Last year, state records show, more than 250 wells were drilled in the two-county area. Of those, about 10 percent showed evidence of heavy-metal contamination. Of those, only four proved to be contaminated after a second test. Another contaminant of concern in the two-county area is trichloroethylene, also known as TCE. The industrial solvent has been found in groundwater near Neosho and Joplin. It, too, has been identified as a possible cancer-causing agent.