Concentrations of H2S in air around the Olkaria Geothermal Power Plant, Kenya

Variations in concentrations of H2S with distance away from the Olkaria Geothermal Power Station, and at one discharging well, were monitored over a period of up to 11 days. The changes in H2S concentrations were correlated with changes in weather parameters. Within the power station, concentrations of H2S may be expected to exceed 7.5 ppm over half an hour period at least once in a 2 weeks period. The levels of H2S then decay with distance away from the power plant to levels below 0.3 ppm within about 0.5 km from the power station. Plant injury levels can therefore be expected to be present within 0.5 km of the power station, and for several hundred meters away from a discharging well. The highest H2S concentrations are obtained when the winds are calm, the humidity is high and the temperatures are lowest. These conditions are found in the Olkaria area during the period 2000 to 0300 hr on a diurnal basis. The study suggests that if these conditions persist for prolonged periods of time, then H2S concentrations around the power plant may build up to unsafe levels. There is therefore a need for an H2S monitoring and early warning system around the power plant, the predictions of which can be aided by observation of weather parameters. Measurements of rain acidity around the Olkaria area show no evidence that the H2S emissions contribute to either high SO4 or low pH values in the area.