The Christchurch City Council (CCC) is currently seeking feedback from the community about new and improved Water Supply, Wastewater and Stormwater bylaws. You can read all the finer details here. In particular, the draft CCC Water Supply and Wastewater Bylaw will improve the powers of the Council to ensure that private wastewater laterals are maintained in working order. Will it be enough to stop the seemingly inevitable pattern of rain, stormwater, sewage that accompanies a rain event?
Rain, stormwater, sewage – in that order. It’s December 2021 and more rain falls in 24 hours than normally falls in the whole of December. The Ōpāwaho Heathcote River rises quickly while the Christchurch City Council (CCC) and Environment Canterbury (ECan) issue warnings about flooding of city streets.
Groundwater infiltrating a cracked pipe.
At the same time, the inbox of the Ōpāwaho Heathcote River Network (OHRN) starts to fill as the CCC issues warnings, one after the other, of sewage overflows into the Ōpāwaho Heathcote River:
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- Steamwarf stream at St Johns St
- Linwood Canal behind Lomond Pl
- Main Road, Moncks Bay to West of Yacht Club
- Corner of Eastern Tce and Waltham Rd
- Corner of Richardson Tce and McKenzie Ave
- Corner of Ferry Rd and Richardson Tce
- Corner of Eastern Tce and Fisher Ave
- Corner of Fifield Tce and Locarno St
- Estuary at Scott Park, south end of gravel beach
- Corner of Cashmere Rd and Shalamar Dr
- Corner of Eastern Tce and Sandwich Rd
The warnings all give the same reason for the overflow of sewage into the river: “Excessive flows in the wastewater network due to high levels of rainwater inflow and groundwater infiltration.”
Sewage entering the river is obviously something that everyone wants to avoid and the CCC has spent, and is continuing to spend, millions of dollars to prevent this happening. So, what causes “high levels of rainwater inflow and groundwater infiltration”?
There are several causes:
- Stormwater systems incorrectly configured to illegally empty directly into wastewater pipes instead of into stormwater pipes
- Wastewater traps below the level of surrounding ground allowing surface water to enter the wastewater system
- Cracks and breaks in the council’s own wastewater system allowing infiltration of groundwater (although much of this has now been repaired post-earthquakes)
- Cracks and breaks in wastewater laterals (the pipes connecting private wastewater systems to the sewer) allowing groundwater to enter the wastewater system
Of all of these, the latter two are probably the greatest issue, particularly since the earthquakes which left few of Christchurch’s older, ceramic pipe sewer laterals intact.
The draft Water Supply and Wastewater Bylaw 2022 bylaw includes a new requirement for owners to repair damaged or broken private wastewater pipes in order to prevent any consequential issues in the public wastewater system, including blockages, damage, infiltration, leakage and overloading the system.
Clause 31 (1) reads:
No person may cause or allow any of the following to enter a wastewater pipe or fitting, a drain connected with a wastewater pipe, or the wastewater system, without the Council’s written approval under clause 27, or an approval or consent under the Council’s Trade Waste Bylaw: (a) stormwater or groundwater (including from a water pipe, an artesian well or spring, surface water, subsoil drainage or roof water)
Clause 32 backs this up with:
(2) Private wastewater drains must be maintained in a state which is free from cracks and other defects which may allow infiltration, leakage, or cause blockages.
(3) If the Council believes that wastewater drains on private property are deficient, damaged, blocked, receiving excessive inflow and infiltration, are leaking, or are otherwise not in a satisfactory operating state; the Council may require the property owner to investigate the drain and rectify any issues, at the owner’s cost.
There are several other clauses which detail what is required of a private owner if the council requires investigation and subsequent repairs of a private sewer lateral. It seems surprising that the CCC has not previously had such express powers to ensure that private sewer connections are not causing issues to the public wastewater system. Once this draft bylaw is approved, let us hope that the new powers are put to good use to help reduce sewage overflows.
It would be a resource-consuming task for the CCC to investigate every old private stormwater system and many will have been renewed anyway as part of post-earthquake repair strategies paid for by insurance claims. Witnessing the inevitable erection of “Polluted water” signs on the banks of the Ōpāwaho Heathcote River should be a call to all house owners who have yet to do so to ensure that their sewage laterals are not cracked and contributing to the overflow problem.
While it is true that wastewater overflows into the river during rain events tend to be short-lived pollution given the flushing effect of high river flows at the time of the overflow, such pollution of the river should be avoided from a health viewpoint, and such events are culturally offensive to Ngāi Tahu, mana whenua of the river.
See also in this series of items relating to the draft Water Supply, Wastewater and Stormwater Bylaws: