AbstractA methodology was developed to determine the potential for aldicarb to leach to ground water and appear at or near concentrations of concern in different areas of the continental United States. Aldicarb use in 11 “ground water regions,”as defined by Heath (1984), was evaluated. These regions were selected based on significant use of aldicarb on citrus, cotton, potatoes, peanuts, and soybeans. The unit of study, therefore, became known as “crop/Heath‐Region combinations”(CHRCs). A total of 32 CHRCs were evaluated. Three measures of leaching potential were used to evaluate each CHRC. One was based on hydrogeologic vulnerability, one was based on agronomic and site‐specific characteristics, and one was based on ground water monitoring data. Each measure was rated as “high,””medium,””low” or “insufficient data” in terms of potential for aldicarb to leach for crop‐growing areas in the region. Using a weight‐of‐evidence approach, each CHRC was given a final rating of “high,”“medium,” and “low” potential to leach based on the three measures within the CHRC. Potatoes in Heath Regions 7 (Glaciated Central) and 9 (Northeast and Superior Uplands) were rated high, whereas potatoes in Regions 1 (Western Mountain Ranges), 3 (Columbia Lava Plateau), and 11 (Southeast Coastal Plain) were rated low. Cotton in Regions 1,2 (Alluvial Basins), 5 (High Plains), 10B (Gulf Coastal Plain), and 11 were rated low. Citrus and peanuts in Region 11 were rated high. All other CHRCs, i
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