Volcanic ashfall, drinking water and public health: recent experiences from the 2011 Puyehue-Cordón Caulle and 2012 Tongariro eruptions

STEWART, CAROL; CRONIN, SHANE J.; WILSON, THOMAS; HEATHER BICKERTON; VILLAROSA, GUSTAVO; OUTES, VALERIA; BAXTER, PETER

Colima

Congreso; Cities on Volcanoes 7; 2012

Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI)

In most cases, the physical presence of volcanic ashfall in raw water sources and water treatment systems will outweigh any chemical contamination problems, despite commonly-held perceptions to the contrary. Suspended ash (turbidity) can cause a range of operationalproblems for water treatment plants, particularly abrasion of pump impellers and blocking of sand filter beds. Plants can usually remain operative throughout an ashfall, albeit with an intensified level of maintenance. The major risk for halting water production as a  consequence of an eruption is an ash-induced power outage.The 4 June 2011 eruption of the Puyehue-Cordón Caulle volcanic complex, Chile, deposited ashfall over a wide area of Argentina, including the population centres of Villa la Angostura, San Carlos de Bariloche and Ingeniero Jacobacci. Argentinian authorities analysed over 500 surface water samples throughout the region, but did not report any appreciable compositional changes. The Bariloche water treatment plant experienced a range of operational problems largely because turbidity in the raw water source (Lago Nahuel Huapi) exceeded the normal operating range of the plant. In Jacobacci, the water supply system was secure as it is entirely based on a groundwater supply and is enclosed,but problems were experienced in meeting water demand for sustained cleanup operations. In Villa la Angostura, repeated problems were experienced with stream-fed community water supplies; the ashfall highlighted pre-existing problems with the microbiological safety of these systems.In the case of the 6 August 2012 eruption of Tongariro volcano, New Zealand, ashfall was rapidly collected and analysed in accordance with a recently-developed protocol for characterizing volcanic ash leachate. Even considering the worst-case scenario of contamination of water tanks, we identified a very low level of hazard to public health. This information was communicated rapidly to public health authorities who in turn reviewed their advice to the public