Gunnison addressing sewer lagoon problems: metering, trash, odor
By Robert Stevens
12-20-2018
GUNNISON—Gunnison City leaders are preparing to make improvements to the sewer system to combat three significant problems.
The city has brought in Jones and DeMille Engineering to find cost efficient solutions to the problems. The firm was scheduled to present its findings to the Gunnison City Council Tuesday night (after press time).
In an interview with the Messenger, Garrick Willden, a Jones and Demille engineer, explained the scope of the improvements which Gunnison Mayor Lori Nay and the city council have asked the firm to address.
The first issue is inability to properly meter the sewage going into the sewer lagoon shared by Gunnison City and Centerfield City.
“This creates a problem because the state requires you to have those numbers, but it also makes it hard to tell how well the lagoon is functioning and at what rate the amount of sewage is increasing each year,” Willden says.
Willden says accurate metering data is needed so the city can increase sewage treatment capacity as the volume of sewage increases.
The inability to meter is caused by the conjoined sewer system and the effect Centerfield City’s sewer output has on the Gunnison City meter.
A meter is already in place, Willden says, but Centerfield sewer system is a type that has to be force-lifted up through the pipes, and when it gets pumped through to the pipe where Gunnison and Centerfield sewers meet, it causes a backflow up the Gunnison City sewer pipe. That influx of reversed sewage throws off the meter and produces inaccurate readings, Willden says.
Willden says the best choice to fix the metering is the installation of a new meter further back upstream in the Gunnison pipes, which will negate the effects from the backflow from Centerfield, restore consistency in the metering data and return the system to state compliance.
Trash
The next problem plaguing the Gunnison City sewer system is trash getting into it. Willden says this is in part due to a large amount of trash that comes through the sewer pipes at the Central Utah Correctional Facility, but also from trash being flushed down the drains of homes and businesses in Gunnison.
The inaccurately named “flushable wipes” that are used primarily for babies are one of the biggest sources of trash coming through the sewer lines, he said.
“People think they can flush baby wipes and stuff like that, but it creates a problem because lagoon systems are setup to handle organic material,” Willden says. “The bugs in the lagoon system can break organic materials down to almost nothing, but systems that have a lot of inorganic trash coming into them can fill up quickly and need drudging. [The sewage] doesn’t break down or go anywhere; it just sits there and fills up [the lagoon].”
The trash that gets flushed at the prison ranges from bed sheets to plastic wrap, and although the prison has a grinder designed to chop up the trash, plenty of sizable pieces get through, contributing to the accumulation of trash in the pipes and lagoon.
It would be economically better if the city moved to a system of screening trash before it gets into the lagoon system, Willden says. By installing a device to screen the sewer trash before it gets to the sewer lagoon, the city can avoid the heavy expense of drudging the lagoon, and instead just clean out the screening device as needed.
Willden says he has been exploring a number of options for the city, and while original cost estimates for a screening device were around $150,000, he says they recently found a unit well-suited for Gunnison’s needs for significantly less—approximately $60,000.
The device would collect trash and automatically rake it into a bin to be removed when full. The system would have a float on it that would read the upstream sewer depth. Once the float sensor kicked in, Willden says it would trigger the device to clear the screen of trash build-up.
Strong odors
The third issue Willden is trying to solve is the strong odor that has become prevalent along the main Gunnison City sewer line, which Willden says effectively begins at the prison and runs through town until it reaches the lagoon.
“They’ve had an odor problem all along that line,” Willden says. “It’s hard to tell how much of that is influenced by the prison, but it does start where the prison sewer comes into the main line.”
Willden says the exact cause of the odor is hard to pin down, but from previous experience, he suspects pipes clogging and backing up, which hinder the sewer’s vital aerobic process. Without a working aerobic process, which breaks down organic sewer materials, the problem can lead to unwanted chemical reactions in the system, and with them, bad microbes, gases and smells.
“What’s worse than the bad smell is the gas created can become concentrated and acidic,” Willden says. “It can eat through concrete.”
Willden says the sewer lines are made up of PVC, so they are resistant to corrosion from acid, but many other components of the system are not PVC. Exposure to the acid can cause problems for the sewer system in the long run.
To solve the odor (and acid) problem, Willden says the most efficient and affordable option is to introduce a specialized microbe into the sewer system.
Manufactured by the company ATS, which specializes in sewer treatment, the microbes compete for the resources that feed bad bacteria.
“They are very specialized,” Wllden says. “It works because they use the same food sources, but you have to continue to put a dosage of these bugs in the system every day to keep it up.”
By eating all the bad microbes’ food, the ATS microbes keep them at bay if they remain at consistent levels in the sewer system.
The cost for the ATS microbes is approximately $8,000 per year, which Willden says is by far the most cost-effective method of combating the issue.
“Right now I am showing the city some of the most cost-effective options out there and once we have honed down which directions to take, we will pursue funding for the project,” Willden says.
