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III. Environmental Setting, Impacts,and Mitigations G. Air Quality gases can be used for cogeneration purposes. The proposed landfill gas control system would include a series of gas extraction wells and connectors,a gas condensate collection system, and a gas blower/flare. The blower/flare would be located near the PEn facility. Methane emissions were estimated using EPA's Landfill Gas Estimation computer model(EPA, 1991b). For projected waste quantities from 1993 onwards,the model estimated an additional methane emission rate of about 940 million cubic feet per year(cu.ft./year)in year 2045;this does not account for methane generated by the wastes currently in place. The existing power plant,operated by PEn,draws approximately 2.6 million cu.ft.of landfill gas per week,or about 135 million cu.ftJyear(Donlon, 1993). This plant is currently operating close to full capacity. Expansion of the existing plant to handle the additional generated gas would depend on several factors,including cost of alternative fuel sources,demand for electricity, and permitting requirements for increased operating capacities. New federal regulations require that landfill as be collected and either flared or taken to g q g cogeneration facilities. If the existing power plant were not to use the additional gas generated by future incoming waste quantities,the landfill operators would have to install flaring devices to eliminate the methane gas. The gas collection system would have to be expanded to cover the complete landfill,instead of the existing 50 percent of the landfill area. Because regulatory requirements would require established gas collection and disposal mechanisms,methane gas generated by additional waste quantities at the landfill would not be a significant effect of the project. Mitigation Measure G3. None warranted. Impact G.4. Landfill wastes would generate toxic air contaminants,which could have adverse health effects at nearby sensitive receptor locations/land uses. (ADVERSE) EPA's initial list of major and area sources of hazardous air pollutants include municipal landfills. If and when the quantities and types of air pollutants allowed under an existing permit change,an application should be filed with the SJVUAPCD for a permit modification. As part of the permit modification process,the project proponent would have to quantify expected emissions,toxic or otherwise,and if TAC emissions exceed trigger levels a screening level health-risk assessment would be required. III.G.14