Turn On The Pumps!

  |   Creeks, History, Mass Transit, The Mission, Watershed   |   2 Comments


If you think the streets are bad after today’s downpour, you should see what’s going on underneath the streets.

San Francisco has an antiquated sewer system, but with a “green” twist. It’s the only community in California that operates a predominantly “combined” system, which means our wastewater and our stormwater flow through the same pipes to the ocean/Bay. More after the jump…

During storms, of course, there’s a sudden surge in flow, which means the North Point Wet Weather Facility fires up to deal with flows from the northeastern section of the city. In one hour, the operators can increase the flow rate from zero to 150 million gallons per day. Is that enough?

And is that the only part of the city that needs the extra capacity? You decide:

When older cities installed combined systems, it was before there was such a thing as water treatment. They’d just route all waste and stormwater into the nearest, largest body of water. Once water treatment was developed, most cities decided to bracket out the water from storms, and build a separate drainage for wastewater in order to lessen the amount of treatment needed.

In San Francisco, this was deemed a bad solution because of the excessive cost and disruption of ripping up every street to install all the new tunnels. So we said screw it and kept the combined system, choosing eventually to treat all of the water, stormwater included. Most combined systems operate in a way that just shuffles any overflow in the system straight to the drainage destination, including wastewater! Kind of like this:

Not ours. We treat it all. (Filthy Canadians.)

This turns out to be smart environmentally, because stormwater is highly polluted since it basically washes loose all the accrued leavings we deposit on paved surfaces. So the Bay and the Pacific Ocean are cleaner than if we had a separated system. All our water gets treated before it’s dumped, and we only swim in our own feces on days like today when the system backs up entirely – yay us!

Additionally, we’ve now begun to mimic natural watershed processes by redirecting some of the runoff to vegetated areas which reduce, filter, and slow stormwater runoff, lessening the burden on the combined sewer system.

Maybe the city should pick up the pace on that last initiative. Obama? Stimulus? Nevermind.

UPDATE: The SF Sewers Blog (yes there is such a thing!) points out that over $150 million has been spent on SF’s sewers over the past 5 years.

  • mat | Oct 19, 2009 at 7:49 pm

    Great post by @thebonobo explaining why rain makes SF’s combined sewer system go Boom!

  • Laura | Oct 23, 2009 at 3:13 pm

    Actually, the majority the actual city of Sacramento (Downtown, midtown, East Sacramento, Land Park) are on a combined sewer system. When pumps can’t clear the storm water fast enough, sewage and storm water can back up into the streets. Nice!