The city report submitted to the federal Environmental Protection Agency on Monday sheds little new light on the reasons a main sewer line in Waikiki ruptured March 24, but it details two small ruptures in the same pipe that occurred in 1993 and 2004.

Attorney Christopher Sproul said those earlier breaks should have prompted the city to pay attention sooner. He said cracks in a pipe would expose the steel reinforcement to corrosion.

"Any engineer worth their salt would have seen that as a red flag," said Sproul, who represents the Sierra Club's Hawai'i Chapter, Hawai'i's Thousand Friends and Our Children's Earth, the environmental groups that pushed for federal intervention to improve Honolulu's sewer system as part of a federal consent decree.

City Environmental Services Director Eric Takamura sent the six-page report along with photos, maps and other supporting documents to the EPA in San Francisco. The report details the sequence of events surrounding the most recent rupture and what steps were taken to address environmental and health risks.

In his cover letter dated Monday, Takamura said the city "is currently focused on addressing the emergency situation surrounding the Beachwalk Wastewater Pump Station Force Main."

The city's report is important because it will influence whatever enforcement action might be taken by the EPA.

In response to the city report, Kathi Moore, chief of the EPA's Clean Water Act Compliance office in San Francisco, said yesterday that the spill "underscores the urgent need to protect the public and environment from the risk of future system failures in this area" and shows that O'ahu's sewer system is vulnerable to breakdowns.

Moore said the federal agency will work with the state, the city and the community to develop measures to address key vulnerabilities in the city's wastewater system which "will require significant and costly work aimed at preventing and better responding to spills."

She added, "we will take the necessary steps to ensure that the city takes prompt action to identify and correct the most urgent weaknesses in its sewage collection system."

Takamura wrote that the report is based on information compiled to date and the city will provide more details as requested. City officials told the EPA that the rupture likely was caused by a combination of heavy rains, soil settlement and pile-driving in the area.

The broken pipe prompted crews to pump 48 million gallons of raw sewage into the Ala Wai Canal over a six-day period while crews worked around the clock to fix the break.

Sproul questioned the volume of the spill reported by the city — 48.6 million gallons.

"It looks like they've substantially underreported the size of the spill," Sproul said. By calculating the average flow and adding some for the rainy weather, "it should have been like 70 million gallons," he said.

According to the report, the average flow of wastewater through that 42-inch pressurized reinforced concrete pipe is 540,000 gallons an hour. That adds up to approximately 67 million gallons total over the duration of the spill.

But Takamura said the spill volume was estimated as accurately as possible. "The way we had to end up tracking the spill volume was what we normally see on those days," he said.

Jeff Mikulina, the Sierra Club's Hawai'i Chapter executive director, was critical of the report. "It falls short in telling EPA and the public what happened and why it happened," he said.

And he faulted the city's overall maintenance.

"They've been managing the system with Band-Aids," Mikulina said. "It was already falling apart and it was bound to break."

Waikiki Councilman Charles Djou called the spill "a bad situation." But he said it appears that the current administration was faced with pumping raw sewage into the canal or allowing it to back up into nearby homes and businesses.

"It appears that the administration did what they had to do," Djou said. "But how and why did we get to this point?"

Reach Robbie Dingeman at rdingeman@honoluluadvertiser.com.