The team overcame a time crunch and multiple technical constraints to keep the multifaceted project moving on its critical path. Work involved transforming a former quarry into a 2.4-billion-gallon raw water storage facility; drilling five miles of 12.5-ft-dia. tunnel through hard gneiss bedrock some 400 ft below the surface for eleven 235-ft-deep to 420-ft-deep tunnel access shafts; and building 200-million-gallon and 135-million-gallon-per-day pump stations for two-way water flow from the Chattahoochee River to the storage site.

Completed pump station    Photo by Brian Grassel

The ambitious scope and schedule made construction management-at-risk the best delivery approach, says Ade Abon, Atlanta’s senior watershed director, while PC Construction project director Bob Huie points to strong project collaboration that enabled fast and innovative solutions to unforeseen challenges.

These included sharply varied soil and bedrock conditions and impact of a pressurized tunnel on groundwater, as well as workers’ ability to operate productively and safely on a nearly nonstop 48-month tunneling effort at four sites.

The tunnel drilling team broke through bedrock in 2018.
Photo by Ulrich Brinkmann Photography

The pandemic kept the German submersible pump fabricator Andritz from sending managers to oversee site installation, so work was supervised virtually using a live video feed. The project finished $5 million below the guaranteed maximum price, with no recordable incidents or lost-time accidents in 209,000 hours.

Months before final commissioning last year, the system proved itself after a major water line break became a supply risk.