Potential air quality impacts of large-scale geothermal energy development in the Imperial Valley

Abstract This report is an assessment of the potential impact on air quality of large-scale (3000 MW) geothermal development in California's Imperial Valley. The assessment is based on the predictions of numerical atmospheric transport models. Emission rates derived from analyses of the composition of geothermal fluids in the region and meteorological data taken at six locations in the valley over a 1-y period were used as input to the models. Hydrogen sulfide is the emission of major concern. Our calculations predict that at the 3000-MW level (with no abatement), the California 1-h standard for H 2 S (42 μg m −3 ) would be violated at least 1% of the time over an area of approximately 1500 km 2 (about 1 3 of the valley area). The calculations indicate that an H 2 S emission rate below 0.8 g s −1 per 100-MW unit is needed to avoid violations of the standard beyond a distance of 1 km from the source. Emissions of ammonia, carbon dioxide, mercury, and radon are not expected to produce significant ground level concentrations, nor is the atmospheric conversion of hydrogen sulfide to sulfur dioxide expected to result in significant SO 2 levels.