The Gore District Council is seeking more information about spikes last month in the level of ammonia gas emissions from the aluminium dross stored at the former Mataura paper mill.
The Council’s resource consent for the storage of the dross has a condition limiting the amount of ammonia gas discharged to the air to 5 parts per million. Since April 2018, the Council has engaged Land and Water Science to conduct continuous monitoring for ammonia gas, both indoors and outdoors, at the site.
On Saturday 8 February, just after midnight, the indoor sensors at the mill registered a level of 149.6ppm. The outdoor sensor maximum level during this time was 5.1ppm.
A second, albeit lower, spike occurred mid-afternoon on Sunday 16 February, when the indoor level registered 89.8ppm. The maximum outdoor level recorded on this day was 4.6ppm.
Gore District Council chief executive Stephen Parry said the spikes were concerning and the Council was investigating further.
Inalco, the company contracted to move the dross, has been notified, Mr Parry said.
Gore District Mayor Tracy Hicks said the incidents reaffirmed the need to get the dross out of its present location as quickly as possible.
“The dross should never have been stored at the mill in the first instance.
“We (the Council) have tried to do the best with the hand we were dealt after dross owner Taha Fertiliser Ltd went into liquidation, but the time has come to expedite its removal from Mataura.”
In its report, Land and Waters says increases in ammonia concentration greater than the threshold occupational exposure limit for ammonia toxicity to humans is often due to the strong relationship between air temperature and ammonia concentration.
“However, these ammonia concentration extremes do not appear to be temperature correlated. Extreme spikes such as these are possibly the result of disturbances caused by movement, agitation, or moisture affecting the product,” the report says.
It recommends any person entering the building should first check the monitoring sensors to ensure concentrations are less than 25ppm.