Shining a Light on Clean Water | PCL

Shining a Light on Clean Water

Over 2.5 million thirsty Bay Area residents count on safe, clean water sourced from the Hetch Hetchy, a valley in California’s Yosemite National Park. The water from this pristine area is naturally quite clean—so clean, in fact, that filtration is not required to make it fit for human consumption. But that does not mean the water doesn’t require treatment before it’s safe for drinking. In fact, the US Environmental Protection Agency (EPA) recently updated regulations mandating that all unfiltered water undergo two stages of disinfection prior to reaching consumers’ faucets.

Looking across the main UV reactor room with twelve 48” diameter UV reactor vessels.Looking across the main UV reactor room with
twelve 48” diameter UV reactor vessels.

Aerial view of the Tesla Water Treatment Plant.Aerial view of the Tesla Water Treatment Plant.

“The EPA’s new requirements for secondary disinfection could not be met by the San Francisco Public Utilities Commission’s (SFPUC) existing system,” said Dan Miller, engineering manager at PCL. “The PCL/Stantec design-build team was selected to help complete modernizations as part of a larger, system-wide project.”
Located 80 miles east of San Francisco in the Western foothills of the San Joaquin Valley, the Tesla Treatment Facility uses ultraviolet (UV) water treatment disinfection technology in addition to traditional treatment procedures. The third-largest water treatment facility of its kind in North America at the time of its construction, the Tesla Treatment Facility treats up to 315 million gallons of water per day.

Blinded By the Light

UV water disinfection technology works by subjecting microorganisms to short wavelength light that disables the potentially dangerous creatures living in the water. Water is forced past clusters of high-powered UV lights located within the existing transmission lines, exposing the pathogens to the treatment as they move past the lights. Parasites like Cryptosporidia and Giardia, both resistant to chemical disinfectants, are susceptible to UV water treatment, meaning that this new technology is essential to protecting consumers from harm.
“The large scale use of UV technology to disinfect water is a relatively state-of-the-art method,” said Miller. “The benefit is that, in combination with traditional disinfection, UV treated water at the Tesla Water Treatment Facility is disinfected to a level above the EPA’s strict standards.”

Leading-edge Technology, Innovative Build

The project’s success hinged on the PCL team’s ability to tie in the new UV piping to the existing water transmission lines within two annually scheduled 36-day system shutdowns. To overcome these challenges, PCL devised a way to complete the installation during just one shutdown. This counterintuitive approach—essentially building a project from the inside out—meant that construction could be completed cheaper, faster, and with fewer disruptions to the water transmission line. Once the UV piping was installed, the remaining project was built over the now live water transmission lines. Comparable projects typically take up to four years to complete. Thanks to this innovative tactic, however, the Tesla Treatment Facility was designed, built, and commissioned in just over two years.
Aside from these novel methods of project delivery, the Tesla Treatment Facility’s legacy is a state-of-the-art, earthquake-resistant facility providing safe, clean water free from any residual chemicals. But for Bay Area residents, knowledge that the water that comes out of their faucets is reliable and healthy is surely enough to prove the Tesla Treatment Facility’s value.

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