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4-125 <br />• as recorded at sixteen state, municipal, and privately <br />operated particulate sampling sites. In undeveloped <br />sections similar to the lease area, particulate concen- <br />trations range from 20 to 40 micrograms per cubic meter. <br />A detailed air quality analysis determined that particu- <br />late concentrations in the Grand Valley in areas away <br />from any sources were approximately 40 micrograms per <br />cubic meter annual geometric mean (PEDCo 1977). The <br />calculated first and second maximum 24-hour concentra- <br />tions were 130 and 112 micrograms per cubic meter, res- <br />pectively. <br />There has been no measurement of carbon monoxide, hydro- <br />• carbon, nitrogen oxides, sulfur dioxide, or other gaseous <br />pollutant concentrations in the vicinity of the proposed <br />mine. Motor vehicle emissions along state highway 139 <br />which crosses the mine site would probably raise concen- <br />trations of carbon monoxide, hydrocarbon, and nitrogen <br />oxides slightly above background or natural levels. <br />Visibility at the site ranges from less than one mile to <br />approximately 100 miles throughout the year. Average vis- <br />ibility is about 54 miles with greatest visibility occur- <br />ring during spring and summer months. <br />A high-volume particulate sampler was established <br />at the meteorological station described above. Data <br />