It wasn't that there was dirt in the water. It was that the water tasted like dirt.
All told, the Gwinnett County received more than 950 complaints about the way the water tasted or smelled over two weeks starting March 29.
The cause was geosmin in Lake Lanier, a substance that is formed when algae die. Gwinnett’s Department of Water Resources tests for it on a monthly basis. It can be detectable on the tongue when levels are as low as 5 nanograms per liter and tastes earthy, like beets. In March, tests near one water intake in Lake Lanier showed levels at 7.4 nanograms per liter.
It’s been nearly two decades since the county has fielded complaints about the taste of the water — ever since an ozonation system was added in 1998 that both disinfects the water and neutralizes any agents that might affect its taste. It took water leaders three days to figure out that complaints were about the taste of dirt, and not actual dirt in the water.
Ordinarily, the addition of ozone to the water would take care of the geosmin, said Tyler Richards, the assistant director of the county’s water department. But the system had been taken down March 26 to repair a bend in a pipe. While workers added chlorine to make sure the water was safe to drink, they didn’t pay attention to the level of geosmin before scheduling the maintenance and weren’t focused on how the water would taste.
“I could smell the chlorine, with a lovely swamp aftertaste,” said Rebecca Shelton, the deputy director of field operations for the water department. “It was not my normal Gwinnett County water.”
Only the northern part of the county was affected. For those 56,000 customers, water was coming from the Lanier Filter Plant. The rest of the county was being served by another part of the lake and was filtered through the Shoal Creek Filter Plant.
Compounding the issue, a pump at the Lanier plant went down early March 29 and had to be restarted. It’s not an uncommon occurrence, Richards said, but such a restart often unsettles sediment and makes the water look cloudy. Employees who were hearing complaints about dirt attributed them to the restarted pump.
Typically, the department flushes the water out of hydrants when such complaints come through, to get rid of the problematic water. But even after flushing occurred, the complaints continued to rise. That was the clue that something more was going on.
On March 31, workers changed the intake to another part of the lake where geosmin levels were lower, preventing more of that water from entering the water system.
But the treated foul-tasting water still lingered in the pipes and through the system. At one point, in Buford, the level was as high as 30 nanograms per liter. So the county flushed again. All told, about 20 million gallons were flushed — insignificant for a water system that produces about 4 billion gallons each month. Still, some complaints came in as late as April 13.
In part, Richards said, the problem took a little bit longer to identify because the county hasn’t had similar issues for so many years. Gwinnett “was a victim of our own success,” she said.
“The lesson we learned is that aesthetics are important,” Richards said. “It’s something everybody is very aware of now.”
Richards and others are debating whether to test for geosmin and other substances more frequently — it costs between $600 and $800 each time samples are taken. Richards said in the future, workers at the filter plants will be alerted when geosmin levels are high.
“We have great water here,” Richards said. “People are not expecting to have this kind of issue.”
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