Solid Energy's random drug and alcohol tests nabbed 45 people at its mine sites in the year to the end of June, in a trend the Ministry of Business, Innovation and Employment today described as "concerning''.
All but three workers tested positive for cannabis or synthetic cannabinoids, while the others had used methamphetamine, said Solid Energy, after it responded to an Official Information Act request from Westport News.
The company carried out 2248 random tests at Stockton opencast, Spring Creek underground, Huntly East underground and Rotowaro opencast mines during the year.
Twenty-seven of the offenders worked for Solid Energy, while the remainder were employed by contractors.
Office sites were also tested, but no offenders were caught there.
Spring Creek had the worst failure rate at three per cent of the workforce, followed by Rotowaro 2.8 per cent, Stockton 2.4 per cent, and Huntly East one per cent.
Miners' union, the EPMU, said the results were disappointing and showed that Solid Energy needed to take a different approach to stamp out drugs at their mines.
Ged O'Connell, assistant national secretary, accepted that the figures highlighted a wider social issue, but wanted the firm to work with the EPMU to try a different approach.
"There's just no place for drugs in the workplace,'' he said.
"Solid Energy has gone down the road of random drug testing and it doesn't appear to be working.
"But if they work with us, I think we could draw up a programme, with check inspectors taking a bigger role, and manage things a lot better.''
At Stockton, which employs about 1086 people, 27 workers tested positive for cannabis/synthetic cannabinoids.
Of the Solid Energy employees, two offenders had already completed a Solid Energy drug and alcohol rehabilitation programme.
When they tested positive a second time, one resigned and the other was fired.
Another Solid Energy worker was fired after a post-incident drug and alcohol test resulted in a further positive result.
The remaining 18 Solid Energy offenders entered the rehabilitation programme, and all but one - who resigned from his job during the programme - completed it.
However, four subsequently reoffended. Three resigned and one was fired.
Solid Energy today said it has four types of drug testing for all of its workforce - not just miners.
It includes testing before they are employed, in the event of an accident, if there is reason to believe someone may be under the influence of drugs or alcohol, and random testing.
Solid Energy spokeswoman Vicki Blyth said the company's aim is to have its sites completely drug- and alcohol-free.
"Our testing regime is designed to reinforce that (drug-free) message to everyone who works for, or with, us - employees, contractors and even occasional visitors to our sites like consultants and delivery drivers,'' she said.
"Many of our workers tell us that our stance is one of the reasons they enjoy working on our sites - they are more confident that their colleagues all have their minds fully on the job.''
The Government's labour service welcomed Solid Energy's "very comprehensive'' drug and alcohol testing programmes.
However, Brett Murray, general manager of the High Hazards Unit, said drug and alcohol use in any workplace, particularly one that involves high hazards, is ``concerning''.
"Employees who work with any kind of drug or alcohol impairment are putting their own, and their colleagues' safety at risk,'' he said.
"The Health and Safety in Employment Act places an obligation on workers to do nothing to put themselves or others at risk.''