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established at levels to protect the most sensitive segments of the population and are not to be exceeded more than once per year. Table 1. State Ambient Air Quality Standards for CO I-Hour Averaging Period State Standard I 30 lMaximum concentration in parts per million (ppm). 8-Hour Averaging Period 9 The potential air quality impacts of the project were identified by estimating future CO concentrations at the three busiest, most congested intersections in the Twin Lakes study area (Figure 6): . Snelling A venue at County Road C . Cleveland A venue at County Road C . Cleveland Avenue at the I-35W Ramps These three intersections represent the worst-case conditions relative to forecast traffic volumes and average vehicular delay. As a result of the projected traffic conditions, these locations are also likely to experience the highest CO concentrations in the study area. The air quality analysis of the proposed redevelopment was conducted using the U.S. EPA MOBILE5a emissions model and the CAL3QHC line-source dispersion model. The modeling was based on the following assumptions: . The analysis was conducted for the Year 2011 to represent conditions one year after completion of the proposed development. . Twenty point six (20.6) percent of the vehicles were assumed to operate in a cold-start mode and twenty-seven point three (27.3) percent of the vehicles were assumed to operate in a hot-start mode. . The composition of the vehicle fleet was derived from 1990 Twin Cities vehicle registration data. . Peak one-hour CO concentrations were modeled using worst-case meteorological assumptions, including a wind speed of 1.0 meters per second, class "D" atmospheric stability, an atmospheric mixing height of 1 ,000 meters, and an ambient temperature of 1 0 Celsius. . A total of 36 wind directions in 100 increments were analyzed to identify the maximum CO concentration at each receptor site. . Eight-hour average CO concentrations were derived from the peak one-hour modeling results using a persistence factor of 0.7. The persistence factor accounts for the lack of persistence of the worst-case traffic and meteorological conditions for eight consecutive hours. . The air quality analysis is based upon the Year 2011 roadway and traffic control assumptions documented in the traffic analysis. #24397 17