Die-off in detected E.coli mirrors Europe

The bacteria E.coli has been detected in the injected underground water in the Gisborne Managed Aquifer Recharge (MAR) trial, but there is no indication it survived, says Gisborne District Council environmental monitoring team leader Peter Hancock.

He also said there had been no indication of arsenic release.

He was responding to a Stuff story looking into MAR trials.

The story said on the Poverty Bay Flats, water is injected through wells to reach the deep aquifer below. In another trial in Canterbury, the underground reservoir sits closer to the surface, so water from the Rangitata River is diverted into filtration ponds, where it is left to percolate naturally into the aquifer.

Early results from both schemes show the method works, in terms of raising the water level in the underground storage aquifers.

But there were risks, the Stuff report noted. It said that in Poverty Bay, the injection water introduced E.coli bacteria.

The river water being injected was oxygen-rich, while the aquifer water was not. Stuff said that the trial report noted the mixing of the two “could in some cases cause pyrite oxidation and the release of arsenic in the aquifer”.

GNS head of hydrology Stewart Cameron is quoted in the article as saying mixing waters of different chemical composition can cause “odd reactions”. He said MAR could work in New Zealand, but one of the biggest barriers was that not enough was known about what was in the country’s aquifers, and how they worked.

Mr Hancock said from the results of the ongoing monitoring programme, the council had no indication of arsenic release caused by the Gisborne MAR injection trial to date.

“Results indicate no release has occurred due to the injection of pre-filtered river water. It can be noted that arsenic is naturally occurring in the Makauri Aquifer at high levels. The highest concentrations recorded during the monitoring programme were found within wells containing the native (natural) groundwater. As such, the injection of clean filtered river water and its mixing with native groundwater has tended to improve the resultant groundwater quality in the Makauri Aquifer locally,” he said.

While E.coli has been detected in 2017 in the injected river water and in the adjacent monitoring well (GPE065) at 20m distance from the injection point on a few occasions, there was no indication that the E.coli survived, Mr Hancock said.

“This mirrors European experience of MAR systems, where E.coli die-off rates in groundwater are generally very high. Therefore, we do not consider the injection trial has caused any concerns with E.coli within the Makauri Aquifer, although continual monitoring during the trial is planned so this outcome is further confirmed.

The Stuff story said managed aquifer recharge has been widely used around the world.

One of the oldest schemes is in California’s Orange County, where in 1933 irrigation dragged so much water from the underground aquifer that seawater seeped into the space, threatening the freshwater supply. Now, the district injects excess river water and treated wastewater into coastal wells to keep seawater out, and inland artificial ponds allow water to seep down to recharge the aquifers.

Los Angeles pumps stormwater into its underground aquifer, for its town drinking supply.

Perth recycles wastewater, letting it filter through purifying soils into the aquifer, then pumps it out in times of high demand.

Bob Bower, a consultant hydrologist and key New Zealand MAR advocate, came across the concept in North America, while trying to restore salmon rivers. He estimates New Zealand is 50 years behind the United States, in that over-allocation of water is only now biting here.

MAR provides an opportunity to be smarter about what’s coming in — and out — of aquifers, Bower says. Climate change will make that increasingly important, with longer and more severe droughts.

“It isn’t a silver bullet. It’s really part of a conversation about living within our means. Because there’s only so much water in a catchment — you can’t argue your way out of that.”

The bacteria E.coli has been detected in the injected underground water in the Gisborne Managed Aquifer Recharge (MAR) trial, but there is no indication it survived, says Gisborne District Council environmental monitoring team leader Peter Hancock.

He also said there had been no indication of arsenic release.

He was responding to a Stuff story looking into MAR trials.

The story said on the Poverty Bay Flats, water is injected through wells to reach the deep aquifer below. In another trial in Canterbury, the underground reservoir sits closer to the surface, so water from the Rangitata River is diverted into filtration ponds, where it is left to percolate naturally into the aquifer.

Early results from both schemes show the method works, in terms of raising the water level in the underground storage aquifers.

But there were risks, the Stuff report noted. It said that in Poverty Bay, the injection water introduced E.coli bacteria.

The river water being injected was oxygen-rich, while the aquifer water was not. Stuff said that the trial report noted the mixing of the two “could in some cases cause pyrite oxidation and the release of arsenic in the aquifer”.

GNS head of hydrology Stewart Cameron is quoted in the article as saying mixing waters of different chemical composition can cause “odd reactions”. He said MAR could work in New Zealand, but one of the biggest barriers was that not enough was known about what was in the country’s aquifers, and how they worked.

Mr Hancock said from the results of the ongoing monitoring programme, the council had no indication of arsenic release caused by the Gisborne MAR injection trial to date.

“Results indicate no release has occurred due to the injection of pre-filtered river water. It can be noted that arsenic is naturally occurring in the Makauri Aquifer at high levels. The highest concentrations recorded during the monitoring programme were found within wells containing the native (natural) groundwater. As such, the injection of clean filtered river water and its mixing with native groundwater has tended to improve the resultant groundwater quality in the Makauri Aquifer locally,” he said.

While E.coli has been detected in 2017 in the injected river water and in the adjacent monitoring well (GPE065) at 20m distance from the injection point on a few occasions, there was no indication that the E.coli survived, Mr Hancock said.

“This mirrors European experience of MAR systems, where E.coli die-off rates in groundwater are generally very high. Therefore, we do not consider the injection trial has caused any concerns with E.coli within the Makauri Aquifer, although continual monitoring during the trial is planned so this outcome is further confirmed.

The Stuff story said managed aquifer recharge has been widely used around the world.

One of the oldest schemes is in California’s Orange County, where in 1933 irrigation dragged so much water from the underground aquifer that seawater seeped into the space, threatening the freshwater supply. Now, the district injects excess river water and treated wastewater into coastal wells to keep seawater out, and inland artificial ponds allow water to seep down to recharge the aquifers.

Los Angeles pumps stormwater into its underground aquifer, for its town drinking supply.

Perth recycles wastewater, letting it filter through purifying soils into the aquifer, then pumps it out in times of high demand.

Bob Bower, a consultant hydrologist and key New Zealand MAR advocate, came across the concept in North America, while trying to restore salmon rivers. He estimates New Zealand is 50 years behind the United States, in that over-allocation of water is only now biting here.

MAR provides an opportunity to be smarter about what’s coming in — and out — of aquifers, Bower says. Climate change will make that increasingly important, with longer and more severe droughts.

“It isn’t a silver bullet. It’s really part of a conversation about living within our means. Because there’s only so much water in a catchment — you can’t argue your way out of that.”

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