Pockets of caustic soda may appear after 6,000 liters spill from truck onto Kaimai Ranges
Rosalie Menzies / SUPPLIED
Six containers overturned a truck on the Kaimai Ranges, spilling 6,000 liters.
Six thousand liters of sodium hydroxide that was spewed out of a truck on a main highway will likely continue to flow into a nearby creek and experts cannot rule out “other pockets of the chemical.”
Six containers – filled with 1,000 gallons of sodium hydroxide each – fell from a truck onto the Kaimai Ranges on State Highway 29 Tuesday morning, shutting the freeway for much of the day while contractors cleaned up the site.
Most of the substance ended up on the road or ran over the adjacent land, but some traveled about 2 km down the hill to the Māhina-a-rangi stream.
The Waikato Regional Council clean-up team is satisfied that most of the chemical is now gone – diluted in the first few miles – but they cannot guarantee that more will not arrive downstream after heavy rains.
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“It has been estimated that around 2000 to 3000 liters would have traveled to the nearby Māhina-a-rangi stream, but it is difficult to be more specific than that at this point,” said Wayne Reed, chief of the incident response team.
The truck reportedly lost its load between Rapurapu Kauri Track and Kaimai Mamaku Lookout, and containers blocked the westbound lane, about five hundred meters south of the summit.
Five of the nearest water take-off authorization holders were told of the expected trajectory of the spill that day, but Reed said the team is now confident that the risk to water users has been significantly reduced.
On Wednesday morning, council staff performed pH tests indicating that the majority of the contaminant had been diluted, with the test returning to neutral.
“Obviously he would have come a very long way, but would have been diluted in the stream for the first few kilometers in our opinion.
“We can only base this opinion on the fact that we performed pH tests about 4 km downstream of the spill and several hours after the incident.
“This was neutral, indicating that the pH was within the normal range for a stream at that time.
“However, we cannot rule out that there are other pockets of chemicals that may still flow downstream in the event of heavy rains.”
Sodium hydroxide, or caustic soda, is a strong alkali with a pH of 0 to 14. It is used in a range of manufacturing industries including pulp, paper, drinking water, textiles, soaps and detergents.
WRC lead scientist Jonathan Caldwell said the concentrated sodium hydroxide solution that was spilled had a pH of 14 – a baseline level normally found in toxic cleaning products.
“It has a very high alkalinity, which is toxic and harmful to fish and plants that live in waterways,” Caldwell said.
Fortunately, however, he said the effects of sodium hydroxide tend to be very short-term.
“Sodium hydroxide will dilute as it mixes with larger water flows downstream, and it will also react with natural acids in the stream to form harmless salts.”
This will help bring the water quality back to a pH range that is protective for the life of the stream, he said.