Draining the basins at New Plymouth's waste water treatment plant for the first time in nearly 30 years has presented an unexpected find.
Golf balls and plenty of beach sand have been found during the process.
The waste water treatment plant is undergoing a $23 million upgrade known as the Wai Taatari project.
As part of that upgrade the facility's two holding basins at the biological treatment stage are getting more efficient aeration diffusers retrofitted into the bottom.
Water and wastes manager Mark Hall said to install the diffusers, the 3.8 metre deep basins needed to be drained.
"The upgrade is about increasing the amount of aeration capacity in the basins," Mr Hall said.
Each basin, which holds about 4500 cubic metres of water, will have more than 2700 diffusers installed.
As the first basin nears completion the second one is taking the load of New Plymouth's waste water - currently operating at 85 per cent capacity.
This was the first time the basins had been emptied since they were commissioned in 1984.
"There were some unknowns about what we would find."
What was found was tonnes of black sand that had settled on the bottom of the basins, most likely from people showering after days at the beach.
"By the time you get 30 years of people washing their feet from sand it all accumulates."
Dozens of golf balls from the neighbouring Ngamotu golf course were also found bobbing in the bottom of the basin.
Of the $23m being spent over the five-year project the aeration filters for the basins would cost $11m.
The empty basin would be refilled and operational by May.
Then the second basin would be emptied and retrofitted with aeration diffusers.
The new diffusers would have a life span of up 10 years.
The aeration diffusers will be pumped full of air by three new blowers which pump out 17,000 cubic metres of air per hour.
"They're like an upside down shower head."
- Taranaki Daily News
What is the purpose of speed cameras?Related story: Hundreds caught by new speed camera