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1 Consent Decree Exhibit C air pollutant background concentrations are from the Agency for Toxic Substances and Disease Registry (ATSDR) toxicological profiles. In some cases, both the background concentration and the cleanup level calculated by Method B are lower than the Practical Quantitation Limit (PQL) for that particular compound. In those cases, MTCA allows the PQL to be used as the cleanup level [WAC 173-340-700(6)]. Table 3-1 presents the cleanup levels for all detected air pollutants at the Everett Landfill/Tire Fire Site. The cleanup level is the concentration calculated by the Method B equation of WAC 173-340-750(3). If the Method B level is less than the natural background, then the background concentration is proposed as the cleanup level. If the laboratory PQL is greater than both the Method B concentration and the background concentration, then the laboratory PQL concentration is proposed as the cleanup level. If the compound is not listed in the MTCA CLARC II Update, then no cleanup level is proposed. 3.1.3 Nature and Extent of Gas Contamination The following conclusions are derived from the information presented in the Brownfield Feasibility Study (BFS) (FSI, 2000): • Generation of landfill gas is approximately 230 cubic feet per minute (cfm) and is declining at a rate of approximately 7.5 cfm per year over the next ten years. In 2010, it is projected to be about 155 cfm and will continue to decline steadily. • The impacts of landfill gas emissions on ambient air do not exceed MTCA cleanup standards. • Insufficient data exists to fully determine the extent and magnitude of subsurface migration of landfill gas beyond the Site boundary. • Landfill gas perimeter monitoring probes along the east, north and west property boundaries are finished in refuse, or in immediate proximity to it, and data from these probes are not representative in relation to establishing whether or not landfill gas is migrating past the Site boundary. These probes are not part of a proposed future compliance monitoring system. Figure 3-1 shows existing landfill gas probes as well as proposed locations for compliance monitoring probes. • Native, organic, peat soils beneath the surface may contribute to the presence of methane on the east and north Site boundaries. • Buried refuse extends beyond some portions of the boundary of the City's property. • There have been two occasions where flammable gas was detected above 100 ppm during off -site building monitoring. One was in a roof drain that connects directly to a manhole of the City's sewer system. The other was recorded from floor cracks where the instrument was drifting between non -detect and a maximum of 120 ppm. Neither measurement has been repeated during subsequent monitoring rounds. • The highest flammable gas concentration measured in the Animal Shelter and Everett Transfer Station from several separate monitoring events was approximately 7,000 ppm within the women's restroom floor drain, approximately 15% of the explosive limit of 50,000 ppm. The flammable gas concentration measured just two inches above the floor drain was less than 20 ppm for all monitoring events. There was no evidence of accumulation of methane gas within the restroom above the floor FINAL - March 2001 3-2 Everett Landfill Tire Fire Site Cleanup Action Plan 1 1 Ll Ll 1 1 1 1 P� 1 1 1 1 '1 1 1 1 1