The normal level of carbon dioxide in a home should not exceed 600 to 1,000 parts per million, officials said.
``I've never heard of this happening before,'' said Jack Kelly, the on-scene coordinator for the U.S. Environmental Protection Agency. ``This carbon dioxide problem is very rare and unusual.''
High readings of the gas were initially found late last week near sump pumps in two of the homes after a young girl fainted in a basement. Township officials contacted the Montgomery County Health Department.
Investigators also are trying to learn if the carbon dioxide levels contributed to the death of a man last week.
About 100 residents attended the meeting last night at the Plymouth Township Municipal Building but left not knowing much more than when they arrived.
``From what you're saying, you don't know how to handle this because it's never happened before,'' Tola Aiyegbusi, a two-year resident of the Kennedy Crossing neighborhood, told officials.
``I'm not comfortable at all,'' she said. ``I get the feeling they think this is a joke and they don't understand the magnitude of this problem.''
Herbert said nine more homes of about two dozen remaining in Kennedy Crossing would be tested by the end of next week. He said high levels also were found in Cardinal View, where neighbors said there were 144 homes.
``It's a first-time phenomenon,'' Herbert said. ``It could be here today and never come back again or it could be back in two weeks.''
A team of federal, state and health officials has been working at the site since last Friday trying to learn if the high carbon dioxide levels could have been released when acidic floodwater from Hurricane Floyd interacted with the geologic limestone in areas of the basements.
The township has urged residents of the 3 1/2-year-old, 45-lot Kennedy Crossing subdivision not to allow children in the basements until levels could be checked and to ventilate the area by opening windows and using fans.