When untreated sewage poured from a treatment plant in southern East Baton Rouge Parish last week, flooding residential streets and homes, it was the fifth time that plant overflowed this year, state records show. 

The sewage flowed from the South Wastewater Treatment Plant along Gardere Lane for about two hours on Sept. 29 amid a downpour. Pumps failed around 3 p.m., causing the waterways to back up and overflow, city-parish Assistant Chief Administrative Officer Kelvin Hill said.

At least 31 apartment units flooded during the event. The cause of the pumps’ failure was still under investigation Tuesday, city-parish spokesman Mark Armstrong said.

It’s unknown how much sewage escaped from the plant during the most recent event. But the two largest incidents earlier this year released a combined 38 million gallons of sewage onto plant grounds and the surrounding areas, according to Louisiana Department of Environmental Quality records.

The four prior events this year all occurred during heavy rainfall that caused flooding at the plant, Armstrong said.

Following the most recent flood, residents who live nearby complained of longstanding issues with sewage odors emanating from the plant.

One of the incidents at the plant occurred Sept. 15, just two weeks before the recent flood, when heavy rain from Tropical Storm Nicholas caused equalization tanks, — the large white storage containers near the back of the property — to overflow. Roughly 22 million gallons of untreated wastewater flowed onto plant grounds and into Bayou Fountain, according to a report of the incident.

A May storm that caused flooding across much of the southern portion of the parish also caused sewage to escape from containers at the plant. On May 18, tanks again overflowed at the plant, although no sewage escaped plant grounds, according to an incident report. The report did not include an estimate of how much wastewater overflowed from the tanks.

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On March 23, another overflow occurred when electrical issues caused a pump to fail amid a storm. An estimated 25,000 gallons of wastewater flooded onto the grounds of the plant during that event, according to an incident report.

The first event of the year occurred Feb. 12, when heavy rainfall caused an overflow at the plant. An estimated 16 million gallons of “sanitary wastewater” spilled onto the plant grounds and into nearby woods over the course of seven hours. Two tanks at the plant were shut down in order to prevent an overflow “near the residential properties to the east of the plant,” according to an incident report.

None of the previous four events caused flooding in any residential properties, Armstrong said.

While the cause of the Sept. 29 flood is still under investigation, Armstrong attributed the four prior overflows to heavy rainfall and “illicit tie ins,” or illegal drainage systems in the area that run into the plant’s pipes. Those causes do not explain the Sept. 29 incident, Armstrong said.

“When the investigation is complete and the cause is determined, corrective action will be taken,” Armstrong said. “A very serious event happened out there, and we’re taking it very seriously.”

The city-parish’s sewage system has been under scrutiny from state and federal regulators for decades. In 1988, the plant and the city-parish’s overall system entered into a consent decree, an agreement with federal regulators aimed at bringing out of compliance systems into compliance with federal laws.

LDEQ was unable to comment on the recent overflows due to the ongoing consent decree because infractions are handled under the agreement with federal regulators, LDEQ Press Secretary Greg Langley said.

The agreement requires the city-parish to make improvements at all of its wastewater plants, which had been violating water quality regulations under the federal Clean Water Act, according to a city-parish factsheet on the agreement.

The agreement has been revised several times since its implementation, most recently in 2009. The city-parish is undertaking projects to improve its wastewater storage and treatment facilities and expand its wastewater storage capacity, according to the agreement.