CCP 01-21-2003 - Laserfiche WebLink

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I Ie I I I I I I I .. I I I I I I .. I I compliance with this contingency, air quality analyses of "worst-case" conditions were performed for the study area to estimate the effect of the proposed campus expansion on future CO concentrations at key intersections the study area. These analyses include monitoring of existing background CO concentrations and modeling future CO concentrations at worst-case intersections. Carbon Monoxide Modeling Methodology and Assumptions Carbon monoxide concentrations near the intersections were predicted using forecasted traffic volumes, current and proposed intersection geometries, optimized signal timing, and with computer models, including the U.S. EPA MOBILE5A' emission model and the U.S. EP A CAL3QHC dispersion model. The scope of the air quality analyses was developed based on input from MPCA staff. The modeling assumptions used in this analysis are shown in Table 17. TABLE 17 CARBON MONOXIDE MODELING ASSUMPTIONS Analysis Year: 2020 Cold Start Percentage: 20.6 percent for all traffie Hot Start Percentage: 27.3 percent for all traffic Cruising Speed: Posted Speed Limits Traffic Mix: National Default Values Wind Speed: 1 meter/second (3.3 feet/second) Temperature: -6.6 degrees Celsius (20 dcgrccs Fahrenheit) Surface Roughness]: 108 centimeters (42.5 inches) Stability Class': D Inspcction Maintenance: No Oxygenated Fuel: Yes 8-Hour Persistence Factor]: 0.7 Wind Direction: 36 directions at 10 degree increments Notes: The Surface Roughness, Stability Class and 8-Hour Persistence Factor arc discussed in Guidelines for Air Quality Maintenance Planning and Analysis Volume 9 (Revised): Evaluating Indirect Sources, U.S. EPA, 1978, and are summarized below. 1 Surface Roughness indicates the initial ground level turbulence into which the exhaust plume will be released. Generally, the higher the rouglmess, the lower the concentration. The number used here is conservatively low for the project area (results in a worst-case). Stability Class characterizes the mixing potential of the atmosphere. Stability Class D is used as a worst- case in suburban and urban areas. The 8-Hour Persistence Factor is used to determine 8-hour localized CO contributions, and takes into account fluctuating wind directions, temperature and traffic, which are morc likely to occur over eight hours than during one hour. The factor is multiplied by the I-hour modeling result. J The EP A has recently released the improved MOBILE6 emissions model. At the time of this analysis, the MPCA bad not yet approved regional assumptions for MOBlLE6 inputs. The MOBlLE5A model is still approved for use by the EP A. Guidant Campus Master Plan Final AUAR and Mitigation Plan - 42- January 2003