HEAVY METAL TRANSPORT PROCESSES IN THE BLACK RIVER OF MISSOURI’S NEW LEAD BELT

A study is being conducted on the West Fork of the Black River in Missouri’s New Lead Belt to characterize the speciation and transport of particulate and dissolved heavy metals in a carbonate-dominated river system (pH varies from 7.6 to 8.2). Water chemistry, sediment composition, particle size distribution, mineral speciation, and flow modeling are being evaluated to characterize the path by which metals are transported during varying hydraulic events. Six sites are being sampled periodically to characterize transport during both seasonal and storm-induced stream flow variations. Information from this study will be used to evaluate metals transport processes in the Black River. This information will also be incorporated into the EPA Unit World Model used to predict metals transport in aquatic systems. The present study includes analyses by optical microscopy (OM), ICP-MS, ICP-OES, XRD, SEM, and IC, as well as a variety of other in-situ and laboratory measurements. ICP-MS data from water samples collected during normal stream flow conditions showed low lead and zinc concentrations. These values increased downstream from the control site, located above any zones of mining, to sites located downstream from tailings ponds. Lead and zinc concentrations from unfiltered water samples collected at the control site were <0.25 and 13 ppb, respectively. Concentrations increased downstream from mine tailings piles where a maximum of 6.7 ppb Pb and 163 ppb Zn were detected. Overall metal contents also increased for all sites during an unanticipated period of gravel removal upstream from the sampling reach. ICP-MS data from sediment samples showed a wide range of lead and zinc concentrations (3-960 ppm Pb and 4-2488 ppm Zn). Sediment metal concentrations at the control site ranged from 3-72 ppm Pb and 6-597 ppm Zn. Sediment data displayed a log linear correlation between Mn and heavy metal concentrations for Pb, Zn, Co, Cu, Ni, and Cd. The highest values of Pb and Zn were found in the smallest size fractions at sites immediately downstream from a mine tailings pile. SEM and OM examinations of selected sand and pebble sized grains showed that heavy metals were associated with Fe and Mn coatings. Metal sulfides have not been found in any samples.