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Past measures have been taken to reduce the levels of flammable gases in the basements of buildings north of the site. In February 1993, traps were installed on the footing drains of basement sumps, and in March and April 1993, vents were placed on these traps. Subsequent monitoring showed that the basement breathing zone levels of flammable gases continued to reach 6 to 10 percent of the lower explosive limit (LEL). The LEL is the lowest concentration at which a fire or explosion may occur.

One building north of the site is a nursing home and another building has businesses on the first floor, including a restaurant, and apartments on the second floor. Several employees work at the restaurant and in these businesses. The highest level detected in the nursing home during March 1998 was 1 percent of the LEL in the sump area and a floor drain. In the other building, the level of flammable gases in the floor cracks, floor drains, and sumps, frequently equaled or exceeded the LEL. During March 1998, the level of flammable gas in one floor drain equaled or exceeded the LEL on 9 of 12 sample dates (Dollhopf 1998; Maximis, Inc . 1998).

The primary concern is the presence of flammable or potentially flammable levels of landfill gas in buildings north of the site, which have persisted in spite of the installation of ventilation systems. Monitoring in buildings north of the site has frequently found flammable gas levels at or above the LEL in cracks, floor drains, and sumps, as well as levels up to 10 percent of the LEL in the basement breathing zone.

Because of the potential fire and explosion danger, U.S. Occupational Safety and Health Administration (OSHA) regulations require the evacuation of a workplace if flammable gases reach 10 percent of the LEL. In one building north of the Yeoman Creek Landfill, 10 percent of the LEL has frequently been exceeded, and flammable levels have frequently been detected in floor cracks and drains. Sump motors and other electrical equipment in these buildings may not be spark-proof. Consequently, there is a danger of fire or explosion.

Chemicals found in basement air samples from buildings north of the site include benzene, cis- 1,2-dichloroethylene, ethyl benzene, styrene, toluene, vinyl chloride, and xylenes. Hydrogen sulfide gas also may be associated with landfill gas. Unfortunately, the levels of these chemicals were not measured, so possible health effects that could result from exposure cannot be evaluated. We do not know whether the levels of these chemicals are elevated when compared with typical indoor air.

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