Navy contractors have begun drilling two new groundwater monitoring wells north of the Red Hill Bulk Fuel Storage Facility as state officials continue to be concerned about the spread of underground fuel from past leaks at the World War II-era site.

The siting of the two additional wells is based on the interest of state and federal officials "to further refine understanding of how groundwater moves near the Red Hill" facility, said Aaron Poentis, environmental program director for Navy Region Hawaii.

Seven groundwater monitoring wells already exist in the vicinity of Red Hill.

Well drilling was started by Valley Well Drilling on Aug. 28 and is expected to be completed by the end of October, the Navy said.

Civilian and Navy lab testing indicate that drinking water sources in the Red Hill vicinity continue to meet federal and state safe drinking standards, the Navy said Wednesday.

"We value this precious (water) resource along with our fellow residents, families and friends," Poentis said in a news release.

In January, the Navy alerted the state Department of Health of the release of up to 27,000 gallons of jet fuel from Tank 5 at the facility that was completed in secrecy in 1943.

Each of the facility’s 20 vertically arrayed tanks is 250 feet tall and 100 feet in diameter and can hold up to 12.5 million gallons of fuel. The upper domes of the tanks lie 100 to 200 feet below ground.

At a Red Hill task force meeting Wednesday, the Navy said more than 600 repair points were identified inside Tank 5 after it was emptied, with 17 pen-size holes discovered as a result of vacuum testing, KITV-4 News reported.

The Navy had just brought Tank 5 back into service in December after repairs were made. When it was filled it started to leak.

Past Navy reports reveal dozens of leaks back to the 1940s at Red Hill, but the records are spotty at best from the once-classified facility.

Water wells at the nearby Halawa and Moanalua shafts provide about 25 percent of the drinking water supply for urban Honolulu. The Halawa Shaft is about 5,000 feet northwest of Red Hill.

In groundwater modeling, an extended jet fuel spill reaching within 1,099 feet of a separate Navy water tunnel resulted in benzene levels greater than federal maximum contaminant levels.

A release as small as 16,000 gallons near Tanks 1 or 2 (those closest to the water tunnel) could result in those conditions, a Navy report found.

The state Health Department said groundwater monitoring wells near Red Hill have shown petroleum levels of concern in the past, while the Navy well, located farther away, does not, because many millions of gallons of water move very slowly through rock, or even remain semi-stationary, and biological action can help break down the fuel.

That makes tracking the movement of fuel through rock a challenge, the state said.

The Navy found trace elements of naphthalene in its drinking water supply, but at levels too low to be of concern.

In February, the state asked the Navy to develop a work plan, contain and remove contamination from the latest fuel release, model the fuel plume in the ground, install additional monitoring wells and provide a plan to reduce or eliminate future spills to protect drinking water.

The installation cost for the two new monitoring wells is expected to be $670,000, the Navy said.