Human waste overflows, fertilizer runoff and floating propane tanks are raising concerns in the flooded Midwest but should not cause severe or long-term environmental problems, health officials say. Serious chemical pollution from factories and chemical plants "aren't concerns because we don't have many reports, just isolated cases and leaks," said Karen Timberlake, Wisconsin's secretary of Health and Family Services. Timberlake, who flew over much of her state's flooded areas in a helicopter Wednesday, said hundreds of homes and acres of farmland are under water, roads are damaged and some towns' water facilities are inundated. But at least for now, she said, health concerns are rather mundane: "bacteria