Complications across various sites are hindering the progress of ultraviolet (UV) disinfectant treatment upgrades across the district.

There was $2.9 million budgeted for treatment upgrades in the Ashburton District Council’s 2023/34 annual plan, but asset manager Andy Guthrie said each project is presenting its challenges.

“Every site has its own unique little complexities which is just slowing everything down.

“We are putting the focus on some of the simpler ones which we can get some progress in the current year.”

The annual plan had outlined upgrades at the Ashburton ($2.1m), Fairton ($198,170), Mayfield ($198,170), Chertsey ($203,000), and Dromore ($211,729) water supplies.

Infrastructure and open spaces group manager Neil McCann said the budgets originally included the physical works of supply and installation of the necessary UV equipment and filtration at some sites.

“The budgets were developed on the assumption that everything would fit within the existing buildings.

“As concept design has progressed the scope of work has expanded.

“These scope changes are different at different sites, such as some sites required entirely new buildings to house the equipment, other sites also need significant consequential upgrades to the power supply and other ancillary systems.”

The council had combined all of the projects spanning three years into a single package of work, he said.

“They are only now being split out as we approach the detailed design phase, in order to progress the physical works more sequentially.”

The focus is now on completing four of the 10 sites by the end of the 2022/23 year, those being Hinds, Fairton, Mayfield, and Dromore, McCann said.

The other sites - Ashburton (four sites), Rakaia and Chertsey, will be completed by the end of 2024/25 “subject to approval of additional funding provision in the proposed long-term plan to address the increased scope”.

The Ashburton upgrade is proving the most challenging because of its four treatment plant sites to consider, Guthrie said.

“All four of the sites are on reserve land of some form and because we are faced with the prospect of having to extend some of the buildings we actually need land use consents [for three of the sites].”

A structural design review is underway to understand the feasibility of reusing the existing buildings.

The council’s other five water supplies are already equipped with UV treatment.

What does UV do?

Ultraviolet disinfection provides a second barrier to bacterial and protozoal contamination (such as giardia and cryptosporidium) of the source water in deep groundwater supplies.

By Jonathan Leask