1. Metal Sorption Properties The binding behavior of Zn, Cu, and Pb relates to the surface complexation constant, K int. Dzombak and Morel, 1990 Assessment of Zinc, Copper, and Lead in the Streams and Streambed Sediments of the Lefthand Creek Watershed, Northwestern Boulder County, Colorado A.R. Wood, J.N. Ryan, R. Cholas, L. Harrington, L. Isenhart, and N. Turner Department of Civil, Environmental, and Architectural Engineering University of Colorado at Boulder Many thanks to all of the individuals who assisted with this research, and to the organizations who provided resources and funding: –Colorado Department of Public Health and Environment –Environmental Protection Agency –Honeywell, International –University of Colorado Laboratory for Environmental and Geological Sciences –Ohana Scholarship Fund –Research Experience for Undergraduates –Undergraduate Research Opportunity Program –University of Colorado Outreach Program –University Government of Graduate Students Conclusions This study shows that tracer tests and synoptic sampling are effective methods for the identification of metal sources and the quantification of metal loads in streams impacted by acid mine drainage. The zinc, copper, and lead data presented here reflected the known solubility properties of these metals, indicating that metal speciation in the Lefthand Creek watershed relates to instream pH. Stream bed sediment metal concentrations exhibited a spatial lag downstream of instream metal spikes. This suggests that bed sediment metal concentration increases are the result of metal sorption onto sediment particles and/or the settling of colloidal metal species onto the bed. ZnCuPb Log K int 0.992.894.65 Research Goal and Hypothesis Goal: Identify and quantify sources of metal loading to Lefthand, James, and Little James Creeks. Hypothesis: Metal inputs from both surface and subsurface flows can be identified and quantified with metal loading tracer tests and synoptic sampling. Analysis of stream bed sediment metal concentrations further defines metal sources. Study Area An active mining past left a legacy of hundreds of abandoned or inactive hardrock mining and milling sites in the Lefthand Creek watershed. Some of these sites leach acidity and toxic metals to surrounding streams, threatening aquatic life and downstream water consumers. Local stakeholders and state and federal agencies desired an understanding of toxic metal sources, transport, and fate to better prioritize contaminated sites and develop efficient reclamation strategies. Methods Sampling was conducted on approximately 300 sites along the three major streams in the watershed, using a conservative LiCl tracer to determine stream flow and synoptic sampling to collect stream water metal concentrations (Kimball, 1997). Metal loads were calculated as the products of stream flows and metal concentrations. An HCl-H 2 O 2 partial digestion of the sub-62 μ m size fraction of stream bed sediments was analyzed at 55 sites following the methods of Church (1993). Balarat Road unnamed gully, south waste rock pile, north Balarat Creek mine waste pile, north unnamed tributary, south “streamside tailings” “Bueno Mtn Gully” waterfall County Road 102J Argo mine Burlington mine Emmett adit “Argo mine gully” Balarat Road unnamed gully, south waste rock pile, north Balarat Creek mine waste pile, north unnamed tributary, south “streamside tailings” “Bueno Mtn Gully” waterfall County Road 102J Argo mine Burlington mine Emmett adit “Argo mine gully” Balarat Road unnamed gully, south waste rock pile, north Balarat Creek mine waste pile, north unnamed tributary, south “streamside tailings” “Bueno Mtn Gully” waterfall County Road 102J Argo mine Burlington mine Emmett adit “Argo mine gully”