October 20, 2009
The First Flush: It is not what you think!
Last week was our first big rainstorm of the season in San Francisco. In the wastewater business the "first flush" refers to the initial rainwater that runs off the street into a storm drain (or San Francisco's case a catch basin!). While the rainwater itself is clean, the stuff it picks up off the street is not. Think of the motor oil, brake dust, garden chemicals, paint, etc., that end up washing into the system.
That's where the beauty of San Francisco's combined sewer system comes into play. Since we have one sewer pipe for both our sewage and stormwater that connects to our treatment plants. Our system provides full treatment for "first flush" pollutants.
Fancy that! So why do you think San Francisco is the one of only two places in California that has a combined sewer system? Can you guess where the other combined sewer system is located. (HINT: It is Old......)
Stay tuned for the answer.