Tauranga City Council's failure to keep up with sludge clearance at the Te Maunga sewerage ponds has resulted in staff asking for $1.68 million to complete the over-due project.

Council approved $3.5 million in 2014 to de-sludge Pond 1 throughout 2014/15 and 2015/16.

The volume of biosolids in the ponds have posed problems. Photo: File.

Revision of the expected timing and total cost of the desludging, which should have seen most of the required work done and paid for in 2014/15, revealed that the budget wasn't carried through in this year's Long Term Plan.

Contractor delays and a higher-than-anticipated volume of biosolids in the ponds have also posed problems– possibly because the ponds are supposed to be de-sludged every three-to-five years. Pond 1 has been de-sludged twice in the last 10 years.

In August 2014, council decided the project would be paid for from $3.5 million, made available over two financial years.

In the 2015-25 Long Term Plan, the budget for desludging in 2015/16 was revised downward to $1.05m based on assumptions about timing of expenditure, the volume of biosolids and the total cost involved.

The assumptions, however, mean it will cost $2.7 million to fully clear the pond of biosolids in the current financial year.

Council staff say the total expenditure still remains slightly below the previously approved $3.5m.

To enable works to continue, $500,000 has been approved by the Chief Executive under his financial delegation, pending the request to council for approval of the additional $1.68m that has to be spent this year.

The Te Maunga Wastewater Treatment Plant produces around three tonnes of excess activated sludge per day.

This sludge is pumped into Pond 1 at Te Maunga to allow it to stabilise further over three to four years. The pond is then periodically de-sludged and the dewatered sludge is buried at the Te Maunga landfill.

There is an option of ceasing desludging once the additional $500,000 expenditure has been completed.

However, this would result in the ponds not being fully cleared and, given the cost of establishing equipment to undertake the desludging, it is considered more efficient to continue to clear the ponds under the current contract.

There is no impact on rates from the requested overspend as sludge removal is funded directly from the Biosolids Reserve which has sufficient funds available.

This expenditure will increase net debt, but with the current debt position and forecast revenue and expenditure, debt is expected to remain below LTP forecasts at year end.