The city of Sacramento told Pocket-Greenhaven residents Tuesday that they could resume drinking tap water after new samples were free of the bacteria that prompted a neighborhood-wide boil-water advisory for nearly two days.
City officials said tests conducted Tuesday came back negative for coliform, a bacteria first discovered Wednesday at a city monitoring site. The city lifted its voluntary boil-water advisory in conjunction with the state Division of Drinking Water.
The advisory was issued late Sunday night after the city found “total coliform” bacteria in five successive samples taken from the area. City officials said Monday afternoon that samples taken Sunday came back negative for the bacteria but wanted another day’s worth of tests before giving the all-clear.
Sacramento officials said the city will continue to investigate the source of the bacteria found in the system. The city also will increase the frequency of sampling in the Pocket area to at least three times a week instead of the standard once-weekly practice.
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The city monitors water at about 60 sites each week.
The city didn’t pinpoint an exact cause of the contamination, but officials are checking into a number of possibilities.
“At this point in time, there is no single thing that we’ve identified that could indicate a reason for it,” said Sacramento Water Quality Superintendent Pravani Vandeyar.
“Coliform” is the classification of various types of rod-shaped bacteria that share similar characteristics with the harmful E. coli found in human and animal feces.
Officials routinely sample total coliform because it can act as a bellwether for more harmful microbes.
“If we get anything that looks kind of like E. coli, we get suspicious,” said George Chang, a retired UC Berkeley microbiologist who studied urban water supplies.
A total coliform test, he said, “is easy to do, pretty general and will pick up E. coli, the fecal bacterium, but it will also pick up a bunch of its relatives.”
One of those relatives – a kind of harmless bacterial slime that grows on the inside of the pipes – may have triggered the positive test, Vandeyar said.
She explained that bacterial sludge she described as “biofilm” is present in every water system. Most is killed during chlorination, but some almost always sticks to the inside of pipes.
“What can happen is, if there’s a change in how the water flows, this biofilm can become loose, and that is the possible reason that we saw those positives,” she said. “It can come loose, but over time the chlorine is going to kill it.”
Vandeyar said the city is checking to learn if there was an unauthorized gush from a local hydrant that might have changed water pressure.
Other urban water-supply experts offered different theories.
Stormwater management expert Stacy Hutchinson said the drought may have caused soils around the Pocket area’s underground lines to dry out. Recent rains may have caused the soil to swell as the water table near the Sacramento River rose. The soggy soil, she said, could increase the pressure on the outside of the lines, allowing coliform microbes in the environment to seep in through a leak.
“If we have enough pressure outside those pipes due to really saturated soils or the rising water table, we can actually have water in the outside of the pipe coming back in those same cracks,” said Hutchinson, an associate professor at Kansas State University’s department of biological and agricultural engineering.
Crews around the city have been working during the drought to upgrade leaky water lines and install meters. The majority of the city’s pipes and water mains are 60 to 100 years old. As they degrade, small leaks pop up and water seeps into the ground. City officials estimate that in the drought as many as one in 10 gallons have leaked out.
Vandeyar and another urban water expert said the scenario Hutchinson described is less likely, given that the water lines are under constant pressure.
“Think about it this way: if you have a balloon that’s full of air and you put it into an environment that is toxic, how do you get the toxic material into the balloon?” said John Shaw, civil engineering consultant based in Reno.
You can’t, he said, because “there’s always positive pressure inside that balloon. The same pressure is in water-distribution systems. You’ve got positive pressure that is pushing out, so really nothing can get in.”
Shaw said the most likely culprit for the coliform contamination was from crews working on the lines.
“It’s tough to make sure that all the crews are doing all the things that they need to do in order to keep contamination from getting into one of the pipes,” Shaw said.
Vandeyar said city water crews have been out in the Pocket area performing meter upgrades.
Whatever the cause, the experts said residents should be fine drinking tap water now.
“If they’ve gone through the protocol for testing and given the all clear, then I’d go with it,” Hutchinson said.
Shaw said that in some cities after a coliform scare residents are advised to take the extra precaution of flushing their lines.
“Go around to all the taps in the home, run them all for, say, five minutes, turn them all off, and you should be good to go,” Shaw said.
Meanwhile, the advisory sent residents scrambling to stores to buy bottled water. Schools shut off drinking fountains.
The water advisory also kept some locals from getting a cup of coffee.
Two Starbucks coffee locations, at 1042 Florin Road and 7600 Greenhaven Drive, posted signs Tuesday announcing they would not serve handmade beverages such as espresso drinks. A Starbucks spokeswoman said the company worked with the city and the state Department of Public Health to decide to keep the stores open, but with limited menus.
Some customers walked away without purchasing anything.
Michele Harris, 23, decided to buy an orange juice.
“I thought about just walking away but I figured I was going to come here and get something anyway, so I’ll grab something a little healthier than all of the sugary drinks I was planning on getting,” she said.