A "robust" plan has been developed to address issues identified in a consultant's report and the situation is being monitored by the Hospital Advisory Committee, the spokeswoman said.
Apex national secretary Deborah Powell confirmed Apex was the union involved in the investigation process.
She said staff came to them with concerns about the management of the department last year.
The union suggested getting a consultant in to deal with the matter so it could be reviewed independently.
She would not comment on what the staff's concerns with management were as she said the process was still ongoing.
Whanganui DHB spent a further $70,000 on external consultants in the current financial year as of February.
The consultants were brought in for tasks such as "Rising to the Challenge" - a long-term project addressing mental health and addiction services.
During the 2014 financial year, the health board spent more than $200,000 on external consultants. In 2013, it spent more than $150,000.
Labour's health spokeswoman Annette King says district health boards spend far too much on external consultants - but Whanganui's strategic and corporate manager Brian Walden says the spending is justified. "We use consultants because we have to, we need to. Some times projects require specialised knowledge in the field.
"If it's a permanent role going forward we would much prefer to have employed staff because we retain the knowledge and expertise, but if we aren't able to recruit the resource and we need to get the work done, then we would have to use a consultant."
As well as being used for specialised areas, consultants were required for independent reviews, he said.
The board always kept an eye on costs because it was required to break even, he said. "We're a complex organisation with $220 million in revenue and 1000 staff.
"We have to deal with those complexities which some times means employing people outside of the organisation.
"That's not unusual for big organisations to do because you can't have the wide range of skills required for some jobs because the work isn't consistent."
However, Ms King believed district health boards needed to have more long-term positions.
"Long-term positions would mean getting people with intellectual knowledge who would know what had gone on before so you wouldn't have to have someone starting from the beginning every time they started a project.
"It'd not only be cost effective but also effective in terms of provision of advice and service. Getting in external consultants that don't have institutional contacts isn't cost saving in the end."
Ms King believed these large sums of money for outside consultants didn't ultimately benefit the public.
