The shafts therefore have a sealed lining, consisting of grouted liner plates, throughout the Edwards and Walnut formations. When a permeable zone was hit, the project team would also over-excavate and add a gravel ring, essentially behind the grouted ring, so that the water could travel around the shaft and continue to feed the same karst structures that it was feeding before. Once below the transition to the Glen Rose aquifer, the temporary rock support becomes bolts and wire mesh.
There was intense coordination while the project team was sinking the shafts. The Environmental Commissioning Group was in the shaft 24 hours a day, and each time a void was found they were required to inspect it and ensure it was not a habitat for endangered species.
In addition to the JTM, the project included the 92-acre water treatment plant site. In an effort to involve the community prior to clearing the site, MWH Constructors teamed with the city and local environmental groups to host two on-site native plant relocation and rescue efforts. The events were well attended by the community. MWH provided safety vests and conducted a safety orientation for volunteers.
Upon completion of the WTP4 project, the administration building, located at the water treatment plant, earned a silver-level LEED certification. The project team worked closely on a daily basis with the city of Austin and its environmental team to enhance and sustain their environmental responsibilities.
Key Takeaways For Project Success
The project team’s focus on safety resulted in an unprecedented safety record for a project of this size and complexity. The project exceeded 1 million man-hours without a lost-time accident. Almost 3 million man-hours were logged at five locations, including work at Lake Travis and tunneling more than 7.5 miles with many crews working around the clock. Safety was emphasized and recognized with celebrations to honor milestones reached. In addition to construction safety, the treatment plant uses a new process that creates nonhazardous chlorine molecules on-site from a simple, safe chemical reaction process. No chlorine or ammonia will arrive on tanker trucks.
The economic impact of this project is also a success. MWH hired 208 subcontractors and vendors and signed 385 subcontracts to work on the project. Eighty-eight percent of the vendors were local or regional. These contractors earned almost $285 million throughout the life of the project. WTP4 exceeded all the participation goals for minority and women-owned businesses; more than $63 million was earned by these businesses.
Public outreach was also a critical success factor for the project. Austin’s citizenry is civic-minded and protective of environmental resources and quality of life. City staff, the consultant, and MWH Constructors worked together to keep the community informed with public meetings and newsletters. The project team also maintained a hotline that connected to a cellphone that was carried by a team member. This cellphone was answered 24 hours a day, seven days a week.
The project team worked together through many challenges, including a tight budget and an environmentally sensitive site, to produce a water infrastructure that will contribute to Austin’s water security for decades to come.
Concrete roofing rebar being installed at the 10-million-gallon clearwell structure
About The Authors
Larry Laws is vice president and project director for MWH Constructors.
Katy Perrino is the communications manager for MWH Constructors.
Joseph Sesil is a construction manager with MWH Constructors.