Contaminated areas of the Hobsonville air base on the outskirts of Auckland will be as "clean as a whistle" when the land is sold for commercial development or housing, the defence force said today.

New Zealand Defence commissioned an audit of the base towards the end of 2001 in preparation for its sale.

The audit revealed some areas of the base were slightly contaminated with radioactivity from old, buried instruments and other areas were contaminated with heavy metals and other pollutants.

Defence spokesman Wing Commander John Seward told NZPA today the contamination was no more than would be found in any industrial site around the city.

He said contaminated soil would be removed to a licensed disposal facility and other areas would be cleaned before the land was sold.

Mr Seward said the report found several areas which may need remedial work.

In a few areas, the surface soil contamination exceeded residential and/or commercial criteria. However, he said none of the areas contained unduly widespread or heavy contamination.

The audit found excess levels of lead and copper in the shooting range but that would be resolved by removing the soil to a disposal facility.

A small dangerous goods store had waste oil spillage and the soil would be removed. The edges of a helicopter wash pad had heavy metal contamination but even the one area with higher than usual contaminants was below the accepted levels set by the Auckland Regional Council.

A vehicle oil change pit would be cleaned of oil-contaminated soil.

The radioactivity in the instrument dump came from radium 266 used in the luminous markings on old instruments. They had been dug up and put in a plastic-lined bin for disposal.

He said in the 1950s burying the instruments was an accepted disposal method.

He said most of the heavy metal contamination was about the same level as would be found on many roadsides from leaded petrol or in many industrial or commercial areas.

He said the Defence Force wanted to put the land in good order before it was sold and the cost of the clean-up would probably be less than $100,000.

He said the report said heavy metal contamination would pose a risk to human health only if the soil was eaten and may threaten sensitive animals which came into direct contact with the soil.

"They are not considered to pose a hazard to personnel or workers on site as the heavy metal concentrations are not significantly elevated beyond background levels and the current land use is appropriate," Mr Seward said.

However, Friends of the Earth spokesman Bob Tait told National Radio today Hobsonsville was a big site and more detailed investigation was needed before the land could be sold for housing.

He said no work had been done to sample ground water near an old, unlined landfill.

"There is a lot more needed to be done and the figure that has been talked about ($100,000) I think is quite unrealistic.

"They have got underground storage tanks to remove, they have got landfill to deal with, they have got the lead problem and contaminated hot spots. They are going to be looking at big money," Mr Tait said.

Housing Minister Steve Maharey said the Housing Corporation was negotiating to buy some of the land for state housing but no money would change hands unless he was satisfied the site was clear.

"I won't be signing anything off unless we get complete clearance from all environmental and resource consent processes so we know the land is completely and utterly safe."

He said he could give a categoric assurance no state house tenants would be put in houses built on contaminated land.

The air force has been at Hobsonville since 1924.