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Indoor Air Quality
EPA conducted basement air sampling in some homes around the former Amoco refinery site in June and July 1999 and in March 2000. EPA is now finishing a third basement air sampling study of six homes which began in August 2000. The purpose of the basement air sampling is to check for unhealthy levels of volatile organic compounds (VOCs) that might enter basements from contaminated groundwater that is under a portion of the Norledge neighborhood.Volatile organic compounds (VOCs) are chemicals that contain the element carbon and vaporize easily into the air. Some chemicals in crude oil and refinery products, such as benzene, toluene, ethylbenzene and xylenes, are VOCs. These chemicals vaporize when they come into contact with air. It is possible for VOCs from contaminated groundwater to vaporize and percolate up through soil into living areas such as basements. Breathing low levels of these chemicals over a long period of time (years) may cause health problems. For example, benzene is known to cause cancer.
Homes often have low concentrations of VOCs in the air because of products used in the home. Benzene and other types of VOC vapors may result from adhesives, solvents, cigarette smoke, paints, stains, varnishes and gasoline. Occupants of homes that are part of the basement air sampling study may be asked questions about recent home improvement activities or types of chemicals that are being stored in the home. If high concentrations of VOCs are measured in a home, the answers to these questions can help determine whether the source of the VOCs is the contaminated groundwater or products used in the home.
There are different methods for collecting indoor air samples for laboratory analysis. For the EPA studies, air was collected in stainless steel containers (SUMMA canisters) in which all air had previously been removed. The vacuum in the canisters caused the air sample to be pulled into the canister. Air may also be collected in sorbent sample tubes. A sorbent is a material, such as activated carbon or charcoal, which traps the VOC molecules in the pores of the material. Amoco and MDNR collected air samples in sorbent tubes for studies done in 1998. The amount of air entering the canister or moving through the sample tube is measured so that the laboratory can determine the concentration (amount per cubic meter or cubic foot of air) of contaminant in the air. For the EPA studies, 24-hour composite air samples were taken at specified intervals over a period of one to two weeks in each home.
EPA Region 7 used a benzene action level for long-term exposure as 7 parts per billion (ppb), the same as22 micrograms per cubic meter (ug/m3). Benzene is the chemical of focus for the studies because it is known to cause cancer in humans. If the measured benzene concentration is greater than 7 ppb, this is an indication that action should be taken to lower the benzene concentration in the home. Where high levels of benzene are measured in a home, the air is usually re-sampled to verify the results of the first test. If the concentration of benzene remains high and the source of the benzene vapors is a product used or stored in the home, the owner may be advised to remove this source and/or to provide more ventilation. If the source is the contaminated groundwater plume, a plan of action will be developed to control the entry of vapors into the home.
The basement air sampling study is a way to screen for possible indoor air problems from the contaminated groundwater. All homes are not screened, only a select few. Homes were chosen for the study based on location over the most contaminated part of the groundwater and access for technicians doing the sampling. The addresses of the homes chosen are confidential to protect the privacy of the occupants. The results of this study will help EPA determine if more basement air sampling is needed.
