Stantec is designing and providing construction administration for the underground aspects of the City of Atlanta's top priority infrastructure project – the Raw Water Supply Program. Current infrastructure includes components dating back to the 1890s, with critical portions well beyond their design life. The new system moves raw water from the Chattahoochee River to a quarry and the Hemphill and Chattahoochee water treatment plants providing water sustainability for over 100 years.
The project consists of 5 miles of 10-foot inside diameter tunnel in hard and abrasive Gneiss bedrock, a 2.4-billion-gallon quarry for raw water storage (one of the largest in the world), 10 shafts, raw water intake, pump station retrofit, and three new pump stations. The tunnel varies in depth from 250 feet to over 500 feet. The project is being delivered via a CM@Risk contract, making it the longest such tunnel ever built in North America.
Challenges include mining near the river and under the City's only active raw water reservoir, the Brevard Fault system, inability to shutdown treatment facilities, and construction near residences. To enhance project completion, we adopted an aggressive design schedule that includes multiple parallel activities, daily reporting of subsurface investigation results, geologic mapping of shaft and tunnel construction, and tunnel lining selection as mining progresses.
We are using the Envision rating system to incorporate sustainable design practices throughout the project.