Wastewater from Smurfit-Stone Container’s Missoula mill is retained in an 800-acre landscape of pondsfor treatment and subsequent release during spring runoff conditions. Anaerobic respiration by pondmicrobes leads to the emission of H2S. The mill’s operating permit limits H2S emissions to 50 ppb on acontinuous monitoring basis (1-hour averaging period). During the summer of 2000, a bloom of sulfurreducingbacteria gave rise to increased H2S emissions from the wastewater ponds. Normal circulation ofair in the Missoula Valley would typically have been able to disperse the H2S below the aesthetic permitlimit. Smoke from wildland fires, however, created summertime inversions that prevented effectiveattenuation of H2S emissions. Hourly averages of H2S exceeded 50 ppb for a total of 158 times. Time/datecharted data are presented to demonstrate typical H2S dispersion, and the stagnant H2S emissions seen inthe summer of 2000. PM-10 data (measured simultaneously at a site 15 km SE) are also presented toillustrate the extent of the inversions.
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