GENERAL40898 - Laserfiche WebLink

Home Browse Search

CNAPTERFIVE Draft EIS Ref~isions ~, The air quality impact pazameters included annual average NOZ concentrations, annual atmospheric deposition of nitrogen, and the impact on visibility at Class I azeas in the project vicinity. The same wind fields and modeling procedures used in the Glenwood Springs EIS were used for the Yankee Gulch Level 2 CACHET/CALPUFF analysis. In addition, the USDA-Forest Service requested that additional visibility modeling analyses be performed for both Yankee Gulch sources alone (i.e., the Proposed Action) and for multiple sources in the region (i.e., cumulative impacts). The Proposed Action impact analysis included all Yankee Gulch NO, and PM,o emission sources at both the Piceance and Pazachute plants" The cumulative sources modeled included the Glenwood Springs EIS "reasonably foreseeable" scenario which assumed current oil and gas NO emission sources would double with foreseeable growth. The estimated annual NO, emissions for the "reasonably foreseeable" oil and gas development sources totaled 1,655 mv. Ambient air quality concentrations were predicted using CALPUFF and discrete model receptors located along selected Class I and sensitive Class II azea boundaries neazest to the Yankee Gulch facilities. Regional haze is chazacterized by general decreases in visual range and reduced contrast of observed landscape features (increased extinction), caused by the scattering and absorbing light by primary particulate matter and secondary nitrate aerosols. Based on CALPUFF modeling results, assumed background visibility conditions can be combined with increased predicted concentrations (and related extinction coefficient increases), and the combined visibility effects can be quantified. " The deciview visibiliri index is desiened to be lineaz with humanly perceived changes under assumed commonly occurring conditions" Deciview values increase with increasing visibility impairment. The deciview unit is a simple logarithmic transformation of the extinction coefficient, and therefore is easily determined from measured or modeled concentrations. As a measure of potentially significant change in visibility, a 1.0 deciview just noticeable change has been proposed by Pitchford and Malm (1994) and was adopted by the Grand Canyon Visibility Transport Commission. A 1.0 deciview change (equivalent to a 10 percent change in extinction coefficient) is a measure of a small but perceptible visibility change under many circumstances. In addition, the USDA-Forest Service has established a % just noticeable change 0.5 deciview Limit of Acceptable Change (LAC) to evaluate visibility impacts at the Flat Tops Class I area. The IWAQM analysis procedures recommend that Mt. Zirkel background visibility data should be used as the baseline against which the change in extinction at the Flat Tops to be calculated. The background visual range at Mt. Zirkel is 16.69 Mm"' (234 km visual range) based on the "mean of the best 20 percentile" IMPROVE particulate matter data. The relative humidity convection factor (2.27) was the same value that was used to reconstruct the annual average extinction from the IMPROVE measured atmospheric constituent data. The IWAQM analysis procedure states that it is important to apply consistent relative humidity adjustment factors to • both the predicted source contribution light extinction and the background light extinction. 5-23