Workers on Friday afternoon were threading about 1,100 feet of plastic pipe into a major sewer line along the Tuolumne River. The work is part of a roughly $1.8 million project to repair the failing section of a sewer line that transports about a third of Modesto’s wastewater.
The plastic pipe is the latest fix after roughly 40 feet of the sewer line failed in February after the river rose because of winter storms. The extra weight of the river water on the ground caused the underground line to collapse and rupture, eventually letting river water pour into it and inundate the city’s sewer system before the city found the problem and patched it.
Utilities Director Larry Parlin said the city researched that section of the sewer line after the failure. He said the drawings and plans show that about 1,100 feet of the line was constructed in the 1940s from corrugated metal lined with asphalt. The industry standard is to use concrete or clay. Parlin said the failing sewer line appeared to be concrete based on video inspections.
The rest of that major sewer line is concrete. Parlin said the plastic pipe will last more than long enough until the city makes its final fix in about five years: replacing the sewer line with a new one that is not along the river and is out of the flood plain.
But the work to start feeding the plastic pipe into the conduit sewer line was an extreme example of the adage “measure twice, cut once.” Engineers had only a short distance to bend the flexible pipe from ground level to the sewer opening perhaps 10 feet below.
A piece of heavy equipment – basically a winch designed for the logging industry – was used to pull the pipe into the sewer. Cable was fed through a manhole into the sewer line, then the roughly 300 yards to where the pipe lay. Thursday, when the cable began to pull the pipe, a coupling broke free, delaying the work until Friday.
Friday, metal beams and concrete manhole tubes had to be removed to allow the pipe to slide unobstructed into the conduit. But the challenge of overcoming obstacles created an air of excitement, said Collin Yerzy, senior civil engineer for the city. “This is the stuff engineers live for,” he said.
Parlin estimated the emergency repairs made when the failure was found in February and the work being done now will cost about $1.8 million. A final accounting has not yet been done. But he expects the Federal Emergency Management Agency will reimburse Modesto for some of its costs because Gov. Jerry Brown declared a state of emergency because of this winter’s massive storms and flooding.
The storms and flooding created more problems for the sewer system.
Because the Tuolumne River water poured into the sewer system, Modesto ran out of storage at its Jennings Road treatment plant and released partially treated wastewater that had not been disinfected into the San Joaquin River from March 2 to March 31 in violation of its state discharge permit. That wastewater normally is stored and then used to irrigate nearby farmland planted with animal feed in the growing season.
Modesto’s wastewater is first treated at its Sutter Avenue plant along the Tuolumne and then sent by pipeline to the Jennings Road plant along the San Joaquin for additional treatment.
The Central Valley Regional Water Quality Control Board issued a notice of violation to Modesto on April 13 because of the discharge into the San Joaquin River and asked the city to provide the board with documents, including sewer system inspection and maintenance records for the past two years, and paperwork on the steps the city has taken and will take to fix the problem that lead to the discharge. The board could fine Modesto.
But a Central Valley water board official told The Bee last month that about 50 wastewater treatment plants within the board’s jurisdiction violated their discharge permits because of the storms and flooding. Notices of violations were sent to other cities and treatment plant operators.
Parlin also is concerned about when the Tuolumne River recedes this summer because its riverbanks are so saturated they could shift. That could damage the sewer line and what is known as the cannery segregation line, which is used in the summer by food processors. But he said the city will solve any problems that develop through such steps as stabilizing the riverbank or installing more plastic sewer line.
“It’s the nature of the business,” he said. “Sometimes you are dealing with old, antiquated infrastructure.”
Bee staff writer Deke Farrow contributed to this report.
Kevin Valine: 209-578-2316