LARGO — It was more than just the rain dumped by Hurricane Hermine that ravaged Largo's sewerage system this month, resulting in an estimated 24 million gallons of overflows.
Construction on three projects contributed to the mess, city officials said — projects aimed at preventing the same spills that led to contamination and an unambiguous stench in some city neighborhoods.
About 24.4 million gallons were discharged from the city's system, as of Tuesday the fourth highest amount in the Tampa Bay area behind St. Petersburg, Pasco County and Clearwater. About half was untreated sewage and rainwater spewing from 22 manholes around the city. Roughly 11.9 million gallons were discharged from the treatment plant into Cross Bayou that hadn't been dechlorinated, the last step of treatment. And the actual total is higher — quantities from nine manholes were labeled "unknown."
The overflows were caused by heavy rainfall coupled with ongoing construction for three projects totaling about $80 million that will increase capacity of the system. Two are the result of a state order issued in 2006 to bring the sewerage system into compliance with state standards. The city has until January 2018 to fulfill it.
When the projects are complete, the system will meet a state requirement to handle a 10-year storm, or one that drops 7.5 inches of rain in 24 hours. Overflows would most likely still happen during a storm that had as much rain as Hermine, which dumped 11 inches on the first day, Kety said.
One project that will change the way sewage is disinfected made two holding tanks unavailable while they're reconstructed. The water that would normally go there was diverted to a long, narrow filtration tank that couldn't hold enough to keep up with the flow during the storm.
"We feel that if we had those other tanks online — if construction was finished — we probably would not have had any discharge to Cross Bayou even with the high flows," Kety said.
Another project, known as the headworks project, includes construction of a 5 million-gallon tank that can hold sewage during events such as Hermine, when flow at the plant is high, and feed it through the treatment process once the flow dies down.
During the storm, the city repurposed two tanks normally used to separate and digest solids to hold incoming sewage. Those hold slightly less than 1.5 million gallons, said Gary Glascock, the city's wastewater manager.
The projects will allow the plant to take about 32 million gallons through the treatment process, Glascock said, with more that can be diverted into the 5 million gallon storage tank. During Hermine, the plant flow hit about 30 million gallons, according to a city storm report. Discharge into Cross Bayou ended Sept. 4, the Sunday after the storm.
The third and most expensive project, with a price tag of about $38 million, will alleviate overflows at some trouble spots around the city in two ways.
Seven pump stations with the highest flows will be upsized to handle higher capacities. For example, one of the stations on Lake Avenue next to Highland Recreation Complex is connected to manholes at Golf Lake Condominiums, City Hall and the police department, where a total of about 2.5 million gallons spilled over, as well as Country Club Drive, one of the unknown quantity spots.
The project includes a pressurized pipe, similar to a hose, that will run through the seven stations. When flows increase, the pipe will push sewage across the city directly to the plant quicker than stations along the way that pump into a pipe that uses gravity to transport sewage.
That project is expected to wrap up this month, with the disinfection project slated for December and the headworks for next fall.
"We have one more wet season to go before all the pieces come together," Glascock said.
To calculate the total amount of rainwater and sewage seeping, and sometimes gushing, from the manholes, city staff monitored the sites and visually compared the flow with a set of nine photos showing manholes overflowing at rates from 5 to 275 gallons per minute, Kety said.
For the nine manholes that weren't counted, he said it was a matter of prioritizing his crews. Some areas of the city were more at risk for sewage backups into homes and businesses, so he focused resources on preventing backups instead of positioning someone at a manhole to monitor the flow.
"We're trying to keep our system functioning so people's homes don't get backed up," he said.
Manhole overflows have since ended. Now, the city is focused on cleanup. Crews are in the process of raking and vacuuming debris and dispersing a powder disinfectant if needed, Kety said. Residents with damage as a result of the overflows can call the city's risk management department at (727) 587-6716.
The city also identified 13 sites to sample for fecal bacteria. As of Tuesday, 12 have been cleared, said Mike Julio, environmental compliance supervisor. The city is still monitoring a retention pond at Golf Lake Condominiums, which Julio is hoping will be cleared by the end of this week.
The pond has no exit site, so the bacteria "has to keep breaking down, breaking down until there's nothing left," which takes longer, Julio said. The city has placed signs around the pond to warn residents of contamination.
Contact Kathryn Varn at (727) 893-8913 or firstname.lastname@example.org. Follow @kathrynvarn.