Reuse Pipeline & Diffuser to Lake Lanier

OWNER: Gwinnett County

ENGINEER: Parsons Engineers

SOUTHLAND HOLDINGS TEAM: Oscar Renda Contracting Inc.

PROJECT HIGHLIGHTS:

This subaqueous project consisted of approximately 6,800 LF of 72” off-shore reuse steel pipeline, approximately 720 LF of diffuser varying in diameter from 36” to 72”. The pipe began in typical open cut method at the pressure sustaining vault and entered the lake approximately 200 ft. up station.  The pipeline continued into the lake with depths ranging to 110 ft.  Pipe was laid on a dredged channel on a 2.5 ft. bed of coarse aggregate.  We executed the subaqueous excavation off of barges using our clam shell bucket and hydro-graphic survey to ensure our line and grade.

Construction at the pressure sustaining vault contained a section of 54” ductile iron pipe, which transitioned into triple barrel 36” ductile iron pipe with 36” butterfly valves, air/vacuum valves and related appurtenances. The pressure sustaining vault consists of a vault structure that was installed in a 53 ft. diameter shaft, at an approximate depth of 45 ft.  Geology made the shoring of this shaft difficult, with a soil to granite transition at 40 ft. of depth.  Critical utilities in the area did not allow for benching, so soil anchor and shotcrete methods were utilized.  The vault piping and pressure sustaining valves are aligned inside the vault structure with 54” butterfly valves installed on each side of the PSV valves.

Due to the proximity of an existing raw water intake in Lake Lanier, water quality had to be strictly monitored. Full depth turbidity curtains were specified to ensure water quality was not affected in this area.  Noise monitoring devices were also installed to allow for a record of equipment noise that could affect the homes in the area.  Federal environmental standards were being monitored at the water to land transition by local federal authorities due to the high profile of this project.

The project was built at Lake Lanier, an urban settings within a very restricted easement. The project was a significant undertaking and was considered a success by Gwinnett County.