Wastewater system damage
The earthquakes have caused several different kinds of damage to our wastewater system:
- Treatment plant damage
- The earthquakes badly damaged the Christchurch Wastewater Treatment Plant and its oxidation ponds, although it continued to operate at a reduced capacity. Clarifiers were also badly damaged. As a temporary measure, for a short period, the effluent that was pumped into the ocean was not treated to the usual safe level.
- The earthquakes cracked pipe walls, allowing all kinds of other liquids and obstructions into the pipes. The liquids include groundwater and liquefaction silt. These are a problem mainly because they reduce the carrying capacity of wastewater systems.
- Some wastewater pipe sections completely collapsed, particularly older earthenware pipes. Wastewater pipes suffered more collapse than fresh water pipes because they had a higher proportion of old materials. Many wastewater pipes had to be diverted before repairs could commence.
- Joint breakage
- Where some pipes have been joined together, the shaking has separated the two parts again, so the pipe is essentially broken.
- Pump station damage
- Sewer pump stations and their pressure mainssuffered varying damage. We need to completely replace some of them. For a brief time, effluent was pumped into urban waterways because the sewer pump station network was so damaged.
- Loss of gradient
- Pipes generally run water in a downward gradient to take advantage of gravity. Liquefaction pushed some pipes up, which reduced the gradient over a widespread area.