The first stages of the Rotorua Aquatic Centre upgrade have begun with essential ground testing under way in the 50 metre outdoor pool area.

Geotechnical engineers and surveyors have been on site at the pool during the past couple of months to test the soil around the facility in order to get a clear picture of what is needed to prepare for refurbishment.

Andy Pomfret and his team from Initia (geotechnical specialists) spent time at the pool testing the ground to gain an understanding of the types of soil that made up the foundations under and around the 50m outdoor pool.

Pomfret, who has been involved in geotechnical testing at pools around the country, said the report would help plans for pool refurbishment to be developed that mitigated issues from subsequent movement due to poor ground conditions.

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"A geotech report is an understanding of the groundwater conditions and it's needed to enable a full design of the pool to go ahead without any issues like settlement, cracking of the pool, the load of the structure.

"So really you need a really good understanding of what's beneath the pool and surrounding areas so when a new facility is constructed it won't have any issues," he said.

The preliminary testing included taking samples from various depths around the facility to get a visual understanding of the water content in the soil.

"In an ideal world we would find something hard so when the pool is revamped or reconstructed then the founding layer is hard enough and it won't settle. Unfortunately given it's Rotorua and we have lake deposits here it's quite soft so we may have to come up with some alternative foundation solutions," Pomfret said.

In order to get a complete picture of the ground condition, geologists from Southern Geophysical have also carried out resistive and ground-penetrating radar testing as a non-invasive way to determine the layers of material under the ground.

Southern Geophysical geologist Richard Mellis said that coupled with the data from the borehole tests the survey results would give designers a really good picture of any issues they needed to take into consideration when planning for the pool upgrades.

"One method of testing is using a resistivity line to measure what's under the ground. The different layers. For instance, a gravel layer will be highly resistive and a clay layer that's saturated will have very low resistance."

In its 2018-2018 Long-Term Plan, Rotorua Lakes Council set aside $7.5 million to go towards the initial stages of the redevelopment of the Aquatic Centre facilities with the expectation that external investor funding would be found and used to carry out subsequent redevelopment stages.

A number of priorities and issues have been identified to be addressed including replacing the roof, repairing and upgrading the 50m outdoor pool and upgrading changing rooms and toilets.

The council said they were committed to ensuring the facilities were modern, safe and fit for purpose.

The $7.5 million investment would be spread over three years and the upgrade would be undertaken in stages.

The council said it had been working with the centre's management company CLM as well as pool users and community members to ensure it met the needs of the people of Rotorua and were continuing to work to secure external funding for future assets like a dedicated Learn to Swim facility, hydroslides, a dedicated bomb pool and a cafe space.