Every year, millions of rounds of ammunition - bullets composed of lead and other heavy metals - are fired into impact berms at small arms ranges. Heavy metals in soil have the potential to impact human health and the environment if not removed or maintained. Current treatment methods are limited to solidification, stabilization, and landfilling, which keep the metals from moving and/or contain them, but do not remove them. Since no current methods are considered permanent, the military services have been developing other processes to remove heavy metals from impact berm soil. This project demonstrated a process derived from mining techniques that removes more than 99 percent of lead and other heavy metals from the soil.
The U.S. Army Environmental Center and the U.S. Naval Facilities Engineering Service Center conducted a joint demonstration of physical separation combined with acid leaching for removal of heavy metals from range soil. Physical separation capitalizes on density differences between metals and soil; when suspended in water, the denser metals settle out of soil for collection and recycling. The project independently evaluated two acid leaching processes using different strengths of acid to dissolve and wash metals from the clay fraction of soil. A full-scale processing plant was established at Fort Polk, Louisiana to demonstrate this technology.
Two different contractors demonstrated soil leaching technologies at the Fort Polk site. The acetic (weak) acid process failed to meet Toxicity Characteristic Leaching Procedure (TCLP) requirements. However, the hydrochloric (strong) acid system coupled with physical separation successfully processed 875 tons of soil and met the required 5 milligrams per liter (mg/L) TCLP and 500 grams per kilogram requirement of total lead. In fact, the TCLP lead concentration was well below the requirement at 1.83 mg/L.
Unlike stabilized or landfilled soil, the site incurs no liability when returning the washed soil to the site provided the soil meets TCLP requirements, and the recovered metals can be recycled. State regulators have selected the physical separation/acid leaching soil washing process as the technology of choice for small arms range remediation. In addition, this technology is cost-effective for the maintenance of ranges with low clay content. This physical separation/acid leaching technology could potentially save the U. S. Department of Defense millions of dollars. Assuming 10,000 tons are processed, physical separation combined with acid leaching costs approximately $168 per ton. Stabilization and landfilling of contaminated soil costs between $200 and $300 per ton plus a $40 per ton transportation charge. In addition to savings with soil processing, recovered lead can be sold to a smelter for approximately $300 per ton.
The results of this demonstration show physical separation/acid leaching is a promising technology ready for technology transfer. (Project Completed - 1997)