A spokesman for the U.S. Pacific Fleet yesterday downplayed reports of a large explosion, water plume and shock wave Sunday off 'Ewa Beach.

Other Navy officials said relatively small explosive charges were used during the underwater demolition training.

Capt. Scott Gureck said the reports from the shore were exaggerated.

"Our guys that monitor what's going on in the observer boats said it was about a 10-foot plume, maybe 20 feet," Gureck said.

As part of ongoing Rim of the Pacific naval exercises, inert dummy mines were detonated by a series of five 5-pound charges and a single 10-pound charge in Pu'uloa Training Range, said Cmdr. Dora Lockwood, a Rimpac spokeswoman.

Gureck, the Pacific Fleet spokesman, also rebutted earlier Navy reports that a 16-inch shell was detonated.

"There weren't any 16-inch rounds, (and) nothing was blown up other than those charges we already talked about," Gureck said.

'Ewa Beach Road residents reported hearing one loud explosion at about 3:30 p.m. Sunday and seeing a plume of water about a mile offshore, not a series of small explosions.

Mary Jay, who lives in the area, said "it was a loud boom, like the depth charge (fireworks) on New Year's Eve, and it rattled all the pictures on my walls."

Others say they saw a water plume and smoke cloud 100 feet to 200 feet high.

"I've had a lot of phone calls. A lot of family members from Makakilo, 'Ewa Beach and Kapolei were worried," said Kurt Fevella, chairman of the 'Ewa Neighborhood Board. "If the military is hiding something ... I hope they're not."

"We triple-checked the facts here," Gureck said, adding, "I think the only thing we've got are witnesses who probably have exaggerated it."

Capt. Steve Barrett of the Ho-nolulu Fire Department's Rescue 2 unit on Sunday said divers searching murky waters for the cause of the explosion "pulled up a bunch of fiberglass containers and yellow floater" with Rimpac written on it.

The Pu'uloa training area, in a restricted area to the west of Pearl Harbor, is 1,000 yards by 1,000 yards, and has been used for training since 1966, officials said.

NO HELICOPTER CRASH

The afternoon explosion and smoke led to incorrect reports that a helicopter might have crashed. Both the Honolulu Fire Department and Coast Guard responded to the scene.

Jeff Lono, 31, who lives in a beachfront house at 91-173 'Ewa Beach Road, had set up his fishing poles on the sand when he heard the explosion, moments after seeing a splash in the water.

"I saw the splash. It was 100 or 200 feet high, and then the sound," Lono said Sunday. "I ran into the house to get my binoculars and saw two boats leaving the area."

Capt. Kenison Tejada, a Fire Department spokesman, yesterday said "we learned like everyone else that Rimpac exercises were in the area."

"People were asking us if we had been notified (ahead of time). We weren't notified," Tejada said. "We found out afterwards, but that wouldn't have changed what we did. We were responding to the residents' concerns."

Naval Special Clearance Team One out of San Diego has been conducting training off Hawai'i as part of Rimpac and was the unit training Sunday, Lockwood said. Hawai'i, Australian and British divers participated in explosive ordnance-disposal training earlier this month.

NOTICE TO MARINERS

The Navy contacted the Coast Guard about a notice to mariners for the underwater demolition, and the Coast Guard said it repeatedly broadcast radio warnings before and throughout Sunday.

Lt. Rob Lyon, a Rimpac spokes-man, said shore notification sometimes is made for underwater demolition training. In this case, it wasn't.

"Since the range is pretty far out in the water, generally what we do is we sweep the range and make sure nobody's actually there," he said. "On the shore, since they didn't even notice the first (charges) going off, the answer would probably be no (shore notification)."

As the monthlong Rimpac enters its final days, the Natural Resources Defense Council yesterday raised concern over a research vessel's report that 400 to 450 melon-headed whales were spotted to the northwest of the Big Island.

The last of three "chokepoint" anti-submarine warfare training exercises was to be held last night with active sonar in the area.

The defense council had sued the Navy over its sonar use, and a settlement was reached incorporating extra safeguards for marine mammals.

NAVY PRECAUTIONS

Among steps the Navy already had agreed to take for this year's Rimpac is powering down sonar when animals are detected within certain proximity.

"We heard the report that they (the whales) are there, but we are taking our own steps to verify where that pod of whales might be," Gureck said. "But I can assure you that we will comply with all the mitigation measures that are in place to protect marine mammals."

Reach William Cole at wcole@honoluluadvertiser.com.