PRELIMINARY WATER QUALITY DATA IN THE SAN JUAN RIVER IN SAN JUAN COUNTY, UTAH FOLLOWING THE GOLD KING MINE SPILL

In response to the Gold King Mine spill in Colorado, the State of Utah selected four monitoring sites on the San Juan River in the San Juan County, Utah, to document potential changes in water quality. Monitoring locations were established at four sites on the San Juan River between the Utah/Colorado boarder and the town of Mexican Hat. Samples from the sites were collected weekly from February through June in 2016 for general chemistry, total metals, dissolved metals and nutrients. Dissolved and total metal concentrations spiked in early August of 2015 and the total fraction for several metals including cadmium, chromium, copper, iron, lead, nickel, silver and zinc peaked at two or three times the initial concentrations two weeks later, while the dissolved metals concentrations returned to background levels. Furthermore, these same metals exhibited a third and broader concentration peak four to six weeks after the initial plume. Total lead concentrations were highest during the third peak reaching levels of over 350 µg/l. This phenomenon indicates that these metals potentially sorbed to particulates of different size and weight that flowed downstream at a reduced velocity.

The preliminary conclusion is supported by data collected during winter and spring 2016 monitoring based on analytic results that show an increase in concentrations of total metals with increasing flow and turbidity. The data suggest concentrations of certain metals have at least weakly bonded with the river's sediments and persist in the San Juan River in Utah, well after the initial spill occurred. Continued monitoring at these sites will help document water quality changes, if any, that have been affected by the spill.