LEAD DISTRIBUTION PATTERNS ON SHOOTING RANGES: MEASUREMENT, ANALYSIS, AND INTERPRETATION

Today the major flux of lead into the environment, recreational shooting, disperses most of the 55,000+ metric tons/year of lead manufactured into ammunition. The bulk of this lead is discharged at formal and informal recreational shooting ranges where there can be intense accumulations of lead. Our detailed sampling of shotgun and rifle ranges at a recreational shooting site in the George Washington and Jefferson National Forests in southwestern Virginia revealed distribution patterns and estimates of lead loading on such sites. Because shotgun shells disperse large numbers of small shot, sampling of 0.25 square meter areas yields reliable data. In contrast, rifles and pistols discharge larger bullets and 1 square meter areas were sampled to obtain reliable results. The positioning of stationary targets along with the use of airborne clay targets produced a very non-uniform distribution of lead on the shotgun range. Sampling was concentrated in the areas of highest lead concentrations in order to define their size and shape. Because of the non-uniformity of the shot distribution and the non-uniformity of the sampling, simple averaging of lead content does not yield accurate estimates of the total lead loading. Kriging, commonly used in the assessment of irregular ore distributions, proved to be an effective means of analyzing the lead distribution. At the shotgun range, lead is dispersed over an area of about 66,000 square meters (300 by 220 meters) and totals more than 11 metric tons. It is being deposited at a rate of about 1.4 metric tons/year. Lead distribution on the rifle range is being analyzed in a three-stage process with separate sampling and analysis of the range surface, the range backstop, and the forested area extending several thousand meters beyond the backstop. Lead concentrates in low berms constructed to reduce ricochets and especially in the earthen backstop. Errant shooting and ricochets result in the dispersal of large quantities of lead into the forest beyond the formal surface of the rifle range.