The scene in Harris County's Southbend subdivision is eerie, like something out of a doomsday movie. Once busy streets with names like South Autumn Drive and South Valley Lane are largely still and deserted. Houses are boarded up. There are few signs of life in this blue-collar neighborhood 18 miles south of downtown Houston, where 2,800 people once thrived.

The reason for the stillness is the neighborhood's proximity to something called the Brio Superfund site, a place that once housed two waste-disposal plants and now contains a witches' brew of toxic effluviums. Southbend's wells have been polluted by such chemicals as...