INDEPENDENT BASELINE WATER QUALITY CHARACTERIZATION OF THE PEBBLE PROJECT AREA IN SOUTHWESTERN ALASKA

Independent investigations of the Pebble Project in southwestern Alaska have examined baseline water quality conditions in streams draining the Pebble site. The Pebble Project is one of the largest copper/gold deposits in the world and is upstream of one of the most important salmon fisheries in Alaska and globally. The baseline geochemistry sampling, which has been coordinated with baseline fisheries and aquatic invertebrate surveys, includes sampling of surface water locations during (May) and after (June) ice break-up in 2009 and after ice break-up in July 2010. The waters that flow through the Pebble region are cold, well oxygenated, and have low concentrations of dissolved solutes. Metal concentrations increased briefly during ice break-up. Most of the waters are calcium-bicarbonate dominant, but low in alkalinity and hardness. Alkalinity and pH were strongly correlated with concentrations of cations, primarily calcium, and inversely correlated with metals. Waters north of the mine lease area (Kaskanak watershed) were found to generally have higher pH and alkalinity values than the South and North Forks of the Koktuli. The water chemistry is influenced by both groundwater and surface runoff. The degree of change in concentrations of calcium and other parameters allowed us to tentatively distinguish streams that are more influenced by groundwater versus those primarily fed by surface runoff. The same methods confirmed that interbasin-transfer of water is important in the area, for example from South Fork Koktuli to an Upper Talarik tributary. The baseline water quality data indicate that waters in and around the proposed Pebble Mine site have very low concentrations of metals, even near the ore body. Waters are also low in parameters that can moderate the toxicity of metals such as alkalinity, calcium, and DOC. Future studies will assess the relationships between water chemistry and fish life stages. Particular attention will be paid to upwelling sites, which are favored by salmon and provide a conduit for transport of mine-related contaminants.