Wednesday, August 19, 2015

Treatment of Locally Stored Peninsula Water Keeps Quality High

The just upgraded Harry Tracy Water Treatment Plant features a new and seismically resistant 11-million-gallon treated water reservoir, along with three new ozone generators and five new filters. 
The improved San Bruno facility now has the capacity to provide 140 million gallons of water per day for 60 days within 24 hours of a major earthquake—enough to supply nearly one million people during that time.

On an average day, Harry Tracy treats about 35 million gallons of water that have been pumped up from storage in the Peninsula Watershed reservoirs below. Within only an hour or so, the raw water undergoes disinfection by ozone, isolation of the solids, filtration and finally post-treatment at the new treated water reservoir. 

The first stop is the ozone station, where this oxidant quickly eats away bacteria and other microbes along with inactivating viruses. Ozone also aids in taste and odor control.

Chemicals are now added to induce particles in the water to coagulate. As the water circulates through a series of rectangular open-air basins, the solids keep merging into increasingly larger clumps called “floc.” 

These are removed in filtration, when the flocculated water passes through two layers-- anthracite (a hard natural goal) and then sand.  (The five newly installed filters raise the plant’s total number to 15.)

Finally, the filtrated water goes to our new treated water reservoir for fluoridation, disinfection, and corrosion control. Now it is ready for distribution to customers in northern San Mateo and San Francisco counties.

The new treated water reservoir rests on 50- to 70-foot-deep pilings, and the entire plant is now capable of withstanding a 7.9 magnitude earthquake. 

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