Given the highly sensitive environmental concerns surrounding the construction of the $80-million State Highway 45 Southwest toll road, the Central Texas Regional Mobility Authority set a goal to not only meet environmental standards for the project, but to exceed them. In designing, engineering and constructing the roadway, the project team was able to accomplish that goal.

The four-lane toll road connects two major thoroughfares in south Austin, addressing a desperate need for traffic congestion relief in the growing area. But the highway’s location on the Edwards Aquifer Recharge Zone presented substantial challenges. The aquifer sustains Barton Springs, which is home to rare and endangered species and provides drinking water for the surrounding communities. The project moved forward in 2016 after 30 years of discourse between the community, environmental groups and transportation agencies.

Experts from multiple agencies spent more than 375 hours meeting to discuss environmental mitigation solutions for the project, and the Mobility Authority invested $2 million to have an independent environmental compliance manager oversee construction.

Among the project’s complex environmental requirements were that any materials generated from the site could not be hauled away, and crews had to reuse them for the project. McCarthy installed an onsite rock-crushing operation so a large number of boulders could be reused.

Environmental considerations sparked innovation in redundant water quality protection measures and resulted in a total suspended solids removal rate of 98% over the aquifer and 92% over the entire project.

Eight solar-powered water quality batch detention ponds were designed for permanent stormwater quality treatment and served as temporary sedimentation basins during construction.

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