Charleston, SC Construction of a large-scale combined sewer overflow (CSO) mitigation system in the Peoplestown area of Atlanta, east of I-85 and south of I-20. The centerpiece CSO storage vault occupies most of a 6-acre city block bounded by Ormond Street SE, Atlanta Avenue SE, Connally Street SE, and Greenfield Avenue NE. All properties have been acquired by the City of Atlanta with all standing structures demolished, except for one 40-foot by 40-foot AGL-owned parcel at 865 Connally Street SE excluded from vault sizing.
Major construction activities include site preparation and clearing, erosion control, installation of temporary groundwater dewatering systems, soil shoring system installation, subsoil preparation, excavation, compaction, and backfill operations. Work may include erection of tower cranes and other specialized construction methods. Utility work encompasses relocation of various existing utilities to accommodate the vault structure.
The Flow Control Area and Dry Weather Channels feature concrete slab-on-grade, walls, and appurtenances, with installation of slide gates and flap gates. This work requires temporary support and construction around several large combined sewer pipes while managing active sewer flows to allow construction activities. Numerous stormwater improvements complete the infrastructure enhancements, providing long-term CSO reduction and improved water quality for the community.
The project presented several complex installation challenges requiring innovative solutions. Bridge crane installation occurred after roof joists and sheeting were already in place, necessitating a dual-crane operation. The bridge crane girders were lifted and positioned at a 45-degree angle to lower through the roof opening and set onto the pre-installed crane rails.
The 40-foot tall stormwater pumps required an intricate multi-stage installation process. The lower pump assemblies were lifted using a coordinated effort between the newly installed bridge crane and a mobile crane boom positioned through a garage bay window opening. Pumps were positioned over their designated bays using temporary assembly steel, then stacked and lowered section by section while being assembled in place above each pump bay.
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