Million of gallons of water wasted in dam safety test

SAN MATEO, Calif. (KGO) -- An estimated 55 million gallons of water was lost on Thursday as part of a safety test carried out by operators of the Hetch Hetchy Water System.

The test was scheduled to coincide with the low tide.

The lower Crystal Springs Dam has been undergoing upgrades and renovation for the past four years, but two new emergency release valves have never been tested. Two state inspectors were on hand to watch as they were opened, sending millions of gallons of water into a basin that feeds into tiny San Mateo Creek.

Every dam in the California needs to be able to reduce volume in case there's a torrential amount of rain or some sort of structural issue with the dam so that we can reduce, in an emergency, what's behind the dam, so there are no issues with that," explained Alison Kastama with the San Francisco Public Utilities Commission, or PUC.

Private homes, apartment buildings and even Mills Hospital sit adjacent to the creek, so this was an important safety test.

It is drinking water that started out as snow melt in the Sierra, which came down by a gravity-fed system to Crystal Springs Reservoir, waiting behind the dam for release to a treatment plant.

The San Francisco PUC, which operates the regional Hetch Hetchy water system, admits it's not a good thing in a drought. But it's necessary.

"It's really a very small percent of what is in the reservoir, which is 22 billion gallons. Unfortunately, sometimes we do have to use water in order to prove that things operate, and the emergency operation of this dam is very critical to the system and to the residents here in the north peninsula," said Kastama.

A team of hydrologic technicians from the U.S. Geological Survey, or USGS, was on hand to measure the amount of water being released.

The creek was checked in advance for debris or logs that might clog the spillway and cause flooding. At one point, the flow was 322 cubic feet per second, raising the creek's level almost two feet.

"It's somewhat fair to think of a cubic foot being a basketball. So to put that in theory, we had 322 basketballs per second going by this bridge - 300, 600, 900. That's a lot of basketballs," said Anthony Guerriero with the USGS.

It took about two and a half hours for the released water to reach the Bay.