When it rains, it pours. This old saw passes for an apt description of the new precipitation regime that climate change has wrought for the Bay Area: larger winter storms, but fewer of them. The implications of this shift for ecosystems, infrastucture, and water storage are widespread, and often highly visible. But behind the scenes, it is also complicating efforts to monitor pollution inputs to the San Francisco Bay and other local water bodies from stormwater runoff.
The Regional Monitoring Program for Water Quality in San Francisco Bay (RMP) has been collecting data in Bay water, sediment, and biota since 1993. RMP monitoring of stormwater flows after rain events, which began in 2006, has shown that runoff is a major pathway to the Bay for “legacy” contaminants like PCBs and mercury, as well as contaminants of emerging concern like PFAS and chemicals used in automobile tires.
Only through careful monitoring during and immediately after storm events can RMP scientists accurately characterize—and thus inform efforts to mitigate—the contribution of stormwater runoff to Bay pollution that may harm wildlife and humans alike. But with fewer, more severe storms, this job is becoming increasingly difficult—and costly.
“Literally every single one of our projects has been impacted, and we just keep having to roll forward funds and scope of work to future years, because we don’t get the data that we need,” says San Francisco Estuary Institute’s Alicia Gilbreath, who leads the RMP’s stormwater monitoring team. “So every year we just keep piling on more and more, both what we’re supposed to do in a given year and all the work from the previous years.”
For example, a pilot study last winter of pollutants entering the Bay at creek mouths was to include data from just two storms, a relatively low bar. But not low enough: “We were able to sample one really early-season storm,” says Gilbreath, referring to the record-setting deluge that hit the region in late October and early November 2021. “We fully expected in February to get another storm, but it never came.”
Another study to screen for a wide variety of emerging contaminants in stormwater flows—including PFAS, organophosphate ester flame retardants, bisphenols, ethoxylated surfactants, and tire ingredients—was supposed to be completed over the course of two wet seasons, from fall 2018 to spring 2020. But it ended up running for twice as long as a result of insufficient sampling opportunities, especially during the second winter. This in turn delayed the launch of a more targeted, longer-term program informed by the preliminary study.
“We had so few storms that were suitable for monitoring that we had to stretch our study out longer than expected in order to get enough data to really have a meaningful conversation about next steps,” says Rebecca Sutton, a senior scientist with SFEI who leads the RMP’s emerging contaminants work.
Adapting to this new reality will entail a greater reliance on remote monitoring where possible—using small devices that automatically sample stormwater when flows reach a certain threshold—and more careful deployment of field staff where required, notes RMP program manager Melissa Foley.
“Storms may hit on weekends or at night, and it’s sometimes hard to mobilize multiple teams to get out there and to hit as many sites as possible,” Foley says. “In the past, it’s been, ‘We’ll, that’s okay, we’ll get the next storm.’ Now it’s at the point where we can’t take that for granted anymore. This might be the last storm we get.”
But storms aren’t only rarer; they’re also bigger. Extreme rainfall events can pose additional risks to field staff collecting stormwater samples: roadways can be dangerous, creeks can flood, trees can topple. Crew members often must be on site for several hours at the storm’s peak, and their safety takes priority, Foley says. This may require additional planning, prioritization, labor, and equipment—all avenues that the RMP is exploring to ensure it can continue its critical work in an era of megastorms. “We can’t squander any opportunity to collect data at this point,” she says.
In some cases, larger storms may also overwhelm green infrastructure such as bulb-outs, swales, and rain gardens intended to capture and filter stormwater before it runs to the Bay, adds Sutton: “They’re designed with a certain sort of storm in mind. If it’s too intense, the water will bypass. If we end up with bigger, less frequent storms, it might mean you have to redesign that infrastructure or it won’t operate as effectively as you want.”
Ironically, efforts to evaluate the effectiveness of green infrastructure at removing legacy and emerging contaminants from stormwater have also been stymied in recent years. But this is one area where automated sampling could play an important role going forward, says Chris Sommers, a stormwater monitoring consultant who works with both the RMP and county-level agencies throughout the Bay Area.
“[Remote samplers] are helpful to not miss storms, or to not spend money on storms that never appear, which is a big issue,” Sommers says. “Our records show that about 25% of all predicted storms that you are ready to go out and mobilize for end up not producing enough rainfall that is sample-able.”
Reducing the number of such “false starts” through automated samplers integrated into green infrastructure could free up funding and personnel for labor-intensive manual sampling required at other sites like creek mouths. And it’s just this sort of innovating and prioritizing that will be required for stormwater monitoring programs to continue meeting regulatory requirements and helping protect water quality in the San Francisco Bay going forward, Sommers says.
“There are requirements to sample a minimum number of events per year, but if you only have five storm events that come through, then you gotta get those five storm events,” he says. “There’s no room for error here. Even if it’s the middle of the night, even if it’s Christmas, that’s what the expectation is.”
Top image: Sampling at the outflow of a stormwater conveyance in Berkeley. Photo: Don Yee.
Related Prior Estuary Stories