WASTE

History made as wastewater flows through treatment plant

Wednesday 29 December 2010, 2:02PM
By Gisborne District Council
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GISBORNE

It’s all go. After years of discussion, debate, design and construction, Gisborne city’s new wastewater treatment plant at Banks Street is in action – on time and under budget.

The first wastewater successfully flowed through the plant from about midday today (28 Dec) after a week of testing the new system with clean water and connecting the new sewerage system to the old. Commissioning the plant before 31 December 2010 was one of the conditions of the 35-year wastewater resource consents for treatment and disposal granted in late 2007.

Representatives from Gisborne District Council, the wastewater technical advisory group, HEB Structures and CH2M Beca were on hand for the historic occasion. The treatment plant is one part of the $39.5 million Gisborne Wastewater Project, which also includes the separation of industrial wastewater.

Gisborne District Council chief executive Lindsay McKenzie today praised the excellent approach to the project and the quality of the consultants, contractors and staff involved. “Given the size of the spend, I am amazed and delighted that few issues have come my way. That is testimony to the quality of the planning, construction and project management team.

“Council has not had a great history of coming in on time and on budget with big capital projects. Let this project be a watershed, a turning point for us, as the hidden cost of not getting these things right is a cost to the ratepayer.”

Mr McKenzie said the original scoping and full costing of the consented project created difficult times. “Many were saying that the project should not proceed because of the cost and global economic crisis, and because it wasn't needed. The prospect of an $80 million plus plant was simply not acceptable; neither was not having a plant at all.

“While the pressure brought out the best in everyone, we were close to meltdown a few times. I hope people now see the value in the work and appreciate the complexity of the project.”

The project cost was reduced to $45M and later to under $40M. Engineering and works manager Peter Higgs said the project had been a great team effort from councillors, council staff, the people involved in the consent process, consultants, contractors, industries and the wider community. “They have all worked together for the common goal of having this treatment plant operational by the date specified.

“It is very pleasing to meet the deadline and to bring the project in under budget.” The plant will be officially opened in March 2011.

How it works

Domestic wastewater is screened by one of two rotating drum screens (one is on duty, one on standby) and then passed through a vortex grit removal chamber. Two more drum screens are used for industrial wastewater.

The screenings and grit removed from these stages will have the water pressed from them before being bagged and trucked to a landfill at Paeroa.

The screened and de-gritted wastewater gravitates into a biological trickling filter pump station before being pumped up through the tank’s central column to a height of 8m, then distributed through six rotating arms to trickle slowly through many different channels in 10 layers of large plastic media blocks.

In so doing, very fine screened and degritted wastewater solids are transformed into plant-like matter. The resulting treated wastewater is pumped via a new outfall pump station to the existing marine outfall, 1.8km out to sea. 

 

Timeline

1987            East Cape Catchment Board looks to prosecute Gisborne City Council over a 50 percent increase (over 20 years) in effluent discharge without notification to the board.

1988            Gisborne City Council begins initial consultation about wastewater.

1991            Milliscreening plant commissioned. First upgrade since 1965.

1998            District council begins series of community meetings to identify public aspirations for wastewater. Consents due to expire at end of 1999.

                     Wastewater Working Party established with council staff and representatives from tourism, health, Department of Conservation, environmental groups and tangata whenua. Tangata whenua appeal to Environment Court on the ground that raw wastewater discharge to the ocean broke their relationship with the sea and kaimoana; call for zero discharge to sea.

2002            Council approves long-term wastewater strategy that includes completion of city stormwater and sewer upgrades, removal of grit and grease, milliscreen replacement, primary sedimentation treatment plant near the airport by 2010 and secondary treatment of activated sludge and ultraviolet disinfection by 2016 with through-land trials in 2017.

2003            Council lodges applications for new resource consents.

                     Existing consents effectively extended to 2005.

                     Council kiboshes idea of disposing all treated wastewater to land as unfeasible.

Sept 05      Engineering and works department applies for suite of resource consents; boulder bed added to address cultural concerns.

April 06       Hearing commissioners adjourn court sitting on first day, praise parties for joint approach, request Wastewater Adjournment Review Group (WARG) be established.

Sept 07      35-year resource consents granted for the treatment and disposal of city wastewater.

Nov07        Council accepts CH2M Beca Ltd as consultants to design and manage the overhaul and upgrade of the city’s wastewater system

Feb 08        Best for Gisborne logo developed for project.

                     Wastewater Management Committee and Independent Review Panel set up as condition of consents.

April 08       Consented scheme scoped and costed at over $84M. Plant to be sited near airport. Doing nothing not an option because of legal and environmental necessity and poor condition of existing plant.

                     CH2M Beca and Council staff investigate cost-saving options; government assistance sought.

May 08       Suggestion made to relocate treatment plant closer to Stanley Road, initially on existing milliscreening plant site, to help trim $32M from cost.

June 08      Council decide to go to consultation to consider Stanley or Aerodrome road options.

Aug 08        Team presents affordable $40M project.

Oct 08        Council buys Banks Street site as viable alternative for treatment plant away from beachfront; community favour Banks Street site after consultation.

Nov 08       Council endorses Banks Street as site for treatment plant. Variations to existing consents lodged for “reduced scope” scheme – full industrial separation, pre-treatment for both industrial and domestic wastewater and one biological trickling filter tank to treat domestic wastewater, rather than two as originally consented.

Feb 09        New resource consent applications for “reduced scope” scheme publicly notified.

May 09       Council gains resources consent for “reduced scope” scheme.

                     Registrations of interest called for construction of treatment plant and separation of industrial wastewater.

Aug 09        Sole appeal against Hearing Commissioners’ go-ahead withdrawn.

Nov 09       HEB Construction wins $21M tender to build new wastewater treatment plant and associated industrial separation scheme.

                     Downer EDI Works wins $1.1M contract to construct western industrial pipeline.

                     First sod turned on 30 Nov 09 as HEB Structures, part of HEB Construction, takes possession of Banks Street site.

28 Dec10 Banks Street treatment plant commissioned with first wastewater diverted from old system to new.