Last week, the mining company notified local residents that it would be releasing water from the lagoon next to the Awonga Point Sewerage Treatment Plant into the Mission River following heavy rainfall.
Under normal operations the Awonga Point STP produces “high quality effluent” that is released via a submerged pipeline about 60 metres offshore, under the Mission River Bridge.
When flow to the Awonga Point STP exceeds plant processing capacity, excess volumes are diverted to an onsite stormwater collection lagoon.
Rio Tinto said the site water team had been monitoring the volumes closely to manage any risk of overtopping the lagoon.
“The measures are part of the Awonga Treatment Facility’s emergency response plans in the event of high rainfall,” a company spokesperson said.
“We have notified the Department of Environment and Science and outflow rates will be strictly monitored to prevent environmental impacts.”
Cape York Weekly understands that in the week leading up to the public notice, the lagoon approached a critical threshold at which it was at risk of overtopping.
While such an incident had not occurred before at Awonga Point rainfall events of this nature are quite common for water treatment plants in high rainfall areas requiring active management.
In order to maintain safe operation of the plant, a small steady volume of water from the lagoon will be diluted with treated water from the plant and released via existing infrastructure under the Mission River bridge until the volume stored in the stormwater lagoon is returned to a safe operating level.
This will occur over a four to six-week period, Rio Tinto said.
Water quality monitoring will be undertaken throughout the discharge period to confirm water quality levels remain in accordance with environmental licence conditions ensuring no harmful impacts are identified.
Theses outcomes will be reported to the Department of Environment and Science.
Rio Tinto said fishing and consumption of shellfish from the Mission River bridge area should be avoided as a precaution until the release is complete.