"...for three smelter studies: 
El Paso, Texas Lead Study [19], Helena Valley Lead Study [20],
 and Silver Valley-Revisited Lead Study [17]. In the Midvale Community Lead Study [22] .... 
The isopleths [i.e. graphs], which show increasing soil-lead concentrations in the vicinity of the smelters,
 “support the conclusion that the smelters are the primary sources of lead contamination in the
 area.” In addition, the Heavy Metal Exposure Study [60] found that 
“there was a general trend
 toward increasing levels of environmental metal burdens with proximity to the smelter.” The
 evidence for the emitter being the contributing source of the lead, therefore, stems from
 increasing soil-lead concentrations with decreasing distance from the emitter." 
 February 1998
 EPA 747-R-98-001a
 FINAL REPORT
 SOURCES OF LEAD IN SOIL:
 A LITERATURE REVIEW
 Prepared by
 Battelle Memorial Institute
 Technical Programs Branch
 Chemical Management Division
 Office of Pollution Prevention and Toxics
 Office of Prevention, Pesticides, and Toxic Substances
 U.S. Environmental Protection Agency
 Washington, DC 20460