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5.12 TRAFFIC AND TRANSPORTATION especially in the winter months (1St and 4th quarters). Under these conditions,any visible plume would be carried south,rather than east toward the airparks, so it is unlikely that any HRSG vapor plume would interfere with visibility at the airparks. 5.12.2.6.5 Cooling Tower Visible Plume Analysis Cooling towers are more likely to form vapor plumes than HRSG stacks because their exhaust is cooler and has a higher moisture content. However,as discussed above regarding potential HRSG vapor plume impacts on nearby airparks,the conditions under which cooling tower vapor plumes would tend to form are likely to carry the plumes to the south rather than to the east toward the airparks. Therefore it is also unlikely that the cooling tower vapor plumes would adversely affect airpark operations. This qualitative analysis is supported by experience with the cooling tower at the existing NCPA STIG plant. As noted earlier,the Lodi (Precissi) and Kingdon airport operators have indicated that existing HRSG and cooling tower plumes have not posed any hazards to flight operations. 5.12.2.6.6 HRSG Thermal Plume Analysis The impact of turbulence from the HRSG stack plume is considered not significant. The existing HRSG plume is hotter than the LEC HRSG exhaust plume (769°F vs.<200°F) and has a higher exhaust velocity (170 ft/sec vs. under 90 ft/sec), so has a higher potential for creating thermal turbulence than the exhaust plume from the new HRSG. As noted earlier, the Lodi (Precissi) and Kingdon airport operators have indicated that the existing HRSG plume has not posed any hazards to flight operations. Therefore,it is unlikely that the proposed project will pose a hazard. The most critical time for turbulence from a power plant stack plume to impact aircraft operations will be when aircraft are on their final approach for landing. At Kingdon Airpark, approaching planes will be landing to the northwest and will be on final approach from the southeast,or landing to the southeast and approaching from the northwest. In either approach, approaching aircraft will be over a mile from the plant site at nearest approach. The wind would have to be from the west for a power plant plume to be transported directly over the nearest runway.Winds from the north or northwest direction occur approximately 12 percent of the time. Since the airpark is over a mile away,it is unlikely that the plume from the LEC would drift over the active approach to the Kingdon runway and potentially impact slow-moving aircraft on final approach. As noted earlier,the HRSG stack is 1.4 miles from the Kingdon Airpark runway approach and at times when the wind flow direction is from the power plant site toward the airpark, at an average daytime wind speed of 5 m/s or 11.2 mph,it will take the plume more than 7 minutes to drift over the approach end of the runway. During this time,plume turbulence will dissipate and will become indistinguishable from ambient atmospheric turbulence. 5.12-26 SAC/371322/082330005(LEC_5.12_TRAFFIC_AND_TRANSPORTATION.DOC)