REMOTE WATER-QUALITY SAMPLING OF NEVADA PIT LAKES USING UNMANNED AIRCRAFT SYSTEMS

Mine pit lakes are geochemically and hydrologically dynamic systems that require regular monitoring of water quality for a wide variety of applications including geochemical and limnologic modeling as well as assurance of regulatory compliance. In addition to being hydrogeochemically dynamic, the environment surrounding pit lakes is often also in flux from a geotechnical perspective. Geotechnical instabilities, combined with other hazards, makes the regular monitoring of some pit lakes dangerous. Competing interests of the need for water-quality samples and considerations of health and human safety create a difficult situation for the long-term monitoring and management of pit lakes. These needs are especially acute in the state of Nevada, which hosts approximately 40 pit lakes.

In order to demonstrate reproducibility and application to regulatory procedures, an unmanned aircraft system water-sampling campaign was conducted in Nevada in August 2017, during which samples were collected from five different pit lakes. The sampled pit lakes covered a wide variety of topographic settings, ranging from pit lakes in steep mountainous terrain to lowland valleys, indicating the flexibility of the methodology. Sampling procedures consisted of profiling each lake with a multi-parameter sonde to evaluate limnologic structure. Water-quality samples were then collected from several depths in the pit lakes representing distinct hydrogeochemical layers.

The remote water-quality sampling methodology allowed access to the hypolimnion of several pit lakes that would have been impossible to access without the unmanned aerial system, thereby collecting samples that add invaluable information to the understanding of the given pit lake. Additionally, results of multi-parameter profiling indicate good agreement between measurements collected by the sonde and field measurements of applicable parameters, and water samples satisfied Nevada regulatory requirements for pit-lake sampling. This presentation reviews these successes as well as aspects of field planning that should be addressed during the planning stage of a sampling campaign.