DETERMINING SOURCES OF WATER QUALITY IMPACTS USING BIOLOGICAL MONITORING: THE MOLYCORP QUESTA MOLYBDENUM MINE EXAMPLE

Biological monitoring was initiated on the Red River in 1997 to evaluate the effects on aquatic biota of open pit mine operations and mine rock piles over nearly a 40-year period. The general public perception was that the mine has had severe effects on the aquatic biota due to the absence of robust biological populations adjacent to the mine. However, initial biological monitoring data provided evidence that the observed negative impacts to fish and benthic invertebrates in the Red River near the mine were actually caused by naturally occurring thermal scars upstream of, and within, the mine area in the Red River drainage. These data indicated the open pit mine and mine rock piles did not measurably impact the suitability of the Red River to support aquatic organisms. Continued biological monitoring has reinforced these earlier conclusions, and has shown that the aquatic biota is most likely limited by episodic summer rain storms which simultaneously add large amounts of sediment and degrade water quality in the Red River downstream of the hydrothermal scars, although groundwater appears to be a contributing factor in low baseflow periods. Fish and macroinvertebrate parameters decreased immediately downstream of the town of Red River, demonstrating that the negative impacts to the aquatic biota begin well upstream of the Molycorp Mine property. Long term biological monitoring has demonstrated the complex nature of factors structuring the aquatic biota in the Red River, and demonstrated the value of well-designed monitoring programs. Additional