'Confident' about siting of bores

Julie Muir
Julie Muir
The siting of the bores for Alexandra's new drinking water supply near an old Clyde dam landfill site presents no issues, Central Otago District Council executive manager infrastructure Julie Muir says.

The bores were upstream of the landfill site, and any potential threat from the site was "thoroughly investigated'' in 2016 by project managers, who consulted Contact Energy, Ms Muir said.

"Our engineers are totally confident that this does not pose a threat, otherwise we would not have chosen this site.''

She also confirmed the scheme had completed appropriate checks and consents.

Alexandra man Gavin Dann has raised concerns about the proximity of the bores to the old landfill site. He said he did not accept there was "an upstream or downstream in a lake that close to a dam'', and was "not sure how well a clay liner [of the old tip site] will perform in the alpine fault rupture''.

The $14.8million drinking water scheme - which may now cost up to an extra $5million because of the recent discovery in Lake Dunstan of the algae that causes lake snow - involves taking filtered lake water from new bores near Lake Dunstan, at the Clyde drinking water supply source; building a new high-tech water treatment plant in Clyde to treat the water; and constructing a pipeline to take the drinking water to Alexandra.

Ms Muir said that the bores that would be used for the new water supply were 350m upstream from what was previously the landfill site.

The design brief for the scheme ensured the drainage path for the scheme "completely'' avoided the landfill site, which was built in the 1990s.

As well, there remained a "well-engineered 400mm clay liner'' in place at the old landfill site to avoid any possible leakage, Ms Muir said.

Monitoring of the disused landfill site is done by Contact Energy.

A Contact Energy spokesman said the landfill had been used for refuse from the construction of the Clyde dam, and some Clyde township refuse.

Ms Muir said consents for four bores were in place and the bores had already been drilled.

The first consented bore had been supplying water to Clyde since 2002. A second test bore did not provide an adequate flow and would not be further developed, so required no further consents.

The third bore would be further developed for the Alexandra supply and a further consent applied for.

A fourth bore would accommodate future growth in the district, and is included in the consent for the third bore.

Otago Regional Council general manager regulatory Peter Winder said resource consents were already in place for the water supply pipeline.

Mr Winder confirmed the closed landfill was lined with an impervious geo-synthetic clay; no leachate had been recorded; and monitoring at wells outside the landfill had not identified any impact on groundwater.

Construction of the pipeline started last week.

pam.jones@odt.co.nz

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