Coast Guard officials are trying to determine how much of 4,400 gallons of diesel fuel in a tank on a University of Hawai'i research vessel docked at Sand Island Wastewater Treatment Plant has leaked into the water and possibly a city sewage line.

As of yesterday morning, about 1,700 gallons of fuel had been cleaned up, said Petty Officer Angela Henderson, spokeswoman with the U.S. Coast Guard.

The master of the Ka'imikai-O-Kanaloa, a 198-foot research vessel belonging to the UH School of Ocean and Earth Science and Technology, contacted the Coast Guard Thursday at about 11:45 a.m., and reported that a crack in the fuel tank had allowed fuel to leak into the water.

According to Gregg Takayama, University of Hawai'i-Manoa spokesman, fuel also was suspected of entering a city wastewater treatment line.

The vessel was moored at Pier 45, where officials had intended to empty its wastewater into the city's wastewater line. During that process, Takayama said, diesel fuel was suspected of mixing with the wastewater and entering the city's line.

"The research vessel is fairly old, I understand, and the wastewater tank and fuel tank are right next to each other," Takayama said.

A crack, which has yet to be found, may have allowed the fuel to mix with the wastewater on the vessel, he said.

The vessel's crew immediately shut down all operations and set up an absorbent boom to contain the spill.

The Ka'imikai-O-Kanaloa also contracted the Pacific Environmental Corporation to assist with the cleanup effort, Coast Guard officials said.

City spokesman Bill Brennan said city crews inspected several manholes and found no evidence that diesel fuel had entered the city's wastewater line. However, crews continued to investigate the matter yesterday.

Crews at the Sand Island treatment plant also pulled samples of wastewater and did not find any evidence of diesel fuel, he said.

Reach Loren Moreno at lmoreno@honoluluadvertiser.com.