Dec 4, 2014

SAN FRANCISCO (KTVU) - In the last few days, many Bay Area storm sewers got their biggest flush out, spewing all kinds of nasty materials out into the Bay.Most Bay Area cities have two sewer systems, one for human waste, the other for storm runoff.

In runoff systems anything that goes into the sewer or is already in it ultimately goes into the Bay. Then huge storms come along, which can dislodge toxics, some of which are stuck in sewers for decades.

Senior scientist Lester McKee of the SF Bay Estuary Institute uses sophisticated instruments to collect and analyze runoff in storm sewers.

A sample taken Wednesday will have oils, grease, fertilizer; pesticides, carcinogens and toxic heavy metals such as mercury, copper and zinc, some decades old.

"Build up and wash off. Especially an intense rain like we've just had, we can see a lot more of that contamination running into the Bay, "says McKee.

In the short-term the toxic brew can injure or kill some wildlife – long-term it can build up in their bodies, which is why eating Bay fish must be limited.

San Francisco, on the other hand, has a combined system. "We treat all the waste water from homes and businesses as well as all the storm water falling on the city streets in the same network of pipes," says Jean Walsh a spokeswoman for the San Francisco Public Utilities Commission.

For most storms, the city can store runoff in huge underground concrete caves, so none gets into the Bay. "On a day like we've had recently with all that rain, we're treating up to eight times as much water," says Walsh.

On such rare occasions, discharge points allow partially treated sewage to get into the Bay for short periods of time to avoid sewage backing up in homes and businesses.

But, the city is trying to eliminate that with what's called green infrastructure. Green infrastructure involves small and large plots of plants, land and special concrete engineered to store water. It's kind of like a giant sponge that holds excessive rainfall.

As water flows into those areas, big debris is trapped on the surface so it never even get into the sewer system.

The water underneath will either soak into the ground, evaporate out or ultimately gravity feed into the treatment plant. Another green feature is porous concrete. The water goes directly into through the concrete which has many openings and then into the ground where it's absorbed.

"Green infrastructure is pretty, it's out on the streets, it's permeable pavement, planters, it's plants and it creates habitat for birds and butterflies," says SFPUC's Walsh.

Full article here:

Associated Staff: 
Programs and Focus Areas: 
Clean Water Program