Stormwater runoff pollution
Why students should avoid swimming 3 days after rainfall
WHITNEY LYNN / CONTRIBUTOR / THE USD VISTA
San Diego beaches play a large role in the lives of locals in the form of recreational activities, like fishing or surfing, and also are a large contributor to the tourism economy. Polluted urban runoff impairs San Diegans and tourists ability to enjoy outdoor spaces.
The County of San Diego’s Department of Environmental Health and Quality’s (DEHQ) Beach Bay and Water Quality Monitoring Program conducts testing on recreational waterways across the county. The testing looks for bacterial indicators that are representative of potential pathogens harmful to humans, like total coliform, fecal coliform, and enterococcus bacteria. Bacterial indicators do not solely come from humans, they can also be from wildlife, pets, soil, or rotting vegetation. Approximately 45 beaches are tested from Trestles in the North to the Tijuana border in the South.
Bacterial levels rise after rainfall due to San Diego’s storm drain system. The drainage system directs stormwater and urban runoff to streams, rivers, bays, and oceans without treatment. Urban runoff travels over hard, impermeable surfaces picking up pollutants before entering drains. Some pollutants include “motor oil, grease, pesticides, fertilizer, particulate metals, pet waste, toxins, bacteria, and viruses”, according to SD Coast Keeper.
The DEHQ issues general advisories after San Diego experiences 0.2 inches or more of rainfall, which recommends the public avoid contact with ocean and bay waters for 3 days. In a city that boasts it’s large number of sunny days a year, this may seem to not be an issue. However, San Diego has received an uncharacteristic amount of rainfall so far this year. According to the National Weather Service, the total rainfall in San Diego has been 11 inches and it’s only the fourth month of 2023. For reference, San Diego received 5.90 inches of rain in 2022, 7.85 inches in 2021, and 7.83 inches in 2020.
Dr. Suzanne Walther, professor of Ocean and Environmental Sciences at USD, shared her insight on the pollution problem.
“It’s a double-edged sword. For a lot of the surfers, it’s the greatest time to have big waves because of the storm, so they want to go out,” Dr. Walther said. “The big risk area is right near drainages where the river runoff comes out. Another risk area is down current, whichever way the currents are moving that water.”
Dr. Walther stated that, while many people will continue surfing everyday rain or shine, it is important that they are aware of the health risks, so they can make an informed decision.
Dr. Walther explained what happens in the 3 days after rainfall that makes oceans safe again for people.
“What happens is it filters. There’s not such a density of bacteria that sticks around for 3 days,” Dr. Walther said. “You basically get more flow pushing it out and the ocean turning. It gets diluted. With many toxins in water that the EPA allows, it’s not that one part per million of that toxin is not going to kill you, it’s a certain amount. There’s actually still parts of that toxin in our water, but it’s if the toxins exceed some health limit that has been determined that can hurt humans.”
Marco León is a senior who surfs competitively for USD’s surf team. He’s in the ocean 5 days a week.
When asked if any weather keeps Marco out of the water he responded, “Back home nothing stops me but here in San Diego I try to stay out of the water if there is heavy rain.” Marco is from the Canary Islands in Spain, so waiting 3 days after rainfall to surf was not a phenomena he was familiar with.
“I heard about it freshman year and I was in shock. I usually don’t have the patience to wait so long, but I at least try to wait 24 hours and go to beaches like Blacks that are the furthest away from river mouths.”
Marco has experienced negative health effects due to the pollution that has made him more cautious of when and where he surfs.
“I actually got an ear infection last year, because I surfed Ocean Beach when it was raining. Since then I am very worried every time I go out.”
Signs are not posted at beaches for general rain advisories, but they are posted for other advisories, warnings, and closures. The DEHQ issues advisories and warnings when testing reveals high bacterial levels or a river or lagoon is evacuated that releases contaminated water into oceans. A beach closure is due to reported sewage spills that have contaminated or have the potential to contaminate oceans and bays. Additionally, closures are issued anytime the Tijuana River is discharging, as it is known to contain sewage. Four beaches are currently closed. Two beaches have been closed this year, Silver Strand Shoreline closed February 22 and Coronado Shoreline closed March 1. Imperial Beach Shoreline is closed and has been since December 28, 2022. The longest closure is Tijuana Slough Shoreline, which has been closed since December 2021. These beaches are adjacent to one another with Tijuana Slough Shoreline being closest to the California-Mexico border followed by Imperial Beach Shoreline, Silver Strand Shoreline, and lastly Coronado Shoreline.
San Diego County encourages beach goers to check water quality before swimming on their website, sdbeachinfo.com. Current advisories, warnings, and closures can be found there. The DEHQ advises that the public “avoid water contact with all types of surface water runoff (storm drains, creeks, rivers, and lagoon outlets) and recreational waters within at least 75 feet from where runoff enters ocean and bay waters.”
San Diego county began using a new water quality testing method in May 2022 called droplet digital polymerase chain reaction (ddPCR). This test looks for bacterial DNA, which the county says “has been proven to be more precise and protective of health” in a report that compared the previous culture based method with the ddPCR method. Results are more rapid, so the public can now be updated on water quality the same day samples are taken. Previously, there was a 24 hour delay between sampling and the results being available to the public.
In September of 2022, San Diego received a federal loan of $733 million to repair its old storm drainage system. $36 million is being dedicated to reducing pollution through green infrastructure projects.
Dr Walther offered up a few ideas on how this money should be used.
“Being able to filter our storm runoff would help some, but a lot of that is still after the fact. Really changing our entire transportation system is what would reduce it significantly,” Dr. Walther said. “We have toxins washing in from car oil and other types of metals because of our industry and urban life.”
Changing our transportation would reduce the amount of toxins entering urban runoff in the first place. Dr. Walther suggested the use of drainage and capture systems, like swales and basins, to keep urban runoff out of our storm drains.
“It’s a type of urban planning and restoration that creates places where the water infiltrates and doesn’t go into storm drains. You create these things called swales, it’s a depression so if the water pours into it, it can actually sink into the ground,” said Dr. Walther.
She explained that this allows water to go through a natural filtration system and reduces the severity of floods, because the ground and plants are taking in water.
“Runoff goes from the street, directly into the storm drain, into a channelized pipe, and then into our river system. It’s a very direct and very fast route. But if you actually let water infiltrate the ground, nature does a really great job of cleaning the world for us,” Dr. Walther explained.
The City of San Diego will be conducting repairs and implementing new projects over the next five years. This funding presents an opportunity for the city to amend a primitive drainage system so the city will see lower pollution levels and an increase in the number of days that beaches are open over the next few years.