Cleaning up after Mother Nature- the Red Dog Mine Experience

Red Dog Creek (RDC) is a tributary of the Ikalukrok Creek/Wulik River system which drains into Kotzebue Sound, the southeasternmost arm of the Chukchi Sea.  In its natural state, RDC was a remarkable aquatic system, perhaps unmatched in the country or the world:  Upper tributaries of the stream crossed or originated in a massive metal sulfide ore deposit that has since been mined as the Red Dog Mine.  Credible pre-mining (1980s) scientific investigations documented natural surface water pH as low as 2.9 and concentrations of cadmium, lead, and zinc several orders of magnitude above aquatic life criteria.  These conditions eliminated or severely stressed in-stream benthos and caused natural mortalities and behavioral abnormalities in resident and anadromous fish in waters directly influenced by the mineralization.  This report will follow the course of waters from the several tributaries of RDC downstream to the Chukchi Sea and describe biological conditions in those waters pre- and post-mining.  Upper tributaries of RDC supported a seasonal population of Arctic grayling and a very few resident Arctic char.  The grayling spawned in a clean tributary but migrated seasonally through the metals-rich lower mainstem of RDC to overwintering areas in relatively clean Ikalukrok Creek.  Typically, the adult upstream migration occurred during spring breakup when high flows from snow melt diluted the metals from the deposit areas.  The fall downstream migration preceded freeze-up and mortality of young-of-the-year migrating downstream through the same metals-rich reach were likely.  Adult grayling mortalities were also documented in live-box tests.  Juvenile Dolly Varden that entered the lower reach of RDC, perhaps in search of overwintering areas, displayed erratic behavior many expired.  As part of mine development, portions of RDC tributaries crossing the ore body (or originating in it) were diverted through a ‘clean ditch’ to lower stream reaches; remaining waters from the ore body and tailings pond have been captured and treated before discharge to RDC.  As a result, studies by Alaska Department of Fish and Game show that water quality in the lower mainstem of RDC has been much improved in recent years.  Grayling now move freely through the system, spawning there, and rearing in substantial densities in areas that, in nature, were certain death.  Tagged fish have been recovered in the lower mainstem after several years indicating longevity and site fidelity.  Dolly Varden are now common in the stream.  Maintaining these conditions will require continued treatment of mine discharges in perpetuity.