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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 dur- ing the design process. In addition, the CMAR used a unique approach to value engineering: asking contract bidders for additional value engi- neering 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 con- struction. 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. 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 devel- oped 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 pro- cess 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 collabo- ration 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 sys- tems 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 aqui- fer at all times. Lowering the tunnel reduced potential environmental impact in the area's fragile karst geology. wateronline.com n Water Innovations CONSTRUCTIONENGINEERING 19 Completed filter building at WTP4