Sewage Spill Probe Hints at Human Error

A buildup of trapped air in a 29-year-old pipe triggered an explosion that, for two months, contaminated beaches here with billions of gallons of partially treated waste, according to preliminary findings by a firm investigating the cause of the rupture.

If the finding proves true, it would bolster the contention of some city sewage workers that human error resulted in the formation of a giant bubble that burst the pipe. City officials have blamed “external forces,” such as heavy wave action, for the rupture.

The disclosure came Friday in the courtroom of U.S. District Judge Rudi M. Brewster, who criticized the city’s plans to spend $61 million on extending the recently repaired outfall and building an adjacent parallel pipe as insurance against the kind of catastrophe that marked one of the worst sewage spills in U.S. history.

The spill contaminated up to 20 miles of beaches from early February until early April, when the pipe was finally sealed. Before then, up to 180 million gallons a day of partly treated waste had spewed into the Pacific 3,150 feet offshore at a depth of 35 feet. Ordinarily, such effluent is discharged 2.2 miles offshore, at a depth of 220 feet.

The independent firm of Failure Analysis Associates of Menlo Park, Calif., came up with the preliminary finding.