“Sludge surveys conducted in May 2019 indicate that the build-up of sludge is significant enough to negatively impact the treatment achieved in these ponds and presents an odour risk,’’ the request says.
The council blamed a Twizel sewerage pond overflow over the 2020/2021 New Year period on “a large increased flow at the oxidation ponds” due to “the numbers of people in Twizel over this period”.
Council spokesperson Chris Clarke said “the desludging process is part of the routine management of oxidation ponds and is carried out periodically to ensure optimum performance’’.
“Geotextile bags are effective at locking in odours from the dredged sludge. The bags are left for a period of time to allow the liquid to leech out (back into the ponds) and then the remaining solids are disposed of,” Clarke said.