They said the council became concerned about Mulholland's work when it processed resource and building consents involving his work. Three pieces of work were peer-reviewed and "significant competence deficiencies and breaches of the Engineers Code of Ethical Conduct" were found.
"The complainant also considered the reviews demonstrate deficiencies in Mr Mulholland's approach to geotechnical analysis and documentation, and an unwillingness to accept advice and recommendations from WDC and independent peer reviewers."
Mulholland's said he could have communicated more clearly with WDC and the investigating committee but said his work met the standard required for a reasonably competent engineer and he had acted in a careful and competent manner. He denied he had been negligent or incompetent manner or that he had worked outside his area of expertise.
The disciplinary committee should dismiss the complaint, he said.
But the disciplinary committee found his work has below the accepted standard and that Mulholland, whose practice fields are structural and civil, worked outside his areas of competence and experience in relation to geotechnical investigations, analysis and design.
The committee said it was concerned he did not do a stability analysis for any of the three sites - or understand why it might be needed. His calculations were flawed and insufficient.
"Mr Mulholland's approach to, and reliance upon, 'construction observation' to deliver a safely engineered and compliant design solution in these cases does not represent good engineering practice.
The committee fined Mulholland $2500 plus GST and $10,615 plus GST, about 50 per cent of Engineering New Zealand's total costs, towards the costs incurred by the Registration Authority inquiry.
Mulholland told the disciplinary committee he accepted its decision and would no longer carry out geotechnical engineering work.
In 2017 Mulholland's company David Mulholland Consulting Engineer Limited appealed to the Environment Court after the council did not accept he was a suitably qualified geotechnical engineer. But he was unsuccessful.
