6.9. SR 09-06-2011 - Laserfiche WebLink

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Air toxics analysis is a continuing area of research. While much work has been done to assess the overall health risk of air toxics, many questions remain unanswered. In particular, the tools and techniques for assessing project-specific health outcomes as a result of lifetime MSAT exposure remain limited. These limitations impede the ability to evaluate how the potential health risks posed by MSAT exposure should be factored into project-level decision-making within the context of the National Environmental Policy Act. The FHWA will continue to monitor the developing research in this emerging field. Because of the uncertainties outlined above, a quantitative assessment of the effects of air toxic emissions impacts on human health cannot be made at the project level. While available tools do allow us to reasonably predict relative emissions changes between alternatives for larger projects, the amount of MSAT emissions from each of the study scenarios and MSAT concentrations or exposures created by each of the study scenarios cannot be predicted with enough accuracy to be useful in estimating health impacts. Therefore, the relevance of the unavailable or incomplete information is that it is not possible to make a determination of whether any of the scenarios would have."significant adverse impacts on the human environment." This document acknowledges that the build scenarios may result in increased exposure to MSAT emissions in certain locations, although the concentrations and duration of exposures are uncertain, and because of this uncertainty, the health effects from these emissions cannot be estimated. Although a qualitative analysis cannot identify and measure health impacts from MSATs, it can give a basis for identifying and comparing the potential differences among MSAT emissions, if any, from the various scenarios. The qualitative ' assessment presented below is derived in part from a study conducted by the FHWA entitled A Methodology for Evaluating Mobile Source Air Toxic Emissions Among Transportation Project Alternatives. For each scenario in this AUAR, the amount of MSAT emitted would be proportional to the average daily traffic (ADT) assuming that other variables such as fleet mix are the same for each scenario. The ADT estimated for each of the build scenarios is higher than that for the no build condition, because the interchange facilitates new development that attracts trips that would not otherwise occur in the area. This increase in ADT means MSAT under the build scenarios would probably be higher than the no build condition in the study area. There could also be localized ' differences in MSAT from indirect effects of the project such as associated access traffic, emissions of evaporative MSAT (e.g., benzene) from parked cars, and emissions of diesel particulate matter from delivery trucks. Travel to other ' destinations would be reduced with subsequent decreases in emissions at those locations. r For all scenarios, emissions are virtually certain to be lower than present levels in the design year as a result of EPA's national control programs that are projected to reduce annual MSAT emissions by 72 percent from 1999 to 2050, as shown in the City of Elk River Draft Alternative Urban Areawide Review August 2011 Page 78 of 90