Every seven to eight years, U.S. Water schedules the two 650,000 gallon aeration tanks at the Seven Springs wastewater plant to be cleaned. The cleaning requires us to rebalance the plant to run off of only one tank. Unfortunately, this year we discovered that the sluice gate, which can lower the contents in the two aeration tanks, was not functioning, and we were unable to drain either tank. To further compound matters, the top of the gate opening rests 10 feet below hundreds of thousands of gallons of raw sewage, and attempts to assess what the issue could be were merely speculative. Robert Rottini (Lift Station Supervisor) suggested bolting a large plate over the opening, which would allow us to drain one side. However, how do you bolt a roughly 150 lb. piece of aluminum plate, suspended 5’ off the ground, in a tank filled with raw sewage that you can’t see through?
Realizing that we would need a certified team of specialty underwater divers that could get this plate over the port opening for us, we turned to Paul Meding, General Manager of U.S. Submergent, a subcontractor we have worked with previously for help. Paul put us in touch with Jeremiah Duncan over at Underwater Engineering Services (UESI), who specializes in commercial dive projects. After explaining our predicament, Jeremiah assured us he could not only get the plate firmly secured but also walked us through some potential pitfalls we had not considered. Understanding that time was a factor, Jeremiah had his team assembled and was onsite within one week of my first call to him. Within a matter of hours, UESI had attached the plate to the transfer port in zero visibility conditions, and we were able to drain one of the tanks successfully.
Once the team drained the tank, we could see the extent of the damage to the gate and the level of sand/grit & rags that had accumulated at the bottom of the tank over the years. Rough estimates put the removable material at around 240-260 tons, but the real question was how we were going to be able to remove that much material from the tank. After spending several days researching and thinking up different options for removal, we determined the best way to remove the debris would be with a vacuum roll-off box. This box allows the user to hook up a vacuum truck (Vactor) to one end and then connect piping to the other to pull material through the hose and into the roll-off without ever going into the Vactor truck. Our cleaning team entered the tank by uniting over 100 feet of hose to the box and removed the material through the hose. Unfortunately, by the time we could get into the tank, the Florida summer sun was beginning to build up. Even though we had a vacuum of sorts, our team still had to break up the accumulation of rags and shovel the wet sand towards the hose, a laborious endeavor in itself.
We realized this work would be better performed under cooler conditions, so we volunteered to switch to a graveyard shift until the tank had been cleaned. Over three weeks, we removed roughly 300 tons of material to be disposed of offsite at a dumping facility. It was filthy work, and going from working in daylight hours to overnights was no easy task for the crew, but everyone who participated in this project gave it their all and did an exemplary job.