Global provided project management, diving and topside services as required to perform outfall repairs on the Richmond, Alki and Carkeek outfalls under a single contract. The work on the Carkeek outfall was performed in approximately 200 feet of water. The work was carried out from a flat-deck barge that had been outfitted to perform deep-diving operations. The barge was moored on location with a four-point anchor system, allowing the barge to be positioned directly over the work at any point along the diffuser section alignment.

 

The project required the removal and replacement of all 11 of the existing steel diffusers. The four bolts per flange were burned off using a Broco underwater cutting rod. Once the existing diffusers were removed, we noticed that the interior of the pipe had filled approximately half-full with sediment. This material was removed with an air lift. The nozzle was inserted into the end diffuser, and once the surrounding materials were removed, the remaining sediment in the pipe was jetted to the air lift using a pressure washer to move the materials. When the pipe was clear of the sediment, the new diffusers were installed using stainless steel hardware, connecting the new diffuser flange to the existing outfall flange.

Due to the depth of the work required for the outfall repairs, divers used a mixed gas, Heliox (86% helium, 14% oxygen). This combination allowed the divers to stay on the bottom longer while also negating the effects of nitrogen at increased pressure. The divers entered and exited the water via a dive stage. The stage is used to control the diver descent and ascent and allow the dive supervisor to control the the diver’s decompression stops. Once the diver had fulfilled their in-water decompression commitment, they were raised to the surface and put into the deck decompression chamber to complete their decompression.