Havelock North outbreak – what might have caused it

The cause of the contamination in Havelock’s water remains unclear. It has been established that bacterial contamination from a ruminant animal (cow, deer, or sheep) resulted in people becoming ill. We also know heavy rain and surface flooding occurred just before the outbreak, and prior to that warm and dry conditions had caused cracks to form in the clay soil at and near ground surface where water might have entered during the flood.

The water bores that supply Havelock North with drinking water have  been contaminated with E. coli bacteria before, that time from a mushroom factory nearby. We know that those bores pump water from the Tukituki/Te Mata aquifer, which is a kind of underground river, but we don’t know if the contamination that affected the aquifer came directly from the Tukituki River when the heavy flooding came through those cracks in the surface and into the aquifer.

But, it’s a distinct possibility. The Hawke’s Bay Regional Council says it would take a relatively long time for contaminants from the river travelling through the aquifer to reach the bores. The Regional Council  also says it tested the river after people started getting sick and the levels of E. coli bacteria measured were “typical“. Typically what, you might ask?

What the scientists say

I listen to freshwater scientists like Dr Russell Death, and they are not ruling out contamination from the Tukituki River. I also talked with hydrogeologist Dr. Gil Zemansky about the aquifer and how underground water can move.

Gil formerly worked for GNS Science and managed projects investigating aquifer issues in Hawke’s Bay, including when the Ruataniwha dam was first being proposed. He told me that “old” groundwater is usually safer from bacterial contamination than “new” groundwater that has entered the aquifer rapidly and may carry contamination.

He said preliminary findings for a recent sample (taken in May 2016) classified water from one of the Havelock North bores as containing a substantial portion of “new” water.  This suggests important changes have occurred since the wells were last sampled for age dating. He said that under stable conditions the water from the Tukituki River could take 100 days or more to travel to the bores via the longest pathway through the aquifer from the Tukituki River, but that there are shorter pathways and there are conditions that could speed up aquifer refilling. For example, the “first flush” of water from a heavy rain carrying the highest levels of contaminants could move part of the way overland before infiltrating into the aquifer. He also said the Tukituki aquifer involved is composed of very coarse gravel that allows high groundwater to move quickly. Bacteria is able to move quickly too, in other aquifers it might be filtered out by fine, sandy material.

All of this is pretty damn technical but the lesson is that in heavy rain, the first flush of water picks up surface pollution and it can move from land to rivers to aquifers and keep moving faster than usual. Gil also said there is a channel of the Tukituki river near the bores which, in combination with cracks in the clay surface would allow contaminated water to infiltrate rapidly into the aquifer from the surface.

People just want their rivers to be cleaned up and the water in them to be safe to drink. The independent scientists are saying we have to look at the bigger picture here, in the river and under the ground. Now is the time for their voices to be heard, but will the Government or Hawke’s Bay Regional Council listen to them? Or are the vested interests promoting the Ruataniwha dam, and large irrigation projects in other locations going to hold sway?

Over 4,000 people have been sick in the Havelock North area from contaminated drinking water. Other small communities in different parts of the country are also having to boil their water. Meanwhile, 62% of lowland rivers are not swimmable let alone drinkable. Water moves and carries pollution with it. Join the dots.

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