Insight and solutions to rain runoff issues in San Mateo County

There are a few main aspects to the water pollution issue.

“It kind of stems from the way the system is designed,” Bogert said.

He explained that when it rains, the water flows through paved streets picking up sediments such as plastic, trash, motor oils, pesticides and other chemicals.

During heavy rainfall, the county’s storm drain system becomes overwhelmed and much of that polluted water washes away into the creeks that eventually lead to the Bay or ocean.

Another issue is that because water is moving through hard surfaces like pipes and streets, the water cycle is disrupted because it’s not able to infiltrate the soil.

“It can impact the way that creeks operate, it can lead to downstream flooding issues or localized flooding in streets and roads. And so that’s another issue especially as we have bigger storms,” Bogert said.

Trash is another cause for concern. The county has worked diligently with its cities to create ordinances and bans to prevent plastic bags, styrofoam boxes and plasticware from being used and provided in the food service industry and commercial industry.

“But there’s a lot of work being done to install trash capture devices in the storm drain system throughout the county. And so the cities and towns and counties have invested heavily in that over the past decade or so to prevent trash issues,” Bogert said.

Another issue with the water in the Bay, ocean and other waterways is the polychlorinated biphenyls, a legacy pollutant left behind from old industrial uses, and mercury through atmospheric deposition.

“There are limits to how much of that type of pollution can enter the Bay. And so the cities, towns and counties are really focused on those in particular,” Bogert said.

Solutions

One way officials are mitigating those issues is by installing more green infrastructure.

“And these are small infrastructure systems that you can add into a roadway project, like street crossing improvement. And they can be extensions of the curb where the water runs through the rain garden or curb extension, and then infiltrates into the soil, cleans up the polluted water before it goes back into the storm system or infiltrates into the groundwater,” Bogert said.

Azalea Mitch, director of Public Works for the city of San Mateo, said that on an average day the city treats around 10 million gallons of sewage.

“When it rains, stormwater enters our sanitary sewer system and reaches our wastewater treatment plant. With the projects and upgrades that are part of the Clean Water Program, we will be able to hold and treat a maximum of 78 million gallons per day when it rains,” Mitch said.

According to the San Mateo Clean Water Program’s website, the Wastewater Treatment Plant expansion project is planned to be completed by summer of 2024. San Mateo is currently under a cease and desist order issued by the Regional Water Quality Control Board to put an end to sanitary sewer overflows. Overflow occurs during heavy rainfall when more water enters the system than its capacity. The Underground Flow Equalization System currently being constructed on Saratoga Drive will be an underground structure that will hold an additional 5.3 million gallons of water to help rid of SSOs in San Mateo that is set to be completed by spring 2023.

Bogert suggests taking a “boots on ground” approach to the water quality issue and wants to raise awareness to residents.

He said there are plenty of opportunities for the county’s residents to take action and be a part of the solution. Rain barrels are a great way to collect rainwater runoff from their roof and use for landscaping or house plants.

Another suggestion, creating rain gardens.

“You can dig out a small area of a lawn, say, replace it with more drought tolerant plants, and create a little recessed area where the water can collect during a storm event. And it prevents it from adding to the runoff that’s flowing through the larger system,” Bogert said.

The county also offers rebate programs for residents to make these green infrastructure projects more financially feasible.