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Disagreement over improving the quality of stormwater could see the Dunedin City Council and the Otago Regional Council at loggerheads for some time - and may even end up in court.
City council infrastructure services committee chairman Cr Andrew Noone says the regional council may be slowly changing its view, but there is a long way to go before the two councils reach a position on which they can agree.
The DCC applied to the ORC late last month to renew four 35-year resource consents - expiring in November - to discharge stormwater into Otago Harbour, the ocean at St Clair and Second Beaches and Andersons Bay inlet.
A report from DCC acting water and waste services manager Laura McElhone to go to city councillors next week says pre-application consultation with the ORC identified some areas of contention.
The first was that the ORC, as indicated in its notification of Plan Change 6A to the Regional Plan: Water, wanted nil mixing of discharges and greater water bodies, a position with which city council staff strongly disagreed.
Removing provisions for any reasonable mixing failed to recognise the "significant social and capital costs" on Otago communities to meet that requirement, and did not adhere to the principles of the Resource Management Act.
The city council had already made a submission to the regional council which outlined its concerns about the legality and effects of removing references to mixing zones, the report said.
Regional council staff also made it clear they intended to apply end-of-pipe water-quality standards and end-of-pipe requirements for treatment to their consideration of the DCC's stormwater consent applications.
But the city council had not included those in the consent applications, as they would require a significant deviation from the past interpretation of the Coastal plan, which would also be open to legal challenge, Ms McElhone said.
Also, end-of-pipe treatment was flawed because it did not marry the required stormwater quality with the assessed environmental effects, which was also contrary to the underlying principles of the RMA.
"The consequence of such an approach could be that the council are required to make a significant investment (in end-of-pipe treatment systems) that does not ultimately lead to any measurable improvement on the values of the receiving environment."
The ORC had also indicated it believed the DCC should install catchment-wide stormwater treatment as part of any renewal of the network, but DCC staff believed the costs and/or technical constraints of that were inappropriate.
Controlling what went into the stormwater at the source was a much better approach that could also be targeted, the report said, but controlling at-source contamination would require some strong regulations.
She said that after five years of developing integrated catchment management plans, DCC staff had a good understanding of the potential effects of Dunedin's stormwater discharges.
Based on that work it believed the current stormwater discharges, given the already modified nature of Otago Harbour, including the presence of historically contaminated sediments, were not having any significant detrimental effect on the ecology of the harbour.
The DCC had an ongoing commitment through its Three Waters Strategy, to improve the quality of stormwater and had already committed $2.6 million to doing so up to the end of the 2013-14 year, she said.
The DCC's application six months before the consent ended meant the status quo would remain until an agreement on new consents was reached.
The report will be considered by the DCC's infrastructure services committee next week.