Master plan of city’s wastewater system will be vital in preventing future sewage spills, Utilities Department director says

Commissioner Brody asks questions about December 2018 incident that led to discharge of about 918,000 gallons of untreated wastewater

The December 2018 wastewater discharge was in the vicinity of the Centennial Park Boat Ramp and Hog Creek, which is located near the intersection of 11th Street and U.S. 41. Image from Google Maps

A Dec. 20, 2018 City of Sarasota pipeline rupture that led to the discharge of approximately 918,000 gallons of untreated wastewater into Sarasota Bay underscores the need to deal with aging infrastructure, Bill Riebe, the city’s Utilities Department director, told the City Commission this week.

City staff is at work on a master plan designed to identify the most problematic pipelines, he said during a report on the incident late last year. Work on that plan began last fall, he pointed out, noting that it is being done by people with real world, hands-on experience with wastewater systems.

The document should be ready for City Commission review in June, Riebe said — in time for discussions of the city’s 2020 fiscal year budget.

The December 2018 rupture of the pipeline, which had a 48-inch diameter, most likely was a result of corrosion produced by hydrogen sulfide buildup at the city’s Water Reclamation Facility, Riebe explained to the commission on Feb. 4. “A large amount of [the discharge] ended up in [Sarasota Bay],” Riebe said.

Staff followed the protocols established by the Florida Department of Health and the Florida Department of Environmental Protection (FDEP) for such a situation, Riebe continued, so adequate public notice was provided, to keep people out of the affected areas of the bay. City staff also took water samples as required by the state guidelines, he said.

The Sarasota County Water Atlas shows the area of Hog Creek. Image from the atlas

The Jan. 24 written incident report Riebe prepared for the commission explained that the pipeline ruptured about 9 a.m. on Dec. 20, 2018; city staff was notified of the situation about 10:30 a.m. At approximately 12:30 p.m., the report continued, staff determined that the untreated wastewater had entered the bay at two locations — the Boat Ramp at Centennial Park, located at the intersection of U.S. 41 and 10th Street, and Hog Creek, at the intersection of 11th Street and U.S. 41.

Utilities Department staff formally notified FDEP and the Florida Department of Health in Sarasota County at approximately 4:05 p.m. on Dec. 20, the report noted. The city issued a public notification about 12:30 p.m. on Dec. 21, and the Department of Health issued an advisory on Dec. 22, following the results of the first set of water samples, the report added. (A period of 24 hours is necessary “for bacteriological samples to mature,” the report said.)

The last round of water samples was collected on Dec. 24, the report continued. By Dec. 25, 2018, “[F]ecal coliform levels at all sampling locations were at or below normal background levels,” the report added. Therefore, on Dec. 26, the Department of Health rescinded its health advisory.

“To the best of [Utilities Department staff’s] knowledge, no health issues from the public” resulted from the discharge, the report pointed out.

Staff did hire a contractor to repair the pipe, because of its 14-foot depth and because it is close to the city’s treatment units, Riebe told the commission on Feb. 4. “The repairs … were completed, I think, on Jan. 24. The pipeline’s back in service.”

Commissioner Hagen Brody told Riebe he was concerned because he understood from the report that the pipe was only about 30 years old; yet, the report noted that “a pipeline such as this should last at least 50 years and more probably 75 years.”

How can the city prevent such incidents in the future, Brody asked.

This is the pipeline involved in the December 2018 incident. Image courtesy City of Sarasota

The structure involved in the December 2018 incident is a lined, concrete pipe, Riebe explained. It has a thin steel tube inside that has been coated with concrete. The exterior of the pipe is wrapped with wire, Riebe added, and then more cement or concrete was used to coat the exterior. Nonetheless, Riebe continued, the area of the city system where the rupture occurred has a lot of hydrogen sulfide gas. That leads to the production of sulfuric acid, which attacked the wall of the pipe, he added.

Staff modified the piping configuration in that area, Riebe noted, to try to prevent a recurrence of the December incident.

As for why the pipe failed after such a relatively short life: Some of the materials used in its production could have been defective, he said, for example, or the workmanship could have been faulty when it was constructed. This type of pipe, he explained, is “more susceptible to corrosion than … PVC or vitrified clay pipe. … It’s complicated.”

This is a stack of vitrified clay pipe. Image by Tera Firma via Wikimedia Commons

“I do want to compliment your response [to the discharge] and [City Manager Tom] Barwin’s response to it,” Brody said. “I do believe it could have been a lot worse.”

The master plan and stormwater intrusion

The work on the master plan, Riebe told the commissioners, will provide details about the city’s pipelines, including their diameter, their type and their approximate date of installation, in most cases. “You have to remember the city’s fairly old,” he said, adding that recordkeeping in the 1940s and 1950s was not the best. “So there’s going to be some ‘guesstimate’ of what we do.”

In conjunction with the master plan, Riebe said, staff is undertaking a conditions assessment, focusing on blockages, breaks and stoppages, for example. “That will be codified in this master plan.” Then cost estimates will be assigned to specific projects, he noted.

“We need to hear the good, the bad and the ugly,” Commissioner Brody responded.

Then Brody asked about parts of the report on the December incident regarding stormwater intrusion. He noted that the report mentioned “the heavy amount of rainfall at the time [of the rupture].”

“I don’t think it was the cause of the break,” Riebe replied. The additional pressure from the rainfall could have been a factor, though, Riebe added. “[The pipe] was going to fail, no matter what. It was just a matter of time,” because of the corrosion, Riebe added.

As for stormwater intrusion: Riebe pointed out that the city last year “treated more wastewater than we produced for water, which defies the law of physics.”

Utilities Director Bill Riebe addresses the City Commission on Feb. 4. News Leader image

On the day of the incident, he continued, instead of the average flow of 6 million gallons to 6.5 million gallons per day of wastewater into the Water Reclamation Facility, “we were running almost 23 gallons a day,” after only two hours of rainfall.

The report on the December incident includes the statement, “This excessive flow is due to storm water entering into the City’s sewer collection system (Inflow and Infiltration).”

Riebe explained to the commission that various types of pipe were used in the city system, including “orangeburg,” which is “tar-impregnated cardboard.” That was “really popular in the 1960s,” he noted, “and it just crumbles.”

With the master plan, he continued, “This is going to be a pretty heavy discussion.

Already, he said, the city spends about $2 million a year lining pipelines to try to prevent problems. “Quite frankly, we probably should do more.”

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