Environmental Monitoring And Assessment: A Statistical Analysis Of Concentrations Of Silver And Indium At Generator Locations

M. Lincoln-Smith, A. Dye, K. Kemsley, J. Denholm


The Snowy Precipitation Enhancement Research Project commenced during2004, following proclamation of the Snowy Mountains Cloud Seeding Trial Act 2004 (NSW). This legislation mandates the use of silver iodide as the seeding agent, permits the use of indium (III) oxide as an inert tracer, and requires that cloud seeding operations be ground based only.  It also requires an Environmental Management Plan to be developed and implemented for the project. That Plan includes an explicit obligation to monitor silver and indium concentrations across the study area. Samples taken prior to the commencement of the trial showed measurable concentrations of silver and indium within all matrices (soil, moss, peat, water, sediment) and at all locations monitored. Routine sampling takes place each year during the winter months and following the cessation of cloud seeding experiments for the season. This paper examines trends in the concentrations of silver and indium in soil samples collected from 13 generator locations (the locations from which the seeder and tracer agents are dispensed) between 2004 and 2009. Comparison of the concentrations with the  relevant environmental Guideline Trigger Values showed mean concentrations and 95% confidence limits were always well below the trigger value, and statistical analysis of the data indicated that temporal trends in concentrations were variable across locations. The analysis of statistical power, used to determine the likelihood of detecting adverse effects before they reach a scale of environmental significance, indicated that a statistically significant increase (i.e. above the pre-seeding levels) would be detectable well before any level of concern is reached.

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