Preface. In coastal areas flooding is likely to be caused from groundwater rise because as sea levels rise, they won’t only move inland, flooding low-lying land near the shore; but also push water up from the saltwater water table, on top of which is a layer of lighter fresh water. As the salt water rises with rising seas, it will push this fresh water upward. In low-lying areas, that water may emerge from the ground.
The consequences are that water will leach inside homes through basement cracks. Toilets may become chronically backed up. Raw sewage may seep through manholes. Brackish water will corrode sewer and water pipes and inundate building foundations. And most hazardous of all, water percolating upward may flow through contaminants buried in the soil, spreading them underground and eventually releasing them into people’s homes. The coup de grace will be the earthquakes, which, when they strike, may liquefy the entire toxic mess, pushing it toward the surface.
The result will be that in places like Oakland, flooding will occur not just at the shoreline, but inland in areas once considered safe from sea level rise. The threat it poses can’t be neutralized with the usual strategy: physical structures that keep the sea at bay. No matter how many seawalls we build, many experts say, groundwater can still gurgle up from below, potentially turning large swaths of the densely populated shoreline around the Bay into unwanted, unplanned, possibly toxic wetlands.
Alice Friedemann www.energyskeptic.com author of “When Trucks Stop Running: Energy and the Future of Transportation”, 2015, Springer and “Crunch! Whole Grain Artisan Chips and Crackers”. Podcasts: Practical Prepping, KunstlerCast 253, KunstlerCast278, Peak Prosperity , XX2 report
Grace Mitchell Tada. March 25, 2019. The Sea Beneath Us Sea level rise has a gotcha-from- behind twin: rising groundwater. It’s already here. And some experts maintain, we’re not ready for it. Bay Nature
In East Oakland, on a residential street in front of a small park, Kristina Hill stopped and got out of her vehicle. She walked to the center of the street as a gaggle of graduate students emerged from their cars and gathered around her. It was midday, early September, the bright, hot sun directly overhead. Hill, a professor of urban and environmental design at UC Berkeley, had chosen the spot because when it rains heavily, water gushes up from storm drains here, forming filthy brown ponds. “That will happen more and more,” Hill said. Then she proceeded to describe a peculiar, almost apocalyptic future.
Water will leach inside homes, she said, through basement cracks. Toilets may become chronically backed up. Raw sewage may seep through manholes. Brackish water will corrode sewer and water pipes and inundate building foundations. And most hazardous of all, water percolating upward may flow through contaminants buried in the soil, spreading them underground and eventually releasing them into people’s homes. The coup de grace will be the earthquakes, which, when they strike, may liquefy the entire toxic mess, pushing it toward the surface.
The future Hill described is caused by a phenomenon called groundwater rise. In a nutshell, as a warming climate raises sea levels, the sea won’t only move inland, flooding low-lying land near the shore; it may also push water up from beneath our feet. That’s because for those of us living near the shore, a sea lurks in the ground—a saltwater water table. On top of that salt water floats a layer of lighter fresh water. As the salt water rises with rising seas, Hill and others think, it will push the fresh water upward. In low-lying areas, that water may emerge from the ground.
The result, Hill explained, will be that in places like Oakland, flooding will occur not just at the shoreline, but inland in areas once considered safe from sea level rise, including the Oakland Coliseum and Jones Avenue, where Hill and her students now stood, more than a mile from San Leandro Bay. In fact, she added, rising groundwater menaces nearly the entire band of low-lying land around San Francisco Bay, as well as many other coastal parts of the U.S.
The threat it poses can’t be neutralized with the usual strategy: physical structures that keep the sea at bay. No matter how many seawalls we build, many experts say, groundwater can still gurgle up from below, potentially turning large swaths of the densely populated shoreline around the Bay into unwanted, unplanned, possibly toxic wetlands. The issue is barely on the radar of Bay Area planners and decision-makers; it’s been mostly overlooked until recently. The public has hardly heard of it. Hill is trying to change all that. She’s on a mission to increase awareness of sea level rise’s gotcha-from-behind twin—groundwater rise.
When we think of the water table, we probably imagine a hard line that runs parallel to the earth’s surface some distance below us and, beneath that line, a big blob-like lake that we call groundwater. But it’s not really lake-like. Groundwater exists within permeable layers of rock, called aquifers, classified as either confined or unconfined. Water fills the space between rock particles. Confined aquifers are usually tucked deep in the earth, pressurized between less permeable layers of rock. Unconfined aquifers, like the one Hill described beneath Oakland, commonly exist in coastal areas and at river mouths. These aquifers often sit close to the surface, and they swell when, for instance, it rains. Only recently have scientists come to understand how sea level rise can affect coastal groundwater.
Around the Bay, most development has occurred on wetlands filled with sand, mud, and building rubble from 19th-century construction efforts, as well as alluvium, the material that washes down from surrounding watersheds.
This will be a disaster in earthquakes, which can exacerbate the problems posed by rising groundwater as it did Christchurch, New Zealand where 80% of the city’s underground infrastructure was obliterated, and thousands of buildings were leveled. Why? The city was built on a sand-and-gravel plain with a high water table. When the earthquake struck, the soil acted like a liquid, partly swallowing vehicles and cracking and tilting buildings. It is a problem shared by and well-known in the Bay Area.
The USGS has liquefaction susceptibility maps for the Bay Area, but these don’t account for sea level rise. Municipalities needed to incorporate the risk posed by rising water tables into their climate adaptation plans. As sea levels gradually rise in the decades to come, water might push up through storm drains or directly through the ground, damaging infrastructure and building foundations. Freeways and airports near the sea (and there are many, SFO and Oakland International Airport included) would likely become soggy messes. Inundation at wastewater treatment facilities, often sited on low-lying land, could trigger leaks of untreated water. Rising salt water might corrode urban drainage systems, which would stop functioning properly as their pipes filled permanently with groundwater. Brackish pools of water could become regular features of the urban environment.
More worrisome, rising groundwater might carry toward the surface hazardous material trapped in the soil. Around the rim of the Bay, once a center of heavy industry, we could see arsenic, lead, benzene, polycyclic aromatic hydrocarbons, PCBs, even possibly radioactive waste.
Another effect of climate change is that rainfall is predicted to become more intense. Flooding would likely become more frequent, bringing to the surface various buried toxic substances, such as the vinyl chloride and TCA of concern in the groundwater beneath the nearby tool and die machine shop, or the gasoline in the groundwater around the neighborhood’s former and existing gas stations.
Even if the water table recedes after the rainy season and the summer dry season sets in, some contaminants could become airborne in buildings. People may inhale them. “Even an event where it’s a seasonal thing for a few days could have really important long-term effects,” Hill told me.
East Oakland is already among the top five percent of polluted California zip codes. The mostly low-income, primarily nonwhite residents who live there have relatively high rates of chronic disease. Life expectancy for African Americans in the Oakland “flats” can be up to 14 years less than in the hills. And now these already beleaguered communities face the prospect of contaminants welling up from beneath their feet.
Rising groundwater is “a whole new game-changer, particularly when you’re talking about sites that are contaminated with industrial solvents,” says Grant Cope, the deputy secretary for environmental policy at the California Environmental Protection Agency. What can be done? Contaminated groundwater could be pumped out of the ground, treated, cleaned, and reinjected into the aquifer, Cope says. Otherwise, it remains unclear whether caps meant to keep pollutants buried—a strategy used at remediated sites in recent decades—would continue to work if groundwater rises. The caps were not designed for this purpose, Cope says.
Judging by what the federal EPA has learned from its experience with hurricanes in other parts of the country, the most acute risk posed by groundwater rise are infections from pathogens in wastewater, according to John Blue, Cal EPA’s manager of climate programs. (Hill disagrees, saying, “I would take a bath in wastewater before I would have any skin contact with benzene”—one of the pollutants she worries about in Oakland. “There’s no safe exposure” level.) And how would affected wastewater be dealt with? Blue pauses. “These are very difficult questions,” he says. “That’s the eight-hundred-million-dollar question. That remains to be seen.”
There are important caveats to the wet, bleak future scenario Hill and Plane’s report describes. Their maps, which have been submitted for publication but haven’t appeared in a peer-reviewed journal yet, are approximate and don’t account for subtleties in the landscape—for instance, streams and valley-like topography that might allow rising groundwater to flow downhill and away, preventing water from pooling. Hill and Plane’s conclusions assume that water tables will rise linearly with sea level rise, which, judging from patterns in local geography, may or may not be true. The report’s data is based on the highest water table levels recorded in the past 20-odd years, which may present an exaggerated picture of what’s likely to happen, says Kevin Befus, assistant professor at the University of Wyoming’s College of Engineering and Applied Science. Tina Low of SFRWQCB maintains that, in conjunction with monitoring, current remediation standards for buried pollutants are sufficient to prevent leaching, even if groundwater rises. (Older sites that don’t adhere to these standards may need to be studied to assess the risk they pose, she adds.)
Still, many planners I queried around the Bay found the study both credible and worrisome. “It’s a really nice data-driven approach that leverages this incredible data set [from] wells to look at where the water table actually is,” says Patrick Barnard of the USGS. Abby Mohan, a marine geographer at Silvestrum Climate Associates, who is working with Hill and Plane to further refine their research, emphasizes that this is pioneering, groundbreaking work. “Ellen and Kristina did something really interesting and great,” she says.
Steve Goldbeck, chief deputy director of the Bay Conservation and Development Commission, says the commission had been aware of the groundwater issue in a general sense before, but with Plane and Hill’s work, “now we know it’s going to be a problem” in the Bay Area.
Thus far in recent history, the three general responses to sea level rise have been to armor, to retreat, or to adapt in place. Around the Bay, many municipalities are considering the least radical strategy: armor. San Francisco aims to rebuild its seawall, a more than $2 billion project that won’t address groundwater issues (though it does, importantly, address seismic hazards). Moreover, as the sea rises, seawall construction could actually increase water levels in the Bay, says Mark Stacey, an environmental engineer at UC Berkeley who has modeled such scenarios. If, for example, Foster City, San Mateo, Redwood City, and Menlo Park all erect seawalls, those barriers together could alter tidal amplification enough to raise water levels in the Bay, potentially worsening flooding in other areas.
Planners elsewhere are taking bold actions to address groundwater rise. Miami envisions using urban green space as a sponge to draw out and absorb groundwater. Boston recently unveiled a plan for its harbor that uses barrier walls to keep the sea out as well as tidal marshes and parks to absorb emergent groundwater. (The Bay Area has restored tens of thousands of acres of wetlands, but unlike in Boston or Miami’s plans, they’re not tightly integrated into the urban landscape. So it’s not clear that they can serve the same “release valve” function, drawing groundwater away from infrastructure.) And in New Zealand, after the devastation of the 2011 earthquake in Christchurch, the government purchased and then razed more than 7,000 homes on land at risk of further liquefaction, essentially an admission that some areas of the city’s plain were too dangerous to inhabit in the short term without greater fortification.
Things have moved more slowly in the Bay Area. That’s partly because the Bay’s geology is more complex than along the Eastern Seaboard and scientists don’t yet have all the data, and partly because Bay Area decision-makers want greater certainty on what to plan for. “We’re ready to apply [the information] as soon as we really understand the risk,” says San Mateo County climate adaptation manager Hilary Papendick. Phil Bobel, Palo Alto’s manager of public works engineering, echoes that view, saying the city leadership now assumes it will have to deal with groundwater rise eventually but wants more research first.
Bay Area planners eagerly await USGS models in development that will allow them to predict, with greater accuracy than Hill and Plane’s maps, how the coastal water table will respond to sea level rise. The models, which use Hill and Plane’s data set for validation, are slated for public release later this year. With them in hand, “we’ll incorporate that understanding into our broader adaptation planning,” Alex Westhoff, a planner at the Marin County Community Development Agency, says.
But even with these models available, next steps aren’t necessarily clear because the problem is so new. Replacing and shoring up infrastructure and implementing other adaptation strategies will be expensive, so the biggest hurdle may be funding. “It’s a multibillion-dollar area, and we struggle in the millions to try to do shoreline restoration,” Paul Detjens of Contra Costa County Flood Control and Water Conservation District says. “We’re talking a whole ’nother order of magnitude.” In 2016, Bay Area voters passed Measure AA to fund wetland restoration, so there is reason to think that as they become aware of the issue, voters might support adaptation initiatives that address groundwater rise.
Hill has her own bold ideas for how the Bay Area can prepare. She, Kevin Befus at the University of Wyoming, and Chip Fletcher at the University of Hawaii think that learning to live with water, rather than trying to keep it out, is the best way forward. “If you wage war with water you will lose,” Fletcher says, paraphrasing a Dutch expression. Hill imagines floating cities in ponds, or neighborhoods linked by canals—a Californian Amsterdam. The idea is to manage emergent groundwater by opening space for it in the cityscape. Canal systems installed in flood-prone areas of East Oakland, for example, would help existing structures remain in place a bit longer; elevating and retrofitting for seismic risks is too expensive, she says. Over time, as groundwater rises, neighborhoods could become what she and her colleagues call “tidal cities.” Homes, apartment buildings, and businesses could rest atop floating pontoons connected to land.
Those ideas may sound far-fetched, but planners welcome them. “We’ll need creative solutions for design and planning,” Westhoff says.
Rohin Saleh, a civil engineer at Alameda County Flood Control who has watched the water table rise over the past 15 years, says Hill’s vision may not be feasible everywhere, but “is a really great component of the type of solution that we need to have in our backpack.”
Many questions remain unanswered. Who will pay for urban adaptation, cleaning and remediation? How will the many municipalities around the Bay come together to manage what is, by definition, a regional problem that no one area can solve alone? And what, for that matter, does a floating apartment building look like? Whatever the answers to these questions, one thing is certain. As Lindy Lowe, the Port of San Francisco’s resilience program director, says, at least people are thinking and talking about groundwater rise now—which they weren’t doing eight to ten years ago. That, she notes, is already a triumph.