LEAD AND ZINC STORAGE WITHIN ALLUVIAL DEPOSITS ALONG LOWER PEARSON CREEK, SW MISSOURI

Contaminated mining sediment deposited within floodplain deposits can be an environmental hazard if remobilized by either physical or chemical processes. Lead and zinc mining near the confluence of the James River and Pearson Creek (58 km²) near Springfield, Missouri began around 1885, peaked around 1912, and ended by 1920. The purpose of this study is to use the historical stratigraphic record in floodplain deposits to determine how mining-related contamination is stored in a confluence zone. The objectives are to (1) determine the magnitude of Pb and Zn within alluvial deposits; (2) identify the downstream and across-valley distribution of contamination using floodplain sedimentology and trace-metal geochemistry; and (3) use the areal extent of contamination to calculate the mass storage of Pb and Zn. A portable X-ray fluorescence analyzer was used to gather geochemical data from soil samples collected along cross-sections. Three geo-stratigraphic assemblages were identified and are used to classify floodplain storage sites: channel fill, floodplain drape, and terrace veneer. Approximately 90.9 Mg of Zn, 22.3 Mg of Pb, and 140,883 Mg of contaminated sediment is stored along lower Pearson. Channel fill assemblages are the site of the most storage containing approximately 50% of the total Zn (51.1 Mg) and 55% of the total Pb (12.2 Mg) present within them. Furthermore, approximately 33% of the Zn (29.8 Mg) and 26% of the Pb (5.9 Mg) stored in the entire study area is located within the channel fill assemblage farthest upstream. The results of this study indicate that any remediation efforts began in the study area should focus on channel fill assemblages, particularly in the most upstream areas. Also, the decrease in storage in the downstream direction suggests that backflooding of the James River appears to dilute pollutant concentrations or shift the locus of deposition further up-tributary in confluence areas.