Stewart, C.; Leonard, G.S. 2019 Assessing the potential of a modified version of USEPA Method 1312 for use in eruption response in New Zealand. Lower Hutt, N.Z.: GNS Science. GNS Science report 2018/41. 12 p.; doi: 10.21420/07QM-Z915
Abstract:
In this study we assess the potential of a standard, commercially-available test method for determining the soluble salt burden of fresh volcanic ashfall, to expand the national capacity for rapid hazard assessment following an explosive eruption. Specifically, we assess the potential for the modified USEPA Method 1312 (offered on a commercial basis as the SPLP profile) for use in eruption response in New Zealand. We supplied a fresh (unrained) volcanic ash sample collected in March 2018 from an ashfall from Manaro Voui volcano, Ambae, Vanuatu, to a commercial laboratory. We had previously characterised leachable element concentrations of this sample in March 2018 using the internationally-ratified IVHHN protocol. This report describes comparative data obtained using the two methods. For eight parameters (sodium, magnesium, conductivity, zinc, manganese, calcium, chloride and sulphate) high levels of agreement between methods (RSD<3%) were found using the 1:20 extraction. Levels of agreement for these parameters were generally lower for the 1:100 extraction. For five further parameters (potassium, copper, fluoride, nickel and aluminium) agreement between methods was poorer (RSD of at least 10%) at both extraction ratios. We suggest that these differences that are apparently between methods may in fact be due to instability of the bulk ash sample in storage over the seven months between the analyses using the IVHHN protocol method and the modified SPLP profile. This finding reinforces the advice given in the IVHHN protocol that analyses for leachable elements be carried out promptly to avoid potential problems associated with instability of ash in storage. This is most likely to affect metals such as aluminium, copper and manganese where extraction efficiency is highly pH-sensitive, and also fluoride, where extraction efficiency is dependent on speciation. Major components appear to be relatively unaffected by storage. Accepting these limitations, this study supports the use of the modified SPLP profile for analysis of volcanic ash for assessment of hazards from leachable elements. However, we note that the IVHHN protocol will still have an important role in eruption response because of its flexibility and adaptability, for example to carry out re-extractions. These are vitally important in providing a more complete picture of the availability of F and S for human and agricultural hazard assessment. (auth)
