Sampling Studies at an Air Force Live-Fire Bombing Range Impact Area

Abstract : Field sampling experiments were conducted at an Air Force live-fire bombing range. The main objective was to assess the effectiveness of using a systematic-random, multi-increment sampling strategy for the collection of representative surface soil samples in areas where bombing practice is conducted with bombs containing high explosives. Replicate surface soil samples were collected within several craters and in different sized grids (1 m x 1 m, 10 m x 10 m, and 100 m x 100 m). One area sampled had been impacted by a low-order 2000-lb bomb detonation and several hundred small chunks of tritonal were present on the surface. Another area sampled had many fewer recognizable chunks of tritonal on the surface. An arroyo located downslope of the heaviest impacted area of this live-fire range where runoff from the area would be captured was also sampled at several locations. TNT was the major energetic compound present within the live-fire bombing area. Short-range heterogeneity in TNT concentrations was very large and the ability to estimate mean concentration using discrete samples even for an area as small as 1 m squared was poor. Much more reproducible estimates of mean concentrations for areas as large as 100 m x 100 m were achieved using multi-increment samples collected with a stratified systematic- random sampling design compared with that achieved using discrete samples. Results from soil profile samples and samples from the arroyo draining this area indicate that the energetic compounds present at the bombing range are not migrating from the site. Another area sampled was a small demolition range where C4 explosive is used to ensure that practice bombs contain no residual explosive prior to removing scrap metal from the range. RDX and HMX were the energetic compounds detected at the highest concentration in surface soil at the demolition range. These compounds originated from the demolition explosive.