Options could trim up to $32M off water project
Wastewater Project Management Group, Gisborne District Council
For immediate release, 22 May 2008
Options could trim up to $32M off wastewater project
Constructing a consent-compliant wastewater treatment plant at the already designated Stanley Road site could cut nearly $11.75M from the $84.37M projected cost of the Gisborne Wastewater Project.
Adding several other options – removing or delaying solids separation and increasing the biological loading – would increase potential savings up to $32.6M and reduce the estimated final cost to $51.72M. This would require some changes to conditions in the 35-year resource consents granted last year.
Removing the solids removal stage of the treatment plant would also reduce operating costs over 35 years by about $42M.
The 1.35ha Stanley Rd site close to Gisborne’s Waikanae Beach is believed to have been designated for treatment plant purposes when the city’s 1.8km submarine outfall was commissioned in 1965.
CH2M Beca project director Garry Macdonald this morning presented six cost-reducing options to Gisborne District Council’s Wastewater Management Committee. Councillors had asked its consultants to further investigate cost-saving concepts presented to them at their April meeting. A separate system for core industries looks set to remain.
Mr Macdonald said placing the treatment plant adjacent to the current milliscreening plant site at Stanley Rd would have a capital saving of $11.75M, including $2.05M risk and escalation and $7.52M for pipelines that would otherwise be required to transfer wastewater between the Aerodrome Road site and Stanley Road. The potential $146,000 a year operating cost savings compound to $4.7M over the 35-year consent period.
All prices quoted exclude GST. Simply adding GST is not correct because some components, such as depreciation on the Stanley Road outfall plant, will not attract the tax.
Mr Macdonald said the Stanley Road option had many advantages including cost savings. Only one building and one construction site would be needed instead of two buildings on two separate sites. Savings would be made on screens, electrical components, power supply, buildings and controls. The site had a good clay base at 10m deep and would require less dewatering than the Aerodrome Rd site.
However, the flood risk at Aerodrome Rd would be replaced by a tsunami risk at Stanley Rd. This would be mitigated by locating the control building at first floor level over the inlet works. The highest buildings would be the 9-10m trickling filter tanks, about 32m in diameter. These would be located at the back of the designated site, halfway between Awapuni and Centennial Marine Drive.
Added features, including a 10m-wide perimeter vegetation buffer within the existing designated area, would be required to lessen any potential odour and visual effects.
The plan would require taking half the 40m width of Stanley Rd, between Awapuni Rd and Centennial Marine Drive, but none of the Adventure Playground other than the area currently designated.
Mr Macdonald said it was important to note that the biological trickling filter treatment plant would still be a more cost-effective solution over the life of the plant than the previously proposed activated sludge system. Many other components of the total new wastewater scheme would have been common to either of these biological treatment systems.