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Contractors have begun on-site preparations for the first stage of work to replace about 5km of old pipes in Edinburgh St and adjoining streets.
“After assessing the sections of pipe as possible causes of lead contamination, we have decided the best course of action is to replace them as quickly as possible," Dunedin City Council 3 Waters group manager Tom Dyer said.
“The source of the intermittent spikes in lead levels has not yet been confirmed, but this work will remove one potential source of contamination."
Residents of Waikouaiti, Karitane and Hawksbury north of Dunedin have been advised not to drink tap water since Tuesday last week after elevated lead levels were detected in the Waikouaiti raw water reservoir last month.
Officials have been unable to pinpoint why elevated lead levels had been found, but the city council is pressing ahead with plans to replace old pipes, removing one potential source of contamination in the Waikouaiti, Karitane and Hawksbury supplies.
New polyethylene pipe has been ordered to replace the old sections of pipe and construction activity is expected to ramp up in the next two to three weeks.
The work is expected to cost $6 million.The council is continuing to provide water tankers in affected communities while testing daily for contamination.
Waikouaiti's raw water reservoir will be drained early next week to allow lead joins to be replaced, and sediment to be tested and cleaned out.
The council has ordered an online lead monitor, which is a piece of equipment that draws water into sampling equipment for analysis and provides results every 20 minutes.
It is expected to take six to eight weeks for the monitor to be delivered, installed and operational.
A conductivity monitor has been installed at the Waikouaiti River intake and a pH meter will be added next week.
Together, the two pieces of equipment will provide real-time information on changes in water chemistry and potentially help detect the presence of lead more quickly.
The first of two auto-samplers is about to be installed at the Waikouaiti water treatment plant. Samples will be taken each hour and then analysed in batches at the University of Otago, helping give confidence in the quality of the water.
Tonkin and Taylor will review data from the treatment plant, seeking to identify any correlation between high lead levels and other water chemistry or operational issues. Results are expected by the end of next week.
The council also reacted to suggestions residents in Hawksbury Village had been overlooked.
Mr Dyer said village residents were among those contacted during a door-knock and letter-drop operation last week. A water tanker has been positioned inside the village since last week.
Blood testing of Waikouaiti, Karitane and Hawksbury is being organised by Public Health South.
The next batch of water test results is expected to be available tomorrow.
The provision of free fruit and vegetables in the community will conclude tomorrow, after consultation with the Waikouaiti Coast Community Board and after advice has shown produce from gardens is safe to eat if washed with clean water.
A follow-up to last Friday's public meeting is being planned.
Council staff will be running drop-in sessions at the East Otago Events Centre in Waikouaiti over the next two weeks, beginning on Tuesday, to answer questions from residents.
No signs of contamination in Waikouaiti River
The Otago Regional Council reported today initial samples taken from the Waikouaiti River show no signs of lead contamination.
Samples were taken of river water upstream and downstream of the intake for the Waikouaiti raw water reservoir on the morning of February 4.
"Lead was below detectable levels in both of the water samples."
ORC chief executive Sarah Gardner said the two samples were useful and would help the council direct its investigation.
“We will continue to investigate because it is absolutely imperative that we deliver an answer about the river water that can be trusted by the impacted communities.
“ORC and the DCC are collaborating on a wide-ranging catchment study of the Waikouaiti River, including water and sediment sampling. The results of this week’s sediment sampling are likely next week, with additional monitoring to be undertaken in the meantime,” Mrs Gardner said.