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■♦V. <br /><!< <br />'k;-. <br />% <br />^ ■:^: <br />■ h',“- <br />■■ <br />92-47 . C'8 <br />These calculations along with subsequent dispersion modeling of <br />the air concentrations of dust included the following <br />assumptions: <br />Emission rates (g/s) paved/unpaved sources are assumed to <br />occur continuously throughout the year. Therefore, <br />concentration and deposition values represent continuous <br />emissions. <br />The particulate emission rate is based in part on the volume <br />of vehicular traffic which was evaluated by the Hennepin <br />County Transportation Planning Division in April 1991 to be <br />325 vehicles/day. This number was assumed to be the average <br />annual daily traffic volume which is constant throughout the <br />year, even during winter months. <br />Reduction of particulate emissions due to wet road surface <br />conditions and snow cover are not considered. <br />The 10 meter receptor is within distance recommended by air <br />quality model to provide conservatism. <br />Highest concentration resultant from the five most recent <br />years of meteorological data were reported. <br />Regulatory default mode of ISC tends to maximize resultant <br />concentrations. <br />Conservative Health Risk Assumptions <br />The main assumptions made in this assessment are: <br />A person spends 24 hours per day outdoors. <br />A person is exposed 24 hours a day, 365 days a year for <br />70 years only at this stretch of the road and always <br />outdoors. <br />Infants are exposed 24 hours per day, 365 days a year for <br />3 years, and they spend all this time outdoors. <br />The inhaled particulates contain the same chemical <br />concentrations for the 70 year period. <br />The entire amount of chemicals contained in the inhaled <br />particles are absorbed by the body. <br />All of the chromium inhaled is in its most toxic form. <br />Chromium VI. <br />. .