City Considers Undersea Outfall Tunnel

San Diego officials will soon decide whether to bore a 4 1/2-mile tunnel hundreds of feet beneath the ocean floor to replace the aging concrete pipe that ruptured nearly two weeks ago, spilling 180 million gallons of partially treated effluent each day into the ocean off Point Loma.

The tunnel proposal has obvious advantages over the current plan to extend the existing 2.2-mile outfall another 2 miles to bring the effluent beyond ocean kelp beds, according to city officials. The $150-million extension is required to bring the city into compliance with the state Ocean Plan.

“It’s more (protected) from seismic disruption,� City Manager Jack McGrory said. “It’s obviously immune from waves because it’s under the ocean floor.� Estimates show that a 4 1/2-mile tunnel would cost about as much as extending the outfall, officials said.

But one Sierra Club attorney calls the city’s tunnel idea “lunatic.�

The plan would require the drilling of a 500-foot shaft into the ocean floor at the shoreline, and construction of a 12-foot diameter, concrete-lined shaft, Deputy City Manager Roger Frauenfelder said.

The pipe would slope gently uphill. At its end, it would be about 200 feet below the ocean’s surface. Vertical pipes punched through the ocean floor would then draw the effluent above the sea bottom, Frauenfelder said.

The sewage would be pushed through the pipe by the natural forces created by the 500-foot vertical shaft, Frauenfelder said.

Digging the tunnel might require construction of a 1-mile-long pier and conveyor belt that would carry mined sandstone out to a barge for disposal, Frauenfelder said. An alternative would be to tunnel half a mile east, through the tip of Point Loma, to use Navy facilities that would handle the rock bored out from under the ocean floor, he said.

Estimates show that the project would cost $130 million to $200 million, McGrory said.

A decision on the tunnel option is expected in the weeks after March 5, when the city will open bids from contractors on the cost of extending the ocean outfall, Frauenfelder said. Contractors have been notified that the tunnel alternative might replace the outfall extension.

City leaders maintain that some external force, such as pounding surf or a ship’s anchor, caused a break in the 9-foot-diameter outfall pipe that ultimately led to damage to 22 sections of the pipe.

But some city employees have told The Times that an in-house diversion of sewage rocked the Point Loma Wastewater Treatment Plant two days before the U.S. Coast Guard discovered the ruptured pipe, perhaps causing the leak.

The effluent, from which about 75% to 80% of solids have been removed, is pouring into the ocean about three-quarters of a mile offshore in 35 feet of water, elevating bacteria counts far beyond legal limits. Normally, the sewage is dispersed at a depth of 220 feet.

Robert Simmons, the attorney who represents the Sierra Club in court proceedings over the city’s upgrade of its sewage treatment system, called the tunnel idea “lunatic.�

“It represents another example in a long series of examples of the city throwing money at a problem� unnecessarily, said Simmons, who is running for county supervisor in the 3rd District.

Simmons said water conservation and reclamation efforts over the next decade will make the huge tunnel, capable of carrying 240 million gallons of sewage each day, unnecessary because the city will be dumping far less effluent out at sea.

City officials believe the major drawback of the plan is legal, not technical: Construction would take three to four years longer than extending the outfall, largely because of extensive environmental review that would be needed.

That delay would require the approval of U.S. District Judge Rudi Brewster, who is overseeing the “consent decree� hammered out between the city and the U.S. Environmental Protection Agency, which has sued the city over violations of the federal Clean Water Act. The document spells out improvements the city must make to its sewage treatment system and the schedule it must follow.

Frauenfelder maintained that “tunneling is a real benign operation as far as environmental impact.�

In recent closed sessions, City Council members have discussed appointing Councilmen Ron Roberts and Bob Filner to ask Brewster whether he would consider a modification of the outfall extension plan, Roberts said. The council also is rethinking other aspects of the consent decree now that it is more unified on the sewage issue, said a council member who asked not to be identified.

The discussions are occurring in closed session because they are related to the litigation over the city’s $5-billion secondary sewage upgrade, Frauenfelder said.