AUTOMATED MINISIPPER SAMPLING FOR TOXIC METALS IN THE UPPER ANIMAS RIVER: HIGH-RESOLUTION MONITORING RESULTS BEFORE AND AFTER THE GOLD KING MINE EVENT

Most environmental water quality monitoring studies rely on hand-collected “grab” samples. However, typical grab sampling only provides a few samples per year and rarely captures the details of transient hydrologic processes such as seasonal runoff and storm or flood events. Grab sampling is also expensive, with significant costs for personnel, equipment, vehicles and travel and field costs can be especially high if the sampling site is remote, dangerous to access, or snowbound for many months of the year. The USGS has developed the MiniSipper, a small, low-cost, high-capacity, in situ water sampler to overcome the limitations of currently available automated or manual water sampling methods. The MiniSipper automatically collects up to 250 five mL water samples which are 0.45 μm filtered and preserved with HNO_3. The MiniSipper operates in situ for up to 12 months unattended and even operates under ice for over-winter sampling. After recovery, samples are pumped out of the sample coil and analyzed by ICP-MS which can provide low ppb detection for over 50 elements.

MiniSippers were deployed at several sites in the upper Animas River from April 2013 to April 2015. Several hundred integrated daily water samples were automatically collected and preserved during the April to August snowmelt runoff and the October to April over-winter periods. Concentrations of less reactive metals (Zn, Cd, Ca, and Mg) were often inversely related to streamflow with lowest metal concentrations occurring during maximum snowmelt runoff and highest metal concentrations during the low flow period in late winter. Metal loading typically tracked streamflow with highest loading during maximum snowmelt runoff. Transient spikes in metal concentrations were observed at some sites in response to episodic rain events. MiniSippers were not in place when the August 5, 2015 Gold King event occurred but an USGS emergency response deployed several MiniSippers a few days after the Gold King event, automatically collecting water samples every 2 hours for over four weeks. This talk will present and discuss: 1) seasonal trends in metal concentrations and metal loading in the Animas River; 2) the effects of episodic rain events on metal concentrations; and 3) an examination of the sub-daily changes in metals soon after the Gold King event.