20 January 2014
Posted in Center Information
University of Florida
The objective of this research was to test the effectiveness of two best management practices on bullet weathering in shooting range soils. The specific objectives were to examine the effects of:
1) Using sand berm to replace soil berm to slow down Pb transformation from metallic to ionic form and thereby reduce Pb leaching;
2) Compare removal of Pb bullets/shot via sieving on Pb weathering from large to small particles.
Considering the weathering effect of rainfall on bullets in different positions, two rainfall scenarios (high and low) and two bullet positions in sand/soil (mixed with sand/soil in1st experiment and placing on the surface of sand/soil in 2nd experiment) were simulated in column experiments. In the 1st experiment, after 16 weeks of incubation, more Pb leached from the soil than from the sand under both rainfall conditions. The properties of sand/soil played an important role in weathering of bullets. Compared with sand, soil had a lower pH (4.52 vs. 5.87; Table 2-2), higher field capacity (26% vs. 22%; Table 2-2) and higher organic matter (1.32% vs. 0.32%; Table 2-2), which resulted in higher total Pb and water-soluble Pb in the soil than in the sand.
In contrast, when bullets were placed on the surface of the sand/soil in the 2nd experiment, bullet weathering was only impacted by rainfall and oxygen availability. After 18 weeks of incubation, the difference in total Pb and water-soluble Pb between the sand and soil was small. More Pb leached from the sand than the soil under high rainfall, while more Pb leached from soil than from sand under low rainfall, yet Pb leachability gradually increased over time. Overall, the results indicated an increased potential for more Pb to leach from sand than the soil. In general, there was a good correlation between total Pb and leachable Pb, with increased Pb leachability in highly-contaminated soils. In this study, the ratio of leachable Pb to total Pb was used to compare Pb leachability in different soils. At the end of the experiment, more Pb leached from soil than sand (except for 2nd experiment under the high rainfall), yet sand showed higher Pb leachability (0.36% vs. 0.01%) than the soil in both column experiments. This could be due to two factors: reduced weathering of metallic Pb to ionic Pb due to sand’s lower field capacity, lower organic matter and higher pH than soil. At the same time, low CEC and silt/clay fraction also led to its high Pb leachability.
As a BMP recommended by EPA, physical separation of Pb bullets from shooting range soils by mechanical sieving has the benefit of removing the source of Pb from the soil thereby reducing the potential for long-term Pb accumulation in the impacted soils. In addition, the separated Pb is recycled, which generates some revenue. However, compared with hand shaken methods, mechanical removal can easily break weathered Pb-bullets into small fragments, resulting in a sharp increase in the total Pb concentration in the soil fraction (<2 mm) in pistol/rifle range soils
For trap/skeet ranges, removing Pb-shot via mechanical sieving and pneumatic separation can effectively remove the Pb source from impacted soils. Since shot is smaller than bullets, it experiences less physical weathering than bullets and the transfer of Pb particles from large to small sizes is less appararent.
Therefore, caution need be exercised when replacing a soil berm with sand and mechanically sieving Pb-bullets in the pistol/rifle range. Overall, mechanical removal of Pb-shot from the trap/skeet range was an effective practice.