Coping with spatial heterogeneity effects on sampling and analysis at an HMX-contaminated antitank firing range

Short-range and mid-range (grid size) spatial heterogeneity in explosives c oncentrations within surface soils was studied at an active antitank firing range. Intensive sampling was conducted adjacent to two target tanks by es tablishing sixteen 6-m-square grids. Each grid was subdivided into four qua drants, and in each quadrant an area-integrated surface sample was formed i nto a pile that included about 10% of the top 5 cm of soil in the quadrant. After in situ homogenization, random aliquots were combined to form replic ate representative samples. Grid composites were also prepared by combining equal portions of soil from the four quadrants for each grid. In nine of t he quadrants, a second area-integrated sample was prepared. On-site analysi s showed concentrations of HMX ranging from as high as 2160 mg/kg near one target to less than or equal to 1 mg/kg at a distance of 20 m from the targ et. TNT concentrations, ranging from less than or equal to 1 to 23 mg/kg, w ere much tower than would be expected based on the 70:30 composition ratio of HMX to TNT in the melt-cast explosive used on site. On-site concentratio n estimates for HMX and TNT were in excellent agreement with laboratory HPL C results; correlation coefficients were 0.992 and 0.975, respectively. Spa tial heterogeneity of HMX concentrations was large on both short- and midra nge scales, and this factor dominated the overall uncertainty associated wi th site characterization. Greater emphasis on sampling is urgently needed t o improve the representativeness of explosives residue determinations in so il. (C) 1999 John Wiley & Sons, Inc.