Modesto’s sewer system fix working

The city’s temporary fix to keep Tuolumne River water from entering and overwhelming Modesto’s sewer system is holding, and city crews continued to work Friday to reinforce and strengthen their work.

But Modesto still faces the real possibility of releasing partially treated wastewater that poses a public health risk into the San Joaquin River. However, the temporary fix means those releases would come later rather than sooner and in smaller volumes.

Modesto noticed increased flows of wastewater into its Sutter plant Monday as the river continued to rise. Utilities Director Larry Parlin has said the plant typically processes 20 million gallons of wastewater per day this time of year, but he has said the flow jumped to 40 million to 50 million gallons per day.

Modesto discovered the culprit Thursday: a hole in the sewer trunk line that runs along one of the banks of the Tuolumne. The trunk line – which carries about a third of the city’s wastewater – was submerged by the swollen river.

Crews built a temporary barrier around the hole Thursday to keep the river water out. They were working Friday to place C-shaped sections of concrete pipe over the hole in the sewer trunk line, which is a concrete pipe. They also plan to build at least one more barrier and take other measures. The hole is in a section of the sewer trunk line near John Thurman Field.

Wastewater Collections Systems Manager Robert Englent said the city believes the temporary repair will hold. He said the flows into the Sutter plant have returned to normal. He said the city will be able to make a permanent repair in the spring when conditions allow for it.

Parlin said Friday that there is a 90 percent chance that within several weeks Modesto will have to release partially treated wastewater into the San Joaquin River because the sewer system is reaching its storage capacity. Modesto had faced releasing wastewater as soon as this week until city workers found the hole. But he said in addition to delaying the release, the temporary fix means less wastewater would need to be released.

Modesto’s wastewater first is treated at the Sutter plant along the Tuolumne and then is sent by pipeline to the city’s Jennings Road treatment plant along the San Joaquin. 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 has said those ponds are nearing their capacity.

The wastewater Modesto may release into the San Joaquin would have about 85 percent 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, and it could face being fined by the state.

This story was originally published February 24, 2017 at 6:59 PM with the headline "Modesto’s sewer system fix working."