“I believe that knowing … construction methodology, [that] the design itself can be improved and become much more effective,” he says, noting that this philosophy underpins all of his work in developing project solutions.

That approach is on full display on the Riachuelo wastewater treatment system, a megaproject to clean up the polluted Matanza-Riachuelo River in Argentina, which completed in summer 2025. Valiante led design, testing and development of a first-of-kind riser system that diffuses pre-treated water back into the river using a vertical, pipe-jacking method inside the tunnel.

The project, 87% financed by the World Bank at a cost of $1.228 billion, has capacity to treat up to 2.3 million cu meters of wastewater per day with an average flow rate of 27 cu m per second and was designed to expand access to sanitation for 1.5 million residents across 14 municipalities.

Valiante developed a solution on a wastewater pretreatment system in Buenos Aires (top) involving 34 vertical risers installed inside a tunnel, a system that required testing (above).  
Photo courtesy of Webuild

Improving on the Original

Owner Agua y Saneamientos Argentinos S.A. (AySA) initially envisioned an outfall tunnel leading to a transition shaft that then connected to a pipeline with a vertical riser system to discharge pre-treated wastewater back into the river, with the shaft and pipeline placed above a system of piles.

Valiante and his team analyzed AySA’s concept and concluded that the initial design could be improved. The team felt the initial concept was more complex than necessary and could create risk by stirring up more pollutants and exposing crews—who would be working in the water—to potential safety risks.

“The game changer [was] we started analyzing if there will be a method, a construction method of the riser from inside the tunnel, and this would have provided many advantages and improvements,” Valiante says. “It became very clear that if we would be able to execute the riser from inside the tunnel, most of the safety concerns would disappear.” Additionally, the schedule could be significantly compressed, and the system itself would operate more efficiently.

The new approach would also increase discharge capacity, from the rate of 24 cu m per second to 27 cu m per second, an increase of 12.5%. The owner agreed to the change, and Valiante and his team spent two years developing the rig system to pipe jack 34 risers inside the tunnel.

Graeme Montieth, a tunneling specialist and secretary of the U.K. Pipe Jacking Association, commented that Webuild “managed to make a bespoke rig that can work within a … tunnel.” He said its team "built and tested the whole system before putting it in. The testing rig is a bit of a triumph.”

Valiante is using the same improvement-minded approach on current projects, including developing a new way to install precast concrete within tunnels at Snowy 2.0, the largest hydroelectric dam project in Australia, he says.