Source: http://www.sfgate.com, February 12, 2013
By: Peter Fimrite and Kevin Fagan

A broken pipe sent thousands of gallons of drinking water cascading into San Mateo Creek over the weekend, killing scores, possibly thousands, of fish from chlorine poisoning.
The dead fish began floating to the surface Saturday when a thousand gallons a minute of chlorinated water flowed down a forested hillside into the creek about a half-mile below Crystal Springs Reservoir, according to utility officials and residents.
Utility officials located the break in a 60-inch-diameter pipe next to a concrete bridge adjacent to Crystal Springs Road, near the border of Hillsborough and San Mateo. It took them eight hours to cut off the flow along a 4-mile section of pipeline, but water was still leaking out Monday at a rate of 200 gallons a minute, officials said.
The exact death toll has not yet been determined, but at least 30 fish could be seen lying on the bottom and floating along a 100-yard section of the creek, which rolls past stately homes beneath towering oak trees. Rare steelhead trout, which have been listed as threatened along the Central Coast under the Endangered Species Act since 1997, were believed to have been killed.
“It’s bad,” said Stephen Rogers, a local resident who stood along the shaded banks looking at the streambed. “The fish here are an indicator species – like the canary in the coal mine. As long as the canary’s alive, things are fine, but when something like this happens, things are not fine.”
San Mateo Creek flows about 5 miles into San Francisco Bay from the reservoir, which collects rainwater as well as water piped in from Yosemite’s Hetch Hetchy Reservoir. Spanish explorer Juan Bautista de Anza is said to have camped by the creek in 1776.
The San Francisco Public Utilities Commission oversees Crystal Springs and the rest of the sprawling network that supplies drinking water to 2.5 million people in San Francisco, San Mateo, Santa Clara and Alameda counties.
The break, which was first reported at 4 p.m. Saturday, sent up a huge geyser of water that flowed 50 yards down a hillside through a backyard into the creek. The 1932-era pipe was between 3 and 8 feet underground and next to two tall oak trees with large root systems that may have played a part in the leak. Utility officials had been replacing pipe in the area, including a large section last fall.
Aging pipes
“We don’t know if it was corrosion or a seal or what,” said Steven Ritchie, the assistant general manager for water at the utilities commission. “There are joints in pipes. Sometimes they shift. We don’t know exactly why it broke, but it was undoubtedly related to its old age.”
Workers found the break within three hours, but it took several hours before the flow could be substantially reduced. Ritchie said the water flow must be throttled down slowly because if it were shut down all at once, the pressurized water would then back up, creating breaks further up the line.
Halting flow
The flow was only a couple hundred gallons a minute by Sunday morning. By Monday, utility workers had channeled the leaking water into a pool carved out halfway down the hill, where they added sodium bisulphate to remove the chloramine, which the utility uses in drinking water to kill bacteria.
“One of the challenges with drinking water is that the things we need to add to it to make it safe can be toxic out in the environment,” Ritchie said. “The chlorine is what makes it safe for us to drink, but it doesn’t do very well in a stream. It’s basically bleach and it kills fish, but it’s far better to kill micro-organisms that might cause disease than to drink water that has disease-causing agents in it, like cholera.”
Besides trout, sculpin, stickleback and suckerfish were killed. Ducks, great blue herons and other wildlife were feeding on the dead fish, which range in size from 6 inches to a foot.
“I don’t know if it killed all the species,” Rogers said, “but the creek looks sterile. It could take years for it to recover.”
Preventive measures
Officials with the Regional Water Quality Control Board and the California Department of Fish and Wildlife were investigating Monday, but it was too early to tell what, if any, penalties will be instituted.
“As far as I’m concerned, any fish that we kill is a problem,” Ritchie said. “We pride ourselves on taking care of the environment, so this is really of great concern to us. Our job now is to make sure it doesn’t happen again.”