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The warning, in a review by LineTech Consultants, which was given to the Otago Daily Times by a fresh source, has prompted renewed calls for Delta and Aurora chief executive Grady Cameron to resign over his failure to address the issues it clearly signalled.
Senior consultant Alastair Glyn-Jones said in the review unless Delta significantly accelerated pole replacement it would be forced in the ''immediate future'' to replace ''very large numbers of poles'' in a short time.
This is exactly what the company is now doing with its $30 million programme to replace almost 3000 poles by the end of next year, which was announced after whistleblower Richard Healey accused it of dangerously mismanaging its network.
Mr Glyn-Jones predicted as many as 32,406 poles would need replacing in the 10 years from 2010, which would have required a 20-fold increase in the number of poles replaced per year.
Even if a ''very optimistic'' approach was taken, a five-fold increase in pole replacements was needed.
''In summary, it is our view, based on the data provided and inspection checks carried out, that there is an ageing pole population that is not being replaced at an appropriate rate to ensure that a major problem (and associated costs) does not occur in the next few years.''
The anonymous source who leaked the review said it laid out in ''black and white'' the problems Delta was facing in managing Aurora's network and the failure to properly address them was ''inexcusable''.
It was more evidence Mr Cameron, who had been in the job for about year and a-half when the report was written for Delta, should take responsibility for the situation the Dunedin City Council-owned companies were in.
''Somebody, somewhere has stopped that report being actioned [and] it's got to be Grady, surely.''
Aurora and Delta spokesman Gary Johnson said Mr Cameron commissioned the report soon after his appointment with the purpose of identifying how asset management could be improved.
Mr Johnson did not respond to questions about why the pole replacement programme had not been ramped up to the extent suggested by Mr Glyn-Jones or whether Mr Cameron should take responsibility for not heeding its warnings.
Instead, he highlighted the changes Delta had made since 2010, which included adding specialist asset management roles and increasing its maintenance budget.
The review said an accelerated programme such as the one Aurora had announced would result in logistical issues and additional costs.
It pointed to a situation in Lower Hutt where a lines company was forced to push through a similar programme, which like Aurora's plan involved bringing in outside resources.
''The costs were significantly above the normal routine pole replacement costs as the contractors were able to extract premiums for being available and willing to provide resources, as well as the need to cover staff costs of travel and accommodation.''
Mr Glyn-Jones also raised wider issues about maintenance of Aurora's network, saying it had ''lower than optimum'' staff numbers working on asset maintenance.
''There is a vicious circle that can develop where staff [are] overloaded, and focus on the day-to-day challenges and requirements.
''Some of the longer-term requirements for analysis, forecasting and trend analysis are thus neglected, and problem areas such as the vegetation and poles are not fully appreciated until they become a significant problem.''
Mr Healey said the review had proven to be ''spookily'' accurate in predicting the scenario Aurora and Delta were facing.
The review was evidence Mr Cameron's actions went beyond ''wilful ignorance'' and were in the category of ''feathering your own nest at the risk of other people's wellbeing''.
Mr Healey said Delta did not make significant changes to the number of poles it replaced per year until four years after receiving the review.
In the past two years it had replaced 802 compromised poles, which roughly represented a doubling of previous replacement levels.
However, the increase was nowhere near the suggestion in the review that at the very least a five-fold increase was needed.