The Council has a wastewater overflow consent from Environment Canterbury, which allows the discharge of untreated wastewater to waterways during large storms when the capacity of the wastewater network is exceeded.
The main purpose of a wastewater network is to protect public health, and to prevent people from coming into contact with untreated wastewater. Constructed wastewater overflows to waterways act as safety valves on the wastewater network, so that when the network is overwhelmed in a large storm, wastewater does not overflow onto people’s properties or on the street. Consent CRC182203(external link) allowing the discharge of untreated wastewater to waterways was granted by ECan in 2016 and expires in 2029. In 2015 Council commissioned an assessment of the human health effects arising from overflow events [PDF, 131 KB].
The Council is compliant with this consent apart from one overflow location (corner of Sandwich Road and Eastern Terrace), which computer modelling shows overflows more often than the allowed twice per year. Projects to increase the capacity of the wastewater network in the area and reduce the frequency of this overflow are included in the Council's Long Term Plan.
The Council maintains a list of recent and historic overflows.
We all want to improve the quality of our waterways and we need to work out the best way to do this. We might get better outcomes by reducing contaminants in stormwater, rather than spending a lot of money reducing wastewater overflows.
For example, eliminating wastewater overflows altogether would require converting most of the city to a pressure sewer system and would cost more than $3 billion to build. However, it would not necessarily result in an improvement in water quality.
The Council carries out extensive monitoring of the water quality in our waterways and in the past year has collected and analysed over 7,000 water quality samples.
The key contaminants were:
Most water quality monitoring sites show remained steady since 2007, with some sites worsening and some improving. Following the removal of large amounts of sediment, the waterways have been returned to pre-quake environments. The Council prepares a water quality monitoring report every year.
The Council has already done a lot to reduce wastewater overflows:
Projects currently underway to reduce overflows are wastewater pipe upgrades at the southern end of Colombo Street and along Beckenham Street.
The Council's 2018 - 2028 Long Term Plan includes $10 million for four further projects to reduce overflows so that we fully comply with our resource consent. These are upgrades to the Eastern Terrace wastewater main, Tilford Street pump station and pressure main and the Opawa pump station, as well as a new pump station and pressure main from Somerfield to Saint Asaph Street.
Improving the quality of our waterways can’t be done by the Council alone – it needs to be done by the whole community. There are several things that you can do: