Thursday, October 2, 2008: 5:00 p.m.
Ochoco Creek basin is a historic mining watershed in Central Oregon containing a number of historic mercury mines that operated between the 1930s and 1960s. The Oregon Department of Environmental Quality (ODEQ) used the Ochoco basin as a test watershed for a pilot project to develop an investigation framework for evaluation of potential impacts to both abiotic and biotic environmental media on both local and basin-wide spatial scales. Three phases of work were performed between 2005 and 2007. Phase one used X-ray fluorescence (XRF) technology to establish basin-specific reference concentrations for metals; phase two evaluated biological integrity of Ochoco Creek using invertebrate community composition; and phase three evaluated mercury bioaccumulation in fish tissue. Results indicate that XRF technology data did not differ significantly from fixed analytical laboratory data, and XRF data was deemed suitable for preliminary site assessment and determining site-specific background concentrations. Bioassessment results indicate that the presence of abandoned mine lands (AMLs) in Ochoco basin did not appreciably impair the biotic community in Ochoco creek relative to a reference basin without AMLs. Finally, a mercury bioaccumulation model was developed that provides reasonable predictions of average fish-tissue concentrations basin-wide. Future work will investigate factors that may determine mercury bioaccumulation within specific mining sub-basins.