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1 Impact Report Pa Draft Envnronmenta a IV.D-17 p p g Forward Landfill Expansion as Proposition 65,both of which require public notification if the incremental risk equals or exceeds 10 in a million. The SJVAPCD CEQA Guidelines also recommend that the cancer risk significance threshold be 10 in a million. The incremental risk from exposure to a given TAC is calculated by multiplying the concentration(or dosage level)of the given TAC by its specific unit risk factor or potency slope. The unit risk factor or potency slope of a TAC is derived from epidemiological studies, and the published values are based on the assumption that a person would be exposed to the given TAC at that dosage constantly for 70 years or for the life of the project. Non-Cancer Health Risk Health risks for each non-carcinogenic TAC are determined using a Hazard Index (HI), which is the ratio of the predicted exposure concentration to a threshold level that could cause adverse health effects other than cancer, as established by the Office of Environmental Health and Hazard Assessment(OEHHA). The ratio (HI) of each non- carcinogenic substance is added to the calculated Hazard Indices of the other non- carcinogens to produce an overall HI. I€the overall HI exceeds 1.0,then the impact would be significant. The HI significance threshold of greater than 1.0 is defined in the SJVAPCD CEQA Guidelines and is consistent with the value requiring public notification in the AB 2588 regulation and in Proposition 65. Cumulative Impacts According to the SJVAPCD GAMAQI, a cumulative impact occurs when two or more individual effects, considered together, are considerable or would compound or increase other environmental impacts. Cumulative impacts can result from individually minor but collectively significant impacts, meaning that the project's incremental effects are considerable when viewed in connection with the effects of past, current, and probable future projects. Notably,any project that would individually have a significant air quality impact would also be considered to have a significant cumulative air quality impact. According to the SJVAPCD GAMAQI, cumulative impacts should be assessed for ozone, PM,(), CO and TAC. Greenhouse Gases As discussed previously, at this time there are no adopted Statewide guidelines for GHG emission impacts,but this is being addressed through the provisions of Senate Bill 97 ("SB 97"). The project would be considered to have a significant impact if the project would be in conflict with the AB 32 State goals for reducing GHG emissions;with the assumption AB 32 will be successful in reducing GHG emissions and reducing the cumulative GHG emissions statewide by 2020. It is important that the state has taken these measures,because no project individually could have a major impact (either positively or negatively)on the global concentration of GHG. Impacts and Mitigation Measures This impact section evaluates the activities described in the Project Description that could potentially result in impacts to air quality, climate change, and human health based on the conditions of the project area. As described in the Project Description,the proposed expansion would increase the permitted Class II refuse footprint from 354.5 acres to 551.8 acres, adding approximately 43,367,810 cubic yards (cy) to the capacity of the landfill. The additional volume is estimated to accommodate an additional 37.7 million tons of landfill decomposable waste. This additional waste is estimated to result in a maximum