CARLSBAD
–
After 7 million gallons of raw sewage poured through a broken pipe into Buena Vista Lagoon two months ago, many said something should be done to prevent such a breach from happening again.
On Tuesday the Carlsbad City Council will likely approve spending $1.2 million over three years to look into installing a system designed to reduce pipe corrosion and possibly prevent such breaks in the future.
The system, called cathodic protection, is included in the proposed $183.3 million capital improvements budget for 2007-08. The budget includes $32.8 million in new projects for 2007-08.
The council also will vote on the proposed $186.2 million operating budget at its meeting at 6 p.m. Tuesday at City Hall, 1200 Carlsbad Village Drive.
Mark Stone, general manager of the Carlsbad Municipal Water District, said the anti-corrosion system is not in direct response to the recent catastrophic break, as the city has installed it on some newer pipes.
The purpose of the project, Stone said, is to test the system on some pipes to see where it would do the most good. For some older pipes, he said, it might not be useful.
“If it's beyond any real benefit to putting it in, we'll put (those pipes) on our replacements program,” he said.
Stone said the idea of cathodic protection is to use one type of metal to attract corrosive material in the ground and shield the pipes the city wants to protect.
“There's certain components in our soils that are corrosive that accelerate the deterioration of our metal pipes,” he said.
Those components react with the metal in sewer and water pipes, decaying them and leaving a brittle shell behind.
The idea is to attach a metal that is more susceptible to corrosion on the pipes, so that the metal gets “sacrificed” and the desired pipe remains intact.
“We redirect that chemical into a sacrificial anode and away from the pipe,” Stone said. “It's kind of the concept of preventing metals from rusting faster than they should.”
He said the technology has been around awhile, and other cities and water agencies have employed it.
The first use of cathodic protection is attributed to Sir Humphry Davy, a British chemist who in 1824 attached iron chunks to a ship's copper hull below the water line. Iron rusts faster than copper, so the copper's rate of corrosion slowed as the iron rusted.
Asked about the disastrous sewer line break at Buena Vista Lagoon, Stone said it's a hypothetical question because the technology the city is studying was not available in 1982, when the pipes were installed. Those pipes were expected to last 50 years.
“If it (cathodic protection) would have been put in years ago, it may have avoided some of it (the break),” Stone said.
An investigation said the pipe breach was caused by corrosion from outside the pipe, which was wrapped in a plastic liner to protect it from the corrosives in the soil.
Something ate away at the plastic and then the pipe, according to the report. The inside of the pipe was in excellent condition, the report said.
Michael Burge: (760) 476-8230; michael.burge@uniontrib.com
