“Hermine’s heavy rains causing sewage woes across Tampa Bay” (Tampa Bay Times)
“Sewage Overflow Again Fouls Tampa Bay After Storm” (New York Times)
“Hurricane Hermine’s Aftermath: Sewage Flowed into Clearwater Harbor, Old Tampa Bay” (Clearwater Patch)
Hurricane Hermine wreaked havoc across Florida’s Gulf Coast during 2016. Unfortunately, its havoc continues in the shape of damaged sewer system lift stations and massive manhole infiltration.
Foundation Professionals of Florida is one of the contractors tackling the problem at its source: down inside sanitary sewer system manholes across the region.
The Nature of the Problem
A gravity fed sewer system flows to a lift station that sends the water to a wastewater treatment facility. When the system gets overrun — which can happen with major rain events such as a hurricane or tropical storm — the additional volume exceeds the capacity of lift station pumps.
When volume overwhelms the system, the system backs up. This further strains the system, causing overflows, sewage backups into houses, and discharges of untreated sewage into waterways and wetlands. This is precisely what happened during and after Hermine hit Florida.
Storm-related inflow aggravates existing infiltration within a system. As they age, sewer systems typically develop leaks that add infiltration, which adds to capacity issues on a day-to-day basis. Inflow and infiltration — or I/I — is a problem from both a capacity and cost issue. The cost of treating additional water can be a budget killer, but I/I can also be a major contributor to system capacity problems. In extreme cases, I/I alone can overwhelm the capacity of the collection system.
Do the math. If one manhole leak adds 5 gallons per minute (gpm), that is 300 additional gallons of water an hour needing treatment. If a system can handle 50,000 gallons per hour, and average daily sewer flow uses — very conservatively — 75 percent of that capacity, it takes only 50 leaking manholes to overburden the system. From a cost perspective, that 5 gpm leak means 2.6 million gallons of additional volume to be treated. If treatment cost is roughly $3 per 1,000 gallons, that is $7,800 per manhole in a year. This does not take into account the cost to run the system longer to keep up with the additional volume nor does it include costly EPA fines for sanitary sewer overflows or failure of the structures while in service.
In the case of central Florida, already high groundwater was raised with rainwater, causing surface inflow and exacerbating infiltration by increasing the hydrostatic pressure on existing cracks. Several overflows have happened in the days and weeks following the storm.
“We’re still seeing problems weeks later because the water table is still elevated and the increased hydrostatic pressure has increased failures,” says Foundation Pros general manager Daniel Stagg. “Cracks have widened and new defects have appeared.”
Challenge of Repairs
The challenge with repairing any collection system is the time and resources needed. An old-fashioned excavation repair or replacement of the failing portions “takes an enormous amount of money and time plus impeded vehicular traffic with road closures,” says Stagg. “That means commuter inconvenience, taxpayer frustration, government official frustration, and so on. It’s a vicious cycle.”
Foundation Professionals of Florida takes a trenchless approach instead. The contractor tackles the challenge of I/I inside the manhole structures and the lift stations themselves with two different polyurethane injection resins from Prime Resins.
“We stop the leaks by pumping out the structure, going down the hole and starting the process from the bottom up,” says Stagg. “We stop the gushing leaks with Hydro Gel, injecting from the bottom up.” Prime Flex Hydro Gel SX is a hydrophilic polyurethane resin from Prime Resins that forms a tenacious bond with concrete and remains flexible after curing, making it a great choice for structures subject to vibration as are many manholes.
“Once the gushing leaks are stopped, we follow that with injection of Prime Flex 920 to encapsulate the problem area,” says Stagg. Prime Resins’ Prime Flex 920 is a hydrophobic polyurethane that forms a watertight, rigid foam. It has the added benefit of being certified as compliant with NSF/ANSI Standard 61 for contact with potable water.
“We like 920 for the ease of application, how well it permeates the soil and because we are able to control the reaction time,” says Stagg. Technicians control the reaction time with the amount of catalyst added to the resin. Prime Flex 920’s reaction time ranges from 4 to 13 seconds and a full cure time of 5 to 90 seconds, depending on catalyst ratio. The speed of the resin allows for efficient and effective curtain grouting.
Once the crew is finished and the manholes are leak-free, some of them are subsequently lined for structural protection, particularly if those manholes are part of an ongoing capital improvement project. Some of the manhole structures are so old they are made of brick and benefit from structural support.
The biggest challenge with the work is the location of the manholes in major intersections and roadways. This requires traffic maintenance protocols and a lot of additional support manpower.
“It’s great to have a customer who is thrilled with the final product,” says Stagg. “They know that the structure is fixed and they can go on to deal with other issues.”
The most rewarding part, however, is benefiting entire areas of communities not just one spot.
“Our work is protecting the environment, people’s homes and their investments,” says Stagg. “It is rewarding to have that much positive impact. We are keeping our drinking water and our rivers clean. We are helping a municipality better serve its customers and doing that in partnership with the municipalities — they are out there with us. When we are successful at eliminating I/I, they can make better use of taxpayer dollars rather than treating extra wastewater.”