The US Environmental Protection Agency (EPA) has laid down the law: the overflow of untreated sewage into rivers and streams, known as "Combined Sewer Overflows", must stop. Since the capacities of sewage plants are inadequate, especially after heavy rainfall, large cities such as Atlanta have decided to initially store the mixed water underground and divert it afterwards to sewage plants for treatment. The two tunnels planned for this purpose in Atlanta will be 13.4 kilometers long and will be able to store about 670 million liters of mixed water.
Two Herrenknecht Gripper TBMs, each with a diameter of 8.23 meters, commenced tunnelling under Atlanta through the gneiss and granite rock in July and September 2005, respectively. The two machines (S-288 and S-289), which were of identical design, achieved tunnelling performances under the former Olympic city of up to 187.5 and 208.5 meters per week respectively. In spring and summer 2007 the two Gripper TBMs successfully finished tunnelling.