Groundwater aquifers report post earthquakes Christchurch

The quality of water sourced from Christchurch’s drinking water aquifers which lie under and around the city has not been significantly affected by the September or February earthquakes and aftershocks.

“It is very pleasing to find water quality in Christchurch’s aquifers is similar to the quality before the earthquakes,” said Ken Taylor, Environment Canterbury’s Director of Investigations and Monitoring.

“There is also no evidence of any change in groundwater flow patterns as a result of the earthquakes.”

Environment Canterbury’s analysis was based on 35 wells around Christchurch which have been monitored for groundwater quality for the past 11 years. “The Earthquake Impacts on Groundwater Update #2”* is available on the Environment Canterbury website and follows the first update on groundwater levels.

For groundwater quality, 21 physical measurements including pH, temperature, dissolved oxygen as well as the level of a number of salts and minerals, were measured from samples taken from the wells.

Only seven of the 35 wells had signs of physical damage as a result of the earthquakes. Four wells in the eastern part of the city had damage to the pump and/or wellhead. Two other wells were silted and one well may have suffered an electrical fault. No wells in the western part of Christchurch were damaged.

“Shallow groundwater in some areas may have been contaminated by breakages in wastewater pipes, but there is very little risk of bacterial contamination to the deeper aquifers where drinking water is drawn from.”

Christchurch City Council’s extensive testing of wells, pump stations and reservoirs found less than 1% of 2500 samples had E.coli contamination and this is being treated by chlorination to ensure safe drinking water.

The Environment Canterbury monitoring found only minor changes to groundwater quality were observed in some of the monitoring wells.

“The minor level of the changes combined with the natural variation in groundwater chemistry means we cannot say with any confidence that the effects have been caused by the earthquakes,” said Ken Taylor.

Fifteen of the wells showed no statistically significant change in water quality pre and post-earthquakes. Several wells had measurements slightly outside the expected range but this was only for two or three of the 21 parameters that make up the water quality measurements.

Groundwater temperature was between 1 and 3° Celsius higher in a number of wells and it is possible this could be earthquake-related (this phenomenon has been noted in other parts of the world following earthquakes).

“We will continue our monitoring programme for the Christchurch wells, which are part of around 300 wells around Canterbury we monitor for changes to water quality, with a particular focus on possible earthquake effects in the city’s aquifers,” said Ken Taylor.

* http://ecan.govt.nz/news-and-notices/Pages/earthquake-2011.aspx#related-documents

The direct link to the 1.59 MB pdf is:
http://ecan.govt.nz/publications/General/earthquake-impacts-groundwater-update-2-130511.pdf