Crunch time for wetlands

Report indicates wetlands will cost up to $64 million, and cheaper options now available.

Report indicates wetlands will cost up to $64 million, and cheaper options now available.

The operation of an algae pond is demonstrated to wastewater management committee members earlier this year. Now the cost has escalated GDC may look at other optioins. Picture by Paul Rickard

THE potential cost of a wetlands option to treat wastewater has increased to between $38 and $64 million, the wastewater management committee will be told on Thursday. Gisborne District Council faces a crucial decision on whether to proceed with a wetlands trial.

If it decides not to, GDC will have to install a clarifier and ultra violet treatment for wastewater at a potential cost of up to $28 million to meet its conditions for the resource consent that allows the continued use of the marine outfall pipe into the bay.

The consent requires the council to have an objective of complete removal of human sewage from the outfall pipe by 2020.

The committee is being advised to pass the issue over to the council at its December meeting. The recommendation is the council undertake consultation and detailed design and planning work on the wetland option to determine whether it should be the preferred option for treating the city’s wastewater.

That decision will have to be made by December 2017 to enable the necessary resource consents to be lodged by 2018.

A report from GDC strategic planning manager David Wilson to the committee says the costs for the wetlands option are far greater than the original estimates of $12 to $15 million.

Detailed costings

Detailed costings now indicate figures of between $38 and $64 million. This is due to the significant capital costs of conveying the water to and from the wasteland, the cost of the pipe required and the large area required for the treatment due to the volume and consistency of the wastewater.

There are also associated costs of forming the bunds, accessways and earth embankments needed for the settlement ponds.

The costs of mechanical disinfection have dropped since the technology was first investigated from $2 million to $800,000. But suspended solids issues identified in 2013 remain and the water is not clear enough for UV disinfection, so a method of clarification would be needed.

The cost of clarification and UV treatment would be $28.5 million and the water would still need to be discharged through the marine outfall pipe.

Proceed or halt the trial

Mr Wilson said the council must decide by December 31 whether to continue with the next stage of the wetlands trial or to halt the trial and proceed with mechanical disinfection.

The wetlands trial so far had not given an obvious option to proceed, but it had identified a number of options that were feasible.

There were ways to lower the costs significantly, including reconfiguring the ponds to require less surface area, downsizing the wetlands, substituting the sludge treatment wetland and incorporating a lamella clarifier to remove solids then dispose of the liquid into a habitat wetland.

The resource consent granted for the continued use of the marine outfall pipe sets a deadline of December 31 for the council to confirm the feasibility of an alternative system.

If it fails to confirm the alternative, or fails to lodge the necessary consent applications by December 2018, it must install wastewater disinfection within 24 months of these dates.

THE potential cost of a wetlands option to treat wastewater has increased to between $38 and $64 million, the wastewater management committee will be told on Thursday. Gisborne District Council faces a crucial decision on whether to proceed with a wetlands trial.

If it decides not to, GDC will have to install a clarifier and ultra violet treatment for wastewater at a potential cost of up to $28 million to meet its conditions for the resource consent that allows the continued use of the marine outfall pipe into the bay.

The consent requires the council to have an objective of complete removal of human sewage from the outfall pipe by 2020.

The committee is being advised to pass the issue over to the council at its December meeting. The recommendation is the council undertake consultation and detailed design and planning work on the wetland option to determine whether it should be the preferred option for treating the city’s wastewater.

That decision will have to be made by December 2017 to enable the necessary resource consents to be lodged by 2018.

A report from GDC strategic planning manager David Wilson to the committee says the costs for the wetlands option are far greater than the original estimates of $12 to $15 million.

Detailed costings

Detailed costings now indicate figures of between $38 and $64 million. This is due to the significant capital costs of conveying the water to and from the wasteland, the cost of the pipe required and the large area required for the treatment due to the volume and consistency of the wastewater.

There are also associated costs of forming the bunds, accessways and earth embankments needed for the settlement ponds.

The costs of mechanical disinfection have dropped since the technology was first investigated from $2 million to $800,000. But suspended solids issues identified in 2013 remain and the water is not clear enough for UV disinfection, so a method of clarification would be needed.

The cost of clarification and UV treatment would be $28.5 million and the water would still need to be discharged through the marine outfall pipe.

Proceed or halt the trial

Mr Wilson said the council must decide by December 31 whether to continue with the next stage of the wetlands trial or to halt the trial and proceed with mechanical disinfection.

The wetlands trial so far had not given an obvious option to proceed, but it had identified a number of options that were feasible.

There were ways to lower the costs significantly, including reconfiguring the ponds to require less surface area, downsizing the wetlands, substituting the sludge treatment wetland and incorporating a lamella clarifier to remove solids then dispose of the liquid into a habitat wetland.

The resource consent granted for the continued use of the marine outfall pipe sets a deadline of December 31 for the council to confirm the feasibility of an alternative system.

If it fails to confirm the alternative, or fails to lodge the necessary consent applications by December 2018, it must install wastewater disinfection within 24 months of these dates.

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Winston moreton - 2 years ago
Every community in the world since the Ming Dynasty has this problem. What we have here is is an example of the replacement of No.8 wire solutions by over-engineered politically-correct flimsy cultural-science tissues. Hope the Crs sack those giving advice and use the saved salaries and consultancy costs to homespin a solution. Mayor Meng must've seen how modern China tackles the crap on his Sino shopping excursions. I bet he could present a good old fashioned and absorbing paper based on his experiences and save ratepayers heaps.

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