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Plymouth Township CO2 Release

EPA Region 3 (Mid-Atlantic)

Montgomery County
Conshohocken Area

EPA ID# PASFN0305547

6th Congressional District

Last Update: April 2000
Final Update

Other Names


Current Site Status

No cleanup action is planned at this time and EPA-funded cleanup would occur only if the assessment reveals a health threat meeting the CERCLA removal action criteria.

Site Description

The Plymouth Township CO2 Site resulted from a hazardous materials incident that occurred during Hurricane Floyd in September 1999. At the height of the storm, a child living in a Plymouth Township residential development lost consciousness while in the home’s basement. A response by the local public utility and two local hazardous materials teams determined that an oxygen deficient atmosphere was present in the lower elevations of the basement; oxygen levels were at a life threatening level. Ventilation measures were initiated to allow for routine home occupancy.

Followup by several agencies, including EPA, determined that carbon dioxide (CO2) had collected in the confined air space of the basement sump drain (reason unknown) and had been released from the sump as a result of the significantly reduced atmospheric pressure during the storm. Apparently, the CO2 level was high enough to displace oxygen in the basement breathing space. No other substances of potential health concern were discovered. As a precautionary measure, the Montgomery County Health Department (MCHD) conducted indoor air monitoring of homes throughout the residential development and the adjacent development (approximately 200 homes in total). Elevated sump CO2 readings were found in approximately fifteen additional homes. Although continuous indoor air monitoring has been limited to a select number of homes, no CO2 levels of concern have been recorded in the basement breathing space air of any house except the residence where the initial incident took place (eventually, a ventilation mitigation system was installed at this house by the homeowner). The majority of the basements are used as recreational rooms.

Three public meetings have been held in Plymouth Township since the initial September 1999 incident.

Site Responsibility
This site is being investigated through EPA CERCLA Removal Program authorities.
NPL Listing History
Not a Superfund NPL or Removal Site.

Threats and Contaminants

EPA’s sampling and monitoring work to date has determined that the presence of elevated readings of CO2 in the sump drains, with the threat of release to the breathing space air in the basement, is the primary concern at this site. Other CERCLA-regulated substances have not been detected at levels of health concern. The threat lies in the potential for CO2 to be released from the sump drains into basement breathing air at levels that might directly present a health concern or cause significant displacement of oxygen. It appears that this threat of release has the most likely chance of occuring during low atmospheric pressure events (i.e. heavy rainstorms).

Cleanup Progress

EPA’s CERCLA Removal Program is currently conducting a Removal Assessment. Activities will include: 1) attempting to determine the source of the elevated CO2 (naturally occurring or “man-made”), 2) performing followup continuous monitoring in home basements with elevated CO2 in sump drains to determine if and under what conditions a significant release to breathing space air occurs, and 3) confirming the most effective mitigation method to prevent a significant release. The assessment will also address the possibility of the presence of other contaminants (although work to date suggests no other substances of concern are present). If EPA determines that another major CO2 release is unlikely and that the past release was confined to the intial incident, EPA’s work will cease.

The investigation has wider implications in that CO2 and/or depressed oxygen levels reportedly were detected by private environmental professionals in the sump drains/basements of other homes in the Delaware Valley during Hurricane Floyd. Generally speaking, CO2 is not a substance targeted for indoor air monitoring during such events and few first responders or public utility personnel monitor for CO2. If the presence of CO2 in basement sumps is not a site-specific occurrence limited to the Plymouth CO2 Release Site, and it appears that this is a potential wider problem under specific weather conditions, our work may be of interest to public utlilty companies, the home building industry and Federal or State agencies who routinely conduct geological investigations.


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