Old pipes being replaced
OLD castiron water pipes with lead joins are being replaced in Waikouaiti, as officials seek to remove one possible cause of drinkingwater contamination.
Contractors have begun preparations to replace about 5km of pipes in Edinburgh St and neighbouring streets.
The work for the Dunedin City Council is expected to cost $6 million.
Waikouaiti's raw water reservoir will be drained early next week, to allow lead joins to be replaced and the sediment will be tested.
A more comprehensive water testing regime is also being brought in.
The extra steps come on top of encouraging signs from recent testing for lead, which has shown the metal at either very low or undetectable levels.
Two samples from the Waikouaiti River on February 4 — one upstream and one downstream of the Waikouaiti reservoir — came back clear, the Otago Regional Council reported yesterday.
Residents of the Waikouaiti, Karitane and Hawksbury communities north of Dunedin have been told since Tuesday last week not to drink tap water after an elevated level of lead was detected at the Waikouaiti raw water reservoir last month.
Five previous spikes at Waikouaiti and Karitane sites since July — including one at 40 times the level of lead considered acceptable — had been recorded but did not immediately result in a public warning.
The source of the contamination is not known and the city council has provided drinking water from tankers while officials try to resolve the issue.
Demand for tanker water is about 10,000 litres a day.
Blood tests of residents have been carried out this week to help authorities establish whether the communities have had longterm or chronic exposure to lead.
Dunedin City Council 3 Waters group manager Tom Dyer said the sections of pipe were assessed as a possible cause of lead contamination and it was decided to replace them as quickly as possible.
“The source of the intermittent spikes in lead levels has not yet been confirmed, but this work will remove one potential source of contamination,’’ he said.
Polyethylene pipe has been ordered to replace the old sections and construction activity is expected to ramp up in the next two to three weeks.
A pH meter will be installed next week and, together with a conductivity monitor, could reveal changes in water chemistry and the presence of metals in real time.
Autosampling at the Waikouaiti water treatment plant is expected to start next week, providing preliminary results hourly.
Tonkin and Taylor is analysing plant operational data to see if there is any correlation between high lead levels and any other operational or water chemistry parameters.
The conductivity monitor and pH meter provided another monitoring tool to identify the presence of metals, city council staff said in a report to be considered by the infrastructure services committee on Monday.
Preliminary results from water autosampling would be tested by the University of Otago and could help officials isolate contamination if it happened again.
An online lead monitor had been ordered and could be operating within two months, allowing testing every 20 minutes.
Council staff also conceded in their report the source of the elevated lead readings may never be identified.
Properties with water tanks would have them drained and refilled when the water supply is deemed safe.
The Otago Regional Council is to carry out further testing of the Waikouaiti River.
“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,’’ regional council chief executive Sarah
Gardner said.
Results from sediment sampling were likely to come in next week.
The city council’s provision of free fruit and vegetables for the communities will conclude today, after advice that produce from gardens is safe to eat if washed with clean water.