City of Atlanta Atlanta, Georgia, United States

Blasting a massive cavern out of solid rock to reduce water pollution in Atlanta

Atlanta tunnel - civil construction project

Saving Atlanta waterways from pollution

Leveraging our civil construction project expertise, Alberici constructed the Custer Avenue Combined Sewer Overflow (CSO) Storage and Dechlorination Facility to help bring the City of Atlanta into compliance with state and federal water quality laws. Historically, sewer systems were designed to combine storm water with wastewater from the sewer system during major storms, polluting waterways. To address this problem, the City of Atlanta enacted a $4 billion overhaul of its combined storm water and wastewater sewer system.

massive cavern excavation - civil construction project

Massive cavern excavation

As a key component of this program, Alberici constructed a 50-foot high by 60-foot-wide cavern with a total length of 750 feet. To allow access, Alberici excavated a reinforced concrete shaft reaching a total depth of 120 feet below the surface. The cavern serves as an underground storage facility with a total capacity of 10 million gallons. Alberici also excavated a new tunnel to connect the cavern to an existing storage facility for a combined capacity of 44 million gallons.

self perform drill and blast - civil construction project

Self-perform drill and blast

Alberici self-performed all underground excavation on the project. Using the drill-and-blast method, horizontal holes were drilled in granite and packed with explosives. The resulting charges fractured the rock, which was then hoisted out of the cavern. In total, Alberici used 1,500 pounds of explosives to remove 1.8 million pounds of rock during excavation. The cavern was then reinforced with 20-foot rock anchors, wire mesh, and shotcrete.

new dechlorination facility - civil construction project

Adding a new dechlorination facility

In addition to the new cavern, the project featured replacement of the adjacent Custer Avenue dechlorination facility. Alberici’s scope of work for this portion of the project included demolition and installation of complex mechanical, electrical, and treatment process equipment, including two bar screens, two rotary drum screens, fine grit screens and grit removal, brush screens, a pump station, new electrical room, filters, and enhanced disinfection systems to control bacteria and residuals.