The city of Atlanta, GA, is taking a proactive approach in keeping its sewage system and pumping stations in the best working condition possible.
In a recently completed job, a sewage pumping station rehab project at Utoy Waste Treatment Facility, was done by Archer Western of Atlanta, GA, and the subcontractor Gould & Associates-NES Pumping Systems, also of Atlanta, GA, and Houston, TX.
“We’re putting in the new valves where the flow comes in on four different pumps, that are 30 in.,” explained Larry Appling of Archer Western.
The project required that the pump station be shut down during the rehab which required a bypass route for the sewage.
Gould & Associates subcontracted a 50-million gallon per day (mgd) bypass on this pump station.
The job was set up with seven pumps. There were manholes right before the sewer line gets to the pump station. Contractors were intercepting the flow there and pumping it into a bypass structure on the other side of the building.
With this system, Appling said, “We don’t have sewage coming into the front of the station now. We have a big plug put in the line so the water that does get by the pumps can’t get into the pump station and they just keep pumping.”
The company was also putting up a new divider wall in the wet well area to hold the sewage. The divider has a gate in it so that the crew can isolate one half of the pump station from the other.
“We remodeled the inflow gates because they were leaking. They are 30 years old and had to have new parts put on them,” Appling added.
The company also put in a concrete grit structure, which is a round concrete tank, with a 13-ft. (4 m) inside diameter. Workers sunk it 56 ft. (17 m) into the ground. According to Appling, the grit structure takes solids such as sands, grit and rock and settles them into the bottom before they get a chance to get into the pump station.
“They come and clean the grit structure out every month so it doesn’t fill up in the bottom. You have a pipe coming in on both sides and the tank sets below the pipe, so it spills into the tank and the tank fills up and runs out the other side. All the solids wind up in the bottom,” he added.
When a bypass is being done, the solids get pumped through the system, Appling said, and goes on to a treatment plant that is about three miles down the road from the station.
Some of the machinery used on the job included: a Grove RT635C, Ingersoll-Rand GR642 telehandler, three 14-in. (36 cm) pumps, two 16-in. (41 cm) pumps and two 12-in. (30 cm) pumps. Together these pumps have a maximum capacity of 53 million gallons per day, according to Ladd Gould, NES Pumping inside project manager and sales rep.
All of the pumps were piped into a header pipe with check valves and an air relieve valve to allow air to escape. This allowed for no problems on the line, Gould said. If one pipe went down, the company can still depend on the other pumps until it is replaced or fixed.
“The header pipe goes down into the sewer system. It is a permanent piece here for this exact type of work. This area was designed to do a bypass if need be,” Gould said.
The pumps used about 500 to 600 gal. (1,892 to 2,271 L) of fuel per day for the pumps. When it rained, Gould said, it went up to 1,000 gal. (3.785 L) per day, he added.
Before Gould and Archer Western were finished with the project, they have to make sure the pump station is working correctly.
They do this by going back online a few days after workers have completed the bypass work. “The pumps will come off line. Then, they will open the valve and turn the pumps they are using right now off. The original pumps will then go back to doing it themselves. We will then remove the plug,” Appling explained.
Before the company shuts the pumps off, it took the pump out while there was still some flow coming in.
“We’ll leave the pumps running until we get the wet well full, then we will turn the pumps on in the pump station. We’ll then turn the bypass pumps off and let them idle so that more water can come back and see if the pump station is operating correctly. If there is no problems, we’ll shut those pumps off and take them around,” Appling said.
The project, Appling noted, lasted five weeks. It could have gone longer, because there are a lot of things that can go wrong with a rehab.
“If you get a big rain storm and the water infiltrates the sewer system, there’s always the possibility that the water can get to be more than the pumps can handle. If that happens, you lose your bypass plug and plug your pumps shut. Luck has a lot to do with these jobs. Luck and weather,” he said.
And there had been some obstacles to this job, he added.
The biggest problem, he said, was sinking the concrete tube in the ground.
“We poured it on top of the ground and dug the center out. The weight of it let it sink as we excavated it from the inside. We had to go through an existing 66 in. (168 cm) concrete pipe that was down in the ground. Once we got to that pipe, from there down it was all rock, so we had to shoot a lot of dynamite [about seven times] to sink it the last 12 ft. That was the biggest challenge of the whole project,” Appling stated.
He added that they knew that the rock was coming so they were prepared for it. He also said that the companies were happy with the way the project is going. “It’s been a real good job,” he said.
Another obstacle occurred during a rain storm, according to Daniel Betancourt of NES Pumping Systems. One time, he said, a piece of 10-in. (25 cm) rock got stuck in the pump and chewed off the blades of the impeller. The impeller is a piece inside the pump that moves the liquid.
There was an influx of water because of the rain storm. All rain water flows into the sewer. On a normal day, there is 10 million gallons of water a day. As all the storm sewers in Atlanta are connected, this can go to 50 million gallons in a matter of minutes when there is a rain storm, Betancourt said.
“When doing a bypass, you have to figure out the peak flow that the pump station can handle. When the rock got sucked up and broke the impeller, it was 3:30 a.m. It was fixed the next day by 4 p.m. and running perfectly,” he added.
Anytime a machine goes down on the site, the crew has been trained to deal with it right away, Betancourt explained.
“We have to get it back on-line as soon as it goes down. We are never down for more than six hours. If we need extra help we call the mechanics,” he said.
According to Gould, there were workers on site around the clock in 12-hour shifts. “If something should happen, we have the tools to fix the pumps. NES is on call 24/7. If something goes wrong, the crew can call the answering service and get a mechanic out here to fix it,” he said.
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