Hole found and sewer trunk fix underway
Modesto appears to have bought itself some time before it may have to release partially treated wastewater that poses a public health risk into the San Joaquin River.
The city’s sewer system has been overwhelmed by the recent storms and rising river water, and it is reaching its capacity to store the wastewater. Utilities Director Larry Parlin said the culprit appears to be water from the swollen Tuolumne River entering the sewer system through a hole in a sewer trunk line along the riverbank.
The trunk line – which is submerged under a few feet of water – ends at the city’s Sutter Avenue sewage treatment plant.
City workers spotted the problem Thursday morning, and city crews in the early afternoon were building a barrier around the section of the trunk line with the hole to keep the river water out. Crews would patch the hole once the river recedes.
Crews worked Wednesday on another section of the trunk line the city believed would be the solution. But they are confident they now have pinpointed the problem.
“We think this is the fix,” said Robert Englent, Modesto’s wastewater collections systems manager.
“This could buy us a few more weeks before (possibly) having to discharge (wastewater into the San Joaquin) unless some other major event occurs,” Parlin said.
Modesto noticed the increased flows of wastewater into its Sutter plant Monday as the river continued to rise. Parlin said the plant typically processes 20 million gallons of wastewater per day this time of year, but he said flow has jumped to 40 million to 50 million gallons per day because of the river water entering the system.
Modesto cannot store that much wastewater. The water first is treated at the Sutter plant along the Tuolumne River and then is sent by pipeline to the city’s Jennings Road treatment plant along the San Joaquin River. The wastewater then receives additional treatment.
The city treats some of the water to a high-enough standard that it can be safely and legally released into the San Joaquin. The rest is stored in ponds at the Jennings plant and is used to irrigate nearby farmland planted with animal feed during the growing season. Parlin said if the ponds overflow, they would flood and damage the Jennings plant and surrounding area.
He said the ponds are near capacity.
The wastewater Modesto could release into the San Joaquin would have about 85 to 90 percent of its pollutants removed. But it would not be disinfected, so the water would have bacteria in it. Modesto would be violating its state-issued discharge permit if it released this water.
“At this point, they need to do what they need to do,” said Wendy Wyels, the environmental program manager for the Central Valley Regional Water Quality Control Board, which issued Modesto its discharge permit. She said Modesto has been diligent in dealing with this crisis, including adding storage at its Jennings ponds and shoring up the levee at its Sutter plant.
As context, Wyels said, several dozen wastewater plants in her agency’s jurisdiction have released wastewater into rivers because of the heavy rains and flooding.
“Floodwater has gotten into their sewer lines or sewer ponds or sewer systems,” she said.
She said these releases are mitigated in part by being diluted by high river flows and this is not the time of year when many people are swimming, boating or engaging in other recreation in waterways.
But she said the releases have the potential to impact public health. She said her agency will ask Modesto once its crisis is over to evaluate what happened and what it can do to prevent it from happening again. Modesto could be fined, but Wyels said it is too soon to talk about that.
Parlin said Modesto plans to replace the sewer trunk line along the Tuolumne River with a new one that won’t be along the riverbank. He said half of the design work has been done for the project, which is expected to be completed in five years.
Kevin Valine: 209-578-2316