20 years after quake, how green is the bridge retrofit?
on October 16, 2009
Tony Anziano’s office is in a trailer just off West Grand Avenue near the Bay Bridge toll plaza. An unmanned guard station squats in the middle of the lot entrance where white trucks with orange stripes come and go, kicking up small puffs of dirt. To an outsider, the mix of buildings and trailers, concrete and dirt, give the place an appearance of indecision, as though this Caltrans field office is teetering between being a temporary command center and settling in for a long, hard slog.
On the inside, Anziano’s office is simple: a few chairs and a desk engulfed by large binders, books and thousands of sheets of paper. He is the Toll Bridge Program Manager for Caltrans and oversees a significant portion of the Bay Bridge retrofit now in its eleventh year. Because of the construction’s location in the heart of major migration routes for birds, fish and marine mammals, the retrofit has raised a host of environmental questions, many of which remain unanswered today.
Twenty years ago this week, the Loma Prieta earthquake pancaked a section of the Bay Bridge, killing a motorist and launching the long, and often troubled, retrofit project. The first decade saw so much squabbling between Bay Area cities, the state and the Navy over design, features, location and cost of the new eastern span that the White House facilitated negotiations in 1999 to break through the stalemate.
The retrofit’s environmental review process wasn’t much easier. The final Environmental Impact Statement (EIS) was released in May 2001 after four years of consultation and struggle between Caltrans and regulatory agencies such as the National Oceanic and Atmospheric Administration (NOAA), the Bay Conservation and Development Commission (BCDC), the California Environmental Protection Agency (EPA) and the SF Bay Regional Water Quality Control Board. “We touch on everything,” Anziano says, “which is why we are probably the most regulated entity in the country.”
Concerns at the time ranged from whether dredging the ocean floor would stir up toxics hazardous to marine life to debates about the extent of Caltrans’ responsibility for cleaning up oily stormwater runoff to the effects of construction sediment on the eelgrass beds that form the habitat and food for many bay-dwelling species.
Now, eight years after the impact statement was released, some of the ecological concerns raised early on have fallen away while other unforeseen problems have sprung up, prompting Caltrans to develop some innovative solutions. The agency is now building a very unusual garden to deal with the problem of stormwater runoff and constructing an entire island to mitigate the retrofit’s encroachment on fading bird habitat.
It also turned to novel new technology to handle one surprise that popped up in 2000 just before construction was set to begin on the new eastern span. The surprise was exploding fish.
The Bubble Curtain
The exploding fish problem had its origins in the sheer size of the pilings needed for the new suspension bridge that will eventually connect Oakland to Treasure Island.
Pilings for the original 1936 Bay Bridge were crafted out of solid rounds of Douglas Fir and driven 170 feet into the top mud layers of the ocean floor. In contrast, the piles for the new eastern span are 365 ton 8 1/2 foot diameter steel rods driven up to 300 feet into bedrock.
Because this was the first time pilings of this magnitude were driven in an urban environment, Caltrans conducted a Piling Impact Demonstration Project in October 2000. They tested the rods by driving three of them into the seafloor.
“These pilings were huge,” says National Marine Fisheries Service biologist David Woodbury, who joined the project in 2000 to monitor its impact on endangered fish species. “They brought in the world’s second largest hammer to deal with them. You take a big hollow steel pole and hit it with the world’s second largest hammer and it’s like an enormous wind chime. The pressure waves were enormous.”
Fisheries expert Bud Abbott was running his own consulting firm when he found out about the demonstration project. He called Caltrans to warn that the pressure waves from such powerful blows could harm, or even kill, fish and marine mammals in the bay.
Caltrans proceeded with the test anyway, which, according to the agency’s web site, struck each pile with the force of a car meeting a brick wall at 365 miles per hour. Enormous pressure waves radiated out and fish began surfacing belly up. Some exploded with such force, Abbott says, that their guts spilled out.
What happened? It turns out that many fish species possess a sac of gas called a swim bladder that helps them regulate buoyancy. When the pressure part of a sound wave contacts the bladder it compresses, and when low-pressure part follows, it quickly expands.
“The expansion,” Abbott says, “is rifle-shot fast. The tissue can’t accommodate such rapid changes. It happens in milliseconds and the tissue in the swim bladder breaks. The fish literally explodes.”
The exact number of fish was hard to determine, says Woodbury, since seagulls ate the kills much faster than biologists could maneuver their boats to collect them. “I would not be surprised if it were thousands of fish,” he says, “considering that the bay is a nursery ground and very small fish are numerous.” Small fish typically travel in dense schools and are highly sensitive to injury from sound pressure. Woodbury says their small size also makes them more vulnerable to currents so they might be unwillingly pushed into areas with dangerously strong sound.
The Bay Bridge is just to the south of a major migration route for young fish, including endangered salmon and steelhead, who make their way from their spawning grounds in the Central Valley out the Golden Gate and into the open ocean.
Caltrans needed to figure out how to hammer in the pilings without killing these protected species, so the agency called Abbott to autopsy what he describes as “ice chests of dead fish,” and to make recommendations about how to avoid future fish casualties.
“I opened up the fish and saw that they’d erupted,” he says. “They were full of blood and their swim bladders had ruptured.”
Abbott suggested using an underwater wall of air called a “bubble curtain” to attenuate, or dampen down, the sound waves produced by pile driving. The explosives industry, he says, had previously used blankets of bubbles to attenuate underwater noise with some positive results. To their credit, Abbott says, Caltrans started the process of designing and implementing the curtain right away.
James Reyff, a hyroacoustics expert with Illingworth and Rodkin, a Petaluma-based firm hired to consult on the project, says a bubble curtain works by exploiting the enormous density difference between air and water. Though it may sound counter-intuitive, air slows sound far more effectively than water. In fact, sound waves travel 4.4 times slower through air than through water.
Furthermore, Reyff says, “Air and water have what scientists and engineers call an impedance mismatch.” This mismatch means that sound loses pressure when the waves cross the boundary from water into air, or vice-versa. So the curtain works two ways: The air itself reduces the strength of sound waves, while the process of traveling between mediums further erodes them.
To create a bubble curtain, the piling to be driven is placed within a perforated tube at the bottom of a large cylinder. Compressed air is then pumped through the tube creating a thick wall of bubbles surrounding the pile. After careful study of existing designs, particularly ones used in Canada and Hong Kong, Caltrans decided to improve the process by adding an additional bubble-producing ring slightly above the bottom one.
In December, 2002, the agency tested its version by driving more piles, some within the curtain and some without. While the range of attenuation varied considerably, Caltrans found that the curtain reduced sound levels by up to 20 decibels — a pressure drop of 90 percent.
“It’s the difference,” says Woodbury, “between fish floating to the surface with exploded swim bladders and not.”
The curtain was a revelation for the Bay Bridge retrofit process and for Caltrans’ other underwater construction projects. Environmental teams at both the Benecia-Martinez bridge and the Richmond-San Rafael bridge had initially failed to use the curtain and, as a result, also ended up killing fish. The curtain’s success on the Bay Bridge project paved the way for its later use on those bridges and throughout California.
Because each curtain does not always attenuate the same amount of sound to the same degree, both NOAA and Caltrans are still monitoring how well they work. ”We are collecting data on every single project throughout the state,” says Anziano. “We don’t just look at peak noise. We look at how the accumulation of sound affects fish behavior.”
In 2004 Caltrans worked with the NOAA, the U.S. Fish and Wildlife Service, the Oregon Department of Transportation, the California Department of Fish and Game, and the U.S. Federal Highway Administration to form the West Coast Fisheries Hydroacoustic Working Group. Together they investigated how spikes in sound affect fish, the factors that influence bubble curtain operation and appropriate noise limits for underwater construction sound. Noise limits were formally proposed in June 2008 and since then, says Galvez-Abadia, Caltrans has held to these standards.
“Caltrans now leads the West Coast in bubble curtain technology,” says Abbott. “In Oregon there are over 400 major bridges that need to be replaced. They’re using California and Washington standards and they’re using bubble curtains.”
The work pioneered on the Bay Bridge project is also piquing the interest of scientists abroad. For example, Danish work crews building wind farms were bumping against similar underwater sound questions. In 2004, they convened a gathering of scientists to pool knowledge on the subject. Woodbury served on the hydroacoustic working group and traveled to the conference.
“My intention in attending the conference was to learn how others were dealing with this issue,” he says. “Interestingly, I found out that we were on the cutting edge. We ended up sending several attendees much of what we had learned on the West Coast.”
Meanwhile, above the water line, Caltrans was undertaking a second environmental engineering pilot project. This one uses an innovative garden to treat oil- and grease-laden stormwater runoff that would otherwise end up in the bay.
The Rainwater Garden
Stefan Galvez-Abadia, Caltrans’ Environmental Compliance Manager for the Bay Bridge retrofit, drives along a side road just off the eastbound lanes of 580 in the no man’s land between the toll plaza, Emeryville and the loading docks of Oakland. Freeway overpasses shout overhead like a quarterback’s count: 580, 80, 880.
He pulls through a chain-link fence, parks and steps out into a large field punctuated by four-foot high earthen embankments surrounding a series of basins. The swimming pool-sized basins resemble small drained lakes, each hosting a variety of shrubs and reeds with a foot-wide concrete canal system winding between them. California blackberry, oatgrass, salt grass, coyote brush and monkey flower appear to scatter randomly across the landscape, but the plants are here for a reason. Their roots to help maintain an open soil structure that water can percolate through. In addition, microbes on the roots may help break down some of the toxins in the stormwater runoff that flows off of the surrounding freeways every time it rains.
Galvez-Abadia dons his yellow safety vest and white helmet, and hops between embankments as he describes the project in an elegant Spanish accent.
“This is a $16.5 to $17 million garden,” he says, “and that’s just the capital costs. It doesn’t include design.”
Combined, the basins and plants form the beginnings of a pilot project that, Galvez-Abadia says, will treat nearly 150 acres of urban stormwater runoff without the use of chemicals. The basins shallowly pool the water for up to 48 hours. This thin spread allows for maximum surface area as the water makes its way through the layers of mulch and sand that form the garden’s primary filter.
While rainwater gardens are not particularly new, this project is noteworthy for its sheer size. Keith Lichten, Senior Water Resource Control Engineer for the San Francisco Bay Regional Water Quality Control Board, calls the garden “an innovation.”
He also says that Caltrans resisted building it.
New Clean Water Act regulations went into effect at the dawn of the retrofit project requiring Caltrans to capture, store and treat stormwater runoff across all its freeway projects state-wide. “Caltrans didn’t want to comply,” Lichten says.
According to Anziano, Caltrans was not against stormwater treatment in principle, but the additional weight of capturing and holding tons of water across the bridge would throw off the engineering and potentially demand an entirely new design.
Lichten, who enforces permit violations for the water board, says that Caltrans ducked the issue by simply designing the bridge without a stormwater system. “So at the eleventh hour we found ourselves in a bind,” he says. The water board could not overlook a major violation, but it was reluctant to further delay an important seismic retrofit that had taken over a decade to break ground.
Caltrans, meanwhile, was caught between a major permit violation and redesigning the bridge. The two parties sat down and hammered out a solution.
The area around and immediately east of the toll plaza was of primary concern to the water board because stop-and-go traffic along the freeways and toll plaza spill more oil, grease and brake fluid than traffic flowing across the bridge. Ultimately, Caltrans agreed to focus its stormwater collection and treatment efforts in that area instead of redesigning the bridge.
The rainwater garden pilot project broke ground in April 2006 and is notable not only for its size, but also because it marked a change in how Caltrans approaches the state’s clean water requirements. Anziano says that the agreement was the first time the agency worked to meet a permit requirement by looking at the bigger picture and negotiating an outside-of-the-box solution. “Now it’s part of regular practice,” he says.
The garden was finished last year, but the monitoring is ongoing and the results of how effectively it filters toxins from stormwater are not in, says Galvez-Abadia. “It might not filter out 100% of everything,” he says, “which is why we’ll continue monitoring it.”
The new garden could have some pleasant side-effects though, he says. “Over there is where the bike path will come in,” he says, pointing to the southeast corner of the basin system. “There will be a viewing station over there where people can see the project.” If the plants and pools provide a habitat for birds, “Well,” he says, “then that would be ok too.”
The reference is a bit of a wink. While the garden is specifically designed to treat stormwater, Galvez-Abadia knows that any bird habitat in the area around the MacArthur Maze is a good thing.
In fact, making sure that birds have a place to roost near the retrofit is one of Caltrans’ newest environmental projects.
Across the highway from the basins is the natural wetlands habitat called “the Emeryville Crescent,” or simply, “the crescent.” Former Golden Gate Audubon Director Arthur Feinstein says the area is such rare and critical habitat for birds that in the late 1990s, the organization partnered with The Sierra Club to sue Caltrans over the expansion of I-880 into the crescent.
According to Feinstein, the crescent is one of the most important bird habitats in the Bay Area. “Sixty to seventy percent of migrating birds use the Albany Mudflats and the Emeryville Crescent,” he says. Migratory birds can lose up to forty percent of their body weight in the journey from the arctic to South America. According to Feinstein, they rely on the crescent as a crucial fattening-up point. “They’re here to rest and to eat,” he says.
Increasing shoreline development, however, means birds are running out of places to stay. “Birds don’t have places to go at high tide because we’ve built up all around it,” he says. “Biologists have seen shorebirds standing on top of shorebirds at high tide.”
In their desperation to find roosting habitat, migrating birds began occupying old duck blinds abandoned by hunters. These blinds are dilapidated, however, and are slowly sinking into the bay.
Although the bridge retrofit is not expected have an enormous impact on the crescent, given the area’s fragile state, bird advocates asked Caltrans for mitigation measures.
“The bridge project,” Galvez-Abadia says, “doesn’t result in significant reduction of roosts, but the Audubon said ‘Wait a minute’ so we sat down with them to try to address their concerns. We came up with seven or eight different options.”
Eventually, he says, Caltrans took a really novel approach: The agency designed an island constructed of large rocks to serve as an alternative bird hangout. The plan calls for a trapezoidal-shaped mound of boulders with 500 square feet of roosting area at high tide. The project is expected to break ground next month.
Mike Lynes, Conservation Director for the Golden Gate Audubon Society, thinks birds will probably take to this artificial resting spot. “I can’t tell you if birds are going to use it, but I think they will,” he says. “I think birds in the bay crave any place they can roost.”
Caltrans does not have a back-up plan if the birds do not take to the man-made island, however, and does not plan to maintain the island after building it. It is also unclear who will monitor the efficacy of the island after construction.
“Agencies recognize that there’s no success criteria,” Galvez-Abadia says. “You can’t say you will have X number of birds per year. Once we’ve built it, that’s it.”
The ultimate success of Caltrans’ other environmental innovations also remains blurry. With at least four years of the retrofit project left to go, the final balance of its ecological impact remains to be weighed. Right now, Galvez-Abadia says, the most the agency can do is monitor the construction’s impacts, gather data and attempt to mitigate environmental consequences.
“No one has the answers right now,” he says. “No one knows that X plus Y equals Z. There are a lot of factors in these things and the only way to know is to monitor. Then more innovations come.”
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[…] 20 years after quake, how green is the bridge retrofit? Midway through the Bay Bridge retrofit, what are the environmental consequences of a major construction project in the middle of the bay? Story by Shannon Service. […]