Wastewater pond desludging in Martinborough is now complete, with 660 tonnes of solids removed after more than 50 years of build-up.
The work was required after new wastewater connections were paused in May 2023 because the plant was operating beyond its capacity.
Although the desludging effort did not solve the capacity issue for Martinborough, it was necessary to address non-compliance issues identified by the regional council.
The regional council issued an abatement notice for the plant in 2023 for exceeding hydraulic load constraints when discharging to land and river, and exceeding E.coli and nutrient limits when discharging to the river.
Desludging would improve operations, support resource consent compliance, enhance environmental outcomes, and reduce public health risks.
The abatement notice for the plant has now been lifted and South Wairarapa District Council would soon meet with Greater Wellington Regional Council to discuss next steps.
A district council spokesperson said options to increase the wastewater treatment plant’s capacity were being explored and were budgeted for in the 2025-34 Long-Term Plan.
“The council is negotiating the purchase of alternate land to Pain Farm for discharge to land treatment,” they said.
Once this was done, the discharge of a higher volume of treated wastewater to land would help efforts to maintain compliance.
“We will keep the community updated on key milestones as we and Wellington Water work together towards full compliance for the plant.”
The council thanked the Glasgow Contractors team which completed the desludging work in Martinborough.
They have taken all of the equipment to Greytown to begin the pond desludging process there later this year.
A pause on new wastewater connections also remained in place for Greytown.
The Greytown wastewater treatment plant was designed to service about 2200 people and the existing population exceeded this by about 500 people.
What is desludging?
South Wairarapa District Council uses wastewater stabilisation ponds, or oxidation ponds, to treat wastewater.
Over time, bio-solids build up in the bottom of these ponds as sludge – a byproduct of the treatment process.
The sludge must be periodically removed, or it will reduce the treatment ponds’ efficacy.
Desludging is a successful method that has been used at other pond-based treatment plants throughout New Zealand.
The process involves pumping or vacuuming sludge into sediment filter bags, or geobags on-site.
The geobags allow water to flow out through the porous fabric of the bags while filtering and retaining the solids.
This process takes between three and five years.
LDR is local body journalism co-funded by RNZ and NZ On Air.
