You'd think 7,000 gallons of diesel fuel would be difficult to misplace. Not so at Colorado's Copper Mountain, where such a quantity has gone missing since January. Apparently, a truck driver delivering the fuel to the resort accidentally pumped it into a water-quality-monitoring well. Though about 150 gallons were immediately recovered, an EPA response team, working with Copper officials, has since drilled more than a dozen test wells and taken several soil samples, but still hasn't found the rest of the errant fuel. Fortunately, tests have indicated that Copper's drinking water has not been affected. Less reassuring is that such accidents occur at all, and not just at ski areas. "It's not common, but it's happened all around the country," says EPA response-team leader Martha Wolf.