Over the course of three years, 198 days on the water, and 916 individual dives, Power Engineering Construction’s ADCI-certified dive team replaced the structural support system of two critical 950-foot parallel seawater intake pipelines in a national marine sanctuary.
On one of those days, beneath bright California skies and with 50–60 feet of visibility underwater, the crew was just about to begin drilling when a humpback whale passed by. Work came to an immediate stop. Topside, onboard the barge’s dive shack, a marine biologist monitored the curious mammal as it moved along before giving the underwater crew the signal to proceed. Moments like this underscore the balance between underwater construction and environmental stewardship that defined this project from start to finish.
Power Engineering Construction is a California-based marine contractor with an in-house ADCI-certified dive team. This project was a surface-supplied and mixed gas nitrox diving effort. It replaced a gravity-supported structural system of concrete blocks with a robust anchored system that secures the pipelines directly into the granite substrate. Following are some notable aspects of the work, illustrating real-time adaptability, communication challenges and solutions, and wildlife protection in a national marine sanctuary.
Working in an offshore subsea environment, one of the challenges was designing the project without knowing the seafloor geology for sure until sand was excavated and rock revealed.
“There were seven drawings with typical details and guidelines, but the appropriate detail for each of the 43 supports could only be determined after excavation by divers.” said Brian Shalk, project manager leading Power’s Commercial Diving Division. Excavation revealed conditions ranging from solid granite, to deep fissures, to decomposed, unsuitable rock. This variability necessitated on-the-spot evaluations by the crew to determine viable support locations. Power’s onsite team frequently consulted with stakeholders to adapt designs and methods based on the exposed conditions, balancing structural needs with permit requirements.
“Communicating the wide range of seafloor findings was challenging,” said Shalk. “A single diver would relay conditions to the dive supervisor, who would interpret that information for the engineer, who then explained it to project stakeholders. It was like a game of telephone—but that’s where strong teamwork made all the difference.”
Also helpful were enhanced remote monitoring practices such as live, internet-streamed broadcast from smart cameras installed on each diver’s helmet. This enabled teams to verify key project elements in real time without stakeholders needing to be physically present. This reduced logistical challenges with third-party QAQC review as well and maintained a streamlined and fully transparent communication process, building confidence in both the quality and environmental compliance of the work.
That same adaptability extended to dive operations themselves. Power’s dive team employed different breathable gas mixes depending on the depth of the work. Surface-supplied dive spreads ensured efficiency for shallow dives up to 40 feet, while mixed gas nitrox spreads enabled longer bottom times for deeper depths, reducing nitrogen absorption and the risk of decompression sickness—critical given the pace of daily diving.
There were essentially two installation methods for the new structural support system, depending on the underlying seafloor geology. Some supports were retrofitted with stainless steel brackets and secured directly to concrete blocks on the seabed. Others, designed for sandy conditions, used socketed pipe-and-beam systems.
For the rock-socketed supports, installation required penetrating at least 30 inches into competent rock—a benchmark that ensured the structural integrity of the system. Divers used a 20,000 PSI water blaster to cut through sound granite. Compared to traditional drilling methods, the water blaster provided precision and minimal environmental impact.
To further protect the marine environment, the team deployed benthic turbidity curtains, which reduced sediment disturbance and limited the spread of particulates typically released during excavation and construction.
Environmental protection was built into daily operations. Each morning before construction began, scuba diving biologists carefully surveyed and cleared the designated work area of invertebrates—animals without backbones such as sea stars, urchins, and anemones—and other sea life. For example, kelp growing on concrete blocks was relocated rather than removed or destroyed. Teams used specially designed tools made from non-plastic materials to reattach the kelp in its new location, preventing contamination in the protected marine sanctuary.
Over the course of the project, more than 12,700 invertebrates were safely relocated. A marine biologist stationed on the barge continuously monitored for marine mammals, and post-construction surveys confirmed no harm to the surrounding ecosystem.
With the work complete, the team reflected on the scope and significance of the effort. “This was an incredible project, and our goal is to do many more like it,” said Shalk. “It’s a reflection of what it’s like to work with Power. We don’t cut corners that put people or wildlife at risk, and we thrive on solving complex engineering challenges with the utmost respect for the marine environment.”
Power Engineering Construction Co.
1501 Viking St. Ste 200
Alameda, CA 94501
Phone: (510) 337-3800