Test results: Toxic wastewater killed plant bacteria, fish
"One hundred percent kill" is how Monett Utilities Superintendent Skip Schaller described the severity of the disruption at Monett's waste treatment plant last week.
All of the fish in Clear Creek and all of the bacteria that process the effluent in the plant died in the process triggered by the injection of the chemical compound Alimet into the system on May 16.
According to test results received Wednesday, the culprit appears to be ammonia levels in the effluent discharged from the plant. Tests from samples taken Friday showed ammonia levels around 20 milligrams per liter. Monett's plant is licensed under the Missouri Department of Natural Resources for ammonia at about six milligrams per liter.
"We really didn't know how bad it was until the beginning of last week." Schaller said.
Schaller referred to the heavy odor that permeated the city that followed the dumping of Alimet into the Tyson Foods pre-treatment plant in Monett on Friday, May 16. Although a Tyson spokesperson said company crews captured almost all of the Alimet and held it for treatment, an unknown quantity of the amino acid compound, used in making feed at Tyson's feed mill in Aurora, got through to the city plant.
Schaller said ithe initial shock of the Alimet hitting the plant on May 16 had a devastating impact on the bacteria that treat effluent at the plant. Because the plant holds 15 to 20 million gallons of water, Schaller said the damage took time for the bacteria to sicken and die.
Five days later, by Wednesday, May 21, the effluent began to smell bad, reported Ron Gajdos, assistant chief operator at the waste treatment plant. By the next day, "there was no life in the oxidation ditch."
The oxidation ditch is a racetrack of about eight cells through which effluent passes. Bacteria in each of the cells helps break down impurities in the effluent, including ammonia. Schaller said part of the process involves depriving the bacteria of oxygen, which prompts discharge of cleansed ammonia into the atmosphere. Without the bacteria, no process offered an alternative way to extract the ammonia, leaving the toxic substance to pass undiluted into Clear Creek.
The Alimet held at Tyson underwent treatment to raise its pH levels. Chlorine was added to eliminate the odor. According to a Tyson spokesperson, the industry began piping its treated Alimet into the city system on Tuesday. When the effluent from Tyson entered the plant, Schaller said the treatment had an obvious effect, as it lacked the smell at the headworks of the plant that accompanied the first wave on May 16.
However, with the death of the plant's bacteria, effluent began flowing through the plant looking cloudy. No tests were available to alert crews to high ammonia levels.
"In talking with the plant guys and the engineers, I'm fairly certain that's what happened," Schaller said. "The ammonia caused the fish to die."
The fish kill in Clear Creek became evident on Friday. Schaller said the lab at the plant tested for pH levels and biochemical oxygen demand (BOD), and showed that throughout the week, discharged effluent held within the standards of the state permit through the Department of Natural Resources (DNR).
Samples were sent to KACI Lab in Springfield to test for more toxic substances. Schaller expected joint samples taken with the Department of Conservation would show similar results.
Based on the dissipation of odor since Friday and a clearing of the effluent, Schaller said he felt confident the ammonia levels had fallen significantly in the following five days, but had no numbers to know exactly where conditions stood. Daily samples were being taken from the creek to track the progress.
Once the bacteria kill was discovered, which coincided with the worst of the odor coming out the facility, steps began to re-supply the plant's biological ingredients. Gajdos said a stored supply of effluent provided the initial reseeding stock. Another 5,000 gallons came from Mt. Vernon. Schaller figured the two loads of effluent probably cost the city about $300 each.
"All the treatment plants around here are good neighbors," Schaller said.
Over the weekend, Schaller stopped by property owners downstream from Monett and talked to them about what was happening.
"The creek smell was bad, definitely noticeable down in the bottom," Schaller said.
Coming back from Neosho on Saturday, Schaller checked on the stream each mile up to the Newton County line. He said the smell gradually increased the closer he got to Monett, but the fish seemed to still be healthy downstream. He did not know how far the fish kill spread. As of Tuesday, Clear Creek near the plant still had an abundance of water habitat creatures such as snakes and frogs, but no evidence of fish.
"I've talked to Dave [Sims, chief wastewater operator for the city] and I've talked to Becky [Thomas, Tyson's complex environmental manager]," Schaller said. "We're going to review the situation when this is done and definitely try not to let something like this happen again, and how to protect the plant better next time.
"If anything, it's proved to me we have to tighten up some of our controls and procedures. Unfortunately, it takes something like this to show where we need to makes improvements."
Schaller said the city will probably face fines from DNR for exceeding its wastewater permit limits.
Worth Sparkman, corporate spokesman for Tyson Foods, said, "We're working cooperatively with city and state officials as they investigate this matter. We're awaiting additional details so we can understand if our operations played a role in what happened."