An estimated 4.7 million gallons of sewage spilled into a Charlotte creek when a tree broke a 36-inch, underground wastewater pipe after a storm Monday evening, the city’s water utility said Wednesday.
The sewage flowed into Mallard Creek just east of the intersection of North Tryon Street and East Mallard Creek Church Road, near UNC Charlotte, Charlotte Water reported. The spill has been controlled, but it’s expected to take crews two to three days to repair the broken pipe.
The spill is the city’s largest since 2003.
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Raw sewage holds bacteria and disease-carrying contaminants that make human contact risky. Mallard Creek flows east into Cabarrus County and into the Rocky River, but the spill appeared to pose no immediate risk to downstream drinking-water intakes or recreational waters.
The break was found after staff members at the Mallard Creek sewage treatment plant noticed unusually low levels of wastewater flowing into the plant on Tuesday morning. Field crews walked upstream until they found the broken pipe at about noon Tuesday.
Neighbors were notified and work began to control the spill by rigging pumps to leapfrog flowing sewage from one manhole to another around the broken pipe, and then to the treatment plant. The spill was stopped by 8:15 p.m. Tuesday.
“We detected the problem quickly, (but) unfortunately it took us a few hours to find the spill location along Mallard Creek and control the discharge from the broken pipe,” Deputy Director Ron Hargrove said in a statement. “We have to estimate that the spill probably started during the storm or soon thereafter.”
Neighborhoods downstream, the town of Harrisburg and the Cabarrus County water system were notified.
Crews from Storm Water Services helped the utility and contractors remove debris from the creek. The state Department of Environmental Quality sent officials to observe operations.
David Caldwell, an environmental supervisor with Charlotte-Mecklenburg Storm Water Services, said local officials are taking water samples and assessing the spill’s damage. No dead fish or other obvious signs of damage have been found, he said, and bacteria levels in the water are normal.
That’s likely because the spill itself is “long gone,” Caldwell said. The large amount of stormwater flowing down Mallard Creek after Monday’s storm, which dropped about 2 inches of rain on Charlotte, not only helped dilute contaminants in the sewage but quickly washed it downstream.
Still, a water-quality monitor near the spill site showed that oxygen levels in the creek plunged for about 24 hours between Tuesday morning and midday Wednesday, Caldwell said. Oxygen in water is vital to fish and other aquatic animals. Any fish in the creek at that time probably died, he said, but left little trace as they washed downstream.
Large sewage spills were once common in Charlotte but in recent years have become anomalies. “We’ve had such a great run here, even as the city has grown, of reducing spills and preventing big spills,” Charlotte Water spokesman Cam Coley said.
Spills from Charlotte Water’s 4,300 miles of pipe have steadily declined since 2007, when the Environmental Protection Agency sanctioned the utility for its spills.
In 2003 alone, more than 21 million gallons of sewage overflowed into creeks and Mountain Island Lake, the county's major water supply. But in the most recent fiscal year, ending June 30, spills totaled only 124,000 gallons.
Charlotte Water credits spill-prevention measures including installing larger sewer pipes to handle heavy rains. The utility spends $12 million a year spent to rehabilitate or reline older pipes and has stepped up cleaning of sewer lines and control of tree roots and grease, the leading causes of overflows.