Small-arms training is a requirement in all branches of the military. In a typical year, small-arms training activities consume over 300 million rounds and add between 1 and 2 million pounds of lead to the ranges in the form of bullet debris. Because elevated levels of lead in groundwater and soils can present a health hazard, the migration of heavy metals can result in environmental regulators imposing training restrictions that ultimately will reduce operational readiness. The innovative use of Shock-Absorbing Concrete (SACON), a low-density, fiber-reinforced foamed concrete, was demonstrated as a bullet-trapping technology to address the lead issues on small-arms ranges at West Point, New York, and at Fort Knox, Kentucky.
SACON bullet traps tested in a 25-Meter Range application contained 87 percent of the bullets fired at the trap. The majority of the released fraction of bullet debris was deposited immediately in front of the trap forming a debris pile. Exposure of the bullet debris to the SACON material resulted in the formation of insoluble lead corrosion products. As a result, even though lead concentrations in the trap and debris pile exceeded 60,000 mg/kg, all weathered SACON debris removed from these ranges was classified as non-hazardous, with Toxicity Characteristic Leaching Procedure (TCLP) levels below 5 mg/l, and was disposed of as a solid waste. Soil erosion resulting from repeated bullet impacts was reduced in front of and behind the target emplacements by burying SACON in these areas. Ricochet testing determined that SACON had no effect on the surface danger zone (SDZ) of the range.
SACON offers significant benefits in comparison to current commercial-off-the-shelf (COTS) technologies, and provides a means of effectively capturing and containing lead on small-arms ranges. It is able to inhibit the leaching of lead corrosion products. Other COTS bullet traps and soil berms do not have this lead stabilization capability. SACON is not flammable and can be formed in any shape, making it adaptable to more range applications than standard COTS technologies. The waste generated from the use of SACON is not classified as a hazardous waste and can be disposed of as a solid waste. Fixed, start-up costs were estimated at $1,600 per 25-Meter firing lane. Annual operating and maintenance costs were between $1,000 (low use) and $3,800 (high use) per firing lane. At low usage (7,500 rounds per year per lane), SACON becomes cost-competitive with conventional soil-berm technology on ranges with medium to high risk of lead transport.
SACON is a technically feasible method of capturing and containing lead on small-arms ranges. However, like all bullet traps, it is an expensive means of mitigating lead transport from ranges, and should be considered as a last resort for keeping ranges environmentally compliant. Other methods of reducing lead transport risk should be investigated prior to installing any bullet trap technology. New methods of stabilizing the lead on the range and mitigating physical lead transport in storm water runoff are being developed and may provide more cost-effective means of reducing lead transport risk and bioavailability.