Groundwater quality survey released

Environment Canterbury has released its annual groundwater quality survey for 2020 (PDF File, 3.0MB).

The report summarises the current state of groundwater quality throughout the region and provides analysis of trends over the past decade.

Nitrate and E. coli levels tested

Groundwater science manager Carl Hanson said each spring, when groundwater levels are usually highest, Environment Canterbury collects samples from wells to help understand the state of the resource and assess changes in water quality over time.

“The results in the latest report are what we expected,” he said. “They are similar to most years, noting that these are ‘snapshot’ surveys.

“Groundwater is vulnerable to contamination, including E. coli and nitrate. For the 2020 survey, 322 wells were sampled region wide. E. coli was detected in the samples from 37 (11%) of these wells, and the samples from 20 (6%) of the wells had nitrate concentrations above the Maximum Acceptable Value (MAV).”

The MAV is the national drinking water standard, set at 50 milligrams per litre for nitrate, equivalent to 11.3 milligrams per litre of nitrate-nitrogen.

Hanson said all wells with nitrate and E. coli above the MAV were privately owned. “The owners of all of these wells have been notified. Most of them are not used for drinking water. Some owners have installed filters if they are drinking the water. Others have replaced the wells, but we still monitor old wells for our long-term trend analyses.”

Strict land-use rules to protect water quality

Nitrate concentrations in groundwater have been increasing for many years, due largely to nutrient losses from agricultural land.

“Environment Canterbury takes nitrate very seriously. Canterbury has some of the strictest land-use rules in New Zealand to protect the region’s water quality. Over time, these steps will help ensure that less nitrate enters Canterbury’s water,” Carl Hanson said.

While Environment Canterbury is responsible for the health of all groundwater and surface water in the region, people with private drinking wells are responsible for ensuring they have a safe supply.

Hanson offers this advice: “Make sure your well is secure and test your water periodically. In most cases, samples can be taken from a kitchen tap and sent to a lab for testing at your own expense.”

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