By COREY NOLES
Statesman Staff Writer
City workers have had a difficult time regulating certain levels within one of the department's wastewater lagoons in recent months.
The problem lies in the city's east lagoon. It began shortly after a project that was aimed at increasing aeration to handle a higher volume of waste coming from the Tyson Foods plant in the southeast section of Dexter was completed.
City Engineer Richard Cochran, Jr. said the city has been working in conjunction with the Missouri Department of Natural Resources (DNR) to monitor and lower the ammonia levels in water leaving the east lagoon.
The problem, he said, is specifically in the northwest cell of the lagoon and it's not a new issue. Cochran confirmed they have been actively working to find a solution for quite some time.
In late March, a new levee was constructed at the lagoon in an effort to remedy this very problem. Additional diffusers and aerators were installed as well to strengthen the aeration process.
"We've had real difficulty mixing the water," Cochran said, noting that the lagoon in question is rather complex in nature.
The concern is that even with additional changes, they are struggling to get the ammonia levels back down into the range of DNR compliance.
Cochran explained that the city has two separate limits--one for summer (3.2 parts per million) and one for winter (4.6 parts per million.)
In October 2013, the city lagoon's ammonia level was 46. It has been decreasing in the months since, and in January tested at 12.5 ppm.
The reason for the disparity between summer and winter numbers is due to bacteria growth. In summer months, bacteria grows at a much faster rate, which in turn does a more efficient job at destroying the settling waste.
In winter months, the bacteria grow more slowly and in many cases can die off, making it more difficult to adequately treat the waste.
"We've been working hard on this to keep us out of trouble," Cochran said, but acknowledged that anticipated regulatory changes may soon make it more difficult than ever.
Since this problem developed, the U.S. Environmental Protection Agency (EPA) has issued new criteria that are expected to drop limits by approximately half when they are officially implemented.
"When that happens, there are going to be a lot more communities that really struggle with this type of problem than what already do," Cochran said.
City Administrator Mark Stidham said that DNR has been very good about working with the city through this period of adjustment.
"When we first started doing this, we had a permit telling us what we could operate and laying out a procedure," Stidham said. "When this [current problem] happened, we had to request permission to re-open a closed cell within the lagoon to give the water another step before discharge."
With water now going into an abandoned cell, the city had to request permission to operate out of its standard permit status.
DNR granted that extension in early 2013, before the additional levee and diffusers were constructed.
"The problem is that it's a long process," Stidham said. "It's not at all uncommon for something like this to take 18-24 months to get a grip on."
The changes made today, he said, won't show any progress for approximately 30 days.
"It takes that long for it to get through the system," he said. "As a result, we've had to ask for extensions. DNR has worked with us really well."
Staying in compliance can be difficult overall, Stidham explained.
"As the criteria are tightened down, a new system installed three years ago now may not be powerful enough to meet the tighter requirements," he said. "There are cities all over the state right now that can't meet compliance standards."
Stidham said the city will continue working to get back within the required limits, and that they are optimistic there will be a "substantial improvement" by summer when temperatures begin to rise.