The new $108 million, four-lane State Highway 45SW near Austin, Texas, lies in the Barton Springs segment of the Edwards Aquifer Recharge Zone that supplies drinking water for San Antonio and Austin, Texas. “Millions of people depend on this aquifer,” said Justin Word, Director of Engineering for the Central Texas Regional Mobility Authority in Austin.
That meant the three-and-a-half mile SH 45SW project needed extra care to ensure construction didn’t harm the water supply. In fact, development spanned decades, with two different court cases affecting the plan. In the 1990s, the Texas Department of Transportation (TxDOT) settled a lawsuit with the Barton Springs Edwards Aquifer Conservation District, creating a consent decree that laid out parameters for water quality protection. More than 20 years later, the Mobility Authority took over development with funding from Hays and Travis Counties, as well as a loan and grant from TxDOT.
“We got the project environmentally cleared, went through our detailed design, then were hit with a new lawsuit from a local environmental group,” Word said. “When the court declined to issue an emergency stop-work injunction, we took a substantial risk – in hindsight the right risk – to move the project forward while the lawsuit played out.” The Fifth Circuit Court of Appeals recently upheld the judgement allowing the project to finish.
“While there was this lawsuit going on, the project had a tremendous amount of popular and community appeal,” said Charlotte Gilpin, Vice President of K Friese & Associates in Austin, Texas, the lead designer for water quality and drainage impacts. With the booming local population, “A lot of the parallel corridors are just not built for the number of cars using them to get through the area. People are tired of the congestion.”
The new SH 45SW toll road will connect two major thoroughfares, speeding travel time and providing much-needed relief to neighborhood roads. McCarthy Building Companies, Inc., of Dallas began work in November 2016 under a$75 million construction contract and expects to finish by next summer.
Throughout the project, “We worked with the City of Austin, the Barton Springs Edwards Aquifer Conservation District, and other agencies to really make the project go above and beyond the protection requirements,” Gilpin said. “We exceeded by 10 percent what we were required to do in terms of water quality treatment.”
Karst All Over
Edwards Aquifer includes many karst features – named caves, unnamed caves, fissures, and more – making it commonplace for water to suddenly disappear into the ground. “Those sensitive recharge features need to be protected from stormwater runoff and other potential contaminants,” said Jason Buntz, Principal-in-Charge for Hicks & Company of Austin, Texas, the project’s Independent Environmental Compliance Manager (IECM).
Many minds contributed to the environmentally sensitive design for the new highway. “We held six multi-hour, technical work group meetings to brainstorm and put the best science and ideas out there,” Word said. “We brought in 20 to 30 subject matter experts from the county, the city, Barton Springs Edwards Aquifer Conservation District, TxDOT, and our staff. A big concern in this karst-rich environment was not having it torn up for years from one end to the other, so we required the contractor to stabilize each section before moving to the next phase.”
To avoid as many karst features as possible, “We perched this roadway,” Word said. “We didn’t want to dig any more than necessary, so we built up the roadway with a little over 600,000 cubic yards of fill. In about 90 percent of the project, we were in a build situation instead of excavation.”
Through the three-and-a-half-mile stretch, designers applied a variety of natural preservation strategies. For instance, “In some parts we used rural sections to maximize vegetative swales and filter strips that help with stormwater runoff; in other locations, urbanized barrier sections narrow the width of the roadway in order to curve around some of the more significant cave features,” Gilpin explained.
To further minimize impact, “We designed the whole corridor around a haul road that’s been there for decades from overhead electric maintenance,” she added. “The contractor used it for their haul road, then at the end of construction it will become a 10-foot-wide bicycle and pedestrian path.”
In one spot, designers added a 100-foot-wide, flat-span bridge. “We had box culverts there early on but decided to switch in order to preserve that small stream,” Word said.
Restricted Construction Zones
During construction, the corridor included 25 zones partitioned off with chain-link fencing to protect sensitive water quality features. “More than a third of the job lies in these restricted areas,” said Chris Kelly, McCarthy’s Project Manager. “It’s very selective where we can put equipment and store items. In some areas we need to bring everything in and out each day.”
Many standard construction activities are limited or prohibited within these zones. “There’s no fueling allowed,” said Lloyd Chance, the Mobility Authority’s Senior Project Manager for Construction. “If equipment breaks down, they need to haul it out for maintenance. We even have a porta-potty on a trailer that comes in and out of the project area every day.”
To ensure adherence to the strict protocols, every construction employee attended an environmental class before setting foot on the job.
Since no native materials can be hauled off the site, McCarthy processed rock and other materials to meet specifications for reuse. Although the work includes installation of 361 bridge beams, the team left as many trees as possible. “That made some of the beam erection more challenging because we had a very small footprint for the big beams and cranes,” Kelly said. “We thoroughly planned the sequencing so we didn’t block ourselves off.”
Best Management Practices
A variety of Best Management Practices (BMPs) reduce contaminants collected by stormwater before it moves into local streams and rivers. For instance, Permeable Friction Course (PFC) asphalt pavement filters pollutants while also reducing noise and spray for drivers. “The pavement is our first line of defense,” Gilpin said.
According to Word, “We included enough PFC that on a normal project it would’ve met the regulatory requirement for total suspended solids removal.”
However, “One thing that makes this project so unique in terms of water quality design is the redundancy,” Gilpin added. “We wanted to not only meet project commitments but go above and beyond to support the goals of the community.”
For instance, eight water quality ponds treat runoff that escapes the PFC. “We implemented a best design in terms of water treatment and combined that with unique technology, using the infrastructure the Mobility Authority installed for the toll system,” Gilpin explained.
Hazardous materials traps guard every creek, waterway, and culverted drainage way, while the vegetated controls and vegetated filter strips slow stormwater runoff and filter it through the soil.
Adapting to the Unknown
To ensure environmental compliance throughout construction, the Mobility Authority awardedHicks & Company a separate contract as IECM, with stop-work authority when needed. “That’s not a role we typically include on projects, but the consent decree specifies – and we thought it was important, too – that we hire a separate contractor to look for karst features and monitor for endangered species,” Word said.
Hicks’ team monitors all construction activity. Although the design worked around known karst features, development of the roadway uncovered 16 previously unknown features. “Every excavation was inspected by the IECM,” Kelly said. “They put cameras down every drill shaft. Any time we found a potential feature we had to cord off a 50-foot buffer zone, stop work in that area, and coordinate with the team to figure out how to handle it.”
In that process, “It’s been a collaborative effort between us (as IECM), the geologist, the contractor, the state, and the engineer, if necessary, to come up with the best combination of erosion and sediment controls to protect the area in and around the feature,” Buntz said. “Sometimes the features were small enough that we could fill them in with gravel and move on. Others needed to be left open and protected. That might mean silt beds or some sort of rock feature. A lot of times they used vegetative erosion control blankets where they covered the exposed soil with a fiber mat that the grass can grow through to prevent sediment from getting into the feature.”
McCarthy supplied their own dedicated environmental team. “They introduced a team at the beginning of the project to help us coordinate protocols and controls,” Chance said. “Once they got going they saw the value in the relationship between our environmental team and theirs, so they kept those folks on the project. They really brought a strong commitment to the table.”
With so many unexpected karst features, “The daily activities in and around some of these areas needed to be adjusted so we could protect the groundwater, but the overall schedule for the project hasn’t been affected,” Buntz said.
When SH 45SW opens next summer, an estimated 18 percent reduction in total vehicle hours traveled in the region will add up to cost savings for drivers of $12.4 million in just the opening year.
“This project was developed with a delicate balance in mind – meeting the population’s need for new infrastructure while still taking appropriate measures to protect one of the most sensitive environmental areas in the region,” said Mike Heiligenstein, the Mobility Authority’s Executive Director. “I’m proud of the thoughtful planning and coordination that went into making this project a truly collaborative approach to sustainable, environmentally sensitive design.”
Key Project Personnel
Our newsletter right to your inbox.
See stories from other regions.