It brought in the contractor despite already employing 45 people in its PR team, for whom it had a budget of $4.5m in salaries this year - 25 percent more than in 2014.
A New Zealand Defence Force spokesperson said since 2015 the NZDF had committed significant resources to investigating the extent to which PFAS from legacy firefighting foams had reached groundwater on NZDF bases and neighbouring properties.
"In 2015, little was known in New Zealand about PFAS compounds and that knowledge has been evolving," the spokesperson said.
But the defence force has largely wrapped up its investigations and the all-of-government programme on foam contamination was disbanded this year, leaving many questions unanswered about the extent and threat from the pollution.
The Environment Ministry's report Environment Aotearoa 2019 named PFAS among "previously unreported contaminants" that have been found recently in some areas, under a heading 'Trends in land, soil and coastal water in urban areas cannot be assessed'.
"Regional councils keep records of sites where land contamination has been confirmed, but there is currently no integrated dataset available for the national scale," it said.
At one of the worst-hit areas, Manawatū, where foam has turned up in water around Ōhakea, Bulls and Palmerston North, the regional council complained the government's response remained uncertain.
"Our position is very clear - we want the government to fund ongoing monitoring," the council said.
The NZDF said they would continue to engage with local authorities and central government agencies.
New data from the US shows that rainwater in some parts of the country contains PFAS chemicals, though at levels under health guidelines.
In the US, companies such as DuPont have been sued and paid out hundreds of millions of dollars in settlements over PFAS contamination.
In New Zealand, the government has distanced itself from liability, despite the Defence Force being the major polluter.
It agreed to pay for three quarters of the $14.5m cost of a community water scheme at Ōhakea, saying "while the Crown does not accept it has a legal obligation at law, we do accept that in the circumstances it is proper for the Crown to fund the lion's share of the scheme", in a letter from Environment Minister David Parker to the district council.
The district council said it expected Ōhakea air base to pay for a lot of the operational costs of the water scheme.