Levels of selected trace elements in Olkaria Geothermal fluids and their implications to the environment

Abstract

The study was aimed at assessing the concentrations of trace elements: zinc, lead, copper, cadmium, boron, mercury and arsenic in geothermal Power Plant, and fluids at Olkaria Geothermal the influence of the fluids on the level of these elements in sediments and plants that they come in contact with. The results show that the mean boron concentration levels in geothermal fluids investigated,exceed the WHO recommended 3.0 ppm limit for irrigation water. Furthermore the boron concentrations in all the sediments and plants studied were exceedingly higher than the 1-25 ppm and 1-10 ppm boron concentration ranges in unpolluted sediments and plants respectively. Lead and cadmium concentrations in some wells 0.005ppm exceeded the concentration WHO recommended limits in 0.05ppm drinking and water respectively. However, the levels were drastically lowered at the points where the fluids enter the infiltration pond due to precipitation of the elements, mixing with steam condensates and excess effluents from the seal pit which have relatively lower lead and cadmium concentrations. The mixing of the alkaline well weirbox fluids and the acidic fluids from the seal pit effectively lowered pH from 9.31 at site PIIB to 4.17 at site PIlI. The element concentrations in the fluids, except for boron, tended to increase towards the far end to evaporative of the infiltration pond due concentration. Furthermore, the results indicate that the element concentrations in sediments and plants are significantly elevated above the respective element concentrations in fluids. The concentration levels of these elements, sediments,were except however,for within acceptable levels, 0.1-1 and agricultural fluids significantly concentration levels,the and Swiss boron,also for in indicate that the influenced except in Ordinance 1-25 ppm respectively, soils. The results pH cadmium the boron, in elements sediments, especially at the infiltration ponds. The trace element concentrations in plants elevated above the element concentrations However,fluids,green had elevated algae the above which element not in sediments. elements concentrations respective were from the significantly concentrations in the fluids. In general the trace elements uptake in plants was favoured at low pH except green algae which tended to absorb the elements more at high pH values. The upward trend of trace element concentrations recorded in the sediments and plants particularly in green algae, shows that geothermal fluids have adverse implications to environmental health of humans and animals at the top of the food chain. Suggestions are made how to sustainably manage the pollution effects of geothermal fluids at Olkaria by using a managed infiltration pond system or re-injection wells for disposal of the waste fluids.