The city of Durham is trying to determine how much untreated sewage spilled into the Eno River late last week after a pump station failed.
The city announced late Friday that as much as 1.3 million gallons made its way into the river before the overflow was discovered and stopped, but a spokesman on Monday said the actual number is probably far less.
The spill look place at the Eno Pump Station, downstream of Old Farm Road Park and near the end of Denfield Street. City officials say a power surge led a valve and pump to fail, causing the station to overflow.
A worker with the city’s Water Management department discovered the overflow during a routine inspection about 6:50 a.m. Friday, said department spokesman Kirk Butts. The department estimates that the pump failure had occurred eight hours earlier, Butts said.
As of late Monday, the city was still trying to determine what caused the power surge and the pump to fail, he said.
The overflow took about five hours to stop, according to a statement from the Water Management department. Temporary backup pumps were used to divert sewage into empty storage tanks on site until a larger pump could be brought in to bypass the station altogether.
City officials think that the majority of solid material in the sewage was trapped behind a coffer dam that had been recently built just downstream of the station as part of a project to replace sewer pipes along the Eno River. The pump station is the largest of 64 in the city’s wastewaster system that keep sewage moving in places where gravity isn’t enough.
Butts said the city initially estimated that 1.3 million gallons had spilled, based on the amount of wastewater that did not make it to the city’s treatment plant. But that figure will likely change when the city accounts for the waste diverted into the storage tanks, he said.
“We are calculating and revising totals but are confident the actual spillage was far less than 1.3 million gallons,” he wrote in an email.
Cleanup efforts continued late Monday. Butts said the city had received no reports of fish kills or other environmental problems downstream of the station. The Eno River flows in to Falls Lake, the largest source of drinking water for Wake County.
Later on Friday, city workers found that sewage had spilled from a pipe off Denfield Street into a tributary of the Eno near the station. City officials estimate that 50,000 gallons of untreated sewage spilled in that case because of a “defect in a manhole.”