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<br />I <br />.. <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />811 <br />I <br />I <br />I <br />I <br />I <br />I <br />Ie <br />I <br />I <br /> <br />Background Carbon Monoxide Concentrations <br /> <br />Background CO concentrations are needed for air quality analysis purposes to represent <br />conditions without the influence of nearby vehicles. By definition, the background CO <br />concentration in any particular area is that concentration which exists independently of <br />direct contributions from nearby traffic. The background concentrations are added to <br />intersection-scale modeled results to yield predicted CO levels at modeled spot receptors <br />adjacent to intersections. <br /> <br />Previously monitored CO background concentrations were used for this project. The <br />Minnesota Department of Transportation monitored background CO concentrations for two <br />weeks (May 21, 1999 - June 12, 1999) at Little Canada Elementary School at 400 Eli Road <br />in Little Canada, (approximately four miles southeast of the Guidant development). <br />Maximum monitored concentrations of 1.23 ppm and 0.82 ppm for I-hour and 8-hours, <br />respectively, were found. <br /> <br />For purposes of the 2020 analyses, the background concentrations were adjusted for <br />region-wide increases in traffic volumes and vehicle emissions. The adjustment factor for <br />traffic growth was based on the regional travel forecast modcl. The adjustment factor for <br />vehicle emission was based on the MOBlLE5A emissions model, which incorporates <br />anticipated decreases in CO emissions from motor vehicles due to emission controls. The <br />Holzworth (temperature) correction factor was required to adjust for worst-case winter <br />conditions. The results are summarized in Tablc 18. <br /> <br />TABLE 18 <br />CALCULATION OF CO BACKGROUND CONCENTRATIONS <br /> <br /> 2020 <br />Factor I-Hour 8-Hour <br />Maximum 1999 Monitored Concentration (ppm) 1.23 0.82 <br />Background Traffic Volume Adjustment Factor 2.28 2.28 <br />Emission Adjustment Factor 0.89 0.89 <br />Holzworth (temperature) Correction 2.00 2.00 <br />Worst-Case Background Concentration (ppm) 5.0 3.3 <br />State Standard (ppm) 30 9 <br />Federal Standard (ppm) 35 9 <br /> <br />Intersection Carbon Monoxide Modeling <br /> <br />Carbon monoxide analyses were performed for the Build alternative in the year 2020 at the <br />following key intersections: Lexington Avcnue/TII 96, Hamline Avenue/TH 96, <br />Lexington Avenue/County Road F, lIamline Avenue/County Road F, and Lexington <br /> <br />Guidant Campus Master Plan <br />Final AUAR and Mitigation Plan <br /> <br />- 43- <br /> <br />January 2003 <br />