The speciation of trace elements in spent geothermal fluids and implications for environmental health around Olkaria, Kenya

Abstract

The greatest environmental challenge in the Olkaria, Kenya, has been the large volume of spent geothermal fluids and the constituent chemicals generated during geothermal development. The potential environmental health risks of trace elements in spent geothermal fluids from Olkaria have been studied fairly intensively but based on the total recoverable and dissolved concentrations. However, there has been extensive evidence that neither total nor dissolved aqueous metal concentrations are good predictors of metal mobility, bioavailability, and toxicity. The current study is, therefore, an attempt to investigate the distribution of the chemical species of selected toxic trace elements in spent geothermal fluids and assess the environmental health risks posed on the ecosystems around Olkaria. The study involved sampling and analysis of the major ions and trace elements in spent geothermal fluids from 4 discharging and 2 shut-in geothermal wells, outfall fluids from the Olkaria I geothermal power station, and the Infiltration Lagoons located in the Eastern sector of the Olkaria. The Ol’Njorowa Gorge thermal spring fluids and Lake Naivasha were used as control samples. A chemical equilibrium model, EQ3/6 solubility-speciation code, was applied to predict the probable distribution of the aqueous Al, As, Cd, Pb, Hg, and Zn with inorganic ligands at in-situ pH and temperatures with the results of analysis of the sampled fluids as input data.........