Denver, the mile-high city, has a deep-down problem. Underneath a neighborhood in the southeastern part of town lies a groundwater plume contaminated with chlorinated solvents. Such contamination is not unusual; chlorinated organic solvents, many of them dry-cleaning and degreasing agents, are among the most common and troublesome groundwater contaminants in the U.S. But in Denver, potentially harmful concentrations of these volatile compounds--all suspected carcinogens--have accumulated in houses by moving up through the soil and foundations, in a phenomenon known as vapor intrusion.

Denver's case, which has led to the installation of fans and venting systems in more than 350 homes, is at the heart of a vigorous national debate among environmental scientists about the prevalence and significance of this problem. Federal and state site managers are charging that the U.S. Environmental Protection Agency's assessments, which are based on theoretical modeling, substantially underestimate the amount of contamination in houses.

This article was originally published with the title A Case of the Vapors.

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