Mapping and modeling three dimensional lead contamination in the wetland sediments of a former trap-shooting range

Legacy lead (Pb) contamination from sport shooting activities is a well-known hazard. Assessing the risk this contamination presents to the environment and public health requires a detailed understanding of its spatial distribution, yet our knowledge in this area is limited, especially for wetland shooting ranges. In this study, we analyzed 1351 sediment samples from 456 surficial (0-5 cm) locations and 38 sediment cores (0.3 to 0.9 m) to quantify the three dimensional spatial distribution of Pb contamination in an urban wetland at the site of a former trap shooting range located in southwestern Wisconsin, USA. Non-destructive X-ray images of the sediment cores were used to quantify Pb shot abundance and burial depth. Surficial and core sediment samples were processed and analyzed for total Pb content via X-ray fluorescence (XRF) analysis. X-ray and XRF results were interpolated to create a three-dimensional model of Pb shot density and sediment concentration across the study area. Over 31,000 m3 of sediment surpassed the US Environmental Protection Agency's contamination threshold of 400 mg/kg Pb, with a maximum calibrated value of 26,700 mg/kg Pb occurring near the center of the expected shot fallout zone. Shot densities of > 50,000 pellets/m2 were found in the shot fallout zone, primarily 10-30 cm below the sediment surface. X-ray image analysis and XRF analysis of sediment cores provide an accurate and inexpensive technique for rapidly mapping Pb contamination associated with gun clubs and hunting; these findings will benefit environmental contamination studies and remediation efforts at active and abandoned shooting ranges worldwide.