8-Mile Tunnel to Replace Clogged Sewer Line

By the end of the decade, miners will start digging an eight-mile sewer tunnel about 70 feet beneath Culver City, Westchester and Los Angeles International Airport to replace the deteriorating North Outfall Sewer, according to Los Angeles Department of Public Works engineers.

Debris and sediment have cut the capacity of the 60-year-old North Outfall Sewer by a third, sometimes causing raw sewage to overflow into Ballona Creek and Santa Monica Bay, said Wayne C. Mohr, project engineer for the replacement sewer.

The tunnel carries about 200 million gallons of San Fernando Valley sewage to the Hyperion sewage treatment plant in Playa del Rey each day.

Four Storage Tanks

In February, 1986, the California Regional Water Quality Control Board ordered the City of Los Angeles to build four storage tanks that can hold a total of 1 million gallons of overflow and to dig a replacement sewer to stop the spills.

The storage tanks in Culver City have been completed and, although they were not large enough to halt a 4.1-million-gallon overflow during a recent rainstorm, Mohr said the tanks have stopped several dry-weather spills.

“The million-gallon tanks are a short-term solution,” he said. “(The replacement sewer) is the long-term solution.”

The replacement tunnel will extend south from Rodeo Road west of La Cienega Boulevard roughly parallel to Jefferson Boulevard beneath oil fields, West Los Angeles College and Holy Cross Cemetery and then southwest beneath the San Diego Freeway, Westchester and the airport to the Hyperion plant.

The tunnel, which will be the fifth major sewer line to the Hyperion plant, will range from 40 to 220 feet beneath the surface, have a 12-foot diameter and a capacity of 300 million gallons a day, Mohr said. The $120-million project is scheduled to be completed by Jan. 1, 1993.

Mohr said the tunnel will be deep enough so that the construction noise and vibrations should not be noticeable on the surface.

Workers, equipment and supplies will enter and leave the tunnel through two portals 35 feet in diameter, one on airport land northwest of Lincoln and Sepulveda boulevards and the other in a Chevron oil field east of Jefferson Boulevard and a few hundred yards north of the Raintree development.

Miners, using a machine that bores a 14-foot-wide hole in the manner of a cookie cutter pushing through dough, could tunnel as much as 100 feet per day, said George Esquer, assistant project engineer. Workers would haul about 850 tons of dirt to the surface daily, filling about 60 dump trucks at each portal, he said.

Culver City Engineer Jim Davis said the city is concerned about noise and possible traffic congestion at the portal site.

Previously, the city opposed a proposed site at West Los Angeles College, citing traffic problems on Overland Avenue and nearby residential streets, Davis said. Traffic, he said, is not as great a concern at the Jefferson Boulevard site because trucks will be routed north through a mostly industrial area.

The city is now concerned with the light and noise generated at night by what could be a round-the-clock operation bringing dirt to the surface at the portal site, he said.