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11 <br />CNAPTERFOUR <br />Parachute Site <br />Environmental IDonsequences ' ' <br />TABLE 4.5-7 <br />SUMMARY OF CUMULATIVE CLASS II INCREMENT ANALYSIS <br />FOR THE PARACHUTE SITE <br />..... <br /> <br /><::;::::'::PultutatttlParaiuefer'::i:'":: <br /> <br />z:.:.::24.;tiour';:::. <br /> <br />::::'::;'::Atutual-:::-::::: <br />,. <br />:-::::. ~ <br />. $pn~i:::::::: <br />Maximum Parachute-only <br />Increment Concentration (µg/m') 20.6 5.6 3.5 <br />Percent of Class II Increment (%) 68.7 32.9 13.9 <br />Maximum Cumulative Increment <br />Concentration (µg/m') 20.6 5.6 11.9 <br />Percent of Class II Increment (%) 68.7 32.9 47.6 <br />Source: R7P 1998b <br />Level I Visibility Analyses <br />Piceance and Parachute Sites <br />Selected National Parks and wilderness azeas aze designated as Class I azeas and ,ire subject to <br />additional protection from degradation of air quality. <br />The USFS has established a 0.5 deciview "Limit of Acceptable Change" (LAC) to evaluate <br />visibility impacts at the Flat Tops Wilderness Area. A Level I regional haze visittility analysis <br />was perfotTrted based on pollutant emission rates, distances to the impact azea, and background <br />visual range using procedures from the Interagency Workgroup on Air Quality Modeling <br />(I WAQM) Phase i Report (EPA 1993). A Level 1 screening analysis is the most conservative, <br />and is performed assuming very conservative (worst case) meteorological data. I:F compliance <br />cannot be demonstrated with a Leve] 1 analysis, a Leve12 analysis may be requin:d. <br />The analysis used a background visual range based on the "mean of the best 20 pt:rcentile" data <br />for the Mt. Zirkel Class I Area 140 mile visual range (234 km), and relative humidity correction <br />factor data (2.27) based on the annual average extinction information from the Interagency <br />Monitoring of Protected Visual Environments (IMPROVE) data (IMPROVE 1995). These <br />factors weze also used by Mr. John Vimont, NPS, for BLM's Glenwood Springs Resource Area <br />Environmental Impact Statement (BLM 1998b). <br />The I WAQM procedures assume a conversion rate of NOx into ammonium nitrate based on the <br />modeled concentrations. The calculation of extinction is based on the interference from <br />ammonium nitrate and primary particulate (PM~o). The combined extinction from NOx and <br />PMto emissions from both the Piceance and Pazachute facilities is calculated and presented in <br />Table D-4 in Appendix D. The calculated visibility change is 0.5 deciview. <br />A 1.0 deciview change is considered "potentially significant", as adopted by the Grand Canyon <br />Visibility Transport Commission and reported in Pitchford and Malin (1994). A deciview is <br />defined as about a 10 percent change in extinction coefficient, which is a small but perceptible <br />scenic change trader many circtunstances. The 1.0 deciview value corresponds to a 2 to 5 <br />4-28 Meteorology and Air Quality <br />