Gwinnett County water department officials have a simple reassuring message for residents: There are no rats in the sewer system as far as they know.
At least not the kind that scurry around on four legs and are likely to make people scream.
They do have a new piece of technology designed to help them fight clogs in the sewer system that has the dubious distinction of sharing a name with the rodent, however. It’s called the Sewer Line Rapid Assessment Tool, or SL-RAT for short, but you’ll be forgiven if you think of something else when you hear it’s other nickname.
The Sewer RAT.
“It’s not a furry (rat), it’s an aluminum one,” Department of Water Resources spokeswoman Karen Shields said.
“And it sings to you,” Preventive Maintenance Tradesman Coordinator Zach Sosebee said.
At its most basic description, the SL-RAT is a sound-based tool used to determine whether there is a clog in a sewer line. It’s the newest tool county officials have in their figurative toolbox to find clogs in Gwinnett’s approximately 3,000 miles of sewer pipes before they can cause a sewage spill in a neighborhood or near one of the county’s waterways.
Each SL-RAT set is comprised of two devices, a transmitter and a receiver, and the county has three sets that have been deployed since it was rolled out last year. Each piece is placed on top of neighboring manholes, meaning each assessment allows crews to confine searches for blockages found by the device to a small area.
“They put a receiver in one end and a transponder at the other end, and it sends acoustic waves all the way through the pipe under here,” Shields said during a recent demonstration of the tool for the Daily Post. “It’s really cool.”
Those acoustic waves can be heard throughout the surrounding area where the assessment is being performed as a repeating series of tones that get progressively louder and higher in pitch. Once the receiver gets the signal, it will evaluate how well the waves traveled through the pipe and give water department workers a score.
The score will tell crews whether the pipe is clean or if there is something in there that could block the flow of sewage.
“It will measure the sound waves that come through the pipe and see how well they come through the pipe,” Sosebee said. “As it does that, it will decide what score it’s going to give. It’s going to rate it, and that will be based on how strong the signal is coming through the pipe.”
The highest number on the scoring scale is a 10, Shields and Sosebee said.
“A 10 is a good score, meaning the pipe is clean, and anything below five means we’ll do certain maintenance things that will flush the line,” Shields said. “Then we’ll check it again. If there’s a low score again, then we’ll put closed circuit TV through it to see what might be going on.”
Sosebee added, “We have gotten a lot of 10s throughout the Gwinnett County system.”
The SL-RATs are somewhat lightweight, weighing about 15 to 25 pounds each, and they are just big enough the stand on top of an open manhole, but they don’t come cheap. Shields said a set costs about $25,000.
The steep cost may be worth the benefits though. The county has also been able to cover more ground in searching pipes for problems with the SL-RAT than they’d been able to do before they had the tool.
From last September to the end of January, for example, crews were able to monitor 189 miles of sewer lines in the county with the SL-RAT.
By comparison, they were able to check 130 miles with closed circuit television monitoring in all of 2016.
Although the SL-RAT is making it possible to check more miles of sewer pipes in a shorter amount of time, water department officials aren’t ready yet to say what impact it’s having on the number of sewage spills that happen in Gwinnett.
“We’ve only had it for five months so it will probably take us at least another five months,” Shields said. “I’d say we’d need to get a good year’s worth of data under our belt in order to go back and see whether we’ve stopped something.”
She added that the department’s data shows that crews found issues in the pipes that needed further inspection in about 5 percent of the inspections that were done in the first five months after the tool was introduced.
“Is that the beginning of a spill? I don’t know,” Shields said. “If we knew where they were going to happen, we’d go and stop them before they did.”
Meanwhile, Sosebee continues to insist that while the county has a new tool with a whimsical name to check sewer lines, there are still none of those other types of rats lurking in the darkened pipes beneath Gwinnett’s streets.
Well, not to his knowledge anyway.
“I’ve heard for years about rats in the sewers, but in my 20 years with Gwinnett County, I’ve never seen a rat in the sewer,” Sosebee said.
Of course, that doesn’t include any singing RATs.